Today's technician classroom manual for automotive brake systems [Seventh ed.] 9781337564533, 1337564532

Table of contents :
Automotive Brake Systems (Classroom Manual)
Contents
Prefece
Classroom Manual
Shop Manual
Chapter 1: Brake System Fundamentals
Introduction
Brake System Overview
Trailer Brakes
Summary
Review Questions
Chapter 2: Principles and Theories of Operation
Introduction
Brake Operation/Conventional System
Brake System Energy
Braking Dynamics
Friction Principles
Energy and Work
Newton’s Laws of Motion
Hydraulic Principles
Vacuum and Air Pressure Principles
Electrical Principles
Summary
Review Questions
Chapter 3: Related Systems: Tires, Wheels, Bearings, and ­Suspensions
Introduction
Tire Fundamentals
Run-Flat Tires
Tire Pressure Monitoring System
Wheel Fundamentals
Wheel Bearings
Wheel Alignment Fundamentals
Effects on Braking Performance
Performance Tires, Wheels, and Alignment
Summary
Review Questions
Chapter 4: Master Cylinders and Brake Fluid
Introduction
Hydraulic Brake Fluid
Brake Pedal and Pushrod
Split Hydraulic Systems
Dual-Piston Master Cylinder Construction and Operation
Fast-Fill and Quick Take-Up Master Cylinders
Central-Valve Master Cylinders
Summary
Review Questions
Chapter 5: Hydraulic Lines, Valves, and Switches
Introduction
Brake Lines and Hoses
Brake Electrical Warning System
Summary
Review Questions
Chapter 6: Power Brake Systems
Introduction
Increasing Brake Force Input
Vacuum Principles
Vacuum and Air Systems for Power Boosters
Vacuum Power Boosters
Hydraulically Assisted Power Brakes
Summary
Review Questions
Chapter 7: Disc Brakes
Introduction
Disc Brake Advantages and Disadvantages
Disc Brake Construction
Caliper Construction and Operation
Types of Disc Brakes
Rear-Wheel Disc Brakes
Performance Disc Brakes
Summary
Review Questions
Chapter 8: Drum Brakes
Introduction
Drum Brake Construction and Operation
Drum Brake Designs
Summary
Review Questions
Chapter 9: Parking Brakes
Introduction
Parking Brake Operation
Parking Brake Controls—Levers and Pedals
Warning Lamps
Parking Brake Linkage
Electrical Parking Brake Systems
Rear Disc Parking Brakes
Summary
Review Questions
Chapter 10: Electrical Braking Systems
Introduction
Common Components and Terms
Antilock Brake System and Vehicle Control
ABS Types and General Operations
ABS Brands
ABS Components
Communications
Traction Control System
Delphi DBC-7 ABS
Summary
Review Questions
Chapter 11: Advanced Braking Systems
Introduction
Stability Control Systems
Stability Control Hardware
Active Braking Systems
Regenerative Braking Systems
Summary
Review Questions
Glossary
Index
Automotive Brake Systems Shop Manual)
Contents
Photo Sequences
Job Sheets
Preface
Shop Manual
Classroom Manual
Chapter 1: Brake Safety
Introduction
Brake System Safety Regulations
Brake Warnings and Cautions
Asbestos Health Issues
Chemical Safety
Safety and Environmental Agencies
Hazardous Communications
Handling of Hazardous Waste
Air Bag Safety
Fire Control
Technician Training and Certifications
ASE-Style Review Questions
Job Sheets
Chapter 2: Brake Service Tools and Equipment
Fasteners
Measuring Systems
Measuring Tools
Selection, Storage, and Care of Tools
Common Hand Tools
Special Brake Tools
Power Tools
Brake Lathes
Lifting Tools
Hoist Safety
Pressure Bleeders
Cleaning Equipment and Containment Systems
Cleaning Equipment Safety
Brake Lubricants
Electronic Test Equipment
Electrical Principles
Service Information
Summary
ASE-Style Review Questions
Job Sheets
Chapter 3: Related Systems Service
Isolating Brake Problems
Tire and Wheel Service
Tapered Roller Bearing Service
Wheel Alignment, Steering, and Suspension Inspection
ASE-Style Review Questions
ASE Challenge Questions
Job Sheets
Chapter 4: Master Cylinder and Brake Fluid Service
Brake System Road Test
Brake Pedal Mechanical Check
Pedal Travel and Force Test
Pedal Free Play Inspection and Adjustment
Brake Fluid Precautions
Master Cylinder Fluid Service
Checking ABS Fluid Level
Master Cylinder Test and Inspection
Integral and Non-Integral ABS Systems
Master Cylinder Reservoir Removal and Replacement
Rebuilding the Master Cylinder
Bench Bleeding Master Cylinders
Installing a Non-Integral ABS Master Cylinder
Master Cylinder Bleeding on the Vehicle
Hydraulic System Bleeding
Brake Fluid Replacement: Flushing and Refilling the Hydraulic System
ASE-Style Review Questions
ASE Challenge Questions
Job Sheets
Chapter 5: Hydraulic Line, Valve, and Switch Service
Introduction
Re-Centering a Pressure Differential Valve (Failure Warning Lamp Switch)
Brake Line, Fitting, and Hose Service
Servicing Hydraulic System Valves
Brake Electrical and Electronic Component Service
Stop Lamp Testing and Switch Adjustment
ASE-Style Review Questions
ASE Challenge Questions
Job Sheets
Chapter 6: Power Brake Service
Types of Power Brake Systems
Vacuum Booster Testing and Diagnosis
Brake Pedal Checks
Vacuum Booster Removal and Installation
Booster Overhaul
Vacuum Booster Pushrod Length Check
Adjusting the Booster Pushrod on a Honda
Hydro-Boost Power Brakes
Servicing the Hydro-Boost
Hydro-Boost Air Bleeding
Servicing Vacuum Boosters on Vehicles with Vehicle Stability Control
Servicing an Electrohydraulic Power Booster System
ASE-Style Review Questions
ASE Challenge Questions
Job Sheets
Chapter 7: Disc Brake Service
Service Precautions
Diagnosing Disc Brake Problems
Inspecting Brake Pads
Disc Brake Service Operations
Brake Pad Replacement for Floating or Sliding Calipers
Disc Brake Cleaning
Brake Caliper Service
Rotor Service
Refinishing Brake Rotors
Rear Disc Brake Inspection and Replacement
ASE-Style Review Questions
ASE Challenge Questions
Job Sheets
Chapter 8: Drum Brake Service
Service Precautions
Diagnosing Drum Brake Problems
Drum Brake Service Operations
Brake Drum Removal
Drum Brake Cleaning
Drum Brake Assembly Inspection
Drum Brake Disassembly
Wheel Cylinder Service
Drum Brake Reassembly
Brake Adjustment
Brake Drum Service
Refinishing Brake Drums
ASE-Style Review Questions
ASE Challenge Questions
Job Sheets
Chapter 9: Parking Brake Service
Parking Brake Tests
Cable and Linkage Adjustment
Cable and Linkage Repair and Replacement
Parking Brake Lamp Switch Test
Electric Parking Brake Service
ASE-Style Review Questions
ASE Challenge Questions
Job Sheets
Chapter 10: Electrical Braking Systems Service
Introduction
Brake System Troubleshooting
ABS Hydraulic System Service
General ABS Troubleshooting
Diagnostic Strategy
Switch Testing
ABS Component Replacement
Testing Specific Manufacturers’ Systems
Delphi DBC-7
Bosch ABS 9.0
ASE-Style Review Questions
ASE Challenge Questions
Job Sheets
Chapter 11: Advanced Braking Systems
Stability Control Systems
Stability Control and the Vehicle Network
System Component Service
Brake Warning Indicators
Active Cruise Control
Regenerative Braking Systems
ASE-Style Review Questions
ASE Challenge Questions
Job Sheets
Appendix: Ase Practice Examination
Glossary
Index

Citation preview

Automotive brake systems

Automotive Brake systems

7

Classroom Manual

7

EDITION

Ken Pickerill SE/Author/Author, Title, 5th Edition   ISBN -978-X-XXX-XXXXX-X  ©2014  Designer: XXX Text & Cover printer: Transcon-Beauceville   Binding: PB   Trim: 8.5" x 10.875"   CMYK

CLASSROOM MANUAL For Automotive Brake Systems

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Classroom Manual For Automotive Brake Systems

SEVENTH EDITION Ken Pickerill

Australia • Brazil • Mexico • Singapore • United Kingdom • United States

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Today’s Technician: Automotive Brake ­Systems, Seventh Edition Ken Pickerill

© 2019, 2015 Cengage Learning, Inc. Unless otherwise noted, all content is © Cengage ALL RIGHTS RESERVED. No part of this work covered by the copyright herein may be reproduced or distributed in any form or by any means, except as

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Book only ISBN: 978-1-3375-6453-3

Vice President, Marketing Services: Jennifer Ann Baker Associate Marketing Manager: Andrew Ouimet Senior Content Project Manager: Cheri Plasse Design Director: Jack Pendleton Cover image(s): Umberto Shtanzman/­ Shutterstock.com

Package ISBN: 978-1-3375-6452-6 Cengage 20 Channel Center Street Boston, MA 02210 USA Cengage is a leading provider of customized learning solutions with employees residing in nearly 40 different countries and sales in more than 125 countries around the world. Find your local representative at www.cengage.com. Cengage products are represented in Canada by Nelson Education, Ltd. To learn more about Cengage Platforms and Services, visit www.cengage.com. Purchase any of our products at your local college store or at our preferred online store www.cengagebrain.com

Notice to the Reader Publisher does not warrant or guarantee any of the products described herein or perform any independent analysis in connection with any of the product information contained herein. Publisher does not assume, and expressly disclaims, any obligation to obtain and include information other than that provided to it by the manufacturer. The reader is expressly warned to consider and adopt all safety precautions that might be indicated by the activities described herein and to avoid all potential hazards. By following the instructions contained herein, the reader willingly assumes all risks in connection with such instructions. The publisher makes no representations or warranties of any kind, including but not limited to, the warranties of fitness for particular purpose or merchantability, nor are any such representations implied with respect to the material set forth herein, and the publisher takes no responsibility with respect to such material. The publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or part, from the readers’ use of, or reliance upon, this material.

Printed in the United States of America Print Number: 01    Print Year: 2018

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Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii Chapter 1  Brake System Fundamentals . . . . . . . . . . . . . . . . . . . . . . . 1 Introduction 1 • Brake System Overview 2 • Trailer Brakes 13 • Summary 18 • Review Questions 18 Chapter 2  Principles and Theories of Operation . . . . . . . . . . . . . . . 20 Introduction 20 • Brake Operation/Conventional System 21 • Brake System Energy 22 • Braking Dynamics 24 • Friction Principles 25 • Energy and Work 31 • Newton’s Laws of Motion 32 • Hydraulic Principles 33 • Vacuum and Air Pressure Principles 39 • Electrical Principles 39 • Summary 41 • Review Questions 42 Chapter 3  Related Systems: Tires, Wheels, Bearings, and

­Suspensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Introduction 44 • Tire Fundamentals 45 • Run-Flat Tires 51 • Tire Pressure Monitoring System 53 • Wheel Fundamentals 54 • Wheel Bearings 56 • Wheel Alignment Fundamentals 58 • Effects on Braking Performance 62 • Performance Tires, Wheels, and Alignment 63 • Summary 66 • Review Questions 66

Chapter 4  Master Cylinders and Brake Fluid . . . . . . . . . . . . . . . . . . 68 Introduction 68 • Hydraulic Brake Fluid 68 • Brake Pedal and Pushrod 74 • Split Hydraulic Systems 75 • Dual-Piston Master Cylinder Construction and Operation 78 • Fast-Fill and Quick Take-Up Master Cylinders 88 • Central-Valve Master Cylinders 91 • Summary 92 • Review Questions 93 Chapter 5  Hydraulic Lines, Valves, and Switches . . . . . . . . . . . . . . . 95 Introduction 95 • Brake Lines and Hoses 95 • Brake Electrical Warning System 112 • Summary 120 • Review Questions 120 Chapter 6  Power Brake Systems . . . . . . . . . . . . . . . . . . . . . . . . . . 122 Introduction 122 • Increasing Brake Force Input 122 • Vacuum Principles 123 • Vacuum and Air Systems for Power Boosters 125 • Vacuum Power Boosters 128 • Hydraulically Assisted Power Brakes 137 • Summary 145 • Review Questions 146 Chapter 7  Disc Brakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 Introduction 148 • Disc Brake Advantages and Disadvantages 149 • Disc Brake Construction 154 • Caliper Construction and Operation 167 • Types of Disc Brakes 172 • Rear-Wheel Disc Brakes 177 • Performance Disc Brakes 177 • Summary 179 • Review Questions 179 Chapter 8  Drum Brakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 Introduction 182 • Drum Brake Construction and Operation 186 • Drum Brake Designs 202 • Summary 208 • Review Questions 208 v

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vi

Chapter 9  Parking Brakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210 Introduction 210 • Parking Brake Operation 210 • Parking Brake Controls—Levers and Pedals 212 • Warning Lamps 214 • Parking Brake Linkage 215 • Electrical Parking Brake Systems 220 • Rear Disc Parking Brakes 221 • Summary 224 • Review Questions 224 Chapter 10  Electrical Braking Systems . . . . . . . . . . . . . . . . . . . . . 227 Introduction 227 • Common Components and Terms 227 • Antilock Brake System and Vehicle Control 232 • Abs Types and General Operations 232 • Abs Brands 234 • Abs Components 235 • Communications 240 • Traction Control System 241 • Delphi Dbc-7 Abs 242 • Summary 247 • Review Questions 247 Chapter 11  Advanced Braking Systems . . . . . . . . . . . . . . . . . . . . . 250 Introduction 250 • Stability Control Systems 250 • Stability Control Hardware 257 • Active Braking Systems 262 • Regenerative Braking Systems 263 • Summary 264 • Review Questions 264

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287

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PREFACE

The Today’s Technician™ series features textbooks and digital learning solutions that cover all mechanical and electrical systems of automobiles and light trucks. The content corresponds to the 2017 ASE Education Foundation program accreditation requirements. They are specifically correlated to the Task Lists contained in each level of program accreditation; Maintenance and Light Repair (MLR), Automotive Service Technology (AST), and Master Service Technology (MAST). Additional titles include remedial skills and theories common to all of the certification areas and advanced or specific subject areas that reflect the latest technological trends. Today’s Technician: Automotive Electricity & Electronics, 7e is designed to give students a chance to develop the same skills and gain the same knowledge that today’s successful technician has. This edition also reflects the most recent changes in the guidelines established by the ASE Education Foundation. The purpose of the ASE Education Foundation program accreditation is to evaluate technician training programs against standards developed by the automotive industry and recommend qualifying programs for accreditation. Programs can earn accreditation upon the recommendation of ASE Education Foundation. These national standards reflect the skills that students must master. ASE Education Foundation accreditation ensures that certified training programs meet or exceed industry-recognized, uniform standards of excellence.

HIGHLIGHTS OF THIS NEW EDITION—CLASSROOM MANUAL The text and figures of this edition are updated to show modern brake technology and its applications, including the integration of stability control and active braking systems. The Classroom Manual covers the complete mechanical-hydraulic automotive braking theories. It introduces the reader to basic brake systems as well as advanced electronics utilized in stability control systems. The following chapters cover basic brake physics theories: discussion of newer components and materials, including a section on electric parking brakes, and any braking functions required for passenger cars and light trucks. The reader is introduced to fundamental information on trailer brakes, DOT requirements for trailer brakes, and a brief introduction to air brakes. Chapter 10, Electrical Braking Systems (EBS), simplifies the discussion on traditional antilock brake systems (ABS) while retaining the information for a complete understanding of ABS. Included in this chapter is a detailed discussion of electro-hydraulic brakes including the Teves Mk60/70, Delphi DBC-7, and the newer Bosch 9.0 are introduced in chapter 11, Advanced Braking Systems goes more into depth on stability control and its relationship to traction control and ABS systems. This chapter also explains some of the ancillary systems that make stability control work more effectively, such as electro-hydraulic and fully electric steering and tire pressure monitoring systems. The very latest technologies, such as active braking and intelligent cruise control systems, are introduced. Lastly, the chapter examines regenerative braking systems in use on the latest hybrid vehicles in production today. The Classroom Manual guides the reader from traditional hydraulic brake to the brake system of the future.

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viii

HIGHLIGHTS OF THIS NEW EDITION—SHOP MANUAL Safety information remains in the first chapter of the Shop Manual, placing this critical subject next to the tasks to be accomplished. Chapter 2, Brake Service Tools and Equipment, covers basic tools with more information on brake special tools and equipment. Figures and technical information have been added to cover the use of common shop tools such as on-car brake lathes. Some of the safety information that is pertinent to a particular piece of equipment is still in the chapter, so safety issues are presented just prior to the operation of the equipment. In keeping with typical shop diagnostic procedures and curriculum sequence, Chapter 3 retains the information on related systems that may have a direct impact on the braking system. Updated information on diagnosing electric parking brakes and electric braking systems has been added to this edition. To clarify the diagnosis and repair procedures for electric braking, three major ABS/TCS brands, Delphi DBC-7 and Bosch ABS 9.0 and Teves Mk 60/70, are retained for discussion instead of an individual discussion on all industry ABS offerings. This helps the reader better understand the technical diagnosing and repairing for all ABS/ TCS. This edition of the Shop Manual will guide the student/technician through all the basic tasks in brake system repair and presents a look into the near-term future of electric brakes and vehicle stability systems. The Shop Manual has several additions in the Advanced Braking Systems chapter, Chapter 11. This chapter deals with the diagnosis and repair of stability control systems and the surrounding technologies, such as electric steering, tire pressure monitoring systems, active braking, and intelligent cruise control.

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ix

CLASSROOM MANUAL Features of the Classroom Manual include the following: C h a pT eR 1

BRake SyST

Cognitive Objectives

eNTalS

Upon comple tion

and review of this chapter, you should be able List and descr to: ibe the opera tion of the basic parts of ■ Descr a brake system ibe the use of . ■ Descr valves ibe the opera to dir ec t and control the and lines tion of the bra system during hydraulic ke fluid. and after peda l application. ■ Discus s the pu rpo se of brake po ■ Discus s the increasin boosters and g use of disc the parking bra wer brakes instea ke. ■ Discus d of drum bra s the general kes. ■ Descr operation of ele ibe a typical bra tronic and act cive braking sys ke hydraulic system. tem s. ■ Discus s the general op era tio n of trailer brakes and air brakes. Terms To know ■

These objectives outline the chapter’s contents and identify what students should know and be able to do upon completion of the chapter. Each topic is divided into small units to promote easier understanding and learning.

Active braking Actuators

Friction Fulcrum Lateral acccel Antilock brake erometer system (ABS) Leverage Automatic rid e control Lockup (ARC) Master cylind Bulkhead er Negative whee Caliper l slip Parking brakes Disc brake Positive whee Drum brake l spin Pressure Force Regenerative braking Air brakes

Terms to Know List A list of key terms appears in the beginning of the chapter. Students will see these terms discussed in the chapter. Definitions can also be found in the Glossary at the end of the manual.

INTRODUCT

4

Margin Notes

em FUNDam

ION

Service brakes Steering whee l position sensor Stroke sensor Stroke simula tor Traction-contro l system (TCS) Vehicle stability control (VSC) Wheel cylinder Wheel speed sensors Yaw age

les of lever The brake system me princip pad applied is one of the mo eel. The sa ake functiteonr 1s: st importawo -spoked wh d the force of the br ph and little entem od nt sys ap a se Ch s oncrea e on to 20 m a solid tir llations in a vehicle. 10 mph s fou meant that early 1. It must slow to the outside ofodern brake pedal instaed well with speeds ofeuItmha atic tiresr basic pn rk m a mo d in wo an vin rk ) es g ak wo nd veh r icle. ese br 2. It must bringthat and beyo using eithe tire. Th a veh ce (30 mph iles were s. the solid to a sto perfo y, automob es. A few internalp. rman ived on automobiletie 3. It must hold to ffic.icle gher th centur a tra veh Hista re short-l drum brak ontracting brakes the twen wery g of es na din de an ca 4. It allows dir wagoicle n braktio xp l-c whenst sto de pp ed internal-e ectional con driveline les. Externa of the fir enlddu brakes . or e early motor vehic um located on the By thetro rinngg ma band tighten m dr xim um brasokin ed on around a and linkage If the brake sys external-contracti re tri lg.wrapped nter; levers famous Model T brakes we ria ce tem nd e ate th ba do m at n es ing ctio t op injured or killed Ford’s fri era e end or expand nolin th on te on wi es pro at ak ed pe ed br rlych, or in anha the drice rvice acc a ba is an veide nt.ndTechnic . Th anedsepa mission. skilled expforc The basnd forver transcou ssethnge ers t er braking whfor erte sthabe brak o ser the wheels. eian causeorthe vicing been highni on wo s wh um inside ectiven tion is the wee e the a drke esld th drum cal servo rk the bet n sys eir eff und do ofFric tionke applied to bra must be bra can ists mo baendlive the mecha resthe sav t hly e band aro ynt lose thtem sys ng nd l, th hig ou tem cti na two ab ra s. of by ter In rn es pre ex thi co sentingle s chapter,u will lea internal ba the surfac g the ternal or bas r incep s of matter. n with an brake tends were a sin brakes, yo wesesta outio r stu o ac es, eitichecon objects or form tsdyan rvrt dy drdum nd par ba l lop stu ts ve na Band brak u of de all brake sys exter to socihen yo an as ult s W . on fic n tem ed lem dif ed tio ob s. ry ac nal force is ne s. It is ve d. Other pr ed. Servo

ter brake shoe e force is thus need drum spee on with ex too and high action of s of fricti higher brak at high brake forces e and los ated and expanded d ter damag brake, and he ab wa er duce gr d e re ov an ak d t um br an e dir k if the dr erheating to make th nd brakes include akes to loc nd and drum ov ba ba of these br ated with the stan- 1 ffer from tendency e e su m th o ca d als be an es brakes bands 50s, rum brak the late 19 ternal band oe-and-d much. In anding sh parking brakes until ernal-exp rce. as braking fo brakes evolved, int were used 1920s. es ak br um e nd As dr cting ba s were the by the lat nal-contra ding shoe linkage were over 1/31/18 10:3 nal-expan dard. Exter as service brakes 9 AM ers and with inter lev ys es da by ak eir br lly th um nica re among but 1920s, dr d mecha odel A we lowerBy the mid- akes were operate 21 Duesenberg M . on es ar ak pe the 19 d to ap rd Drum Br as drum br rte Fo . ch sta rly th su es Ea le. cars brak Plymou general ru Expensive luxury brakes . Hydraulic came the , which be -3). odel year. aulic drum (Figure 1 r’s Light Six e 1938 m have hydr th Chrysle l brakes through th the first to the mid-1920s wi ca ni ha in ed mec priced cars wever, us mpany, ho Motor Co sed use of the increa ) The four asons for o major re lly-applied ones: (1 e same time tw re we e nica at th Ther ing force the mecha ake the ’S NOTe akes over me amount of brak -adjustment to m br aUThOR ed pli re s the ally ap ply the sa constant actical wa hydraulic emed to ap s required almost re ever pr se r we ve es ne ak ge brakes ds. e linka nical br ee ak ha sp br ec e m gh th hi ) on at because (2 e only reas be traveled rk at all. Th ugh and couldn't brake wo ro e flexible ads were ger than th fact that ro made stron rred with greater es could be occu hydraudrum brak kage problems that ith th W . wi ter ed s us brea and fas most cars brake shoe ns. This eliminated powerful got more system for andards The rigid s sig ile ing de ak ob e m br ak y St ndard as auto rlier br hicle Safet ade front bands of ea s that were required es remained the sta Motor Ve ak ce of Federal rmance tests that m ntury, braking for four-wheel drum br e coming ce on, s. With th ecific perfo of the twenty-first 60 sp 19 ss e lic actuati pa lat to g d s. iddle and systems ha Even at the beginnin cars and light truck into the m 67, brake y s. 19 of an 70 in m 19 5 e of 10 eels aft brakes rule in th (FMVSS) the rear wh from aircr g pressure the general in developed still used on disc brakes brakes are akes were akes work by apply wheel hub br um sc dr r, di ve br e ive c howe hed to th n automot “spot” brakes, dis : A braking rotor attac es. Moder lly as Disc Brakes forces two t Disc Brak a spinning n origina system tha e sides of ar II. Know on opposite World W e pads on opposit brake pads nning rotor ak es of a spi to two br

ke ke is a bra A drum bra tion is in which fric brake by generated g against bin rub shoes a surface of the inside 64533_ch01_h attached to r_001-019.ind d 1 brake drum the wheel.

The most important terms to know are highlighted and defined in the margin. Common trade jargon also appears in the margin and gives some of the common terms used for components. This helps students understand and speak the language of the trade, especially when conversing with an experienced technician.

sid vehicle to stop the

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x

Related Systems:

ons

ings, and Suspensi

Tires, Wheels, Bear

45

in proper lems if they are not create braking prob e systems and the e components can ionships between brak springs. Any of thes relat key the ines chapter outl working order. This ings, and suspensions. els, tires, wheel bear related systems of whe

talS tIre Fundamen

perof weight, size, and many vehicle factors tires neered in relation to tread design of the truction, size, and Brake systems are engi the tires and the factors are the cons een e thes betw ng lable Amo . avai formance be ld expected to be ion shou els frict or whe ion tract at all four and the amount of performance, tires most reliable brake road. For the best and and tread pattern. size, , tion truc identical in cons

Shop Manual page 98

on mendations information placard since 1968 have a tire The tire informaand light trucks built ment (Figure 3-1). Most passenger cars e the glove compart recommended insid any or r, and pilla size tire door a door, on a inal equipment and manufacturer’s orig inflation pressures, Gross vehicle weight tion placard lists the d cold front and rear are engilists the recommende WR). Brake systems rating (GVWR) is the optional sizes. It also e ard. cle weight rating (GV plac vehi s the on gros d total weight of a vehicl rear liste s and pressure sizes maximum front and e tire som the of plus its maximum rated with rear t efficiently the front and at tires and els payload, including pasneered to work mos ance sports rent sized whe diffe form ll -per fuel insta s full high and of aker rs ge senge A few carm a small percenta inally tice is reserved for tank. on the road are orig vehicles, but this prac percent of the vehicles turers may 911. More than 99 Although manufac cars like the Porsche inal e size at each corner. orig t sam fron the of the tires than r rear that are large fitted with wheels and the at ing brak sizes to tire tion can lead two optional aker’s recommenda recommend one or variation from the carm systems. equipment size, a large uce with other vehicle front to rear may prod from ter 2lems, as well as problems eters approb diam Ch e tire t in e than thos 22 eme differenc the concep s much largerysi GY andals eR cs,sign eN For example, an extr sTeM phnsor d sensors of ABSs. Tireor “laspee ” of spee s in el ws whe d-se sY the e from es cle als rk anrd come l aK te vehi d sign ncipl wolarge cura pri do inac uce to few unequal speeBR y a prod ica ilit to may are ab er ctr ing ele cles mak y is sthe if all four tires the vehi erg exist work accord lem energy, and prob ce. En sam recommendedl by scieen systemrol ule.phThis mod ysical brake energy, heat Al ABS cont rt of or the s. s. chanical basic par’s y, me to the PCM of y is aufac energtion recomml enda ergman otive system To slow and stop a enthe ture ms : chemica us forms in all autom er. for r oth ilia or smaller than an y through many fam energy to most obvio to heat energ er, they of physical among the s one form y of motion energy are anoth tem convert kinetic energ e form of energy to the ge an A brake sys kes ch change on icle, the bra y. g veh ytion. When the brakes or resis energ vinoF hIStor by drivers to using tance BIt amo lot of using is the easaing was ion of fric of rel 70s, plicat ultthere Kinetic energy ical have enough uced in theres the apwere introd firstrk. han driving” to “they don’t Work is the when energy of mec . When radial tiresdo funny wo le “feels ing from aren. Complaints ranged from a brand-new vehic energy. work or motion the new desig to remove radial tires resisstroy deard die-h rs even went so far as ate or crethis tire overc e toame radia of the air in them.” Some drive r cylinder is also ste thil s timfile cteristics ssi have at ma chara r e today ble of majo Th o Two tires er. po r-proto anoth is im nverted int and to install bias tires. 's and fuel mileamge.onLowe ased e formrinfla increIt ” brake pedal is co mechaniOR ride NOTe ted. fro ther ed unde aUTh g the ert earin of nv “app y to tance: a much smoo co tires erg about the mechanical en ents be , it can erted back comm nv ver the co of we er most Ho lat the eliminated s happens: er bore. It is one place thi y in the master cylind erg hydraulic en the wheels. cal energy at

carmakers’ recom

starts, d automobile , and spee ergy n. When an s, Weight of kinetic en rk or motio ergy, Mas chanical wo e at The amount

Kinetic en

A Bit of History

Cross-References to the Shop Manual References to the appropriate page in the Shop Manual appear whenever necessary. Although the chapters of the two manuals are synchronized, material covered in other chapters of the Shop Manual may be fundamental to the topic discussed in the Classroom Manual.

Author’s Notes This feature includes simple explanations, stories, or examples of complex topics. These are included to help students understand difficult concepts.

the rat y of me y is at work. speed, and y is the energ kinetic energ ss (weight), Kinetic energ , and stops, vehicle’s ma decelerates mined by a ter objects on de accelerates, is ibe nt y mome ly to descr aand lists at work at an changinisg.located on the driver door interchangeab same. Mass is a me the can be used ed is This placard spe3-1 eight” Figure “winflati asurement on pressure. are not technically which d me an a cold ” is and ass size ht tire ed “m recom terms to a two terms ject. Weig e ob The mend the sho t an ke bu , up m a steel bra of the Earth s that make the surface of molecule l objects have mass, fro ing too deeply into the measure of the number Related Sys out go ss. Al t and Mass is the tems: Tires, surement of springs.lec ressor. With an object y on that ma s in an objec re Wheels, Be y of the inertia of mo Anule an air comp ect of gravit of these commo in its eff er arings, and or air mb the tter the nu of ma ponents can1/31/18 9:44 AM to the working Suspensions ject and the or form of t ober. create brakin draulic fluid the greater Thigh ss of thaord is cha t. pter outlines g problems if quart of hy the marel be said that r resistance to also is we can ate ate it t’s gre d cs, jec sys the they are not it the key relationsh the s are, of is that ob tems ofthi ce of physi wh t ule acceleration; en ing in eel jec lec of sci nk proper s, ob ips mo tire sity an bet den s, ween brake sys lar 45 mass of rstood by mplex the 67.indd molecu .wheel bearings, and de co the ther_044-0 rth un re on Ea y tem be 64533_ch03_h mo vit the s and the the suspensions. gra d weight can the launch pad, on an object. The effect of een mass an 2-2). Its on dense it is. ss (Figure ference betw out 1,000,000 pounds tIre ightle nd amentalS The basic dif y, it is weFu ighs ab Earth’s gravit , which we the a ttle s de ha tsi shu ed ou ce Brake system it, spa but spe arey,eng ttle is in orb etic enserg ine bedcal forte kin incu itu When the shu same, however. relation to ma nce. Am obgject canere speed const ma ny vehicle fac the these y movingon weight and and of an mass stays tors of weigh the amount of tra factors are the construct d effects of etic energy ine t, size, and per kin mb e co ion, size, and Th ctio e t. n or friction Th road. For the n weigh tread design expected to be bes simple: r effect tha Shop Manual of the tires available bet identical in con t and most reliable brake much greate formula, which is quite ween the tire performance s page 98 struction, siz thi th s and the wi , ed tire e, lat and tread pat s at all four wh ter eel n. s should be carmakers’ 2 recommen mv 5 Ek dations Most passen ger cars and 29.9 light trucks bu a door, on a do ilt since 1968 or pillar, or ins have a tire inf tio ide n ere the glove com placard lists wh ormation pla partment (Fi card on optional sizes. the manufacturer’s origin gure 3-1). Th unds po in al equipment It ht) e tire inform also lists the eig tire size and ma rec ur xim m 5 mass (w om ho r um me nded cold fro front and rea any recomme amiles pe in ) eed r nt gro nded (sp and neered to wo ss vehicle we rear inflation v 5 velocity s rk most pressures, and 2,000 ight rating (GVWR). ciently wit foot-pound ighhs the A few carma pheffi Brake system c energy in ). One we tire sizes and ker (m s ins s Ek 5 kineti ur are ho tall eng pre r dif pe veh ssu ifer res icle ent sized wh listed on the Gross vehicle 30 miles s, but this practic eels and weight placard. traveling at car e is reserved rating (GVWR) like).the Porsch res 2-3 for a small per tires at the front and rea o cars, both pounds (Figu is the e 911. More r of some total weight of centage of hig Consider tw 00 4,0 fitt s ed tha igh a wit n we 99 percent of h-performanc h wheels and other plus its maximu vehicle the tire e spo veh s of m rated rts pounds; the recommend icles on the roa payload, inclu one or two opt the same size at each cor d are ding originally ner. Although ional tire sizes equipment siz sengers and full pasmanufacturers at the rear tha e, a large variati fuel tank. 1/31/18 t9:42 may areAMlarger tha problems, as on from the car n the front ori well as proble ginal ms with other maker’s recommendation For example, can veh lead to brakin icle systems. unequal speed an extreme difference in g tire diameter sig s from front recommended nals from the wheel speed to rea sensors of AB by the vehicle d 22 Ss. Tires much r may produce to the PCM or ma r_020-043.ind larger than tho the ABS contro ker may produce inaccu 64533_ch02_h rate vehicle spe se or smaller tha l module. Th is same proble ed-sensor sig n the manufac nals m exists if all turer’s recom four tires are mendations. larger

45

a BIt oF

This feature gives the student a sense of the evolution of the automobile. This feature not only contains nice-to-know information, but also should spark some interest in the subject matter.

hIStory When radial tire s the new design. were first introduced in the 70s, there was Com a lot of resista air in them.” Som plaints ranged from “fee nce by drivers ls funny when e drivers even to driving” to “the and to install went so far as y don’t have eno using bias tires. Two ugh major characteri to remove radial tires from tance: a much a brand-new veh stics of the rad smoother ride icle ial tire overcame and eliminated mo st of the comme increased fuel mileage. Low this die-hard resi er-profile tires nts about the stires “appearing of underinflated.” today have also

Figure 3-1 This recommended placard is located on the driv tire size and cold er doo inflation pressure r and lists .

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Chapter 4

In most instances, only one dual-piston cylinder is used with some type of split system. However, some race crews opt for two identical single-piston master cylinders. The two master cylinders act like a split hydraulic system in that one master cylinder serves the front wheels, whereas the other serves the rear wheels. The master cylinders are applied by one brake pedal acting through a balance bar between the pedal lever and the two push-rods. Some race units are equipped with a brake power booster, and others are not. In this case, it is more an issue of weight than of driver endurance. Of primary importance to race vehicle braking is the type of brake fluid used. On short tracks with a lot of braking, the boiling point of the fluid can be reached quickly and may be sustained for long periods. Brake fluids developed for racing purposes generally have the same chemical properties as conventional fluids, but they have much higher boiling points. Castrol offers a blend of polyglycol ester of dimethyl silane, ethylene polyglycols, and oxidation inhibitors. This blend has a dry boiling point of 4508F(2328C) and helps prevent fluid contamination during operation. Another brand, GS610, offers a fluid with a dry boiling point of 6108F(3218C). There are several manufacturers and suppliers of racing brake components. Brembo is one of the larger manufacturers of racing components, and some of its products are now being installed on some production performance vehicles.

Summary Each chapter concludes with summary statements that contain the important topics of the chapter. These are designed to help the reader review the contents.

Review Questions Short-answer essay, fill in the blank, and multiple-choice questions follow each chapter. These questions are designed to accurately assess the student’s competence in the stated objectives at the beginning of the chapter.

sUMMARY Brake fluid specifications are defined by SAE hydraulic systems. Each of the two pistons in the Standard J1703 and FMVSS 116. master cylinder has a cup, a return spring, and a Fluids are assigned DOT numbers: DOT 3, DOT 4, seal. ■ During application, the piston and cup force fluid DOT 5, DOT 3/4, and DOT 5.1. ■ Always use fluid with the DOT number recomahead of the piston to activate the brakes. ■ During release, the return spring returns the mended by the specific carmaker. ■ Never use DOT 5 fluid in an ABS or mix with any piston. ■ Fluid from the reservoir flows from the reservoir other brake fluid. ■ HSMO fluids are very rare and should never be through the replenishing port around the piston used in brake systems designed for DOT fluids. cup. ■ The brake pedal assembly is a lever that increases ■ Excess fluid in front of the piston flows back into 93 pedal force to the master cylinder. the reservoir through the vent uid ports. Brake Fl ■ The brake pedal lever is attached to a pushrod, ■ Quickyltake-up ordfast-fill master cylinders have a inders an aster C M which transmits force to the master cylinder pistons. step bore, which is a larger diameter bore for the ■ A front-to-rear split hydraulic system has two masrear section of the primary piston. ■ Quick take-up master cylinders have a valve that ter cylinder circuits. One is connected to the front s: a partlow-pressure provides rapid filling spool area brakes and the other to the rear brakes. o maiofn the _. der has tw linprimary ______ ■ A diagonally split hydraulic system is one in which the reservoir. r cythe ______from masteof s __piston a N he d T IO an 8. T _ to valves in s Emaster cylinder circuit is connected to the left ____ ed ■ __ ____ ABS master cylinders U Some have check one nt Q ve e ar W __ __ coversto reduce REVIE _ as and pedal the headsr of theorpistons front and right rear brakes and the other circuit is caps ______piston ________ ter cylinde and m- rear brakes. _____ wear. connected to the right front and left 9. All mas vibration ________ cup is not reco rvoir. __ se id a t re flu e Essay en e th ak ■ The master cylinder has two main parts: a reser- prev ■ Portless master s in cylinders do not use T 5 br der aisreplenishlevel drop r. e cylin n why DO aancylinder thflow the fluid ing or vent port. can between the reserufacturebody. id is rear of 1. Explai voiranand theFluid at the brake flu by y m bly at onemaster int aofseparate semthe thethe asand pobe d of . can piece or cast as one voir area ahead cylinder mende■d The reservoir an on ng , st ili on pi bo st the ___ piston _ pi . The __ __ hy 10 __ __ w n __ __ ai 5 __ __ with the cylinder. pistons by means of a valve machined into the DOT 2. Expl piece the ______ cylinder is the ____ ea to mix idcylinder ■ an e od At.dual-piston master has two separate pismaster cylinder pistons when the master cylinder th go import of a front is not n why it pressure is at rest. DOT 4. for two independent ation 3. Explai tonsDproviding OT 3 and contamin id ith flu w e s fluid gn of brak e a sure si ch an ge s is Choice 4. Describ eral oil. cy lin de r free-play Multiple e m as te r da l to dal linkage with min A says th l fo rce on th e pe brake pe an hy ci w ni n ch ai ca 1. Te says th is 5. Expl m echa ni ni ci an B to system. dr iv er ’s ch ssar y. e lic Te ce th . au ne re dr r. 64533_ch04_hr_068-094.indd 92hy pres su d ba ck n the split site master cylinde d how it is hy dr au lic es su re is ch an ge br akes . W ho is 6. Explai an pr el e a compo cup seal hy dr au lic l fo rce at th e w he 7. Describ a master cylinder ca e m echa ni 8. Describ and B of the m t? tto . Both A ec bo . C rr co used B rts in the do er A nor th are the po servoir, and what ly t ei N ha on . A W D 9. A. linder re for a aster id m master cy ly p flu t on -u gh B ke B. at if ng the ri a quick ta they do? ys choosi the simple idea th ntage of cian A sa n the adva d on d DOT 2. Techni 10. Explai better, an mancle is base hi be ve t c us r. ifi m de spec T4 hicle cylin good, DO ys most ve DOT 3 is . Technician B sa Who is correct? better still mmend DOT 4. 5 s is nk A and B reco e Bla cylinder C. Both ufacturers Fill in th p master sa rB ick take-u design that create ther A no qu ly ei or N on . ill A D -f . A al bore 1. A fast by the du _______ of brake t ly in on po B identified _____ or ________ B. cony boiling g. __ ys the dr of new, un ________ _____ of the castin cian A sa ng point ne__ glycol flu 3. Techni e minimum boili ________ polyalkyle ___ for says poly e B th ar s is an id do ci id __ ni flu 4 flu they ____ fluid. Tech eans that and DOT d ______ taminated oscopic, which m e air. Who is 2. DOT 3 er mixtures, calle gr r from th glycol-eth ids are hy po va er at rb w ids short. not abso DOT 4 flu air, A and B OT 3 and from the C. Both correct? e both D _______ B . 3. Becaus _______ ________ er A nor ed pp ca D. Neith A . A only ________ containers tightly r de ng ili ep un bo ke ly tly ture always B. B on ake _____ sligh -tempera ake fluid ________ slightly spongy br ys a high e fluid __ a cian A sa ent that br id also 4. Silicon which can cause 4. Techni e only requirem e flu ak br , th re ys pressu point is d must cian B sa _ . t. Techni oration an ________ pedal feel must mee freezing and evap w temperatures. ry ______ ve a ve sist at lo s ha s re id t st te us flu m ol ity yc ific viscos 5. Polygl ___ pass spec ect? ________ A and B shelf life. rr -to- ____ C. Both Who is co split _______ rB st __ de __ ol __ e ther A no ly ei N on . 6. The __ split system is th A D . A hydraulic ly _ on __ B __ B. ____ system. a ______ cars have te-model 7. Most la aulic system. split hydr ■

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xii

Shop Manual To stress the importance of safe work habits, the Shop Manual also dedicates one full chapter to safety. Other important features of this manual include: C h a p Te R

1

feTy BRake Sa

Basic Tools Lists ls

Basic Too le to: g should be ab s or ts for workin s chapter, you Safety glasse requiremen review of thi ety saf and n the tio t ■ Lis goggles Upon comple fluid. d methods with brake os tor an est pira ed asb Res ne of the ■ Explain the hazards working HEPA ■ Describe ing a safe Vacuum with for maintain filter materials. with solarea. ety concerns issues tem saf sys ety the saf ean in e t-cl We ■ Expla s. discuss som er chemical ide ■ List and eration in the vents and oth Carbon monox h vehicle op ns of the dealing wit neral functio system t ge ven of s the in cie ■ Expla tal agen en nm shop. er(s) se ish viro sen ngu en mmon Fire exti safety and Canada. e of the co States and ■ Explain som wer the United rking with po hazardous of s ple rules for wo nci pri ■ Discuss the Master Cy nt in equipment. tions. linder an and equipme rns communica d Brake per clothing safety conce Fluid Se ■ Wear pro s some of the ck brake and air rvice cus Dis ■ a shop. with antilo remove ed iat to p oc ste ass first aid the in s. pla tem ■ Ex eyes. bag sys d the an m g fro s inin t chemical hnician tra governmen ■ Discuss tec purpose for and . ■ Explain the rformance certification of brake pe regulations standards. tion (OSHA) Administra ow tal Canada Terms To kn osgene Environmen Ph n tal Protectio tal inflatable Asbestos Environmen Supplemen A) tem (SIRS) Agency (EP restraint sys Asbestosis Figure 4-2 ures (EP) ced thylene Ch Pro for n r eck roe nte ctio ing stop lamp Extra Tetrachlo Canadian Ce Health op era le tion. al BR tor Vehic roethane AK Occupation Federal Mo 1,1,1-Trichlo (CCOHS) E pEDAl Mndards (FMVSS) lene and Safety Safety Sta EChAniC et Trichloroethy Ch Al Ch noxide ecking the brak ial safety data she zardous mo n Ha e E rbo Ca shooting. Klac rkp pedal mec Maeter WoC on arb W ha ormation hether(M nical oper hydroc S) yoSD Materials Inf u do Chlorinated test, check th it as pa and ation is an im fetofy th ese points ation rt Sa t al ts po ee Classroom ven Sh rta e brake sy sol nt part of ■ Ch Occupof pedal op Manual ste ec k m brake tro fo eration: road test page 74 r frictio Health t of (w ubleor during Departmen ith th T)e engi n and noise by pr a system (DO on ati es ne ort sin leak running g and Transp return

Performance-Based Objectives These objectives define the contents of the chapter and define what the student should have learned on completion of the chapter.

■

Move

s with no

lag or no

re for powe r brakes). leasing the brake pe Be ise

Each chapter begins with a list of the basic tools needed to perform the tasks included in the chapter.

t also

the brake da bu sure the is wearing . peda ov l, severaan l times N peda an IO peCT dal m ounting pa l from side ttoonsid at the technici is lifmon smhn eestec ooici lye.wh INTRO■DU thly and rts. olves no Chec Exce e here

inv k stop lam ivetag injpury side mov keeping the shop ld adssvan operataiosaf d Htectioancofrom e. The twofo indicaavo are n by uipment anement ce Personal pro avepin wo er rk depr te iding estec singtioanndeq check th rn l pro eakee g therkwo na od chan of s wo rso pe at re e nd lea th ng e fitby sta e ari making and ch tim sinag go lam we theme ps t will provid vishtitoears leased (F ployee sel is re or lig br s sto ntetha him ak g pl igh tin ig uip pedal seve ch t. It is im er emure 4-2), in practices tim andeeq is protec ha oth th the ral times e po all pe n clu rta se da ding the ntdis vee,tothe l is presse s tho . tocu sse 4 no ha ve te th R er d th th clean and saf ird apt an E at e or center d go off som T ury. This chignition in ru Aorpinj —high nts n before e vehicles equipp ideh accC . ed with lig -mounted— the brake rsonal safety lamps wi hting mod overallpand pe ll operate. ules EDA

Special To

ols

Coworker

1

R linDE viCE ER CY luiD SER T S A l F TRAv M E E K l A A nD FOR R Air inD CE TEST n the B hydraulic A us system ually

Terms To Know List Terms in this list are also defined in the Glossary at the end of the manual.

ed ■ Ble r cylin lyze the cond . maste system ck the cessary. Ana id from its Che 4_hr_133ned 198.ind l as rake flu and fil vehi cl135e’s b a tion of nce. ra appea l ABS Integra Know ing To s l bleed Term g Manua ABS leedin b ch tegral Ben Non-in w ing re ed sc er re ble su Bleed es Pr ing bleed Brake g in ed ble Gravity

Special Tools Lists Whenever a special tool is required to complete a task, it is listed in the margin next to the procedure.

rep

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er tomet Refrac ty c gravi Specifi ing ed le b Surge ing bleed Vacuum

system a brake presof nents of TEST compo b the system r and D lic A au ro de O r hydr e lines can ter cylin ged or TEM R d othe the mas der an E SYS chan r or brak ter cylin aster cylinde which is why linings are correcte d BRAK as m e or be ds ly, th the m conditions, ate safe s must brake pa eaks in g To oper k properly. L us operatin henever the ny problem A w ro or ce: must w cause dange be inspected or braking. orman rf o d pe t p e sure an system mus plains of use or brak m tires ca lic cause po ed at n fl ca hydrau customer co n -i a ons that or over If the when tely. conditi flated, power. g in g in rin w de ia ak one follo immed pull to more br ched, un for the quires may grab or mismat , re Check n e cl or vehi s. W akes m ed br le e ad ob th lo , e pr g. ■ Tir to side heavily l brakin ing. A back or side unequa vehicle load front to qual ■ Une ual from eq un load is side.

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solves th e problem causes most lowtem, inco pedal prob s. Low pe rrec dal als lems, brake shoe t pushrod length adjustmen o can be caused by and bleeding s, or a dr thse syste um brake t, a service a aseic Tool When a m d 1 sh 4.ind brake that leak inBth 1-04 oe gi r_00 ven amou adjuster an’saulic sysexceed a 64540_ch01_h cidr is out of technihy th nt at of is sp not woan force is rkding. Basic adsejut stment, wo about 2.5 ecified maximum able to: applied to leak s rn r e peda tool th inches (6 di be fo sta l ld er nc d we e. Th l, brake pe n shop to 4 shou linis m fications ter cy aximum da can ter, you mm) when m0aspo Special To d l sp Cleal tratve unds (445 is chapbe found inInth ect a10 anve wrlenmchust etra ols Fath ilu re to exha ■ spe ve ew of arele)akofagfo eed ecifiFlca tionun is no not rN . cle service er fo tshi d revim ust brak ed is appl Brake peda rmally easurem def st lindinformmatine nerc e ec teen etion an ied cy bo r pl l effort . The exac os te em m t. t io er pr st n. Us as co et e a brake st a m essut re gauge dd t specikethsy es wi Upon an e ra ll fiv Te b pe re e ■ en su dal ef procedur lt in an in der mrt safe apfo Tape meas es gauge to lincorrect pe orm a air entr ure pedal : meaas ■ Perf da 1. Tuernbra suterer cy am Service ma ofke Aeden rcdeerapplied l travel or force pairs. th justgi cyfolin place drive. nual ms in rese ssarfy.th ne. On re to the pe and re the master cerve vacu proble as ne ve ovse wi da hi se m cle l wi ed no Re th r um r’s le g is exha■us chthb vacun. repai 2. an ■ Dia Inuf aclltuthre d en sta um b an te as d d e sist, .pum e brake pe tio m an from th linkag e la lay to3. Hook p the nc booster.cylinder e instal peeda orug free p the lip dofrag, dal effort befga ter e l a th pedal . mas g seque in l until all e tape m the digsta e brakice b auon brake th cations leedin ea vererhov hicle line fro pin , ncte specifi ■ Osu l ifi raul peda r cym (Fcigve ereth th ur hyedto r stop ec as ya e e pe rd oo m 4sp th p p da sti y 3). a l to caeteste r ge of th foed ede som gnose al caused b ck on e ake pe erct need vehicles■inLoth inio ■ Dia g ns wh stru ped een.l rim (F br erform d einof plac ulic dal an atio an dra or hard lems and p hyur a fo tarm in e 4-4). Yo d measure ke ig pe e ra b m ic b ea rv ro e su p u can use se l der sh th re. id leve ia and flu der flu airs.

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138

Chapter 4

SERviCE Tip  The vehicle’s brake light switch must be activated any time the brake pedal is moved downward any amount. There is “no free play” allowed with regard to the brake light switch.

Author’s Notes

AuThOR’S nOTE The following procedure is based on a Honda S2000. Other vehicles have similar procedures. Many vehicles do not have an adjustment for pedal height.

This feature includes simple explanations, stories, or examples of complex topics. These are included to help students understand difficult concepts.

Adjusting pedal height 252

One to adjust the brake pedal height and free play follows. Disconnect and loosen Cha ptemethod r6

the brake pedal position switch until it is no longer touching the brake pedal lever (Figure 4-7, A and B). Gain clear access to the floorboard by lifting the carpet and the CE(Figure insulator 4-8C). Measure the pedal height, (Figure 4-8), from the right center of 10

PhOTO SEqUEN

Typical Pro theced brake pad to the floorboard. In the case of this Honda, the pedal height should ure Caution For vaccleared uum oster Tes be 179 mm or 7 ¹/₆ inches). IfBo necessary to adjust ting the pedal height, loosen the locknuts, and If the switch is not adjusted correctly, the brakes will drag. This may cause heat problems with the friction materials and poor braking performance.

turn the pushrod to obtain the correct measurement (Figure 4-9). With the correct height obtained, hold the pushrod in place while tightening the locknut to 15 Nm (11 ft. lb.). Install the brake pedal position switch until its plunger is against the pedal lever and completely pushed into the switch (Figure 4-10). Unscrew the switch until there is 0.3 mm (0.01 inch) between the switch’s threaded end and the mounting pad. Connect the switch to its electrical harness. Have an assistant check the brake lights as the brake pedal is depressed and released.

Photo Sequences Many procedures are illustrated in detailed Photo Sequences. These photographs show the students what to expect when they perform particular procedures. They also familiarize students with a system or type of equipment that the school might not have.

Adjusting pedal Free play Using the same Honda vehicle as the example, the pedal free play is checked and adjusted

P10-1 With the engin idling, attach a vacu gauge to an intake in ethe manner. The engine should be off. Push on the brake by hand while um P10manifoldfollowing 2 Disconnect the port. Any reading below 14 in. Hg of from the intake mani vacuum hose that runs vacuum may indic P10-3 If you do not ate an fold to the booster engine problem. feel a quickly place your thumb over it befor andPushrod step 2, shut off the engin strong vacuum in e e, remove the hose engine stalls. You and see if it is colla should feel strong the , psed, crimped, or vacuum. clogged. Replace it ifLocknut needed. (A) Brake switch

Lift floor mat

(C) Measuring point (B) Pedal bracket

(E) Pedal height

P10-4 To test the operation of the vacu check valve, shut P10-5 Remove the off the engine and um check valve from the Standard pedal height wait for 5 minutes. Apply the booster. (with carpet P10-removed): 6 Test the check power assist on at brakes. There should be valve by blowing into least one pedal strok 179 mm in.) intak(7e mani the fold end of there is no power e. If Figure 4-7 Remove the pedal assist on the first be a complete block the valve. There should appli the check valve is catio position switch Figure 4-8 Remove the floor mat and a portion n, or stop lamp age of of airflow. leaking. switch from the pedal bracket. the carpet to gain clear access to the floorboard.

replace th e the wiring parking brake sw Hydrau itch. If th harness lic Line, 1/31/18 10:33 AM between e Valve, an the body lamp is still off, d Switc find and control co h Service Brake Fl repair th mputer uid leve 223 e op an en circui d the sw l Switch With the itch. t in Test ig to alert th nition on and th e brake flu e driver of a low-f into the id level sw reservoi itch clos r body; ot luid condition in for both ed, the br hers are types. ake warni attached the master cylin ng lam Begin by de to the re P10-7 Apply vacu en servoir ca r. Some switche p lights ring that th um to tio the boostersu s are built p. Test pr end the valve. Vacuume igni th of e flu8idChec on and ob P10inciples should be nblock le at k ve the th boos ed. l se If you do rve thperfo is at or ter air control valve not get the state resule switc are simila h. ne e by rming ts w in ar If r a step ar P10brake th 6 th 9 ni and Turn the front whee finkdvalve e la7,mp th of the e fu step replace the chec ng lamdrag test. With the ll m an.d repa whee ls by hand and note p. ar ls vehic en k If le the raise on it amount go out, d off the floor, ir the sh is , discthe th is ort circ brake es To verif replace th litpump pedal to exha onnect th e reseofrvdrag oir.that Turnpresent. ual e sw vacu e um w twter.een th ust resid thet be from iri boos the switc y that the warni ui itc ng h. If the connec e switch ng h lamp do and the lamp do float or remove lamp will light es not go tor lamp. w es not lig th out, ht with th e cap with an hen the fluid leve and the integral lamp. If l is low, m e switch sw ci cl rc an itc osed, ch uit contin As a fin eck for an h and let the flo ually depress wire betw al check, discon uity is good, re at drop. open circ pl ne If the ee ace the sw uit betw If it does n the two term ct the wiring ha een the itch. rness fro inal switch not, find m the sw 64540_ch06_hr_2 compute and repa s in the harness 47-284.indd itch, and 252 r. ir the op co connect en circui nnector. The w a ju ar t betwee n the sw ning lamp shou mper electric ld itch and al wirin the body light. g Repai 1/31/18 8:57 control Wire siz AM r e is determ drop allo ined by th w e amount or in met ed. Wire size is of cu rrent, th specified ric crosse leng in se tor. A 20 gauge is ctional area. Th either the Amer th of the circuit, e higher much sm ican Wir and the When the voltage alle e wiring di replacing a wire r than a 12 gaug number in AWG Gauge (AWG) syst agrams or , the corr e. the smal prevent ler the co em ect size An America chafing or in parts books. wire mus nducn wire Each ha t be used to splice damage gauge (A rness to aw as show WG n on appl wires. Ro ire, and use insu the insulation du or wire must be system for ) is a e ic sin flux he specifying la to ab tin ld vi le g se br tape cure atio wire size clea does acid (conductor -based flu ns the connectio or heat-shrink n. Always use ro ly in place to cross-secti complet sin flux tubing to n during x. Apply on ely sold ing heat cover all solderin by a serie al area) seal unde seal the wiring g withou to shrin splices or er s an k t rground numbers; of gauge electrical d connections. U tubing causes th eroding the mat bare the lower Many el er the e tu tility com supp ia number, ectrical make th panies us bing to contra l as system re ly cables. the wire cro the larger ese ct ed heat-s ss section shorts or repairs in a way pairs require re hrink tu and . bing to placing gr that does damaged with man ounds in the re no t in crea pa w y accessib factors influenci ired area. Severa se the resistanc ires. It is import Caution ility of th e in the ng the ch an l methods t to circuit or ew oice requirem are used Never rep lead to ents. Th iring, the type of . These factors to lace a wi e three m include th repair damag re with one ed wire of ost com conductor and e type of 1. Wrapp siz mon repa size. Using a smaller re ing ir metho e of wire needed pair required is damag the damaged insu rect size the incords are: , and the ed co la uld tio an ci d th cause nw rcuit 2. Crimpi repeated ng the co e wiring is unha ith electrical tape failure an d 3. Solder rmed) damage nnections (in cases to ing splic with a so where th cle electr the vehies e insulatio lder-less ical syste connecto When de n m. r ciding w connectio here to ns cut a da of each ot . As a rule, do Rosin flu maged w x solder not her. Use ire, avoi is solder us a wire of have two splices d points ed Crimping close to the sam trical rep for elec. e size or or connections other sp A solder airs. tors . So w la lic le ith rg es ss er in or co than the me man 1. ufacture nnection uses a wire bein 5 inches (40 mm repairs. rs re com g replaced ) Crimping Heat-shrin . selfsealin quire the use of pressed junction k g solder to connec se plastic tub tubing is less conn lf-sealing sold t two co ing that er ections shrinks in is an acce less connections nducdiameter ptable w on wh en al exposed l ay to splic to heat. e wire,

64540_ch04_hr_133-198.indd 138

Margin Notes The most important terms to know are highlighted and defined in the margin. Common trade jargon also appears in the margins and gives some of the common terms used for components. This feature helps students understand and speak the language of the trade, especially when conversing with an experienced technician.

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Master

Lower l the peda

d Service

ake Flui

r and Br

Cylinde

139

Pedal lever

(A) ) (0.01 in.

0.3 mm

Pushrod

knut hin its loc switch wit ned. The cleartai 0 Turn the Figure 4-1 per clearance is ob mm (0.01 0.3 until the pros switch should be ance on thi int A. inch) at po

Raise pedal

the d turn locknut an or Loosen the longer Figure 4-9 to make the rod vement rod sh mo pu the the pending on shorter de needed.

(C) Locknuts

dal Brake pe pad y Pedal pla 1–5 mm Vacuum booster

Power Brake Service

271

Check valve

free the pedal n C 1 Check tur Figure 4-1 tment is needed, ved. hie jus play. If ad per free play is ac n. tio pro opera until the stop lamp’s Check the

rement is measu e is felt. Th to 3/16 inch) ch resistanc in iff /6 st a (1 e brake mm before mm to 5 the locknut on th is corl travels the peda ould be 1 ing play e distance l foot pad and sh play by loosen the free l free play th til the g un rin n e Brake peda table on recheck e fre measu rectio ake peda adjust th e appropriate di ent is made and at the br is not adjus m th is taken 11). If necessar y, st in ju . h itc the ad itch all vehicles e 4g the sw nut after (Figur Figure 6-26 , check sw The booster on this d turnin an the lock l linkage itch Honda ispe part a VSA daofl sw system. ake peda Vacuum to tighten htened. br et e rg th fo tig not h on .source hose rect. Do ter the locknut is l stop lamp switc g pedal free play Figure 6-28 Do not remove the check valve from this af hanica adjustin free play has a mec necessar y after type of booster. Remove the hose from the check valve If the car it if st instead. ju ad n and io at Electrical er ch op it connectors s lamp Sw 300 Serie Chrysler the Stop on 2010 Figure 6-27 Before removing the booster Adjusting is based ureelectrical edESP oc fasteners, disconnect all of the pr g win llothe connectors booster and master cylinder. The foon TE R’S nO AuThO m vehicle. its nubattery. Remove the windshield wiper module warping negative cableanfrom the d Mag and justed by usually adcomponents to gain access to the booster. could be are p switch p lamp switches ts lam ac p nt sto Disconnect the electrical connections at the e, a booster and remove s or co y’s sto the master cylinder. one tim switche ever, toda rms the ownot internalthe brake Move the master cylinder E Tip  At thelin booster. up. H Do bend re orntdamage that info dal SERviCback from ger ed a sensor lines. five diffe plunthe Disconnect the vacuum four orbut hose t thefrom check are usingthe check e brake pe dohinot to valve, s remove thvalve up cle of ) nt to ge ith ve w ou e CM m PP) m (E from the booster Figure ional units ter systems. So Module Pedal Position (B ct6-28). Control pu e multifun itch. any com or Engine named the Brak e BPP sw at serve m Module (BCM) th is th to or g ns in se steering column, WARNiNG Before working in or around rol l. Thethe Cont ps accord ensure that the Body nt of trave Failure brake lam air bag system has had totedischarge. and ex erate the to properly disarm the air bag iontime positin M will op system could result serious e BCinjury. Switch. Th

Service Tips Whenever a shortcut or special procedure is appropriate, it is described in the text. Generally, these tips describe common procedures used by experienced technicians.

measure

136

apter 4

Ch

Tape Move inside the passenger compartment, and, if sufficient time has elapsed for the air bags to disarm, disconnect and remove the stop lamp switch (Figure 6-29). The switch will be replaced with a new one upon installation of the booster. Use a screwdriver to Caution remove the retaining clip from the booster pushrod, and slide the pushrod from the pedal Before even beginpin (refer back to Figure 6-29). Remove the booster’s four mounting nuts, and remove the ort Brake eff e ning to work on a 139compartment. booster from the d engine .ind ug 33-198 hybrid or electric pedal ga ch04_hr_1 64540_ Before installing the new booster, ensure that a new booster seal is present on the vehicle, make certain bulkhead side of the booster (Figure 6-30). Slide the booster into place ap that you are aware of plied the bulkUn through l da pe head and tighten the four mounting nuts to specifications. Position the brakebooster pushrod or the procedure to dismeasure able the high a tapelamp voltage over the pedal pin and install a new retaining clip. Install and adjust the4-4 ce Usestop the distan l. Figure new supply system to measure ering wheepower switch. Under the hood, install the master cylinder onto the booster dstick reconnect a yarand l to the ste all da according to service pe the electrical connections. Install the wiper module and other removed components. from Connect information. the battery and road test the vehicle. Brake pedal e ug effort ga

pedal effort

pedal. the brake gauge on

ke tall the bra SERviCiNG ANInsELECTROhYDRAULiC Figure 4-3 POWER BOOSTER SYSTEM

Hybrid vehicles, as well as some conventional gasoline vehicles, use an electric brake booster pump (often referred to as a hydraulic power unit Figure 6-31) used to pressurize brake fluid for use in a hydraulic booster system, which has the master cylinder

References to the Classroom Manual

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References to the appropriate page in the Classroom Manual appear whenever necessary. Although the chapters of the two manuals are synchronized, material covered in other chapters of the Classroom Manual may be fundamental to the topic discussed in the Shop Manual.

Apply the

specified

ec til the sp e pedal un the brak . 4. Apply uge (Figure 4-5) ga effort

Classroom page 75

Cautions and Warnings Cautions appear throughout the text to alert the reader to potentially hazardous materials or unsafe conditions. Warnings advise the student of things that can go wrong if instructions are not followed or if an incorrect part or tool is used.

Manual

amount of

dal force.

pe

force re ified test

gisters on

e pedal the brak

sservice hi vehicle’s for exam fer to the ir order, nosis, re any diag ning to this repa quick, accurate g tin ar rtai to a fore st pe ay Be y w   e or p st th Ti E cent hi ay point SERviC ote any re repair m ailable. N A recent brake tory if av w. e pedal lo d ple, brak e increase . rdstick. Th cle service diagnosis hi sure or ya tape mea n listed in the ve rod adjuste th on sh n tio l positio check pu e also can specifica ge in peda the maximum aulic system and rking brak the chan t exceed the hydr 5. Note justed pa should no ok for a leak in poorly ad a or distance lo s, , er it does adjust If oe l. sh ua d man s, ba orn shoe l travel. ment. W da cessive pe EnT cause ex DJuSTM d the AnD A shrod an at ECTiOn oster pu p bo S so th or l in da lAY ake pe must exist pedal p br ay E e pl E th e R n F e betwee ific amount of fre ased and so that pEDAl clearanc ay is the r. A spec dal is rele dal free pl e master cylinde ied when the pe Brake pe appl in th lly on ia st rt pi primar y y piston is not pa ar the prim

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Figure 4-5

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Chapter 4

Stoplamp switch Stoplamp switch mou nting bracket

Brake pedal

lever Figure 4-12 Pull before installa the switch plunger all the tion way out and not release . The pedal should be lock ed d until the swit ch is installed. down

Use a brake pedal for a depressor depressor to hold the brake pedal ). Rotate the down (check stop lamp sw and pull rea the alig rward on the itch approxim sw ately 30 degree nment machine hand force only, pull the itch. It should separate s counterclock from its mo switch plung should be hea wise unt (Figure er out to its rd as the plu 4-12). Using ful ng ly er ext ratchets out. Ensure the bra ended positi on. Low clic ke ped al is down as switch’s index ks far as it will key to the no go and is firm switch about tch in the bra ly held in pla 30 deg cket and pu ce. Align the sh the switc Apply foot for rees clockwise until it loc h int o pla ks. ce ce. to the brake Rotate the to gently ris pedal and rem e until it sto ove the pedal ps. Using gen stops movin depressor. All tle hand for g. This will ow the pedal ce, pull up on ratchet the adjustment switch plung the brake ped is initially che er to the cor al until it cke pedal is dep rect position ressed and rel d by having an assistant . The switch obser ve the eased. Howe where the cru brake lights ver, the final ise as the brake check requir at a safe speed. control can be safely use es a d. road test on Once the sys During the roa a roa tem is stabilize should turn d test, engage off. If not, the d, depress the the cruise con d n the switch brake slightl trol must be che y. The cruise cked and rea djusted as nee control ded. CuSTOMER CARE A cus tomer’s only his or her car contact, lite is rally, with the mance by “pe through the brake pedal. brake dal feel.” It is Customers ten always a goo brake pedal d to judge bra system in d idea to eva before startin ke perforluate the fee g any brake pedal feel sho l and action job. Then wh uld be notic of the en you delive eably impro brake pedal r the ved action is air in the system . The biggest cause of spo finished job, lot to ensure , so careful ble ngy or low customer con eding of the fidence. system will do a

Caution

Do not release the brake pedal by pul ing the depress lor and letting the out pedal slam up to its sto The stop lamp p. switch will not adjust properly and may be damaged.

Customer Care This feature highlights those little things a technician can do or say to enhance customer relations.

Brake peda

l position

Switch Many late-m odel vehicle s use a BPP sen the brake ped sor to inform al the body con supplies a 5-v position (Figure 4-13). trol module Th olt reference (BCM) of signal and gro e BPP sensor is a poten tiometer. Th und to the sen e BC sor and the sensor suppli M es an

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Name ______

____________

____________

DIAGNOSIN

G DRUm BR

Drum Brake

________

Date ______ ___________

AkE PROB Upon comple LEmS tio ing, grabbing, n of this job sheet, you will be able dragging or to pedal pulsat ion problems diagnose poor stopping, ASE Educa tion Founda . noise, pulltion Correlat This job she ion et addresses the following C.4. MLR task: Inspect wheel needed. (P-2) cylinders for leaks and proper operat ion; remove This job she et addresses and replace as the following AST/MAST C.1. Diagnose po tasks: or pulsation con stopping, noise, vibrat ion, pulling, cerns; determ grabbi C.5. ine necessary Inspect wheel action. (P-1) ng, dragging or pedal and replace cylinders for leaks and proper operat as needed. (Pion; remove 2) Tools and Ma terials • Basic hand tools Protective Clo Goggles or saf thing ety glasses wit h side shield Describe the s vehicle being worked on: Year ______ ________ Ma ke _________ Engine type _____ Model and size ___ ____________ ____________ __ VIN ______ Procedure ____________ ________ ____________ ____________ _________ 1. Begin the inspec unusual wear tion of the drum brake or improper sys inflation. Wh tem by checking the tire at did you fin s for excessive d? or 2. Wheels for bent

or warped rim

s. What did

3. Wheel bea rin

gs for loosen

4. Suspensio n

ess or wear.

system for wo

5. Brake flu id lev

rn or broken

el in the ma

ster cylinder.

Service

425

JO 1/31B /18 Sh 10:33 EE AM T

36

Job Sheets Located at the end of each chapter, the Job Sheets provide a format for students to perform procedures covered in the chapter. A reference to the ASE Education Foundation task addressed by the procedure is included on the Job Sheet.

you find?

What did you

find?

components. Wh

What did you

at did you fin

d?

find?

6. Signs of leakag at each wheel e at the master cylinder, . What did you in brake line s or hoses, at find? all con

nections, and

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424

Chapter 8

can be used S depth gauge B says n A says a tire . Technician 4. Technicia ng thickness e, lini lath a re lining thickon asu um m me to cify a minim unting a dru spe mo to s g s ker sin above the unt ) ma cus most car or 0.75 mm ece drum mo 1. While dis says a two-pi inch (0.030 in. t rivet head. Who is cones. ness of 1/32 Technician A ses d or spherical ed above the clo ter or with tapere or cen le arb is e tab m e lath sho the ece dru says a one-pi d cone and B correct? Technician B spring-loade C. Both A and adaptarbor with a cup-shaped on the lathe nor B A. A only by two large ce D. Neither A pla in ed clamp y onl B t? B. rec hn cor . Tec ician B ers. Who is ng discussed C. Both A and se inders are bei inder may4cau 5. Wheel cyl nor B 99s that A. A only king wheel cyl lea D. Neither A a say t e tha s icia A say rvic n B s Sehn cylb or loctek.mTec nA B. B only wheel to gra ng Sysfou ide the wheel the sed. Technicia ins nd cus dis e ki ng ke Braseepag ms are bei ssl or pneca may cause bra d a cause for dam 2. Brake dru Electri t boot is not considere ts in the drums is t? spo rec ing d cor har tter t is dus cha o inder says tha s that er. Wh hnician B say wheel cylind Who B replacing the chattering. Tec fluid-soaked brake pads. C. Both A and by is not y usually caused nor B A. A onl l years mD. Neither A ra ve t? B is correc lastB.se B onl yother co y e C. Both A and th an hin ispla ome ilt wBit er Aunor A. A only ld to d ly bec D. Nehith icles b has actual actually to strument y e of ve B. Bponl ority t p,anel d lights ar ch. Most in ster that ting mkeajlath cut menbits am s e e u an l it ru th s cl st g n sw bra a uld ge g in u sho sor or es er osin p. The inthe cut er is ting stcus e gabit ile dis n d Warn 3.mWh any tim hile a clust or shsothe tipetofwork. Th mhtly ent cluciapnicAalsay y sende ps. M n n B saysgafrslig stru hni ty o anrou ve cia airl sho own time w rogrammed otihni The in bleTec in theor esha retpwil Tec adin dru tom rp. meltha t re ea raz pan ce d ec the e rep t u b ir into d n th au spi d en ove to re a servic odube gro m d s le ocan t is o ral y instru ration. Wh elp o also nee m bit al dcut ata,an ec lt ke ope ich h ill puter n se ri se noi sp erriaatic braged, wh sytoand uster w o nt out ilt is exchan strument cl based arcau , t? rebu s e serecn e in C. Both A and B th , ements ee ly cluster adcor b al mon el laced. y ition re y A.onl nor B y com ays make d Add as been rep has al pA. D. Neither A lw are man As re aireBnonl ce yit h use sh n is used. A ncerned. n, being ze o B. in d s co io li em io format st syst vehicle reinitia format the late the right in pair for the st service in at ost of late ific re Ip M to verify th e spec , consult the ic testing. ICe T th v ry r R sa fo e st n rs S s neces diagno r repai rmatio is alway service info show up fo r up-to-date but it tins fo check egin to sure to er systems b service bulle al the new and technic , ry low recalls at a ve be okay, to tivating ABS ac ng appeared g to a slow of the in ythi ng m er ni co ev ai d d y compl inspected, vement an tool an of r D ne an U pa ST e sc ere e ow on dr y akes w with th read th e source CaSe e shop ere made, br the vehicle e technician had to be th oblem. th to in w pr th V with checks e BPM e came e while e same tivated an to A vehicl l the normal the ABS ac t out to driv cided that th e still had th the technici amiAl at an de be cont an told e vehicl speed. r the fact th ok an assist cian finally ator, th lp. The forem t appear to replaced fo ni to ul ch pt an od te ce ci no m e ex e he e d e techni rmal. Th an for pensiv they di e shoes wer s here: Start stop. Th ng looked no acing the ex shop forem en though th help. ev e When pl o lesson ever ythi lem. After re d to go to th the drums, placement. There are tw hen you need re ce w de the prob int he deci and resurfa t of needing ed normally. technician s po in rm ed oe is po rfo nc th sh e pe rie th At the rear vehicle ore expe worn to replace any way or achined, the to ask a m cusid m in with a k be afra nated drums were as 2b3lem 4ro do not e ant to keing p and th basics, and Saebrvraic it is import ician B sayg e ke in th ra ss n B with S dismcu ian A says urs. Tech the ru N e D il IO h ri du ng nic occ eST 3. W done blem , Tech W qU tomer when a pro k what was AM as RevIe tly ssed. 1/31/18 10:16 to e ac cu t B l t? is ex st d an y d T port A an correc eing -7 mu aSe-S B BS is b elphi DBC in sit is im ice. Wbhraokeis lathe, i-C. Both A nor x D g an A rv on a sem stdru appro of. Neither leedin ys that the three times ol f la b o e g d k D nin 1. Bra nician A sa rakes bleSd at a scan to espe- achining a . A in le spee ondly a series . BS w ar n B N ys th 424 d h em, henrm A usesAa sp ialyn B makes diameter ia ice b b er A Tec r_373-434.ind 64540_ch08_h n B sa e servUEnSicTiaIO BS syst6. W m that the am n. Te chnic can sthonician e th loec . hBnoicn final druys anicA havIE e, of fluid T Wceq m. TBec lered nctio lamp also . Tech sa e rp b rv fu th 0 A V t se to al 5 n en E n 1 in R sequ ou S md B arning irded btae chnicia t?mately m fo B u o E am q ec A L . ru e to ? rr re er Y rg w an e ts ct T ke as a la b just cu is co A anK E 4. T als corre might a brae w dB allow ASE-S t? p sig n C.e BreodthBR A n shoe ad . Who B or hBo is remalolyveif the er brake replapceardking . Both A ansh hroBis correc lam that th m. W A and thberleA ying to ci C ff th no V wasin the . Both ks oB . SNpeiro AW says ore tr DB or B PalM g C l slack an A either 1. Bef nician A bac ths eup in only N er A n al in A . n -l . g D si Ain an B . Neith o m-to Tech ian B take . co d D oneclyt? tw ru t d n an e A rr ly ly e A A oifnth ic of th prese B. B on A s e . at er ar B A th Techn ble. Who is only C. Both et r as ys nodes ng iam ca bleAco n A sa . t,Bth B. B onelyd atter as lo . ouer brake trth Nei d. hnicia t is corrBec . le nec on ot m ltDip 7.uT gro only t do n imensi en mu n men ician A mmon A. A adjust n an axle se e discard d iameters o 2. Wh look for:der, Technat a co t o ly d o n o , th n n o b s S ti ton AB heel cyliconnec . drum not exceed at the drum me. Who is B. B o kind the pis on this fact sa th do ng a .wa wbea e ti ys ey th eh . ec sa y it th ed Afluid tl en insp errcbuas ees.l cylinder ician B e exac ndci oplien 8 2. Wh liquid brake Bh. ee Techn les must b dB anl cy 1/31/1 gnhal ho is thesiw ax th A an finds uilds the w ot w W builltdage given C. Bo nor B b n lo re-vo the ebosiogt.nals. t? ec and re ian B doesC. und inolt ther A rr ag co fohigh-v ic D. Nei n is h s ly B ec es n . e T n D o d b A. A damp must und th A an rums o if only C. Bo nly nor B new d fing comp at t? B. B o ther A o th ys that correc D. Nei n A sa the rustpro ician B says ia ly all n ic h o n it rw move move Tech echn A. A re ca . T re 8 a to e. to n rfac ned ly es o the ned ho is n o su s ea ea o cl W sh ve m cl B e o e. B. e dru rfac ust b e brake nician A m heel. th su m th s m m g o m fr w ru stin d 49s, 9 Tech the dru e star hed d e the nd en adr_ju 1-51 refinis articles from dB g4.ibrake ay from th to just forc en3. Wh0_ch10d_h st46in p th A an 54lf-a ju ver aw 64se ut dis policy metal C. Bo or B sting le it is best juster witho t? ju d er A n ec -a ys rr co self Neith B sa lf-ad . n se D ia e h ic th only gs wit B A Techn eel against in d . n t? an li A h rrec h th A icate a kes wit star w . Who is co C. Bo B only nor B at bra der end ind that if . A it B th g er ys in th gag n A sa wheel cylin ician B says re D. Nei hnicia n e only mo heel 9. Tec wear at th ition. Tech A. A e and e is worn corthe to more wear cond er vo brake installed in nly orn at says that th B w B. B o e al o-s ly norm e bad hnician A echnician may b n a du o ar es g o gs in linin o is . Tec d drum. T e lin the sh B h , n m gs o d er W in ru . th an n li m n eo 4. D ect? th A of the out-of-rou tapered dru B than th ho is corr C. Bo areas A nor W m is a m is an either rectly. N B . proble the proble d D rn A an nly at tu o th th re o A n B . ys A sa C. nor B broke to one t? nly g ther A eak or correc B. B o that w g or pullin roblems D. Nei only p A says dra A. A nician use brake at the same or an inop is c ard hich h d ec m T ca . nly 10 ys th king plate e dru e ter to w can sa th gs B n B. B o at ri n sp diam ic ian B ys th nicia a loose bac rrect? h sa m u ec A T n im is co side. d by dB nic ian e ma x the d. Te ch cause . Who th A an 5. Te ch sion is th refinishe iame ter is can be self-adjuster not C. Bo or B dimen ms c an b e dis c ard d n and e er A n ensio erativ Neith . D the dru the drum we ar dim ter. Who is only at le A e . th ab m A w lo says g dia um al nly hinin B. B o ma xim w able mac dB lo th A an the al ? C. Bo nor B A ct er e th corr D. Nei only A. A nly B. B o

LENG ASE ChAL

Ase Challenge Questions Each technical chapter ends with five ASE challenge questions. These are not mere review questions; rather, they test the students’ ability to apply general knowledge to the contents of the chapter.

Case Studies Each chapter ends with a Case Study describing a particular vehicle problem and the logical steps a technician might use to solve the problem. These studies focus on system diagnosis skills and help students gain familiarity with the process.

Ase-Style Review Questions Each chapter contains ASE-style review questions that reflect the performance objectives listed at the beginning of the chapter. These questions can be used to review the chapter as well as to prepare for the ASE certification exam.

E qUESTION

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xvii Disc Brake Service

___

Name ___________________________________

Date _________________

DIAGNOSING DISC BRAkE PROBLEMS

355

Job Sheets

JOB ShEE T

30

Located at the end of each chapter, the Job Sheets provide a format for students to perform procedures covered in the chapter. A reference to the ASE Education Foundation task addressed by the procedure is included on the Job Sheet.

be able to diagnose poor stopping, noise, Upon completion of this job sheet, you will n problems. pulling, grabbing, dragging, or pedal pulsatio ASE Education Foundation Correlation AST task: This job sheet addresses the following AST/M pulling, grabbing, dragging, Diagnose poor stopping, noise, vibration, D.1. y action. (P-1) or pulsation concerns; determine necessar Tools and Materials Basic hand tools

Protective Clothing Goggles or safety glasses with side shields

Describe the vehicle being worked on: _ Model ______________ VIN ______________ Year _______________ Make ______________ Engine type and size _______________ Procedure

e or system by checking the tires for excessiv 1. Begin the inspection of the disc brake did you find? unusual wear or improper inflation. What ___ ___________________________________ ___________________________________

did you find? 2. Wheels for bent or warped wheels. What ___ ___________________________________ ___________________________________ find? you did What wear. or ss 3. Wheel bearings for loosene ___ ___________________________________ ___________________________________ find? you did components. What 4. Suspension system for worn or broken ___ ___________________________________ ___________________________________

. What did you find? 5. Brake fluid level in the master cylinder ___ ___________________________________ ___________________________________ and ions, connect all at hoses, , in brake lines or 6. Signs of leakage at the master cylinder find? Ap at each wheel. What did you pe nd ix ___ ___________________________________ _______ _______ _______ ______________ As e pr Ac tic e and travel e excessiv for ex check Am in At io n brake pedal, 7. Road test the vehicle. As you apply the sponginess. What did you find? _______________________________ _______ _______ _______ _______ ______________ but 1. Technicia obvious sounds of grinding pads or pad linings, justifthe notthat n A says for noises, 8. Listen the master cylin did you find? 6. A vehi and rattles. Whatder pushrod clunks, icalisclanks, adjusted mechan cle drift too long, the brakes migh s to the ___right while driving. _______ not be able ______________t ______________ Tech_______ to fully nician A says that a crim _______ _______ appl_______ _______ y. Technicia n B says that if ped line to the left the master cylinder push whefor el caliper coul bad a d be check the rod applied, caus are is e. Technician B says that adjuthe brakes sted too short, pulls to one side when vehicle thebrak the 9. If may that es migh fluid inter brake ior of t drag the . Who Also signs of grease orthe for righ check is t corr brak wheel. ect? e one hose could be damat caliper or loose pads. d brake damage . Who A. A only is corr rotor. Check for distorted oraged ect? have contaminated the pads and C. Both A and B A. A only B. B only C. Both A and B D. Neither A nor B B. B only 2. While discussing mas D. Neither A nor B ter cylinders, Technicia nA says normal brake linin 7. Technician A says serv g wear causes a slight ice information circuit drop in fluid level. Technicia diagrams or schematics mak n B says a sure sign of e it easy to identify com brake fluid contamination mon circuit problems with mineral oil is the . Technician B says if seve 02/02/18 swelling of the master ral circu its fail at the same time cylinder cover diaphrag , check for a common m. Who 355 is correct? power or ground conn 64540_ch07_hr_285-372.indd ection. Who is correct? A. A only A. A only C. Both A and B C. Both A and B B. B only B. B only D. Neither A nor B D. Neither A nor B 3. Technician A says that 8. Tech nician A says that ther master cylinder leaks e is a vacuum check can be internal or external valve in line between man . Technician B says that ifold vacuum source a leaking master cylinder and the booster. Technicia will remove paint from n B says this check the area below the mas valve is to allow air pres ter cylinder. Who is sure into the booster durcorrect? ing wide-open throttle operation of the engine. Who is correct? A. A only C. Both A and B A. A only B. B only C. Both A and B D. Neither A nor B B. B only 4. While discussing brak D. Neither A nor B e lines, Technician A says that copper tubing can 9. Dru m brak es are being discussed. Tech be used for brake lines . nician A Technician B says that says that a grabbing brak brake lines can use doub e could be traced to a leflare or an ISO flare fittin leaking axle seal. Tech gs. Who is correct? nician B says that a leak ing wheel cylinder can also A. A only cause drum brake grab C. Both A and B bing. Who is correct? B. B only D. Neither A nor B A. A only C. 5. Technician A says to Both A and B replace a double-flare B. B only fitting with an ISO-type fittin D. Neither A nor B g as new brake lines are required. Technician B 10. Befo re tryin g to remove a brake drum says that flexible brake for service, hoses allow movement Technician A uses the of components. Who self-adjuster to back off is correct? the brake shoes. Technicia n B adjusts the parking brake cable to remove A. A only the slack . Who is corr C. Both A and B ect? A. A only B. B only C. Both A and B D. Neither A nor B B. B only D. Neither A nor B

Ase Practice Examination A 50-question ASE practice exam, located in the Appendix, is included to test students on the content of the complete Shop Manual.

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SUPPLEMENTS Instructor Resources The Today’s Technician series offers a robust set of instructor resources, available online at Cengage’s Instructor Resource Center and on DVD. The following tools have been provided to meet any instructor’s classroom preparation needs: ■■ An Instructor’s Guide provides lecture outlines, teaching tips, and complete answers to end-of-chapter questions. ■■ Power Point presentations include images, videos, and animations that coincide with each chapter’s content coverage. ■■ Cengage Learning Testing Powered by Cognero® delivers hundreds of test questions in a flexible, online system. You can choose to author, edit, and manage test bank content from multiple Cengage Learning solutions and deliver tests from your LMS, or you can simply download editable Word documents from the DVD or Instructor Resource Center. ■■ An Image Gallery includes photos and illustrations from the text. ■■ The Job Sheets from the Shop Manual are provided in Word format. ■■ End-of-Chapter Review Questions are also provided in Word format, with a separate set of text rejoinders available for instructors’ reference. ■■ To complete this powerful suite of planning tools, a pair of correlation guides map this edition’s content to the NATEF tasks and to the previous edition.

MindTap for Today’s Technician: Automotive Brake Systems, 7e MindTap is a personalized teaching experience with relevant assignments that guide students to analyze, apply, and improve thinking, allowing you to measure skills and outcomes with ease. ■■ Personalized Teaching: Becomes yours with a Learning Path that is built with key student objectives. Control what students see and when they see it. Use it as-is or match to your syllabus exactly—hide, rearrange, add, and create your own content. ■■ Guide Students: A unique learning path of relevant readings, multimedia, and activities that move students up the learning taxonomy from basic knowledge and comprehension to analysis and application. ■■ Promote Better Outcomes: Empower instructors and motivate students with analytics and reports that provide a snapshot of class progress, time in course, engagement and completion rates.

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xix

REVIEWERS The author and publisher would like to extend special thanks to the following instructors for reviewing the draft manuscript: Rodney Batch University of Northwestern Ohio Lima, OH

Larry Stanley Arizona Western College Yuma, AZ

Christopher J. Marker University of Northwestern Ohio Lima, OH

Claude F. Townsend Oakland Community College Bloomfield Hills, MI

Tim Pifer Midlands Technical College Columbia, SC

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Chapter 1

Brake System Fundamentals

Upon completion and review of this chapter, you should be able to: ■■ ■■

■■ ■■

List and describe the operation of the basic parts of a brake system. Describe the operation of the brake system during and after pedal application.

■■

Discuss the increasing use of disc brakes instead of drum brakes. Describe a typical brake hydraulic system.

■■

■■

■■

Describe the use of valves and lines to direct and control the hydraulic fluid. Discuss the purpose of brake power boosters and the parking brake. Discuss the general operation of electronic and active braking systems. Discuss the general operation of trailer brakes and air brakes.

Terms To Know Active braking Actuators Air brakes Antilock brake system (ABS) Automatic ride control (ARC) Bulkhead Caliper Disc brake Drum brake Force

Friction Fulcrum Lateral acccelerometer Leverage Lockup Master cylinder Negative wheel slip Parking brakes Positive wheel spin Pressure Regenerative braking

Service brakes Steering wheel position sensor Stroke sensor Stroke simulator Traction-control system (TCS) Vehicle stability control (VSC) Wheel cylinder Wheel speed sensors Yaw

INTRODUCTION The brake system is one of the most important systems on a vehicle. It has four basic functions:

1. It must slow a moving vehicle. 2. It must bring a vehicle to a stop. 3. It must hold a vehicle stationary when stopped. 4. It allows directional control during maximum braking.

If the brake system does not operate properly, the driver and passengers could be injured or killed in an accident. Technicians who service the brake system must be highly skilled experts because the work they do can save lives. In this chapter, we start our study of the brake system by presenting the basic concepts and parts of all brake systems. 1

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Chapter 1 Anti-lock brake system (ABS) is a braking system that is designed to prevent the brakes from locking up on hard stops so that the driver can maintain control of the vehicle.

Service brakes: The brakes that are used to stop the vehicle. Parking brakes: The braking system that is used to hold the vehicle stationary while parked. Regenerative braking recapture some of the lost energy during ­braking on hybrid vehicles.

This chapter also highlights some of the dynamics associated with braking and controlling a vehicle. If all the various dynamics are not considered during the design stage, most braking systems will under brake or over brake. When the brake system is not designed or operating correctly, it will be up to the driver to compensate, usually with poor results. In many cases, the human response is either too slow or too quick to react to a braking situation. In both cases, a loss of vehicle control is probably unavoidable. To prevent this, antilock brake system (ABS) and stability control have been added to help the driver maintain control.

BRAKE SYSTEM OVERVIEW The complete brake system consists of the major components shown in Figure 1-1. These are the service brakes, which slow and stop the moving vehicle, and the parking brakes, which hold the vehicle stationary. On late-model vehicles, the ABS is a third major subsystem; and new cars now also include traction control and stability control as part of the brake system functions. Hybrid and electric vehicles make use of regenerative braking, which captures some of the energy normally lost as heat on the pads and rotors while stopping. Regenerative braking systems use electrical generators to help slow the vehicle during gradual stops and help recharge the electric batteries. Electric and hybrid vehicles still have conventional hydraulic brakes to stop the vehicle quickly when necessary. Regenerative brakes are a blending of the generators’ ability to help slow the vehicle and conserve energy and the hydraulic systems’ ability to stop the vehicle quickly.

Leverage and the Brake Pedal Design Author’s Note  A fulcrum is the point at which one lever pivots or sits to apply force to another lever or device. A seesaw pivots on a fulcrum. Hydraulic power brake booster Rear disc or drum brakes

Master cylinder and ABS hydraulic unit ABS wiring harness

ABS computer

Brake pedal

Parking brake lever

Front disc brakes

Figure 1-1  A typical automotive brake system comprises these major components and subsystems.

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Brake System Fundamentals Brake pedal pivot (fulcrum)

2 inches 250 pounds of force 10 inches Master cylinder

50 pounds of force

Lever Bulkhead

Brake pedal

Figure 1-2  The brake pedal assembly uses leverage to increase force applied to the master cylinder.

Braking action on an automobile begins with the driver’s foot on the brake pedal. The driver applies force to the pedal (which we learn more about later), and the pedal transfers that force to the master cylinder pistons. The brake pedal also multiplies the force of the driver’s foot through leverage. The brake pedal is mounted on a lever with a pivot near the top of the lever. The movement of the pedal causes a pushrod to move against a master cylinder. The master cylinder is mounted inside the engine compartment on the rear bulkhead. The master cylinder is a hydraulic pump that is operated by the driver through the brake pedal. Most brake pedal installations are an example of what is called a second-class lever. In the science of physics, a second-class lever has a pivot point (or fulcrum) at one end and force applied to the other end. A second-class lever transfers the output force in the same direction as the input force, and multiplies the input force, depending on where the output load is placed. The brake pedal installation shown in Figure 1-2 has a 10-inch lever, and the load (the master cylinder pushrod) is 2 inches from the fulcrum (8 inches from the pedal). The pedal ratio, or the force multiplying factor, is the length of the lever divided by the distance of the load from the fulcrum. In this case, it is:

The bulkhead separates the engine compartment from the passenger compartment. The fulcrum is the support for a lever to pivot on.

10 5 5 :1 2 If the driver applies 50 pounds of force to the pedal, the lever increases the force to 250 pounds at the master cylinder. When the driver applies 50 pounds of input force, the pedal may travel about 2.5 inches. When the lever applies 250 pounds of output force, the pushrod moves only 0.5 inch. Thus, as leverage in a second-class lever increases force, it reduces distance by the same factor: 2.5 inches 5 0.5 inch 5

Leverage is the use of a lever and fulcrum to create a mechanical advantage, usually to increase force applied to an object.

Service Brake History and Design Modern automobile brakes evolved from the relatively crude brakes of horse-drawn vehicles. The earliest motor vehicle brakes were pads or blocks applied by levers and linkage

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Chapter 1

Friction is the force that resists motion between the surfaces of two objects or forms of matter.

A drum brake is a brake in which friction is generated by brake shoes rubbing against the inside surface of a brake drum attached to the wheel.

to the outside of a solid tire on a wooden-spoked wheel. The same principles of leverage that work in modern brake pedal installations increased the force of the brake pad applied to the solid tire. These brakes worked well with speeds of 10 mph to 20 mph and little traffic. Higher performance (30 mph and beyond) and pneumatic tires meant that early wagon brakes were short-lived on automobiles. By the end of the first decade of the twentieth century, automobiles were using either external-contracting band brakes or internal-expanding drum brakes. A few internalexpanding band brakes were tried on some early motor vehicles. External-contracting brakes have a band lined with friction material wrapped around a drum located on the driveline or on the wheels. The band is anchored at one end or at the center; levers and linkage tighten the band around the drum for braking force. The service brakes on Ford’s famous Model T were a single contracting band applied to a drum inside the transmission. Band brakes, either internal or external, lose their effectiveness when higher braking force is needed. When you study drum brakes, you will learn about the mechanical servo action of brake shoes. It is very difficult to develop servo action with an internal band brake, and higher brake force is thus needed. Servo action on an external band brake tends to make the brake grab at high brake forces and high drum speed. Other problems associated with band brakes include dirt and water damage and loss of friction with external bands and the tendency of these brakes to lock if the drum overheated and expanded too much. Internal band brakes also suffer from band and drum overheating and reduced braking force. As drum brakes evolved, internal-expanding shoe-and-drum brakes became the standard. External-contracting band brakes were used as parking brakes until the late 1950s, but their days as service brakes were over by the late 1920s. Drum Brakes.  By the mid-1920s, drum brakes with internal-expanding shoes were the general rule. Early drum brakes were operated mechanically by levers and linkage (Figure 1-3). Expensive luxury cars such as the 1921 Duesenberg Model A were among the first to have hydraulic drum brakes. Hydraulic brakes started to appear on lowerpriced cars in the mid-1920s with Chrysler’s Light Six, which became the Plymouth. Ford Motor Company, however, used mechanical brakes through the 1938 model year. Author’s Note  There were two major reasons for the increased use of hydraulically applied brakes over the mechanically-applied ones: (1) The four brakes never seemed to apply the same amount of braking force at the same time because (2) the brake linkages required almost constant re-adjustment to make the brake work at all. The only reason mechanical brakes were ever practical was the fact that roads were rough and couldn't be traveled at high speeds.

Disc Brakes: A braking system that forces two brake pads on opposite sides of a spinning rotor to stop the vehicle

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The rigid brake shoes used with drum brakes could be made stronger than the flexible bands of earlier brake designs. This eliminated breakage problems that occurred with greater braking forces that were required as automobiles got more powerful and faster. With hydraulic actuation, four-wheel drum brakes remained the standard braking system for most cars into the middle and late 1960s. With the coming of Federal Motor Vehicle Safety Standards (FMVSS) 105 in 1967, brake systems had to pass specific performance tests that made front disc brakes the general rule in the 1970s. Even at the beginning of the twenty-first century, however, drum brakes are still used on the rear wheels of many cars and light trucks. Disc Brakes.  Modern automotive disc brakes were developed from aircraft brakes of World War II. Known originally as “spot” brakes, disc brakes work by applying pressure to two brake pads on opposite sides of a spinning rotor attached to the wheel hub

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Brake System Fundamentals Brake pedal

Brake pedal rod

Brake pedal pivot Cam

Brake shoes

Drum

Figure 1-3  A simple mechanical expanding drum brake.

(Figure 1-4). Disc brake pads are mounted in a caliper that sits above the spinning rotor. The caliper is either fixed or movable on its mounting. With a fixed caliper, hydraulic pressure is applied to pistons on both sides to force the pads against the rotor (Figure 1-5). With a movable caliper, pressure is applied to a piston on the inboard side only. This forces the inboard pad against the rotor, and the reaction force moves the outboard side of the caliper inward so that both pads grip the rotor (Figure 1-6). All the friction components of a disc brake are exposed to the airstream, which helps to cool the brake parts and maintain braking effectiveness during repeated hard stops from high speeds. This, in turn, leads to longer pad life and faster recovery from brake fade. Disc brakes do not develop the mechanical servo action that you will learn about as you study drum brakes. Therefore, disc brakes require higher hydraulic pressure and greater force to achieve the same stopping power as a comparable drum brake. These pressure and force requirements for disc brakes are met easily, however, with large caliper pistons

A caliper is a major component of a disc brake system that houses the piston(s) and supports the brake pads.

Caliper Boot

Seal

Caliper Hydraulic pressure

Hydraulic pressure

Hydraulic pressure

Piston

Piston Hydraulic pressure

Figure 1-4  Hydraulic pressure in the caliper forces the disc brake pads against the spinning motor.

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Rotor

Figure 1-5  Hydraulic pressure is applied equally to pistons on both sides of a fixed caliper.

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Chapter 1 Reaction

Caliper

Action Piston

Hydraulic pressure

Figure 1-6  Hydraulic pressure in a movable caliper forces the piston in one direction and the caliper body in the other. The resulting action and reaction force the pads against the rotor.

A BIT OF HISTORY Hydraulic brakes were invented in 1918 in the California shop of Malcolm Loughead. He later changed the spelling of his name to Lockheed, and he and his brother founded the aircraft c­ ompany of that name. The Lockheed hydraulic brake first appeared on the 1921 Duesenberg Model A.

and power brake boosters. Because their advantages far outweigh any disadvantage, disc brakes have become the universal choice as the front brakes on all cars and light trucks built since the 1970s. Additionally, four-wheel disc brakes became standard equipment on high-performance automobiles, SUVs, and some trucks.

Brake Hydraulic Systems The master cylinder is the liquid-filled cylinder in the hydraulic brake system in which hydraulic pressure is developed when the driver depresses a foot pedal.

Although brake systems have been changing recently, hydraulic operation of service brakes has been the universal design for more than 70 years. The complete hydraulic system consists of the master cylinder, steel lines, rubber hoses, various pressure-control valves, and brake apply devices at each wheel. Master Cylinder.  The master cylinder is the start of the brake hydraulic system. It actually is a cylindrical pump. The cylinder is sealed at one end, and the movable pushrod extends from the other end (Figure 1-7). The pushrod moves a pair of in-line pistons that Secondary output port

Primary output port Primary reservoir

Secondary reservoir

Pushrod Piston return spring Seal

Spring

Seal Seal

Seal

Seal

Figure 1-7  The master cylinder is a cylindrical pump with two pistons that develop pressure in the hydraulic lines to the front and rear brakes.

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Brake System Fundamentals Right front

Master cylinder

Right rear

Secondary piston

Primary piston

Left front

Left rear

Figure 1-8  Each master cylinder piston feeds one system of a split hydraulic brake system. Shown is a diagonally split system.

produce the pumping action. When the brake pedal lever moves the pushrod, it moves the pistons to draw fluid from a reservoir on top of the master cylinder. Piston action then forces the fluid under pressure through outlet ports to the brake lines. All master cylinders for vehicles built since 1967 have two pistons and pumping chambers, as shown in Figure 1-7. Motor vehicle safety standards require this dual-brake system to provide hydraulic system operation in case one hose, line, or wheel brake assembly loses fluid. Because the brake hydraulic system is sealed, all the lines and cylinders are full of fluid at all times. When the master cylinder develops system pressure, the amount of fluid moved is only a few ounces.

Pressure is the force exerted on a given unit of surface area—force divided by area— measured in pounds per square inch (psi) or kilopascals (kPa).

Split Systems.  Modern-day vehicles have split brake systems. The pre-1970s vehicle had a single hydraulic system serving all four wheels. A leak anywhere in the system resulted in a complete braking failure. The split system was designed to prevent a total system failure. This required the use of a dual-piston master cylinder and the inclusion of various valves. A split system is fed by one piston in the master cylinder and feeds two wheel brakes of the vehicle. There are two types of split systems: diagonal and front/rear. The diagonal has one system feeding a front-wheel brake and the rear, opposing-side-wheel brake, that is, left front and right rear (Figure 1-8). The second diagonal split is to the other wheel brakes. The front/rear split is exactly as it sounds. One side or split feeds the rear-wheel brakes, and the other feeds the front wheels (Figure 1-9). Both types of split have advantages and disadvantages, but each prevents complete system failure from a single leak.

Hybrid Master Cylinders Hybrid vehicles braking systems have some significant differences as compared to most conventional automobiles. One reason for this is regenerative braking used during light to moderate braking. Regenerative braking can slow the vehicle and recover much of the energy used by using the drive motor as a generator. Another reason is that the engine may not be running to provide vacuum to the conventional brake booster. These two factors produce a master cylinder used somewhat conventionally to produce pressure, but this pressure is amplified by the brake actuator (Figure 1-10) to apply the appropriate pressure to the wheel calipers. The brake stroke sensor ( Figure 1-11) informs the brake

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Stroke sensor informs the brake controller how fast and how much pressure the driver applied to the brakes.

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8

Chapter 1 Right front

Right rear

Master cylinder

Secondary piston

Primary piston

Left rear

Left front

Figure 1-9  A front/rear split dual hydraulic brake system.

Stroke sensor

Figure 1-10  A hybrid brake actuator for a Toyota Camry contains a pump to boost brake pressure instead of using a vacuum booster.

Stroke simulator provides brake pedal feedback to the driver.

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Figure 1-11  A brake pedal stroke sensor tells the braking system how far and how fast the brake pedal is being depressed.

controller how fast and how much pressure the driver applied to the brakes; the brake controller then decides on what ratio of regenerative braking to hydraulic braking needs to be applied. If the braking is light, then the controller may decide to use only the regenerative braking system to stop the vehicle. If the stop is moderate, the controller may command regenerative and hydraulic braking. If the stop is panic in nature, then the hydraulic braking system will be the dominant choice. In these systems, the stroke ­simulator (Figure 1-12) provides appropriate brake pedal feedback to the driver; in other words, the brakes should feel normal to the driver. Brake Lines and Hoses.  The rigid lines or pipes of a brake hydraulic system are made of double-walled steel tubing for system safety. Flexible rubber hoses connect

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9

Pressure sensor 3

Pressure sensor 1

Fluid Reservoir

Pump

Accumulator

Stroke simulator

Master cylinder

Pressure sensor 2

Isolation valves

Pressure sensors

Rear left

Rear right

Front left

Front right

Brake System Fundamentals

Figure 1-12  Hybrid ABS system showing stroke simulator that gives a normal pedal feel to the driver.

the wheel brakes to the rigid lines on the vehicle body or frame (Figure 1-13). The front brakes have a rubber hose at each wheel to allow for steering movement. Rear brakes may have separate hoses at each wheel or a single hose connected to a line on the body or frame if the vehicle has a rigid rear axle. Brake lines and hoses contain the high-pressure fluid, and the fluid acts as a solid rod to transmit force to the wheel cylinders and caliper pistons.

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Chapter 1

Slot for mounting

Connection between steel and flexible hose

Mounting clip

Caliper connection

Flexible hose

Figure 1-13  A flexible hose provides a connection between the vehicle’s rigid frame and the movement of the wheel and suspension assemblies.

An ABS is a service brake system that modulates hydraulic pressure to one or more wheels as needed to keep those wheels from locking during braking. If the wheel locks during braking, steering control becomes very difficult. ABS allow the driver to maintain control of the vehicle during a panic stop.

Dynamic rear proportioning and electronic brake distribution are names for the electronic function of the proportioning valve by the ABS braking system.

The increasing use of four-wheel disc brake systems instead of the front disc/rear drum systems has also reduced the need for metering valves. A wheel cylinder is the hydraulic cylinder mounted on the backing plate of a drum brake assembly.

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Pressure-Control Valves.  Older and a few newer vehicles depended on metering and proportioning vales to control braking application. Metering and proportioning valves were used to modulate hydraulic pressure to front disc or rear drum brakes to provide smooth brake application and reduce the tendency to lock the rear brakes. Although there are many vehicles on the road that use metering and proportioning valves, on most newer vehicles, ABS and stability control replaces the need for using mechanical control valves. Although some systems retain proportioning valves for use in the event that the ABS system fails, most are no longer in use. Metering valves, which slowed the application of the front disc brakes to allow the drum brakes to apply, have been less common since most late model vehicles have disc brakes in both front and rear. Older vehicles had a pressure differential switch that was used in some systems to turn on the instrument panel warning lamp if half of the hydraulic system loses pressure. Today’s systems use a fluid level switch to detect the loss of fluid in the system, in addition to the ABS system, which can be utilized to detect problems in the hydraulic braking systems as well. As was noted earlier, even though pressure-control valves have been part of brake systems for more than 60 years, ABS and stability-control systems are beginning to make some valves obsolete. An ABS electronic control module can modulate hydraulic pressure for normal braking better than metering and proportioning valves can. As ABS installations became standard equipment, some older hydraulic functions have been given over to the electronic modulator. The electronic function of the proportioning valve has been called “dynamic rear proportioning” and “electronic brake distribution” by various manufacturers. Wheel Cylinders and Caliper Pistons.  The wheel cylinders of drum brakes and the caliper pistons of disc brakes operate in response to the master cylinder. These hydraulic cylinders at the wheels change hydraulic pressure back into mechanical force to apply the brakes. Most systems with drum brakes have a single, two-piston cylinder at each wheel (Figure 1-14). Hydraulic pressure enters the cylinder between the two pistons and forces them outward to act on the brake shoes. As the shoes move outward, the lining contacts the drums to stop the car. Wheel cylinder construction and operation of drum brakes are covered in Chapter 8 of this manual. The caliper pistons for disc brakes also act in response to hydraulic pressure that enters a fluid chamber in the caliper. Hydraulic pressure in a stationary caliper is applied to one or two pistons on each side of the caliper to force the pads against the rotor, as shown in Figure 1-5. Pressure is applied to a single piston in a movable caliper on the

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Brake System Fundamentals

11

Brake drum

Piston

Piston

Wheel cylinder

Hydraulic pressure

Brake shoes

Figure 1-14  Hydraulic pressure in the wheel cylinder moves the two pistons outward to force the shoes against the drum.

inboard side to force the inboard pad against the rotor. As explained later, in Chapter 2, hydraulic pressure is equal in all directions in a sealed chamber. This equal pressure creates a reaction force that moves the outboard side of the caliper inward so that both pads grip the rotor, as shown in Figure 1-6. More details about caliper construction and operation of disc brakes are found in Chapter 7 of this manual.

Power Boosters Almost all brake systems have a power booster that increases the force of the driver’s foot on the pedal (Figure 1-15). Most cars and light trucks use a vacuum booster that uses the combined effects of engine vacuum and atmospheric pressure to increase pedal force. Some

Figure 1-15  The power brake booster increases the brake pedal force applied to the master cylinder.

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12

Chapter 1

vehicles without a ready vacuum source may have a hydraulic power booster that may be supplied with fluid by the power steering system or that may be a part of the brake system and driven by an electric motor. Alternatively, as was discussed earlier, the brake actuator can amplify the brake pressure applied to the wheel calipers based on input from the brake stroke sensor. Chapter 6 in this Classroom Manual explains power boosters in detail.

Parking Brakes After the service brakes stop the moving car, the parking brakes help to hold it stationary. Parking brakes are mistakenly called “emergency” brakes, but their purpose is not to stop the vehicle in an emergency. The amount of potential stopping power available from parking brakes is much less than from the service brakes. Because the parking brakes work on only two wheels or on the driveline, much less friction surface is available for braking energy. In the rare case of total hydraulic failure, the parking brakes can be used to stop a moving vehicle, but their application requires careful attention and skill to keep the vehicle from skidding or spinning. Parking brakes on most cars and light trucks are applied with cables. On rear drum brakes, the brakes’ shoes are applied by the cable pulling a shoe into the drum. On some rear disc brakes, a cable applies the caliper mechanically, while most late model disc parking brakes are applied by a small set of brake shoes that sit inside a special brake rotor on the rear wheels. In either case, the parking brake shares the components of the disc and/ or drum braking systems. Some parking brakes are applied through the use of an electric motor on the calipers instead of a cable, and some parking brakes use an electric motor to apply tension to the brake cables, but the basic concept is still the same. traction control systems are designed to prevent wheel slip in low-traction situations by applying the brakes to the free spinning wheel. vehicle stability control is an electronic assisted braking system that can selectively apply and release brakes during critical maneuvers to help the driver maintain control. Lockup or negative wheel slip is a condition in which a wheel stops rotating and skids on the road surface. ABS prevents tires from skidding during braking. Positive wheel spin happens with no traction and the wheel spins but does not move the vehicle.

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Electronic Braking Systems Electronic braking covers all systems from ABS and traction-control systems (TCSs) up to and including vehicle stability control (VSCs). While there are different terms used by the various manufacturers for the same operation, all operate with electronic sensors and actuators with little or no input from the vehicle operator. Some systems such as VSC are in the second and third stages of development and application. The National Highway Traffic Safety Administration (NHTSA) mandated VSC for all models built after 2012. Now we are seeing additional developments, such as cruise control that reacts to traffic conditions, blind spot detection, lane departure alerts, and parking assist. Whenever the brakes are applied with heavy pressure, the wheel may totally stop rotating. This condition is called wheel lockup or negative wheel slip, which does not help the car stop. Rather, the tire loses some frictional contact with the road and slides or skids. As the tires slide, the car is no longer stopping under control, and the driver is in a dangerous situation. Experienced drivers try to prevent wheel lockup by pumping the brake pedal up and down rapidly. This stops and starts hydraulic pressure to the brakes and gives the driver control during hard braking. All late-model cars have an ABS. The ABS does the same thing as an experienced driver would, only it does it faster and more precisely. It senses when a wheel is about to lock up or skid. It then rapidly interrupts the braking pressure to the brakes at that wheel. Speed sensors at the wheels monitor the speed of the wheels and send this information to an on-board computer. The computer then directs the ABS unit to pulse the pressure going to the wheel that is starting to lock up.

Traction-Control Systems (TCS) The TCS controls wheel spin or positive wheel spin during hard acceleration or slippery road conditions. The TCS has some options to control wheel spin. It can reduce engine power via the throttle actuator control (TAC), reduce engine timing through the ECM,

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13

Brake System Fundamentals

and apply the brakes to the spinning wheel. This allows the torque to be transferred to the wheel, which has traction, allowing the vehicle to move.

Automatic Ride Control Automatic Ride Control (ARC) is an electronic suspension system designed to provide a more comfortable ride to the passengers and allow better control of the vehicle during cornering. To some extent, it can command reduced engine power, thereby slowing the vehicle. The major component shared between ARC and active braking is the yaw sensor. Active braking systems take the data from shared components, perform certain calculations, and apply the brakes without any driver input at all. There are more details on active braking and stability control in Chapter 10.

Vehicle Stability Control Vehicle stability control (VSC) will be covered more in depth in later chapters, but a brief overview is given here to help you understand how all these systems interact. VSC is the result of advances in technology that is expected to save many lives, in particular by preventing single vehicle crashes due to loss of driver control. VSC systems depend on a vehicle responding to the application of the brakes to help control the vehicle that is in a skid. Like steering a bulldozer by locking the treads on the right or left sides, a vehicle with the brakes applied individually on one side can help steer the vehicle into control from a skid. The yaw or lateral accelerometer determines the direction and speed at which the vehicle is skidding so the VSC can apply the appropriate wheel brake(s) to correct the skid. The direction the driver is trying to steer is determined by the steering wheel position sensor, which is also a factor in the VSC decision on brake(s) application. The VSC can also determine if a wheel is slowing down too quickly or speeding up too fast by comparing it to the other wheels by use of the wheel speed sensors (WSS) and apply TCS or ABS braking at the appropriate times.

Active Braking Mass-produced active braking systems are systems that can act to prevent a collision without input from the driver. In the context here, “active” means the brake system will perform some functions without input from the operator. The ABS could be considered as the first active braking system, but it functioned only if the driver had applied the brakes and if certain conditions, such as wheel skid, were present. The active braking systems of today use components from the ABS, TCS, VSC, and radar or cameras to determine how close the vehicle is to another vehicle or an obstruction. Most systems warn the driver of an impending collision. If the driver does not respond, then the braking system acts on its own to bring the vehicle to a stop, or at least reduce the severity of a collision if it cannot come to a complete stop. Each of the systems listed normally has its own controller or computer module.

TRAILER BRAKES Normally a textbook of this type does not deal with trailer brakes. However, with the advent of active braking systems and the increasing sales and usage of ¾- and 1-ton pickups, it is important that some information is provided. Consult local and state laws for specific requirements. Older trucks used to tow trailers heavy enough to warrant a brake system always used an add-on system. This system was not efficient in some cases, and its efficiency in many cases was based on “you got what you paid for.” If the trailer was lightly loaded or the road was slick, the trailer brakes could lock and the trailer would probably jack-knife. Heavy trucks over 1 ton did have a trailer brake system that was either “hard-wired” at the factory

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Throttle actuator control is electronic control of the throttle by electric motor instead of a conventional throttle cable. Automatic ride control is a suspension system that can be electrically tailored to supply optimum passenger comfort and cornering ability action in a wide range of road surfaces. Shared components among ABS and TCS are the wheel speed sensors and hydraulic modulator. TCS is an outgrowth of the ABS. Lateral accelerometer determines the direction and speed at which the vehicle is skidding. Steering wheel position sensor determines which direction the driver is trying to steer. Wheel speed sensors are mounted at selected (or all) wheels to monitor wheel speed during vehicle operation. Yaw is the deviation in the line of travel commonly referred to as roll or lean during cornering. Active braking systems can apply the brakes without the driver touching the brake pedal. Meant to be used during an emergency stop.

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14

Chapter 1

or at least had to meet stringent Department of Transportation (DOT) standards. The newest ¾- and 1-ton truck models offer a factory-installed trailer brake system. This system borrows from the ABS and active braking systems. Trailer brake systems are usually divided into two types: hydraulic surge and electric.

Hydraulic Surge A hydraulic surge brake system is completely mounted on the trailer. It may be a disc or drum type and operates hydraulically and mechanically in a very similar manner to the drum brakes on the tow vehicle. There is a pressure differential valve mounted somewhere in the tow vehicle’s rear brake system, usually at or near the vehicle’s master cylinder. This valve operates so the pressure supplied to the trailer’s master cylinder is in direct proportion to the pressure being directed to the tow vehicle’s rear brake. The valve works very similarly to the regular proportioning valve found on almost every roadworthy vehicle. The pressure delivered to the trailer’s master cylinder applies a mechanical pushrod, which, in turn, creates the correct pressure to apply the trailer brake. Trailer drum brakes may be uni-servo with one wheel cylinder and one pushrod or duo-servo with one wheel cylinder and two pushrods. The uniservo type is the most common because of lower cost compared to the duo-servo system. The disc-brake type operates almost exactly like the disc brakes on a standard vehicle.

Electric Brakes Electric trailer brakes are most commonly used on utility and RV units, whereas boat trailers or others that are designed to be submerged underwater use the hydraulic surge. This is because water severely shortens the life expectation of electric brake components. A trailer electric brake system requires a brake controller mounted in the tow vehicle within hand control of the vehicle driver. It is usually mounted on the dash near the steering column (Figure 1-16). The driver may reduce or increase the power of the trailer brakes or lock them down as a kind of parking brake. The controller is not readily switched between different tow vehicles, so each tow unit must be equipped with its own controller. There are three types of controllers, but each performs basically the same function. For detailed information on the controllers and troubleshooting trailer brakes, investigate Champion Trailers at its website at http://www.championtrailers.com/techsup.html. The regulated electric power from the controller is sent to magnets within the wheel drum. The energized magnets are pulled toward a specially machined flat surface of the drum. As the magnets move, they, in turn, move a lever or levers attached to the brake shoe. The

Figure 1-16  This is a typical add-on trailer brake controller.

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Brake System Fundamentals

15

brake shoe is applied against the rotating drum in direct proportion to the braking action of the rear brakes of the tow vehicle.

Trailer Breakaway Condition The DOT requires any trailer with its own braking system to have a method to apply its brakes in case the trailer disconnects from its tow vehicle. On an electric system, an emergency power battery is mounted on the trailer. If a breakaway condition occurs, the pull pin at the trailer/vehicle hitch is pulled loose, triggering a switch that connects the full power of the emergency battery to the wheel magnets. This effectively locks the wheels. The hydraulic surge system uses a slightly different method to accomplish the same result. A chain or cable runs from the tow vehicle to a lever positioned to apply force to the piston in the trailer’s master cylinder. When a disconnect situation occurs, the lever is moved by the chain/cable and applies the trailer brakes. In either case, both breakaway systems may be used as parking brakes when the trailer is stored or being loaded/unloaded.

Reverse Braking Trailer brakes do not recognize reverse braking from forward braking. Usually it is best if the trailer does not have braking during reverse operation. To prevent this, the hydraulic surge brake may be standard or free backing (Figure 1-17). The standard type requires a reversing solenoid that is triggered when the tow vehicle backup lights are activated (Figure 1-18). The solenoid is plumbed into the system at the outlet of the trailer’s master cylinder. With the solenoid energized, pressurized fluid from the master cylinder is blocked from the wheels and is directed back into the master cylinder’s reservoir. Free backing operation recognizes that the wheels are rotating backward and deactivates the brakes. The brake system reactivates when the wheels rotate forward. This is the system of choice for most trailers because it can be manufactured into the system. It should be noted that disc brakes on trailers must have a free backing (reversing) solenoid. Electric brake systems use only a reverse solenoid to prevent the trailer brakes from functioning in reverse. The solenoid is triggered by the backup lights circuit. Author’s Note  Technicians or do-it-yourselfers can get into difficulties if they do not understand how to connect an add-on trailer brake system. Also, if the ­add-on system is on the less expensive side, the rule “you get what you pay for” applies. There are some add-on units that meet DOT standards but have no ­leeway if the trailer is loaded or too heavy for the brake system.

Standard

Free backing

Figure 1-17  The free backing brake on the right recognizes reverse movement and the brake cannot be applied.

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16

Chapter 1 Brake fluid reservoir Fluid return line To brake switch

To wheel cylinders

Reversing solenoid

Trailer master cylinder

Figure 1-18  The reversing solenoid is needed with the standard brakes in Figure 1-15 to prevent braking in reverse.

Before installing an add-on system, read the specifications carefully, and talk to the customer about the weight and number of axles on the trailer. On multiple-axle trailers, braking components may be installed at each wheel or only on one axle. The total weight of the loaded trailer, not just the payload of one axle, must be considered when selecting the capacity of the braking system. Author’s Note  This short section on air brakes is to give an overview to the reader should he or she end up working for a fleet or having to provide some type of emergency assistance to an air brake–equipped vehicle. Remember that more in-depth training will be required to provide air brake maintenance and repair. Air brake systems must comply with DOT requirements and inspection procedures.

Air Brakes Air brakes are brakes applied by using compressed air. Only used on heavy-duty trucks.

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Air brakes require at least 100 psi to operate correctly. This pressure is provided by a belt-driven air compressor, and the compressed air is held in one or two air reservoirs (tanks). A governor mounted on the compressor limits the amount of pressure to about 125 psi. The reservoirs and the brakes are connected via steel tubing to a manifold valve (foot valve) usually mounted on the engine side of the bulkhead. A three-way valve directs the air dependent on the action of the driver. The wheel brake friction components, drum or disc, are actually applied by a springoperated diaphragm within a brake chamber at each wheel. The diaphragms are held off (brakes released) by air pressure on the brake side of the diaphragm. Slack adjusters are placed between the chamber pushrod and the S-cam in the wheel brake mechanism. Slack adjusters allow the operator or technician to adjust the brakes for wear and are one of the first items checked during a DOT inspection. When the brakes are applied, some portion of the air pressure retaining the diaphragm is released, and the spring pushes the diaphragm, thereby moving the pushrod (Figure 1-19). The pushrod in turn rotates the S-cam and applies a proportional amount of movement to the brake shoes in relation to the amount of air released. A red button on the dash labeled PARK applies the parking brakes by releasing all of the air in all of the

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Brake System Fundamentals Pushrod

17

Slack adjuster

Air chamber

AXLE SIDE

Brake applied

Brake released

S-cam Drum

WHEEL SIDE Brake shoe

Anchor

Figure 1-19  The S-cam is rotated by actions of the air chamber. As the “S” turns, the wings of the “S” push the brake shoe outward.

brake chambers. Anytime the vehicle is parked, the parking brakes should be engaged. On the steering column is a lever that allows the driver to apply only the trailer brakes from full lock to a moderated braking effect. The hissing noise commonly heard around air brake vehicles is from brakes being applied, parking brakes being applied, or a release of excess pressure from the air reservoirs. When the tractor is attached to a trailer, two flexible air lines connect the tractor and trailer brakes. A tractor protection valve is located on the tractor to prevent a loss of brakes on the tractor if the trailer brake system develops a leak or becomes disconnected. The lines extending from the tractor are self-sealing while the connections on the trailer side are not. When the hoses are disconnected, the trailer brakes lock down (park mode). Although this overview does not provide sufficient information to become an air brake technician, there is still enough information for the average automotive technician to make a quick safety inspection. With the system fully charged at 100 psi or more, shut down the engine and perform a walk-around inspection. Any hissing sound at this time usually denotes an air leak, and the leak can be traced by following the sound. At this point in your training, do not attempt a repair. Notify a trained heavy truck technician of your findings. If the air pressure does not reach 100 psi, there are several devices that can cause this problem, and repairs are best left to a properly trained technician.

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18

Chapter 1

SUMMARY ■■

■■

■■

■■

■■

■■

An automotive brake system consists of a master cylinder and control valves connected hydraulically through lines to disc and drum brake units that stop the wheels. A hydraulic or vacuum power assist is used on most cars to decrease the braking effort required from the driver. A stroke sensor is used to tell the brake actuator how fast and how far the driver applied the brake pedal. A stroke simulator is used to give the driver a ­normal pedal feel. A mechanical brake, operated by levers and cables, is used for parking. All late model cars have an ABS to improve brake operation during emergency stopping.

■■

■■

■■

■■

■■

Active braking systems may function with or ­without driver input. Vehicle stability control systems share components with the ABS, TCS, and ARC to provide better vehicle control and comfort. Trailer brakes may now be controlled or regulated by components similar to those used in active ­braking systems. Air brake systems use compressed air to control the movement of a diaphragm. Regardless of the type of braking system, ­mechanical, hydraulic, or electronic, the final ­braking action occurs between the tire and the road.

REVIEW QUESTIONS Short-Answer Essays 1. Name the four basic functions of the braking system. 2. Briefly describe the modern master cylinder. 3. Briefly describe why the split system is needed on modern vehicles. 4. Describe the purpose of the brake stroke sensor on a hybrid vehicle. 5. Describe the two types of split hydraulic systems.

Fill in the Blanks 1. _______________ braking systems use electrical generators to help slow the vehicle during gradual stops and help recharge the electric batteries. 2. The _______________ _______________ is mounted on a lever with a pivot near the top of the lever. 3. Modern automotive _______________ _______________were developed from aircraft brakes of World War II. 4. Disc _______________ _______________ are mounted in a caliper that sits above the spinning rotor. 5. The _______________ _______________ is the start of the brake hydraulic system.

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6. Describe regenerative braking. 7. Describe the lines and hoses used on vehicle braking systems. 8. Why is it wrong to call the parking brake an “emergency brake.” 9. Describe what is meant by negative wheel slip. 10. Explain how the traction control system works to control wheel spin. 6. All master cylinders for vehicles built since 1967 have _______________ _______________ and pumping chambers 7. There are two types of split systems: _______________ and front/rear. 8. The electronic function of the proportioning valve has been called “_______________ _______________ _______________” and “_______________ _______________ _______________” by various manufacturers. 9. Most systems with drum brakes have a single, _______________ cylinder at each wheel. 10. The ABS does the same thing as an _______________ _______________ would, only it does it faster and more precisely.

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Brake System Fundamentals

Multiple Choice 1. Technician A says all the friction components of a disc brake are exposed to the airstream. Technician B says this helps to cool the brake parts and ­maintain braking effectiveness during repeated hard stops from high speeds. Who is correct? A. A only C. Both B. B only D. Neither 2. Technician A says that with a fixed caliper, hydraulic pressure is applied to pistons on both sides to force the pads against the rotor. Technician B says that with a movable caliper, pressure is applied to a piston on the outboard side only. Who is correct? C. Both A. A only B. B only D. Neither 3. Technician A says drum brakes do not develop the mechanical servo action that you will learn about as you study drum brakes. Technician B says drum brakes require higher hydraulic pressure and greater force to achieve the same stopping power as a comparable disc brake. Who is correct? A. A only C. Both B. B only D. Neither 4. While discussing the brake stroke sensor, Technician A says the brake stroke sensor informs the brake controller how fast the brake pedal is being pushed down. Technician B says the stroke sensor also informs the controller how much pressure the driver is applying to the brakes. A. A only C. Both B. B only D. Neither 5. Technician A says the stroke simulator is used to make hybrid brake application feel normal to the driver. Technician B says the stroke simulator is an electrical switch for the brake lamps. Who is correct? A. A only C. Both B. B only D. Neither

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19

6. Technician A says that all new vehicles have metering and proportioning valves. Technician B says that the function of these valves has been taken over by the ABS system on most vehicles. Who is correct? A. A only C. Both B. B only D. Neither 7. While discussing wheel cylinders and caliper ­pistons, Technician A says wheel cylinders of drum brakes operate in response to the master cylinder. Technician B says the caliper pistons of disc brakes operate in response to the wheel cylinders. Who is correct? A. A only C. Both B. B only D. Neither 8. Technician A says almost all brake systems have a power booster that increases the force of the ­driver’s foot on the pedal. Technician B says most cars and light trucks use a vacuum booster that uses the combined effects of engine vacuum and atmospheric pressure to increase pedal force. Who is correct? A. A only C. Both B. B only D. Neither 9. Technician A says some vehicles without a ready vacuum source may have a hydraulic power booster. Technician B says the hydraulic booster can be supplied with fluid by the power steering system or may be a part of the brake ­system and driven by an electric motor. Who is correct? C. Both A. A only B. B only D. Neither 10. Technician A says automatic ride control (ARC) is an electronic braking system designed to ­provide a more comfortable ride. Technician B says ARC also allows betters control of the vehicle during cornering. Who is correct? A. A only B. B only

C. Both D. Neither

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Chapter 2

Principles and Theories of Operation

Upon completion and review of this chapter, you should be able to: ■■ ■■ ■■ ■■

■■ ■■ ■■ ■■

Discuss the conversion of energy from one type to another. Discuss braking dynamics. Explain the importance of kinetic and static frictions in brake system. Describe the effects of pressure, surface area, and friction material on producing friction during braking. Discuss coefficient of friction. Explain why heat dissipation is important in a braking system. Explain how work is accomplished. Explain how the laws of motion affect the design and operation of a vehicle.

■■

Discuss hydraulic principles and how they may be applied in a vehicle.

■■

Explain the method for calculating mechanical advantage.

■■

Discuss how hydraulics can be used to transmit force.

■■

Discuss how a hydraulic brake system can produce mechanical advantage.

■■

Define and explain the basic electrical terms: amperes, voltage, and resistance.

■■

Explain how to use Ohm’s law to calculate the amount of resistance, voltage, and current in a circuit.

Terms To Know Adsorption Ampere (A) Brake fade Ceramic Coefficient of friction Force Gas fade Inertia Kinetic energy

Kinetic friction Lining fade Mass Mechanical advantage Mechanical fade Momentum Ohms (Ω) Ohm’s law Perpetual energy

Rolling resistance Static friction Tensile force Thermal energy Vacuum Voltage (volt) Weight

INTRODUCTION No vehicle or any other device will function correctly if the laws of physics are not considered during design and manufacturing. On the other hand, there is no current technology to make all designs meet all factors of physics. The automotive industry has performed well in making compromises between different physics laws to design and manufacture vehicles that work and are affordable. In this chapter, various laws of physics are discussed so that the reader will have a basic understanding of the physical environment that the designers, the manufacturers, the driver, and even you must overcome to operate any type of vehicle. 20

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21

BRAKE OPERATION/CONVENTIONAL SYSTEM Before discussing the energy and dynamics associated with braking, a review of brake system operation is essential. This may help when trying to understand the next sections. When the driver decides to slow or stop the vehicle, the first action is to remove force from the accelerator pedal. The slowing engine, in most cases, begins to slow the vehicle. The driver then applies force to the brake pedal. The movement of the brake pedal activates the brake power booster, which, in turn, boosts and transmits the driver’s input force to the master cylinder pistons via pushrods (Figure 2-1). The master cylinder pistons turn mechanical action into hydraulic action by pressurizing the brake fluid and forcing it out through the hoses and lines to the wheel braking components (see Chapter 5). Older vehicles use proportioning valves and metering valves. Valves between the master cylinder and wheels control the pressure and volume of brake fluid reaching the wheels. These valves do not control actual braking force, but they mainly divide the force between the front and rear brakes for a smooth stop without allowing the rear wheels to lock up on hard activation. At the wheels, hydraulic pressure is converted into mechanical action and applies the last segment of the braking mechanism. In drum brakes, this action is accomplished by the wheel cylinders, brakes shoes, and brake drums. On disc brakes, the same action is performed by the calipers, brake pads, and brake rotors. The antilock brake system (ABS) becomes involved only if it senses one (or more) wheels about to lock up. The ABS can then modulate hydraulic pressure to that wheel(s) to reduce braking effects. Most late-model vehicles use the ABS to replace proportioning valves with hydraulic modulation of the brake pressure to prevent wheel lockup. Everything told, the braking system is a straightforward and simple concept and operation, but it is one of the more critical systems on a vehicle.

Force converted to hydraulic pressure

Applied force

Hydraulic pressure converted to mechanical action (force) at each wheel

Figure 2-1  The energy exerted to brake a vehicle is converted from mechanical to hydraulic and back to mechanical.

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Chapter 2

BRAKE SYSTEM ENERGY

Kinetic energy is the energy of mechanical work or motion.

All brake systems work according to a few principles or “laws” of physics, and the concept of energy is a basic part of physical science. Energy is the ability to do work and comes in many familiar forms: chemical energy, mechanical energy, heat energy, and electrical energy are among the most obvious forms in all automotive systems. A brake system converts one form of physical energy to another. To slow and stop a moving vehicle, the brakes change the kinetic energy of motion to heat energy through the application of friction. When the brakes change one form of energy to another, they are doing work. Work is the result of releasing or using energy. AUTHOR'S NOTE  It is impossible at this time to create or destroy energy. However, it can be converted from one form to another. The master cylinder is one place this happens: the mechanical energy of the brake pedal is converted into hydraulic energy in the master cylinder bore. It is later converted back to mechanical energy at the wheels.

Kinetic Energy, Mass, Weight, and Speed

Mass is the measure of the inertia of an object or form of matter or its resistance to acceleration; it also is the molecular density of an object.

Kinetic energy is the energy of mechanical work or motion. When an automobile starts, accelerates, decelerates, and stops, kinetic energy is at work. The amount of kinetic energy at work at any moment is determined by a vehicle’s mass (weight), speed, and the rate at which speed is changing. The terms “mass” and “weight” can be used interchangeably to describe objects on the surface of the Earth, but the two terms are not technically the same. Mass is a measurement of the number of molecules that make up an object. Weight is a measurement of the effect of gravity on that mass. All objects have mass, from a steel brake shoe to a quart of hydraulic fluid to the air in an air compressor. Without going too deeply into the science of physics, it can be said that the greater the number of molecules in an object and the more complex the molecules are, the greater the mass of that object and the more dense it is. The effect of gravity on the mass of an object is that object’s weight. The basic difference between mass and weight can be understood by thinking of the space shuttle, which weighs about 1,000,000 pounds on the launch pad, on the Earth. When the shuttle is in orbit, outside the Earth’s gravity, it is weightless (Figure 2-2). Its mass stays the same, however. The combined effects of weight and speed constitute kinetic energy, but speed has a much greater effect than weight. The kinetic energy of any moving object can be calculated with this formula, which is quite simple: mv 2 5 Ek 29.9 where m 5 mass (weight) in pounds v 5 velocity (speed) in miles per hour Ek 5 kinetic energy in foot-pounds Consider two cars, both traveling at 30 miles per hour (mph). One weighs 2,000 pounds; the other weighs 4,000 pounds (Figure 2-3).

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Weightless

In Orbit

4,000 miles One million pounds

Equal mass Different weight

On the Earth

Figure 2-2  The space shuttle has equal mass but different weights on the Earth and in orbit.

2,000 3 30 2 5 60,200 foot - pounds of kinetic energy for the lighter car 29.9 4,000 3 30 2 5 120, 400 foot - pounds of kinetic energy for the heavier car 29.9 Doubling the car weight doubles the kinetic energy when the speeds are equal. Therefore, kinetic energy increases and decreases proportionally with weight. Now let us accelerate the lighter car to 60 mph (Figure 2-4). 2,000 3 60 2 5 240,802 foot - pounds of kinetic energy for the lighter car 29.9 When the speed is doubled, kinetic energy increases not two times, but four times. Kinetic energy increases as the square of the speed. If we accelerate the same 2,000-pound

60,200 foot-pounds of energy

2,000 pounds

2,000 pounds 30 mph

30 mph

120,400 foot-pounds of energy

4,000 pounds

60,200 foot-pounds of energy

240,802 foot-pounds of energy

2,000 pounds

30 mph

Figure 2-3  Kinetic energy increases proportionally with vehicle weight.

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60 mph

Figure 2-4  Kinetic energy increases exponentially with vehicle speed.

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car to 120 mph, its kinetic energy is 16 times greater than it was at 30 mph—almost 1,000,000 foot-pounds. Remember the brake performance test described in Chapter 1 of the Shop Manual, in which the required stopping distance at 30 mph was 57 feet, but increased to 216 feet at 60 mph. That is a practical example of kinetic energy at work. The effects of kinetic energy are also why a high-performance car needs a brake system with much greater stopping power than an economy car with only modest performance.

Inertia and Momentum Inertia is the tendency of an object in motion to keep moving and the tendency of an object at rest to remain at rest.

Momentum is the force of continuing motion; the momentum of a moving object equals its mass times its speed.

When a car is accelerated and then decelerated and brought to a stop, two forms of inertia are in play. Inertia is simply the resistance to a change in motion. An object at rest tends to remain at rest; an object in motion tends to remain in motion. In both cases, the object resists any change in its motion. Static inertia is the inertia of an object at rest; dynamic inertia is the inertia of an object in motion. When the brake system slows and stops a vehicle, it overcomes dynamic inertia and imposes static inertia. The brake system also must overcome the vehicle’s momentum. Momentum is another way to view kinetic energy at work because it, too, is the mathematical product of an object’s mass times its speed. Physical force starts an object in motion and gives it momentum. Another kind of force must overcome the momentum to bring the object to a stop. That force is friction.

BRAKING DYNAMICS One important brake system dynamic is called weight transfer. You have probably had the experience of applying the brakes hard for an emergency stop. During such a stop, the front of the car lowered and you could feel yourself being thrown forward against your seat belt. This is caused by the vehicle weight being transferred from the rear to the front during braking, which means that more of the braking must be done by the front wheels and less by the rear wheels. AUTHOR'S NOTE  When the driver applies the brakes, the vehicle—not the driver or the passengers—is being slowed. Without seat belts and air bags, the vehicle occupants tend to keep moving in the same direction and at the same speed of the vehicle as before the brakes were applied. Hence, the use of safety restraints is required to reduce injuries.

The weight of a car is not distributed evenly on all four wheels even when the vehicle is standing still. The position of the heavy engine and powertrain components determines weight distribution. During braking, the weight of these components transfers forward. On a rear-wheel-drive car, about 70 percent of the weight shifts to the front. On a frontwheel-drive car, as much as 90 percent of the car weight is shifted to the front during braking. The vehicle’s momentum and weight combine to cause the rear wheels to lift (have less down force applied) and the front wheels to be forced down (Figure 2-5). Therefore, front brake systems are larger than rear units. Another dynamic to think about is braking power. As the previous section of this chapter about kinetic energy explained, the more the car weighs and the faster it is moving, the greater the braking power must be to stop the car. The brake system is designed with more power than the engine. Consider a typical car with a 200-hp engine. This car can accelerate from 0 to 60 mph in 10 seconds. The brake system must be able to

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Direction of travel Braking tends to force down front wheels

Braking tends to lift rear wheels

70–90% of weight on front

Figure 2-5  Weight transfer during braking can place as much as 90 percent of the vehicle weight on the front brakes.

decelerate the car from 60 to 0 mph in nearly one-fifth that time. This means that the comparable power to stop this car is about 1,000 hp. This chapter focuses on the friction between the brake linings and the brake rotor or drum. However, remember that the vehicle is actually stopped by the friction between the tire and the road. Large, effective brake assemblies will stop the wheels from rotating, but the car will stop only if the tires maintain traction with the road. When the brake system completely stops the tire so that it can no longer maintain traction with the road, the tire locks up or skids. A car with locked brakes takes much longer to stop because hot molten rubber can form between the tire and the road, causing a lubricating effect. Steering control can be lost, sending the car out of control. Even if the car stops before hitting something, lockup can damage the tires by causing flat spots on them.

FRICTION PRINCIPLES Service brakes use friction to stop the car. The parking brakes use friction to hold the car stationary. Friction is used in the wheel brake units to stop the wheels. The friction between the tires and the road stops the car. Because friction is so important to the brake system, it is necessary to understand some of its principles.

Kinetic and Static Frictions Two basic types of friction are at work in the brake system (Figure 2-6). The first is called kinetic, or moving, friction. The second is called static, or stationary, friction. When the brakes are applied on a moving car, the frictional parts (brake shoes or pads) are forced against the rotating parts of the car (brake rotors or drums). The friction causes Direction of travel

Static friction

Kinetic friction

Static friction

Figure 2-6  Both static friction and kinetic friction are at work during braking.

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Kinetic friction is the friction between two moving objects or between one moving object and a stationary surface. It is used to stop, control, or reduce kinetic energy. Thermal energy is the energy of heat. Static friction is friction between two stationary objects or surfaces. Rolling resistance is a combination of inertia of the mass to moving, including the friction between all moving parts of the vehicle and the outside environment.

the rotating parts to slow down and stop. Just as the energy of the rotating parts is called kinetic energy, the friction used to stop them is called kinetic friction. Kinetic friction changes kinetic energy into thermal energy (heat). For a simple example of kinetic friction changing kinetic energy to heat, rub the hands together. Rub them together fast enough and the palms will feel warm. Brake parts and tires get very hot during braking because of kinetic friction. For example, the temperature of the brake friction material in a typical car going 60 mph (95 km/h) can be more than 4508F(2308C) during an emergency stop. Static friction holds the car in place when it is stopped. The friction between the applied brake components and between the tire and the road resists movement. To move the car, the brake components must be released. Then, the power of the engine must be great enough to overcome the rolling resistance between the tires and the road. The car can then begin to move.

Friction and Pressure One important factor in the amount of friction developed in a braking system is the amount of pressure used to force the friction material against the rotating brake part. The more pressure applied to two frictional surfaces, the harder they grip each other and the harder they resist any movement between them. Figure 2-7 shows the basic frictional parts of a disc brake system. The rotor is the part connected to and rotating with the car wheel. The friction pads are forced against the frictional surfaces or sides of the rotor. The friction causes the rotor to slow and stop, which stops the wheel from turning. Braking force in the brake system is achieved by using mechanical leverage, hydraulic pressure, and different kinds of power-assist systems. The more force used to push the friction pads against the rotor, the more friction developed. The more friction developed, the more braking action—and heat—achieved.

Friction and Surface Area Another important factor affecting the amount of friction produced is the amount of frictional surface being contacted. Two hands will stop a revolving shaft faster than one hand. The larger of the two brake units shown in Figure 2-8 has more frictional contact area than the smaller unit. The larger unit will stop a car faster than the smaller unit, which is why large cars and trucks require larger brake components than do small cars. Pressure Friction pads Small friction pads

Large friction pads

Rotor

Figure 2-7  The greater the pressure against the friction pads, the greater the braking force.

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Rotor

Rotor

Figure 2-8  The larger the frictional contact area, the greater the braking force.

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Coefficient of Friction It takes more force to move some materials over a surface than others, even though the applied pressure and the amount of surface in contact are the same. Different materials have different frictional characteristics or coefficients of friction. It is easier to slide an ice cube over a surface than it is a piece of sandpaper. To calculate the coefficient of friction, measure the force required to slide an object over a surface and then dividing it by the weight of the object. The moving force that slides an object over a surface is tensile force. The weight of the object is the force pushing the object against the surface. As an example, assume it takes about 100 pounds of force to slide a 100-pound block of iron over a concrete floor, but only about 2 pounds of force to slide a 100-pound block of ice over the same surface (Figure 2-9). When the amount of force is divided by the weight of the object, we find that the coefficient of friction for the metal block is 1.0, whereas the coefficient for the ice block is 0.02. Tensile force (motion) 5 coefficient of friction Weight force of object 100 pounds of tensile force 5 coefficient of friction :1.0 100-pound iron block

Coefficient of friction is a numerical value that expresses the amount of friction between two objects, calculated by dividing tensile force (motion) by weight force; it can be either static or kinetic.

Tensile force is the moving force that slides or pulls an object over a surface.

2 pounds of tensile force 5 coefficient of friction : 0.02 100-pound ice block The results of these calculations provide the coefficient of friction between two materials. The coefficient of friction between brake friction components is always less than 1.0. A coefficient of friction greater than 1.0 means that material actually is transferred from one surface to another. Although brake friction surfaces wear, material is not transferred from pads to rotors or from shoe linings to drums. The coefficient of friction between a tire and the road can exceed 1.0, however. When material transfers from the tire to the road, we see a skid mark. That means that the coefficient of friction momentarily exceeded 1.0. 100-pound block of iron 100 pounds of tensile force

100-pound block of ice 2 pounds of tensile force

Figure 2-9  A high coefficient of friction requires greater force to move one surface against another.

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Designing or selecting brake materials in relation to the coefficient of friction is not a simple matter of picking the highest number available. If the coefficient of friction of a material is too high, the brakes may grab and cause the wheels to lock up and slide. If the coefficient of friction is too low, excessive pressure on the brake pedal would be required to stop the car. Automotive engineers carefully determine the required coefficient of friction for the best braking performance on a particular vehicle. The friction materials selected for brake pads and rotors or brake shoes and drums are designed to give the best cold and hot temperature performance. The best materials have a coefficient that stays within narrow limits over a wide range of temperatures. If the selected material increases or decreases its coefficient of friction as temperature changes, then the brakes can fade, grab, or work erratically. This illustrates an important reason to use approved replacement brake parts so that the brake performance will meet the system design requirements. Three factors affect the coefficient of friction in a brake system: 1. The surface finish of both friction surfaces 2. The material: the metal of the rotors and drums and the friction material of the pads and linings 3. Temperature Surface Finish.  The 100-pound metal block previously used to calculate a basic coefficient of friction can be used to show how friction can be easily changed. By polishing the metal surface and waxing the concrete floor, the required tensile force to move the block may be changed from 100 pounds to 50 pounds. The metal block still weighs 100 pounds, but the coefficient of friction is now: 50 pounds of tensile force 5 0.5 coefficient of friction 100-pound metal block In a brake system, the surface finishes of pads, rotors, linings, and drums must be a trade-off between smoothness for long life and roughness for good stopping power. Friction surfaces as rough as coarse sandpaper could provide excellent stopping action— for just a few brake applications before wear becomes excessive. Materials.  The kinds of materials being rubbed together also have a big effect on the coefficient of friction, as the earlier comparison of a 100-pound block of metal with a 100-pound block of ice shows. Just as it is with selecting a surface finish, selecting the kinds of brake friction materials is a trade-off. Iron and steel work best as rotors and drums because of their combined characteristics of strength, their ability to hold a surface finish for a long time, and their ability to transfer heat without being harmed by high temperatures. One of the newer materials used for brake rotors is carbon ceramic. Carbon ceramic rotors have low weight and good wear characteristics. Friction materials for pads and linings can be allowed to wear but must have a reasonable lifespan. If pads and linings are soft and wear fast, the vehicle may have very good braking ability, but friction material life will be short. However, if friction material is hard and wears slowly for long life, it will create a low coefficient of friction and poor stopping ability. Asbestos was used almost universally for decades as the basis of brake friction material. The health hazards of asbestos led to its removal from most pads and linings. Today, most friction materials are semi-metallic or organic compounds. All of them have different coefficients of friction, and engineers select material that best matches the intended use of a vehicle and its braking requirements.

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Temperature.  Temperature also affects the coefficient of friction, but it affects different materials in different ways. A moderate amount of heat actually increases the coefficient of friction of most brakes. The semi-metallic and carbon fiber materials of some racing brake linings must be heated quite a bit for maximum efficiency. Too much heat, however, reduces the coefficient of friction (Figure 2-10), and as heat increases, the coefficient of friction continues to drop. This leads to brake fade, discussed later in this chapter, and braking efficiency is reduced. Heat Dissipation.  The weight and speed of the car during braking determine how much frictional energy is required to stop the vehicle. As mentioned previously, heat is a natural result of friction. The more frictional energy needed to stop the car, the greater the amount of heat generated during braking. The heat caused by friction must be removed or it will damage the brake system. Heat is removed from the friction surfaces as it passes through the friction material and metal of the brake components into the surrounding air. This heat removal is called heat dissipation.

Brake Fade The buildup of heat from continuous braking can cause the friction material to become glazed or polished and the metal surface of the rotors or drums to become hardened. As a result, the driver will need to push harder on the brake pedal to stop the car. Brake drums and rotors must absorb heat faster than they can dissipate it to the surrounding air. Drum or rotor temperature can rise 1008F(558C) in just a couple of seconds during a hard stop. Dissipating that same heat to the air can take 30 seconds or more. Repeated hard stops in a short period of time can overheat brake components severely and reduce braking effectiveness. This is called brake fade. A brake system is designed to provide the best possible heat dissipation. Parts are often vented to allow maximum airflow around the hot surfaces. The sizes of the friction surfaces are carefully designed with heat dissipation in mind. The larger the frictional contact area of the brake system, the better the heat dissipation and its resistance to brake fade. Severe heat causes three kinds of brake fade: 1. Lining fade. Lining fade occurs when the pad or lining material overheats to a point at which its coefficient of friction declines severely. Pressing harder on the brake pedal may further overheat the lining and increase—not decrease—the fade. Lining fade affects both disc and drum brakes but is usually less severe with discs. The rotor friction surfaces are exposed directly to cooling airflow, whereas drum surfaces are not. Ventilated and slotted rotors also aid the cooling process and counteract lining fade.

Brake fade: A loss of braking ability due to heat produced from repeated application of the brakes.

Lining fade occurs when the brake linings are hot enough that the coefficient of friction changes.

High

Coefficient of Friction

Low Low

High Temperature

Figure 2-10  Initially, the coefficient of friction increases with heat, but very high temperatures cause it to drop off.

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Mechanical fade: Brake fade resulting from the expansion of the brade drum.

Gas fade results from adsorption, which is the condensation of a gas on the surface of a solid.

2. Mechanical fade. Mechanical fade occurs with drum brakes when the drums overheat and expand away from the shoes. More pedal travel is then needed to move the shoes farther and let the linings contact the drum. Extreme mechanical fade can cause the pedal to travel to the floor before braking action starts. Pumping the brakes rapidly sometimes can force more fluid into the lines and move the shoes farther. Large and heavy drums and drums with cooling fins help to dissipate heat and reduce mechanical fade. Mechanical fade is not a factor in disc brake operation. 3. Gas fade. Gas fade is a rare condition that occurs under very hard or prolonged braking. A thin layer of hot gas develops between the pads or linings and the rotors or drums. The thin layer of gas—although only a few molecules thick—acts as a lubricant and an insulator and reduces friction. Gas fade is a greater problem with friction materials that have large surface areas that trap the gas. Slots cut in pads and linings provide airflow that aids cooling and a route for hot gases to escape. Gas fade is one of the reasons there are signs at the top of some hills requesting truck drivers to select a lower gear before heading down.

Brake Friction Materials The friction material for a disc brake is bonded, riveted, or molded to a metal brake pad (Figure 2-11). The friction material for a drum brake is bonded or riveted to a metal brake shoe (Figure 2-12). Some brake pad manufacturers are also employing the use of hooks to hold the brake material onto the metal backing. Several different friction materials are

Metal pad

Metal pad

Brake lining

Rivet

Riveted Pad

Bonded Pad

Figure 2-11  The friction material of a disc brake pad is bonded or riveted to the metal pad.

Bonded Lining

Riveted Lining

Lining

Shoe Rivet

Figure 2-12  Drum brake lining also can be bonded or riveted to the metal shoe.

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used for brake pads and shoes. Each of these has different characteristics. Five of the most important characteristics are:

1. The ability to resist fading when the brake system temperature increases 2. The ability to resist fading when the parts get wet 3. The ability to recover quickly from heat or water fading 4. The ability to wear gradually without causing wear to brake rotors or drum surfaces 5. The ability to provide a quiet, smooth frictional contact with a rotor or drum

Asbestos was the most common brake lining friction material for many years. Asbestos has very good friction qualities and provides long wear but its health hazards caused its removal from most brake friction materials. The most common types of non-asbestos lining materials can be divided into four general categories: 1. Nonmetallic materials are made from synthetic fibers bonded together to form a composite lining. 2. Semi-metallic materials are made from a mix of organic or synthetic fibers and metals molded together. Semi-metallic linings are harder and more fade-resistant than nonmetallic materials but require higher brake pedal effort. They are often blamed for wear to the rotors and drums. 3. Fully metallic materials have been used for many years in racing. The lining is made from powdered metal that is formed by heat and pressure in a process called sintering. These materials provide the best resistance to brake fade but require high brake pedal pressure and create the most wear on rotors and drums. 4. Ceramic pads are based on clay or porcelain material blended with copper fibers. They provide suitable life, provide good stopping, and reduce chances of fading, but they retain heat. This heat can distort or damage other adjacent brake components. Chapter 7 in this Classroom Manual provides more detailed information on friction materials used in disc and drum brake linings.

ENERGY AND WORK No matter how much a person may enjoy the task being performed, work is being done. Work is the expenditure of energy. Energy, in a loose definition, is the fuel for work. Energy cannot be created nor can it be destroyed. However, and this is the key, energy can be converted or changed from one form to another. Many times, the phrase “that plant produces or makes electrical energy” is heard. Not really. The process is much simpler than making electrical energy, a task that no one can do at this time. It is actually using the energy of falling water or heat to operate a mechanical device rotating within a magnetic field and converting that input energy into electrical energy. Although the mechanics and engineering required to perform that process are complex, the actual concept is very simple. Let’s move a little closer to home. The human body uses a lot of energy just to function without seemingly doing any work. The heart, lungs, and other organs work all the time. The body changes the chemical and heat energy of food into electrical energy for the brain and muscle control that, in turn, allows most organs to perform some type of chemical, electrical, or mechanical function. When the energy supply is low, the organs may become exhausted or unable to work. It is feeding time, and the process continues. The same is true of vehicles. The most common vehicle fuel of today is gasoline derived from crude oil. Crude oil is a by-product of all types of ancient animals and plants that died, decayed, and then heated under enormous pressure. This oil is recovered by the petroleum industry and eventually distilled into fuel for a vehicle. The original energy from the plants and animals has been converted into a chemical energy contained in the fuel. That chemical energy is

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compressed and burned in the engine and is converted into radiant heat and expanding gases. The gases push downward on a piston, and the last change in this process is the piston’s mechanical action or energy. Run out of gas, and everything stops. Hybrid-powered vehicles currently use an electric motor to drive the vehicle that is touted to save gasoline. But the electric power comes from a battery that must be recharged at intervals. The recharging can be accomplished using an on-board generator powered by the gasoline engine or by plugging into the electric grids where the electricity is produced by a power plant. Either way, some other source of power or energy is needed to achieve electric drive. This leads to a search for a never-ending energy source.

A BIT OF HISTORY The first friction materials used in brake systems were wood, leather, and camel hair. These materials would burn or char easily, causing erratic brake action. In 1908, the Raymond Company of Bridgeport, Connecticut, developed an asbestos and copper wire mesh brake lining. This material worked much better than the other materials because it did not char and provided a smooth and grab-free pedal effort. The company later became known as the Raybestos Corporation.

Perpetual energy is everlasting, continuous energy.

There is one major drawback to all energy-conversion devices used today. It is a fact that a machine or device cannot produce more energy than it consumes, or, in other words, there is no perpetual energy device today. An example of a device that seems to contradict that statement is the alternating current generator or alternator on a vehicle. The magnetic fields in an alternator are both energized or charged by electricity from the vehicle battery or from the output current flow of the alternator. Typically, a fully charged battery has about 12.6 volts of direct current, 13.7 volts to 14.7 volts with the engine operating. However, if the alternator’s regulator fails and goes to “full field,” it is possible for the alternator to produce up to 20 volts. This seems to prove that the alternator is a perpetual-energy device until the engine power needed to drive the alternator is considered. The result is a large use of energy to produce a mere 20 volts of electrical current. The preceding text is a simplistic overview of energy, but it shows that energy is neither destroyed nor created. It is just changed, and the changes can be used to do work. So, whether engaging in a fun-filled activity or working the graveyard shift at the local factory, energy is being used and work is being performed. In the next sections, the discussion highlights how various physics or theories of operation must be considered and how the engineers may use those theories to accomplish work with the amount of energy available at any given time.

NEWTON'S LAWS OF MOTION

Inertia is the tendency of an object to continue doing what it is already doing.

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One of the biggest uses of energy in transportation is the energy to overcome the laws of motion. Every object on the Earth must deal with these basic theories of motion. Newton developed several basic laws about motion that apply directly to the automobile. The first one deals with inertia. This unchanging action applies to an object in motion or an object at rest. Without an outside force being applied to the object, its actions will not change. A stationary object will remain stationary, whereas a moving object will continue to move. And it will move in a straight line. Obviously, this would not work well with a vehicle. Although natural forces such as wind, gravity, and terrain will affect the vehicle, the driver may have to wait a while before the vehicle begins to move, and the driver still would not have control of it. An engine and a driveline are used to power the vehicle, with steering and suspension providing some means of control. The brake system is used to overcome the inertia of

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APPLIED ACTION Horsepower (torque) + friction = driving power

OPPOSING ACTION Inertia + mass + air resistance = resists driving force

Figure 2-13  The force needed to move and accelerate a vehicle must be greater than the opposing force. When the two forces are equal, the vehicle cannot achieve more speed or torque.

motion and helps stop the vehicle. A typical vehicle uses large amounts of energy to move the vehicle from stationary and even more energy to stop it. The steering system also requires energy to move the vehicle out of a straight-line motion so it can follow the road. But there are other factors involved. For every action, there is an opposite and equal reaction. This is generally the second law. The force applied to the drive wheels must create enough friction (see next paragraph) against the road to produce that equal, opposite reaction (Figure 2-13). A spinning tire wastes that reaction, and the vehicle does not move as it should. On the other end, the same wheels must grip the road so the applied braking force can provide the slowing action. The problem with stopping a vehicle is the speed at which it is traveling. Upon acceleration, the energy is used to move the mass of the vehicle. During braking, the speeding mass must be overcome and still retain driver control. Inherent in this law is a rule regarding acceleration of an object. The acceleration of a vehicle is directly proportional to the driving forces applied to it. This applied force must overcome the friction of the various moving components, the tire against the road, and the total mass of the vehicle and its load. Mass is not the weight of the object but the amount of matter in that object. A vehicle weighing two tons on Earth will weigh about 670 pounds on the Moon, but its mass will be the same. When calculating the acceleration rate of a vehicle, other forces must be considered. As the drive wheels’ force is applied against the road and begins to accelerate the vehicle, it is resisted by a force equal to the vehicle’s mass multiplied by its acceleration rate. Aerodynamic forces act simultaneously against the vehicle in the opposite direction of the driving force, reducing the acceleration rate. In general, this reduces the amount of force available to keep the acceleration rate high. At some point, the driving forces equal the resisting forces, indicating that the vehicle has reached its maximum speed. Most light vehicles will accelerate quickly to a certain speed before the rate of acceleration drops off. This can be checked easily with a stopwatch and an open, clear stretch of road. Measure the time taken to accelerate from 0 to 25 mph. Record the time but continue running the clock until the speed reaches 50 mph. The acceleration time between 25 and 50 will be a little slower than the time between 0 and 25. The distance needed for that extra acceleration will also be a little greater.

HYDRAULIC PRINCIPLES Automotive brake systems use the force of hydraulic pressure to apply the brakes. Because automotive brakes use hydraulic pressure, a study of some hydraulic principles used in brake systems is needed. These include the facts that fluids cannot be compressed; fluids can be used to transmit movement and force; and fluids can be used to increase force.

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Fluids Cannot Be Compressed

Fluid resistance to compression allows it to transmit motion and pressure.

Fluid trapped in a sealed system such as the brake system will act like a steel rod when force is applied to it. That force will be transmitted to every interior surface of the system equally. It is measured in pounds per square inch of pressure.

Hydraulic devices such as the brake system work because fluids, unlike gases, do not compress. If a container with a top on it is filled with a gas, as shown in Figure 2-14, and a weight is placed on the top, the weight will push the top down. The top moves down because the gas can be compressed. If filled with a fluid, however, the weight will not push the top down, because fluid in a sealed container cannot be compressed. If air is introduced into the hydraulic system when pressure is applied, the air (or gas) in the system is compressed instead of transmitting movement and force effectively (Figure 2-15).

Fluids Can Transmit Movement Fluids can be used to transmit movement. Two cylinders of the same diameter are filled with a fluid and connected by a pipe, as shown in Figure 2-16. If piston A is forced downward, fluid will push piston B upward. Because piston A starts the movement, it is called the apply piston. Piston B is called the output piston. If the apply piston moves 10 inches, the output piston also will move 10 inches (Figure 2-17). The principle that motion can be transmitted by a liquid is used in hydraulic brake systems. A master cylinder piston is pushed when the driver applies the brakes. The

Weight Gas

Weight

Fluid

Figure 2-14  Gases are compressible, but fluids are not.

Weight Piston A (Apply piston) Fluid

Bubbles of gas in fluid

Fluid

Bubbles of gas compressed by pressure

Figure 2-15  When air is in the brake system hydraulics, the force applied at the master cylinder simply compresses the gas instead of doing work.

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Piston B (Output piston)

Pipe

Fluid

Figure 2-16  Fluid can transmit motion through a closed system.

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Apply piston

Rear wheel cylinders

Front wheel cylinders Master cylinder

Brake pedal

Figure 2-17  The master cylinder is an apply piston, working as a pump, to provide hydraulic pressure to the output pistons at the wheel brakes.

master cylinder piston is the apply piston. The fluid in the master cylinder is connected by tubing to pistons in each of the car’s front and rear wheel brake units. Each of the wheel brake pistons is an output piston. They move whenever the master cylinder input piston moves.

Fluids Apply Pressure to Transmit and Increase Force Fluids are not just used to transmit movement; they are also used to transmit force. Force is power working against resistance; it is the amount of push or pull exerted on an object needed to cause motion. Force is usually measured in the same units that are used to measure weight: pounds or kilograms. Piston A and piston B (Figure 2-18) are the same size. If a 100-pound force is applied to piston A, the same force will be applied to piston B. This demonstrates that force is transmitted from the apply piston to the output piston. This principle can be used to increase the output force of a hydraulic system. To do this, change the sizes of the input and output pistons and calculate the amount of pressure developed in the system. Output Force Creates System Pressure.  Pressure is the force exerted on a given unit of surface area. Therefore, pressure equals force divided by surface area: F 5P A where

100 pounds 100 pounds

Piston A

Pipe

Piston B

Figure 2-18  As hydraulic fluid transmits motion through a closed system, it also transmits force.

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200 pounds 500 pounds Piston A 20 square inches

Piston B

10 psi Input

Pipe

Output

50 square inches

Figure 2-19  A hydraulic system also can increase force.

F 5 force in pounds ( or kilograms )

A 5 area in square inches ( or centimeters ) P 5 pressure The pressure of a liquid in a closed system such as a brake hydraulic system is the force exerted against the inner surface of its container, which is the surface of all the lines, hoses, valves, and pistons in the system. In customary English units, pressure is measured in pounds per square inch (psi). In the metric system, pressure can be measured in kilograms per square centimeter, but the preferred metric pressure measurement unit is the Pascal. Regardless of how it is measured, pressure applied to a liquid exerts force equally in all directions. When pressure is applied to a movable output piston, it creates output force. In Figure 2-19, input piston A is smaller than output piston B. Piston A has an area of 20 square inches, and in the example, 200 pounds of force are applied. Therefore, 200 pounds ( F ) 5 10 psi ( P ) 20 square inches ( A) If that same 200 pounds of force is applied to a piston of 10 square inches, system pressure is 20 psi, because 200 pounds ( F ) 5 20 psi ( P ) 10 square inches ( A) Therefore, pressure is inversely related to piston area. The smaller the piston, the greater the pressure that is developed with the same amount of input force. Pressure and Output Piston Area Determine Force.  Apply the 10 psi of pressure in the first example to an output piston with an area of 50 square inches. In this case, output force equals pressure times the surface area: P 3A5F where

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Principles and Theories of Operation Pressure gauge

37

50 psi

100 square inches

Output = 5,000 pounds Input 500 pounds Output = 250 pounds Sectional area = 10 square inches

5 square inches

Figure 2-20  Different-size output pistons produce different amounts of output force from the same hydraulic pressure.

F 5 force in pounds (or kilograms) A 5 area in square inches (or centimeters) P 5 pressure Therefore, 10 psi of pressure on a 50-square-inch piston develops 500 pounds of output force: 10 3 50 5 500. Brake systems use hydraulics to increase force for brake application. This is called mechanical advantage. Figure 2-20 shows a hydraulic system with an input piston of 10 square inches. A force of 500 pounds is pushing on the piston. The pressure throughout the system is 50 psi (force 500 4 area 10 5 50 psi ). A pressure gauge in the system shows the 50-psi pressure. There are two output pistons in the system. One has 100 square inches of area. The 50-psi pressure in the system is transmitted equally everywhere in the system. This means that the large output piston has 50 psi applied to 100 square inches to deliver an output force of 5,000 pounds (100 square inches 3 50 psi 5 5,000 pounds). The other output piston in Figure 2-20 is smaller than the input piston with a 5-squareinch area. The 5-square-inch area of this piston has 50-psi pressure acting on it to develop an output force of 250 pounds (5square inches 3 50 psi 5 250 pounds). In a brake system, a small master cylinder piston is used to apply pressure to larger pistons at the wheel brake units to increase braking force. It is important that the pistons in the front brakes (now almost exclusively caliper pistons) have a larger surface area than the pistons in the rear brakes. This creates greater braking force at the front wheels to overcome the weight transfer that momentum creates during braking.

Mechanical advantage: With hydraulics, the multiplication of force by using a larger output piston than input piston.

Hydraulic Pressure, Force, and Motion.  Hydraulic pressure acting on pistons of different surface areas creates different output forces. As the output pistons move, another effect of pressure and force appears. When output force increases, output motion decreases. If the 10-square-inch input piston moves 2 inches as it applies 50 psi to the 100-square-inch output piston, that output piston will move only 0.2 inch as it applies 5,000 pounds of output force (Figure 2-21). The ratio of input motion to output motion is the ratio of the input piston area to the output piston area, and you can use this simple equation to calculate it: A1 3S 5M A2 where

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Chapter 2 Pressure gauge

50 psi 0.2 inch of output travel

5,000 pounds of force

2 inches of input travel

100 square inches

500 pounds of input force 10 square inches

250 pounds of force 4 inches of output travel

5 square inches

Figure 2-21  The output pistons’ movement and their created force will be proportional to their size in relationship to the input piston size.

A1 5 input piston area

A2 5 output piston area S 5 input piston stroke (motion) M 5 output piston stroke (motion) A1 3S 5M A2 10 square inches (input piston) 1 5 3 2 inches (input stroke) 100 square inches (output piston) 10 5 0.2 inchof output motion If the output piston is larger than the input piston, it exerts more force but travels a shorter distance. The opposite also is true. If the output piston is smaller than the input piston, it exerts less force but travels a longer distance. Apply the equation to the 5-squareinch output piston in Figure 2-21: 10 square inches (input piston) 2 5 3 2 inches (input stroke) 5 square inches (output piston) 1 5 4.0 inches of output motion In this case, the smaller output piston applies only half the force of the input piston, but its stroke (motion) is twice as long. This relationship of force, pressure, and motion in a brake system is shown when the force applied to the master cylinder pistons and the resulting brake force and piston movement at the wheels is considered. Wheel cylinder pistons move only a fraction of an inch to apply hundreds of pounds of force to the brake shoes, but the wheel cylinder piston travel is quite a bit less than the movement of the master cylinder piston. Disc brake caliper pistons move only a few thousandths of an inch but apply great force to the brake rotors.

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A BIT OF HISTORY All the hydraulic principles that are applied in a brake system are based on the work of a seventeenth-century scientist named Blaise Pascal. Pascal’s work is known as Pascal’s law. Pascal’s law says that pressure at any one point in a confined liquid is the same in every direction and applies equal force on equal areas. Additionally, liquids take the path of least resistance. One of the most important results of Pascal’s work was the discovery that fluids can be used to increase force. Pascal was the first person to demonstrate the relationships of pressure, force, and motion and the inverse relationship of motion and force. On an automobile, Pascal’s laws are applied not just to the brake system. These same hydraulic principles are at work in the hydraulic system of an automatic transmission and other systems. Pascal’s laws are even at work in the movement of liquid fuel from a tank to the fuel-injection system on the engine.

Hydraulic Principles and Brake System Engineering Engineers must consider these principles of force, pressure, and motion to design a brake system for any vehicle that will give maximum stopping efficiency but still be easy to control. If the engineer chooses a master cylinder with relatively small piston area, the brake system can develop very high hydraulic pressure, but the pedal travel will be extreme. Moreover, if the master cylinder piston travel is not long enough, this high-pressure system will not move enough fluid to apply the large-area caliper pistons regardless of pressure. If, however, the engineer selects a large-area master cylinder piston, it can move a large volume of fluid but may not develop enough pressure to exert adequate braking force at the wheels. The overall size relationships of master cylinder pistons, caliper pistons, and wheel cylinder pistons are balanced to achieve maximum braking force without grabbing or fading. Most brake systems with front discs and rear drums have large-diameter master cylinders (large piston area) to move enough fluid and a power booster to increase the input force.

VACUUM AND AIR PRESSURE PRINCIPLES Vacuum is another force used in most brake systems. Many power brake systems use vacuum to provide a power assist for the driver. Because the most significant use of atmospheric pressure and vacuum in a brake system is in the operation of a power booster, these principles are covered in Chapter 6 of this manual on power brake systems.

Vacuum is generally considered to be air pressure lower than atmospheric pressure (a true vacuum is a complete absence of air).

ELECTRICAL PRINCIPLES Many of the brake system components requiring repairs are controlled or powered by electricity. Examples are brake system warning lamps, stop lamp switches, brake fluid level sensors, and ABS components. Therefore, a basic understanding of some of the electrical principles, including amperage, voltage, and resistance, is needed.

Amperage, Voltage, and Resistance Think of electricity in terms of the same principles that work in hydraulic systems. The flow of electricity through a circuit is similar to the flow of fluid through a hydraulic line.

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Chapter 2

Ampere: A measurement of the number of electrons passing a point in one second, which is 6.28 x 10 (need to place the 18th power on the ten as it is in the text).

Voltage is the electromotive force that causes current to flow; the potential force that exists between two points when one is positively charged and the other is negatively charged.

Current is the movement of free electrons, under pressure, in a conductor. A flow of current through a conductor requires a source of free electrons to supply the demand, just as fluid in a tank or reservoir is a source of flow in a hydraulic system. The rate of fluid moving through a line often is measured in gallons per minute. The rate of current flowing in a conductor is measured in amperes (A). One ampere (A) equals 6.28 3 1018 electrons passing a given point in a circuit per second. Just as pressure is necessary to move fluid through hydraulic lines, there must be pressure to move electrons through a conductor. The pressure pushing the electrons through an electrical circuit is called the voltage, measured in volts (V). Friction between the walls of a hydraulic line and the fluid will cause some resistance to the flow of fluid. Similarly, some resistance to electron flow through a circuit is offered by any material. Electrical resistance is measured in ohms (Ω). To summarize the comparison of electrical and hydraulic systems, the following apply: ■■

Electrical resistance is measured in ohms.

■■ ■■

Voltage is the pressure (or electrical force) that moves electrons (current or amperes) through a wire just as pressure moves fluid through a pipe. Amperage, or current, is similar to the amount of fluid flowing in a line. Electrical resistance is a load on the moving current that must be present to do any useful work, just as a hydraulic system must have the load of an output piston or motor to do work.

Ohm’s Law

Ohm’s Law: Ohm’s law states that it takes one volt of electrical pressure to push one ampere of current through a resistance of one Ohm.

The amount of fluid flowing through a pipe will increase if the fluid pressure is increased. Likewise, the amount of fluid flowing in the pipe will decrease if the resistance offered by the hydraulic system increases. In the same way, the amount of current flowing in an electrical circuit will increase if the voltage is increased. It will decrease if the resistance of the circuit increases even when the voltage is constant. The relationship of these electrical factors (voltage, current, and resistance) is summarized by a mathematical equation known as Ohm’s law (Figure 2-22). Ohm’s law states that it takes 1 volt of electrical pressure to push 1 ampere of current through a resistance

If E is unknown, cover it with a finger and the formula becomes: I

(Volts) E (Amperes) I

R

I×R (I multiplied by R )

(Ohms)

If I is covered with a finger, the formula reads:

E

R

R

E R (E divided by R )

E I

If R is covered with a finger, the formula is: E I (E divided by I)

Figure 2-22  If you know two of the three electrical factors of voltage, current, and resistance, you can calculate the third as shown here.

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41

of 1 ohm. Mathematically, Ohm’s law is expressed by the following equations, using the symbols E for voltage, I for current, and R for resistance: E 5 I 3 R to find voltage I 5 E 4 R to find current R 5 E 4 I to find resistance For example, if a 12-volt circuit has 2 amperes of current flowing, you can use Ohm’s law to determine the resistance as follows:

Georg Simon Ohm (1787–1854) wrote the law regarding electrical theory and measurement. It came to be known as Ohm’s law.

R 5E 4I 5 12 4 2 5 6 ohms The resistance of the circuit is 6 ohms. These equations can be used to calculate the voltage, current, or resistance of a circuit. In most cases, you can use electrical testing instruments to measure these values. There are times, however, when this is not possible. Then, if you know two of the values, you can find the third value by using the problem-solving wheel, which is based on Ohm’s law (Figure 2-22).

A BIT OF HISTORY Early experiments with electricity by Volta and Ampere led to names for the new phenomenon that remains today. The term electromotive force is now called volts. The term intensity is now called amps.

SUMMARY The energy used by the braking system is based on the kinetic energy, mass, weight, and speed of the vehicle and its braking system. ■■ Inertia is an object’s resistance to change. ■■ Vehicle subsystems are used to overcome inertia. ■■ The acceleration rate of a vehicle is the force applied against the opposing forces. ■■ Kinetic and static frictions are at work in the brake system. ■■ The amount of friction in a brake system depends on the pressure (force) exerted on the friction components and the surface area. ■■ Friction materials may be made from organic, metallic, or ceramic compounds. ■■ Energy provides the fuel for work. ■■ Work is accomplished any time energy is expended. ■■ The laws of motion affect the vehicle and all its subsystems. ■■

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■■

■■

■■

■■

■■

■■

■■

Hydraulic fluid can transmit motion and force because a fluid cannot be compressed. A small hydraulic input piston and a large output piston can increase force at the wheel braking components. Mechanical advantage in a hydraulic system is proportional to the size of the input piston versus the output piston. Electrical circuits have an electrical pressure (force) that is used to move electrons through a circuit. In Ohm’s law, E = voltage, I = current (ampere), and R = resistance (ohm). In electrical terms, a change in E, I, or R will cause a change in one or both of the other two. Resistance in a circuit is needed to change electrical energy into mechanical energy (action).

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Chapter 2

REVIEW QUESTIONS Short-Answer Essays 1. Briefly explain how a braking system converts one form of physical energy to another. 2. Explain the brake system dynamic called weight transfer. 3. Explain the difference between static and dynamic inertia. 4. Explain the relationship between pressure and friction. 5. Explain what the term coefficient of friction means. 6. Explain why heat dissipation is important in a braking system and how it is removed. 7. Briefly describe inertia. 8. Explain what happens if air is introduced into a hydraulic system. 9. Explain how the force from a small master cylinder piston is multiplied by the caliper piston. 10. Briefly describe amperage, resistance, and voltage.

Fill in the Blanks 1. _______________ is the ability to do work. 2. The brake system is used to overcome the _______________ of motion and helps stop the vehicle. 3. Mass is not the weight of the object but the amount of _______________ in that object. 4. For every _______________, there is an opposite and equal _______________. 5. If the _______________ piston is larger than the _______________ piston, it exerts more force but travels a shorter distance. 6. _______________ is the mathematical product of an object’s mass times its speed. 7. The rate of current flowing in a conductor is measured in _______________. 8. The pressure pushing the electrons through an electrical circuit is called _______________.

Multiple Choice 1. Technician A says kinetic energy is the energy of mechanical work or motion. Technician B says when an automobile starts, accelerates, decelerates, and stops, kinetic energy is at work. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 2. Technician A says weight is a measurement of the number of molecules that make up an object. Technician B says mass is a measurement of the effect of gravity on that mass. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 3. Technician A says the weight of a car is not distributed evenly on all four wheels even when the vehicle is standing still. Technician B says the position of the heavy engine and powertrain components determines weight distribution. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 4. Technician A says on a rear-wheel-drive car, about 70 percent of the weight shifts to the front. Technician B says on a front-wheel-drive car, as much as 60 percent of the car weight is shifted to the front during braking. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. Technician A says a car can accelerate from 0 to 60 mph in 10 seconds. Technician B says the brake system must be able to decelerate the car from 60 to 0 mph in nearly one-fifth that time. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

9. Electrical resistance is measured in _______________. 10. The _______________ ____________________ ______________ becomes involved only if it senses one (or more) wheels about to lock up.

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6. Technician A says this chapter focuses on the friction between the brake linings and the brake rotor or drum. Technician B says to remember that the vehicle is actually stopped by the friction between the tire and the road. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

9. Technician A says it takes more force to move some materials over a surface than others, even though the applied pressure and the amount of surface in contact are the same. Technician B says different materials have the same frictional characteristics or coefficients of friction. A. A only C. Both A and B B. B only D. Neither A nor B

7. Technician A says a car with locked brakes has a shorter stopping distance. Technician B says this is because hot molten rubber can form between the tire and the road, causing a grabbing effect. A. A only C. Both A and B B. B only D. Neither A nor B

10. Technician A says if pads and linings are soft and wear fast, the vehicle may have very good braking ability, but friction material life will be short. Technician B says if friction material is hard and wears slowly for long life, it will create a high coefficient of friction and good stopping ability. C. Both A and B A. A only B. B only D. Neither A nor B

8. Two basic types of friction are at work in the brake system. These are: C. Moving and A. Static and dynamic stopping B. Disc and drum D. Kinetic and static

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Chapter 3

Related Systems: Tires, Wheels, Bearings, and Suspensions

Upon completion and review of this chapter, you should be able to: ■■

Describe the basic kinds of tire construction and identify the most common construction method for modern tires.

■■

Identify and explain the various letters and numbers used in tire size designations and other tire specifications.

■■

Explain the basic effects of tire tread design on vehicle handling and braking.

■■

■■ ■■

Explain the most important effects of tire design and condition on brake performance.

■■ ■■

■■

Explain how wheel and tire runout and wheel rim width and offset affect braking. Identify the common types of wheel and axle bearings used on cars and light trucks. Identify the basic wheel alignment and steering angles. Explain how wheel alignment and ­steering angles can affect braking. Explain how the condition of steering and suspension parts can affect braking.

Terms To Know Aspect ratio Belted bias ply tire Bias ply tire Camber Carcass Casing Caster Cold inflation pressure Geometric centerline Gross vehicle weight rating (GVWR) Hydroplane Lateral runout National Highway Transportation and Safety Agency (NHTSA)

P-metric system Pressure-sensor base (PSB) Radial ply tire Radial runout Run-flat Scrub radius Section width Setback Side-to-side Steering axis inclination (SAI) Thrust angle Thrust line Tire load range

Tire pressure monitoring system (TPMS) Toe angle Toe-out on turns (turning radius) Tread Tread contact patch Tread wear indicator Unidirectional tread pattern Uniform Tire Quality Grading (UTQG) indicators Wheel offset Wheel-speed base (WSB)

Introduction The brake shoes or pads apply friction to the wheels, but it is the friction between the tires and the road that actually stops the car. Tire design, condition, and inflation pressure can affect braking, and attention to these factors often can solve braking problems. The tires are mounted on wheels, which ride on bearings on steering knuckle spindles and axles. Steering and axle components, in turn, are supported by suspension struts and 44

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45

springs. Any of these components can create braking problems if they are not in proper working order. This chapter outlines the key relationships between brake systems and the related systems of wheels, tires, wheel bearings, and suspensions.

Tire Fundamentals Brake systems are engineered in relation to many vehicle factors of weight, size, and performance. Among these factors are the construction, size, and tread design of the tires and the amount of traction or friction expected to be available between the tires and the road. For the best and most reliable brake performance, tires at all four wheels should be identical in construction, size, and tread pattern.

Shop Manual page 98

Carmakers’ Recommendations Most passenger cars and light trucks built since 1968 have a tire information placard on a door, on a door pillar, or inside the glove compartment (Figure 3-1). The tire information placard lists the manufacturer’s original equipment tire size and any recommended optional sizes. It also lists the recommended cold front and rear inflation pressures, and maximum front and rear gross vehicle weight rating (GVWR). Brake systems are engineered to work most efficiently with the tire sizes and pressures listed on the placard. A few carmakers install different sized wheels and tires at the front and rear of some vehicles, but this practice is reserved for a small percentage of high-performance sports cars like the Porsche 911. More than 99 percent of the vehicles on the road are originally fitted with wheels and tires of the same size at each corner. Although manufacturers may recommend one or two optional tire sizes at the rear that are larger than the front original equipment size, a large variation from the carmaker’s recommendation can lead to braking problems, as well as problems with other vehicle systems. For example, an extreme difference in tire diameters from front to rear may produce unequal speed signals from the wheel speed sensors of ABSs. Tires much larger than those recommended by the vehicle maker may produce inaccurate vehicle speed-sensor signals to the PCM or the ABS control module. This same problem exists if all four tires are larger or smaller than the manufacturer’s recommendations.

Gross vehicle weight rating (GVWR) is the total weight of a vehicle plus its maximum rated payload, including passengers and full fuel tank.

A BIT OF HISTORY When radial tires were first introduced in the 70s, there was a lot of resistance by drivers to using the new design. Complaints ranged from “feels funny when driving” to “they don’t have enough air in them.” Some drivers even went so far as to remove radial tires from a brand-new vehicle and to install bias tires. Two major characteristics of the radial tire overcame this die-hard resistance: a much smoother ride and increased fuel mileage. Lower-profile tires of today have also eliminated most of the comments about the tires “appearing underinflated.”

Figure 3-1  This placard is located on the driver door and lists recommended tire size and cold inflation pressure.

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Chapter 3

AUTHOR’S NOTE  Changing the size of the driving tires/wheels may result in an incorrect speedometer reading. This could lead to two traffic tickets: exceeding the speed limit and improper equipment.

Tire Construction Every tire is constructed of these basic parts (Figure 3-2): Carcass: Steel beads around the rim and layers of cords or plies that are bonded together to give the tire its shape and strength. Casing: Additional layers of sidewall and undertread rubber added to the carcass. Tread: The layer of rubber that contacts the road and contains a distinctive pattern to provide the desired traction. Before radial ply tires became the standard of the industry, tires were made with the plies laid at an angle or bias to the tire beads. This construction was called bias ply (Figure 3-3). The cords in a bias ply tire run at an angle closer to the tread, giving a much stiffer sidewall but creating a rougher ride than a radial tire. A second ply is added to the first so that its cords run in the opposite direction across the first ply. Additional plies can be added for more strength. Bias ply tires can carry more load and are still used on large trucks and most trailers. Most passenger car and light truck tires were made with two, four, six, or eight plies. The cords of bias ply tires were usually made of nylon or polyester. This construction provided decent stiffness to prevent unnecessary twisting while still allowing enough flexibility to absorb some road shock and cushion the ride. Belted bias ply tires incorporate the belts used in radial ply tires with the older bias ply construction. Two or more belts of nylon, fiberglass, or steel cords are wrapped around two or more bias plies (Figure 3-4). The belts keep the tire from deforming out of round at high speeds and thus improve tire stability. Belted bias ply tires were basically an interim design that combined some of the features of radial ply tires with the older bias ply construction. They are still used on some vehicles today. Since the mid-1970s, almost all original equipment and replacement tires for cars and light trucks have been the radial ply type. The cords in a radial ply tire run at 90 degrees to the tread, creating a more flexible sidewall and creating the impression that the tire is low on air pressure (Figure 3-5). Each cord is parallel to the radius of the tire circle, which Tread

Carcass and casing

Beads Bias ply body cords Rim

Figure 3-2  Major parts of a tire.

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Figure 3-3  Bias ply tire construction.

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Radial ply body cords

Belted bias ply body cords

Figure 3-4  Belted bias ply tire construction.

Figure 3-5  Radial ply tire construction.

RADIAL

BIAS

Vehicle in left turn (outward force)

Road surface Inside edge of tread tends to remain flat

Inside edge of tread tends to lift

Figure 3-6  A radial tire tread tends to remain flat on the road, whereas the bias tread tends to lift the inner edge from contact with the road.

gives the tire the name radial ply. Two or more additional belts of cords are added around the tire circumference between the radial plies and the tread for more strength and stability. These belts may be made of nylon, rayon, fiberglass, or steel. The radial plies provide maximum flexibility in the tire sidewall, and the belts ensure excellent tread stiffness for good road contact. Of the three types of tire construction, radial ply tires have the best braking performance. The flexible sidewalls of a radial ply tire provide a larger tread contact patch than a comparable size bias ply or belted bias ply tire. Radial ply construction also has greater flexibility on the wheel during cornering without decreasing tread contact with the road (Figure 3-6). The circumferential belts give a radial ply tire maximum stability and protect against deforming at high speed.

Tire Size All tire sizes are based on three dimensions: the inside diameter, the section width, and the aspect ratio. The inside diameter is the same as the wheel size, or rim diameter, on which the tire fits: for example, 15 inches, 17 inches, or 21 inches. This diameter is measured across the tire beads or across the bead seat of the wheel rim. The section width is the width of the tire across the widest point of its cross section, usually measured in millimeters. The aspect ratio is the ratio of the cross-sectional height to the cross-sectional

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The aspect ratio is the ratio of the cross-sectional height to the cross-sectional width.

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Chapter 3 P

215

65

R

15

89

H

TIRE TYPE P - Passenger T - Temporary LT - Light Truck

SPEED SYMBOL LOAD INDEX RIM DIAMETER (Inches)

SECTION WIDTH (Millimeters)

14 15 16

205 215 etc.

CONSTRUCTION TYPE

ASPECT RATIO Section Height Section Width 60 65 70

R - Radial B - Bias Belted D - Diagonal (Bias)

Section height

Section width

Figure 3-7  Typical tire markings.

The P-metric system of measurement is an alpha-numeric size identification for tires.

width, expressed as a percentage. A high aspect ratio indicates a tall tire. Most modern tires have aspect ratios from 45 to 80. Modern tires are sized by the P-metric system. The first character indicates the type of service for which the tire is designed (Figure 3-7). The most common designation is “P” for passenger car, which gives the size identification system its name. The numbers after the first letter indicate the tire section width in millimeters, and the numbers after the slash indicate the aspect ratio. An optional speed-rating letter may follow the aspect ratio, and the final letter indicates the construction type. The last numbers indicate the wheel diameter. The European metric variation of this size specification system omits the first letter, such as “P” or “C,” but includes the speed-rating letter.

Other Tire Specifications Tire load range is the load-carrying capacity of a tire, expressed by the letters “A” through “L.”

Other tire specifications appear on tire information placards, in owner’s manuals, and on the tire sidewall itself. The tire load range is indicated by the letters “A” through “L,” which often appear after the size specification on the tire sidewall. The load range letters replace the older method of rating tire strength by the number of plies used in its construction. Load range “A” corresponds to a two-ply rating, and load range “L” corresponds to a 20-ply rating. Most tires for cars and light trucks are load ranges “B,” “C,” and “D.” As an alternative, tires may be marked with load index numbers that range from 65 to 104. These numbers indicate the load capacity of the tire from 639 pounds to 1,984 pounds. Most passenger car tires have a load index from 75 to 100. Many tires have a maximum inflation pressure molded into the sidewall. This is not the recommended operating pressure but the pressure that may cause the tire to burst if exceeded.

Low-Profile Tires The modern trend has been toward lower-profile tires. These tires have an aspect ratio that is lower than 50. The height of the tire sidewall is smaller than those of a more conventional tire (Figure 3-8). The advantages of a low-profile tire are handling and ease of

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Related Systems: Tires, Wheels, Bearings, and Suspensions

Regular profile tire

49

Low profile tire

Figure 3-8  Comparison of low profile to regular profile tire and wheel combinations.

steering. Low-profile tires, like many of the advances in tire technology, were developed in racing. Low-profile tires do not flex as much as a higher profile tire during hard cornering (Figure 3-9). The larger wheel size can allow for the use of larger brakes. The disadvantage of low-profile tires is the fact that there is less tire sidewall to absorb shocks from hitting irregularities in the road, which can lead to a rougher ride, and can also lead to wheel damage. How far will the trend towards lower-profile tires? Kumho and Nexen have shown tires with a profile of 15 at the SEMA show! The maximum cold inflation pressure for any tire is molded into the tire sidewall (Figure 3-10). This is the inflation pressure after the tire has been standing for 3 hours or driven less than 1 mile after standing for 3 hours. The vehicle manufacturer’s recommended inflation pressures are usually slightly less than the maximum cold inflation pressure.

Low-profile tire

High-profile tire

Figure 3-9  During cornering, the high-profile tire tends to distort more than the low-profile tire.

TRALIA AND AUS ADA, N A C 0 kPa (35 PS1) .A., S. AT 24 U.S 33 LB 4 1 R g FO 50 K D6 A LO X. A M Tire load and inflation information

Figure 3-10  The maximum cold inflation pressure specification is molded into the sidewall of every tire.

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Chapter 3

As tire aspect ratios or profiles have gotten lower, inflation pressures have gotten higher. Until the early 1980s, most passenger car tires were equivalent to the old load range “B” with a maximum pressure of 32 psi. Maximum pressures then moved upward to about 36 psi. Today, a popular ¾-ton pick-up-trucks list front tire inflation at 55 psi front and 80 psi rear. With the older maximum pressures of 32 psi to 36 psi, it was common to inflate tires to the maximum for best handling, tire life, and gas mileage. With today’s higher pressures and tire pressure monitoring systems, the best practice is to follow the manufacturer’s recommendations found on a late-model vehicle’s tire placard, and remember that the inflation pressure listed is with cold tires.

AUTHOR’S NOTE  Starting in 1996, there were many accidents involving a brand of SUVs equipped with a particular brand of tire. There were two opposing arguments concerning these accidents. First, the vehicle manufacturer claimed that the tires came apart during normal operation because of poor tire manufacturing. Second, the tire manufacturer claimed that the vehicle manufacturer’s recommended tire pressure could critically damage the tire during operation. Both the SUVs and tires were recalled at a huge cost to both manufacturers and the general public. Regardless of the root cause, it is obvious that tire pressure can affect overall operational durability, particularly if there is a problem with the tire’s manufacturing process.

Uniform Tire Quality Grading

Uniform tire quality grading indicators gives consumers a standard with which to compare the performance of tires.

Hydroplaning is the sliding or skidding brought on by the vehicle riding on a thin film of water, risking a serious loss of traction. Hydroplaning is aggravated by having worn tires and excessive speed.

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The Uniform Tire Quality Grading Standards were developed by an association of tire manufacturers, vehicle manufacturers, and governmental agencies in the early 1980s. The Uniform Tire Quality Grading (UTQG) indicators have been molded into the sidewall of every tire sold in the United States since 1985. The UTQG indicators are a number to indicate relative tread life, a letter to indicate wet weather traction, and a second letter to indicate heat resistance. The treadwear rating starts at 100. A tire with a treadwear rating of 200 should last twice as long as a tire rated at 100, on the test track set up by the NHTSA. The wet traction rating is designated by an AA, A, B, or C; the best traction rating is AA; and the worst acceptable is C. A tire’s resistance to heat is A, B, or C. The UTQG indicators are intended to be a way that consumers can compare tires when making a purchasing decision. In addition to the UTQG markings, the U.S. National Highway Traffic Safety Administration (NHTSA) requires all tires to have a tire identification number. This data set is prefixed by the letters DOT followed by 10, 11, or 12 numbers, which give the place of manufacturer, tire size, manufacturer code, and week and year of manufacture. The date of manufacture is the last four digits in the identification number. The first two digits represents the week and the last two the year. In Figure 3-11, the last four digits are 5116 representing the 51st week of the year 2016. The date of manufacture is of importance to the owner because tires can dry rot sitting on the shelf.

Tire Tread Design The best possible traction and braking performance on dry pavement can be had with the treadless, slick tires used on race cars. Unfortunately, all of the great traction of a slick tire goes away on wet pavement. On wet pavement, a slick tire will hydroplane on a layer of water trapped between the tread and the pavement. Therefore, all street tires have a tread pattern of ribs and grooves that lets water be displaced from under the tire while still maintaining good traction.

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Figure 3-11  The number 5116 indicates that this tire was manufactured in the 51st week of year 2016.

Wear-indicator bars

Figure 3-12  When wear indicator bars appear across any two tread grooves, the tire is ready for replacement.

Tread designs vary widely, but most original equipment tires have some kind of mudand-snow or all-weather tread pattern. In fact, the characters “M+S” or “M/S” often appear on a tire sidewall to indicate a mud-and-snow tread pattern. In addition to providing traction, the tread pattern acts as a radiator to expose more tire surface area to the air and improve tire cooling. Some high-performance tires have a unidirectional tread pattern, which means that each tire can be installed on only one side of the car. Tread depth is measured from the top of the tread ribs to the bottom of the groove and usually is expressed in thirty-seconds of an inch. The tread on a new passenger car tire is usually in the range of 9/32 inch to 15/32 inch. The tread on truck tires and some mud-and-snow tires may be deeper. All passenger car and light truck tires made since 1968 have tread wear indicators that appear as continuous bars across the tread when the tread wears down to the last 2/32 (1/16) inch (Figure 3-12). Note that the tire should be replaced when the indicator is visible across two or more grooves. However, if the vehicle is extremely out of alignment, the tire may wear completely to the steel cords before wearing the indicator in the second groove. The two-groove indication assumes that the vehicle is maintained and properly aligned.

Tires with a ­unidirectional tread pattern are specific to the side of the vehicle they are installed on.

Tread wear indicators are meant to make it obvious when a tire is worn out.

Run-Flat tires Self-sealing tires.  While not technically considered a run-flat tire, these tires can seal themselves against most minor punctures up to about 3/16 inch (4.8 mm). These tires are lined with a sealant layer under the tread. When an object punctures the tire, the sealant

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acts to seal the area around the intrusion. When the intrusion is removed, then the sealer flows into the opening, permanently repairing the tire. It should be noted that this does not mean the tire cannot be punctured; a large piece of debris can still result in a flat tire. Also, some manufacturers have a compressor and a can of sealant instead of a spare tire. Sealant that is sprayed into the tire at the time of the flat is not considered a permanent repair. Run-flat tires prevent quick air loss during punctures or minor damage to the tire.

Run-flat tires.  The air pressure inside the tire is normally needed to hold the vehicle weight and maintain the shape of the tire. Once the air is lost on a normal tire and it is driven even a very short distance, the tire, and possibly the rim, is destroyed. To prevent this from happening, some tires have an inner structure or are reinforced to help prevent damage from driving up to 50 miles at speeds of 50 mph. The advantage is that you can get the vehicle to a shop instead of fixing the tire on the road. There are two types of run-flat tires, self-supporting (Figure 3-13) and auxiliary supported (Figure 3-14). In the self-supporting design, the tires are made stiffer by adding layers of rubber to the tire and the utilization of heat resistant cords to prevent breakage of the cord layers. These also utilize a bead design that allows a better grip on the wheel in case the tire goes flat. Self-supporting tires are best used with a tire pressure warning system because the driver may not realize that the tire is actually Special bead design: * Enhanced retention after pressure loss * Acceptable seating pressure

Sidewall reinforcement: * Flexible low-hysteresis rubber * Thermal resistive material * Metallic and/or textile tissues

Appropriate summit adjustments: *Maintain inflated performance (comfort & handling like std. tires)

Figure 3-13  A run-flat tire.

Support ring

Minimum intrustion well

Support ring locked by the external bead of tire

Single piece wheel

Protection of the external rim edge

Figure 3-14  Run-flat tire with inner support inside wheel.

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flat. As stated before, these tires are not intended to be driven over long periods or high speeds without being properly repaired. In the auxiliary supported design, the tire and the wheel are both specially designed to work together to support the vehicle when the tire is flat. In case of a flat tire, a supporting ring attached to the wheel itself holds the vehicle weight. The tires and wheels must made specifically for this purpose. Some racing tires use race-proven technology by installing a tire-within-a-tire, but this is expensive and not suitable for mass-produced units. The most common design weaves the tire fabric in such a way that it will grip small penetrating objects in the tire. Another design weaves the fabric so it will attempt to close the hole if the penetrating object is withdrawn from the tire. In both cases, air inside the tire cannot escape quickly and, under the right conditions, will support the vehicle up to 50 miles at reasonable speeds and loads. Neither type will prevent the complete air loss because of a major incident such as a blowout. Leaking run-flat tires affect braking and steering of the vehicle the same as would any tire with insufficient air pressure.

Tire Pressure Monitoring System Tires that are underinflated not only affect fuel mileage and tire life; they may also lead to problems in braking and steering. The Transportation Recall Enhancement, Accountability and Documentation (TREAD) Act of 2000 directed the National Highway Transportation and Safety Agency (NHTSA) to research and develop rules as a means of continuously monitoring tire pressure. After several years of testing, it was determined that two viable tire pressure monitoring systems (TPMSs) could perform the job. The wheel-speed base (WSB) system uses the wheel speed sensors that are used with ABS to detect the faster spinning or rotation caused by an underinflated tire. This illuminates a light in the dash, warning the driver of the condition. A second option, pressure-sensor base (PSB), has a pressure sensor located on each wheel and reads tire pressure directly. Currently, most vehicles have a direct pressure measurement of tire pressure. If the tire pressure drops 25 percent below the specified cold inflation pressure, the tire pressure warning light is illuminated on the dash. Maintenance of the TPMS system is discussed in Chapter 11 of the Shop Manual. The TPMS systems were phased in from 2003–2005. During 2005, the NHTSA developed and issued the final ruling based on any new data collected during the 2003–2005 time period. The NHTSA mandated that vehicles manufactured after October 2006 (2007 model year) must have a TPMS (type determined by the vehicle manufacturer). A standard warning icon (Figure 3-15) is used in the dash to alert the driver if one or more tires have a pressure that is less than 25 percent of the cold inflation recommendation. The system also has to be able to indicate which tire(s) is underinflated. Based on current data, it appears that the PSB system is slightly more responsive, but advances in ABS technology may change that shortfall. A wheel-mounted pressure sensor uses wireless communication to send the pressure signal to a PSB computer, which, in turn, illuminates the warning light or icon in the dash. Factory sensors are usually installed in place of the regular tire valve stem. Specific repair and reset procedures are mandated by the manufacturer. Aftermarket units usually have a pressure sensor installed on the valve stem in lieu of the valve cap. If a tire, pressure sensor, or TPMS module is replaced or repaired or if the tires are rotated, the system must be reset so the sensor can determine the rotational speed of the new/ repaired/rotated tires and determine its own location on the vehicle. This reset and training procedure was one problem that the NHTSA found with the WSB and PSB systems.

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The NHTSA is a federal agency assigned to develop regulations for highway safety, including vehicle safety features.

The TPMS systems have been referred to as direct (pressure-based system) and indirect (wheel-speed-based system).

Besides being dangerous and wasting fuel, underinflation of tires is the most common cause of premature wear.

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Figure 3-15  The standard symbol for the tire pressure monitoring system.

Wheel Fundamentals Wheel offset and rim width are design factors of the wheel itself that affect brake performance. Their effects are most significant on the front wheels, which provide steering control as well as most of the braking force.

Rim Width Rim width is measured between the inside surfaces of the rim flanges (Figure 3-16). Every tire has three or four rim widths on which it can be mounted. Similarly, every rim has Bead seats

Flange height

Rim diameter

Rim width

Figure 3-16  The principal wheel dimensions are diameter and width.

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three or four tire sizes that it can safely hold. Although there is not a rigid one-to-one correlation between tire sizes and rim sizes, there are a limited number of combinations for any given wheel or tire. If a tire is mounted on a wheel rim that is too wide or too narrow, the beads will not seat properly and the contact patch area will be affected. The tire may shift excessively on the rim and cause uneven braking. In the worst cases, the tire may lose air and be pulled off the rim under hard cornering or braking.

Wheel Offset

Negative offset

Wheel offset is the distance between the centerline of the rim and the mounting plane of the wheel.

Scrub radius is the distance from the tire contact patch centerline to the point where the steering axis intersects the road.

Outside

Outside

Outside

Wheel offset is the distance between the centerline of the rim and the mounting plane of the wheel (Figure 3-17). If the mounting plane is outboard of the centerline, the wheel has positive offset. This is the more common design, particularly for front-wheel drive (FWD) cars. If the mounting plane is inboard of the centerline, the wheel has negative offset. Negative offset is common on many aftermarket wheels, particularly for trucks and SUVs. Along with low-profile tires, reverse center rims were also used to change the appearance of the vehicle. This type of rim pushed the tire away from the centerline of the body. Some tires were almost completely out of the wheel well. Reverse center rims and low-profile tires completely change the steering and suspension geometry and affect the braking characteristics of the vehicle. This involves extra cost over the price of the tires and rims. The amount and direction of wheel offset are important design factors because they affect the load-carrying capacity of axles, spindles, hubs, and bearings. Wheel offset also affects the steering scrub radius and overstresses the wheel bearings. The scrub radius is the distance from the tire contact patch centerline to the point where the steering axis intersects the road. If the tire contact patch centerline is outboard of the steering axis at the road, the car has positive scrub radius (Figure 3-18). If the tire contact patch centerline is inboard of the steering axis at the road, the car has negative scrub radius (Figure 3-19). Scrub radius is a design factor that is engineered for each vehicle. Negative scrub radius is the more common design because it tends to push the tires inward as they roll. In case of a blowout or a failure of half of a diagonally split brake system, negative scrub

Zero offset

Positive offset

Figure 3-17  Wheel offset is the distance between the centerline of the rim and the mounting plane of the wheel.

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Chapter 3 Steering axis inclination (SAI)

Vertical reference

Steering axis inclination (SAI) Vertical reference

Camber line

Steering axis

Camber line

Steering axis

Positive scrub radius

Figure 3-18  When the pivot point is inside the tire contact point, the scrub radius is positive.

Negative scrub radius

Figure 3-19  When the pivot point is outside the tire contact point, the scrub radius is negative.

radius helps to maintain vehicle stability. If scrub radius is changed from negative to positive by the installation of extremely offset wheels, the vehicle become unstable in case of tire or brake failure.

AUTHOR’S NOTE  Scrub is not the amount of rubbing an oversize tire does on a vehicle component. Scrub is an engineering term involving the movement of the tire on the road and must be considered during steering, suspension, and other system designing.

Wheel Bearings Three basic kinds of wheel bearings are used on late-model cars and light trucks: Shop Manual page 106

1. Tapered roller bearings 2. Straight roller bearings 3. Ball bearings Different types of bearings are designed for different types of loads. Radial loads are from the top down; the weight is on the radius of the bearing. An axial load is along the axis or side of the bearing. Ball bearings (Figure 3-20) have a small point of contact and therefore offer less resistance to turning and can handle radial as well as axial loads. For added strength, ball bearings can be installed in double rows. Straight roller bearings

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Figure 3-20  Ball bearing assembly.

(Figure 3-21) have a line contact that offers more resistance but can handle higher loads. Tapered roller bearings are designed for a high radial load as well as a high axial load, in one direction, and therefore are installed in pairs Tapered roller bearings are commonly used on the front or rear wheels of a vehicle. A complete tapered roller bearing assembly consists of an outer race (bearing cup), an inner race (cone), tapered steel rollers, and a cage that holds the rollers in place (Figure 3-22). The inner race, the rollers, and the cage are a one-piece assembly and cannot be separated from one another. The outer race is normally pressed into the wheel hub. Tapered roller bearings are designed to take a radial as well as an axial load in one direction, so tapered roller bearings are installed in pairs with one large bearing set on the inboard side of the hub and a smaller bearing set on the outboard side. Tapered roller

Inner race (cone) Outer race

Grease seal

Spindle

Rolling element Cotter pin

Separator

Nut and retainer

Inner race Cage

Figure 3-21  Roller bearing assembly.

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Outer race (cup)

Hub

Figure 3-22  Typical tapered roller bearing installation.

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Chapter 3 Sealed bearing

Seal

Raceway Axle

Cage

Bearing Flange Axle tube

Figure 3-23  Straight roller bearings are used on most RWD axles.

AXIAL LOAD

Ball AXIAL LOAD RADIAL LOAD

Figure 3-25  A typical sealed bearing may be pressed into the hub or may be an integrated part of the hub.

Figure 3-24  Typical ball bearing construction.

bearings must be cleaned and repacked with grease periodically and then have the end play adjusted. These bearing services are usually part of a complete brake job. Straight roller bearings are used on the drive axles of most rear-wheel drive (RWD) vehicles (Figure 3-23). These bearing assemblies consist of an outer race pressed into the axle housing, straight steel rollers, and a cage to hold the rollers in place. The axle shaft acts as the inner bearing race. Because straight roller bearings are installed in the drive axle housing, they are lubricated by the final-drive lubricant. Periodic adjustment and repacking are unnecessary. Ball bearings may be used on rear drive axles, and sealed double-row ball bearings are used on the front and rear wheels of many FWD vehicles. A typical ball bearing assembly consists of inner and outer races, steel balls, and a cage to hold the balls in place (Figure 3-24). Although ball bearings were used on the nondriven front wheels of many cars before 1960 and required periodic service, most modern ball bearing assemblies are sealed and permanently lubricated. Most late-model cars have sealed double-row ball bearings or tapered roller bearings in an assembly that includes the wheel hub, the bearing races, and a mounting flange (Figure 3-25). These are nonserviceable, nonadjustable assemblies that must be replaced if damaged or defective.

Wheel Alignment Fundamentals Shop Manual page 118

Wheel alignment service is based on maintaining the geometric relationships designed into the front and rear suspension and steering systems of a vehicle. These relationships are a series of angles in the suspension and steering. Some of these angles affect braking more than others. Improper alignment angles can cause a pull to one side during braking and improper handling. Traditionally, there are five basic steering and suspension angles: 1. Camber 2. Caster 3. Toe 4. Steering axis inclination 5. Toe-out on turns, or turning radius

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Two other steering and suspension angles indicate the relationship among all four wheels. They are: 1. Thrust angle 2. Setback

Camber Camber is the inward or outward tilt of the wheel measured from top to bottom and viewed from the front of the car. If the wheel tilts outward at the top, it has positive camber. If it tilts inward, camber is negative (Figure 3-26). Each front and rear wheel has its individual camber angle. Camber is measured in degrees.

Caster Caster is the backward or forward angle of the steering axis viewed from the side of the car. If the steering axis tilts backward at the top, the wheel has positive caster. If the steering axis tilts forward at the top, caster is negative (Figure 3-27). Each front Negative camber (–)

0° Camber

Improper camber will wear the tire on one edge and cause steering problems based on the camber error. A vehicle will pull to the side with the most positive camber. Improper caster usually will not cause abnormal tire wear but may cause steering problems.

Positive camber (+)

Figure 3-26  Camber is the inward or outward tilt of the wheel measured from top to bottom and viewed from the front. Positive (+)

0° Steering axis

Lead point

0°

Negative (–)

Caster

Figure 3-27  Caster is the backward or forward angle of the steering axis viewed from the side.

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wheel has its individual caster angle. Most vehicles have a positive caster angle. Although front wheel drive vehicles are not as sensitive as rear wheel drive vehicles, a vehicle will pull toward the side with the most negative caster. Because the rear wheels are not steering wheels, rear caster is always zero. Caster is measured in degrees.

Toe Improper toe will feather wear the tread and may cause steering problems.

Toe angle is the difference in the distance between the centerlines of the tires on either axle (front or rear) measured at the front and rear of the tires and at spindle height. If the centerlines of the tires are closer together at the front of the tires than at the rear, the wheels are toed in (Figure 3-28). If the centerlines of the tires are farther apart at the front of the tires than at the rear, the wheels are toed out. If the centerline distances are equal from front to rear on the tires, the toe angle is zero.

Steering Axis Inclination Steering axis inclination (SAI) is the angle formed by the steering axis of a front wheel and a vertical line through the wheel when viewed from the front with the wheels straight ahead (Figure 3-29). SAI is measured in degrees independently for each wheel. SAI works with camber to maintain the vehicle load inboard on the larger front-wheel bearing. SAI is not adjustable, but it may be measured to identify suspension component damage. SAI, toe-out on turns, thrust angle, and setback are sometimes measured by alignment shops to determine why the wheel alignment cannot be brought to specifications. The technician uses measurements to determine if the vehicle has suffered accident damage or perhaps the steering wheels were bounced off a road curb.

Included angle True vertical Steering pivot axis Toe-in or positive toe (+)

Toe-out or negative toe (–)

Figure 3-28  The toe angle is the difference in the distance between the centerlines of the tires measured at the front and rear of the tires.

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Camber and centerline

SAI angle

Positive (+) scrub radius

Figure 3-29  Steering axis inclination is the angle formed by the steering axis of a front wheel and a vertical line through the wheel.

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Toe-Out on Turns Toe-out on turns (turning radius) is the difference between the angles of the front wheels in a turn. Because of suspension and steering design, the inside front wheel turns at a greater angle during a turn (Figure 3-30). Thus, it toes out. Toe-out on turns is measured in degrees by turning one wheel a specified amount and then measuring the angle of the other wheel. The difference between the two is the turning angle or the toe-out on turns. Toe-out on turns prevents tire scuffing and tire squeal during cornering. Toe-out on turns is not adjustable, but it may be measured to identify suspension or steering component damage.

Thrust Angle To understand the thrust angle, you must understand the geometric centerline of the vehicle and the thrust line of the vehicle. The thrust angle is the angle between the geometric centerline and the thrust line (Figure 3-31). The geometric centerline is a static dimension represented by a line through the center of the vehicle from front to rear. It can be used as a reference point for individual front- or rear-wheel toe, but it does not represent the direction in which the rear wheels are steering the vehicle. The thrust line is the bisector of total toe on the rear wheels. Put more simply, the thrust line is the direction in which the rear wheels are pointing.

Setback Setback refers to a difference in wheelbase from one side of the car to the other (Figure 3-32). Some vehicles are built with setback as a design feature. Ford trucks with twin I-beam front suspension are some of the best-known examples. Setback also can be

Centerline of rear axle

Geometric centerline Turning radius

Common center

Angle outside wheel

Angle inside wheel

Figure 3-30  Toe-out on turns is the difference between the angles of the front wheels in a turn.

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Thrust line

Thrust angle

Figure 3-31  The thrust angle is the angle between the geometric centerline and the thrust line.

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Example: 107.5 inches

Example: 108 inches

Figure 3-32  Setback is the difference in wheelbase from one side of the car to the other (exaggerated examples).

Shop Manual page 121

present in a vehicle where it is not supposed to be. This is usually the result of a collision in which the frame is bent or suspension components are severely knocked out of position. Accidental setback also can change the vehicle thrust angle and cause handling problems.

Effects on Braking Performance The bottom line of the braking system performance is how the tire contacts and holds the pavement, or the tread contact patch (Figure 3-33). The previous sections outline the overall requirements for tires, suspension, and related components. Major deviations from these requirements not only can result in poor ride and control through the steering, but may and will in some cases affect the braking ability of the vehicle. Free diameter Rolling diameter

Free diameter

Rolling diameter

Contact patch area

Figure 3-33  Tire diameter and contact patch area are important factors in troubleshooting brake performance.

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Lateral runout

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Radial runout

Figure 3-34  Lateral and radial runout.

The tread contact patch’s friction ability is determined not only by the tire size, but also by how the tires contact the road. One primary failure is over- or underinflated tires. This causes a larger or smaller contact patch and a corresponding reduction or increase of braking friction. The angle at which the tire contacts the road may also affect braking. Camber, caster, or toe angles that are excessively negative or positive will affect tire wear and the angle and, to some extent, the size of the contact patch. The “perfect” contact patch has all the treads on the bottom of the tire in contact with the road. Excessive alignment angles may cause the tire to push toward one side during driving. This push or pull can be greatly increased as the tire tries to push but the vehicle is trying to go straight ahead. Even if the alignment is correct, worn or broken steering and suspension components may cause the same problem. Wheels and tires that do not meet the vehicle manufacturer’s specifications can and do cause the steering and suspension angles to change. Lifting or lowering the vehicle will also change those angles. Worn or damaged wheel or axle bearings can cause the wheel and tire assembly to wobble during operation. Excessive wobble is called runout. Runout around the outside is called radial runout, so the tire moves up and down. Excessive side-to-side variation is called lateral runout, or side-to-side (Figure 3-34). Technicians must pay attention to what their customers are saying when they complain of a brake problem. Chapter 3 of the Shop Manual discusses ways and means for the technicians to isolate apparent braking problems from reduced performance of related systems and components. Remember that the engineers designed each system to work together. If one system fails to perform properly, then the other systems will not perform properly. This is especially true of brake, suspension, and steering systems because of their shared components and overlapping operation.

Performance Tires, Wheels, And Alignment AUTHOR’S NOTE  This section should give the reader an idea of differences between production vehicles and race vehicles. There are two classifications of “performance” vehicles. One classification consists of production lines like the Viper, Corvette, and Mustang, whereas the other consists of actual racing vehicles. The theory of operation for all performance vehicles is the same as that of a straight production product. However, race vehicles are usually “hand- engineered” and “hand-built.” In other words, they work well on a controlled track, but not very well in downtown Atlanta traffic. A short section on the major differences between production and race products is included at the end of appropriate chapters.

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Tires Racing tires are engineered and manufactured for one reason: to provide traction for a particular track with a specific surface for speed and control. Most oval track (NASCAR) tires have no tread, but they provide much better traction than a typical treaded tire. However, there is one very distinct drawback: They do not work well on a damp track. Have you ever seen a NASCAR race conducted in the rain? Road course racers (Formula 1, Grand Prix) do use treaded tires because they run the race regardless of rain, but many times the rubber and chemical compound that these tires are made of is very similar to that of oval track tires. Race tires for NASCAR are actually leased from the respective tire suppliers. A set of racing tires could cost more than some cars on the road. Goodyear is the primary tire supplier for NASCAR and develops a tire specifically for a certain track. Other tire manufacturers like Bridgestone and Michelin supply tires for road course competitors like Formula 1 and Grand Prix. The tire may be of a softer compound with a short life and better grip or a hard compound with long life but not quite as much traction. The tire used on the short track at Martinsville, Virginia, with top speeds of about 130 mph is very different from the tire for Atlanta with top speeds in the 200-mph range. Race vehicles are usually equipped with an “inner” tire to help prevent blowouts. This is basically a little smaller tire mounted inside the visible tire. Racing tires provide an excellent proving ground for tire engineers to test rubber compounds for wear and traction. Most of today’s production tire designs and chemical compounds originated from research data collected during races. In fact, some of the ideas behind run-flat tires came from the oval track.

Wheels Like the tires, the basic design of a racing wheel is very similar to that of a production wheel. Depending on the track and expected speeds, it may have more positive or more negative offset. Also, the bead-holding area of the wheel is usually a little deeper for a better grip on the tire bead. They are almost never made of anything other than highquality steel, although some manufacturers are working on designs from carbon-fiber. The side forces occurring during any race will destroy a production wheel in a fairly short period of driving. Typically racing wheels are a little wider than production wheels with the same size diameter mounted. Other than the extremely high cost to purchase wheels of this type, they could be used on production vehicles. Generally speaking, racing wheels are bland in appearance so few people want to pay an extra $5,000 to get wheels that would never wear out but do not look any better or racier.

Wheel Alignment This area contains probably the biggest and most noticeable difference between production vehicles and racers. The theory behind wheel alignment is the same, but the application of that basic theory to racers is extreme. Road course racers use an alignment setup close to that of production, but oval track vehicles definitely appear to be completely abnormal to a nonexperienced passerby. If a vehicle is set up for Atlanta, Daytona, or Talladega, it would appear that all four wheels are laid in (negative camber) (Figure 3-35). The camber is set very negative compared to production vehicles. This odd setup also has a very positive effect on vehicle handling. Because of the downforce on the vehicle racing on high-speed tracks, the wheels are forced out at the top, creating zero or positive camber. This is true of all vehicles when they are loaded or in some other condition in which the body is forced downward. However, routine operation on the public roads does not create the speed and resulting downforce required to change the camber setting. Also most oval track race vehicles are

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AT SPEED

Negative camber

Zero camber

65

AT SPEED, BANKED TRACK

r be am k c ro ac Ze to tr

*Angles exaggerated

Figure 3-35  A simplistic race setup has the wheels set at negative camber (top left), and the downward force of the airflow and vehicle mass cause the wheels to move to zero or positive camber (bottom).

set up with a more positive camber on the left wheels than on the right. During that 200mph left turn, the vehicle body is forced downward and leans or tilts hard right. This changes the camber of the right-side tires to be more positive than the left. If done correctly, all four tires try to stand straight up, and the tread becomes flat on the pavement during those high-speed turns; hence, more and better traction is present when it is needed the most. Short-track ovals require a different camber setup because the speeds are much slower and the track surface is flatter. Toe on a racer is not quite as important as camber, but it is set up with some differences from production vehicles. Because of body lean, excessive camber, and the construction of the suspension system, toe measurements are set up not only to control the vehicle but also to help keep the tread straight on the track surface. Of more importance to a race vehicle is toe-out on turn. Like production vehicles, this angle is determined by the construction and initial service on the suspension and steering systems and is not adjustable. Another factor influencing racing setup is the banking angle of the track surface when compared to horizon. The high-speed tracks have up to 36 degrees of banking in the turns. This banking is one of the main factors for selecting the camber and toe settings. A highbank track does not require as much offset camber as a short track (1 mile or less in length) with little banking. This is because the centrifugal forces at a low-bank track affect the sideways movement of the vehicle much more. The vehicle tends to slide sideways because the centrifugal force is about 90 degrees to the surface of the track or horizon. The camber is set to account for this force and body lean. A vehicle on a high-bank track tends to be pushed into the pavement because the pavement is at an angle to the horizon. Although the centrifugal force may be much greater, the track surface is flatter with regard

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Chapter 3

to the vehicle chassis, forcing the vehicle into the track instead of across it. All of this means nothing, however, unless the suspension and steering systems are also matched to the track and vehicle. It would not be a good idea to set up a production vehicle like a racer with regard to tires, wheels, suspension, and steering. Setting the high costs aside, the tires would wear out very quickly and the vehicle would ride like a horse-drawn wagon. That is assuming the driver has the strength to fight for control during straight-ahead and right-turn driving because most racing vehicles do not steer easily until operating at high speeds. It is suspected that the driver would wear out before the tires.

SUMMARY ■■

■■

■■

■■

If a vehicle has identical tires at all four wheels of the size and type recommended by the car manufacturer, brake performance should be at its best. Radial ply tires are used almost universally on latemodel cars and light trucks. Tire size identification, maximum inflation pressure, and other specifications are molded into tire sidewalls. Tire and wheel runout, as well as wheel rim width and offset, can contribute to brake problems if they deviate from the car manufacturer’s specifications.

■■

■■

■■

■■

Late-model cars and light trucks use tapered roller bearings, straight roller bearings, and ball bearings at their wheels and axles. If wheel bearings have too much end play (looseness), wheel runout may be excessive and cause uneven braking and a pull to one side. Excessive runout also can contribute to pedal pulsation. The traditional wheel alignment angles of caster, camber, and toe can contribute to brake pull problems if they are out of specification or vary greatly from side to side. Loose or damaged steering and suspension parts also can cause brake pull problems.

REVIEW QUESTIONS Essay

Fill in the Blanks

1. Explain the problem with having tires of different sizes on a vehicle as it relates to the ABS system. 2. Describe the information contained on the tire information placard. 3. Explain two characteristics of radial tires that won over drivers in the 70s. 4. Explain why radial tires have the best braking performance. 5. Describe the three most common tire measurements in the P-metric system. 6. Describe what is meant by a low-profile tire. 7. Describe the treadwear rating of the UTQG. 8. Explain how to decode the NHTSA date from the DOT number on the sidewall. 9. Explain why street tires all have a tread pattern, even though racing slicks have the best traction. 10. Describe how a straight roller bearing is suited to handling a radial load.

1. Brake systems are engineered in relation to many vehicle factors of _______________, _______________, and_______________.

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2. The cords in a _______________ply tire run at 90 degrees to the tread, creating a more flexible sidewall 3. The inside _______________is the same as the wheel size, or rim _______________on which the tire fits. 4. The tire _______________ _______________ is indicated by the letters “A” through “L,” which often appear after the size specification on the tire sidewall. 5. Runout around the outside of the tire is called _______________ runout, so the tire moves up and down.

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Related Systems: Tires, Wheels, Bearings, and Suspensions

6. The bottom line of the braking system performance is how the tire contacts and holds the pavement, or the _______________ _______________ _______________. 7. _______________ refers to a difference in wheelbase from one side of the car to the other. 8. The _______________ _______________ is a static dimension represented by a line through the center of the vehicle from front to rear. 9. Because of suspension and steering design, the inside front wheel turns at a _______________ angle during a turn. 10. _______________ angle is the difference in the distance between the centerlines of the tires on either axle (front or rear) measured at the front and rear of the tires and at spindle height.

Multiple Choice 1. Technician A says brake shoes or pads apply friction to the wheels. Technician B says it is the friction between the tires and the road that actually stops the car. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 2. Technician A says manufacturers may recommend one or two optional tire sizes at the rear that are larger than the front original equipment size. Technician B says a large variation from the carmaker’s recommendation will not cause any problems. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 3. Technician A says the tire casing is steel beads around the rim and layers of cords or plies that are bonded together to give the tire its shape and strength. Technician B says the tire tread is additional layers of sidewall and under-tread rubber added to the carcass. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 4. Technician A says section width is the width of the tire across the widest point of its cross section, usually measured in inches. Technician B says aspect ratio is the ratio of the cross-sectional

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67

height to the cross-sectional width expressed as a percentage. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. Technician A says a high aspect ratio indicates a tall tire. Technician B says most modern tires have aspect ratios from 45 to 80. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 6. Technician A says the advantage of a low-profile tire is handling. Technician B says an advantage of a low-profile tire is ease of steering. A. A only C. Both A and B B. B only D. Neither A nor B 7. Technician A says an advantage of low-profile tires is the fact that there is more tire sidewall to absorb shocks from hitting irregularities in the road. Technician B says more sidewall of the lowprofile tire can lead to a smoother ride and can also prevent wheel damage. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 8. Technician A says the maximum cold inflation pressure for any tire is molded into the tire sidewall. Technician B says this is the inflation pressure after the tire has been standing for 1 hour. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 9. Which is true of the Uniform Tire Quality Grading (UTQG) indicators? A. They have been used since 1985. B. They use a number to indicate relative tread life. C. They use a letter to indicate wet weather traction and heat resistance. D. All the above 10. All passenger car and light truck tires have tread wear indicators that appear as continuous bars across the tread when the tread wears down to the last 2/32 (1/16) inch. This practice started in: A. 2002 C. 1955 B. 1968 D. 1974

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Chapter 4

Master Cylinders and Brake Fluid

Upon completion and review of this chapter, you should be able to: ■■ ■■ ■■ ■■ ■■

Explain the differences between different DOT brake fluid specifications. Explain proper brake fluid handling procedures. Identify the parts and explain the operation of a brake pedal and pushrod.

■■

Describe the mechanical advantage provided by the brake pedal and linkage. Explain the purpose and operation of the front-to-rear and diagonally split hydraulic systems.

■■

■■ ■■

■■

Describe the purpose of the master cylinder. Identify the main parts of a master cylinder. Explain the operation of a basic master cylinder. Describe the parts and operation of a dual-piston master cylinder. Describe the parts and explain the operation of a quick take-up master ­cylinder with a fast-fill valve.

Terms To Know Cup seal Diaphragm Free play Hydraulic system mineral oil (HSMO)

O-ring Polyglycol Quick take-up master cylinder Quick take-up valve

Replenishing port Reservoir Residual pressure check valve Vent port

INTRODUCTION This chapter covers hydraulic fluid, which makes the brake system work, as well as the master cylinder construction and operation. The master cylinder converts the force on the brake pedal to each of the four wheel brakes to stop the car. The master cylinder changes the driver’s mechanical force on the pedal to hydraulic pressure, which is changed back to mechanical force at the wheel brakes. The master cylinder uses the fact that fluids are not compressible to transmit the pedal movement to the wheel brake units. The master cylinder also uses the principles of hydraulics to increase the pedal force applied by the driver. The brake pedal’s construction and operation are also discussed in this chapter as part of the master cylinder operation.

HYDRAULIC BRAKE FLUID The specifications for all automotive brake fluids are defined by Society of Automotive Engineers (SAE) Standard J1703 and Federal Motor Vehicle Safety Standard (FMVSS) 116. Fluids classified according to FMVSS 116 are assigned DOT numbers: DOT 3, DOT 4, 68

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DOT 3/4, DOT 5, and DOT 5.1. Basically, the higher the DOT number, the more rigorous the specifications for the fluid. These specifications list the qualities that brake fluid must have, such as: ■■ Free flowing at low and high temperatures ■■ A high boiling point (over 4008F or 2048C) ■■ A low freezing point ■■ Noncorrosive to metal or rubber brake parts ■■ Ability to lubricate metal and rubber parts ■■ Ability to absorb moisture that enters the hydraulic system Choosing the right fluid for a specific vehicle is not based on the simple idea that if DOT 3 is good, DOT 4 must be better, and DOT 5 better still. Almost all carmakers specify DOT 3 fluid for their vehicles; but Ford calls for a heavy-duty variation, which meets the basic specifications for DOT 3 but has the higher boiling point of DOT 4. Import manufacturers are about equally divided between DOT 3 and DOT 4. DOT 3 and DOT 4 fluids are polyalkylene-glycol-ether mixtures, called polyglycol for short. The color of both DOT 3 and DOT 4 fluid ranges from clear to light amber. DOT 5 fluids are all silicone based because only silicone fluid—so far—can meet the DOT 5 specifications. No vehicle manufacturer, however, recommends DOT 5 fluid for use in its latest brake systems. Although all three fluid grades are compatible in certain aspects, they do not combine if mixed together in a system. DOT 5, a silicone-based fluid, should never be mixed with or used to replace other types of brake fluids. Therefore, the best general rule is to use the fluid type recommended by the carmaker and to not mix fluid types in a system.

69

Shop Manual page 142

Polyglycol stands for polyalkylene-glycol-ether brake fluids that meet specifications for DOT 3 and DOT 4 brake fluids.

Brake Fluid Boiling Point The most apparent differences among the five fluid grades are the minimum boiling points as listed in Table 4.1. The boiling point of brake fluid is important because heat generated by braking can enter the hydraulic system. If the temperature rises too high, the fluid can boil and form vapor in the brake lines. The stopping power of the system then will be reduced. The pedal must be pumped repeatedly to compress the vaporized fluid and build up pressure at the brakes to stop the vehicle. However, it would require a lot of frequent, very hard braking action to bring clean brake fluid to its boiling point. About the only people who would do this are race drivers during a race. But old contaminated brake fluid may contain water that could boil during braking. The dry boiling point is the minimum boiling point of new, uncontaminated fluid. After brake fluid has been in service for some time, however, the boiling point drops because of water contamination. Polyglycol fluids are hygroscopic, which means that they readily absorb water vapor from the air. Brake systems are not completely sealed, and some exposure of the fluid to air is inevitable. SAE field evaluation program R11 showed that the average 1-year-old car has about 2 percent water in its brake fluid. Even this small TABLE 4-1  MINIMUM BOILING POINTS FOR THE SIX BRAKE FLUID GRADES

Boiling Point

DOT 3

DOT 4

DOT 5

DOT 3/4

DOT 5.1

Dry

4018F(2058C)

4468F(2308C)

5008F(2608C)

5008F(2608C)

5858F(3078C)

2848F(1408C)

3118F(1558C)

3568F(1808C)

3478F(1758C)

3658F(1858C)

Wet

1

1 Wet means the fluid is saturated with water. DOT 5.1 long-life has the same dry and wet boiling point of 4248F(2188 C)

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Figure 4-1  Brake fluid should be purchased only in the quantities needed for the job.

amount is enough to lower the boiling point of DOT 3 fluid from 4018F(2058C) to less than 3208F(1608C). DOT 4 fluid absorbs less moisture and maintains a higher boiling point than DOT 3 fluid. Because both DOT 3 and DOT 4 fluids absorb moisture from the air, always keep containers tightly capped. Reseal brake fluid containers immediately after use. Although brake fluid is available in containers as small as 12 ounces to as large as 5 gallons (Figure 4-1), it is often wise to buy small containers and keep them sealed until needed. Taking these steps to minimize water in the brake fluid helps reduce corrosion of metal parts and deterioration of rubber components. It also keeps the brake fluid boiling point high to minimize the chance of vapor formation.

AUTHOR’S NOTE  Although brake fluid may be purchased in quantities larger than 1 quart, it will be a special-order item. Very few public parts vendors or repair shops keep anything larger than a 1-quart container of brake fluid. Even a “brake-only” repair shop would seldom need brake fluid in quantities that would justify storing 5-gallon containers of it. Plus, when you consider that brake fluid must be placed in a smaller container for ease of pouring and labeled accordingly, it is not worth the trouble. It is recommended that brake fluid should always be purchased in 1-quart or smaller containers.

The DOT rating is found on the container of brake fluid (Figure 4-2). The vehicle service information and owner’s manual specify what rating is correct for the car. Do not use a brake fluid with a lower DOT rating than specified by the vehicle manufacturer. DOT 3 fluid will last longer than DOT 4 under ideal conditions; that is, the system is clean, sealed, and kept sealed or “perfect.” DOT 3 is considered to be a lifetime fluid under those conditions, whereas DOT 4 still must be flushed out and replaced every 1–3 years under the same conditions. It is best to completely flush light vehicle brake systems about every 2–3 years because no typical brake system is “perfect.” The synthetic fluids have higher wet and dry boiling points. This makes them, at least in theory, better for braking and durability while in the braking system. The service life of DOT 3/4 is about 24 months (2 years), whereas DOT 5.1 is rated for about 60 months (5 years). Long-life DOT 5.1 is rated at a service life of up to 10 years.

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71

Figure 4-2  The DOT number is always on the label of a brake fluid container.

Other Brake Fluid Requirements A high-temperature boiling point is not the only requirement that brake fluid must meet. Brake fluid must remain stable throughout a broad range of temperatures, and it must retain a high boiling point after repeated exposures to high temperatures. Brake fluid also must resist freezing and evaporation and must pass specific viscosity tests at low temperatures. If the fluid thickens and flows poorly when cold, brake operation would suffer at low temperatures. In addition to temperature requirements, brake fluid must pass corrosion tests, it should not contribute to deterioration of rubber parts, and it must pass oxidation-­ resistance tests. Finally, brake fluid must lubricate cylinder pistons and bores and other moving parts of the hydraulic system.

DOT 5 Silicone Fluid DOT 5 Silicone fluid does not absorb water. This purple fluid has a very high boiling point, is noncorrosive to hydraulic system components, and does not damage paint as does ordinary fluid. However, DOT 5 fluid has other characteristics that are not so beneficial. Silicone fluid compresses slightly under pressure, which can cause a slightly spongy brake pedal feel. Silicone fluid also attracts and retains air more than polyglycol fluid does, which makes brake bleeding harder; it tends to out gas slightly just below its boiling point; and it tends to aerate from prolonged vibration. DOT 5 fluid has other problems with seal wear, water accumulation, and separation in the system. All of these factors mean that DOT 5 silicone fluid should never be used in an ABS.

Synthetic Fluids As mentioned earlier, synthetic brake fluids are now available on the market. DOT 3/4 and DOT 5.1 are compatible with DOT 3 and DOT 4 fluids and can be mixed with them.

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DOT 5.1 is based on polyglycol chemistry. Both can be used to flush and replace DOT 3 or DOT 4 fluid in a brake system and can be used in an ABS. They are distinguished from each other by color: DOT 3 and DOT 4 are clear and amber, DOT 3/4 is clear and pale blue, DOT 5.1 is crystal clear, and the long-life version of DOT 5.1 is clear and yellow in color. DOT 5.1 has extra solvency to put gum and sludge deposits into suspension with additional anticorrosion additives in the long-life version. DOT 5.1 and DOT 5.1 long-life brake fluids are not silicone-based fluids. Do not mix or replace DOT 5 fluid with DOT 5.1 or DOT 5.1 long-life fluids. Damage to the brake system and possible injury could occur due to damage to brake system components.

Hydraulic System Mineral Oil Fluids HSMO fluid has some good should only be used in Jaguar and Rolls Royce vehicles because it is mineral oil based.

Hydraulic system mineral oil (HSMO) is the rarest kind of brake fluid, used by only two carmakers: Jaguar and Rolls Royce. HSMO is not a polyglycol or silicone fluid; rather it is made from a mineral oil base. It has a very high boiling point, it is not hygroscopic, it is a very good lubricant, and it actively prevents rust and corrosion. HSMO fluid can be identified by its green color, and the reservoir cap will also be green in color. Because HSMO is petroleum based, systems designed for its use also require seals made of special rubber. If polyglycol or silicone fluid is used in a system designed for HSMO, these fluids will destroy the HSMO system seals. Similarly, if HSMO is used in a system designed for polyglycol or silicone fluid, it will destroy the seals of those systems. HSMO is not covered by the DOT classifications of FMVSS 116 and is not compatible with DOT fluids.

Fluid Compatibility Although the performance requirements of DOT 3, DOT 4, DOT 5, and synthetic fluids are different, FMVSS 116 requires that the four grades of fluid must be compatible with each other in a system. Mixing different types of fluid in a system is not recommended, but it can be done without damaging the system or creating a damaging reaction between two types of fluid. It is important to remember that if DOT 3 and DOT 4 fluids are mixed in a system, for example, the boiling point of the DOT 4 fluid will be reduced by the same percentage as the percentage of DOT 3 fluid in the mixture. Thus, overall system performance may be compromised by mixing fluids. Although FMVSS 116 requires DOT fluids to be compatible, it does not require them to be homogeneous. They are not required to blend into a single solution unless the fluids are of a single type, such as two DOT 3 fluids or two DOT 4 fluids. Silicone DOT 5 fluid has a lower specific gravity than polyglycol fluid. If the two types are mixed, they do not blend; the silicone fluid separates and floats on top of the polyglycol fluid. Although the synthetic fluids may be compatible with the DOT 3 and DOT 4 fluids, they also should not be mixed except in an emergency. They will blend, but the performance level of the synthetics will decrease in proportion to the amount of polyglycolbased fluid remaining in the system. If a synthetic fluid is requested by the customer, then a complete flushing and removal of all polyglycol fluids must be accomplished. This would also be a good time to check for any damage to the brake seals. If the fluid has been in the system for several years, it would benefit the customer to replace or rebuild those brake components housing flexible or fixed seals. The best practice is to use a single, high-quality brand of brake fluid of the DOT type specified for a particular vehicle. Avoid mixing fluids whenever possible.

Brake Fluid Storage and Handling Polyglycol fluids have a very short shelf life. As soon as a container of DOT 3 or DOT 4 polyglycol fluid is opened, it should be used completely because it immediately starts to

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73

absorb moisture from the air. DOT 5 silicone fluids and HSMO fluids are not hygroscopic and can be stored for long periods of time. All brake fluids must be stored in clean containers in clean, dry locations. Preferably, brake fluid should be stored in its original container with all labeling intact. Containers must be kept tightly closed when not in use. Transfer containers must be properly labeled. When working with brake fluid, do not contaminate it with petroleum-based fluids, water, or any other liquid. Also keep dirt, dust, or any other solid contaminant away from the fluid. When filling a system with polyglycol fluid, keep it off painted surfaces and off your skin. If possible, buy brake fluid in small quantities to limit storage times. Plastic containers could allow air and/or moisture to seep through the container material, contaminating the fluid even when the container has not been opened. This is particularly true when the container is sitting in a shop or home garage where it is exposed to the environment to some extent. Contamination is not as great a concern at the vendor where the stock is stored and sold in a short period of time.

Other Brake Fluid Precautions Brake fluid is considered a toxic and hazardous material. Used brake fluid must be disposed of in accordance with local regulations and EPA guidelines. Do not pour used brake fluid down a wastewater drain or mix it with other chemicals awaiting disposal. Observe these general precautions when working with brake fluid: ■■ Never mix polyglycol and silicone fluids because the mixture could cause a loss of brake efficiency and possible injury. ■■ Brake fluid can cause permanent eye damage. Always wear eye protection when handling brake fluid. If you get fluid in your eyes, rinse them thoroughly with water, then see a doctor immediately. ■■ Brake fluid may also irritate your skin. Wear chemical-resistant gloves. If fluid gets on your skin, wash the area thoroughly with soap and water. ■■ Always store brake fluid in clean, dry containers. Protect brake fluid from contamination by oil, grease, or other petroleum products, as well as contamination by water. Never reuse brake fluid. ■■ Do not spill polyglycol brake fluid on painted surfaces. Polyglycol fluid will damage a painted surface. Always flush any spilled fluid immediately with cold water.

Contaminated Fluid Problems Always use the type of brake fluid recommended in the vehicle service manual or owner’s manual. Using the wrong kind of fluid or using fluid that is contaminated with any other liquid can cause the brake fluid to boil or rubber parts in the hydraulic system to deteriorate. Swollen master cylinder piston seals are the best indicator of contamination in the brake fluid. Deterioration also may be indicated by swollen wheel cylinder boots, swollen caliper boots, or a damaged master cylinder cover diaphragm. If water or other contaminants is found in the brake system and the master cylinder piston seals have been damaged, replace all sealing parts in the system, including the brake hoses and any valves or switches with rubber seals. Also check for brake fluid on the brake linings. If you find any, replace the linings.

AUTHOR’S NOTE  There is a quick, easy test to check the brake fluid for contamination. It is covered in the Shop Manual.

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74

Chapter 4 Steering column Bulkhead

Master cylinder

Pushrod Booster

Pedal

Figure 4-3  The brake pedal is suspended under the dash on modern vehicles. Its lever action will increase the driver input braking force depending on the length and curve of the pedal arm.

If water or contaminants are present in the system, but the master cylinder seals appear undamaged, check for leakage throughout the system or signs of heat damage to hoses or components. Replace all damaged components found. After repairs are made, or if no leaks or heat damage are found, drain the brake fluid from the system, flush the system with new brake fluid, refill, and bleed the system.

BRAKE PEDAL AND PUSHROD

Shop Manual page 152

Braking action begins when the driver pushes on the brake pedal. The brake pedal (Figure 4-3) is a lever that is pivoted at one end, with the master cylinder pushrod attached to the pedal lever near the pivot point. This section explains how this lever arrangement multiplies the force applied at the brake pedal several times as it is applied to the master cylinder pushrod. One end of the pushrod engages the master cylinder piston, and the other end is connected to the pedal linkage. The pushrod often is adjustable, with many made in two parts so they can be lengthened or shortened. Adjusting pushrod length is explained in the Shop Manual. AUTHOR’S NOTE  Vehicles with power brakes will have two pushrods, one between the pedal and power booster and another between the power booster and master cylinder. Both may be adjustable.

The brake pedal and master cylinder must be mounted close to each other to shorten the pushrod and so the pedal pushrod can operate the master cylinder pistons. All late-model cars use a suspended pedal assembly. The pedal assembly is mounted to a support bracket that is attached to the inside of the engine compartment cowl or bulkhead under the dash. The pushrod that connects the pedal linkage to the master cylinder goes through a hole in the bulkhead. The pedal, pushrod, and master cylinder are

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Clevis

75

Master cylinder

Front bulkhead

Free play at pushrod 1 – inch 2 (1.5 mm)

Pushrod

Brake pedal assembly

Power brake booster unit Pedal free play 1 – to 1 – inch 8 4 (3 to 6 mm)

Bulkhead Brake pedal

Figure 4-4  A suspended pedal installation with a vacuum power booster.

Figure 4-5  Free play at the master cylinder pushrod is multiplied by the pedal ratio, which increases free play when measured at the pedal.

mounted so, regardless of pedal position, the pushrod always pushes directly in line with the master cylinder pistons. The master cylinder is mounted on the opposite side of the bulkhead in the engine compartment. The booster is mounted to the bulkhead, and the cylinder is mounted to the booster (Figure 4-4). With this arrangement, the master cylinder is easy to get to for checking or service.

Brake Linkage Free Play All brake pedal linkage must provide some amount of free play between the master ­cylinder pistons and the pushrod. This free play is necessary to let the master cylinder pistons retract completely in their bores. Free play at the master cylinder is usually very slight: about 1/16 inch (1.5 mm to 20 mm). At the brake pedal, the free play is multiplied by the pedal ratio. Thus, if free play at the master cylinder is 1/16 inch (1.5 mm) and the pedal ratio is 4:1, free play at the pedal will be 1/4 inch (6 mm) (Figure 4-5). Free play as measured at the pedal is usually specified by the vehicle manufacturer, at least as an inspection point. Free play is adjustable on some installations and not adjustable on others. Most adjustments are made by loosening a locknut at the pushrod clevis and turning the pushrod to lengthen or shorten it. Vacuum power brake boosters have a second pushrod that transmits motion from the booster to the master cylinder. The booster pushrod may require adjustment separately from the brake pedal pushrod. The Shop Manual explains all necessary free play and pushrod adjustments.

Brake pedal free-play is needed to allow the master cylinder pistons retract fully in their bore.

SPLIT HYDRAULIC SYSTEMS The dual master cylinder has two independent hydraulic systems. These two hydraulic systems can be connected to the wheel brake units in either a front-to-rear or diagonal arrangement.

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Chapter 4

Figure 4-6  Typical front-to-rear split hydraulic system.

Figure 4-7  Typical diagonally split hydraulic system.

The front-to-rear hydraulic split system is the oldest split system. This system has two master cylinder outlets (Figure 4-6). One is connected to a line going to the two rear brakes and the other to a line going to the two front brakes. Although this system provides two independent hydraulic systems, it has some disadvantages. The front brake system does 60 percent to 70 percent of the braking. If the front hydraulic system were to fail, all of the braking would have to be done by the rear wheels. This means that the car would have to be stopped with only 30 percent to 40 percent of its brake power. Most late-model cars have a diagonally split hydraulic system. The diagonally split system (Figure 4-7) has one of the master cylinder circuits connected to the left front and right rear brakes. The other circuit is connected to the right front and left rear brakes. The connection can be made directly to the master cylinder outlets or externally with a valve. The advantage of this system is that if one system fails, the vehicle will have less than 50 percent of the braking action from one front and one rear brake. The driver may experience a left or right brake pull.

Split Hydraulic System Operation In the released position, the cups of the primary and secondary pistons uncover the vent ports as is shown in Figure 4-13. Under normal conditions, when the brakes are applied, the primary piston moves forward, and a combination of hydraulic pressure and the force of the primary piston spring moves the secondary piston forward. When the pistons have moved forward so that their cups cover the vent ports, hydraulic pressure is built up and transmitted to the front and rear wheels. The replenishing ports work as described previously. If there is a hydraulic failure in the brake lines served by the secondary piston (Figure 4-8), both pistons will move forward when the brakes are applied, as under normal conditions, but there will be nothing to resist piston travel except the secondary piston spring. This lets the primary piston build up only a small amount of pressure until the secondary piston bottoms in the cylinder bore. Then, the primary piston will build enough hydraulic pressure to operate the brakes served by this half of the system. In case of a hydraulic failure in the brake lines served by the primary piston (Figure 4-9), the primary piston will move forward when the brakes are applied but will

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Master Cylinders and Brake Fluid

2 Secondary piston bottoms

No pressure

Rear brakes

77

1 Primary piston applies front

brakes and secondary piston

High pressure

Front brakes

Figure 4-8  Dual master cylinder operation with a primary (front) circuit failure.

2

1

Secondary piston applies rear brakes

High pressure

Rear brakes

Primary piston moves forward and applies secondary piston

No pressure

Front brakes

Figure 4-9  Dual master cylinder operation with a secondary (rear) circuit failure.

not build up hydraulic pressure. Very little force is transferred to the secondary piston through the primary piston spring until the piston stem comes in contact with the secondary piston. Then, pushrod force is transmitted directly to the secondary piston, and enough pressure is built up to operate its brakes.

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Chapter 4

Shop Manual page 148 After 3 years brake fluid can contain at least 7 percent moisture. Some manufacturers call for periodic replacement of brake fluid; however, many do not. The piston bore in a disc caliper is usually much larger than the one in a wheel cylinder, which is an additional reason for the disc side to have a larger reservoir chamber on a front/rear split system. a master cylinder reservoir holds excess brake fluid for use in the braking system. O-rings are circular rubber seals shaped like the letter “O.”

The master cylinder diaphragm allows the level of the brake fluid to change without direct contact with the air preventing moisture contamination.

DUAL-PISTON MASTER CYLINDER CONSTRUCTION AND OPERATION Figure 4-10 is a simplified illustration of how the master cylinder and the brake hydraulic system work. The master cylinder pushrod is connected to a piston inside the cylinder, and hydraulic fluid is in front of the piston. When the pedal is pressed, the master cylinder piston is pushed forward. The fluid in the master cylinder and the entire system is noncompressible and immediately transmits the force of the master cylinder piston to all the inner surfaces of the system. Only the pistons in the drum brake wheel cylinders or disc brake calipers can move, and they move outward to force the brake shoes or pads against the brake drums or rotors.

Master Cylinder Reservoir The master cylinder has two main parts: a reservoir and a body (Figure 4-11). The reservoir supplies brake fluid for cylinder operation. All master cylinders and reservoirs built since 1967 are split or dual-chamber designs, meaning they have two separate chambers areas for two separate piston assemblies. The split design separates the hydraulic system into two independent sections providing reserve braking operation in case one section fails. Old master cylinders were cast as a single unit, but the vast majority of master cylinders in use today are called composite master cylinders. The composite master cylinder has a separate aluminum body and a molded nylon or plastic reservoir. (Figure 4-12). All reservoirs have a removable cover so that brake fluid can be added to the system. The one-piece reservoirs typically have a single cover that is held on the reservoir with a retainer bail. Nylon or plastic reservoirs may have a single cover or two screw caps on top of the reservoir. Separate reservoirs may be clamped or bolted to the cylinder body, or they may be pressed into holes in the top of the body and sealed with grommets or O-rings. All master cylinder caps or covers are vented to prevent a vacuum lock as the fluid level drops in the reservoir. A flexible rubber diaphragm at the top of the master cylinder reservoir is incorporated in the screw caps or the cover. The reservoir diaphragm separates the brake fluid from the air above it while remaining free to move up and down with changes in fluid level. The diaphragm keeps the moisture in the air from entering the brake fluid in the reservoir. Moisture in the brake fluid will lower the fluid boiling point.

Master cylinder

Rotor

Pushrod

Front calipers

Rotor

Rear wheel cylinders Brake lines

Figure 4-10  Simplified diagram of master cylinder and hydraulic system operation.

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Figure 4-11  This master cylinder as viewed from the passenger side of the engine compartment. Note the power booster between the master cylinder and bulkhead. Also note that this master cylinder has a detachable reservoir.

Reservoir conver

Diaphragm

Separate Reservoir

Cast reservoir

Grommets

Bail

Cylinder body

Cylinder body

Figure 4-12  The master cylinder assembly to the left is the most common one in use today. The master cylinder on the right is an old style cast iron one-piece type.

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A BIT OF HISTORY American Motors Corporation introduced the dual hydraulic system on its 1960 cars. In 1963, several manufacturers added dual tandem in-line master cylinders to their cars. By 1967, DOT established FMVSS 105 that requires that all cars sold in the United States have split brake hydraulic systems. In 1978, Chrysler Corporation introduced the first mass-produced cars with a diagonally split hydraulic system.

If a vehicle with front disc and rear drum brakes has the brake system split so that the front brakes are on one circuit and the rear brakes on the other circuit, the reservoir chamber for the disc brakes is larger than the chamber for the drum brakes. As disc pads wear, the caliper pistons move out farther in their bores. More fluid is then required to keep the system full from the master cylinder to the calipers. Drum brake wheel cylinder pistons always retract fully into the cylinders regardless of brake lining wear so the volume of fluid does not increase with lining wear. Vehicles with four-wheel disc brakes or diagonally split hydraulic systems usually have master cylinders with equal-size reservoirs because each circuit of the hydraulic system requires the same volume of fluid. Plastic reservoirs often are translucent so that fluid level can be seen without removing the cover. Although this feature allows a quick check of fluid level without opening the system to the air, it should not be relied on for a thorough brake fluid inspection. Stains inside the reservoir can give a false indication of fluid level, and contamination cannot be seen without removing the reservoir caps or cover.

Master Cylinder Ports

The vent port is the forward port in the master cylinder bore. The replenishing port is the rearward port in the master cylinder bore.

The cup seal is the circular rubber seal with a depressed center section that is surrounded by a raised sealing lip to form a cup; cup seals are often used on the front ends of hydraulic cylinder pistons because they seal high pressure in the forward direction of travel but not in the reverse.

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Many different names have been used for the ports in the master cylinder, and often the same name has been applied to each of the ports. For the sake of uniformity, this text refers to the forward port as the “vent” port and the rearward port as the “replenishing” port, which are the names established by SAE Standard J1153. The vent port has been called the compensating port and the replenishing port by some manufacturers. To further confuse the nomenclature, the replenishing port has been called the compensating port by some manufacturers, as well as the vent port, the bypass port or hole, the filler port, or the intake port by many manufacturers. However, it is not so important what these ports (or holes) are called as there is a good understanding of their purposes and operations. Figure 4-13 is a cross section view of a dual master cylinder including the location and names for the two ports. Although the vehicle and parts manufacturers have not always observed the nomenclature of SAE Standard J1153, its use in this manual maintains consistency and understanding.

Master Cylinder Construction Figure 4-14 is a disassembled view of a dual piston master cylinder. A single-piston bore contains two piston assemblies with two pressure chambers. The piston assembly at the rear of the cylinder is the primary piston, and the one at the front of the cylinder is the secondary piston. Each piston has a return spring in front of it. Both pistons have a long extension at the front that is used in case of a hydraulic failure. There is a cup seal at the front of each piston and a cup or seal at the rear of each piston. The seals retain fluid in the cylinder chambers and prevent seepage between the cylinders. The secondary piston has a cup at each end. The front cup is to generate pressure in the secondary hydraulic system. The rear cup seals the primary chamber, and the hydraulic pressure generated by the primary piston is used to apply the secondary piston. This also causes the pressure generated by the secondary piston to be equal to that generated by the primary piston.

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Replenishing ports

Pushrod

Secondary piston

Primary piston

Figure 4-13  Cross section of a dual master cylinder.

Reservoir cover

Diaphragm

Separate reservoir

Grommets

Cylinder body Spring Spring retainer Cup Secondary piston Cup

Primary piston Lockring

Figure 4-14  Note how the two pistons and related components slide into the master cylinder bore. The primary piston will be the one closest to the driver and will serve the front wheel brakes in most cases.

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Two ports are at the bottom of each reservoir section. One set of ports is called the vent ports; the others are replenishing ports. The vent ports and replenishing ports let fluid pass between each pressure chamber and its fluid reservoir during operation. Two spool-shaped pistons are inside the cylinder. Figure 4-15 is a simplified illustration of a spool-shaped piston. The piston has a head on one end and a groove for an O-ring seal on the other end. The seal seats against the cylinder wall and keeps fluid from leaking past the piston. The smaller diameter center of the piston is the valley area, which lets fluid get behind the head of the piston. This prevents low pressures developing here as the piston moves forward. Each master cylinder piston works with a rubber cup seal that fits in front of the piston head (Figure 4-16). The cup has flexible lips that fit against the cylinder walls to seal fluid pressure ahead of the piston head. The cup lip also can bend to let fluid get around the cup from behind. When the brakes are applied, pressure in front of the cup forces the lip tightly against the cylinder wall and lets the seal hold very high hydraulic pressure. The lip of a cup seal is always installed toward the pressure to be contained or away from the body of the piston. The cup seals only in one direction. If pressure behind the lip exceeds pressure in front of it, the higher pressure will force the lip away from the cylinder wall and let fluid bypass the cup. Pistons have small coil springs (Figure 4-17) that return the pistons to the proper position when the brake pedal is released. Sometimes the springs are attached to the pistons; sometimes they are separate parts. A dual master cylinder has two piston assemblies. The piston nearest the pushrod is the primary piston; the other is the secondary piston. Each piston provides a separate hydraulic system for the front and rear brakes or, on a diagonally split system, between one set of front brakes and one set of rear brakes. Two outlet holes provide the connection for the hydraulic lines. A snap-ring holds the components inside the cylinder, and a flexible boot fits around the rear of the cylinder and pushrod to keep dirt from entering the cylinder. Figure 4-18 shows the major parts of the two-piece master cylinder. This master cylinder has an aluminum body to lower the weight of the assembly. Aluminum offers the advantage of being much lighter than cast iron but has large pores in the metal that can damage the lip seals of the bore pistons. The interior walls of the bore are rolled, or bearingized, to close these pores. The aluminum master cylinder bore should not be honed during service because the pores will be reopened. Replacement is required if the interior bore is worn or damaged. The removable nylon or plastic reservoir is also much lighter than a cast-iron unit. Because the master cylinder is made from two materials, it is often called a composite master cylinder. The pistons, cups, and springs used in a composite Cup seal Valley area

Valley area

Lips

Piston head

O-ring seal

Figure 4-15  Simplified spool-shaped piston for master cylinder.

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Piston head

O-ring seal

Figure 4-16  A cup seal and O-ring seal the piston in the cylinder bore.

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Cup Spool area

Spring Piston head

O-ring seal

Figure 4-17  Note how the two pistons and related components slide into the master cylinder bore. The primary piston will be the one closest to the driver and will serve the front wheel brakes in most cases.

Figure 4-18  A two-piece composite master cylinder has a plastic reservoir mounted on an aluminum body.

master cylinder are essentially the same and work the same way as those in a one-piece master cylinder.

Portless Master Cylinder Some Toyota master cylinders do not use replenishing or compensating ports. Instead they use a valve that is machined into the master cylinder pistons (Figure 4-19). When the master cylinder is at rest, fluid can flow into the area in front of the pistons. When the master cylinder is applied, the valves close under spring pressure

Master Cylinder with Hydraulic Brake Assist A special master cylinder is required for vehicles with hydraulic brake assist. Brake fluid can be applied directly to the master cylinder pistons when necessary, as determined by the brake control module, via the brake stroke sensor (Figure 4-20). The brake control

Max Min Reservoir

Valve assembly

Stopper pin

Secondary piston

Primary piston seal

Valve assembly

Primary piston

Figure 4-19  The portless master cylinder does not use the conventional vent and replenishing ports, but instead uses special valves in the primary and secondary pistons to refill the master cylinder.

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Figure 4-20  Brake pedal stroke sensor.

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module on a hybrid vehicle can also determine how much braking can be taken care of by regenerative braking versus the hydraulic braking.

Master Cylinder Operation The primary and secondary pistons of the master cylinder operate in the same way during normal braking. Figure 4-21 through 4-26 show the operation of the primary piston. The secondary piston is moved forward by the pressure created ahead of the primary piston. Each of the two pistons has a stop at its front end. This provides a means to allow one piston to build pressure if there is an external leak in the brake system. As the noted figures are examined, the secondary piston is performing the same action as the primary piston. The low-pressure area is created by the fast-rearward movement of the piston and the slow-moving brake fluid. This sudden increase of empty volume causes the pressure to drop. Figure 4-21 shows a piston assembly and reservoir with the piston in the released position. The reservoir is full of brake fluid. The vent port in the bottom of the reservoir is located just ahead of the piston cup. Fluid flows from the reservoir through the vent port into the pressure chamber in front of the piston cup. The replenishing port is located above the valley area of the piston, behind the piston head. The O-ring seal on the primary piston keeps the fluid from leaking out the rear of the cylinder. The return spring in front of the piston and cup returns the piston when the brakes are released. When the driver presses on the brake pedal, the pushrod pushes the master cylinder piston forward (Figure 4-22). As the piston moves forward, the piston pushes the cup past the vent port. As soon as the vent port is covered, fluid is trapped ahead of the cup. The fluid, under pressure, goes through the outlet lines to the wheel brake units to apply the brakes and applies the secondary piston. When the driver releases the brake pedal, the return spring forces the piston back to its released position. As the piston moves back, it pulls away from the fluid faster than the fluid can flow back from the brake lines to the pressure chamber. When this happens, low pressure is created ahead of the piston.

Fluid Vent port

Replenishing port

Reservoir

Pushrod

Fluid to wheel

Pressure chamber

Return spring

Cup

Piston

O-ring seal

Figure 4-21  Basic operating parts of a single piston within a dual-piston master cylinder.

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85

Replenishing port

Valley area Fluid pressure

Piston

Cup seal

Figure 4-22  As the piston moves forward, the cup seal closes the vent port and lets the pressure develop ahead of the piston.

The piston must move back to the released position rapidly so it can be ready for another forward stroke, if necessary. The low-pressure area must be filled with fluid as the piston moves back. A path for fluid flow is provided from the valley area (Figure 4-23), past the primary cup protector washer and through several small holes in the head of the piston, or by having enough clearance between the piston head and the cylinder bore. Fluid flows through the piston or around the lip of the cup and into the chamber ahead of the piston. This flow quickly relieves the low-pressure condition. The fluid that flows from the valley area to the pressure chamber must be replaced. Figure 4-24 shows how the replenishing port lets fluid from the reservoir flow into this area. When the piston is fully returned to its released position, the space in front of it is full of fluid. The piston cup again seals off the head of the piston. In the meantime, the fluid from the rest of the system has begun to flow back to the high-pressure chamber. If this fluid pressure were not released, the brakes would not release. Figure 4-25 shows how the returning fluid flows back to the reservoir through the vent port. The vent port is covered by the piston cup at all times, except when the piston is released.

Vented port

The vent port allows pressure in the brake pressure chamber to be relieved back into the master cylinder when the brakes are fully released.

Replenishing port

Valley area

Piston

Figure 4-23  As the piston retracts, fluid in the valley area flows past the piston’s cup seal.

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Replenishing port

Valley area

Piston

Cup seal

Figure 4-24  The low-pressure valley area is refilled through the replenishing port.

Vented port

Replenishing port

Fluid flow static

Piston

Figure 4-25  On the return stroke, fluid flows from the high-pressure chamber back to the reservoir through the vent port.

The replenishing port provides fluid to the spool valve valley from the master cylinder to prevent air pockets in front of the pistons on brake release. It also allows fluid from the master cylinder to compensate for brake wear. The replenishing port also has another important job. There are times when the amount of fluid in the wheel brake units and lines must be increased. When disc brake pads wear, there is more space in the brake calipers for hydraulic fluid. When drum brake lining wears, before the automatic adjusters work, more fluid is needed in the wheel cylinders. When the brake system is serviced and air is in the system taking up space, more fluid is needed in the system to force the air out. This is accomplished in the same way low pressure ahead of the piston is relieved. On the return stroke, fluid flows through the head of the piston and around the lip of the cup (Figure 4-26). When the piston returns, the vent port is open. There is not as much fluid returning from the wheel brake units and lines, so less fluid flows through the vent port and back into the reservoir. If the drum brakes are adjusted or new pads are installed on disc brakes, the system will automatically compensate for the amount of fluid needed on the next piston cycle.

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Replenishing port

Piston

Figure 4-26  Fluid can flow around the cup seal when more fluid is required.

Master Cylinder Operation with an External Hydraulic Leak The dual-piston master cylinder was designed to reduce total brake failure when an external hydraulic leak is present. Assume there is an external leak in the rear hydraulic circuit of a front/rear split hydraulic system. The application of the primary piston applies hydraulic pressure against the rear of the secondary piston (remember the rear cup). However, the rear system is open and secondary pressure cannot be generated, so both pistons move forward with little braking effect. The extension at the front of the secondary piston contacts the front of the bore and stops further movement of that piston. Now the secondary piston’s rear cup becomes a seal, and the primary piston can build hydraulic pressure within its own hydraulic system applying that system’s brakes. A leak in the front (primary) hydraulic system works similarly except the extension at the front of the primary piston mechanically contacts and applies the secondary piston. Hydraulic pressure is now generated within the secondary circuit. The driver immediately senses a much lower brake pedal and poor braking in both conditions. The vehicle takes longer to stop, but at least there is no total brake system failure.

A BIT OF HISTORY Single-piston master cylinders used before 1967 had one piston and one hydraulic circuit for all four-wheel brake units. The problem with this system was that a hydraulic failure in the master cylinder could cause a complete loss of brakes to all four wheels. They were used on four-wheel drum brakes without power boosters.

Residual Pressure Check Valve Residual pressure check valves were once used on almost all drum brake systems, but their use has decreased since the late 1980s. Piston cup expanders were developed for wheel cylinders to hold the cups against the cylinder walls and to keep air from being drawn into the wheel cylinders (Figure 4-27). Cup expanders are simpler, cheaper, and more reliable than check valves.

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Residual pressure check valves were once used to hold slight pressure on the drum brake pistons to maintain seal contact with the walls of the wheel cylinder- cup expanders are used now.

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Figure 4-27  The cup expander, centered and attached to the spring, has eliminated the need for a residual check valve in the master cylinder.

FAST-FILL AND QUICK TAKE-UP MASTER CYLINDERS

The larger diameter primary piston in the quick take-up master cylinder moves a comparatively large amount of fluid with less pedal travel. The quick-take-up valve allows fluid into the primary piston area from the high pressure area behind the primary piston on brake application.

Several carmakers use fast-fill or quick take-up master cylinders. These cylinders fill the hydraulic system quickly to take up the slack in the caliper pistons of low-drag disc brakes. Low-drag calipers retract the pistons and pads farther from the rotor than do traditional calipers. This reduces friction and brake drag and improves fuel mileage. If a conventional single-bore dual master cylinder were used with low-drag calipers, excessive pedal travel would be needed on the first stroke to fill the lines and calipers with fluid and take up the slack in the pads. To overcome this problem, fast-fill and quick takeup master cylinders provide a large volume of fluid on the first stroke of the brake pedal. A fast-fill or quick take-up master cylinder is identified by the dual bore design that creates a bulge or stepped outside diameter of the casting (Figure 4-28). The cylinder has a larger diameter bore for the rear of the primary piston than for the front of the primary piston. Inside the cylinder, a fast-fill or quick take-up valve replaces the conventional vent and replenishing ports for the primary piston (Figure 4-29). The quick take-up valve contains a spring-loaded check ball that has a small bypass groove cut in the edge of its seat. The outer circumference of the quick take-up valve is sealed to the cylinder body with a lip seal. Several holes around the edge of the hole let fluid bypass the lip seal under certain conditions. Some valves (those more often called “fast-fill” valves) are pressed into the cylinder body and sealed tightly by an O-ring. A rubber flapper-type check valve under the fast-fill valve performs the same bypass functions as a lip seal of a quick take-up valve. The following sections explain the operation of a quick take-up or fast-fill valve. Brakes Not Applied.  When the brakes are off, both master cylinder pistons are retracted, and all vent and replenishing ports are open. Fluid to both ports of the primary piston must flow through the groove in the check ball seat, however. Brakes Applied.  As the brakes are applied, the primary piston moves forward in its bore. Remember that the diameter of the primary valley area is larger than the diameter of the rest of the cylinder. As the primary piston moves forward into the smaller diameter, the volume

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Figure 4-28  A typical quick take-up master cylinder.

Quick take-up valve Bypass groove Peripheral holes

Reservoir

Secondary high-pressure chamber

Check valve

Secondary low-pressure chamber

Lip seal

Primary high-pressure chamber

Figure 4-29  A quick take-up valve serves as the primary piston in this master cylinder designed for use with low-drag calipers.

of the valley area is reduced. This causes hydraulic pressure to rise instantly in the lowpressure chamber. The higher pressure forces the large volume of fluid in the valley area past the cup seal of the primary piston (Figure 4-30), providing the extra volume of fluid to take up the slack in the caliper pistons. The lip seal of the quick take-up valve keeps fluid from flowing from the valley area back to the reservoir. Initially a small amount of fluid bypasses the check ball through the bypass groove, but this small amount is not enough to affect quick take-up operation. As brake application continues, pressure in the valley area rises to about 70 to 100 psi. The check ball in the quick take-up valve then opens to let excess fluid return to the reservoir (Figure 4-31). Pressures in front and behind the primary piston equalize, and the

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Check ball

Fluid from large bore to small bore

Primary piston

Forward direction of piston

Figure 4-30  As the brakes are applied, fluid flows from the large bore to the small bore for the primary piston.

Pressure equal in both large and small bores

Primary piston

Forward direction of piston

Figure 4-31  When pressures equalize in both chambers, fluid returns to the reservoir.

piston moves forward to actuate the secondary piston. These actions all occur in a fraction of a second. All the actions described above apply to the primary piston if it is serving front disc brakes and the secondary piston is serving drum brakes. If the hydraulic system is split diagonally, or if the car has four-wheel, low-drag discs, the quick take-up fluid volume must be available to both pistons. Some master cylinders have a second quick take-up valve for the secondary piston. Others provide the needed fluid volume through the design of the cylinder itself. If the primary quick take-up valve stays closed, the fluid bypassing the primary piston cup causes the secondary piston to move farther. This provides equal fluid displacement from both pistons and maintains equal pressure in the system. When the quick take-up valve opens, both pistons move together just as in any other master cylinder. Brakes Released.  When the driver releases the brake pedal, the return springs force the primary and secondary pistons to move back. Pressure drops in the pressure chambers, and fluid bypasses the piston cup seals from the valley area. Low pressure is created in the valley area, which lets atmospheric pressure in the reservoir force fluid past the seal of the quick take-up valve (Figure 4-32). Fluid from the reservoir then flows through both the vent and replenishing ports to equalize pressure in the pressure chambers and valley areas. On the return stroke, fluid flow to the secondary piston is through a normal replenishing port unless the secondary piston also has a quick take-up valve. If a secondary quick take-up valve is installed, it works as described for a primary quick take-up valve.

Seal opens

Primary piston

Reverse direction of piston

Figure 4-32  When the piston returns, low pressure draws fluid into the valley area.

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CENTRAL-VALVE MASTER CYLINDERS Some ABSs use master cylinders that have central check valves in the heads of the pistons. If the master cylinder provides pressure during antilock operation (a so-called open system) and the system also has a motor-driven pump, the master cylinder pistons may shift back and forth rapidly during antilock operation. This could cause excessive pedal vibration and, more important, wear on the piston cups where they pass over the vent ports. To prevent seal damage and pedal vibration, spring-loaded check valves are installed in the piston heads (Figure 4-33). When the brakes are released, fluid flows from the replenishing ports to the valley areas, through the open central check valves, and into the pressure chambers. As the brakes are applied, the central valves close to hold fluid in the pressure chambers. When the brakes are released again, the central check valves open to let fluid flow back through the pistons to the valley areas and the reservoir. The central check valves in this type of master cylinder provide supplementary fluid passages to let fluid move rapidly back and forth between the pressure chambers and the valley areas during antilock operations. This is not much different in principle from nonABS fluid flow, but the extra passages reduce piston and pedal vibration and cup seal wear. Chapter 10 in this Classroom Manual provides more information on ABS master cylinders.

Performance Fluids and Master Cylinders The pedal assembly, master cylinder, and brake fluid for racing vehicles are almost the same as those on a production vehicle. There are some differences in weight and increased performance, however. Most race vehicles are equipped with low-drag disc brakes at all four wheels. To meet the initial braking requirement, a quick take-up master cylinder is needed. Racing master cylinders can be purchased with different bore sizes, resulting in more fluid pressure with reduced force by the driver.

Primary chamber

Secondary chamber Central valves

Figure 4-33  This ABS master cylinder has central valves in the piston heads in place of vent ports.

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In most instances, only one dual-piston cylinder is used with some type of split system. However, some race crews opt for two identical single-piston master cylinders. The two master cylinders act like a split hydraulic system in that one master cylinder serves the front wheels, whereas the other serves the rear wheels. The master cylinders are applied by one brake pedal acting through a balance bar between the pedal lever and the two push-rods. Some race units are equipped with a brake power booster, and others are not. In this case, it is more an issue of weight than of driver endurance. Of primary importance to race vehicle braking is the type of brake fluid used. On short tracks with a lot of braking, the boiling point of the fluid can be reached quickly and may be sustained for long periods. Brake fluids developed for racing purposes generally have the same chemical properties as conventional fluids, but they have much higher boiling points. Castrol offers a blend of polyglycol ester of dimethyl silane, ethylene polyglycols, and oxidation inhibitors. This blend has a dry boiling point of 4508F(2328C) and helps prevent fluid contamination during operation. Another brand, GS610, offers a fluid with a dry boiling point of 6108F(3218C). There are several manufacturers and suppliers of racing brake components. Brembo is one of the larger manufacturers of racing components, and some of its products are now being installed on some production performance vehicles.

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Brake fluid specifications are defined by SAE Standard J1703 and FMVSS 116. Fluids are assigned DOT numbers: DOT 3, DOT 4, DOT 5, DOT 3/4, and DOT 5.1. Always use fluid with the DOT number recommended by the specific carmaker. Never use DOT 5 fluid in an ABS or mix with any other brake fluid. HSMO fluids are very rare and should never be used in brake systems designed for DOT fluids. The brake pedal assembly is a lever that increases pedal force to the master cylinder. The brake pedal lever is attached to a pushrod, which transmits force to the master cylinder pistons. A front-to-rear split hydraulic system has two master cylinder circuits. One is connected to the front brakes and the other to the rear brakes. A diagonally split hydraulic system is one in which one master cylinder circuit is connected to the left front and right rear brakes and the other circuit is connected to the right front and left rear brakes. The master cylinder has two main parts: a reservoir and a cylinder body. The reservoir can be a separate piece or cast as one piece with the cylinder. A dual-piston master cylinder has two separate pistons providing pressure for two independent

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hydraulic systems. Each of the two pistons in the master cylinder has a cup, a return spring, and a seal. During application, the piston and cup force fluid ahead of the piston to activate the brakes. During release, the return spring returns the piston. Fluid from the reservoir flows from the reservoir through the replenishing port around the piston cup. Excess fluid in front of the piston flows back into the reservoir through the vent ports. Quick take-up or fast-fill master cylinders have a step bore, which is a larger diameter bore for the rear section of the primary piston. Quick take-up master cylinders have a valve that provides rapid filling of the low-pressure spool area of the primary piston from the reservoir. Some ABS master cylinders have check valves in the heads of the pistons to reduce piston and pedal vibration and cup wear. Portless master cylinders do not use a replenishing or vent port. Fluid can flow between the reservoir and the area ahead of the master cylinder pistons by means of a valve machined into the master cylinder pistons when the master cylinder is at rest.

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REVIEW QUESTIONS Essay 1. Explain why DOT 5 brake fluid is not recommended by any manufacturer. 2. Explain why the boiling point of brake fluid is important. 3. Explain why it is not a good idea to mix DOT 5 fluids with DOT 3 and DOT 4. 4. Describe a sure sign of brake fluid contamination with mineral oil. 5. Explain why brake pedal linkage free-play is necessary. 6. Explain the split hydraulic system. 7. Describe a composite master cylinder. 8. Describe a master cylinder cup seal and how it is used. 9. What are the ports in the bottom of the master cylinder reservoir, and what do they do? 10. Explain the advantage of a quick take-up master cylinder.

Fill in the Blanks 1. A fast-fill or quick take-up master cylinder is identified by the dual bore design that creates a _______________ or _______________ _______________ of the casting. 2. DOT 3 and DOT 4 fluids are polyalkylene-­ glycol-ether mixtures, called _______________ for short. 3. Because both DOT 3 and DOT 4 fluids _______________ _______________ from the air, always keep containers tightly capped. 4. Silicone fluid _______________ slightly under pressure, which can cause a slightly spongy brake pedal feel. 5. Polyglycol fluids have a very _______________ shelf life. 6. The _______________ -to- _______________ hydraulic split system is the oldest split system. 7. Most late-model cars have a _______________ split hydraulic system.

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8. The master cylinder has two main parts: a _______________ and a _______________. 9. All master cylinder caps or covers are vented to prevent a _______________ _______________ as the fluid level drops in the reservoir. 10. The piston assembly at the rear of the cylinder is the _______________ piston, and the one at the front of the cylinder is the _______________ piston.

Multiple Choice 1. Technician A says the master cylinder changes the driver’s mechanical force on the pedal to hydraulic pressure. Technician B says this hydraulic pressure is changed back to mechanical force at the wheel brakes. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 2. Technician A says choosing the right fluid for a specific vehicle is based on the simple idea that if DOT 3 is good, DOT 4 must be better, and DOT 5 better still. Technician B says most vehicle manufacturers recommend DOT 4. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 3. Technician A says the dry boiling point of brake fluid is the minimum boiling point of new, uncontaminated fluid. Technician B says polyglycol fluids are hygroscopic, which means that they do not absorb water vapor from the air. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 4. Technician A says a high-temperature boiling point is the only requirement that brake fluid must meet. Technician B says brake fluid also must resist freezing and evaporation and must pass specific viscosity tests at low temperatures. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

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5. Technician A says DOT 5 Silicone fluid does not absorb water. Technician B says DOT 5 silicone fluid is a purple fluid with a very high boiling point, is noncorrosive to hydraulic system components, and does not damage paint as does ordinary fluid. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 6. Technician A says synthetic DOT 3/4 and DOT 5.1 are compatible with DOT 3 and DOT 4 fluids and can be mixed with them. Technician B says DOT 5.1 is based on polyglycol chemistry. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 7. Technician A says if water or other contaminants are found in the brake system and master cylinder piston seals have been damaged, it is okay to flush the system with clean fluid and put it back in service. Technician B says replace all sealing parts in the system, including the brake hoses and any valves or switches with rubber seals. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

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8. Brake pedal linkage free play at the master cylinder is usually very slight generally about: A. 1/16 inch (1.5 mm to 20 mm) B. 1/4 inch (6.25mm) C. 1/8 inch (3.17 mm) D. 5/16 inch (7.9mm) 9. Technician A says most modern vehicles have a diagonally split hydraulic system. Technician B says the advantage of this system is that if one system fails, the vehicle will have less than 50 percent of the braking action from one front and one rear brake. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 10. Technician A says each master cylinder piston works with a rubber cup seal that fits in front of the piston head. Technician B says the cup has rigid lips that fit against the cylinder walls to allow fluid leakage around the seal. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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Hydraulic Lines, Valves, and Switches

Upon completion and review of this chapter, you should be able to:

Describe the purpose and types of

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Identify the two types of flares used on brake line tubing.

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Explain the purpose and identify the types of brake line fittings.

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Describe the purpose and explain the mounting of flexible brake line hoses .

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hydraulic brake lines.

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Explain the reasons for strength requirements for tubing and hoses and identify the construction features that fulfill these requirements.

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List the general precautions for working with brake tubing and hoses. Explain the purpose, parts, and operation of a metering valve. Explain the purpose, parts, and operation of a proportioning valve. Define the split point and slope of a proportioning valve. Explain the purpose and describe the operation of a fluid level switch and a stop lamp switch. Explain the function of a brake pedal position switch.

Terms To Know Banjo fitting Brake pedal position (BPP) sensor Center high-mounted stop lamp (CHMSL)

Double flare Dynamic rear proportioning (DRP) Fittings ISO fitting

Metering valve Pressure differential valve Proportioning valve Split point

INTRODUCTION Hydraulic lines made of tubes and hoses transmit fluid under pressure from the master cylinder to each of the wheel service brakes (Figure 5-1). Valves are used in the system to control hydraulic pressure and as safety devices. Electrical switches to operate the stop lamps, as well as sensors to indicate low brake fluid level, also are important parts of the brake system.

BRAKE LINES AND HOSES Brake lines or tubing consists of steel tubes or pipes and flexible hoses connected with fittings. Rigid tubing is used everywhere except where the lines must flex. Flexing of the brake lines is necessary between the chassis and the front wheels and between the chassis and the rear axle or suspension. Brake tubing and hoses are manufactured to strict specifications developed by SAE and the International Standards Organization (ISO).

Brake lines are made up of solid brake lines and flexible brake hoses. Brake lines are also called tubing, or tubes by some technicians.

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Figure 5-1  Brake lines consist of rigid tubing or pipes and flexible hoses that carry brake fluid from the master cylinder to the service brakes.

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The general requirements for automotive brake fluid tubing and hoses are: Good corrosion resistance against chlorides (road salt) Strength, high burst pressure, and good fatigue or corrosion resistance Smooth bores allowing non-restricted flow Good resistance to surface fretting and stone pecking Ready availability at a realistic cost Easy to form

Brake Tubing The hydraulic tubing used in the brake system is double-wall, welded steel tube that is coated to resist rust and other corrosion. Double-wall tubing is made in two ways: seamless and multiple ply. Each must meet the specifications of SAE Standard J1047 as amended. WARNING  Double-wall steel brake tubing is the only type of tubing approved for brake lines. Never use 100 percent copper tubing as a replacement; it cannot withstand the high pressure or the vibrations to which a brake line is exposed. Fluid leakage and system failure will result.

There is a copper-nickel alloy brake tubing that meets SAE Standard J1047 and ISO 4038. The alloy is 10 percent nickel, 1.7 percent iron, 0.8 percent manganese, and about 90 percent copper. This tubing meets all international and U.S. requirements for brake tubing, and it has the added advantage of being more corrosion resistant. Audi, Porsche, and Aston Martin vehicles use the copper-nickel brake tubing for their hydraulic brake systems. This chapter confines the discussion to steel tubing, however, because it is the most common, and the use, treatment, and fittings for the copper-nickel alloy tubing are exactly the same as those for steel. Seamless tubing is made by rolling a steel sheet twice around a mandrel so the edges do not adjoin each other to form a seam (Figure 5-2). The tubing is then run through a furnace where copper plating is applied and brazed to form the tubing into a single, seamless piece.

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1 2

3

1. Tinned copper–steel alloy protects outer surface. 2. Long-wearing and vibration-resistant soft steel. 3. Fused copper–steel alloy unites two steel walls.

Figure 5-2  Cross-sectional view of a brake line.

Multiple-ply tubing is formed as two single-wall tubes, one inside the other. The seams of each section must be at least 120 degrees apart. Then the two-ply tubing is furnace brazed, just like seamless tubing, to form a single, seamless length. All brake tubing is plated with zinc or tin for corrosion protection. In addition, all brake tubing must meet the burst specification of SAE Standard J1047, which requires that an 18-inch length of tubing must withstand an internal pressure of 8,000 psi. These requirements by themselves make it clear why copper tubing cannot be used for brake lines. Tubing Sizes.  Brake tubing is made in different diameters, lengths, and shapes (Figure 5-3). The most common diameters for steel tubing in the inch system are 3/16 inch, ¼ inch, and 6 /16 inch. Other tubing diameters from ⅛ inch to ⅜ inch also are available. Some vehicles use tubing sized in metric diameters. Metric diameters are specified in millimeters by SAE Standard J1290. Common metric diameters are 4.75 mm, 6 mm, 8 mm, and 10 mm. AUTHOR’S NOTE  It is almost impossible to get metric-sized brake tubing in a small town. Most parts vendors sell “metric” brake tubing, but in reality, it is an SAE-sized tubing (usually 3/16-inch inside diameter) with metric-sized and metricthreaded fasteners. A standard double flare tool will work on these lines, but the ISO flare tool will not work because the tubing collapses before flaring. The problem with double flaring an SAE-sized tube for connection to a vehicle’s ISO fitting is the flare angles. They are a little different and will not seal properly. Wire coil

Armored Tube

Diameter

Flare nut fittings

Plain Tube Length

Figure 5-3  Brake tubing (line) comes in various sizes and lengths, flared with flare-nuts. Armored tubing uses a wire coil for protection.

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It is important to note that ISO flare fittings may have a different pitch thread depending on the make and model of the vehicle. Make sure to carefully choose any replacement fittings.

ISO flares tend to seal better while using less torque on the threaded nut.

Tubing Installation.  Tubing installed on a car when it is manufactured is shaped properly to fit into the brake system. As are other parts made by the carmaker, tubing is referred to as an original equipment manufacturer (OEM) part. Aftermarket replacement tubes are most often available straight and in different lengths. If available, however, it is preferable to use an OEM-shaped, prefabricated tube as a replacement. Most often, the tubing is purchased as a coil of tubing, and the technician will fabricate a new line. Generally, one-piece tubing is used between the different components of the brake system. For instance, there is a brake tubing from the master cylinder to a control valve, then another tubing from the valve to either a wheel or the junction block where the tubing is branched to each wheel. If possible, do not cut the tubing to add a section. Replace the whole section of tubing instead of patching it. Each end of the tubing has a fitting for connection into the system. The fitting, which is described later, fits over the tube and seats against a specially formed end of the tubing. The formed end of the tubing is called a flare. There are two common types of flares formed on the end of brake tubing, the double flare and the ISO flare (Figure 5-4). The inverted double flare has the end of the tubing flared out, then it is formed back onto itself. The ISO flare has a bubble-shaped end formed on the tubing. Each type of flare is used with a different type of fitting, and they are not interchangeable. Tools are available to form these flares when fabricating new tubing for a repair. Flares and their fittings are described in more detail later in this chapter. The brake line tubes are routed from the master cylinder along the car frame or body toward the wheel service brakes (Figure 5-5). Clips hold the tubes in position. The clips

Inverted Double Flare

ISO Type Flare

Figure 5-4  Inverted double flares and ISO flares are used on brake lines. Right rear brake line Right front brake hose

Clips Left front brake line

Right front brake line Clip

Rear brake hose

Left rear brake line

Rear brake line

Left front brake hose

Figure 5-5  Typical installation of brake tubing and hoses. Brake tubing is held to the vehicle frame by clips and brackets.

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Tubing

99

Flexible hose to body tubing

Figure 5-6  Tubing may also be routed on driveline and suspension parts, such as a solid rear axle housing.

usually have rubber isolators to cushion the tubes. Clips are important because they prevent the tubes from vibrating, which could cause metal fatigue and eventual rupture. Tubing also may be routed on suspension and driveline parts, such as a rigid rear axle and differential (Figure 5-6).

Brake Hoses Brake hoses (Figure 5-7) are the flexible links between the wheels or axles and the frame or body. Hoses must withstand high fluid pressures without expansion and must be free to flex during steering and suspension movement. Figure 5-8 shows the parts of a brake hose. The hose is made from materials that resist damage from both brake fluid and petroleum-based chemicals. Brake hoses are manufactured and tested to the specifications of SAE Standard J1401 and FMVSS 106. Among these specifications is the requirement that a brake hose must withstand 4,000 psi of pressure for 2 minutes without rupturing. The test pressure is then increased at a rate of 25,000 psi per minute until the hose bursts. The burst pressure is recorded as the final test measurement. These performance requirements make it clear why brake hoses are important safety devices. FMVSS 106 further requires that brake hoses must be marked with raised longitudinal ribs or two 1/16-inch colored stripes on opposite sides to indicate twisting of the hose during installation. Twisting creates stress that could lead to rupture. Twisting also may cause the hose to kink, cause ply separation, and block fluid pressure. To further prevent

Figure 5-7  Brake hoses are the flexible sections of the brake line.

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Fabric plies

Inner liner

Outer jacket Rubber separator layer

Figure 5-8  Brake hoses are made with two fabric layers alternating with two rubber layers. The outer jacket is ribbed to ­indicate if the hose is twisted during installation.

twisting, at least one end fitting on a hose usually can be rotated with the hose before fastening. This normally is the end at the body or frame. Brake hoses are reinforced with metal or synthetic cords to withstand high pressures. Each end has a fitting so that it can be connected to other parts of the brake system. The brake hose length is specified from the end of one fitting to the end of the other fitting. Hose diameter is specified as the inside diameter of the hose. Hoses are available in both inch and metric diameters. Brake hoses come in different sizes and lengths with various end fittings for different vehicle requirements and are interchangeable between different makes and models.

AUTHOR’S NOTE  Unlike the brake tubing, metric-sized brake hoses are, in fact, metric sized. This is primarily because the metric fittings are crimped or swagged to the hose. Using metric fittings on an SAE-sized hose could cause the same problems as a double flare fitting connected to a metric fitting.

When purchasing brake hoses, make sure to get a hose that is DOT approved to ensure the hose has been tested for quality.

The fittings are crimped, or swagged, to the brake hose ends at very high pressures. Clamp-on or crimped fittings used with low-pressure hydraulic hoses or oil hoses cannot be used for brake hoses. For all of their strength and durability, brake hoses are the weakest links in the brake hydraulic system. Atmospheric ozone attacks the rubber material and, over a long period, causes the hoses to deteriorate. Slight porosity of the hose material also lets air enter the system, which contaminates the brake fluid—again, over a long period of time, however. Hoses also are subject to wear, both externally and internally. Hoses must be installed so that they do not rub against vehicle parts. Some hoses have rubber ribs around their outer circumference to protect them from rubbing on suspension and chassis parts. A bulge in a hose usually indicates that the hose is failing because of internal wear or damage.

AUTHOR’S NOTE  There are many technical service bulletins (TSBs) on brake diagnosis and service. When starting the repair order, consult the shop’s service database to determine if any of these TSBs apply to the job at hand.

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Retaining clip

101

Brake pipe

Groove

Bracket

Figure 5-9  The retaining clip fits in a groove at the end of the hose fitting. Brake hose clip

Figure 5-10  Typical brake hose mounting.

Another internal hose problem can occur when the inside of the hose wears to the point that a flap of rubber loosens from the hose wall. If the flap stays secured to the wall at one end and its loose end faces the master cylinder, it can delay fluid pressure to the wheel brake and cause uneven braking or pulling. If the loose end of the flap faces the wheel brake, it can delay pressure release from the wheel brake and cause brake drag. This type of hose defect is impossible to see from the outside and is difficult to pinpoint with any kind of test. If the symptoms described above exist, hoses usually are replaced to try to eliminate the problem. The point at which a hose connects to a rigid tube usually is secured to a bracket on the frame or body. This is the end that can be moved so the hose is not twisted. A clip fits in a groove in the end of the hose fitting (Figure 5-9), and the end of the hose is inserted through a support bracket (Figure 5-10). The steel line is then threaded into the fitting on the end of the hose. The fitting on one side of the bracket and the clip on the other side hold the hose securely in position.

Brake Fittings The threaded parts used to connect brake hoses and tubing together and to other brake components are called fittings (Figure 5-11). Fittings are made from steel to withstand brake system pressures. Fittings are threaded to allow connection to other brake parts. The ends of brake tubing are formed into either an inverted double flare or an ISO flare (described later) and fitted with a flare nut. Brake hoses can have either male or female

A complete fitting usually consists of a nut fitted around a tube. The nut may be male (external threads) or female (internal threads) and will screw into or around its counterpart on a device or another tube. The flare is trapped and compressed by the two pieces of fitting.

Fittings is a term applied to all plumbing connections used on the car. They may be referred to as flare nut, nut, or line nut. The term fitting is used in this text.

Wrench flats Threads

Line Fitting

Figure 5-11  Typical flare-nut fitting for an inverted flare connection.

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Step-up/Step-down Adapters (double flare)

Brake Line Union (double flare)

Brake Line Tee (double flare)

Brake Line Flare Nuts

Metric Line Adapter

Figure 5-12  Assorted adapter and fittings are used for brake line connections.

fittings. The threaded connections of master cylinders, wheel cylinders, calipers, and most valves are female. Fittings are made with both SAE inch and ISO metric threads. Threads from one system do not fit threads of the other system.

AUTHOR’S NOTE  Every time a fitting is added to a hydraulic circuit, a place is created for a leak. I would suggest that the number of fittings installed during a brake line repair be held to a minimum. Also, do not use “adapters” to join two sections of brake tubing or tube-to-hose connections. If the parts do not match, buy ones that do.

Figure 5-12 shows an assortment of different brake line fittings. Adapters can be used to connect two different sizes of fittings. Unions and tee fittings are used to connect two lines together. Again, the use of adapters should be held to a minimum; it is much more desirable to use lines that fit properly. SAE Fittings.  All SAE fittings used in brake systems have a 45-degree taper on the male nut and on the inside of the flare (Figure 5-13). The tubing seat in the female fitting has a 42-degree taper. The 3-degree mismatch forms an interference fit that creates a leak-free, high-pressure seal. SAE standards also exist for 37-degree fittings, but these are not used in brake systems. A fitting with an external taper is simply called a standard flare (Figure 5-13A). When the fitting is tightened, the tapered surfaces of the male and female fittings create the seal. A fitting with an internal taper is called an inverted or LAP flare (Figure 5-13B). These are more common than standard flares on brake tubing. The male flare fitting compresses the bell-mouthed inverted flare against the seat in the female fitting, and the tubing is sandwiched between the two halves of the fitting to form the seal.

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Tubing wall Fitting body

Fitting

45-degree flare

A Tubing wall

Fitting body

Fitting

45-degree inverted flare B

Figure 5-13  SAE 45-degree fittings are commonly used for brake connections.

Single Flare

Double Flare

Figure 5-14  Brake line steel tubing must have a double flare. The copper-nickel alloy tubing requires the same flaring.

The flared tubing end can be formed as either a single flare or a double flare (Figure 5-14). A single flare does not have the sealing power of a double flare and is subject to cracking. Preformed replacement brake tubing is sold with a double flare on each end and the fittings in place on the tubing. If you cut and form a brake pipe from bulk tubing, you will have to form double flares on both ends. Flaring procedures are covered in the Shop Manual. ISO Fittings.  The ISO fitting is a metric design, originally used on imported vehicles but now common on domestic brake systems. An ISO flare is not folded back on itself as is a double flare. The unique shape of an ISO fitting causes it to be called a “bubble” flare. Figure 5-15 shows the differences between the shapes of an inverted double flare and an ISO fitting and the ways that the tubing ends are held in their fittings. Like a standard or an inverted flare, an ISO fitting uses interference angles between the flare and its seat to form a leak-free seal. The angle of the outer surface of an ISO fitting flare is approximately 32.5 degrees. The flare seat is 30 degrees, and the angle at the end of the flare nut is 35 degrees.

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Double flare refers to a tubing connection in which the end of the tubing is flared out then formed back on itself.

ISO fitting refers to a tubing flare in which a bubble-shaped end is formed on the tubing; also called a bubble flare. It does not need a separate tubing seat as an inverted flare does.

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Chapter 5 42° 45°

Inverted Double Flare 30°

35° 32°

ISO Flare

Figure 5-15  ISO and inverted flares are distinguished by the shape of the flare. An ISO flare does not need a separate tubing seat as does an inverted flare.

Compressed washer fittings are so named because the seal is made by compressing a washer. Change the washer if the fitting is loosened or removed.

A banjo fitting is a round, banjo-shaped tubing connector with a hollow bolt through its center.

Always replace the washer(s) when the banjo fitting is loosened or removed.

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ISO fittings have become popular with both domestic and foreign vehicle manufacturers because the outer surface of an ISO fitting will form a leak-free seal against a mating surface in a cylinder or caliper body that is simply drilled and countersunk with the right taper (see Figure 5-15). Manufacturing operations are simplified because an inverted, cone-shaped seat for an inverted flare is not required. A seat for an inverted flare requires extra machining operations or the addition of a steel insert. The seat for an ISO fitting is much simpler to machine and provides a seal that is equal to—or better than—a traditional inverted flare. Compressed Washer Fittings.  Straight compressed washer fittings are usually found on the ends of brake hoses that attach to calipers or wheel cylinders. As the rigid fitting on the end of the hose is tightened, it compresses a soft copper washer against a flat, machined surface on the cylinder or caliper (Figure 5-16). Because the fitting is usually attached rigidly to the end of the hose and does not swivel, this end of the hose should be connected before the end with a swivel fitting. Compressed washer fittings also are sometimes used on hydraulic junction blocks and valve bodies. Tightening and loosening of a compressed washer fitting will permanently compress the copper washer. Whenever a fitting is disconnected, replace the washer. Banjo Fittings.  A banjo fitting is a circular fitting that looks like the instrument of the same name. A banjo fitting is used to attach a hose or tube to a port on a cylinder or caliper at a close right angle (Figure 5-17). Fluid passes from the brake line into the cutaway section inside the banjo fitting and then through the hollow bolt to the cylinder or caliper. A banjo fitting is a kind of compressed washer fitting, and both flat surfaces of the fitting are sealed with soft copper washers. The washers should be replaced anytime the banjo bolt is loosened.

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Compression washer

Hose fitting

Caliper inlet fitting

Figure 5-16  A copper washer is used with compressed fittings.

Sealing washers

Banjo bolt Banjo fitting

Figure 5-17  Banjo fittings are typically used at right-angle connections.

A BIT OF HISTORY Dual-chamber master cylinders and split hydraulic systems became standard brake system hardware in 1967 by federal regulation. However, the first safety backup brake system was more than 30 years old by then. In 1936, Hudson introduced Duo-Automatic Hydraulic Brakes, which used four-wheel mechanical parking brake linkage superimposed on the hydraulic service brake system. Override linkage on the brake pedal applied the brake shoes mechanically if the pedal dropped low enough. Hudson’s competitors apparently thought the system was more monkey business than safety business, and it remained a Hudson exclusive for more than 20 years. The last Duo-Automatic Hydraulic Brakes were used on some 1957 models, the last of the Hudsons, before the merger with Nash created American Motors.

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Brake Line and Fitting Precautions Brake lines and fittings have important safety requirements. Service instructions in the Shop Manual contain specific WARNINGS and CAUTIONS where needed. The following paragraphs summarize universally important precautions and guidelines for installing these parts: ■■

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Never use straight copper tubing in place of double-wall steel brake tubing. Copper cannot withstand the high pressure or the vibrations to which a brake line is exposed. Fluid leakage and system failure can result. The approved copper-nickel alloy tubing is accepted. For similar reasons, never use copper fuel line fittings as a replacement for steel brake line fittings. Never use spherical-sleeve compression fittings in brake lines. Spherical compression fittings are low-pressure fittings for applications such as fuel lines. They will fail and leak under the high pressures and vibrations of a brake hydraulic system. Many states have outlawed the use of compression fittings on brake lines.Do not interchange metric-sized and SAE fittings. They have different threads and cannot be mixed. Do not interchange ISO flare nuts with SAE inch-sized flare nuts. Either of these conditions can cause fluid leakage and system failure. Do not use low-pressure fuel or oil hoses in place of brake hoses. Hoses not made for brake system use can fail under the high system pressures and may deteriorate when exposed to polyglycol brake fluids. Fluid leakage and system failure can result. When installing a brake hose, be careful not to twist or kink it. Fluid leakage and system failure can result.

Brake Hydraulic Valves Before 1967, when most brake systems had drum brakes at all four wheels and master cylinders had only one chamber, the systems worked well enough with hydraulic pressure operating uniformly throughout the lines and cylinders. The development of combination disc and drum brakes required that the timing of pressure application had to be altered in certain ways. The requirement for dual-chamber master cylinders and split hydraulic systems also called for control valves and switches to operate warning lamps. The general kinds of control valves that may be used include: Shop Manual page 214

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Metering valve Proportioning valve Pressure differential valve (warning lamp switch)

With the advent of ABS and or four-wheel disc braking systems, many of these valves have been eliminated or incorporated into the ABS hydraulic modulator, although some manufacturers continue to use some of these valves or a variation of them. More on this in Chapter 10.

Metering Valve Metering valves function only during the initial stage of braking.

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Some cars with front disc and rear drum brakes have a metering valve in the hydraulic system to achieve balanced braking between the front and rear wheels. Figure 5-18 is a simplified brake hydraulic system diagram that shows a metering valve in relation to the front disc brakes and a proportioning valve (described later) in relation to the rear drum brakes. Metering valves were used primarily on rear-wheel drive (RWD) vehicles. A metering valve (Figure 5-19) is in the line to the front brakes and keeps the front disc pads from operating until the rear drum brakes have started to work. The valve delays pressure application to the front disc brakes because disc brakes are fast acting, whereas drum brakes have spring tension and linkage clearance to overcome.

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Figure 5-18  Metering and proportioning valves in relation to front disc and rear brake drums. Use of metering and proportioning valves has been reduced due to ABS braking systems. Line connections

Body

Bleeder stem

Figure 5-19  This traditional metering valve slightly delays application of front disc brakes while hydraulic pressure builds up in rear drum brake wheel cylinders.

Metering valves appeared with the first disc brake systems of the mid-1960s. Vehicles of that era were almost entirely RWD vehicles with front disc and rear drum brakes. Metering valves were required for all the reasons just described. With the increased use of front-wheel drive (FWD) and diagonally split hydraulic systems used since the early 1980s, however, metering valves have been eliminated from many vehicles. On an FWD car, 80 percent of the braking is done by the front brakes, so it is desirable to apply them as quickly as possible. Until all clearance in the brake system is taken up, braking force is not great enough to overcome the torque of the front drive wheels. This driving torque and the forward weight bias of an FWD car eliminate the problem of front wheel lockup and any need for a metering valve. Furthermore, diagonally split brake systems used on most FWD cars would require two metering valves, one for the front brake on each side of the hydraulic system. Avoiding the complication of extra parts is another good reason to eliminate the metering valve. On a vehicle with four-wheel disc brakes, the application times for the brakes at all wheels are about equal. A metering valve is therefore unnecessary.

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Proportioning Valve The proportioning valve restricts fluid to the rear wheels, thereby lowering the pressure to help prevent wheel lockup in the rear.

The amount of fluid restriction by a proportioning valve is changed proportionally to the vehicle load and amount of braking force being applied.

The proportioning valve was introduced in 1969 to help balance front and rear pressure on cars with disc and drum brakes. A metering valve controls the timing of pressure application to front disc brakes. A proportioning valve controls the actual pressure applied to rear brakes. Inertia and momentum cause weight to shift forward during braking. The weight shift is proportional to the braking force and the rate of deceleration. During hard braking, the weight shift unloads the rear axle and reduces traction between the tires and the road. With reduced traction, the rear brakes may lock, and the vehicle may spin. Rear brake lockup can be avoided, however, by modulating the hydraulic pressure applied to the rear brakes. The goal for the best possible braking is to maintain an equal coefficient of friction between all tires and the road. Disc brakes require higher hydraulic pressure than do drum brakes for equal braking force at the tires. Drum brakes use mechanical servo action (explained in Chapter 8 of this Classroom Manual) to increase force applied to the brake shoes. Because of this servo action, drum brakes require less hydraulic pressure to maintain braking force than to establish it. Disc brakes require a constant hydraulic pressure for a given amount of braking force. Overall, disc brakes always require higher hydraulic pressure than do drum brakes. A proportioning valve does exactly what its name indicates. It proportions hydraulic pressure between disc and drum brakes to maintain equal braking force at the tires. Proportioning valves were originally designed for use with front disc, rear drum combinations for all the reasons just explained. The earliest proportioning valves were separate components, installed in the line to the rear brakes in front-to-rear split hydraulic systems (Figure 5-20). Some vehicles with four-wheel disc brakes also have proportioning valves for the rear disc brakes. The goal of efficient braking always remains to maintain equal an coefficient of friction between the front and rear tires and the road. To reach this goal, the pressure to the rear disc brakes on some vehicles must be modulated to prevent lockup. A proportioning valve has an inlet passage from the master cylinder at one end and an outlet to the rear brakes at the other end. Inside, a spring-loaded piston slides in a stepped bore. One end of the piston has a larger area than the other. The actual proportioning is done by a spring-loaded, check-valve-type stem that moves in a smaller bore through the center of the piston. When the brakes are first applied and under light braking, the proportioning valve does nothing. Fluid enters the valve at the end with the smaller piston area (Figure 5-21), passes through the small bore around the stem, and exits to the rear brakes. The end of In from master cylinder

Out to rear brakes

Figure 5-20  A simple proportioning valve is installed in the line to the rear in front-to-rear split hydraulic systems.

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3

Hydraulic system pressure to front brake

1600

Rear brake pressure

1200 To rear brakes

From master cylinder

800

Split point

400

Approaching Split Point

From master cylinder

Output pressure (psi)

400

To rear brakes

Figure 5-21  This proportioning valve serves a single rear brake circuit; typically found in a diagonally split hydraulic system.

Slope =

400

100 200

1200

= 0.50

1600

Input pressure (psi)

Figure 5-22  Split point and slope are the operating factors of a proportioning valve.

the valve piston at the outlet side of the valve is the end with the larger surface area. As outlet pressure rises in the valve, it exerts greater force on the piston than inlet pressure does and moves the piston toward the inlet, against spring pressure, thus closing the center valve stem and blocking additional pressure to the rear brakes (item 3 in Figure 5-21). The pressure at which the proportioning valve closes is called the split point because the uniform system pressure splits at that point, with greater pressure applied to the front disc brakes and lower pressure applied to the drum brakes (Figure 5-22). As pressure continues to increase from the master cylinder, inlet pressure at the proportioning valve overcomes the pressure at the large end of the piston and reopens the valve. Fluid again flows through the center of the valve, pressure at the large end of the piston rises, and the valve closes again. The opening and closing action repeats several times per second. The valve piston cycles back and forth and lets pressure to the rear drum brakes increase but at a slower rate than pressure to the front disc brakes. The pressure increase to the drum brakes above the split point is called the slope. The slope is the numerical ratio—or proportion—of rear drum brake pressure to full system pressure (refer to Figure 5-22). If half of the system pressure is applied to the rear brakes, the slope is 1:2 or 50 percent. When the brakes are released, pressure drops, and the spring moves the proportioning valve piston. This opens the valve for rapid fluid return to the master cylinder. The first proportioning valves used since the early 1970s were installed in the single line to the rear brakes. One valve controlled pressure equally to both brakes. Diagonally split brake systems separated the rear brakes from each other, however. If a proportioning valve is required, two are needed.

Pressure Differential Valve (Failure Warning Lamp Switch) The pressure differential switch was in use largely before the advent of ABS braking. Since there are so many still operating, we will include a small segment on their operation here. A pressure differential valve is a hydraulically operated switch that controls the brake failure warning lamp on the instrument panel. Each side of the pressure differential valve is connected to half of the hydraulic system (one chamber of the master cylinder). Each master cylinder piston provides pressure to a separate front/rear or diagonal hydraulic

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Chapter 5 Instrument lamp A leak in either system drops pressure to that system

Rear brake pressure is applied here

The piston moves toward the reduced pressure side

Front brake pressure is applied here

Trigger is pushed in to close switch and illuminate brake warning lamp on instrument panel Switch body Piston is normally held centered by equal pressure at both ends. Switch trigger extends into groove and switch is open

Figure 5-23  This warning lamp switch is part of a combination valve, but the operation is the same whether it is an individual component or combined with other valves.

system. If one of the systems fails, the brake pedal travel will increase and more brake pedal effort will be required to stop the car. The driver might not notice a problem, however, but the lamp on the instrument panel will provide a warning in case of hydraulic failure. Figure 5-23 shows the operation of a pressure differential valve and warning lamp switch. The switch is a grounding switch, meaning it connects the light circuit to ground.

Combination Valve Since the combination valve was actually a mix of metering and proportioning valves, combination valves have been replaced by ABS components. Combination valves were introduced in the 1970s to save money and to simplify the brake hydraulic system. As the name indicates, a combination valve has two or three valve functions in one valve body. The most common three-function valve has three separate sections as shown in the sectional view (Figure 5-24)

Hydraulic Pressure Control with ABS Antilock brakes are now standard equipment on new vehicles. Antilock brakes have a single, very simple operating principle: to prevent wheel lockup by modulating hydraulic pressure to the brake at any wheel that is decelerating faster than the others and is about to lock up. An ABS accomplishes this with wheel speed sensors and a control module that processes the wheel speed information and controls hydraulic pressure with electrically operated valves and a small high-speed pumps (Figure 5-25). ABS has prevented carmakers at having to guess at what the vehicle would do in a vast

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Switch terminal

From master cylinder

From master cylinder

To front wheel

To rear wheels Metering valve stem

Valve stem

Piston To front wheel

Metering valve seal

Pressure Differential Valve

Metering Valve

Proportioning piston

Proportioning Valve

Figure 5-24  Cross-sectional view of a three-function combination valve.

LF wheel speed sensor

RF wheel speed sensor

LF wheel speed sensor

RR wheel speed sensor

Inputs

ABS control module

HCU Pressure Sensor

Valve Solenoids

Pump Motor

Outputs

Figure 5-25  The ABS control module makes the necessary calculations and adjustments to hydraulic pressures to prevent wheel lock-up.

assortment of possible low-traction and panic braking circumstances. Instead, the vehicle itself could determine the conditions and apply corrections to all four wheels several times per second. The pressure modulation or dynamic rear proportioning (DRP) provided by antilock brakes is no different than the modulation provided by metering valves and proportioning valves. In fact, ABS pressure control is more precise than a hydraulic or mechanical metering valve or a proportioning valve. Since antilock brakes became standard, engineers had the opportunity to eliminate the old valves and replace them with

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Shop Manual page 216

a computer-controlled system. Very few systems still use proportioning and metering valves in addition to the ABS function. This ensures that, in case of an ABS failure, the vehicle would still have safe braking. Chapter 10 in this Classroom Manual covers ABSs in detail.

AUTHOR’S NOTE  ABS uses simple-function electrical solenoids that are switched on/off at a very fast rate. This switching allows instantaneous and continuous control of fluid pressures.

BRAKE ELECTRICAL WARNING SYSTEM The following sections cover parking brake, fluid level, brake pad wear, stop lamp switch, and warning lamp operations.

Parking Brake Switch The parking brake is used to hold a vehicle stationary. If the parking brake is even partially applied when driving, it will produce enough heat to glaze friction materials, expand drum dimensions, and increase pedal travel. On rear disc brake systems with integral actuators, it will distort rotors and reduce brake pad life. A normally closed, single-pole, single-throw (SPST) switch is used to ground the circuit of the red warning lamp in the instrument cluster. This switch is located on the ratchet mechanism that locks the parking brake apply lever in place. Vehicles with daylight running lights (DRLs) use the parking brake switch to complete a circuit that prevents the headlights from coming on if the parking brake is applied when the engine is started. When the parking brake is released, the DRLs function normally.

Electric Parking Brakes A recent addition to the growing list of electronic devices on late-model vehicles is the electronic parking brake. These systems operate via electric actuators located on the rear brake calipers, or by electric cable actuators. These actuators are controlled by their own control module, which receives information from the vehicle's stability control system that the vehicle is moving, and automatically releases the parking brake. Of course, this system also has a "Parking Brake" indicator to alert the driver that the brake is applied and also to inform the driver that there could be a problem in the parking brake system itself. These systems have diagnostic trouble codes as well. More on these systems in Chapter 11.

Brake Pad Wear Indicators Brake pads generally have a way to alert the driver when the brake pads are worn to the point of needing replacement. Most pads use a simple scraper built into the brake pad itself that touches the rotor when the pads are worn, producing an annoying squealing sound when the brakes are not applied; the sound goes away when the brakes are applied. Both domestic and import car manufacturers have also built systems with an electronic wear indicator in the disc brake pads on some models. As the brake pads wear to a predetermined point, the red warning lamp notifies the driver they need attention. In some systems, a small pellet is contained in the brake pad friction material. It is wired to ground the red warning lamp circuit whenever the brakes are applied. Each set of brakes contains a pellet. Each set offers a parallel leg to ground. In other systems, the pellets are wired into a series electrical circuit. As the pellet wears, it opens the electrical circuit and turns the red warning lamp on. This system self-tests the brake pad wear detection circuit all the time.

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Master Cylinder Fluid Level Switch Because brake fluid level is important to safe braking, many vehicles have a fluid level switch located in the reservoir to turn on the red brake warning lamp on the instrument panel when the fluid level drops too low. The fluid level switch has replaced the pressure differential valve warning switch on most vehicles. An added advantage of a fluid level switch is that it will alert the driver of a dangerous fluid level caused by inattention and poor maintenance practices. Fluid level sensors are built into the reservoir body or cap. One kind of switch has a float with a pair of switch contacts on a rod that extends above the float (Figure 5-26). If the fluid level drops too low, the float will drop and the rod-mounted contacts touch a set of fixed contacts to close the lamp circuit; see item 4 in Figure 5-26. Another kind of switch uses a magnet in a movable float. If the float drops low enough, the magnet pulls a set of switch contacts together to close the lamp circuit. The contacts typically provide a ground path for the brake warning lamp (Figure 5-27). AUTHOR’S NOTE  If the lamp is on, then the fluid level is low. Before topping off the brake fluid, however, have the brakes checked. The fluid had to go somewhere, and unless there is an external leak, the only place for the fluid to go would be to the enlarged cavities in the wheel cylinders and calipers as the brake linings wore down. Battery Warning light

4

4

Switch

Float

Figure 5-26  Float switches such as these are used in some master cylinders to warn of low fluid level. Ignition switch

Brake warning bulb

Ignition switch (closed during crank)

Fuse 11

Park brake switch

Low brake fluid switch

Figure 5-27  The low-fluid-level switch with the parking brake switch and the ignition switch on the ground side of the warning lamp.

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Many European vehicles have a separate indicator lamp and circuit to indicate low brake fluid level. Manufacturers such as Mercedes-Benz, BMW, Jaguar, and Porsche use an electronic module to activate a special lamp on the dash.

Stop Lamp Switch and Circuit

Stop lamp switches and lamps are more commonly referred to as brake light or stoplight switches.

Many older vehicles use a mechanical stoplight switch is mounted on the brake pedal bracket and activated by movement of the pedal lever (Figure 5-28). Mechanical switches have been more common for many years because they can be adjusted to light the stop lamps with the slightest pedal movement. Stop lamp switches also may be single-function or multifunction units. Single-function switches have only one set of switch contacts that control electric current to the stop lamps at the rear of the vehicle. Multifunction switches have one set of switch contacts for the stop lamps and at least one additional set of contacts for the torque converter clutch, the cruise control, ABS, body control module (BCM), and the powertrain control module (PCM). Some multifunction switches have contacts for all of these functions. Many switches require specific adjustment procedures. Consult the service information. The stop lamp switch is a normally open, momentary contact switch. The switch is attached to the brake pedal with a small clearance between the pedal arm and the switch lever or plunger (Figure 5-29). When the driver presses the pedal, the switch closes to complete the circuit and light the stop lamps. This same circuit is used to alert the ABS to monitor the wheel sensors during braking. The conventional stop lamp switch receives direct battery voltage through a fuse. Therefore, the lamps operate even when the ignition is off. When the normally open switch is closed, voltage is applied to the stop lamps. The lamps on both sides of the vehicle and in the center high-mounted stop lamp (CHMSL) are wired in parallel. The bulbs are grounded through their mountings or by the use of remote grounds to complete the circuit.

Figure 5-28  Mechanical stop lamp switches.

Switch (open contacts)

Switch (Closed Contacts)

Lamp B+

Brake pedal arm pin

Brakes Not Applied

Lamp B+

Brake pedal arm pin

Brakes Applied

Figure 5-29  Most mechanical brake lamp switches have multiple circuits to open and close with the application of the brakes.

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B+

Stoplamp and ABS

Torque converter clutch and cruise

Figure 5-30  Stop lamp switches control the lamp circuit on the battery (B+) side of the circuit, and the switch contacts are always open.

The brake lamp contacts are usually connected to the brake lamps through the turn signal and hazard flasher switch. The switch contacts for the stop lamps are always normally open contacts (Figure 5-30). Another set of contacts is normally closed and will open when the brake pedal is depressed. This set of contacts supplies battery power to the cruise control and torque converter clutch (TCC). Both the TCC and cruise control must disengage when the brakes are applied. Some vehicles use a separate switch to control these systems.

Brake Pedal Position Sensor Late-model vehicles use a brake pedal position sensor (Figure 5-31) in place of brake lamp switches. The advent of multiple uses for the brake input by the BCM, ABS, Transmission Control Module (TCM), and in particular, stability control systems required a finer input than the mechanical switch. The brake pedal position (BPP) sensor is a potentiometer, so it can inform the BCM that the brake lamps need to be illuminated, but it can also inform the computers how far and how fast the brakes have been applied. This information is very useful to the stability control system.

The CHMSL and rear taillights are actually LED arrays on many models. The LED lamps come on almost instantaneously (which might give drivers that split second they need to stop) and consume small amounts of current, not to mention that the bulbs have a very long life.

Stop Lamps and Bulbs Stop lamps are included in the right and left taillamp assemblies. Vehicles also have a center high-mounted stop lamp (CHMSL) located on the vehicle centerline no lower than 3 inches below the rear window (6 inches on convertibles). Some tail lamp systems are two-bulb assemblies with dual-filament bulbs that perform two functions (Figure 5-32). The stop-lamp circuit and the turn signal and hazard lamp

Figure 5-31  A brake pedal position sensor.

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Figure 5-32  Taillamp bulbs. (A) bayonet style dual filament (B) bayonet style single filament (C) later style plug-in bulb.

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circuit usually share a single dual-filament bulb, with the stop-lamp circuit connected to the high-intensity filament of the bulb. The taillamps are the separate, single-filament bulbs in a two-bulb assembly. Many late-model vehicles use a dual filament plug-in bulb even when only one filament is used (Figure 5-33). In a two-bulb circuit, the stop lamps are wired through the turn signal and hazard switches. If neither turn signal is on, the current flows to both stop lamps (Figure 5-34). If the left turn signal is on, current for the right stop lamp is sent to the lamp through the turn signal switch and wire labeled 18 BR RD. The left stop lamp does not receive any current from the brake switch because the turn signal switch opens that circuit (Figure 5-35). In a two-bulb circuit, the CHMSL can be wired in one of two ways. The first way is to connect the stop lamp circuit between the stop lamp switch and the turn signal switch Hot at all times

Hot in run, bulb test, or start

Stop/Haz fuse 20A

Turn/BU fuse 10A

Fuse block

Brake switch

Turn/hazard flasher

Turn/hazard headlight switch

Ppl

Brn

Wht

(Hazard)

Right turn

Left turn

Lt Blu

18 BR RD (Front)

Left tail/ stop/turn light

(Right)

Yel

A

C

Drk Blu

B

A

B

(Front)

Right tail/ stop/turn light

C

G300

Figure 5-33  Stop lamp operation with the turn signals in neutral.

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Hot in run, bulb test, or start

Stop/Haz fuse 20A

Turn/BU fuse 10A

Fuse block

117

Brake switch

Turn/hazard flasher

Turn/hazard headlight switch

Ppl

Brn

Wht

(Hazard)

Right turn

Left turn

Lt Blu

18 BR RD (Front)

Left tail/ stop/turn light

Drk Blu (Right)

Yel

A

C

B

A

B

(Front)

Right tail/ stop/turn light

C

G300

Figure 5-34  Stop lamp current path through the hazard flasher with turn signal switches in left-turn mode.

(Figure 5-36). However, this method increases the number of conductors needed in the harness. Therefore, most manufacturers prefer to install diodes in the wires that are connected between the left and right side bulbs (Figure 5-37). If the brakes are applied when the turn signal switch is in its neutral position, the diodes allow voltage to flow to the CHMSL. When the turn signal switch is placed in the left turn position, the left lamp must receive a pulsating voltage from the flasher. However, the steady voltage being applied to the right stop lamp would cause the left lamp to light continuously if the diode were not used. Diode 1 blocks the voltage from the right lamp, preventing it from reaching the left lamp. Diode 2 allows the voltage from the right stop lamp circuit to reach the CHMSL. In a one-bulb system, one dual-filament bulb, one on each side of the vehicle, performs all of the rear warning light’s functions. The high-intensity filament is for stop, signal, and

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Chapter 5 Brake switch

B+

Turn signal switch

Dash turn indicator and left front light

Flasher B+

Dash turn indicator and right front light

To headlight switch

Turn

Turn

CHMSL

Figure 5-35  This CHMSL is connected directly to the brake switch and controlled by diodes.

Brake switch B+ Turn signal switch

Dash turn indicator and left front light

Flasher B+

1 Turn

Dash turn indicator and right front light

2 To headlight switch

Turn

CHMSL

Figure 5-36  This CHMSL is wired through the turn signal switch and controlled by diodes.

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Lighting module Turn signal switch Left turn signal input

Right turn signal input

Figure 5-37  The turn signal switch on this vehicle is an electronic input to the lighting control module.

hazard. The low-intensity filament acts as the tail or marker light. The stop lamp is wired through the turn signal switch. With the brakes applied and assuming the left turn signals activated, power is routed through the turn signal to the right stop lamp. The left stop lamp is interrupted by the position of the turn signal switch. Power from a different fused circuit is routed through the turn signal switch and to the left-side dual-filament bulb. When the hazardous warning circuit is activated, front marker lights and both rear bulbs pulse on/off unless the brakes are applied. In that case, the front marker lights still blink but the stop lamp circuit is “powered” around the hazardous warning switch. This causes the rear stop lamps to be illuminated continuously as in normal braking operations. The CHMSL in this system may be wired directly to the stop lamp switch bypassing the turn signal switch. Understanding this fact can assist the technician in determining which component is at fault: stop lamp fuse, stop lamp switch, turn signal switch, or one or more bulbs.

Turn Signal/Brake Lamp Operation with Lamp Module Control The brake lamps, turn signals, and hazard flashers on many late-model vehicles are operated by a lighting module connected to the computer network. The BPP sensor and turn signal switch are actually inputs to the lighting module (Figure 5-37). When the turn signal or brake lamps are needed by the driver, the respective sensing circuit inside the lighting module is grounded. The module outputs power directly to the respective bulbs as shown in Figure 5-38. With this design, the bulbs are flashed electronically for a turn signal, or both rear taillamps are illuminated for brake lamps, depending on the need. This eliminates the need for complicated multi-position mechanical switches and the associated wiring. Exterior lamps module

Turn signal switch input Left turn putput

Right turn output

CHMSL

Brake pedal position input

Figure 5-38  The turn signal switch on this vehicle is an electronic input to the lighting control module.

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Chapter 5

SUMMARY ■■

■■

■■

■■

Hydraulic lines made of tubes and hoses transmit fluid under pressure from the master cylinder to each of the wheel service brakes. Brake hoses are the flexible links between the wheels or axles and the frame or body. The threaded parts that connect brake hoses and tubing together and to other brake components are called fittings. The metering valve keeps the front disc brakes from operating until the rear drum brakes have started to work.

■■

■■

■■

The proportioning valve reduces the hydraulic pressure at the rear drum brakes when high pressure is required at the front disc brakes. Brake systems also include switches for parking brakes, pad wear, stop lamps, and to warn of low brake fluid level in the master cylinder. The BPP sensor sends a signal to the lighting module concerning the brake lamp position. The lighting module then operates the external lamps.

REVIEW QUESTIONS Essay 1. Explain why 100% copper line should never be used as brake lines. 2. Describe an ISO flare. 3. Why are brake hoses marked with raised ribs or colored stripes? 4. Describe how an internal brake hose problem can cause brake pull and/or brake drag. 5. Describe how a leak-free fitting is achieved with SAE flare fittings. 6. Describe why a double flare is a better choice than a single flare. 7. Explain how the ABS system has taken the place of many of the hydraulic control valves. 8. Describe the electronic brake pad wear indicator system used on some vehicles 9. Explain the operation of the BPP sensor. 10. Describe an ISO fitting.

Fill in the Blanks

3. SAE Standard J1047 requires that an 18-inch length of tubing must withstand an internal pressure of _______________ psi. 4. An ISO flare is not _______________ on itself as is a double flare. 5. _______________ fittings have become popular with both domestic and foreign vehicle manufacturers. 6. Straight ______________________________ fittings are usually found on the ends of brake hoses that attach to calipers or wheel cylinders. 7. A ______________________________ is used to attach a hose or tube to a port on a cylinder or caliper at a close right angle 8. Late-model vehicles use a _______________ _______________ position sensor in place of brake lamp switches.

1. Brake lines or tubing consist of _______________tubes or pipes and flexible _______________ connected with fittings.

9. The brake lamps, turn signals, and hazard flashers on many late-model vehicles are operated by a _______________ _______________ connected to the computer network.

2. There are two common types of flares formed on the end of brake tubing, the _______________ flare and the _______________ flare.

10. The _______________ _______________ switch has replaced the pressure differential valve warning switch on most vehicles.

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Multiple Choice 1. Technician A says that a 100 percent copper tube is often used as a brake line material. Technician B says there is a copper-nickel alloy brake tubing that meets SAE Standard J1047 and ISO 4038. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 2. The flare on the end of a brake line has a bubble, or ball, shape. Technician A says that this is a bubble flare. Technician B says that this is an ISO fitting. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 3. Technician A says fittings with an external taper is simply called a standard flare. Technician B says a fitting with an internal taper is called an inverted or LAP flare. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 4. Technician A says that a metering valve delays the application of the rear drum brakes. Technician B says that the metering valve is only needed on four-wheel disc brake vehicles. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. Technician A says on many vehicles the lighting module controls the brake lamps and turn signals. Technician B says that these vehicles use the turn signal switch as an input to the lighting module. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

121

7. While discussing electrically actuated parking brakes, Technician A says these systems operate via electric actuators located on the rear brake calipers, or by electric cable actuators. Technician B says these actuators are controlled by their own control module. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 8. Technician A says some vehicles use tubing sized in metric diameters. Technician B says some common metric diameters are 4.75 mm, 6 mm, 8 mm, and 10 mm. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 9. While discussing mechanical brake lamp switches, Technician A says the stop-lamp switch is a normally open momentary contact switch. Technician B says the same circuit is used to alert the ABS to monitor wheel speed sensors during braking. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 10. While discussing brake pad wear indicators, Technician A says that many brake pads utilize a simple scraper built into the brake pad itself that touches the rotor when the pads wear down. Technician B says the scraping sound goes away when the brakes are released. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

6. Technician A says that a proportioning valve provides greater pressure to the rear drum brakes during normal vehicle load. Technician B says that a proportioning valve provides lower pressure to the front disc brakes during initial brake application. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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Chapter 6

Power Brake Systems

Upon completion and review of this chapter, you should be able to: ■■ ■■

■■ ■■ ■■

Explain the relationship between atmospheric pressure and vacuum. Describe the relationship between atmospheric pressure and vacuum in a power brake vacuum booster.

■■

Describe the parts and operation of a vacuum power booster. Identify and describe the parts of a vacuum diaphragm assembly. List the three major kinds of vacuum boosters.

■■

■■

■■ ■■

Describe the parts and operation of the single diaphragm with a lever-reaction vacuum booster. Describe the parts and operation of the single diaphragm with a reaction-disc vacuum booster. Describe the parts and operation of the tandem diaphragm vacuum booster. Explain the parts and operation of the air and vacuum systems in a vacuum booster. Describe the parts and operation of a hydro-boost hydraulic power-assist system.

Terms To Know Accumulator Atmospheric pressure Brake assist Check valve Diaphragm Electrohydraulic brake (EHB)

Electronic brake system (EBS)

Stroke sensor

Hydro-boost Lands Pressure differential Reaction disc (or reaction plate and levers) Spool valve

Tandem Tandem booster Vacuum Vacuum suspended Valleys

INTRODUCTION A power brake system is used on most cars to reduce the braking effort required from the driver. The power brake system reduces driver fatigue, increasing safety.

INCREASING BRAKE FORCE INPUT Four methods can be used to reduce pedal pressure requirements or to boost the force applied to the master cylinder: 1. Pedal Force. The simplest way to increase braking force is for the driver to step on the pedal harder. This simple approach has definite limits, however. A 120-pound driver does not have the weight and probably not the leg strength of a 220-pound driver, but the braking requirements of the car do not change to compensate for the size and weight of the driver. Driver strength then becomes the limiting factor in how the car stops. 122

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2. Mechanical Advantage (Leverage). Chapter 4 of this Classroom Manual explains the brake pedal ratio and how it provides leverage to increase force applied to the master cylinder. Mechanical limitations allow the pedal ratio to be increased only to a given point, however. The pedal arm can be only so long to fit into the car; and the longer the pedal arm, the greater the amount of pedal travel. 3. Hydraulic Advantage (Force Multiplication). Just as the pedal ratio multiplies force applied to the master cylinder, hydraulic piston size can be used to multiply hydraulic pressure applied by the master cylinder to the wheel cylinders and caliper pistons. These piston size and pressure relationships also are explained in Chapter 2 of this manual. Hydraulic force multiplication has its limits too. If wheel cylinder and caliper pistons are made larger for greater force, master cylinder piston travel may increase along with brake pedal travel. All brake systems use hydraulic multiplication to increase braking force, but it has limitations just as pedal leverage does. 4. Power Boosters. The fourth way to increase brake application force is to install a power booster in the system, and such boosters are the subject of this chapter. There are three general kinds of power boosters. One uses intake manifold vacuum acting on a diaphragm to help the driver apply pedal force to the master cylinder. The second type uses hydraulic pressure from a hydraulic pump to operate a hydraulic booster attached to the master cylinder. The third power brake booster is not really a brake booster, but a system that controls brake hydraulics through the use of electronics. In this system, sensors on the brake pedal mechanism combined with signals shared with the ABS and vehicle stability system apply the brakes at each wheel. This is done through various configurations that share certain properties. One property is the sharing of sensors and controlling computers. The second is the installation of electronic valves (solenoids) within the brake’s hydraulic lines or at each wheel. In either case, fluid pressure can be controlled to each wheel, resulting in better braking performance and vehicle control. Power boosters are add-on devices that do not alter the basic brake system. They still allow braking, even if the booster fails or loses its power supply. All boosters have a power reserve to provide at least one power-assisted stop if power is lost. FMVSS 105 contains brake performance requirements for brake systems with the power boosters disabled. Because modern brake systems are designed to include the advantage of a power booster, pedal effort increases significantly if power is lost.

VACUUM PRINCIPLES To understand vacuum booster systems, the relationship between atmospheric pressure and vacuum must also be understood. The air around us has weight. For example, every 1-square-inch column of air extending from the Earth’s surface to the edge of the atmosphere weighs about 14.7 pounds (Figure 6-1). The weight of this air is called atmospheric pressure. Atmospheric pressure varies with altitude and temperature; but at sea level and at 688F, it is 14.7 psi. If you were to drive up in the mountains, you would find that atmospheric pressure gets lower. As you go up in altitude, the column of air is not as high, so there is less pressure. Vacuum is a pressure lower than atmospheric pressure. When an engine is running, the intake strokes in the cylinders create low pressure. This low pressure draws in the mixture of air and fuel. In automotive work, we commonly call this low pressure a vacuum. A true vacuum, however, is a complete absence of air and is found only in the laboratory or out in space. Atmospheric pressure and vacuum can be used as a strong force to make things move. Figure 6-2 shows a piston that is free to move up and down in a cylinder. One end of the

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Atmospheric pressure is basically the weight of the atmosphere that is applying force. It amounts to approximately 14.7 pounds per square inch at sea level. A vacuum is pressure less than atmospheric pressure.

Shop Manual page 248 Atmospheric pressure is reduced by about 1 pound per each 1,000 feet of elevation above sea level. Vehicles operated in Denver, Colorado, are tuned slightly different from vehicles on the Pacific Coast.

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Atmospheric pressure

15 psi

Atmosphere Piston

Vacuum pump

Vacuum

Figure 6-2  Vacuum (low pressure) works with atmospheric pressure to develop force.

Figure 6-1  A 1-square-inch column of air, the height of the Earth’s atmosphere, exerts 14.7 pounds of pressure on the Earth at sea level.

cylinder is connected to a vacuum pump. The vacuum pump is used to lower the pressure under of the piston to below atmospheric pressure. When atmospheric pressure is applied on the other side of the cylinder, the piston will move down: toward the lower pressure. The amount of force that is created depends on the pressure differential or the difference between the low pressure on one side of the piston and atmospheric pressure on the other. If a perfect vacuum exists on one side of the piston and atmospheric pressure is applied to the other side, the pressure differential equals: 14.7 psi 2 0 psi 5 14.7 psi (atmosphere pressure) 2 (vacuum) 5 (pressure differential) Remember, however, that a perfect vacuum does not exist in an intake manifold, and vacuum is not usually measured in psi. To get a realistic example of a typical pressure differential in a vacuum brake booster, two factors must be accounted for. First, pressure may be measured as either absolute (psia) or gauge (psig) and in two different measurement units: pressure in pounds per square inch (psi) or vacuum in inches of mercury (in. Hg). Atmospheric pressure at sea level may be expressed as 14.7 psia or 29.9 in. Hg. Similarity, vacuum can be expressed as either 29.9 in. Hg below atmospheric pressure or –14.7 psig below atmospheric pressure.

AUTHOR’s NOTE  The metric measurement for pressure is the kilopascal, abbreviated kPa. Atmospheric pressure (at sea level) is 100 kPa. At a perfect vacuum the measurement is 0 kPa. The reading on a scan tool with the engine running will show pressure above 0 kPa. The metric system of measurement does not go from psi to in. Hg so it can help in the understanding of vacuum and pressure.

However, most technicians do not normally rely on absolute pressure/vacuum measurements but use gauges in almost every instance. Gauges, vacuum, and pressure will register 0 in. Hg or 0 psi at sea level. In a complete vacuum a vacuum gauge would register 29.9 in. Hg, whereas a pressure gauge would register –14.7 psig. However, any math would have to use absolute measurements for accuracy.

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A vacuum-suspended booster has two chambers. The front chamber is under vacuum, and the rear can be exposed to atmospheric pressure. A flexible diaphragm separates the two chambers. The amount of vacuum available in the intake manifold and the vacuum chamber will change as the engine load changes. To calculate the approximate booster force increase, the vacuum and pressure measurements must be in the same unit. Rounding 14.7 psia to 15 psia and 29.9 in. Hg to 30 in. Hg gives a rough conversion factor of –2 – because pressure and vacuum are on opposite sides of zero). To convert from psi to in. Hg multiply psi by – 2 and from in. Hg to psi divide in. Hg by – 2. As an example, assume that the sea-level atmospheric pressure is 15 psia, the vacuum is 20 in. Hg, and the booster has 50 square inches of area. 15 psia (atmosphere pressure) 20 in Hg/22 5 210 psi 210 psia 1 15 psia 5 5 psia 15 psia (atmopshere pressure) 2 5 psia (vacuum booster pressure) 5 10 pounds of differential pressure 10 pounds of pressure (psi) 3 50 square inches 5 500 pounds of force This 500 pounds from a vacuum brake booster helps the driver apply the brakes.

VACUUM AND AIR SYSTEMS FOR POWER BOOSTERS Enough vacuum and air must be delivered to the power booster for it to work correctly. Most power boosters have the same method of delivering air, with vacuum provided by either the intake manifold or an auxiliary vacuum pump.

Air Systems Figure 6-3 shows the air system for a typical power booster. Air enters through passages in the pedal pushrod boot. The air passes through a fine mesh material called a silencer, which slows down the air and reduces any hissing sounds. The boot and air inlet are inside the car, so any noises could be heard by the driver. The air then passes through a filter to remove any dirt that could damage the valve. Air then flows into the power piston passages to the air valve.

Intake Manifold Systems The vacuum for most power brake systems is supplied by the engine intake manifold. On older cars, a simple vacuum hose was attached from the intake manifold directly to the housing of the brake booster. A check valve was used to protect the booster against loss of vacuum. The problem with this system was that intake manifold vacuum decreases and increases as the engine is accelerated and decelerated. A check valve helps prevent these fluctuations in vacuum. Many late-model cars that use intake manifold vacuum as the power source for the power brakes have a vacuum reservoir (Figure 6-4). The reservoir stores vacuum so it is always available, regardless of the changing vacuum in the intake manifold. A check valve is installed between the manifold and the reservoir to prevent air from entering the reservoir during wide-open throttle. The check valve also is a safety device, protecting the system from losing vacuum in case of a leaking supply line or other failure in the vacuum supply. The check valve is typically mounted on the front of the booster where the vacuum hose is connected. The check valve can also prevent the complete loss of vacuum in case the engine stalls, providing at least one vacuum-assisted stop.

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A check valve allows fluid or air to flow in one direction but not in the opposite direction.

Diesel engines do not create a vacuum in their intake manifold. Most diesel engines use hydraulically assisted power brake boosters. The pressure for the assist is developed in the power steering pump on some diesel engines.

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Air valve

Floating control valve

Filter AIR

Silencer Air passage

Vacuum Atmospheric pressure

Figure 6-3  The air system for a vacuum brake power booster.

Vacuum booster

Check valves Reservoir

Hose

Hose

Figure 6-4  Many power brake systems have vacuum reservoirs to ensure a steady vacuum supply to the booster.

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Vacuum Check Valves Whether a power brake system has just a vacuum booster or a vacuum booster and a vacuum reservoir, it must include one or more vacuum check valves. The check valve uses a spring-loaded ball or disc to close the vacuum line if pressure in the line gets higher (closer to atmospheric pressure) than the vacuum in the booster or reservoir. Figure 6-5 is a sectional view of a typical vacuum check valve. The valve has a small disc backed up by a spring. Manifold vacuum pulls and holds the disc off its seat. Vacuum is allowed into the booster. When vacuum drops below the calibration of the spring, the spring moves the disc against its seat. When the disc is seated, the valve closes and does not allow vacuum to leak out of the system. The check valve will keep vacuum in both sides of the booster when the engine is off. The vacuum check valve has a secondary function of keeping fuel vapors out of the vacuum booster. Without a check valve, vacuum in the booster could draw part of the air-fuel mixture into the booster when the engine is at wide-open throttle with little or no manifold vacuum. As an extra safety precaution, some systems have a charcoal filter between the manifold and the vacuum check valve to trap fuel vapors before they can get near the booster. Most systems have a single check valve as part of the inlet fitting of the vacuum booster (see Figures 6-3 and 6-6). Some vehicles, however, have an in-line check valve in the vacuum line. If the power brake system has a vacuum reservoir, as well as the booster, it will have two check valves. One valve is part of the booster inlet fitting; the other is between the intake manifold and the reservoir (see Figures 6-4 and 6-7). Spring

To diaphragm housing

To intake manifold

Seat

Disc valve

Figure 6-5  This cutaway view shows the parts of a typical vacuum check valve. To engine vacuum

Vacuum inlet check valve

Vacuum booster

Vacuum booster Vacuum reservoir Vacuum inlet check valve

Vacuum inlet check valve

Master cylinder

To engine vacuum

Figure 6-6  A typical vacuum brake booster.

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Figure 6-7  Booster vacuum connection to engine.

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AUTHOR’s NOTE  A worn or mistuned engine can cause damage to the check valve by pushing carbon and combustion gases into the check valve. The customer may not even notice that the boost is not working right after engine start up. If the other vacuum hoses show carbon or heat damage, inspect the vacuum check valve.

Shop Manual page 249

VACUUM POWER BOOSTERS Vacuum-operated power boosters have different shapes, but they all work the same way. The booster is mounted between the master cylinder and the engine compartment bulkhead or fire wall. The booster is between the brake pedal pushrod and the master cylinder (Figure 6-8). A vacuum hose is connected from the engine intake manifold to the booster (Figure 6-9). The following sections describe the operation and construction of common vacuum boosters

A BIT OF HISTORY Today, power brakes are universally standard equipment on all domestic and imported cars and light trucks. But this was not always so. Modern power brakes appeared as extra-cost options on luxury cars in the early 1950s. The new, longer, lower, wider, heavier postwar cars brought drivers more power to go, and this required more power to stop. Power brakes, along with power steering and automatic transmissions, made driving these luxury liners a pleasure. Without these options, driving would have been a real chore. Power brakes originally were a marketing feature and a driving convenience. At their introduction, one could also assert that power brakes were a safety feature that provided braking power for drivers who might not have the strength (or weight) to really stomp on the pedal for a hard stop. When disc brakes arrived on the scene a decade later, power boosters became a virtual safety necessity. The dual servo drum brakes of the 1950s and early 1960s used the selfenergizing action of primary and secondary shoes to increase braking force when the driver pressed the pedal. Disc brakes, which began to appear in quantity by the mid-1960s, do not develop the self-energizing action of drum brakes. Although disc brakes develop greater braking energy at the wheels, they require greater application force from the driver. Disc brakes made some kind of power assist a necessity for almost all drivers.

Vacuum Booster Construction

The booster diaphragm is a large hemispherical shaped piece of rubber and is acted upon by atmospheric pressure and vacuum.

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Most vacuum boosters have essentially the same parts. Figure 6-10 is a disassembled view of a typical vacuum booster. The parts are contained in a steel housing or shell that is divided into front and rear halves, held together with interlocking tabs. The rear housing has mounting studs to mount the unit on the fire wall. The diaphragm is a large, hemispherically shaped part made from rubber. The flexible diaphragm moves back and forth as it is acted on by atmospheric pressure and ­vacuum. The center of the diaphragm is supported by a metal or plastic diaphragm support. The brake pedal is connected to the brake pedal pushrod, which is contained in the booster. One end of the pushrod sticks out of the center of the rear housing when the

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Vacuum booster

Master cylinder

Vacuum hose Intake manifold

Figure 6-8  A vacuum booster mounted on the vehicle. Note the area close around the booster. Figure 6-9  A vacuum hose from the intake manifold supplies vacuum to the booster.

Figure 6-10  Disassembled vacuum booster. This is not a job for inexperienced technicians and is shown only to illustrate internal components.

booster is assembled. A rubber boot seals the area between the pushrod and the housing. The other end of the pushrod is attached to the power piston.

AUTHOR’s NOTE  One thing that should be clarified here is the front and back of a brake booster. The rear or back of the booster is that part nearest the driver and that abuts the bulkhead. The front or forward part of the booster is where the master cylinder is installed.

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The power piston is attached to the center of the diaphragm. The piston is often described as being suspended in the diaphragm. The power piston contains and operates the vacuum and air (atmospheric) valves that control the diaphragm. The power piston also transmits the force from the diaphragm through a piston rod to the master cylinder. Because the pedal pushrod is mechanically connected through the booster, any vacuum failure will not cause loss of braking action. The piston rod also may be attached to another rod called a reaction retainer. A large coil spring is mounted between the front housing and the power piston and diaphragm assembly. The spring returns the diaphragm and piston to the unapplied position when the driver releases the brake pedal. Two valves are located on the pedal side of the diaphragm. One, called the air valve, controls the flow of air at atmospheric pressure into one side of the booster. The other, called the vacuum valve, controls the buildup of vacuum in both sides of the booster. Both valves are connected to, and operated by, the pushrod. Diaphragms can be and are used in thousands of applications. The booster diaphragm separates the pressure chamber from the vacuum chamber.

Diaphragm Suspension The operation and construction of a vacuum booster and the booster diaphragm often are described as vacuum suspended. The brake boosters on almost all vehicles built since the mid-1970s have vacuum-suspended diaphragms. This means that when the brakes are released and the engine is running, vacuum is present on both sides of the diaphragm. When the pedal is pressed, atmospheric pressure is admitted to the rear of the diaphragm to develop booster force. Vacuum reservoirs also are used with some vacuum-suspended boosters to ensure adequate vacuum with a lot of vacuum-operated devices such as emission controls and air conditioning. A reservoir is not as essential with a vacuum-suspended booster, however.

Types of Vacuum Boosters Three general types of vacuum power boosters are (Figure 6-11): 1. Single diaphragm with a reaction disc 2. Single diaphragm with a reaction lever 3. Tandem booster (dual diaphragm) with a reaction disc The single diaphragm with a reaction disc provides force (or reacts back) to the brake pedal through a rubber reaction disc. The single diaphragm with a reaction lever reacts back to the pedal through a lever arrangement. The tandem diaphragm has two diaphragms that work together to provide force. The following sections explain how a single diaphragm booster with a reaction disc works. The other two booster types operate similarly. Vacuum booster operation can be divided into the following five stages:

1. Brakes not applied (released) 2. Moderate brake application 3. Brakes holding 4. Full brake application 5. Brakes being released

Brakes Not Applied.  When the brakes are off, the return spring for the input pushrod holds the pushrod and the air control valve rearward in the power piston (Figure 6-12). The rear of the air control valve seats to close the atmospheric port. The plunger also compresses the air valve against its spring to open the vacuum port. This valve action closes the booster to the atmosphere and opens a passage between the front and rear of the booster chamber. Equal vacuum is present on both sides of the diaphragm. The power piston return spring holds the diaphragm rearward so no force is applied to the output pushrod and master cylinder.

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Reaction disc Reaction piston

Single diaphragm with disc reaction

Reaction lever

Single diaphragm with lever reaction

Reaction disc Reaction piston

Tandem diaphragm with disc reaction

Figure 6-11  Three types of vacuum boosters.

Moderate Brake Application.  When the driver applies the brakes, pedal pressure overcomes the input pushrod return spring to move the pushrod and air control valve forward (Figure 6-13). Spring pressure then moves the air valve to close the vacuum port to the rear chamber. As the air control valve continues to move forward, it opens the atmospheric port to the rear chamber. Vacuum (low pressure) still exists in the front chamber of the booster, and higher pressure (atmospheric) exists in the rear. The resulting pressure differential moves the diaphragm and power piston forward against the return spring to apply force to the master cylinder pushrod. Brakes Holding.  As long as the driver maintains unchanging foot pressure on the pedal, the input pushrod does not move. The diaphragm and power piston continue to move forward until the air control valve on the piston seats against the rear of the vacuum valve

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Air valve plunger Diaphragm

Vacuum control port (open)

Valve rod return spring

No Force to Master Cylinder Pushrod

Power piston

Figure 6-12  When brakes are released, vacuum is present on both sides of the diaphragm, and the air valve is closed to exclude atmospheric pressure.

Air valve

Floating control valve

Filter AIR

Silencer Air passage

Vacuum Atmospheric pressure

Figure 6-13  Air fills the rear chamber when brake application opens the air valve and closes the vacuum valve. The front chamber is kept in vacuum.

plunger to close the atmospheric port (Figure 6-14). This all happens very quickly, and as long as the atmospheric port is closed, the diaphragm does not move. It is suspended by a fixed pressure differential between the front and rear chambers of the booster. The booster always seeks the holding position when pedal force is constant or unchanging.

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Air valve plunger

Engine vacuum

Diaphragm

Vacuum control port (closed)

Reaction disc Pushrod Reaction force from brake fluid pressure

Reaction force to brake pedal

Atmospheric pressure Atmospheric control port (closed)

Figure 6-14  When the brakes are held at midpoint, both valves are closed to trap vacuum and atmospheric pressure and keep the diaphragm in a balanced position.

Full Brake Application.  If the driver increases pressure on the pedal, she or he may push hard enough to force the air control valve plunger fully forward against the power piston. This action closes the vacuum port to the rear chamber and fully opens the atmospheric port. Maximum atmospheric pressure then exists in the rear chamber, and the booster supplies its maximum power assist. This condition sometimes is called the booster vacuum runout point. At this point, additional braking force can be applied to the master cylinder, but it must come entirely from foot pressure on the pedal. Because the booster is supplying its maximum force at this point, the driver will feel that the pedal becomes harder to press with additional foot pressure. Brakes Being Released.  When the driver releases the pedal, the input pushrod spring moves the pushrod and the air control valve rearward in the power piston. The rear of the air control valve closes the atmospheric port and opens the vacuum port. Vacuum then is applied to the rear chamber, and pressure equalizes on both sides of the diaphragm. The large return spring moves the diaphragm, the power piston, and the output pushrod rearward. The booster returns to the released position, as was shown in Figure 6-12.

Brake Pedal Feel A power brake booster must provide some kind of physical feedback to the driver. This feedback is called brake pedal feel. Without pedal feel, the booster would apply the power assist in sudden steps and cause very poor braking control. Also without pedal feel or feedback, when the booster reached the holding position, the driver would feel only the

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Pedal feel is provided by the reaction disc and levers.

The earliest power brake felt as if the driver was pushing his or her foot into a sponge without any brake feel.

foot pressure applied to the pedal, not the actual force applied to the master cylinder. In fact, many early power brake systems had very poor pedal feel. Pedal feel is provided in vacuum boosters by a reaction disc (or reaction plate and levers). Reaction simply means that as the driver’s foot, the pedal, and the booster apply force to the master cylinder, an equal force develops in the opposite direction. The driver normally feels this equal and opposite reaction force as the resistance to application force. Simply put, when the brake pedal is applied as hard as possible, it stops moving. This means that the reaction force has equaled the maximum force that is capable of being applied to the pedal. AUTHOR’s NOTE  A simplistic means of understanding pedal feel is to press on a small coil spring with either your hand or your foot. The more you press, the more reaction force is generated to force your foot or hand back.

Using reaction force to provide pedal feel requires some interesting engineering. If the hundreds of pounds of force developed by the booster were applied as reaction, or feedback, to the driver’s foot, the brakes could never be applied past the booster vacuum runout point. Theoretically, the booster could even force the pedal back to the unapplied position. To get around these problems, power boosters use the reaction disc or the reaction plate and levers to feed back only 20 percent to 40 percent of the booster force. The feedback force applied as pedal feel is always less than booster output force, but it also is always proportional. Whether the booster is applying 100 pounds or 400 pounds of force on the master cylinder, the feedback will be a constant percentage of whatever the output force is.

Reaction-Disc Booster In a booster with a reaction disc, the input pushrod and vacuum valve plunger bear on a rubber disc (Figure 6-15). This reaction disc is located in the power piston and compresses under the force of the pedal. Its ability to compress lets it absorb reaction force back from the master cylinder when the brakes are applied. As the disc compresses and feeds back Front housing

Rear housing

Vacuum check valve

Reaction disc Control valve

Master cylinder

Piston

Pedal pushrod

Diaphragm return spring Diaphragm plate Diaphragm

Figure 6-15  Reaction-disc vacuum booster.

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reaction force to the pedal pushrod, it also modulates the action of the vacuum and air control valves to adjust pressure on the diaphragm. The harder the brake pedal is pressed, the more the disc compresses and the greater the feedback feel applied to the pedal.

Plate-and-Lever Booster A plate-and-lever booster (Figure 6-16) uses a lever mechanism to react force back to the brake pedal. The connection between the pedal pushrod is through the reaction plate and levers in the power piston. When the brakes are first applied, the fixed ends of each lever are in contact with the power piston. The other ends are spring loaded and free to move. The force back to the driver’s foot on the brake pedal is kept low. As brake application continues, the springs deflect enough to allow contact between the movable ends of the levers and the vacuum and air valves. The operation of the air valve and vacuum valve begins to bleed out vacuum and adds atmospheric pressure to the brake pedal side of the diaphragm. The reaction force back to the brake pedal increases. The lever and reaction plate provide a resistance and feel to the pedal similar to a nonpower brake system.

Tandem Boosters Automotive engineers are constantly working to save car weight and space. Lighter cars have been made possible by making components out of lighter materials and making components smaller. Master cylinders are one example. They are now much smaller than they were in the past and are made from lighter materials. Brake power boosters have not escaped this trend. The amount of braking power from a vacuum booster is directly related to the area of the diaphragm. A booster with a smaller diaphragm would provide less power assist. Engineers Reaction retainer

Reaction plate

Reaction lever Air valve

Floating control valve

Filter

Power piston return spring

Valve seat Air passage Air valve spring

Figure 6-16  Reaction plate-and-lever vacuum booster.

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Tandem refers to two or more devices placed one behind the other in line.

solved this problem by designing a smaller diaphragm housing and using two smaller diaphragms in tandem. The amount of force is proportional to the total area of both diaphragms. Two 10-square-inch diaphragms can provide the same power as one 20-square-inch diaphragm. Figure 6-17 is a disassembled view of a tandem booster; Figure 6-18 is a sectional view. The front and rear housings are the same as those of a single-diaphragm booster. The booster contains two separate diaphragms, however, both with support plates. Some units have a housing divider between the diaphragms and others do not. Both diaphragms

Primary diaphragm

Primary support plate

Secondary piston bearing

Diaphragm retainer Silencer

Rear housing Power piston bearing Silencer Boot

Secondary support plate

Grommet

Vacuum check valve

Secondary diaphragm Housing divider

Front housing seal

Piston rod

Return spring

Front housing

Reaction retainer

Power piston Filter

Figure 6-17  Disassembled view of a tandem or dual diaphragm booster.

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137

Rear housing

Reaction disc

Control valve

Filter

Front diaphragm plate

Air passage

Front diaphragm Rear diaphragm

Silencer

Rear diaphragm plate

Figure 6-18  Sectional view of a tandem booster.

are connected to the power piston. A reaction disc or lever assembly is used, just as in a single-diaphragm booster. The two diaphragms work the same way as a single diaphragm except that the air and vacuum valves must control vacuum and atmospheric pressure on both diaphragms at the same time. When the brakes are released, vacuum is on both sides of each diaphragm. During brake application, the air valve and vacuum valve operate to admit air on the brake pedal side of both diaphragms. With a vacuum on the master cylinder side of both diaphragms and atmospheric pressure on the opposite sides, power assist is developed.

HYDRAULICALLY ASSISTED POWER BRAKES Diesel engines do not produce intake manifold vacuum. Hybrid vehicles gas engine may not always be running. A way to provide for brake booster operation is to eliminate vacuum as a power source and use hydraulic power instead. The three kinds of hydraulic boosters are:

Shop Manual page 249

1. A mechanical hydraulic power-assist system operated with pressure from the power steering pump. This unit is a Bendix design called hydro-boost. 2. An electrohydraulic power-assist system with an independent hydraulic power source driven by an electric motor. These systems are used on vehicles with integral ABS systems. 3. An electrohydraulic system in which the brake fluid flow and pressure are controlled by solenoids.

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Bendix developed the hydro-boost system to be used with the light-duty diesel engines. Hydro-boost refers to the hydraulic power brake system that uses the power steering hydraulic system to provide boost for the brake system. A spool valve is a cylindrical sliding valve that uses lands and valleys around its circumference to control the flow of hydraulic fluid through the valve body.

Hydro-Boost Principles The hydro-boost power booster (Figure 6-19) fits in the same place as a vacuum booster, between the brake pedal and the master cylinder. Similar to a vacuum booster, the hydroboost unit multiplies the force of the driver’s foot on the brake pedal. The hydraulic systems for steering and service brakes are completely separate from each other in a hydro-boost system. The brake hydraulic system uses DOT 3 or DOT 4 brake fluid as specified by the carmaker. The power steering system uses the manufacturer’s specified power steering fluid. The fluids cannot be mixed or substituted one for the other. Figure 6-20 is a simplified block diagram of the main parts of a hydro-boost system. The power steering pump develops pressure that is routed to the hydraulic booster assembly. The hydraulic booster helps the driver apply force to the master cylinder pushrod. The booster has a large spool valve that controls fluid flow through the unit. When the brakes are applied, the spool valve directs pressure to a power chamber. The boost piston in the power chamber reacts to this pressure and moves forward to provide force to the master cylinder primary piston. The master cylinder operates the same as a conventional master cylinder. The boost piston in the hydro-boost does the same job as the vacuum diaphragm and power piston in a vacuum unit. An accumulator is a pressurized storage reservoir. Loss of the power steering drive belt on a hydro-boost system means total loss of brake boost. The accumulator provides sufficient boost for one to three controlled stops. The accumulator can be used as a fluid shock absorber or as an alternate pressure source. A spring or compressed gas behind a sealed diaphragm provides the accumulator pressure.

Hydro-Boost Operation Hydro-boost operation can be divided into the following five stages: 1. Brakes not applied (released) 2. Moderate brake application Power steering pump

Master cylinder

Belt

Hydro-boost unit

Pressure hose

Power steering gear

Figure 6-19  A hydro-boost unit is attached between the master cylinder and the firewall.

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Power steering gear

Pressure Return

Pressure Return

Hydro-boost Power steering pump

Figure 6-20  The hydro-boost system shared hydraulic power (pressure) with the power steering system.

3. Brakes holding 4. Brakes being released 5. Reserve brake application Brakes Not Applied.  Figure 6-21 shows the booster in the unapplied position (brake pedal released). Fluid under pressure from the power steering pump enters the booster through the pump port in the housing. The fluid is directed through internal passages to the spool valve. The spool valve is held rearward by its spring so that the lands and v­ alleys direct the fluid from the pump directly through the valve to the steering gear. The spool valve also opens a passage to vent the power cavity back to the reservoir. The power cavity has no pressure, so no force is applied to the output pushrod. Moderate Brake Application.  Moderate brake application causes the input pushrod to press on the reaction rod in the end of the power piston. The reaction rod moves forward and causes the lever to pivot on the power piston and to move the spool valve forward in its bore (Figure 6-22). Spool valve movement opens the pump inlet port to the power chamber and closes the vent port. Hydraulic pressure now increases in the power chamber and moves the power piston forward to operate the master cylinder. As the spool valve moves forward, it also restricts fluid flow out to the steering gear. Closing the vent port and restricting flow to the steering gear causes pressure to rise in the brake booster. The farther the valve moves, the more the flow to the steering gear is restricted and the more the booster pressure increases. At maximum boost, hydraulic pressure in the brake booster can exceed 1,400 psi.

Lands are raised surfaces on a valve spool. Valleys are annular grooves, or recessed areas, between the lands of a valve spool.

Brakes Holding.  As long as the driver maintains unchanging foot pressure on the pedal, the input pushrod does not move. As pressure rises to this holding point, the power piston moves forward and makes the lever pivot on the lever pin, which moves the spool valve back toward the rear of its bore. This closes the fluid inlet port and reopens the bypass

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Chapter 6 (Low pressure) Return to reservoir

(Pump pressure) Pump Steering pressure gear

Spool valve

Non-pressurized fluid

Spool valve Power piston Fluid Body Seals

Figure 6-21  When the brakes are released power steering fluid flows past the spool and continues to the steering gear.

port to the steering gear. The vent port stays closed, however, so pressure in the power chamber reaches a steady state. The booster always seeks the holding position when pedal force is constant or is unchanging. This all happens very quickly. As booster pressure increases, fluid flows through a small port to a space behind the reaction rod. This creates a counterforce that moves the rod and lever rearward, which also moves the spool valve rearward and moderates application force. The reaction rod provides the same kind of proportional feedback brake feel that the reaction disc or levers in a vacuum booster provide.

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Power Brake Systems

(No flow) Return to reservoir

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(Restricted flow) Steering Pump gear pressure

Spool valve

Power cavity Pressurized fluid Lever

Output pushrod

Input rod Power piston

Pedal rod

Reaction rod

Spool valve Power piston Fluid Body Seals

Figure 6-22  During brake apply, fluid at pump pressure is directed around the spool valve into the power cavity and charges the accumulator. Pressure is applied to the power valve. Fluid flow to the steering is restricted.

Brakes Being Released.  When the brake pedal is released, the spool valve moves fully rearward to the unapplied position and vents pressure from the pressure chamber. Return springs on the power piston and lever quickly return the piston to the released position. Spool valve movement also blocks the fluid inlet port to the power chamber and lets fluid bypass the booster and flow to the steering gear. The hydro-boost returns to the released position as was shown in Figure 6-21.

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Reserve Brake Application.  A failure in the power steering system, such as a broken power steering hose, a broken power steering drive belt, pump failure, or a stalled engine could cause a loss of pressure to the hydro-boost system. The hydro-boost has a backup system, powered by an accumulator, that allows two or three power brake applications. When the pressure from the accumulator is needed, the gas or spring pressure inside the accumulator moves the pressurized hydraulic fluid to the brake booster. Figure 6-23 shows the hydro-boost accumulator. During normal operation, the pump pressure fills the accumulator cavity in front of the piston. The piston compresses the accumulator spring. A check ball and plunger in the passage to the accumulator allow pressure in but prevent it from escaping. This keeps the spring compressed or charged. A loss of pressure from the pump opens a passage for the pressure stored in the accumulator to be routed to the power chamber to help the driver apply the brakes. The accumulator stores enough energy for two or three brake applications. Loss of hydraulic power from the hydro-boost only means that the driver loses power assist. It does not mean there is a loss of braking. A mechanical connection exists from the brake pedal through the pedal rod, through the input rod, through the power piston to the output pushrod. The driver’s pedal effort will increase, but the brakes will still work. (No return)

(No pressure to steering gear) (No pump pressure)

Dual function valve

Plunger and check ball

Spool valve

Accumulator pressure cavity

Accumulator spring

Accumulator piston

Spool valve Power piston Fluid Body Seals

Figure 6-23  In case of pump failure, fluid under accumulator pressure is directed through the check valve to the power cavity. Fluid is preventing from entering the steering, pump, and return ports.

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Power Brake Systems

Integral ABS Electric Brake Booster Integral ABS systems combine the master cylinder, electric pump motor, and hydraulic modulator into one unit. An electric pump motor pressurizes brake fluid and uses this pressurized brake fluid to supply hydraulic boost pressure for the master cylinder (Figure 6-24). These units have an accumulator to store hydraulic pressure. The accumulator allows for a few booster-assisted stops if the pump should fail. The unit has a pressure switch that activates the pump when the pressure falls too low. These units should never be serviced without first relieving the stored accumulator pressure.

Vacuum Booster with Brake Assist The vacuum booster has recently been fitted with electronic sensors and actuators that will apply the brakes more quickly during panic stops (Figure 6-25). A brake assist (BA) unit is added to the vacuum booster. This unit detects the brake pedal application speed; in other words, how fast the driver is pushing on the pedal. During a panic stop, the driver naturally tries to move the pedal as fast as possible so the brakes will react quickly. When this condition is detected, the BA will more quickly activate the brake booster or signal the electronic brake system (EBS) controller. The brake fluid pressure is increased much more rapidly, and the brakes, in turn, react almost instantaneously. Although the time difference between non-BA units and assisted units is measured in fractions of a second, it may make the difference between vehicle control and a possible accident.

Electrohydraulic Brake As discussed before, an electrohydraulic brake (EHB) systems control hydraulic braking action through the use of electrical solenoids. EHB and BA units share information with ABS, TCS, and electronic suspension. The most common sensors are the yaw, wheel speed, and steering wheel angle. The most common electronic actuator is the hydraulic modulator, which is shared with ABS and TCS. The EHB have basically replaced the ABS and TCS and incorporated them into a single unit which also includes Vehicle Stability Control (VSC). In Figure 6-26, the EHB is compared to the BA unit discussed earlier. If the BA unit is removed (left side of figure), a conventional brake system with the ABS/ TCS would be displayed. In this case, the BA unit is part of the EHB. The bottom of

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Caution Whenever an integral ABS system is serviced, relieve the pressure according to service procedures. This usually involves pumping the brake pedal with the key off until the pedal feels solid. This may take as many as 25 applications of the brake pedal. This is necessary, because the brake pressure stored in the accumulator can be as high as 1,500 psi. Electronic Brake Systems is a term for systems that combine electronic control with the conventional hydraulic braking.

Master cylinder

Release switch

EBS Brake assist unit

Figure 6-24  A hydraulic power booster assembly.

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Solenoid

Figure 6-25  The brake assist unit measures pedal ­application speed and either actuates the vacuum booster or sends a signal to the EHB control module.

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Master cylinder and reservoir EHB unit and ECU

Steering wheel angle sensor

Brake booster

Brake pedal and linkage Sensor cluster (yaw rate and lateral movement)

Front brake caliper

Rear brake caliper

Wheel speed sensor

Wheel speed sensor CONVENTIONAL BRAKE SYSTEM

Master cylinder and reservoir EHB unit and ECU

Steering wheel angle sensor Brake pedal and linkage

Sensor cluster (yaw rate and lateral movement)

Front brake caliper

Rear brake caliper

Wheel speed sensor

Wheel speed sensor EHB BRAKE SYSTEM

Figure 6-26  Note that the primary visual difference between the two layouts is the absence of the brake booster on this system. The EHB control module is more complex than the hydraulic model.

The stroke sensor tells the electrohydraulic controller how fast and how far the brake pedal has been applied to judge the driver’s needs.

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Figure 6-26 shows a complete setup for an EHB. Note that the brake components at the wheels are the same as the conventional brakes. The main components of an EHB are the electronic control unit and the electronic pedal module. A stroke sensor/module/master cylinder is shown in Figure 6-27. The main advantage of an EHB is shorter stopping distances and better vehicle control. When the brake pedal is depressed on an EHB system, pedal movement and speed are detected by a stroke sensor, and the signal is sent to the EHB control module mounted on or near the hydraulic module. The pedal stroke sensor/master cylinder module also has components that will create a reaction or feedback to the driver’s input. The EHB control module collects data from the yaw and wheel speed sensor and commands the individual hydraulic valves within the hydraulic modulator to apply fluid to or release fluid from the brakes individually, as needed for the situation. In this manner, the EHB can control pressure to each wheel individually, preventing wheel lockup while maintaining maximum stopping power. In the opposite direction, if a wheel loses traction

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Figure 6-27  An EHB electronic pedal module with a master cylinder.

on acceleration, the EHB with the proper programming can act as a TCS. The EHB becomes an active brake system once it is married completely into other braking, steering, and ride control systems. During normal operation of the EHB, the master cylinder supplies pressurized fluid to the modulator. Its function as the primary brake pressure-generator stops at that point, but it still provides the backup or redundancy in the event of electrical component failure. If the EHB should fail in part or completely, the driver will still have the ability to brake the vehicle using the brake’s conventional operational hydraulics. As with the loss of the booster, the driver will have to apply more force, but the vehicle will be controllable and can be stopped.

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Vacuum is simply air pressure below atmospheric pressure. Vacuum power brakes are by far the most common kinds of power brakes. They operate on power provided by the pressure differential between atmospheric pressure and vacuum. The basic vacuum power booster consists of a diaphragm in a housing along with vacuum and air valves. The air valve is the vacuum booster valve that controls atmospheric pressure on the vacuum diaphragm. The vacuum valve is the valve in the power booster that controls vacuum on the vacuum diaphragm. The power piston is a part of the power booster that controls the air and vacuum valves and transmits force to the master cylinder. The diaphragm return spring returns the diaphragm and power piston to the unapplied position when brakes are released. The three types of vacuum power boosters are the single diaphragm with lever reaction, the single

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diaphragm with disc reaction, and the tandem diaphragm with disc reaction. The air system for a vacuum booster consists of a silencer and air filter. A check valve and a reservoir prevent vacuum loss. Light-duty diesel trucks use hydraulically assisted power brake systems. These braking systems use hydraulic power developed in the power steering pump for power assist. One popular system is called hydro-boost. The BA unit measures brake pedal application speed and activates the booster quicker or signals the electronic brake module. The hydro-boost system uses a spool valve to control the flow of pressurized fluid to a power chamber. An accumulator stores energy for several brake applications if the hydraulic system fails. An EHB combines signals from sensors shared with ABS, TCS, steering, and suspension systems to control braking forces at individual wheels.

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REVIEW QUESTIONS Short-Answer Essays 1. Explain the three general kinds of power boosters used to increase braking force. 2. Brake pedal feel is provided in vacuum boosters by a reaction disc or a reaction plate and levers. Explain how this works. 3. What is the purpose of the power piston in a ­vacuum power unit? 4. Explain how the braking system can still apply the brakes if the booster fails completely. 5. Why are hydraulic power assist units used on vehicles with diesel engines? 6. Briefly explain how the hydro-boost power brake booster operates. 7. List the four methods that can be used to reduce pedal pressure requirements or to boost the force applied to the master cylinder 8. Explain the general operation of the BA system used on a vacuum booster. 9. Explain the purpose of the stroke sensor on an EHB system. 10. Explain the purpose of an accumulator in a hydraulic brake power assist system.

Fill in the Blanks 1. During normal operation of the EHB, the master cylinder supplies pressurized fluid to the _______________. 2. To understand vacuum booster systems, the relationship of atmospheric _______________ and _______________ must also be understood. 3. Atmospheric pressure varies with _____________ and _______________, but at sea level and at 688F, it is 14.7 psi. 4. Without pedal feel, the booster would apply the power assist in _______________ steps and cause very poor braking control. 5. _______________ _______________ is provided in vacuum boosters by a reaction disc (or reaction plate and levers ). 6. The amount of braking power from a vacuum booster is directly related to the _______________ of the diaphragm.

8. The hydro-boost system booster has a large _______________ valve that controls fluid flow through the unit. 9. Vacuum is air pressure less than _______________ pressure. 10. An _______________ is a pressurized storage reservoir.

Multiple Choice 1. Technician A says the pedal ratio multiplies force applied to the master cylinder. Technician B says hydraulic piston size can be used to multiply hydraulic pressure applied by the master cylinder to the wheel cylinders and caliper pistons. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 2. Technician A says the amount of braking power from a vacuum booster is directly related to the area of the diaphragm. Technician B says a booster with a small diaphragm would provide more power assist. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 3. Technician A says that when the brakes are released, vacuum is on both sides of the booster diaphragm. Technician B says that when the brakes are released, atmospheric pressure may be on one side of the booster diaphragm. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 4. Technician A says the power piston contains and operates the vacuum and air (atmospheric) valves that control the diaphragm. Technician B says the power piston also transmits the force from the diaphragm through a piston rod to the master cylinder. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

7. Because the pedal pushrod is mechanically connected through the _______________, any vacuum failure will not cause loss of braking action.

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5. Technician A says that the EHB system is a direct power booster. Technician B says the EHB and the BA units share information with the ABS, TCS, and electronic suspension. Who is correct? A. A only B. B only

C. Both A and B D. Neither A nor B

6. Tandem brake boosters are being discussed: Technician A says tandem diaphragm boosters use one large diaphragm. Technician B says that a tandem diaphragm can provide more brake boosting power in a smaller housing. Who is correct? A. A only B. B only

C. Both A and B D. Neither A nor B

7. Technician A says that a hydro-boost system uses brake fluid for the booster. Technician B says the hydro-boost system uses power steering fluid for the brakes. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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8. Power brake boosters are being discussed. Technician A says power brake boosters do not alter the basic brake system. Technician B says all boosters have a power reserve to provide at least one powerassisted stop if power is lost. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 9. The BA system is being discussed. Technician A says that the BA system can build pressure in the brake system rapidly in case of a panic stop. Technician B says that the BA system can make a difference between vehicle control and a possible accident. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 10. Technician A says if the EHB should fail completely, the vehicle will have to be towed to the nearest shop. Technician B says the driver can stop the vehicle but may have to press on the pedal harder than normal. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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Chapter 7

Disc Brakes

Upon completion and review of this chapter, you should be able to: ■■ ■■ ■■ ■■ ■■

Explain the advantages and disadvantages of disc brakes. Describe the basic parts of a disc brake assembly. Describe the different kinds of rotors and the types of hub-and-rotor assemblies. Describe how a caliper works to stop a vehicle. Name the kinds of friction material used on disc brake pads and explain the advantages and disadvantages of each.

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Identify the parts of a typical caliper. Describe the two principal kinds of caliper designs and the variations of each. Describe how a low-drag caliper works compared to other kinds of calipers. Describe the different kinds of parking brakes used with rear disc brakes. Explain how brake pad wear indicators operate.

Terms To Know Aramid fibers Automotive Friction Material Edge Code Binder Bonded lining Brake caliper Brake fade Brake pad Caliper support Ceramic Ceramic brake pad Composite rotor Curing agent Drum-in-hat

Filler Fixed caliper brake Fixed rotor Fixed seal Floating caliper Floating rotor Friction modifier Gas fade Lathe-cut seal Metallic lining Mold-bonded lining Organic lining Pad hardware Pad wear indicators

Phenolic plastic Riveted lining Rotor Semi-metallic lining Sliding caliper Solid rotor Square-cut piston seal Steering knuckle Swept area Synthetic lining Two-piece rotor Unidirectional rotor Ventilated rotor Water fade

INTRODUCTION Disc brakes are used on the front wheels of almost all cars and light trucks built since the early 1970s and on all four wheels of many vehicles. Although no law or regulation requires disc brakes on the front wheels of cars and light trucks, the brake performance requirements of FMVSS 105 make front disc brakes virtually mandatory. Disc brakes provide greater stopping power than do drum brakes, with less brake fade and fewer problems such as grabbing and pulling. Disc brake 148

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efficiency is even more important on front-wheel drive cars, which require 60 percent to 80 percent of the stopping power at the front wheels. This chapter explains the construction and operation of disc brake systems and begins with a summary of their advantages and disadvantages.

DISC BRAKE ADVANTAGES AND DISADVANTAGES Disc brakes have several very important strong points and a few relatively small disadvantages. The principal advantages of disc brakes are strong fade resistance, self-adjustment, and reduced pulling and grabbing. Disc brake disadvantages are generally minor, but they include the lack of self-energizing (servo) action, noise, and poorer parking brake operation with complicated linkage.

Shop Manual page 286

Fade Resistance Remember that brake operation is a process of changing kinetic energy (motion) into thermal energy (heat) through the application of friction (Figure 7-1). When any brake installation reaches its limit of heat dissipation, brake fade sets in. Brake fade is simply the loss of braking power because of excessive heat that reduces friction between brake linings and the rotors or drums. One major factor that makes disc brakes more fade resistant than drum brakes is that the friction surfaces are exposed to more airflow. Many brake rotors also have cooling passages or fins to dissipate heat even more (Figure 7-2). Another factor that contributes directly to heat dissipation and fade resistance is the swept area of a disc brake rotor. With drum brakes, almost the entire swept area is in direct contact with the friction materials during the entire braking operation. With disc brakes, most of the swept area is cooling while only a small area directly contacts the friction materials at any given time (Figure 7-3). The greater the swept area, the greater

Brake fade is the loss of braking power because of excessive heat that reduces the friction between the brake and the rotor.

The swept area is the total area of the brake drum or rotor that contacts the friction surface of the brake lining.

Caliper

Friction energy

Friction energy

Airflow Heat

Heat

Heat

Heat

Heat

Heat Dirt and water Rotor

Figure 7-1  The clamping action of friction material in the rotating disc or rotor creates heat.

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Figure 7-2  Cooling fins increase heat dissipation in many rotors, and centrifugal force helps to keep the rotor clean by throwing off dirt and water.

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Swept area two surfaces

100 square inc hes

Swept area one surface

60 square inc hes

Figure 7-3  For any given size wheel, a disc brake always has 35 percent to 50 percent more swept area to dissipate heat.

Water fade occurs when water is trapped between the brake pad and the rotor. Disc brakes are less prone to water fade than drum brakes because of their open design. Gas fade occurs when a layer of hot gas and dust particles become trapped between the brake pad and rotor. Disc brakes are less prone to gas fade because their open design promotes cooling.

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the heat dissipation ability. Although a brake drum can have a relatively large swept area, the entire area is on the inner drum surface. The swept area of a disc brake comprises both sides of the rotor. For any given wheel size, the swept area of a disc brake will always be larger than the swept area of a drum brake. For example, a 10-inch-diameter rotor will have almost 50 percent more swept area than a 10-inch drum. Freedom from mechanical fade is another disc brake advantage. Mechanical fade is a problem that can occur with drum brakes when the drum becomes very hot and expands outward, away from the brake shoes. The shoes then must travel farther to contact the drum surface with normal braking force. As a result, the pedal drops lower as the brakes are applied. The increased heat at the braking friction surfaces also reduces the coefficient of friction. The combined result is brake fade. Disc brakes do not suffer from mechanical fade because the rotor does not expand away from the pads. If anything, the rotor expands very slightly toward the pads if it becomes very hot. Disc brake design also reduces the effects of lining fade, water fade, and gas fade. Lining fade occurs when the linings are overheated and the coefficient of friction drops off severely. Some heat is needed to bring brake linings to their most efficient working temperature. The coefficient of friction rises, in fact, as brakes warm up. If temperature rises too high, however, the coefficient of friction decreases rapidly. Because disc brakes are exposed to more cooling airflow than drum brakes, lining fade is reduced due to this cooling air flow. Water fade occurs when water is trapped between the brake linings and the drum or rotor and reduces the coefficient of friction. Severe water exposure can eliminate friction almost entirely and prevent braking until the friction surfaces dry themselves. Gas fade is a condition that occurs under hard braking when hot gases and dust particles are trapped between the brake linings and the drum or rotor surfaces. These gases build up pressure that acts against brake force on the drum or rotor surface. More importantly, these hot gases actually lubricate the friction surfaces and reduce the coefficient of friction.

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Disc Brakes

The basic design differences between disc and drum brakes make disc brakes much more self-cleaning to greatly reduce or eliminate water and gas fade. The rotor friction surfaces are perpendicular to the axis of rotation, and centrifugal force works to remove water and gas from the braking surfaces. In addition, the leading edges of the brake pads help to wipe the rotor surfaces clean, and many pad linings have grooves to drain water and help prevent gas buildup.

Disc Brake Self-Adjustment Brake adjustment is the process of compensating for lining wear and maintaining correct clearance between brake linings and the drum or rotor surfaces. Disc and drum brakes both require adjustment, but unlike drum brakes, disc brakes do not need cables, levers, screws, struts, and other mechanical linkages to maintain proper pad-to-rotor clearance for the service brakes. On some vehicles, the emergency brake is incorporated into the rear calipers. These brakes have a mechanical function to turn the caliper piston out to apply the pads for the emergency brakes. Most late-model vehicles have the emergency brake shoes separate from the caliper, mounted into the rear brake rotor. When disc brakes are applied, the caliper pistons move out far enough to apply braking force from the pads to the rotors. When the brakes are released, the caliper pistons retract only far enough to release pressure (Figure 7-4). The pads always have only a few thousandths of an inch clearance from the rotor, regardless of lining wear. In later sections of this chapter, brake caliper operation and disc brake self-adjustment are explained in detail.

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Drivers must beware when driving around construction or road repair sites on clear days. Sufficient water may be on the road to cause water fade and cause a rear-end collision in the stop-and-go traffic at these sites.

Brake Servo Action Drum brakes have an operating feature by which they develop mechanical leverage as the lining contacts the drum. One end of the lining contacts the drum before the other does and becomes a pivot point as friction increases quickly. The brake shoe becomes a selfenergizing lever and adds its own mechanical leverage to hydraulic force to help apply the brakes. This self-energizing action, called duo-servo, is shown in Figure 7-5.

Dust boot

Piston seal

A Retracted Position Piston Seal deflection

Outboard brake pad

Rotor Inboard brake pad

B During Application

Figure 7-4  When the brakes are released, the caliper piston seal holds the piston in a retracted position. (A) When the brakes are applied, the seal warps (B) and then returns to the relaxed position retracting the piston and providing clearance between the pads and the rotor.

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Chapter 7 Drum rotation

Actuator force

Friction force

Resulting ro tati o

n

a un ro dh inge

Hinge (anchor)

Figure 7-5  Drum rotation adds leverage to the brake shoe as it contacts the drum. This is called self-energizing action.

AUTHOR’S NOTE  The self-energizing or servo action of drum brakes created enough braking force that many older vehicles with four-wheel drum brakes did not have power brakes. Disc brakes require more stopping pressure because they are not self-energizing and they have a smaller contact area.

A servo action is using one component to increase the input force so the second component of the assembly is applied with greater force.

As more and more vehicles became smaller and predominantly front wheel drive, the need for heavy braking action diminished. Most brakes became the leading-trailing type. Leading-trailing brakes servo action is limited to the leading shoe, since the anchor pin is located at the bottom of the brake assembly. The trailing shoe has little effect because the rotation of the brake drum is actually pushed back into the wheel cylinder (Figure 7-6). Because disc brakes do not develop mechanical servo action, they less prone to severe grabbing or pulling. Slight pull may occur in a front disc brake installation because of a sticking caliper piston or problems in hoses or valves. Because equal hydraulic pressures are applied to both surfaces of the rotor during braking, no distortion of the rotor occurs regardless of the severity or duration of application. This is another reason that grabbing and pulling are reduced with disc brakes. AUTHOR’S NOTE  Many times the customer will define a slight pulling to one side as a drift; for example, “the vehicle tends to drift toward one side as I apply the brakes slowly.” Such a slight pull or drift may be caused by a brake or alignment problem on either side of the vehicle.

Lack of servo action in disc brakes may eliminate some operational problems, but it also means that disc brakes require higher application force from the hydraulic system than drum brakes require. The greater size ratio between master cylinder pistons and

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Primary shoe

Link

Secondary shoe

Link

RH Front

RH Front A

B Anchor

RH Front C

Figure 7-6  Self-energizing action of the primary shoe applies force to the secondary shoe. This is called servo action.

caliper pistons, along with universal use of power boosters with disc brakes, provides the necessary braking force without requiring undue pedal effort from the driver.

Disc Brake Noise A common complaint about disc brakes is that they are noisy. The metallic brake pad used by many manufacturers is the loudest of all. Noise usually occurs when the brakes are applied and released and most commonly results from slight high-speed rattling of the pads. Modern disc brakes built for sale in North America use various devices and techniques to minimize noise. Anti-rattle springs and clips hold pads securely in calipers and help to dampen noise. Adhesive to hold pads to pistons and caliper mounting points further dampens squeaks and rattles. On some installations, metal or plastic shims between pads and calipers and pistons help to reduce vibration and noise. Simple squeaks and rattles may be annoying to the driver, but they are generally not a problem for brake operation. When the noise becomes a continuous grinding or loud scraping sound as the brakes are applied, it often indicates that the linings have worn to the metal surfaces of the pads. These sounds mean that it is time for brake service before vehicle safety is jeopardized further. Many disc brake pads have audible wear indicators, which are small steel pins or clips that rub on the rotor to create a constant squeal when the pads have worn to their minimum thickness. However, with the radio on and traffic noise the sound created by the

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Most disc brake silencers do not eliminate the squeaking noise. They cause the frequency to change so the human ear will not hear it.

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Chapter 7 Caliper assembly

Brake shoes or pads

Hydraulic pressure

Rotor

Disc or rotor

Figure 7-7  The brake caliper fits in a U-shape over the rotor.

Figure 7-8  Pads, lined with friction material, are forced against the rotating disc to stop the car.

wear indicators is masked out. As a result, the driver may not be aware of the problem until the rotor and possibly the caliper piston are ruined. In an effort to combat this problem, many vehicles have disc brake pads equipped with an electronic wear indicator (Figure 7-7). A ground wire within a warning light circuit is installed onto the inboard pad. When the pad wears down, the wire touches the rotor, grounding the circuit and lighting a warning light in the instrument panel (Figure 7-8).

Disc Brake Parking Brake Disadvantage Drum brakes provide a better static coefficient of friction than do disc brakes. The brake linings grab and hold the drums more tightly than disc pads can hold a rotor. The servo action of drum brakes contributes to this feature, as does the larger area of brake shoe linings compared to disc brake pads. Because most brake installations have discs at the front and drums at the rear, the parking brake weaknesses of disc brakes are not a problem. Four-wheel disc brake installations, however, must have some way to mechanically apply the rear brakes. With movable (floating or sliding) calipers, this is usually done with a cam-and-lever arrangement in the caliper that mechanically moves the piston to develop clamping force. Many latemodel rear disc brakes with sliding calipers also have small drum-type parking brakes built into the rotors.

DISC BRAKE CONSTRUCTION Shop Manual page 307

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The principal parts of a disc brake are a rotor, a hub, and a caliper assembly (Figure 7-7). The rotor provides the friction surface for stopping the wheel. The wheel is mounted to the rotor hub by wheel nuts and studs. The hub houses wheel bearings that allow the wheel to rotate. The rotor has a machined braking surface on each side. The hydraulic and friction parts are housed in a caliper that straddles the outside diameter of the rotor. When the brakes are applied, pistons inside the caliper are forced outward by hydraulic pressure. The pressure of the pistons is exerted through the pads or shoes in a clamping action on the rotor. A splash shield on most installations helps to keep water and dirt away from the rotor and caliper and directs airflow to the rotor for improved cooling. Figure 7-8 illustrates basic disc brake operation.

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Disc Brakes

Rotors, Hubs, and Bearings The disc brake rotor has two main parts: the hub and the braking surface (Figure 7-9). The hub is where the wheel is mounted and contains the wheel bearings. The braking surface is the machined surface on both sides of the rotor. It is machined carefully to provide two parallel friction surfaces for the brake pads. The entire rotor is usually made of cast iron, which provides an excellent friction surface. The rotor side where the wheel is mounted is the outboard side. The other side, toward the center of the car, is the inboard side. The size of the rotor braking surface is determined by the diameter of the rotor. Large cars, which require more braking energy, have rotors measuring 12 inches in diameter and larger. Smaller, lighter cars can use smaller rotors. Generally, manufacturers want to keep parts as small and light as possible while maintaining efficient braking ability. The rotor is protected from road splash on the inboard side by a sheet metal splash shield that is bolted to the steering knuckle (Figure 7-10). The outboard side is shielded by the vehicle wheel. The splash shield and wheel also are important in directing air over the rotor to aid cooling.

155

The rotor is the rotating part of a disc brake that is mounted on the wheel hub and contacted by the pads to develop friction to stop the car. It is also called a disc.

A BIT OF HISTORY The kind of disc brakes that we know today were originally called spot brakes because caliper action clamped a friction pad against a rotor. Braking action takes place at the “spot” of the brake pad. The earliest automotive disc brakes, however, actually used a pair of circular discs lined with friction material. These systems consisted of large finned housings mounted on the hubs or axles and in turn held the wheels and tires. Two lined pressure plates inside each housing were forced outward hydraulically during brake application. The plates—or discs—did not rotate but clamped against the inside of the rotating housing to provide braking force. A rampand-ball mechanism on each disc provided servo action to aid brake application. These early disc brake systems appeared on the subcompact Crosley and heavyweight Chrysler Imperial models of 1949. Although they provided improved braking action, they were complicated, costly, and prone to trouble. They also added too much unsprung weight to each wheel. The Crosley version lasted one model year. Chrysler discontinued its system in 1955. Ten years later, modern disc (spot) brakes were taking over the industry.

Braking surface

Hub nut Hub and wheel bearings Outboard side Inboard side

Figure 7-9  Major parts of a typical rotor and hub assembly.

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Steering knuckle

Splash shield

Hub Grease shield Inner seal Inner bearing

Outer bearing Washer

Figure 7-10  The splash shield is mounted on the steering knuckle inboard of the rotor. A fixed rotor has the hub and rotor cast as a single part. A floating rotor and its hub are two separate parts. They are also known as two-piece rotors.

Fixed and Floating Rotors Rotors can be classified by the hub design as fixed (with an integral hub) or floating (with a separate hub). A fixed rotor has the hub and the rotor cast as a single part (Figure 7-11) and is commonly known as a one-piece rotor. Floating rotors and their hubs are made as two separate parts (Figure 7-12) and may be known as a two-piece rotor. The hub is a conventional casting and is mounted on Hub Rotor

Rotor hub flange

Knuckle

Braking surface Cooling fins

Figure 7-11  The wheel hub and the rotor are cast as a single part in a fixed or integral rotor.

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Figure 7-12  A rotor that is cast as a separate part and fastened to the hub is called a floating rotor.

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wheel bearings or on the axle. The wheel studs are mounted in the hub and pass through the rotor center section. This kind of rotor is called a hubless or floating rotor. One advantage of this design is that the rotor is less expensive and can be replaced easily and economically when the braking surface is worn beyond machining limits.

Composite Rotors Traditionally, brake rotors, as were drums, were manufactured as a single iron casting. The development of floating, two-piece rotors and the need to reduce vehicle weight led to the development of composite rotors. Composite rotors are made of different materials, usually cast iron and steel, to reduce weight. The friction surfaces and the hubs are cast iron, but supporting parts of the rotor are made of lighter steel stampings. The steel and iron sections are bonded to each other under heat and high pressure to form a onepiece finished assembly (Figure 7-13). Composite rotors may be fixed components with integral hubs, or they may be floating rotors mounted on a separate hub. Because the friction surfaces of composite rotors are cast iron, the wear standards and refinishing methods are generally the same as they are for other rotors.

AUTHOR’S NOTE  The latest material being utilized for high-end vehicles is for carbon ceramic rotors. A few manufacturers have utilized Formula One braking for their supercars such as the Mercedes-Benz SLR, Aston Martin DBS, and the Chevrolet Corvette ZR1. These brakes provide the advantages of reducing weight and increasing life of the rotor, but costs are still prohibitive.

Solid and Ventilated Rotors A rotor may be solid or it may be ventilated (Figure 7-14). A solid rotor is simply a solid piece of metal with a friction surface on each side. A solid rotor is light, simple, cheap, and easy to manufacture. Because solid rotors do not have the cooling capacity of ventilated rotors, they usually are used on small cars of moderate performance or on rear disc brake installations.

Cast iron friction surfaces

Shop Manual page 322 Composite rotors do require a special adaptor when machining on a bench lathe.

A solid rotor is usually a floating rotor.

In general, solid rotors cannot be machined to the extent that ventilated rotors can be, if at all.

Steel web

Figure 7-13  A composite rotor combines a steel web with a cast iron friction surface, which saves weight.

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Ventilated rotor

Braking surfaces

Solid rotor

Figure 7-14  A solid rotor, left, and a large ventilated rotor, right.

A ventilated rotor has cooling fins cast between the rotor surfaces.

A unidirectional rotor can also be called a directional rotor, because the rotor is designed to turn in a certain direction.

A ventilated rotor has cooling fins cast between the braking surfaces to increase the cooling area of the rotor. When the wheel is in motion, the rotation of these fins in the rotor also increases air circulation and brake cooling. Although ventilated rotors are larger and heavier than solid rotors, these disadvantages are more than offset by their better cooling ability and heat dissipation. Some heavy ventilated rotors may have weights between the fins, or in an area near the fins, ground away to balance the rotor. Some ventilated rotors have cooling fins that are curved or formed at an angle to the hub center. These fins increase centrifugal force on rotor airflow and increase the air volume that removes heat. Such rotors are called unidirectional rotors because the fins work properly only when the rotor rotates in one direction. Therefore, unidirectional rotors cannot be interchanged from right to left on the car and the fins of the installed rotor must point forward when viewed from the top. A few high-performance sports cars have solid rotors with holes drilled through the friction surfaces. These drilled rotors are not made to increase cooling so much as they are to release water and hot gases from the rotor surface that can cause water or gas fading. Drilled rotors are typically very light and can have very short service lives. Therefore, they are used mostly on race cars and dual-purpose, high-performance cars. Rotors that are “hash-cut” are actually less prone to stress cracking than rotors that have been drilled.

AUTHOR’S NOTE  Drilled or slotted rotors have become increasingly common on passenger cars. While the gas and water release properties are still engineering correct, slotted and drilled rotors are more often selected more for the cost-­ effective “cool” look they add to a dressed-out car.

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Rotor Hubs and Wheel Bearings Tapered roller bearings, installed in the wheel hubs, are the most common bearings used on the front wheels of rear-wheel drive (RWD) vehicles and the rear wheels of front-wheel drive (FWD) cars. The tapered roller bearing has two main parts: the inner bearing cone and the outer bearing cup. A tapered roller bearing has the rollers set at an angle to the centerline of the bearing assembly. The rollers are held in place by the bearing cage mounted to the inner race. The race is the precision machined area where the rollers run. The bearing cup acts as the outer race and can usually be removed from the bearing assembly. The bearing fits into the outer cup or race, which is pressed into the hub. This provides two surfaces, an inner cone and outer cup, for the rollers to ride on. See Chapter 3 for details on tapered roller bearings and their service. Almost every FWD vehicle has a sealed double-row ball bearing pressed into the front hubs (Figure 7-15). Some vehicles also use a sealed wheel bearing and hub that is serviced as an assembly. The bearing usually requires no periodic service and is replaced when necessary. The FWD axle stub slides through the inner bearing race. A typical sealed bearing may last several hundred thousand miles, and some will last the life of the vehicle. The rear wheels on front-wheel drive vehicles also have pressed-in, single-roll roller bearings, or bearings serviced with the hub as an assembly like the front wheels.

Shop Manual page 327

Brake Pads Each brake caliper contains two or four brake pads. Pads are the disc system braking friction surfaces. They perform the same function as the shoes in a drum brake system. The brake pads are positioned in the caliper on the inboard and outboard sides of the rotor. The caliper piston, or pistons, forces the brake pad linings against the rotor surfaces to stop the car. Fundamentally, a brake pad is a steel plate with a friction material lining bonded or riveted to its surface (Figure 7-16). The simple appearance of a brake pad, however, hides some sophisticated engineering that goes into its design and manufacturing. Chapter 2 of this Classroom Manual introduced the subject of friction materials and summarized the common requirements of both drum brake linings and disc brake pads. Friction materials

Brake pads are the disc brake system friction surfaces.

Friction material

Rivet

Inboard pad

Figure 7-15  Most FWD vehicles have a pressed-in, double-roll sealed ball bearing.

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Outboard pad

Metal backing

Figure 7-16  Parts of a disc brake pad.

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are classified as organic (nonmetallic), semi-metallic, fully metallic, and—in some advanced systems—synthetic.

Brake Friction Materials (Drum and Disc) The friction material used for disc brake pads is generally harder than that used on drum brake linings because the friction surface is smaller and higher pressures are used to push the pads into contact with the rotor. The friction material used for drum brake lining is generally softer than that used on disc brake pads because the friction surface is larger. Asbestos has excellent friction qualities and long service life. Therefore, it was the most common brake lining material for years. The health hazards of asbestos have led to its drastic reduction or removal from most brake friction materials. Today’s basic types of disc pad lining materials are organic, semi-metallic, metallic, synthetic, and ceramic. Organic linings are made from non-metallic fibers bonded together to form a composite material.

Friction materials help provide the frictional stopping power, such as graphite, powdered metal, and nut shells.

Organic Linings.  Organic linings usually wear faster than do semi-metallic linings, but they have the benefit of breaking in faster. Organic linings are made from nonmetallic fibers bonded together to form a composite material. For decades, asbestos was the main ingredient in organic linings. Asbestos is actually an inorganic mineral but not truly a metal. Regardless of its chemistry, the organic name stuck to friction material based on asbestos. Health regulations have caused asbestos content in organic linings to drop from as high as 75 percent to below 25 percent. The goal is to eliminate asbestos from all brake linings, and it has been achieved for friction materials made in North America. The problem is imported brake linings can contain asbestos material. Another factor is that some of the compounds used to replace asbestos may be as dangerous to health as asbestos itself. Today’s organic brake linings contain the following kinds of materials: ■■

■■ ■■

Curing agent refers to a class of materials used in brake linings to accelerate the chemical reaction of the binders and other materials.

Semi-metallic friction material can seriously damage or destroy some types of rotor. Semi-metallic linings contain about 50% iron and steel, are more fade resistant than organic materials but require a higher braking effort.

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■■

Friction materials and friction modifiers are the materials that help provide the frictional stopping power. Some examples are graphite, powdered metals, and even nut shells. Fillers are secondary materials added for noise reduction, heat transfer, and other purposes. Binders are glues that hold the other materials together. Curing agents accelerate the chemical reaction of the binders and other materials.

Organic linings have a high coefficient of friction for normal braking; they are economical; they are quiet; they wear slowly; and they are only mildly abrasive to rotors. Organic linings fade more quickly than other materials, however, and they do not operate well at high temperatures. High-temperature organic linings are available for high-­ performance cars, but they do not work as well at low temperatures and they wear faster than common organic linings. Semi-metallic linings.  Semi-metallic materials are made from a mixture of organic or synthetic fibers and certain metals molded together; they do not contain asbestos. ­S emi-metallic linings are harder and more fade resistant than organic materials but require higher brake pedal effort. Most semi-metallic linings contain about 50 percent iron and steel fibers. Copper also has been used in some semi-metallic linings and, in smaller amounts, in organic linings. Concerns about copper contamination of the nation’s water systems has led to its reduced use in brake linings, however. AUTHOR’S NOTE  A few vehicles, and not necessarily high-end ones, will work quietly only with the manufacturer’s brand of brake pads. Aftermarket pads, particularly semi-metallic pads, make a lot of noise even when first installed. This is usually caused by the composition of the rotor’s friction area, the friction area finish, and the makeup of the pads themselves. At times the only possible solution to the noise problem is to buy pads from the local dealership. Luckily this problem applies to only a few models of a few brands.

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Semi-metallic linings operate best above 2008F to2508F(908C to1208C) and actually must be warmed up to bring them to full operating efficiency. Consequently, semi-metallic linings often have poorer operating characteristics than organic linings at low temperatures. Semi-metallic linings often are blamed for increased rotor wear, but this is not entirely true. Early semi-metallic linings were more abrasive than current materials, which may cause no more wear with the properly matched rotors than organic materials. Also, the better heat transfer characteristics of semi-metallic linings can reduce rotor temperatures and help to counteract abrasiveness. Many small, FWD cars built since the early 1980s have smaller front brakes that require the better high-temperature friction characteristics and heat transfer abilities of semi-metallic linings. Currently, semi-metallic linings are used only on front disc brakes of passenger cars and light trucks. The lighter braking loads on rear brakes, particularly on FWD cars, may never heat semi-metallic linings to their required operating efficiency. Semi-metallic linings also have a lower static coefficient of friction than organic linings, which makes them inferior for parking brake use. Metallic Linings.  Fully metallic materials were used for many years in racing, particularly in the heyday of drum brakes. Metallic lining is made from powdered metal that is formed into blocks by heat and pressure. These materials provide excellent resistance to brake fade but require high brake pedal pressure and create the most wear on rotors and drums. Metallic linings work very poorly until they are fully warmed. On the other hand, metallic linings tend to heat quickly and develop heat fading more quickly. Improved hightemperature organic linings and semi-metallic materials have made metallic linings almost obsolete for late-model automotive use. Metallic linings are extremely noisy, which must be considered when talking about choices to a customer. Synthetic Linings.  The goals of improved braking performance and elimination of the disadvantages of current lining materials has led to a new generation of synthetic lining friction materials. They are called synthetic because that term generally describes nonorganic, nonmetallic, and nonasbestos materials. Two principal kinds of synthetic materials show promise as brake linings: fiberglass and aramid fibers. Fiberglass was introduced as a brake lining material to help eliminate asbestos. As does asbestos, it has good heat resistance, good coefficient of friction, and excellent structural strength. The disadvantages of fiberglass are its higher cost and its reduced friction at very high temperatures. Overall, fiberglass linings perform similarly to organic linings, but the higher costs have confined their use primarily to rear drum brake linings. Aramid fibers are a family of synthetic materials that are five times stronger than steel, pound for pound, but weigh little more than half what an equal volume of fiberglass weighs. Friction materials made with aramid fibers are manufactured similarly to organic and fiberglass linings. Aramid fibers have a coefficient of friction similar to semi-metallic linings when cold and close to that of organic linings when hot. Overall, the performance of aramid linings is somewhere between organic and semi-metallic materials but with much better wear resistance and longevity than organic materials. Ceramic Brake Pads.  Many automotive manufacturers are now supplying brake pads of ceramic materials as the pad of choice. Akebono is supplying many vehicle manufacturers with their OEM ceramic brake pads. In addition, some aftermarket vendors such as Raybestos Brakes’ “Quiet Stop” and NAPA’s “Ceramix” are two brands of ceramic pads used to replace semi-metallic types. Combining ceramic material and copper fibers is the typical formula for ceramic pad manufacture. Many of the drawbacks of semi-metallic pads have been reduced or eliminated entirely. The steel in semi-metallic pads tends to make noise, wear rotors, and create lots of brake dust, which affects the appearance of the wheel and rims. Ceramic and copper composite pads make much less noise, are not as damaging to the rotors, and create

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Metallic linings are made from powered metal, and are very hard on brake rotors.

Synthetic lining may be used on disc or drum brakes. Aramid fibers are a family of synthetic materials that are five times stronger than steel but are very light weight.

Ceramic brake pads are made from ceramic and copper and make less noise and do not damage rotors as badly as semi-metallic pads do. Ceramic brake pads are a combination of ceramic material and copper or some other metal fibers.

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Regardless of wear pattern, all of the pads on an axle should be replaced at the same time to prevent uneven braking and wear.

virtually no dust. These benefits are much more satisfactory to the owner/driver. Ceramic pads are usually slotted vertically, horizontally, or diagonally to change the noise frequency to a range beyond human hearing. The slots also provide an escape route for gases and dust, thereby reducing brake fades at higher temperatures. Some ceramic pads have chamfered leading and trailing edges, which also help to reduce noise. Porsche offers ceramic pads and rotors on some of its top-of-the-line vehicles. Ceramic brake pads do have a few disadvantages over semi-metallic. The main disadvantage is primarily the result of improper pad/rotor configuration. Some operators may wish to add “high-performance” ceramic pads in lieu of the specified semi-metallic pads. Many times, this configuration would warp or wear the rotor(s) very quickly, even during normal driving and braking. The high-performance ceramic pad does not dissipate heat as quickly as semi-metallic pads and the heat is trapped in the rotor, caliper, and brake fluid. As mentioned earlier, there are aftermarket ceramic pads for many cars, but they are made to directly replace those specified by the vehicle manufacturer. The technician or service writer needs to caution the customer on the use of ceramic brake pads. Many times the customer only wishes to keep the wheels and rims looking neat. Another item the technician and customer must consider is the cost of ceramic pads. Typically, a set of ceramic brake pads cost three to four times the cost of standard semimetallic or organic pads. The labor cost should be the same. In most cases, ceramic brake pads are overkill braking for the typical driver and vehicle. However, the appearance of the vehicle may be of more concern to the customer than the price of the parts.

Friction Material Selection

T he codes on some inexpensive brake pads often cannot be read because of the printing and paint used.

The friction material of a new brake pad can be identified from a code printed on the edge of the pad or shoe (Figure 7-17). This code is called the Automotive Friction Material Edge Code. Letters and numbers in the code identify the manufacturer, the material, and, of most importance, the cold and hot coefficients of friction. In the example shown in Figure 7-17, the first letters “NRSS” identify the manufacturer. The numbers “12041” identify the lining material, and the last two letters “FF” identify the cold and hot coefficients of friction, respectively. From a service standpoint, the friction codes are probably the most important. The technician may be able to compare them to a decoding chart in brake parts catalogs to determine the friction material and whether it is recommended for a specific vehicle. The following chart gives definitions of different DOT Automotive Friction Material Edge Codes (Table 7-1). Note that EE coded pads have roughly the same coefficient of friction of steel on steel or bare caliper piston against steel rotor. A pad with the edge HH would probably not work well on a conventional vehicle when noise, brake wear, and cost are considered. The two different temperatures given are considered as cold and hot. It is important to use the recommended friction material when replacing brake pads or drum brake shoes. The incorrect type of friction material can affect the stopping characteristics of the car. These codes, however, indicate only the coefficient of friction. They do not address lining quality or its hardness. Hard and soft are terms applied to linings within a general category of material. Thus, any particular organic lining may be considered as a hard or a soft organic material. Overall, organic linings have been considered softer than semi-metallic linings, and

Figure 7-17  Automotive Friction Material Edge Code.

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Table 7-1  AUTOMOTIVE FRICTION MATERIAL EDGE CODE

DOT Edge Code

Coefficient of Friction (C.F.) @ 2508F and @ 6008F

Fade Probability

EE

0.25 to 0.35 both temps

0% to 25% @ 600oF

FE

0.25 to 0.35 @ 250oF temp 0.35 to 0.45 @ 600oF temp

2% to 44% fade at 600oF

FF

0.35 to 0.45 @ both temps

0% to 22% fade at 600oF

GG

2.45 to 0.55

Very rare

HH

0.55 to 0.65

Carbon/carbon only. Glow at about 3000oF

semi-metallic linings are considered softer than fully metallic linings. Typically, a hard lining has a low coefficient of friction but resists fade better and lasts longer than a soft lining. A soft lining has a higher coefficient of friction but fades sooner and wears faster than a hard lining. Additionally, a soft lining is less abrasive on rotor and drum surfaces and operates more quietly than a hard lining. It also is important to know that carmakers sometimes specify different friction materials for the inboard and outboard disc pads. Original equipment installations may have an organic disc pad on one side of the caliper and a semi-metallic disc pad on the other. The reason for using these different coefficients of friction can be in the difference of cooling from the inboard to outboard pad, noise reduction, or simply the results of testing for a particular rotor and pad operation. It also is common to use linings with a lower coefficient of friction on the rear brakes than on the front brakes to minimize rear brake lockup. Always follow the manufacturer’s recommendation for brake lining friction to maintain the original design performance of the braking system.

A BIT OF HISTORY In the 1950s, it was not uncommon for the technician or DIYer to install the lining onto the old brake shoe web. You could buy the asbestos linings and the rivets at most parts stores. The old lining would be knocked off and the rivets removed with a hammer and chisel. The new lining was then riveted to the web generally using only a hammer and a punch. The ends of the lining would be chamfered a little (using a hand file) to prevent the lining from grabbing the drum. The result was a satisfactory brake shoe for then, but now the result would be much different because of the average driving speeds and the almost universal use of power brakes. Now the lining would probably be ripped from the web at the first near-panic stop.

Although the coefficient of friction and hardness of linings can vary quite a bit for the same kind of material, these general rules for the coefficient of friction will assist in comparing different materials: Organic—cold: 0.44; warm: 0.48 Semi-metallic—cold: 0.38; warm: 0.40 Metallic—cold: 0.25; warm: 0.35 Synthetic—cold: 0.38; warm: 0.45 When troubleshooting a brake performance problem, a noise problem, or a problem with premature rotor wear, it often is a good idea to install new brake pads that match the

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original equipment exactly. This establishes a baseline of what should be original brake performance for further diagnosis.

Friction Material Attachment Both disc brake and drum brake linings are attached by rivets or adhesive bonding or a combination of riveting and bonding to the metal backing (Figure 7-18). Riveted linings are attached to the metal backing plate with rivets.

Bonded brake linings are attached to the steel backing with adhesive.

Mold bonded linings are molded to the steel backing plate that has had adhesive applied,

Riveted Linings.  In a riveted brake pad or shoe assembly, the riveted lining is attached to the steel pad or shoe by copper or aluminum rivets. Riveting allows a small amount of flexing between the pad and lining to absorb vibration and reduce noise. Riveting also is very reliable, and rivets maintain a secure attachment at high temperature and high mileage. Rivets require that about one-third to one-quarter of the lining thickness remain below the rivet for secure attachment. This places the rivet head closer to the lining friction surface and reduces the service life or mileage of the pad. In some cases, the holes above the rivet heads can trap abrasive particles that can score the rotor. Historically, riveting was the most common method for lining attachment. Since bonding was perfected, however, rivets are used more with semi-metallic linings than with organic linings. Bonded Linings.  Bonding is a method of attaching the friction material to the pad or shoe with high-strength, high-temperature adhesive. Bonded linings can provide longer service life because more material is available for lining wear before the steel pad or shoe contacts the rotor or drum. This feature can be misleading and provides false comfort to many motorists, however. If a driver neglects lining wear until a disc pad hits the rotor, it often severely scores the rotor and destroys it. In contrast, minor scoring from rivet heads can often be resurfaced. Bonded linings do not have the flexibility between the pad and shoe lining that riveted linings have. Therefore, they can be noisier than riveted linings. A noise complaint often can be fixed by replacing bonded linings with riveted linings that have the recommended friction characteristics. Mold-Bonded Linings.  In a disc brake pad assembly with mold-bonded lining, an adhesive is applied to the pad, and the uncured lining material is poured onto the pad in a mold. The assembly is then cured at high temperature to fuse the lining and adhesive to the pad. Holes drilled in the pad are countersunk from the rear so that the lining material flows through the holes and rivets itself to the pad as it cures. Many high-performance pads are made this way to avoid the stress-cracking problems associated with rivets while providing very secure pad attachment. Some pad manufacturers mold bond the friction material to the pad by using small hooks machined into the pad backing plate.

Figure 7-18  The linings can be bonded (left) or riveted (right) to the disc brake pads.

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Anti-rattle spring

165

Backing plate

Tab Lining Wear indicator

Figure 7-19  Tabs on the metal backing plate locate the pad in the caliper.

Figure 7-20  Typical anti-rattle and retaining hardware for brake pads.

Pad-to-Caliper Attachment Most brake pads are held in the caliper by locating tabs formed on the end of the metal backing plate (Figure 7-19). The pads also may be retained by retaining pins that go through holes in the metal pad backing. Many pads have anti-rattle or support clips, which are spring steel clips that hold the pads in position to keep them from rattling when the pads are out of contact with the rotor. These small parts are called pad hardware and should be replaced when the pads are replaced. Figure 7-20 shows a selection of typical pad hardware.

Pad hardware refers to miscellaneous small parts, such as anti-rattle clips and support clips, which hold brake pads in place and keep them from rattling.

AUTHOR’S NOTE  Test driving a brake repair and a clicking noise is heard each time the brakes are applied and released. Check the installation of the pad hardware. Chapter 7 of the Shop Manual gives the details.

Brake Pad Wear Indicators Many current brake systems have pad wear indicators or sensors to warn the driver that the lining material has worn to its minimum thickness and that the pads require replacement. The most common types are audible contact sensors and electronic sensors. The audible sensor is the oldest type. The audible system uses small spring clips on the brake pads and lining that make a noise when the linings are worn enough to be replaced. The spring clips are attached to the edge of the brake shoe or into the shoe from the pad side. They are shaped or positioned to contact the rotor when the lining wears to where it should be replaced. When the linings wear far enough, the sensor contacts the rotor (Figure 7-21) and makes a high-pitched squeal to warn the driver that the system needs servicing. This squeal usually goes away when the brakes are applied. Unfortunately, many drivers are deaf to the sound of these wear indicators when the radio is on or there is a lot of traffic noise or they just ignore noise.

Wear sensors warn the driver that the brake pads will need attention soon.

AUTHOR’S NOTE  In defense of some drivers, we experienced an incident where the brake pads were completely gone, the pad metal backing was rubbing on the rotors, and on one side the backing was gone to the point where the caliper piston was almost out of the bore. I questioned the owner, a fellow faculty member, as to why the car was not brought in when it started to make a lot of noise during braking. The owner stated that there was never any noise, and that the car just got to the point where it did not want to stop. As soon as the owner left and before we put the car on the lift, I drove it around the parking lot several times and applied the brakes both in easy and in panic modes just to prove a point. But the owner was right. The car did not stop well, and there was absolutely no noise that would be associated with extremely worn pads. So sometimes when the owners say there was no noise, they may be correct.

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Chapter 7 Pad

Pad

Rotor

Rotor

Wear indicator

Wear indicator

Worn Pad

New Pad

Figure 7-21  As the linings wear, the wear indicator eventually hits the rotor and creates noise to warn the driver that new pads are needed.

Electronic sensors provide a warning lamp or message on the instrument panel to inform the driver of brake pad wear or circuit problems. The electronic sensor uses pellets embedded into the friction material for circuit completion. Early systems used a grounding logic to complete a parallel electrical circuit and turn on the warning lamp (Figure 7-22A). If a circuit wire became grounded, this too would turn on the warning lamp. An open circuit, however, could not be detected and may disable the detection circuit. Later systems were designed to use an open logic to do the same thing. Open logic allows the system to detect both opens and grounds in the circuit (Figure 7-22B).

B+

B+

Voltage detector

Voltage detector

Pellets

Pellets

A

B

Parallel Circuit

Series Circuit

Figure 7-22  Electronic wear sensors are used in both parallel (A) and series (B) circuits.

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A BIT OF HISTORY Automotive disc brakes were developed for racing, and the first practical disc brake system was used in 1953 on a C-type Jaguar that won the 24-hour endurance race at Le Mans. The effectiveness of the brakes in this event led automotive engineers to develop disc brakes for passenger cars by the 1960s and 1970s.

A wear indicator that is commonly overlooked is the narrow slot running across the pad (Figure 7-23). It may not have been the intention of the design engineers, but that little slot provides a quick visual indication of brake lining remaining. In most cases, it can be observed without removing the tire-and-wheel assembly. The more shallow the groove depth, the less lining remaining.

CALIPER CONSTRUCTION AND OPERATION The disc brake caliper converts hydraulic pressure from the master cylinder to mechanical force that pushes the brake pads against the rotor. The caliper is mounted over the rotor (Figure 7-24). Although there are many design differences among calipers (described in a later section of this chapter), all calipers contain these major parts: ■■ Caliper body or housing ■■ Internal hydraulic passages ■■ One or more pistons ■■ Piston seals ■■ Dust boots ■■ Bleeder screw

Figure 7-23 Note the depth of the slot on the old pad (left) compared to the one on the new pad (right).

The brake caliper converts hydraulic pressure to mechanical force that applies the brake pads.

Shop Manual page 288

Figure 7-24  The caliper is bolted to the caliper support, which is bolted to the steering knuckle.

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Chapter 7 Pads

Bleeder screw

Reaction

Caliper

Brake line connection

Action

Pad spring

Piston Caliper body

Hollow piston

Hydraulic pressure Piston seal

Rotor

Figure 7-25  Cross section of a floating caliper. Sliding calipers are similar.

Figure 7-26  Hydraulic pressure in a sliding or floating caliper forces the piston and one pad in one direction and the caliper body and the other pad in the opposite direction. This is an application of one of the Laws of Motion: For every action there is an equal and opposite reaction.

Figure 7-25 is a sectional view of a caliper. A brake line from the master cylinder is attached to the caliper body. When the brakes are applied, fluid under pressure from the master cylinder enters the caliper. The caliper has at least one large hydraulic piston located in a piston bore. During braking, fluid pressure behind the piston increases. Pressure is exerted equally against the bottom of the piston and the bottom of the cylinder bore. The pressure applied to the piston is transmitted to the inboard brake pad to force the lining against the inboard rotor surface. Depending on caliper design, fluid pressure may be routed to matching pistons on the outboard side of the caliper, or the pressure applied to the bottom of the cylinder can force the caliper to move inboard on its mount (Figure 7-26). In either case, the caliper applies mechanical force equally to the pads on both sides of the rotor to stop the car.

Caliper Body A steering knuckle is the outboard part of the front suspension that pivots on the ball joints and lets the wheels turn for steering control.

The caliper body is a U-shaped casting that wraps around both sides of the rotor (Figure 7-27). Almost all caliper bodies are made of cast iron. Single-piston caliper bodies are usually cast in one piece, but caliper bodies with pistons on the inboard and outboard sides of the rotor are usually cast in two pieces and bolted together. Front calipers are mounted on caliper supports or adapters that may be an integral part of the steering knuckles. The steering knuckle provides a spindle for the wheel to rotate on and provides connections to the vehicle’s suspension steering systems. Although

Caliper

Rotor

Pads

Caliper support

Figure 7-27  The brake caliper straddles the rotor.

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one-piece steering knuckle and caliper support forgings are the simplest and most economical way to manufacture these components, most front caliper supports are separate pieces that bolt to the steering knuckle. Rear calipers are mounted on caliper supports that bolt to the rear suspension or the axle housing. Most caliper bodies have one or two large openings in the top of the casting through which the lining thickness can be inspected. Although these openings are handy inspection points, that is not their primary purpose. Caliper bodies are cast with these openings to reduce weight and, of more importance, to minimize large masses of iron that can cause uneven thermal expansion of the assembly. A few caliper bodies are without these openings because they are not needed structurally.

Caliper Hydraulic Passages and Lines The fitting for the brake line is located on the inboard side of the caliper body, as is the bleeder screw. The bleeder screw is almost always at the top of the caliper housing. A movable caliper with one or two pistons on the inboard side has hydraulic passages cast into the inboard side of the body. A fixed caliper with pistons on both the inboard and the outboard sides requires crossover hydraulic lines to the outboard side. These usually are cast into the caliper halves and sealed with O-rings when the caliper body is bolted together (Figure 7-28). Some fixed calipers, however, have external steel passages to carry fluid to the outboard pistons.

Caliper Pistons Depending on its design, a caliper may have one, two, or four pistons, with single-piston calipers being the most common by far. The piston operates in a bore that is cast and machined into the caliper body (Figure 7-29). The piston is the part that actually converts hydraulic pressure to mechanical force on the brake pads. To do its job, the piston must be strong enough to operate with several thousand pounds of pressure, and it must resist corrosion and high temperatures.

Bleeder screw

Boot

Piston Caliper body Fluid passage Seal

Piston

Fluid inlet Pad O-ring seal

Figure 7-28  This cross section shows the fluid crossover passages in a fixed caliper.

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Dust boot

Figure 7-29  The piston operates in a machined bore in the caliper body.

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Phenolic plastic is plastic made primarily from phenol, a compound derived from benzene; phenol is also called carbolic acid.

Fixed-seals do not move. A lathe-cut seal or square-cut piston seal is a fixed seal for a caliper piston that has a square or irregular cross section; it is not round like an O-ring.

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The inner side of the piston contacts the brake fluid in the caliper bore, and the outer side bears against the steel brake pad. The brake pads operate at temperatures above the boiling point of brake fluid, and the piston must help to insulate the fluid from this extreme heat. The piston surface that contacts the pad is hollow or cup shaped, which reduces weight and reduces the area available to absorb heat from the pad. The ability to absorb heat and not transfer it to the fluid also is an important design consideration for the piston materials. Caliper pistons typically are made of steel, cast iron, phenolic plastic, and aluminum. Chrome-plated cast-iron and steel pistons are the most common. Iron pistons were used in many early disc brakes, but steel is more common in late-model designs. Steel pistons are strong and thermally stable, but they are heavier than desired in late-model brake assemblies, and they can conduct excessive heat to the brake fluid. To reduce both weight and heat transfer, manufacturers turned to phenolic plastic pistons in the mid-1970s. Today, phenolic plastic pistons are original equipment on about half the light-duty vehicles sold in North America. Phenolic plastic pistons are strong, light, excellent insulators, immune from corrosion, and economical to make. In addition, the plastic surface is not as slippery as chrome plating and grips the piston seals better than a steel piston does. Phenolic pistons do have some disadvantages; among them is a tendency to wear faster and score more easily than steel pistons. Early designs also tended to stick in their bores because of caliper bore varnish and corrosion. Improved dust boots and seals have reduced that problem, however. Phenolic plastic pistons also may be damaged if mishandled. Aluminum would seem to be a good material for caliper pistons because of its light weight. In fact, aluminum has been used for pistons in some high-performance brakes where weight is critical, but it has serious drawbacks that limit its use in passenger car and light truck brakes. Aluminum expands faster that iron or steel, and aluminum pistons must be made with more clearance in their caliper bores. This additional clearance, in turn, increases the possibility of leakage, as does aluminum’s greater tendency toward scoring and corrosion. The major problem with aluminum caliper pistons, however, is their ability to transfer heat. Aluminum is a very poor thermal insulator and increases the danger of boiling the brake fluid.

AUTHOR’S NOTE  Some racing calipers are equipped with as many as 12 pistons made of stainless steel or titanium. Some specialty calipers are nickel-coated forged steel. The large number of pistons can help even out and increase the force applied to the brake pad. Several smaller pistons can have more surface area than one large piston. As noted earlier, these brake systems can also use carbon ceramic brake rotors. The expense of some racing equipment can be prohibitive on a production car, but many of today’s technology, just like disc brakes themselves, came from the racing industry.

Caliper Piston Seals Brake calipers require seals to keep fluid from escaping between the pistons and their bores, but caliper piston seals also perform other functions. Disc brakes do not have return springs to move the pads out of contact with the rotor. This is accomplished by the caliper piston seal. Movable calipers use fixed seals, also called square-cut piston seals or lathe-cut seals.

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Fixed Seals.  A fixed seal, used with a movable caliper, is installed in a groove in the inner circumference of the caliper bore. The piston fits through the inside of the seal and is free to move in the seal. The outer circumference of the seal remains in a fixed position in the caliper bore. Many seals are square or rectangular in cross section, but others have different cross-sectional shapes. Because all seals are not identical, it is important to be sure that replacement seals match the shape of the originals. During braking, the piston seal is deflected or bent by the hydraulic pressure. When the pressure is released, the seals relax or retract, pulling the pistons back from the rotors. Figure 7-30 is a cross section of a piston and seal that shows the seal action from relaxed (before application) to an applied position and back to a relaxed position. The seal flexing releases pressure from the rotor but maintains only very slight clearance of 0.006 inch or less between the pad and the rotor. The seal fits closely around the piston and holds it in position. Because the seal is installed at the outer end of the caliper bore, it keeps dirt and moisture out of most of the bore and away from the piston. This minimizes corrosion and damage to the caliper bores and pistons. As the brake linings wear, the piston can move out toward the rotor to compensate for wear. The seal continues to retract the piston by the same amount, however. Thus the piston can travel outward, but its inward movement is restricted by the flexibility of the seal. This action provides the inherent self-adjusting ability of disc brakes, and pedal height and travel remain constant throughout the life of the brake linings. However, the increased cavity will require a larger volume of brake fluid. Steel pistons used with fixed seals have very close clearances in their bores. Manufacturers typically specify 0.002 inch to 0.005 inch of clearance. Phenolic plastic

Before Application

Seal deflection

During Application

After Application

Figure 7-30  These cross sections show how a seal deflects during brake application and then returns to the relaxed position to retract the piston.

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Chapter 7 Piston seal Piston

Boot

Caliper body

Figure 7-31  A rubber boot keeps dirt and moisture out of the caliper bore.

pistons require slightly more clearance to allow for more expansion. They are typically installed with 0.005 inch to 0.010 inch of clearance. The close fit of the pistons in their bores and the close running clearances between pads and rotors keep pistons from cocking in the calipers and minimize piston knock back because of rotor runout or warping. Close piston-to-bore clearances also keep the seals from flexing too much and rolling in their grooves. Low-Drag Caliper Seals.  Low-drag calipers increase the clearance between the brake pads and rotors when the brakes are released. This increased clearance reduces friction and improves fuel mileage. In a low-drag caliper, the groove for the fixed seal has a tapered outer edge. This lets the seal flex farther as the brakes are applied. This increased flexing outward as the brakes are applied is matched by equal inward flexing as the brakes are released. The result is more clearance between the pads and rotors. Low-drag calipers require a quick take-up master cylinder as described in Chapter 4 of this Classroom Manual. The quick take-up master cylinder provides more fluid volume with the initial pedal movement to take up the greater pad-to-rotor clearance. The combination of low-drag calipers and quick take-up master cylinder maintain normal brake pedal height and travel.

Caliper Dust Boots A rubber boot fits around every caliper piston to keep dirt and moisture out of the caliper bore (Figure 7-31). The opening in the center of the boot fits tightly around the outer end of the piston. The outer circumference of the boot may be attached to the caliper body by a retaining ring in the caliper or by tucking it into a groove inside the bore.

TYPES OF DISC BRAKES Although all disc brakes have the same kinds of common parts—calipers, rotors, pistons, pads, and so on—they are commonly classified into two groups in terms of caliper operation: fixed and movable. Fixed calipers are bolted rigidly to the caliper support on the steering knuckle or on the rear axle or suspension. Fixed calipers have pistons and cylinders (bores) on the inboard and outboard sides. Hydraulic pressure is applied equally to the inboard and outboard pistons to force the pads against the rotor. Moveable calipers slide or float on the caliper support. Sliding or floating calipers have a piston only on the inboard side, and hydraulic pressure is applied to the piston to force the inboard pad against the rotor. At the same time, hydraulic pressure on the bottom of the caliper bore forces the caliper to move inboard and clamp the outboard pad against the rotor with equal force. Remember: For every action, there is an opposite and equal reaction.

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Fixed Calipers Fixed caliper disc brakes are the oldest type of disc brake. Their use on production cars in high volume dates to the mid-1960s. Probably the best-known fixed caliper brake is the four-piston Delco Moraine brake used on Chevrolet Corvettes from 1965 through the early 1980s. Fixed caliper brakes from other suppliers such as Bendix, Budd, and KelseyHayes were used by other domestic carmakers through the mid-1970s, and some latemodel imported vehicles continue to have fixed caliper brakes.

A fixed caliper brake has a brake caliper that has piston(s) on both the inboard and the outboard sides, is bolted to its support, and does not move when the brakes are applied.

AUTHOR’S NOTE  Ford and other light- and medium-duty truck manufacturers (F-350 and above) were using fixed, four-piston calipers up through the mid-1990s. This was primarily because of the length of the pads used on these trucks. Compared to lighter trucks and passenger cars, the pads were about twice as long and could not be evenly applied along their full length by one piston and a sliding caliper without making the single piston very large.

A fixed caliper is bolted to its support and does not move when the brakes are applied. A fixed caliper must have pistons on both the inboard and the outboard sides. The most common are four-piston brakes, with two pistons on each side of the caliper (Figure 7-32). Two-piston fixed caliper brakes were common on some lighter imported vehicles, and a few three-piston designs also were manufactured (with one large inboard and two small outboard pistons). The pads for a fixed caliper brake are held in the caliper body by locating pins. They are mounted more loosely than the pads of a movable caliper brake because the outboard pad cannot be attached solidly to the caliper body. Anti-rattle clips and springs reduce vibration and noise, however. Fixed calipers must have equal piston areas on each side so that equal hydraulic pressure will apply equal force to the pads (Figure 7-33). When the brakes are released, the pistons are retracted by their seals as explained earlier in this chapter. Inboard pistons

Caliper

Pad and plate retaining pin

Boot

Seal Caliper

Outboard pistons

Hydraulic pressure

Hydraulic pressure

Rotor Piston

Rotor

Figure 7-32  A fixed caliper is mounted rigidly over the rotor and has one or two pistons on the inboard and outboard sides to apply the brake pad.

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Figure 7-33  Equal hydraulic pressure on both sides of a fixed caliper applies equal force to the inboard and outboard pistons.

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Chapter 7

Dimension C

Dimension C

Dimension D

Figure 7-34  A fixed caliper must be parallel to the rotor surface (Dimension D) and spaced equally on each side of the rotor (Dimension C).

Because the body of a fixed caliper brake is mounted rigidly to the vehicle, it must be aligned precisely over the brake rotor. Piston travel must be perpendicular to the rotor surface, and the pads must be exactly parallel to the rotor (Figure 7-34). If the caliper is misaligned or cocked on its support, the pads will wear unevenly and the pistons may stick in their bores. Just as important, the caliper must be centered over the rotor so that the inboard and outboard pistons move equal distances to apply the pads. If the caliper is offset to one side or the other, unequal piston travel can create a spongy brake pedal feel and uneven pad wear. Moreover, it may be more difficult to bleed all air from the caliper during service. Shims often are used to align fixed calipers on their supports. Fixed calipers are large and heavy, which provides good heat dissipation and strength to resist high hydraulic pressures. Because a fixed caliper is mounted rigidly to the vehicle, it does not tend to flex under high temperature and pressure from repeated use. Fixed calipers can provide consistent braking feel under repeated, hard use. The use of fixed calipers has declined over the past 40 years, and they are not found on many late-model, lightweight cars. The greater weight of a fixed caliper is its biggest disadvantage, and that caliper weight increases the percentage of unsprung weight on the steering knuckle. Fixed calipers also are more expensive to make than floating or sliding calipers, as well as harder to service. Because fixed calipers are built with a two-piece body, they require more time to service and leaks have more opportunities to develop around O-rings and crossover line fittings. In summary, cost, weight, and complexity have made fixed caliper disc brakes less common on late-model vehicles.

Floating Calipers A floating caliper has a one-piece caliper body and one large piston on the inboard side.

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By far, most late-model cars and light trucks have disc brakes with movable calipers. Movable caliper brakes are further subdivided into floating calipers and sliding calipers, which identify the ways in which the calipers are mounted on their supports. Floating calipers began to appear on domestic and some imported vehicles in the late 1960s. A floating caliper brake has a one-piece caliper body and usually one large piston on the inboard side. Some medium-duty trucks, particularly Fords, and some GM front-wheel drive cars have floating caliper brakes with two pistons on the inboard side (Figure 7-35). The caliper is mounted to its support on two locating bolts or guide pins that are threaded into the caliper support (Figure 7-36). The caliper slides on the pin in a sleeve or bushing. The bushing may be lined with Teflon or have a highly polished surface for

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Pistons

Seal Inboard pad

175

Boots

Caliper housing body Seal

Outboard pad

Figure 7-35  Some late-model floating calipers have two pistons.

Mounting pin

Caliper support (anchor plate)

Caliper housing

Rotor and hub

Mounting pin

Mounting sleeve

Figure 7-36  A floating caliper rides on two bolts or guide pins in the caliper support.

low friction. The pins let the caliper move in and out and provide some flexibility for lateral movement to help the caliper stay aligned with the rotor. The pads are attached to the piston on the inboard side and to the caliper housing on the outboard side. When the brakes are applied, the fluid pressure behind the piston pushes the piston outward in its bore. The pressure is transmitted directly to the inboard pad, which is forced against the inboard rotor surface. The pressure applied to the bottom of the cylinder bore forces the caliper to slide or move on the guide pins toward the inboard side. This movement causes the outboard section of the caliper to apply equal pressure against the back of the outboard pad, forcing it against the outboard rotor surface.

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In a floating caliper, the piston and the bottom of the caliper bore are both hydraulic pressure surfaces of equal size, and equal pressure is applied to both the piston and the caliper. Hydraulic pressure against the bottom of the caliper bore creates a reaction force that moves the caliper body inward as the piston moves outward. As a result, the rotor is clamped between the piston on one side and the caliper body on the other. When the driver releases the brakes, the pressure behind the piston drops. The seal relaxes, or springs back, and moves the piston back. As the piston moves back, the caliper relaxes and moves in the opposite direction on the guide pins to the unapplied position. The piston seals provide the self-adjusting action and required pad-to-rotor clearance described earlier in this chapter. Floating calipers (and sliding calipers, described in the next section) are lighter, easier to service, and cheaper to build than fixed calipers. Because of their simpler design, they also are less likely to develop leaks. The flexible mounting of a floating caliper provides some beneficial self-alignment of the caliper with the rotor. If the flexibility becomes excessive, however, the pads can wear at an angle or become tapered, which decreases pad life.

Sliding Calipers sliding calipers have a one piece caliper and a piston on the inboard side and move on slides instead of pins.

Sliding calipers operate on exactly the same principles as floating calipers, but their mounting method is different. The caliper support has two V-shaped surfaces that are called abutments or ways (Figure 7-37). The caliper housing has two matching machined surfaces. The caliper slides onto the caliper support, where the two parts are held together with a caliper support spring, a key, and a key retaining screw. An anti-rattle spring is used to prevent noise from vibration. When a sliding caliper is replaced, the caliper ways on the caliper support should be inspected closely and caliper movement should be checked to be sure that the replacement caliper slides correctly. It may be necessary to polish the caliper ways with a fine file or emery cloth for proper clearance.

Caliper support (anchor plate)

Caliper ways

Caliper housing

Retaining screw Caliper support spring

Anti-rattle spring

Caliper support

Figure 7-37  A sliding caliper moves on machined ways on the caliper support.

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The pins on a floating caliper should be lubricated according to the carmaker’s instructions, but lubrication is even more important on a sliding caliper. Both the caliper ways and the mating surfaces on the caliper should be cleaned and then lubricated with hightemperature brake grease, which ensures smooth operation, reduces wear, and prevents corrosion on the sliding surfaces.

REAR-WHEEL DISC BRAKES Rear-wheel disc brake calipers may be fixed, floating, or sliding, all of which work just as do the front brake assemblies described previously. The only difference between a front and rear disc brake caliper is the need for a parking brake in the rear. Many rear disc brakes have a small brake drum built into the center of the rotor (Figure 7-38). This is commonly known as a drum-in-hat design. Two brake shoes are expanded into the brake drum when the parking brake is applied (Figure 7-39). The adjustment of this system is covered in Chapter 9 of the Shop Manual. Some rear disc emergency brakes rely on a cable that moves the caliper piston to apply the brake (Figure 7-40). The piston is connected to a lever system that can be operated either mechanically by the parking brake lever or pedal or by hydraulic force from the master cylinder. Chapter 9 covers parking brakes in detail.

Shop Manual Pages 347

PERFORMANCE DISC BRAKES The overall operation of disc brake systems for racing or high-performance vehicles is exactly the same as that for a small subcompact passenger car. The components are made of different materials, however, and are usually a little larger. Many calipers manufactured for racing vehicles are made of aluminum or an aluminum alloy. Pads and possibly rotors could be made of ceramic. Ceramic’s main disadvantage is that it does not dissipate heat well. The heat is trapped in the caliper, rotor, pads, and eventually the brake fluid. Carbon fiber may be another material that could be used in racing and eventually on production Drum-type brake shoes

Caliper mounting pads

Parking brake drum

Rotor surface

Figure 7-38  This parking brake system has a drum internal to the disc. It is known as a drum-in-hat design.

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Figure 7-39  Shown is the shoe-type parking brake used with some rear disc brake systems. The actual size is not much larger than the size shown.

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Chapter 7 Piston seal Cone

Piston

Screw

Outboard brake pad

Rotor

Parking brake lever

Inboard brake pad Internal thread nut

Figure 7-40  Many rear disc brakes have a lever-and-screw mechanism to apply the service brakes for parking.

vehicles. Carbon fiber is light and fairly resistant to heat, but it is expensive. One system used on racing vehicles to dissipate heat that generally has not been installed on production vehicles is the air duct system that moves air from the front bumper or grille and directs that air over the braking mechanism. In general terms, this ductwork is not required on production vehicles. Some aspects of racing rotors are making it to the production line. The slotted and/or drilled rotors are being installed on many production vehicles. In this case, the industry is finally catching up to motorcycles, which have been using drilled rotors for years. Drilled rotors offer two advantages that take nothing away from braking performance. The first is weight. Drilling a hole removes metal, hence producing a weight reduction. The second advantage is heat dissipation. Passing air can flow through the holes and remove more heat from the rotor. This airflow does nothing to decrease the stability of the vehicle during braking action. The main advantage of slotted rotors is the removal of heat and dispersion of any gas that may form between the pad and rotor. The slots can also help clean the pad. The material used in rotor construction is of a different makeup than the material used for production rotors, so they are more resistant to warping during the hard braking required of a race vehicle. This material is usually cast iron or steel. Racing calipers may be made of cast aluminum because it allows for weight decrease. However, aluminum does not dissipate heat as well as steel or other heavier metals. In most races, this does not cause a lot of concern because the calipers are supposed to last only for a specific time or distance. Selecting a racing caliper requires the vehicle crew to estimate the amount of braking and how hard the braking will be during an entire race. The caliper manufacturers and the vehicle crews have gotten this estimate down to a nearperfect science, although there were instances when the rotor blew apart during a race, thereby damaging most of the adjacent components. At times the fluid heats up so much in the caliper and attaching hose that vapors increase rapidly and the brakes “go away.” Like most other components on a race vehicle, short tracks that require a lot of hard brak-

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ing require the vehicle to have a larger rotor, pads, and caliper. The long, high-­ speed-track vehicle has smaller braking components because in a perfect race they need to work only during a pit stop. The final consideration when selecting a racing caliper and pads is drag. As mentioned earlier, a low-drag caliper where the pads actually separate from the rotors reduces that slight amount of drag inherent in standard disc brakes. Because brake drag reduces the horsepower available to drive the vehicle and increases fuel consumption, low-drag calipers are the best choice for racers. As a reminder, if low-drag calipers are used, then some version of a quick take-up master cylinder must be used or the brakes may engage too late. Racing pads may be carbon fiber, ceramic, or semi-metallic. Selecting the pads involves several considerations: weight, rotor wear, and durability. As mentioned earlier, the pads are selected based on the use they will endure during a race. The pads are no good, however, if they tend to wear the rotor excessively. The pads and rotors have to match for good braking effect throughout the entire race. Like most racing equipment, the racing brake components may lead the way to better brakes for production. The manufacturer has two problems adapting racing equipment to production, however: durability and cost. Professional racers with some well-paying sponsors can afford to buy calipers, rotors, and pads that are thrown away after the race is completed. The average consumer is not willing to pay this additional cost without some really great improvements in durability, however.

SUMMARY ■■

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■■ ■■

■■

■■

The major parts of a disc brake are the rotor, the hub, the caliper, and the pads. The hub contains the wheel bearings and is where the wheel is mounted. Rotors come in two types: solid or ventilated. The four general kinds of friction pad materials are asbestos, organic, semi-metallic, and metallic. The coefficient of friction of the pad materials is indicated by letters and numbers stamped on the edge of the friction material. These letters and numbers are known as the Automotive Friction Material Edge Code. Anti-rattle clips and springs are used to keep the pads from making noise when the pads are not in contact with the rotor.

■■

■■

■■

■■

■■

Brake pad wear indicators alert the driver when the brake linings need servicing. Piston seals are used to seal the hydraulic brake fluid and retract the piston and pad from the rotor. The two types of calipers are fixed and movable. Movable calipers can be either the floating style or the sliding style. Low-drag calipers are movable calipers that move the pads away from the rotor, leaving no contact or drag. Rear-wheel disc brakes are similar to frontwheel disc brakes but must operate from hydraulic pressure and from the parking brake cables.

REVIEW QUESTIONS Short-Answer Essays 1. List the basic parts of a disc brake. 2. Explain the advantages and disadvantages of an aluminum caliper. 3. Why do manufacturers use two-piece rotors on some vehicles? 4. In addition to keeping road splash off the brake assembly, why are splash shields used on disc brakes?

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5. Why is asbestos no longer used for brake pad and shoe linings? 6. What are common classifications of brake pad and shoe friction materials? 7. What is the difference between fixed and sliding calipers? 8. How does a low-drag caliper operate? 9. Explain how a floating caliper applies the brake pads. 10. Explain the purpose of a drum-in-hat rotor.

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Chapter 7

Fill in the Blanks 1. Front calipers are mounted on _______________ _______________ or adapters that may be an integral part of the steering knuckles. 2. When any brake installation reaches its limit of heat dissipation, _______________ _______________ sets in. 3. _______________ rotors are made of different materials, usually cast iron and steel, to reduce weight. 4. _______________ linings usually wear faster than do semi-metallic linings, but they have the benefit of breaking in faster. 5. With disc brakes most of the _______________ area is cooling while only a small area directly contacts the friction materials at any given time. 6. Disc brakes do not suffer from _______________ fade because the rotor does not expand away from the pads. 7. Low-drag calipers require a quick take-up _______________ cylinder. 8. The _______________ _______________ _______________ converts hydraulic pressure from the master cylinder to mechanical force. 9. Many rear disc brakes have a small brake drum built into the center of the _______________. 10. Sliding or floating calipers have a piston only on the_______________ side.

Multiple Choice 1. The advantages and disadvantages of disc brake systems are being discussed. Technician A says that disc brakes are more likely to develop brake fade and water fade. Technician B says that reduction of mechanical fade and gas fade is an advantage of disc brakes. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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2. The operation of disc brake systems is being discussed. Technician A says that composite rotors were developed to save weight. Technician B says that a fixed rotor assembly is part of the hub. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 3. Disc brake calipers are being discussed. Technician A says that a single caliper may have one, two, or more pistons. Technician B says that the piston seal is known as a square-cut seal. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 4. Technician A says that solid rotors can usually be machined several times before their minimum thickness limits are reached. Technician B says that composite rotors have cast-iron hubs with steel friction surfaces. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. When discussing disc brake work, Technician A says that organic linings are a composite material made from bonding nonmetallic fibers. Technician B says that semi-metallic linings require higher brake pedal effort but are more fade resistant compared to organic linings. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 6. Two technicians are discussing a disc brake caliper: Technician A says that calipers use springs to retract the seals after a brake ­application. Technician B says that sliding calipers typically use one piston on each side of the rotor. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 7. Technician A says that a return spring is used to retract a caliper piston. Technician B says that the piston seal retracts the caliper piston when hydraulic pressure is released. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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Disc Brakes

8. Technician A says that inner and outer pad friction materials may have different coefficients of friction. Technician B says to follow the manufacturer’s recommendation for inboard and outboard pad linings when replacing brake pads. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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10. Technician A says that synthetic brake linings are nonorganic, nonmetallic, and non-asbestos materials. Technician B says that synthetic brake linings are made of aramid or fiberglass. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

9. Technician A says that when the driver hears the audible brake pad wear indicator, he or she should immediately park the car and not use it until the brakes are replaced. Technician B says that the wear pad indicators alert the driver to worn pads that should be replaced soon. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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Chapter 8

Drum Brakes

Upon completion and review of this chapter, you should be able to: ■■ ■■ ■■ ■■

Describe the basic parts of a drum brake assembly. Describe how a drum brake stops a vehicle. Describe different types of brake drums. Describe the types of friction linings and the three placements of the lining on the shoe.

■■

■■ ■■

Describe the components that make up a wheel cylinder and the purpose of each one. Describe the two major drum brake designs and how they differ in operation. Describe the different types of ­self-adjusters used on duo-servo and leading-trailing shoe brake systems and how they work.

Terms To Know Arcing Backing plate Brake shoes Cam-ground lining Composite drum Cup expander Drum web Duo-servo brake

Hold-down springs Leading shoe Leading-trailing brake Overload spring Pawl Piston stop Primary shoe Return spring

Secondary shoe Self-adjusters Self-energizing operation Shoe anchor Star wheel Table Trailing shoe Web

INTRODUCTION For more than 80 years, drum brakes at all four wheels were the standard of the automobile industry. Although four-wheel disc brakes have become standard equipment of most cars and light trucks, drum brakes continue in use for a few rear-wheel brakes. No law or regulation requires disc brakes, but the brake performance requirements of FMVSS 105 make front disc brakes virtually mandatory. Nevertheless, drum brakes have certain advantages that will make them an important part of vehicle engineering and service for many more years. This chapter explains the construction and operation of modern drum brake systems and begins with a summary of their advantages and disadvantages. The major drum brake advantages are self-energizing and servo action, lack of noise, and efficient parking brake operation without complicated linkage. Drum brake disadvantages include poorer heat dissipation and less fade resistance than disc brakes, lack of self-adjustment without special linkage, and a greater tendency than disc brakes to pull and grab. 182

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tation Drum ro

Actuator force

Friction force

Resulting ro tati o

n

a un ro dh inge

Hinge (anchor)

Figure 8-1  Drum rotation adds leverage to the brake shoes as they contact the drum. This process is called self-energizing action.

Drum Brake Self-Energizing and Servo Action One end of the lining on one shoe of a drum brake contacts the drum before the other end does and becomes a pivot point as friction increases quickly. The brake shoe becomes a self-energizing lever and adds its own mechanical leverage to hydraulic force to help apply the brakes (Figure 8-1). When a component is operated, or applied and that component uses the initial input force to increase that force and transfer it to a matching component, the entire operation is said to be self-energizing. This self-energizing operation may be confined to one shoe of a drum brake installation, which is the leading shoe in relation to the direction of wheel rotation. When the self-energizing operation of one shoe applies mechanical force to the other shoe to assist its application, it is called servo action (Figure 8-2). Self-energizing operation and servo action can have both operational advantages and disadvantages. Selfenergizing drum brakes that use servo operation can always apply more stopping power for a given amount of pedal force than disc brakes can.

Self-energizing ­operation is the action of a drum brake shoe when drum rotation increases the application force of the shoe by wedging it tightly against the drum.

Drum Brake Pulling and Grabbing Servo action increases braking force at the wheels, but it must develop smoothly as the brakes are applied. If servo action develops too quickly or unevenly, the result can be brake grabbing or lockup. This is usually experienced as severe pull to one side or the other or reduced vehicle control during braking.

Lack of Noise Drum brakes are almost noise free. Heavy return springs and hold-down springs hold the brake shoes against the wheel cylinders, anchor pins, backing plates, and away from the drum. Linings are securely bonded or riveted to the brake shoes, and the entire assembly is encased in the brake drum. About the only time that noise is a concern with drum

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Chapter 8 Primary shoe

Link

Secondary shoe

Link

RH front

RH front

Anchor

RH front

Figure 8-2  Self-energizing action of the primary shoe applies force to the secondary shoe. This process is called servo action.

brakes is when it is the sound of steel brake shoes grinding against the brake drum after the linings have worn away.

Drum Brake Parking Brake Operation Drum brakes provide a better static coefficient of friction than do disc brakes. The brake linings grab and hold the drums more tightly than disc pads can hold a rotor. In addition, the self-energizing and servo actions of drum brakes contribute to this feature, as does the larger area of brake shoe linings compared to disc brake pads. For brake installations that have discs at the front and drums at the rear, the parking brake weaknesses of disc brakes are not a problem. Many disc brake applications now use a drum-in-hat style rotor that allows the use of drum style parking brakes. The parking brake shoes are small, but all they have to do is hold the vehicle stationary. Some rear disc brake applications still use a parking brake mechanism that is integral with the disc brake caliper. In most cases, the driver operates a pedal or a lever that pulls on cables attached to the rear brakes. The cables operate levers that mechanically apply the brake shoes. Some vehicles are equipped with electric cable actuators or electric motors that are attached directly to the back of the rear rotors. All mechanical motion is in a straight longitudinal line from the front to the rear of the vehicle.

Drum Brake Self-Adjustment Brake adjustment is the process of compensating for lining wear and maintaining correct clearance between brake linings and the drum or rotor surfaces. Disc and drum brakes

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both require adjustment, but self-adjustment is a basic feature of disc brake design. Drum brakes need extra cables, levers, screws, struts, and other mechanical linkage just to provide self-adjustment and proper lining-to-drum clearance.

Fade Resistance Brake fade is the loss of braking power due to excessive heat that reduces friction between brake linings and the rotors or drums. One factor that contributes to heat dissipation and fade resistance is the swept area of brake drum or rotor, which is the total area that contacts the friction surface of the brake lining. The greater the swept area, the greater the surface available to absorb heat. Although a brake drum can have a relatively large swept area, the entire area is on the inner drum surface. The swept area of a disc brake comprises both sides of the rotor. For any given wheel size, the swept area of a disc brake will always be larger than the swept area of a drum brake (Figure 8-3). For example, a 10-inchdiameter rotor will have almost 50 percent more swept area than a 10-inch drum. Mechanical fade is a problem that occurs with drum brakes when the drum becomes very hot and expands outward, away from the brake shoes. As a result, the shoes then must travel farther to contact the drum surface with normal braking force, and the pedal drops lower as the brakes are applied. The increased heat at the braking friction surfaces also reduces the coefficient of friction. The combined result is brake fade. Lining fade occurs when the linings are overheated and the coefficient of friction drops off severely (Figure 8-4). Some heat is needed to bring brake linings to their most efficient working temperature. The coefficient of friction rises, in fact, as brakes warm up. If the temperature rises too high, however, the coefficient of friction decreases rapidly. Because disc brakes are exposed to more cooling airflow than drum brakes, lining fade due to overheating is reduced. Water fade occurs when water is trapped between the brake linings and the drum or rotor and reduces the coefficient of friction. Gas fade is a condition that occurs under hard braking when hot gases and dust particles are trapped between the brake linings and the drum or rotor and build up pressure that acts against brake force. These hot gases actually lubricate the friction surfaces and reduce the coefficient of friction.

Prior to the installation of self-adjusters, periodically the vehicle brakes would have to be adjusted by a technician or an experienced owner.

Swept area two surfaces

100 Square Inches

Swept area one surface

60 Square Inches

Figure 8-3  For any given size wheel, a disc brake has 35 percent to 50 percent more swept area to dissipate heat.

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Chapter 8

Coefficient of Friction: 1,000 ft.-lb.

Temperature

°F × 100

Figure 8-4  Initially, the coefficient of friction increases with heat, but very high temperatures cause it to drop off and cause the brakes to fade.

AUTHOR’S NOTE   You can use a piece of sandpaper to demonstrate the effect of heat on friction. Slide the sandpaper slowly over a hard surface, and you can feel the drag or friction. Speed up the sliding action, and shortly you will feel the heat and the reduction of the drag.

Tinnerman nuts are generally discarded the first time the drums are serviced. They are used to hold the drums in place at the assembly plant.

The basic design differences between disc and drum brakes make disc brakes much more self-cleaning to greatly reduce or eliminate water and gas fade. Centrifugal force also works to remove water and gas from the braking surfaces. Additionally, the leading edges of the brake pads help to wipe the rotor surfaces clean. Due to the design of the drum brake, it will trap heat, water, and gases inside the drum. This makes the drum brake more susceptible to brake fade and pull.

DRUM BRAKE CONSTRUCTION AND OPERATION Shop Manual page 374

Floating drums are the rule for latemodel vehicles that still use drum brakes. One-piece drums were common on older vehicles.

The backing plate ­provides the mounting platform for the brake assembly and closes the rear of the mounted brake drum.

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The basic parts of a drum brake are a drum and hub assembly, brake shoes, a backing plate, a hydraulic wheel cylinder, shoe return springs, hold-down springs, and an adjusting mechanism (Figure 8-5). Rear brakes also include a parking brake. The drum and shoes provide the friction surfaces for stopping the wheel. The drum has a machined braking surface on its inside circumference. The wheel is mounted to the drum hub by nuts and studs. On later-model vehicles, that drum is usually separate from the hub or axle flange (floating) and fits over the wheel studs for installation. Separate or floating drums are sometimes held to the hub or axle flange by thin push-on nuts commonly referred to as speed nuts or Tinnerman nuts. Screws may also be used to hold drums on. The hub houses the wheel bearings that allow the wheel to rotate. The hydraulic and friction components are attached to the backing plate (Figure 8-6), which is mounted on the axle housing or suspension. The backing plate provides the mounting platform for the brake assembly and closes the rear of the mounted drum. The drum encloses and rotates over these components. When the brakes are applied, hydraulic pressure forces the pistons in the wheel cylinder outward. The pressure on the pistons is transmitted to the shoes as the shoes are forced against a pivot or anchor pin and into the rotating drum. Through this action, the shoes tightly wrap up against the drum to provide the stopping action.

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Wheel cylinder Shoe return spring

Adjusting mechanism

Hold-down springs

Backing plate

Shoe and lining

Drum

Figure 8-5  Basic parts of all drum brakes. A leading-trailing system is shown. Wheel cylinder Backing plate

Shoe and lining

Shoe and lining

Hold-down springs

Self-adjuster mechanism

Figure 8-6  The hydraulic and friction components are mounted on the backing plate.

The frictional energy on the drum surface creates heat. This heat is dissipated to the surrounding air as the drum rotates with the wheel. Some drums are finned to help them dissipate heat more efficiently.

Brake Drums and Hubs The brake drum mounts on the wheel hub or axle and encloses the rest of the brake assembly except the outside of the backing plate. Brake drums are made of cast iron or steel and cast iron. In these variations, iron provides the friction surface because of its excellent combination of wear, friction, and heat-dissipation characteristics. The drum is a bowl-shaped part with a rough-cast or stamped exterior and a machined friction surface on the interior. The open side of the drum fits over the brake shoes and other parts mounted on the backing plate (Figure 8-7). It is the side of the drum that is visible when

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Chapter 8 Backing plate

Outer bearing race or cup

Brake assembly Drum web

Inner bearing cone Cage Roller

Inner race

Figure 8-8  The outer race or cup is a separate part of a tapered roller bearing. The remaining parts are combined in one assembly.

Drum

Figure 8-7  The drum fits over the brake shoes and other parts mounted on the backing plate. The drum web ­is the closed side of the drum. The web also holds the wheel bearings in a onepiece drum.

the wheel assembly is removed. The closed side of the drum is called the drum web and contains the wheel hub and bearings (one-piece drum) or has mounting holes through which the drum is secured to the axle flange or separate hub (two-piece drum). Tapered roller bearings, installed in the hubs on drums equipped with hubs, were common on older vehicles; later-model vehicles use sealed wheel bearings on floating drums as the most common bearings used on the rear wheels of FWD cars. The tapered roller bearing has two main parts: the bearing cone and the outer cup (Figure 8-8). The bearing cone contains steel tapered rollers that ride on an inner cone and are held together by a cage. The bearing fits into the outer cup, which is pressed into the hub to provide two surfaces, an inner cone and outer cup, for the rollers to ride on. Sealed wheel bearings are used on most frontwheel drive vehicles on the rear wheels with floating drums. Chapter 3 in this Classroom Manual contains more detailed information on different kinds of wheel bearings. On RWD vehicles, the brake assembly is mounted to the backing plate, which is fastened to the rear axle housing (Figure 8-9). The axle extends outward past the brake Backing plate Brake assembly

Rear axle

Drum web

Axle housing

Axle bearing in housing Studs

Drum

Figure 8-9  Drum removed with the axle partially withdrawn. Shown is the general layout of RWD axle and brake drum.

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Cooling fins

Figure 8-10  This drum has cooling fins cast into its outer circumference.

assembly and has the wheel studs installed into the axle flange. The axle bearing fits into the end of the axle housing. The drum is fitted over the studs and held in place by the placement of the wheel assembly. The outer end of the axle and the brake assembly are enclosed within the drum. Information and service on axle bearings may be found in Today’s Technician Manual Transmissions and Transaxles. Some drums have fins cast into the outer circumference to aid in cooling (Figure 8-10). The braking surface area of a drum is determined by the diameter and the depth (width) of the drum. Large cars and trucks, which require more braking energy, have drums that measure 12 inches in diameter or larger. Smaller vehicles use smaller drums. Generally, manufacturers try to keep parts as small and light as possible while still providing efficient braking. Brake drums can be categorized as either solid or composite and by the different ways in which the drums are made. Solid Cast-Iron Drums.  One-piece cast-iron drums are rarely seen on late-model vehicles because of their weight. A solid drum is a one-piece iron casting (Figure 8-11). Cast iron has excellent wear characteristics and a coefficient of friction that make it ideal as a braking friction surface. Iron also dissipates heat very well, and it is easy to machine when refinishing is necessary. Along with these advantages, cast-iron drums have some disadvantages. A large iron casting can become brittle and may crack if overstressed or overheated. Small cracks may be almost invisible to the naked eye, but they can lead to drum failure or heat checking and glazing.

Cast iron

Figure 8-11  Cross section of a ­cast-iron drum.

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Chapter 8 Table (where lining is attached) Cast iron Stamped steel web

Anchor end (near wheel cylinder)

Lining

Figure 8-12  Cross section of a ­composite drum.

Web (welded to and supports table)

Adjusting end (at self-adjuster or anchor pin)

Figure 8-13  A typical brake shoe with the lining detached.

composite drums are composed of a stamped steel web mated with the edge of cast-iron drum. Brake shoes are the components that mount the friction material to the backing plate. The brake shoe table is the metal part of the brake shoes to which the linings are attached.

Some aftermarket brake shoe sets are fitted with equal amounts of lining on each shoe. This allows one brake shoe set to replace several types of original manufacturer shoe. Brake linings react against the brake drum with friction that is dissipated as heat.

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A one-piece cast-iron drum is the heaviest of all drum types, which is both an advantage and disadvantage. The weight and mass of a one-piece drum make it very good at absorbing and dissipating heat. The drum weight, however, adds a lot of weight to the vehicle, and it is all unsprung weight at the wheels. Engineers consider brake drum weight more a disadvantage than an advantage for late-model cars, so most vehicles are being built with composite drums of the following kinds. Steel and Iron Drums.  Steel and iron composite drums are made in two ways. The most common type has a stamped steel web mated with the edge of a cast-iron drum (Figure 8-12). The other type of composite drum has a centrifugally cast iron liner inside a stamped steel drum. To make this kind of drum, a stamped steel drum is rotated at high speed while molten iron is poured into it. Centrifugal force causes the molten iron to flow outward and bond tightly to the inner circumference of the steel drum. Steel and iron composite drums are lighter and cheaper to make than one-piece castiron drums, but they are less able to absorb and dissipate heat and resist fade. They work well on the rear drum brakes of compact cars, however.

Brake Shoes and Linings Brake shoes are the components that mount the friction material or linings that contact the drums. The shoes also provide the area to mount the shoe to the backing plate. Brake shoes are usually made from welded steel, although some drum brakes use aluminum shoes. The outer part is called the table (or sometimes the rim) and is curved to match the curvature of the drum (Figure 8-13). The brake lining is riveted or bonded to the brake shoe table (Figure 8-14). Many brake shoes have small notches or nibs along the edge of the table that bear against the backing plate and help to keep the shoe aligned in the drum. The web is the inner part of the shoe that is perpendicular to the table and to which all of the springs and other linkage parts attach. Duo-servo and leading-trailing non-servo brakes are described in detail later in this chapter, but all drum brakes have a pair of shoes at each wheel. The front shoe on duoservo brakes is called the primary shoe, and the rear shoe is called the secondary shoe. The front and rear shoes on leading-trailing brakes are called just that: the leading shoe and the trailing shoe, respectively.

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Lining

Shoe Rivet

High Position

Bonded Lining

Riveted Lining

Figure 8-14  Linings may be bonded or riveted to the shoe.

Low Position

Centered Position

Figure 8-15  Lining can be attached to the shoe in different positions, depending on the desired stopping characteristics.

On leading-trailing brakes, the lining on the leading and trailing shoes are usually the same length and positioned in the same location on each shoe. On a duo-servo brake, however, the primary shoe lining is shorter than the secondary lining and may even have a different coefficient of friction. As explained later in this chapter, the primary shoe of a duo-servo brake is self-energized by drum rotation and then applies servo action to the secondary shoe. The secondary shoe applies most of the stopping force and thus requires a larger lining. The coefficient of friction for the secondary lining is often higher than for the primary lining to provide good stopping power. However, the lower coefficient of friction for the primary lining helps to keep the brakes from applying too harshly and locking. Lining for the secondary shoe is almost always centered from top to bottom on the shoe table. Primary lining may be centered from top to bottom on the table, or it may be offset toward either the top or the bottom (Figure 8-15), depending on the operating characteristics of a specific brake installation. Brake Friction Materials.  Both drum and disc brake friction materials are covered in Chapter 7 of this Classroom Manual.

AUTHOR’S NOTE  On a few older light-duty trucks and large passenger sedans, the shoes were marked “L” or “R” and were to be mounted on either the left (L) or right (R) side of the vehicle. This was necessary because the shoe web had a ­reinforced area at the top outside of the web. If installed on the wrong side, this reinforced area would drag on the backing plate and cause grabbing. The ­reinforcement enabled the manufacturer to use an older model shoe web on heavier vehicles. The original web design could not withstand the braking forces of the heavier vehicle. In theory, this was supposed to save manufacturing costs, but it was basically a failure and was discontinued after a few model years.

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Chapter 8

Some brake linings are fitted to provide more clearance at the ends than the center. Arcing used to be done as part of the brake job, but today most linings are manufactured with a cam ground lining at the factory.

Lining-to-Drum Fit.  When disc brakes are applied, a flat pad contacts a flat rotor, so the surface fit of the pad to the rotor is usually not a concern. With drum brakes, however, a semicircular lining contacts a circular drum, and the lining does not move in a straight line toward the drum. The complete lining surface does not contact the drum all at the same time, so the surface fit of the lining to the drum is an important operating consideration. The leverage that operates in drum brakes and the motion of brake shoes as they are applied work against full lining contact with the drum. Therefore, lining shape must be adjusted to overcome these natural conditions and work toward providing full lining-todrum contact. The hydraulic force of the wheel cylinder pistons and the rigid positions of the shoe anchors tend to force the upper ends of the shoes into contact with the drum before the center of the shoes. Most drum brake noise complaints are caused by binding at the ends of the shoes as they contact the drum before the center does. More important, if the full surface of new brake linings does not contact the drum as the linings are broken in, the linings can overheat and become glazed, which reduces braking effectiveness. To compensate for these natural characteristics of drum brakes, linings are fitted to shoes to provide more clearance at the ends than at the center. This process is known as arcing the shoes, and it forms either cam-ground or undersized linings. Arcing or camgrounding of the lining is sometimes very visible on some brake shoes. On others, the arc or ground is not noticeable without close inspection. A cam-ground lining is thinner at the ends than at the center (Figure 8-16), and the lining surface is not a portion of a circle with a constant radius. An undersized lining has a uniform thickness and a constant radius (Figure 8-17), but it has a smaller outside diameter than the inside diameter of the drum. A fixed-anchor arc is a variation of an undersized lining in which the overall arc is offset slightly so that one end of the lining is thicker than the other (Figure 8-18). Arc grinding, or arcing, of new brake linings used to be a standard part of brake s­ ervice. Today, however, brake shoe linings are seldom arced as part of the brake installation job. Lined shoes are sold with the lining surface already contoured for proper drum fit. Several factors led to the decline of arc grinding, and concerns about airborne asbestos and brake dust in general were the leading cause. In addition, rear drum brakes used with front disc brakes provide a smaller percentage of overall braking for late-model FWD cars. Lining Anchor

Drum radius 5.000 inches Uniform lining thickness overall Lining radius 4.980 inches

Drum

Figure 8-16  A cam-ground lining is thinner at the ends than in the center (clearances exaggerated).

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Lining

Lining

Anchor

Anchor

Drum radius 5.000 inches Uniform lining thickness overall

Lining has constant radius

Lining radius 4.980 inches Shoe is off-center in drum

Drum

Drum

Figure 8-17  An undersized lining has a shorter radius than the drum radius (clearances exaggerated).

Figure 8-18  The overall arc of a fixed-anchor lining is offset slightly, and one end of the lining is thicker than the other (clearances exaggerated).

Brake linings and drums are less prone to overheating, and lining wear is not as severe as it was in the past. Therefore, arcing requirements are not as great, and precontoured linings are more easily provided by manufacturers.

Backing Plate The backing plate is bolted either to the steering knuckle on the front suspension or to the axle flange or hub at the rear (Figure 8-19). The backing plate is the mounting surface for all other brake parts except the drum. The circumference of the backing plate is curved to form a lip that fits inside the drum circumference and helps to keep dirt, water, and road debris out of the brake assembly. Brake shoe anchors are attached to the backing plate to support the shoes and keep them from rotating with the drum. Most modern brakes have a single anchor that is either

Brake shoe anchors hold the brake shoes on the backing plate.

Anchor pin

Support pads

Support pads

Backing plate

Figure 8-19  The backing plate holds the complete drum brake assembly. The shoe slides across the lubricated shoe contact pads as they are applied and released.

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Chapter 8

Piston stops keep the wheel cylinder pistons from coming out of the wheel cylinder.

Shop Manual page 395

a round post or a wedge-shaped block. Some older drum brakes and a few late-model versions have separate anchors for each shoe. All backing plates have some form of shoe-support pads stamped into their surfaces. The edges of the shoes slide against these pads as the brakes are applied and released. The pads thus keep the shoes aligned with the drum and other parts of the assembly. A light coat of brake lubricant should be applied to the pads to aid shoe movement and reduce noise. Many backing plates have piston stops, which are steel tabs at the ends of the wheel cylinder. These stops keep the pistons from coming out of the cylinder during service. The wheel cylinder must be removed from a backing plate with piston stops for disassembly.

Wheel Cylinders Wheel cylinders convert hydraulic pressure from the master cylinder to mechanical force that applies the brake shoes. Historically, many kinds of wheel cylinders have been used on different kinds of drum brakes. These included single-piston cylinders and steppedbore cylinders with pistons of different diameters. Some wheel cylinders were installed to slide on the backing plate as they applied the brake shoes. Wheel cylinders for late-model drum brakes, however, are almost all two-piston, straight-bore cylinders that are mounted rigidly to the backing plate. The basic parts of all cylinders are the body, the pistons, the cups (seals), the spring and cup expanders, and two dust boots (Figure 8-20). Some cylinders include two shoe links, or pushrods, to transfer piston movement to the shoes. In other designs, the shoe webs bear directly against the cylinder pistons. AUTHOR’S NOTE  Some drums have a slot extending around the outer edge of the drum. The lip of the backing plate fits into this groove, providing better ­protection for the brake components.

The wheel cylinder body is usually cast iron, but aluminum cylinder bodies are becoming more common. The cylinder bore is finished to provide a long-wearing, corrosionresistant surface. A fitting for a hydraulic line is provided at the center of the cylinder, between the two pistons. The bleeder screw also is tapped into the cylinder body at its highest point. A piston is installed in each end of the wheel cylinder, and the inside end of each piston is sealed with a cup seal. Hydraulic pressure against the seal forces the seal lip to

Cup

Cup expander

Bleeder screw near top Piston

Dust boot

Shoe link (pushrod) Spring Inlet port

Figure 8-20  Almost all modern drum brakes use straight-bore, twopiston wheel cylinders such as the one shown in this cross section.

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Bleeder screw

Link

Link

Cup

Cup Boot

Boot Piston

Return spring with cup expanders

Piston

Figure 8-21  An exploded view of a typical wheel assembly.

expand against the cylinder bore and form a leak-free seal. Most wheel cylinders also have spring-loaded metal cup expanders that bear against the inner sides of the cups (Figure 8-21). Piston cup expanders were made to keep the lips of the seal in place when the brakes are released. The spring takes up any slack between the pistons and their pushrods and helps to center the pistons in the cylinder bore.

piston cup expanders hold the piston seals against the wheel ­cylinder walls when the brakes are released.

AUTHOR’S NOTE  The wheel cylinder springs are not return springs. The shoe return springs push the pistons back in place.

Each end of the wheel cylinder is sealed with a dust boot to keep dirt and moisture out of the cylinder. The dust boots also prevent minor fluid seepage from getting onto the brake linings.

Return and Hold-Down Springs Strong return springs retract the shoes when the brakes are released and hold them against their anchors and the wheel cylinder pushrod. Most return springs are tightly wound coil springs in which the coils touch each other when retracted (Figure 8-22).

###

Orange

3 7/16 "

35 lb.

###

Purple

3 3/ 8"

45 lb.

###

Black

4 1/ 4"

###

White

3 3/ 6"

50 lb.

###

Bronze

2 5/ 8"

55 lb.

###

Blue

3 3/ 16 "

65 lb.

return springs retract the brake shoes when the brakes are released.

50 lb.

Figure 8-22  Return springs are identified by their part number, free length, and tension. Most are color coded to identify tension differences among similar-looking springs.

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Chapter 8 Anchor Secondary return spring Primary return spring

Front

Self-adjuster return spring

Figure 8-23  Typical return spring installation on a duo-servo system.

Shop Manual page 398 Hold down springs are part of the brake shoe anchor.

Return springs often are color coded to indicate different tension values among springs of the same size and shape. The type, location, and number of springs vary, but return springs are installed either from shoe to shoe or from each shoe to an anchor post (Figure 8-23). Hold-down springs, clips, and pins also come in various shapes and sizes, but all have the same purpose of holding the shoes in alignment with the backing plate. Holddowns must hold the shoes in position when providing flexibility for their application and release. Figure 8-24 shows some of the varieties of hold-down springs and clips. Some GM cars and some imported vehicles use a single large horseshoe-shaped spring that acts as both a shoe return spring and a hold-down spring (Figure 8-25).

Figure 8-24  Various kinds of hold-down springs are used on different drum brakes.

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Spring tension acts to release shoe

Return and hold-down spring Spring fits over notch

Figure 8-25  The big horseshoe-shaped spring serves as both a shoe return spring and a shoe hold-down on some late-model GM rear brakes.

Self-Adjusters As the brakes are applied, the lining wears and becomes thinner. As the distance between the shoe and the drum becomes greater, the shoes must move farther before the lining contacts the drum. Therefore, the pistons of the wheel cylinder also must move farther, and more brake fluid must come from the master cylinder to apply the brakes. To provide more brake fluid, brake pedal travel will increase. Brake adjustment compensates for lining wear and maintains correct clearance between brake linings and the drum. Disc and drum brakes both require adjustment, but self-­ adjustment is a basic feature of disc brake design. Drum brakes, however, need extra cables, levers, screws, struts, and other linkage to provide self-adjustment and proper lining-­ to-drum clearance. Many different kinds of manual and automatic adjustment devices have been used on drum brakes over the years, but today automatic self-adjusters that operate star wheel or ratchet adjustment mechanisms are the most common. Automatic self-­ adjusters use the movement of the brake shoes to maintain proper shoe/drum clearance. Duo-Servo Star Wheel Adjusters.  The bottoms of the shoes in duo-servo brakes are connected to each other by a link, and the shoes are held against the link by a strong spring (Figure 8-26). The link keeps the shoes aligned with each other and transfers the servo action of one shoe to the other during braking. It is not attached to the backing plate, but it moves back and forth with the shoes. One half of the link is internally threaded, and the other is externally threaded. The externally threaded part has a star wheel near one end. When the two halves of the link are assembled, rotating the star wheel screws them together or apart. In this way, the adjustment link is lengthened or shortened to adjust the lining-to-drum clearance. Even with self-adjusters, the initial adjustment of a duo-servo brake is made this way after new shoes are installed and the drum is resurfaced. Further adjustment is done automatically, however, by the self-adjustment mechanism for the life of the linings. Duo-servo brakes commonly have self-adjusters operated by the secondary shoe. A cable, a heavy wire link, or a lever is attached to the secondary shoe. The cable, link, or lever is attached to a smaller lever or pawl that engages the star wheel (Figure 8-27). During braking in reverse, the secondary shoe moves away from the anchor post. If the lining is worn far enough and the shoe can move far enough, it will pull the cable, link, or lever to move the pawl to the next notch on the star wheel. When the brakes are released,

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self-adjusters maintain proper brake shoe to drum clearance automatically.

A pawl is a hinged or pivoted component that engages a toothed wheel or rod to provide rotation or movement in one direction while ­preventing it in the opposite direction.

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Spring

Link

Detail

Star wheel

Cable plate Adjuster spring

Figure 8-26  The link between the shoes of a duo-servo brake contains the adjustment star wheel.

Adjuster cable Adjusting pawl

Adjusting screw assembly

Figure 8-27  A cable-operated self-adjuster on a duo-servo brake moves the lever (pawl) upward when the secondary shoe moves off its anchor during reverse braking.

Figure 8-28  As the adjuster spring pulls the lever (pawl) downward, it turns the star wheel one notch to expand the adjuster link.

the pawl spring moves the pawl to rotate the star wheel (Figure 8-28). The rotation of the star wheel then expands the link one notch to take up the clearance between the linings and the drum.

A BIT OF HISTORY Self-adjusters on drum brakes became common and quickly progressed to standard equipment on cars of the late 1950s and early 1960s. Mercury and Edsel models from Ford are credited with leading the industry to self-adjusting brakes with their 1958 models. Ford was not the first carmaker to make self-adjusting brakes standard equipment, however. A decade earlier, Studebaker models of 1947 featured self-adjusting brakes, and they remained a Studebaker exclusive through 1954. Public disinterest (and technician distrust) caused Studebaker to drop this feature until the early 1960s when the rest of the industry finally recognized the benefits. Automatic adjusters for drum brake systems were first used in 1957. Automatic adjusters have been used on all domestic cars and some import cars since 1963. A few years later even trucks had automatic brake adjusters installed.

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Adjuster link

Adjuster lever Bushing

Pawl

Spring

Pivot nut

Socket Adjusting screw

Washer

Figure 8-29  Some duo-servo self-adjusters are operated by a link and a lever instead of a cable.

Quite a bit of variety exists in the specific linkage used on different duo-servo brakes. Cable- and link-operated self-adjusters usually move the pawl to engage the next notch in the star wheel as the brakes are applied in reverse. Lever-operated self-adjusters (Figure 8-29) usually move the pawl to rotate the star wheel as the brakes are applied. Some cable-operated self-adjusters move a pawl mounted under the star wheel to adjust the brakes during application, not release. These cable-operated adjusters usually have an overload spring in the end of the cable that lets the cable move without breaking if the pawl or star wheel is jammed. The overload spring also prevents overadjustment during very hard braking when the drum may distort and let the shoes move farther out than normal. To prevent this, the overload spring stretches with the cable and does not let the pawl actuate. Overadjustment will not occur during hard braking when the brakes are in normal adjustment. Left- and right-hand threaded star wheel adjusters are used on the opposite sides of the car. Therefore, parts must be kept separated and not intermixed. If a star wheel adjuster is installed on the wrong side, the adjuster will not adjust at all and may unadjust, causing excessive shoe/drum clearance.

Self-adjuster overload springs let the cable move without breaking if the pawl or star wheel is damaged.

AUTHOR’S NOTE  Duo-servo brakes only self-adjust in reverse, but leading-­ trailing brakes will self-adjust as necessary going in either direction, or even when the parking brake is applied.

Leading-Trailing-Shoe Star Wheel Adjusters.  Even more variety exists in the linkage used for star wheel adjusters on leading-trailing-shoe brakes. The star wheel self-adjusters can be operated by either the leading or the trailing shoe and can work whenever the brakes are operated in either forward or reverse. The star wheel is usually part of the parking brake strut that is mounted between the two shoes. A pawl can be operated by either the leading or the trailing shoe to engage and rotate the star wheel as the brakes are applied or released.

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Chapter 8 Gap Leading shoe

Strut shoulder

Lever return spring

Parking brake lever Trailing shoe Spacer strut Strut shoulder

Figure 8-30  The ratchet-type self-adjuster for leading-trailing brakes is operated by the parking brake lever.

Leading-Trailing-Shoe Ratchet Adjusters.  A lever-latch ratchet adjuster has a large lever and small latch attached to the leading shoe. Teeth on the lever and the latch form a ratchet mechanism that moves the shoes outward to take up excess clearance as the brakes are applied. Another kind of ratchet adjuster consists of a pair of large- and small-toothed ratchets and a spacer strut mounted between the shoes (Figure 8-30). The strut is connected to the leading shoe through the hand brake lever and the inner edge of a large ratchet. As the gap between the shoes and the drums becomes greater, the strut and the leading shoe move together to close the gap. More movement will cause the large ratchet on the trailing shoe to rotate inward against a small spring-loaded ratchet and reach a new adjustment position. Other similar systems are actuated by the parking brake and adjust when the parking brake is applied and released. An adjustment strut is attached to the parking brake lever (Figure 8-31). As the lining wears, application of the parking brake will restore the proper lining clearance. Retracting spring

Strut and rod adjuster

Wheel cylinder

Trailing shoe and lining

Adjuster lock

Parking brake lever Rod assembly

Hold-down clip

Positioning adjuster assembly

Parking brake cable

Leading shoe and lining Front

Adjuster position for new shoes (index hole half covered)

Figure 8-31  Semiautomatic self-adjuster for leading-trailing brakes.

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The strut-quadrant self-adjuster is a variation of the strut-rod adjuster shown in Figure 8-31. The strut-quadrant adjuster has a rotating semicircular quadrant as half of the engaging ratchet mechanism. AUTHOR’S NOTE  Installation of these types of self-adjusters can be a real nightmare at times. Nothing seems to fit and the springs are strong and awkward to grip. The service manual instructions usually leave a lot to the imagination. The best method I have found is to look for a technician with experience on these systems and pick his or her brain for the best and quicker way to assemble and mount the different parts.

Leading-Trailing-Shoe Cam Adjusters.  Cam-type adjusters use cams with an adjuster pin that fits in a slot on the shoes (Figure 8-32). As the brake shoes move outward, the pin in the slot moves the cam to a new position if adjustment is needed. Shoe retraction and proper lining clearance are always maintained because the pin diameter is smaller than the width of the slot on the shoe. These brakes can be adjusted even while the vehicle is at a standstill because brake pedal application is all that is needed to move the cams into proper adjustment. Because the brakes can be adjusted completely with one application of the brake pedal, this adjuster is sometimes called the one-shot adjuster. Self-Adjuster Precautions.  The self-adjuster mechanisms described in the preceding paragraphs are just a few common examples of such devices used on late-model drum brakes. When servicing these brakes, examine the self-adjuster parts closely and pay attention to how they are assembled. One previous paragraph mentioned that left- and righthand parts exist for the left and right wheels of most systems. If parts are interchanged from side to side, the self-adjusters will not work. Examine self-adjuster parts closely for wear and damage. Teeth wear off and adjusters freeze up. All threaded parts must move freely. Cable guides wear at the points where cables slide back and forth. Spring anchors can bend, stretch, or wear. Holes and slots wear where parts pivot or springs are anchored. Cables stretch with age and use. Many shop owners make it standard practice to replace self-adjuster cables whenever brakes are serviced and other parts when they show any sign of wear. Finally, if unfamiliar with a Pin Wheel cylinder Leading shoe

Strut Adjusters

Parking brake lever Anchor

Adjuster Detail

Trailing shoe

Front

Figure 8-32  Cam-type self-adjuster for leading-trailing brakes.

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In most cases of current drum leadingtrailing brake systems, it is assumed that the leading shoe is always the shoe toward the front of Shop Manual the vehicle. This is pages ? because the assumed vehicle is normally braked while moving forward, and the wheel cylinder is at the top of the assembly.

particular self-adjuster installation, service one wheel at a time and use the opposite brake assembly as a reference for parts installation.

Parking Brake Linkage Almost all rear drum brake installations include mechanical parking brake linkage. The linkage basically consists of a cable, a lever, and a strut. The lever and strut spread the shoes against the drum when the cable pulls on the lever. The parking brake strut may contain part of the self-adjuster as explained in previous paragraphs. Chapter 9 covers parking brakes in detail.

DRUM BRAKE DESIGNS Dozens of drum brake designs have been used over the decades of automobile manufacturing. Full-servo, partial-servo, non-servo, two-leading-shoe, two-trailing-shoe, and centerplane are just a few of the brake designs that are part of automobile history. Today, two designs account for almost all of the drum brakes installed on late-model vehicles: 1. Leading-trailing brakes (Figure 8-33), also called partial-servo or non-servo brakes 2. Duo-servo brakes (Figure 8-34), also called dual-servo or full-servo brakes The following sections describe these brake designs and explain their operations.

Self-Energizing and Servo Actions Two terms used to describe drum brake operation are “self-energizing” and “servo.” They refer to the leverage developed on the brake shoe as it contacts the drum and the action of one shoe to help apply the other. Brake shoes are described as leading or trailing and primary or secondary. Leading and trailing shoes are components of leading-trailing (servo) brakes. The assumption is that the leading shoe is the one that moves from the wheel cylinder’s end that points in the direction of drum rotation. To identify the leading brake shoe, put a hand at the

Wheel cylinder

Parking brake lever retaining clip

Trailing shoe

Leading shoe

Parking brake

Anchor

Figure 8-33  A typical leading-trailing brake.

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Anchor

Return spring

Return spring

Wheel cylinder

Backing plate

Secondary shoe Primary shoe Connecting spring

Front

Shoe link and adjuster

Figure 8-34  Typical duo-servo brake.

position of the wheel cylinder, and then point in the direction of drum rotation: clockwise or counterclockwise. The shoe that is pointed to first is the leading shoe. Think about this for a moment, and it is obvious that the leading shoe can be the front or the rear shoe, depending on whether the drum is rotating forward or in reverse. When the brakes operate, the wheel cylinder forces one end of the leading shoe outward against the drum. The other end of the shoe is forced back solidly against its anchor post or anchor block. The cylinder end of the leading shoe contacts the drum first and develops friction against the rotating drum. The drum friction actually pulls the shoe into tighter contact with the drum (Figure 8-35) and aids the hydraulic force of the cylinder Drum rotation

Actuation force on force Fricti

Result i

ng

ro ta tio

na

d hinge roun

Hinge (anchor)

Drum

Figure 8-35  Self-energizing operation of a brake shoe develops as friction against the rotating drum pulls the shoe into tighter contact with the drum.

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Chapter 8

to apply the brake shoe. As drum-to-lining contact increases, the rest of the lining is forced by the cylinder and pulled by friction against the drum to stop rotation. This is selfenergizing action by the leading shoe. In a leading-trailing brake, the reaction of the trailing shoe to drum rotation is ­opposite to the reaction of the leading shoe. As the wheel cylinder tries to force the trailing shoe outward against the drum, rotation tries to force the shoe back against the cylinder. Eventually, hydraulic force overcomes drum rotation as the wheel slows, and the trailing shoe contributes to braking action. The trailing shoe, however, is said to be non-­ self-energizing (Figure 8-36). In another brake design, the self-energizing action of one brake shoe can be used to help apply the other shoe. In a duo-servo brake, the primary shoe has the position of the leading shoe in a leading-trailing brake. The primary shoe is the shoe toward the front of the vehicle and many times has a shorter lining than the secondary shoe. The ends of both shoes opposite the wheel cylinder are not mounted on a rigid anchor attached to the backing plate as in a leading-trailing brake. The ends of the two shoes are linked to each other through the star wheel adjuster, and the ends (normally by the bottom) of the shoes float in the drum. As the primary shoe is applied by the wheel cylinder, it develops self-energizing action as in a leading-trailing brake. Instead of being forced against an anchor, however, the primary shoe is forced against the secondary shoe and applies leverage to force the secondary shoe against the drum. This is duo-servo action (Figure 8-37), or the action of mechanically multiplying force. The secondary shoe is then forced against the drum by the wheel cylinder force at one end and the servo action of the primary shoe at the other. Self-energizing action and servo operation are forces that naturally occur in internalexpanding drum brakes but do not exist in disc brakes. Engineers put these actions to work in different ways in different brake designs that are described and illustrated in the following sections.

Energization area

Energization area

Drum rotation

Trailing shoe

Leading shoe Anchor Front

Figure 8-36  The leading shoe is self-energizing, but the trailing shoe is non-­ self-energizing in a leading-trailing brake.

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Primary shoe

Link

Secondary shoe

Link

Front

Front

A

B Anchor

Front C

Figure 8-37  Self-energizing action for the primary shoe begins as the wheel cylinder forces it against the rotating drum (A). Reaction force of the primary shoe is transferred through the link to the secondary shoe (B). This transfer of force is servo action. The servo action of the primary shoe against the secondary shoe causes it also to become self-energizing (C). The top of the secondary shoe is forced against the anchor to complete the brake application.

Leading-Trailing Brakes Operation Leading-trailing or non-servo brake design was common in four-wheel drum brake systems up to the late 1960s but was steadily replaced by duo-servo four-wheel drum brakes as cars got heavier and faster. Duo-servo brakes are a more powerful drum brake design, and leading-trailing brakes almost vanished from the industry in the 1960s. They began to reemerge, however, as rear brakes on smaller and lighter cars with front disc brakes in the 1970s. Today, leading-trailing brakes are used as rear drum brakes on most FWD automobiles, as well as on some light trucks with front discs. In a typical leading-trailing brake installation, the wheel cylinder is mounted at the top of the backing plate, and the cylinder pushrod or shoe links bear against the upper ends of the shoe webs. The lower end of each shoe bears against, or is held onto, an anchor block or anchor post toward the bottom of the backing plate. One or two strong return springs usually hold the lower ends of the shoes against the anchor, and another return spring usually is installed between the upper ends of the shoes to hold them together and hold them against the wheel cylinder pushrod. Various kinds of self-adjusters and parking brake linkage described earlier in this chapter also are installed.

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Chapter 8 Wheel cylinder force

Leading shoe

Trailing shoe

Anchor Front

Figure 8-38  Wheel cylinder force pushes both the leading and trailing shoes against the fixed anchor in a leading-trailing brake.

The wheel cylinder of a leading-trailing brake acts equally on each brake shoe (Figure 8-38). The cylinder forces the top of each shoe outward toward the drum, and each shoe pivots on the anchor at the bottom. Each shoe thus operates separately and independently from the other. The leading shoe develops self-energizing action as described previously, however, and provides most of the braking force. The force of drum rotation works against the wheel cylinder force on the trailing shoe, so the trailing shoe is not self-energizing. The trailing shoe often is said to be nonenergized even though it is technically energized by the wheel cylinder. Because of this operation, the leading shoe wears much faster than the trailing shoe, so during a brake inspection, this situation is not unusual. The front shoe is the leading shoe for forward braking in a leading-trailing brake as described here. For reverse braking, however, the roles are reversed, and the rear shoe becomes the self-energized leading shoe. When comparing a leading-trailing brake to a duo-servo brake described in the next section, it will be understood that a duo-servo brake provides greater braking force. One might then ask why engineers would install a “weaker” brake on an advanced, late-model automobile. Part of the reason is that FWD automobiles generate up to 80 percent of their braking force on the front wheels. Overly powerful duo-servo brakes at the rear could easily cause the rear wheels to lock as weight shifts forward and the rear end becomes very light during braking. Ironically, a more powerful drum brake could reduce overall braking performance. Equally important, antilock brakes make overall brake balance at all four wheels a critical factor. To make brake lockup easier to control while maintaining the best total braking efficiency, engineers have actually had to “detune” the rear drum brakes on some FWD cars. For the sake of brake balance and overall efficiency, leading-trailing brakes will be used on the rear wheels of many vehicles for a long time to come.

Duo-Servo Brakes Operation Just as do leading-trailing brakes, duo-servo brakes have a single, two-piston wheel cylinder mounted toward the top of the backing plate. A return spring holds each shoe

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against the cylinder pushrod. A duo-servo brake is distinguished from a leading-trailing brake by a single anchor post at the top of the backing plate. The top of each shoe web has a semicircular notch, and the return springs hold the notches tightly against the anchor post. The cylinder pushrod acts on the shoes a couple of inches below the anchor. The bottoms of the shoes are not anchored to the backing plate but are joined to each other by the adjuster link. Another spring holds the shoes tightly together and against the adjuster link. Think of the shoes of a duo-servo brake as hanging from the anchor post and floating within the drum at the bottom, and that is the key to their operation. The forward shoe of a duo-servo brake is called the primary shoe, and its lining is shorter than the lining on the rear shoe, which is called the secondary shoe. As the wheel cylinder applies force against both brake shoes during forward braking, the cylinder force pushes the top of the primary shoe away from the anchor. The top edge or leading edge of the primary shoe contacts the rotating drum first and develops self-energizing action just as does the leading shoe of a leading-trailing brake. The self-energized primary shoe is both drawn and forced against the drum, but its lower end does not bear against a fixed anchor. Instead, the lower end of the primary shoe applies servo force to the bottom of the secondary shoe. The secondary shoe then becomes self-energized, with the self-energizing action beginning at the bottom of the shoe. This combined servo and self-energized action actually works against the wheel cylinder, but servo force applied by the primary shoe to the secondary shoe is greater than the hydraulic force of the wheel cylinder alone. Servo force and the self-energizing action of the secondary shoe force its upper end against the anchor post and wrap the shoe tightly into the drum. The secondary shoe—with its longer ­lining—thus applies most of the braking force for forward braking. During reverse braking, the roles of primary and secondary shoes are reversed. The forward shoe with its smaller lining becomes the secondary shoe and receives servo action from the rear shoe. Even though the forward shoe with smaller lining must apply most of the braking force in reverse, it is not a problem because vehicle speed is usually much lower and the vehicle travels a shorter distance in reverse. Braking efficiency remains within safe limits. Duo-servo brakes can apply a lot of braking power very efficiently, but excessive servo action can lead to brake grabbing and locking. Engineers, therefore, must balance several factors to take full advantage of servo power but maintain smooth braking. These factors include lining size on both shoes and placement of the lining on the primary shoe, which can be centered or mounted high or low on the shoe. Primary and secondary linings also can have different coefficients of friction to achieve smooth brake application.

AUTHOR’S NOTE  Duo-servo drum brakes can develop a lot of braking force through combined hydraulic and mechanical actions. From the 1950s through the mid-1960s, duo-servo brakes with large diameter drums, wide linings, and cooling fins to help heat dissipation provided powerful braking for powerful cars. Disc brakes, however, provide even more powerful and efficient braking. By the mid1960s, disc brakes began to replace drum brakes on front wheels and on all four wheels of some high-performance cars. The 1976 revision to FMVSS 105 made disc brakes the most practical designs to achieve the brake system performance requirements. However, duo-servo drum brakes are still used on the rear wheels of older vehicles, particularly RWD cars, trucks, and sport utility vehicles. Today, four-wheel disc brakes are found even on trucks.

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Chapter 8

SUMMARY ■■

■■

■■

■■

■■

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The basic parts of a drum brake are a drum, a hub, brake shoes, a backing plate, a hydraulic wheel ­cylinder, shoe return springs, hold-down springs, an adjusting mechanism, and a parking brake. Rear drums mount on a flange attached to the axle on RWD vehicles. The wheel cylinder has pressurized brake fluid applied to the pistons inside the cylinder. These pistons act on the brake shoes to move them into contact with the brake drum. The wheel cylinder and brake shoes are mounted on a solid backing plate, which is attached to the axle housing or steering knuckle. The brake shoes are a primary (or a leading) shoe and a secondary (or trailing) shoe. Brake linings are primarily made of semi-metallic or synthetic materials that have replaced asbestos materials. Lining materials are attached to the shoes by either bonding or riveting. Brake shoes are held against their anchors and adjusters by springs.

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■■

■■

■■

■■

■■

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Servo brakes are systems in which one brake shoe increases the braking force of the other brake shoe. In a self-energizing brake, the rotation of the drum increases the braking force of the lining against the drum. The force of the brake drum is added to the force supplied by the wheel cylinder. A duo-servo brake is a servo brake in which servo action takes place whether the vehicle is moving forward or backward. A non-servo brake is a brake in which one shoe does not apply a force to the other shoe. In a leading-trailing brake, the leading shoe is ­self-energizing but the other is not self-energizing. Primary shoes and leading shoes face to the front of the vehicle. Secondary shoes and trailing shoes face to the rear of the vehicle. Self-adjusting brakes automatically adjust liningto-drum clearances.

REVIEW QUESTIONS Essay 1. List the components of a typical drum brake assembly. 2. Describe the function of a wheel cylinder. 3. Describe brake gas fade. 4. What are the major advantages to using drum brakes? 5. Since duo-servo brakes supply more braking force than leading-trailing drum brakes, why would engineers use the leading-trailing design? 6. What determines the braking surface area of a drum brake? 7. What is the function of a self-adjuster? 8. What is a self-energizing brake? 9. What is the difference between the braking action of leading-trailing and duo-servo brakes? 10. How are the brake shoes returned to their released position when the brake pedal is released?

Fill in the Blanks 1. _______________ are the components that mount the friction material or linings that contact the drums. 2. The hydraulic and friction components are attached to the _______________.

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3. _______________ operation is the action of a drum brake shoe when drum rotation increases the application force of the shoe by wedging it tightly against the drum. 4. The _______________is usually part of the p ­ arking brake strut that is mounted between the two shoes of leading-trailing brakes. 5. A duo-servo brake is distinguished from a ­leading-trailing brake by a single anchor post at the _______________ of the backing plate. 6. _______________brakes, also called partial-servo or non-servo brakes. 7. Duo-servo brakes commonly have self-adjusters operated by the _______________ shoe. 8. Cam-type adjusters use cams with an _______________ pin that fits in a slot on the shoes. 9. Wheel cylinders convert _______________ ­pressure from the master cylinder to _______________ force that applies the brake shoes. 10. The forward shoe of a duo-servo brake is called the _______________shoe.

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Drum Brakes

Multiple Choice 1. Technician A says that for the same brake pedal force, duo-servo brakes apply a greater braking force than leading-trailing-shoe brakes. Technician B says that the servo action of the duo-servo brakes takes place only when the car is moving forward. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 2. Technician A says that the leading shoe lining receives the greatest wear on a leadingtrailing shoe brake. Technician B says that leading-trailing brakes are non-servo brakes. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 3. Technician A says that some leading-trailingshoe brakes with an adjustable parking brake self-adjust when the service brakes are applied. Technician B says that some brakes with an adjustable parking brake strut self-adjust when the parking brake is applied. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 4. Technician A says that on a duo-servo brake, the force applied by the drum to the primary shoe aids the force applied by the wheel ­c ylinder. Technician B says that on a leadingtrailing brake, the force applied by the drum to the primary shoe opposes the force applied by the wheel cylinder. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. Two technicians are discussing automatic brake adjusters. Technician A says that self-adjusting brakes were first used in 1947 by Studebaker. Technician B says that self-adjusting brakes were used on all domestic drum brakes in 1963. Who is correct? A. A only B. B only

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C. Both A and B D. Neither A nor B

209

6. Technician A says that rear brake drums are usually separate assemblies from the rear hubs. Technician B says that Tinnerman nuts at the wheel studs hold the drum onto many rear hubs. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 7. While discussing a typical leading-trailing brake installation, Technician A says the wheel cylinder is mounted at the top of the backing plate, and the cylinder pushrod or shoe links bear against the upper ends of the shoe webs. Technician B says the lower end of each shoe bears against, or is held onto, an anchor block or anchor post toward the bottom of the backing plate. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 8. Technician A says that most self-adjusters are the same for both sides of the vehicle. Technician B says that some technicians service one side of the vehicle at a time and use the other side as a reference while assembling drum brake assemblies. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 9. Technician A says on leading-trailing brakes, the lining on the leading and trailing shoes are usually the same length and positioned in the same location on each shoe. Technician B says on duoservo brake, however, the primary shoe lining is shorter than the secondary lining and may even have a different coefficient of friction. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 10. Technician A says that self-adjusters perform liningto-drum adjustments without driver intervention. Technician B says that self-adjusting duo-servo brakes occur when the vehicle is moving forward and the brakes are applied. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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Chapter 9

Parking Brakes

Upon completion and review of this chapter, you should be able to: ■■ ■■ ■■

Explain the function of parking brakes. Identify the basic types of parking brake systems. Identify types of parking brake controls.

■■ ■■ ■■

Identify the types of cables used to operate the parking brakes. Identify and explain the operation of disc brake and drum brake parking brakes. Explain the operation of electric p ­ arking brakes.

Terms To Know Ball-and-ramp Conduit Eccentric

Equalizer Intermediate lever

Parking brake control Screw-and-nut

INTRODUCTION After the service brakes stop the moving car, the parking brakes hold it stationary. Parking brakes are often mistakenly called “emergency” brakes, but parking brakes are not intended to be used as an alternative to the service brakes to stop vehicles. The stopping power available from parking brakes is much less than from service brakes. Because the parking brakes work only on two wheels or on the driveline, much less friction surface is available for braking energy. Also, since the hydraulic system has two circuits, total hydraulic failure should be a very rare occurrence.

PARKING BRAKE OPERATION Many vehicles have a “press-to-release” feature on the parking brakes. To release the parking brakes, pressure (force) is applied to the parking brake pedal. This releases the locking ratchet and allows the pedal to return to the off or up position.

The parking brake system is not a part of the hydraulic braking system. It is either mechanically operated by cables and levers to apply the rear brakes, or it can be operated mechanically or by its own hydraulic system to activate a drum brake on the transmission or drive shaft. Most parking brake systems use the service brake shoes or disc pads. Some heavy-duty trucks use a separate set of shoes or pads, such as transmission or drive shaft parking brakes, which are called independent parking brakes. These brakes actually lock the drive shaft in place to keep the vehicle from rolling. Parking brake actuators may be operated either by hand, foot, or electronically. Many small- and medium-size vehicles use a hand-operated parking brake lever mounted in the console between the front seats (Figure 9-1). When the lever is pulled up, the parking brakes are applied. A ratchet-and-pawl mechanism acts to keep the brake lever applied. To release the lever and the brakes, a button on the lever is pressed and the lever is moved

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Parking lever

211

Cables to wheels

Equalizer

Front cable Warning lamp switch (may be mounted under or to side of lever)

Figure 9-1  A typical lever-operated parking brake control.

to unlock the ratchet. Many late-model vehicles use an electronically actuated parking brake system, where an electric motor is used to apply the cables with the push of a button. The electrically applied parking brake can also be released at the touch of a button or when the vehicle is taken out of the park mode. Some medium trucks and mobile construction equipment use the hydraulic service brakes as the parking brakes. With the vehicle/equipment stopped and the service brakes applied, an electric solenoid is activated. The solenoid closes the hydraulic lines between the wheels and master cylinders, effectively locking all wheels. The service brake pedal can be released until it is time to unlock the wheels. Figure 9-2 shows a typical foot-operated pedal with a ratchet and pawl. Stepping on the pedal applies the brakes and engages the ratchet and pawl. A release handle and rod or cable is attached to the ratchet release lever. When the release handle is pulled, the pawl is lifted off the ratchet to release the brakes. Some vehicles engage and disengage the parking brakes with a switch (Figure 9-3). These parking brakes are applied by an electric motor (Figure 9-4) or the parking brakes Brake release mechanism

Electric switch

Release handle

Front cable assembly

Figure 9-2  A typical foot-operated parking brake with a mechanical release handle.

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Figure 9-3  Parking brakes are applied and released electronically on many vehicles.

Figure 9-4  An electric parking brake actuator can be used to apply the parking brake cable.

disengage whenever the vehicle starts to move. Some electronic parking brakes can be utilized as a “hill hold” feature for use in vehicles with a manual transmission, or some are equipped with an autostop feature that applies and holds the vehicle whenever it comes to a complete stop and releases as soon as the accelerator is reapplied. This chapter explains the most common types of parking brake levers, handles, cables, and other linkage parts as well as warning lamps and switches. The final sections of this chapter describe typical drum, disc, and drive shaft parking brake assemblies and their operation.

PARKING BRAKE CONTROLS—LEVERS AND PEDALS

Shop Manual page 435

The parking brake on many late-model vehicles is applied and released electrically by a parking brake actuator (Figure 9-4). Many older and a few current vehicles have a handle under the instrument panel that is pulled to release the parking brake (Figure 9-5). Aside from the operation of the parking brake control the linkage for most parking brakes remains the same.

Instrument panel

Parking brake handle

Figure 9-5  Many vehicles still use a manual release for the parking brake.

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Most parking brakes use the service brake shoes or pads to lock the rear wheels after the vehicle is stationary. The parking brakes can be set most securely if the service brake pedal is pressed and held when the parking brake control lever or pedal is applied. The hydraulic system applies greater force to the shoes or pads than the parking brake mechanical linkage can apply. When the hydraulic system is used to set the brakes, the parking brake linkage simply takes up slack in the system and holds the shoes or pads tightly against the drums or rotors.

Levers The control lever for lever-operated parking brakes usually is installed between the two front seats. As the lever is pulled upward, the ratchet mechanism engages to keep tension on the cables and hold the brakes applied. To release the brakes, the springloaded button in the end of the lever is pressed and held while the lever is lowered to the floor. The lever-operated parking brakes on some Chevrolet Corvettes are examples of a design in which the lever drops back to the floor after the brakes are applied. The cables and linkage hold the brakes applied, but the lever returns to the released position. To actually release the parking brakes, pull up on the lever until some resistance is felt; then press and hold the button in the end of the lever while moving the lever back to the released position. The parking brake control lever on these Corvettes is located between the driver’s seat and the door sill. If the control lever stayed in the upward position with the brakes applied, it would be difficult to climb in and out of the car.

AUTHOR’S NOTE  For those of you who are lucky enough to operate or maintain a right-handed vehicle (steering wheel on right), the parking brake lever will be to the left of the driver and a braking brake pedal under the right side of the dash. Other than that, all other aspects of the parking brake system are the same.

Pedals In a pedal-operated parking brake system, the pedal and its release mechanism are mounted on a bracket under the left end of the instrument panel. As the pedal is pushed downward by the driver’s foot, the ratchet mechanism engages to keep tension on the cables and hold the brakes applied (Figure 9-6). A spring-loaded handle or lever is pulled or the pedal is pressed to release the brakes. A return spring moves the pedal to the released position. A rubber bumper is used to absorb the shock of the released parking brake pedal. If this bumper is missing, the pedal will break the warning light switch after a few operations. FMVSS 105 requires that parking brakes must hold the vehicle stationary for 5 m ­ inutes on a 30 percent grade in both the forward and reverse directions (Figure 9-7). FMVSS 105 also specifies that the force needed to apply the parking brakes cannot exceed 125 pounds for foot-operated brakes or 90 pounds for hand-operated brakes. Some heavy full-size cars built in the late 1970s and early 1980s had trouble meeting the brake-holding requirements without exceeding the allowed maximum application force. Manufacturers solved the problem with a pedal that had a very high leverage ratio but required two or three applications with the foot to set the brakes completely. The first pedal stroke partially applied the brakes, and the ratchet mechanism held the linkage in this position when the pedal was released. The second or third pedal stroke applied the brakes completely. A single pull on the release handle released the brakes.

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Figure 9-6  The pedal ratchet is part of the parking brake pedal assembly.

30 percent grade

Figure 9-7  The parking brake must hold the vehicle on a 30 percent grade for 5 minutes in both the forward and reverse directions.

Automatic Parking Brake Release An automatic parking brake release mechanism is a convenience feature offered by many carmakers. Electric parking brake systems can be released by turning the key on and pressing on the service brake pedal and turning the parking brake off, or by simply putting the vehicle in gear and hitting the accelerator pedal.

WARNING LAMPS

Shop Manual page 435

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On many vehicles, the same warning lamp used to indicate a low fluid level in the master cylinder will also indicate that the parking brake is applied. A normally open switch on the control linkage closes as the pedal is pressed or the lever is pulled. The lamp will not light, however, unless the ignition is on. Parking brake lamp switches are adjusted so that the lamp stays lit until the brake is released completely. In most vehicles, the red brake

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warning light will come on during key on, engine off, even if the fluid is correct and the parking brake is off. This is part of the “lamp check” or “prove out mode” to check the operation of the various warning light systems. The lamp should switch off when the engine is running if everything is correct. In electronic parking brake systems, the parking brake module controls the warning lamp function by providing a message to the instrument panel cluster that the brake has been released.

PARKING BRAKE LINKAGE Parking brake linkage transmits force equally from the control pedal or lever to the shoes or pads at the rear wheels. There are as many different linkage designs as there are different vehicles, but all have the same job and work in basically the same way. The following paragraphs explain the cables, rods, levers, and equalizers or adjusters used in a typical parking brake linkage.

Shop Manual page 438

Cables Most parking brakes use cables to connect the control lever or pedal to the service brakes (Figure 9-8). The cables are constructed of high-strength strands of steel wire that are tightly twisted together. In vehicles with electronic parking brake actuators, an electric motor controls the application of the parking brake cables and, in some cases, the parking brake cable tension. Parking brake cables must transmit hundreds of pounds of force without jamming, breaking, or stretching. The ends of the cables have different kinds of connectors that attach to other parts of the linkage. Some cables have threaded rods or clevises at their ends. Others have ball or thimble-shaped connectors that fit into holes and slots on other parts of the linkage. The front cable connects the parking brake lever or pedal to the equalizer, which provides balanced braking force to each wheel. The equalizer is only a lever mounted on a pivot or a U-shaped grooved guide. Pulling the front cable moves the lever or guide. The lever or guide transmits the force equally to the two wheel cables (Figure 9-9). Some vehicles have a three-part cable installation, which includes an intermediate cable that passes through the equalizer. Typically, one of the two rear cables is attached directly to this intermediate cable with a connector (Figure 9-10). The other rear cable is attached to the intermediate cable with some kind of cable adjuster, usually a turn buckle.

Parking brake cables are made of highstrength strands of steel wire that are tightly twisted together.

The equalizer may be referred to as the parking brake adjuster. In some cases, it is the point at which the parking brake is, in fact, adjusted.

Rear cable Equalizer Front cable Front cable conduit

Adjuster nut Equalizer Mounting clips

Figure 9-8  Typical parking brake cable installation showing an adjusting mechanism.

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Front cable

Figure 9-9  This parking brake equalizer is under the center console.

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Chapter 9 Front cable

Rear cable Hook and rotate down Connector

Figure 9-10  Parking brake cable connector.

A conduit is a flexible metal housing or jacket that houses the parking brake cables to protect them from dirt, rust abrasion, and other damage.

Some lever-operated parking brakes have a separate cable for each rear wheel attached to the control lever. Each cable is adjusted separately, and an equalizer is not necessary. The wheel cables run from each wheel all the way to the pedal or lever mechanism within the passenger compartment. Adjustment of the cables may be made at the pedal or lever. Cable retainers and hooks maintain cable position on the rear axle, frame, and underbody of the vehicle (Figure 9-11). These retainers allow the cable to flex and move at their point of body attachment and help the equalizer to provide its equalizing action. Most control cables and rear brake cables are partially covered with a flexible metal conduit or housing (Figure 9-12). The cable slides inside the conduit and is protected from chaffing or rubbing against the underside of the vehicle. One end of the cable conduit is fastened to a bracket on the underside of the vehicle with some type of retaining clip, and the other end is attached to the brake backing plate (Figure 9-13). Many cables are coated with nylon or plastic, which allows them to slide more easily through the conduit. The coatings help to reduce corrosion and contamination and make parking brake application easier.

AUTHOR’S NOTE  Conduits are common in other systems as well. Check the area around your house or shop, and note the conduits that protect the electrical wiring. Parking brake conduits perform the same protective function for the brake cables.

Rods The most common use of solid steel rods in parking brake linkage is in lever-operated systems to span a short distance in a straight line to an equalizer or intermediate lever. The linkage rod is usually attached to the control lever by a pin. The other end of the rod is often threaded to provide linkage adjustment. This control system has been dropped from typical passenger cars and light trucks.

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Brake release mechanism

Bracket Retainer clips

Spring clip

Figure 9-11  Cable retainers and clips hold the cables in position.

Outer conduit cover

Conduit

Protector

Spring

Adjusting screw

Inner cable

Outer cable

Figure 9-12  Typical cable and conduit.

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Chapter 9 Cable anchor

Rear cable

Cable retainer Brake backing plate

Figure 9-13  A cable retainer secures the conduit to the backing plate.

A BIT OF HISTORY A historic cause of anxiety for novice drivers learning to cope with manual transmissions is learning how to start from a complete stop, going up hill. Many student drivers panic while trying to hold the brake pedal, release the clutch, and apply the throttle at the same time. If only they had a third foot, life would be so much easier. In 1936, the Wagner Electric company patented the NoRol hill holder, which first appeared on Studebaker models of that year. The NoRol hill holder consisted of linkage from the clutch pedal to the brake master cylinder that maintained hydraulic pressure after the brake pedal was released and until the clutch was engaged. Pontiac and Graham also offered versions of the hill holder as optional equipment, and it continued as standard on Studebakers with manual transmissions through 1964. Several later Subaru models had similar automatic hill-holding devices. Now some vehicles with electronic parking brakes have a feature that applies the brakes called auto-hold. Whenever the vehicle comes to a complete stop auto-hold (Figure 9-14) can maintain the vehicle on a hill until the accelerator pedal is applied.

Figure 9-14  An electronic parking brake with an auto-hold feature.

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Levers Chapter 2 of this Classroom Manual explains how levers are used to multiply force in mechanical linkage. Mechanical leverage is necessary in parking brake linkage to make brake application easy for the driver. The parking brake pedals and control levers multiply the force applied by the driver. Many parking brake installations also have an ­intermediate lever under the vehicle body to increase the application force even more. The intermediate lever also is designed to work with the equalizer to ensure that force is applied equally to both rear wheels. Intermediate levers are most common on large cars and trucks that need greater force to apply the parking brakes.

Equalizers and Adjusters Parking brakes that use the service brakes—either shoes or pads—to lock the wheels must apply equal force to each wheel. If application force is unequal, the parking brakes may not hold the vehicle safely. To meet this requirement, most parking brake linkage installations include an equalizer mechanism. The equalizer also usually contains the linkage adjustment point. The simplest example of an equalizer is a U-shaped cable guide attached to a threaded rod. The rear cable (or an intermediate cable) slides back and forth on the guide to balance the force applied to each wheel. In some installations, the equalizer guide is attached to a lever to increase application force. Another kind of equalizer is installed in a long cable that runs from the driver’s position to one rear wheel. A shorter cable runs from the equalizer to the other wheel. When the parking brakes are applied, the long cable applies its brake directly and then continues to move forward after the shoes or pads lock the wheel. The continued forward motion pulls the equalizer and the shorter cable to lock the brake at the other wheel.

Rear Drum Parking Brakes Rear drum parking brakes that use the rear service brakes to lock the wheels are a common kind of parking brake system. Mechanical linkage that works with drum brake shoes is a relatively simple and economical design, and the self-energizing action of the brake shoes provides excellent holding power. Figure 9-15 shows a typical parking brake installation with rear drum brakes. The brake cable runs through a conduit that goes through the backing plate. The cable end is attached to the lower end of the parking brake lever. The parking brake lever is hinged at the top of the web of the secondary or trailing shoe and connects to the primary or leading

Front

Figure 9-15  A parking brake is applied by a lever working on the trailing or secondary shoe, depending on the system.

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Chapter 9 2. Lever moves link against primary shoe and shoe against drum.

3. Lever works against link, and pivot forces secondary shoe against the drum.

Spring

1. Cable pulls lever.

Conduit

Figure 9-16  Parking brake lever and strut operation.

The parking brake strut connects the primary shoe to the secondary shoe.

shoe through a strut. When activated, the lever and strut move the shoes away from both the anchor points and into contact with the brake drum (Figure 9-16). When tension on the cable is released, the return springs move the shoes back to their unapplied positions. The details of parking brake parts vary with different brake designs, but all work in the same way basically. Many parking brakes include various springs and clips to prevent rattles and to hold the parts in alignment.

ELECTRICAL PARKING BRAKE SYSTEMS As discussed earlier, true electric parking brakes are being introduced today. The first is an extension of the ABS and active brake systems. When parking, the driver can switch on the parking brakes, and the hydraulic modulator applies fluid pressure to at least the rear wheels. The switch can also be activated by the movement of the transmission shift mechanism into park. Some of the most recent electric parking brakes are available from Continental Teves North American and Siemens. Both manufacturers offer electric parking brake systems that can be found on many top-line luxury and midsize models. Both systems dispense with lever/pedal controls and both will provide some form of emergency braking should the service brakes completely fail. The Continental Teves system uses an electrical motor or solenoid that moves cables running to the rear wheels (Figure 9-17). It is designed for drum-in-hat or disc caliper parking brakes. The system is an active parking brake that can be integrated into an electronic stability program (ESP) with appropriate interfaces. The system offers the advantages of automatically locking in park, releasing when engaging a drive gear, reducing or preventing rollback on slopes, increasing theft deterrent, and assisting in parking if integrated with a distance sensor system. One version of the parking brake system has an electric mechanism at each rear wheel caliper that applies the rear disc brake when activated (Figure 9-18). The two mechanisms are mounted just inside of the rear calipers (Figure 9-19). The manual switch to activate and deactivate the system is mounted near the transmission’s console shift lever or at a central point on the dash. An electrical signal can be mounted to sense transmission shift lever movement and engage/disengage the parking brake accordingly.

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Electrical connector

Parking brake cable

Drum-type brake shoes Electric motor assembly

Electric motor

Disc caliper

Figure 9-17  This electric motor assembly pulls on the cables to apply the parking brakes.

Figure 9-18  This parking brake is applied by an electric motor and cam operating directly on the caliper.

Electric motor assembly Disc caliper

Figure 9-19  The electric motors are connected to the caliper and its adapter.

REAR DISC PARKING BRAKES Two different types of parking brakes are used with rear disc brakes: auxiliary drum parking brakes and integral caliper-actuated parking brakes. Both are more complicated designs than parking brakes that are part of rear drum service brakes.

Shop Manual pages 443

Auxiliary Drum Parking Brakes Many sliding caliper rear disc brakes have a small drum cast into each rotor (Figure 9-20). A pair of small brake shoes is mounted on a backing plate that is bolted to the axle housing or the hub carrier. These parking brake shoes operate independently from the service brakes. They are applied by linkage and cables from the control pedal or lever. The cable at each wheel operates a lever and strut that apply the shoes in the same way that standard rear drum parking brakes work. These auxiliary drum parking brakes must be adjusted manually with star wheels that are accessible through the backing plate or through the outboard surface of the drum. They do not have self-adjusters.

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These types of auxiliary parking brakes are sometimes called drum-in-hat parking brakes.

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Chapter 9 Parking brake shoes

Caliper

Rotor with internal parking brake drum

Rear axle

Figure 9-20  An auxiliary parking brake installation for rear disc brakes.

Assuming that the driver does not drive with the parking brakes applied, the parking brake shoes within the drum will last the life of the car. However, they may get corroded over a period and should be checked when servicing the rear service brakes. Screw-and-nut and ball-and-ramp are two different calipers with integral parking brake mechanisms. See ­figures 9-21 and 9-22 on the page 223. Eccentric means not round or concentric.

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Integral (Caliper-Actuated) Parking Brakes Some floating or sliding caliper rear disc brakes have components that mechanically apply the caliper piston to lock the pads against the rotors for parking. These parking brake mechanisms are termed integral because the parking brake mechanism is part of the caliper. All caliper-actuated parking brakes have a lever that protrudes from the inboard side of the caliper. The caliper levers are operated by linkage and cables from the control pedal or lever. As with most brake assemblies and subassemblies, detail differences exist from one brake design to another. The two most common kinds of caliper-actuated parking brakes are the screw-and-nut type and the ball-and-ramp type. A few imported cars have a third kind that uses an eccentric shaft and a rod to apply the caliper piston. This type is not as common as the first two, however. An eccentric acts like a cam. One portion of the shaft is oval shaped. As the shaft turns, the high part of the oval pushes the operating rod out of applying the brakes. Screw-and-Nut Operation.  General Motors’ floating caliper rear disc brakes are the most common example of the screw-and-nut parking brake mechanism (Figure 9-21). The caliper lever is attached to an actuator screw inside the caliper that is threaded into a large nut. The nut, in turn, is splined to the inside of a large cone that fits inside the caliper piston. When the parking brake is applied, the caliper lever rotates the actuator screw. Because the nut is splined to the inside of the cone, it cannot rotate so it forces the cone outward against the inside of the piston. Movement of the nut and cone forces the piston outward. Similarly, the piston cannot rotate because it is keyed to the brake pad, which is fixed in the caliper. The piston then applies the inboard brake pad, and the caliper slides as it does for service brake operation and forces the outboard pad against the rotor. An adjuster spring inside the nut and cone rotates the nut outward when the parking brakes are released to provide self-adjustment. Rotation of the nut takes up clearance as the brake pads wear.

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Piston seal Cone

Piston

Screw

Outboard brake pad

Rotor

Parking brake lever

Inboard brake pad Internal thread nut

Figure 9-21  A GM screw-and-nut parking brake mechanism for rear disc brakes.

Ball-and-Ramp Operation.  Ford’s floating caliper rear disc brakes are the most common example of the ball-and-ramp parking brake mechanism (Figure 9-22). The caliper lever is attached to a shaft inside the caliper that has a small plate on the other end. Another plate is attached to a thrust screw inside the caliper piston. The two plates face each other, and three steel balls separate them. When the parking brake is applied, the caliper lever rotates the shaft and plate. Ramps in the surface of the plate force the balls outward against similar ramps in the other plate. As the plates move farther apart, the thrust screw forces the piston outward. The thrust screw cannot

Caliper housing

Operating shaft

Operating lever

Balls

Automatic adjuster

Piston

Figure 9-22  A Ford ball-and-ramp parking brake mechanism for rear disc brakes.

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rotate because it is keyed to the caliper. The piston then applies the inboard brake pad, and the caliper slides as it does for service brake operation and forces the outboard pad against the rotor.  When the caliper piston moves away from the thrust screw, an adjuster nut inside the piston rotates on the screw to take up clearance and provide self-adjustment. A drive ring on the nut keeps it from rotating backward. It should be noted that each of these systems are still in use by other vehicle manufacturers in addition to General Motors and Ford.

SUMMARY ■■

■■

■■

■■

The parking brake prevents the vehicle from moving when parked. Parking brakes may be operated by electronically controlled electric motor or either hand lever or foot pedal. The release mechanism may be either a manual release or an automatic release using an electrical switch or when the vehicle begins moving on electronic parking brakes. Electronically operated parking brakes are released when the vehicle is taken out of park. Equalizers are used to balance the forces applied to the parking brakes during application.

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■■

■■

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Equalizer levers are used to multiply the effort of the driver applying the parking brakes. Rear drum brakes use a lever and strut to move the shoes into contact with the drum. Electric parking brakes may operate conventional parking cables or directly apply the rear disc brakes. Integral disc parking brakes use the normal disc calipers as parking brakes to hold the vehicle while it is parked. Auxiliary drum parking brakes are contained inside the rotor of some rear disc brakes.

REVIEW QUESTIONS Short-Answer Essays 1. Explain the purpose of a parking brake. 2. Describe why a parking brake should not be used as an “emergency” brake. 3. How do the levers connected to equalizers on some brake systems multiply the driver’s application effort? 4. What is the function of an equalizer in a parking brake system? 5. What is the construction of a parking brake cable? 6. Why are some parking brake cables plastic coated? 7. How are integral disc parking brakes applied? 8. Describe how the rear drum brakes are applied to hold the vehicle when it is parked.

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9. Describe how the internal-expanding shoe transmission-type brake works. 10. How are rods used in some parking brake assemblies?

Fill in the Blanks 1. The parking brake system is not a part of the _______________braking system. 2. Parking brake actuators may be operated either by _______________, _______________, or _______________. 3. The front cable connects the parking brake lever or pedal to the _______________, which provides balanced braking force to each wheel. 4. The two most common kinds of caliper-actuated parking brakes are the _______________ type and the _______________ type.

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Parking Brakes

5. The parking brake _______________ is hinged at the top of the web of the secondary or trailing shoe. 6. The parking brake_______________ connects the primary shoe to the secondary shoe. 7. Ford’s floating caliper rear disc brakes are the most common example of the _______________ and _______________parking brake mechanism. 8. General Motors’ floating caliper rear disc brakes are the most common example of the _______________and _______________ parking brake mechanism. 9. Two different types of parking brakes are used with rear disc brakes: auxiliary _______________ parking brakes and integral _______________ _______________ parking brakes.

Multiple Choice 1. Technician A says that the parking brakes are provided with equal cable tension by the cable adjusters. Technician B says that the parking brakes are provided with equal cable tension by the equalizer. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 2. Technician A says that the parking brakes are mechanically operated because mechanical brakes are much more effective than hydraulic brakes. Technician B says that parking brakes are mechanical because the parking brakes must operate separately from the service brakes. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 3. Technician A says that the usual device that releases the parking brakes whenever the transmission gear selector is in drive or reverse is an electronic parking brake controller. Technician B says that the device that releases the parking brakes can be a lever controlled by the driver. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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4. While discussing FMVSS 105, Technician A says it requires that parking brakes hold the vehicle stationary for 15 minutes on a 30 percent grade in both the forward and reverse directions. Technician B says FMVSS 105 also specifies that the force needed to apply the parking brakes cannot exceed 200 pounds for footoperated brakes or 190 pounds for hand-operated brakes. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. Technician A says that some electric parking brakes use a special feature called auto-hold. Technician B says that some electric parking brakes may be applied by moving the vehicle. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 6. Technician A says that a nut-and-screw type ­caliper assembly forces the disc pads against the rotor in a rear disc parking brake system. Technician B says that a ball-and-ramp type ­caliper assembly forces the disc pads against the rotor in a rear disc parking brake system. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 7. Which of the following applies the rear caliper by cables for parking? C. Lever control A. Continental Teves B. Pedal control D. All of the above 8. Technician A says that another name for a rear (drum-in-hat) parking brake is auxiliary drum brake. Technician B says that another name for a rear (drum-in-hat) parking brake is integral brake. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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9. Technician A says that it is important to remember that the parking brake is not part of the vehicle hydraulic brake system. Technician B says that it is important to remember that the parking brake is applied mechanically. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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10. While discussing console mounted emergency brakes, Technician A says some lever-operated parking brakes have a separate cable for each rear wheel attached to the control lever. Technician B says each cable is adjusted separately, and an equalizer is not necessary. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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Chapter 10

Electrical Braking Systems

Upon completion of this chapter, you should be able to: ■■

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Define and understand the electronic terms commonly associated with ­electrical braking systems. Identify the components of a typical ABS.

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Explain the operation of a typical ABS. Describe the differences between integrated and non-integrated ABS systems. Discuss the general operation of Bosch 9.0 ABS.

Terms To Know CAN protocol Class 2 protocol Controller antilock brake (CAB) module Dynamic rear proportioning (DRP) Electrohydraulic unit

Electronic brake control module (EBCM) Electronic brake traction control module (EBTCM) Enhanced traction system (ETS) Flux lines

Isolation/dump valve Negative wheel slip Permanent magnet (PM) generator Reluctor

INTRODUCTION Although 1987 was not the first year when antilock brake systems (ABSs) were used, it was the first year when they were installed on all light trucks and small vans. The systems were first used to reduce rear-wheel lockup during hard braking. The types of vehicles noted were the ones that were most likely to lock the rear wheels during braking. Since then rear-wheel antilock systems have evolved to today’s initial offering of full electrical braking systems. Certain technical terms and components from ABSs have been incorporated into the newer systems and are discussed in the first section.

COMMON COMPONENTS AND TERMS Sensors Sensors are electrical devices that measure some physical action and change that action to an electrical signal (Figure 10-1). They also are used to measure electrical voltage or frequency. Common actions measured by sensors are mechanical movement, temperature, pressure, and speed. Most sensors are simple to operate although the engineering design may be complex. The simplest are on–off switches, whereas others are actually small electrical generators, or digital signal generators.

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Figure 10-1  The throttle position sensor (TPS) is mounted to the side of the throttle body. As the throttle valve is moved by the accelerator cable, a wiper arm inside the TPS moves over a variable resister wire. This changes the input 5-volt signal to a return signal between 0.5 volt and 4.5 volts.

A BIT OF HISTORY Ford Motor Company was the first U.S. carmaker to experiment with ABSs on a production car when it offered an antiskid option on the 1954 Lincoln Continental Mark II. It worked—sort of—but added too much weight to the car and cost too much, so it wound up in the technological trash can.

Wheel Speed Signals

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Signals refer to the electrical signal sent from the sensor to the controller. They may be analog or digital (Figure 10-2). Digital signals are more consistent because they have the same amplitude (voltage level) regardless of wheel speed. With digital signals, only the frequency changes, and the digital wheel speed sensors are accurate all the way down to a stopped wheel. An analog voltage signal is infinitely variable; in other words, it flows smoothly as it changes voltage levels. The wheel speed signal is compared to the ones from different wheels, and the electronic brake control module determines which wheel is about to lock up or skid; the slower the wheel, the lower the frequency produced. The frequency of the signal is still being measured because the signal is changed from analog to digital by the EBCM (electronic brake control module), but the voltage level of the signal (amplitude) varies greatly based on the wheel speed. At low speeds, the signal may not be readable. The digital signal could be on or off, high or low, or yes or no. For simplicity in this discussion, the signal is either on or off. Digital signals can differ in the amount of on or off time and the rapidity of repeating signals over time, known as frequency. (Figure 10-3). A slow wheel as monitored by the wheel speed sensor will produce a low-frequency signal, whereas a faster wheel will cause a comparatively higher frequency, In this case, the computer can compare wheel speeds between individual wheels and determine if one wheel or wheels is slowing down faster than the others, compared to vehicle speed. The hydraulic modulator can then determine the proper command, if any, to be issued to the hydraulic modulator. Digital wheel speed sensors (WSSs) are now used on most vehicles.

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AC voltage signal +12 V

0

−12 V One cycle

Digital signal +12 V

0 One cycle

0

−12 V One cycle

Figure 10-2  An analog signal switches from positive to negative to positive. A digital signal is usually positive or negative, but not both.

One cycle

ON

+12 V

OFF

0 Number of cycles within a given time frame = frequency

Figure 10-3  This signal indicates the amount of time on versus time off.

Actuators Actuators are the workhorse of electrical/electronic systems. Actuators convert electrical energy into mechanical movement. They perform some action based on commands from their controllers, and many are based on duty cycle. Different levels of activity (duty-cycle) can be based on the percentage of “on” time verses “off” time. Actuators are usually motors or solenoids. Some of the most common actuators are cooling fans, fuel injectors, and transmission shift solenoids (Figure 10-4). In most cases, the controller can determine if the actuator is electrically and mechanically active by measuring the current flowing through that circuit. If the current is too high or too low, the controller may disable the actuator and/ or illuminate a light in the dash.

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Figure 10-4  A fuel injector is a solenoid that will allow a specific amount of fuel to flow when commanded to open.

Controller A controller is a computer programmed to perform certain decisions based on sensor signals and to issue electrical commands to actuators (see Figure 10-4). Controllers are simple computers compared to the ones at work or school that can use multiple programs to perform different tasks. The automotive computer works within its own programmed parameters to control the engine, transmission, climate control, and other systems. Data are shared with other onboard computers to reduce the number of sensors and actuators needed to control multiple vehicle systems.

Automotive Networking Consider networking to be a small Internet on the vehicle (Figure 10-5). Each computer has access to all data, but an individual computer will use only the data pertinent to its programming. The most common and most powerful controllers are the engine control module (ECM), the body control module (BCM), and the transmission control module (TCM). They control many smaller computer modules that have an even more specific function, such as adjusting the blower speed on an automatic climate control. There may be over 50 different controllers on a single vehicle, all networked. AUTHOR’s NOTE  The advantage of networking is the elimination of redundant sensors and the accompanying wiring. An example of this is that several years ago, vehicles had a temperature sensor to control the engine cooling fan, a temperature sensor for the warning lamp in the instrument cluster, and finally, a temperature sensor for the ECM. Now, the engine coolant temperature (ECT) for the ECM takes care of all three. The coolant temperature sensor information is shared among modules as necessary. The ECM controls the cooling fan directly, and the instrument cluster is provided temperature readings directly over the vehicle network.

Hydraulic Modulator The hydraulic modulator is the electrical/hydraulic unit used on ABS, traction control system (TCS), and other braking systems to control hydraulic braking pressure to one or more wheels (Figure 10-6). The hydraulic modulator can hold or release pressure for ABS action, or increase, hold, or decrease pressure for traction and stability control. The hydraulic modulator is sometimes called the electrohydraulic modulator because the EBCM is often attached to the unit.

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G101 HS CAN +

B Module communications network

VDB04 7 3 4

5 6

Data link connector (DLC)

A 11 13

14 16

8

VDB05

Smart junction box F4 (50A) Battery junction box F3 (50A)

Powertrain control (PCM) module To B+

Instrument cluster

HS CAN –

2

44

C220

6

18

17

2

1

C199

C310B

C281B

Transmission assembly

Restraints control module

Four-wheeldrive control module

23

11

12

13

C175B

C155

Powertrain control (PCM) module

ABS control module

18

9 C3159

Occupant classification sensor (OCS)

Figure 10-5  Note the different modules connected in this wiring diagram. Also note the CAN1 and CAN2 shown on most modules. This is a controlled area network (CAN).

Figure 10-6  A typical ABS hydraulic control modulator.

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Commands Commands are nothing more than an electrical signal or output signal to an actuator. A command from a module can be performed by completing a power circuit, a ground circuit or both power and ground to an actuator. When the circuit is complete, the actuator can then function.

ANTILOCK BRAKE SYSTEM AND VEHICLE CONTROL Negative wheel slip means the wheel is locked up and skidding. Skidding wheels have lost traction and can not be steered, so directional stability and control have been lost.

The ABS is not the end-all to safe braking. The system was designed to provide some means of controlling wheel skid or negative wheel slip. If the driver overdrives the road condition or the capability of the vehicle, however, the ABS will not assist much in controlling the vehicle. Assuming the vehicle is operating within road and vehicle limits, the ABS is excellent in directional stability and directional control. Stability is achieved when the vehicle can be stopped in the shortest possible distance without wheel skid, whereas control refers to the fact that the driver can steer the vehicle during a panic or ABS stop. A locked wheel (which is sliding) has little, if any, traction and will not grip the road surface sufficiently for braking or steering. It should also be noted that the ABS will not necessarily stop the vehicle quicker than standard brake systems. AUTHOR’s NOTE  One thing I have learned is that you cannot steer a vehicle if the front wheels are sliding. I missed a turn one day, many years ago, and slammed on the brakes of a 1969 VW Fastback. The front wheels locked, and I steered to the right. The car continued to go straight ahead. I realized I was going to miss the turn anyway so I released the brakes. The wheels stopped sliding and the car immediately went into a hard right turn—I missed the turn and aged 10 years in less than 5 seconds. This experience has stayed with me for over 40 years: Do not try to steer the vehicle if the front wheels are locked and sliding. The ABS reduces this possible problem to almost zero.

ABS TYPES AND GENERAL OPERATIONS

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Basically, the ABS controller is monitoring all four wheel speeds while driving. When the ABS senses a wheel slowing faster than the other wheels, the hydraulic modulator (Figure 10-7) goes into “isolation” mode. In isolation mode, brake pressure is isolated from the master cylinder even if the driver applies more pressure to the affected wheel. If the wheel continues to slow down faster than the other wheels, and the ABS goes into a “pressure release” or “dump” and the fluid is returned back to the reservoir, or in some systems a low-pressure reservoir. If the wheel speed gets back into line with the speeds of the other wheels, then the pressure is allowed build up again from the master cylinder. This process can happen several times per second. This action also causes the pedal to click and drop when the ABS is active and is entirely normal. The commands are based on the signals from the WSSs, and the commands are to the hydraulic modulator. With all newer vehicles since the advent of stability control (and a few before) the ABS will be able to control all four wheels individually. This wasn’t always the case, as many of the earlier systems controlled either the rear wheels only as an axle set, meaning if one wheel locked up, both wheels were treated the same way. Later, we had three-channel systems that controlled the rear wheels as an axle set but the front wheels individually. Finally, we saw four-channel systems, in which all four wheels were controlled individually. We really needed to have four channels to implement vehicle stability control.

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Controller Valves

ICU

Figure 10-7  A hydraulic modulator showing the ABS control valves.

Integrated and Nonintegrated ABS There were two major types of earlier ABS braking systems: integrated and nonintegrated. The integrated systems have a hydraulic brake booster, a master cylinder, and an ABS computer referred to as an EBCM all built into one unit. For the most part, these units had very few serviceable parts (Figure 10-8). This led to some problems with the earlier versions. The earlier ABS modulators went through some growing pains that are typical of new systems, but these were particularly painful to some vehicle owners. Some modulator/ master cylinder units cost as much as $3,000. Because this is an integrated unit with few, if any, parts serviced separately, any failure required the owner to spend a large amount of money to fix the vehicle properly. The nonintegrated system was also called an “add-on” system, because it used a conventional vacuum booster and basic brake system with a separate hydraulic modulator. The nonintegrated ABS system was a benefit to all concerned, from the manufacturer to Cap and connector Fluid reservoir

Solenoid valve connector Solenoid valve block Pressure warning switch

Figure 10-8  An integrated ABS combines the master cylinder, brake booster, and ABS components in a single unit.

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the technician and especially the vehicle owner. The hydraulic modulator was separated from the master cylinder and usually was installed just below the master cylinder or somewhere on the left side of the engine compartment. This left the master cylinder as a separate unit that could be replaced alone. The cost of separating the two was nominal because the biggest cost was in engineering and a few extra feet of brake tubing and wires. The overall efficiency of the system was not affected.

Rear-Wheel ABS (RWAL or RABS) One of the most difficult vehicles to design a braking system for was the light truck. A manufacturer had no way of knowing how or even if the vehicle would be loaded. The first attempts at a solution was the height-sensing proportioning valve, followed by rear wheel antilock braking. This was the first true mass-production ABS installed on vehicles. The RWAL/RABS system was first installed on minivans and pickup trucks in late 1987. RWAL means rear-wheel antilock and is the most common term used by most manufacturers. RABS means rear antilock brake system and is the term commonly used by older Fords and some other manufacturers. The system essentially controls wheel skid only on the rear wheels. Usually the speed sensor was located on the differential housing and measured the speed of the differential ring gear.

Four-Wheel ABS After the rear-wheel ABS was developed, it was quickly followed by four-wheel ABS. It can control the braking effect at each wheel through one of two systems: three-channel and four-channel. The three-channel was the first four-wheel ABS system. In the threechannel system, the rear-wheel brakes are controlled as one, but the two front wheels were controlled independently of each other. For example, if the right rear wheel started to skid, the ABS would reduce the brake pressure to both rear wheels. To do this requires three WSSs and a larger, more sophisticated hydraulic modulator. Each front wheel has a speed sensor, whereas another is placed to measure the rear wheels. The hydraulic modulator basically has three “isolation/dump” valves in a single unit (see Figure 10-9). The basic principle of operation remained the same, but the different components improved drastically in design and serviceability. The controller’s programming was increased to handle the additional workload and to effectively control the hydraulic module. The three-­channel system works best with front disc and rear drum brake systems. This is mainly because the speed of release or application of drum brakes is a little slower than disc brakes. The four-channel ABS works along the same lines as the three-channel, but all four wheels have a speed sensor with dedicated valves for each wheel. The hydraulic modulator is a full-fledged hydraulic unit housing four or more valves commanded by a stronger controller and usually with the controller integrated into the modulator. The time span for development between the first RWAL/RABS and the four-channel system allowed for better programming, better manufacturing, better materials, and a better fit into the service brake’s hydraulic system. The four-channel works best with four-wheel disc but will work satisfactorily with a disc/drum combination. Its best feature is its adaptability to TCSs and braking systems.

ABS BRANDS ABS components are not manufactured by automotive manufacturers. They are designed and built for a specific vehicle line, but all function in much the same manner. Two of the different brands are discussed later. The primary manufacturers of ABSs are Bosch (and Delco-Bosch), Continental Teves, Kelsey-Hayes, Delphi Chassis, Bendix, Nippondenso, Nissan, and Sumitomo.

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Figure 10-9  This early rear wheel antilock is an example of a separate isolation/dump valve.

ABS COMPONENTS ABS components are additions to the standard braking hydraulic/mechanical components covered in earlier chapters. Common components are the controller, hydraulic modulator, WSSs, and brake switch.

Shop Manual page 493

Controllers The antilock controller or microprocessor is the computer for the ABS. It is commonly referred to as the electronic brake control module (EBCM) although different manufacturers use different names. Controller antilock brakes (CAB) module is another common term for ABS controllers. If the controller is built into or attached to the hydraulic modulator, then the whole assembly is known as the integrated control unit (ICU), or an electrohydraulic modulator or electrohydraulic unit. All controllers do basically the same thing: receive input signals, process the signals, store the signals for possible use later, and issue output commands. Most automotive computers, including the EBCM, are programmed with an adaptive memory capability or learning mode. This seems to mean that the computer can “learn,” but that is not exactly true because computers do not have the ability to learn. Computers can process signals and determine exactly how this particular sensor or actuator, including the vehicle driver, responds to different conditions, however. This “learning” can be done only within the program parameters. For instance, if a new WSS is installed, the computer will determine the limits of the sensor. The new sensor’s high/low signals may be a little (tenths of a volt) different from the old one. If the new signals are within set limits, the computer can accept them as the norm for that sensor. If not, then the computer activates the ABS warning light on the dash and disables the ABS entirely.

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Anti-lock brake controllers are known as electronic brake control module (EBCM) or controller anti-lock brake (CAB). If the hydraulic modulator has the controller attached, then the unit may be called integrated control unit (ICU) or electrohydraulic modulator.

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Incorporating the EBCM with the hydraulic modulator helps to eliminate unnecessary external wiring and connections which helps build more reliability into the unit. As mentioned before, input signals may be analog or digital. Analog signals are produced by small AC electrical generators called permanent magnet (PM) ­g enerators. The most common ones on a vehicle are the WSS and vehicle speed ­sensor (VSS).

Wheel Sensors

Flux lines are the magnetic force that ­surrounds a magnet. The reluctor is the metal-toothed ring used to influence the ­magnetic flux lines of the PM generator.

The PM wheel speed sensor (also called a magnetic reluctance sensor) is composed of an ALNICO permanent magnet and a coil of copper wire. ALNICO is an abbreviation for the aluminum, nickel, and cobalt elements used in the metal alloy (Figure 10-10). The ALNICO magnet is very stable; that is, it loses only a very small percentage of its strength each year. This characteristic makes the ALNICO magnet ideally suited for its use in the wheel sensor because of its longevity. A metal-toothed ring (tone ring or tone wheel) is placed in proximity to the permanent magnet and coil. One of the metal teeth on this ring attracts the magnetic lines of force of the magnet. These magnetic lines of force are called flux lines. The flux lines must pass across the copper wires in the coil as they are attracted to the metal tooth of the reluctor. The principle of magnetic induction states that whenever a magnetic flux line crosses a conductive wire, it induces voltage in that wire. When that wire is in an electrical circuit, it generates an AC electrical current, which is termed an analog signal. The tooth rotates and aligns the valley between the teeth with the magnet. The distance between the metal of the reluctor and the permanent magnet is great enough to allow the flux lines to return to their original location. The flux lines reverse themselves as the magnetic pull weakens; as they travel in the reverse direction across the copper wire, they induce voltage once more. However, this time the voltage induced by the flux lines is the opposite of the initial induced voltage. Movement of the flux lines between the permanent magnet and the reluctor produces an AC voltage for use by the ABS (Figure 10-11). The PM generator circuit was designed to self-test at power on self-test (POST). The technician needs to understand how this circuit works in case a wheel sensor code is stored in the diagnostic program of the microprocessor. Service technicians who do not understand the circuit are likely to start yanking expensive components, such as the microprocessor, the wiring, and the sensor, or, in a worst-case scenario, all three, and

Induction coil

Reluctor

ALNICO permanent magnet

Figure 10-10  PM generator.

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Half wave

237

= Full wave

Half wave

Figure 10-11  Wheel sensor output.

replacing these perfectly good components with identical parts. This is both expensive for the customer and labor intensive for the service technician. The microprocessor has a regulated power supply that produces a stable direct current (DC) voltage. The voltage signal is usually 1.5 volts. That voltage begins its journey at the power supply inside the microprocessor and travels through an electronic circuit board until it arrives at an R1 fixed-value resistor. The R1 resistor value is usually 10,000 ohms. The current flow continues its forward movement from the microprocessor until it arrives at the PM generator. The resistance of the coil in the PM generator is usually 1,000 ohms. The current returns to the microprocessor power supply through the return wiring and electronic circuit board. This completes the series circuit. A typical ABS wheel speed ­sensor circuit is illustrated in Figure 10-12. Anything that consumes electricity (voltage) is called a load. Voltage drops occur across each resistance in a series circuit. The resistance may be a coil of wire or it may be a carbon fixed-value resistor. The total of the voltage drops in a circuit must equal the power supply. A voltage-monitoring detection circuit sees the voltage drop. The monitor expects to see a voltage of 136.3 millivolts. The technician can detect that voltage by test probing the body wiring with a voltmeter. If the monitor sees no voltage, it assumes there is a problem. That problem could be with the power supply or with the electronic circuit board at the resistor. The problem also could be with the body wiring to the PM generator. The generator coil could be shorted to ground or open. The PM generator (magnetic reluctance sensor) is a variable reluctance sensor in that the amount of voltage produced is directly related to the speed of the wheel. As the wheel slows, the strength of the voltage may not be detectable by the EBCM. So if the wheel begins to skid at a low speed, the ABS may not function correctly. Although this may be acceptable with standard ABSs, it is not acceptable with the brake systems that are discussed later. Continental Teves uses a magnetoresistive sensor as its WSS in the

B+

PM generator 1,000 ohms

R1 10,000 ohms

Figure 10-12  PM generator circuit.

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The magnetoresistive sensor produces a digital signal and has its own power supply. The amplitude of the signal is constant, which means the voltage level does not change with wheel speed, only the frequency. A magnetic reluctance sensor can produce a readable signal even with the wheel stopped.

Caution Servicing a magnetoresistive sensor is different from servicing a PM generator sensor. Follow the manufacturer’s instructions closely or damage to the sensor or electronic circuits could occur. Details about testing and diagnosis are discussed in the Shop Manual.

Continental Teves Mk60/Mk70, brake system (Figure 10-13). As a matter of fact, most all systems that have stability control use magnetoresistive sensors. The magnetoresistive sensor cannot produce a voltage, so it must be supplied with 12-volt power provided by the EBCM (Figure 10-14). This creates an electromagnet at the head of the sensor. The return voltage or signal is changed based on the resistance or disturbance of the magnetic field around the sensor and the relationship of a tone ring tooth to the sensor. This sensor has two integrated circuits (ICs) that increase or amplify the resistance change into a DC signal (digital) that is returned to the EBCM. The output signal of one IC is a constant 7 mA at 0.9 volt when no tooth on the tone ring is near the sensor. When a tooth aligns or enters the sensor’s magnetic field, the second IC produces the same amount of current and voltage. As a result, the return signal voltage is increased to 14 mA at 1.65 volts (Figure 10-15). Because the voltage output signal strength is not dependent on how fast the wheel turns, this sensor is more accurate and allows for the precise braking control demanded by active brake and active suspension systems. The speed of the wheel is calculated by how often or how fast the voltage changes from low voltage, 0.9 volt, to high voltage, 1.65 volts, or the cycle frequency. A fast wheel produces very quick repetitive cycles (high frequency), whereas slow cycles represent a slow wheel (low frequency). It should be noted that some sensors may have different voltage levels, so always consult service information for the specific vehicle being diagnosed. At times, like when turning a corner, all four wheels may be traveling at different speeds. A four-wheel ABS has to take this speed difference into account on braking actions on curves and when cornering. Even simple RWAL/RABS had to allow for this condition. It is probable that most roads have more curves than straight sections. On the other hand, most panic stops are done when the vehicle is traveling straight ahead even if only for short distances. Brake Switch.  Most switch inputs to computer logic circuits are grounding devices. They complete the circuit to ground. The computer monitors a circuit with a voltage-dropping resistor. The ABS switch is different from these circuits because it sends a B1 voltage signal

12 V

5 V reference

Tooth aligned

Return signal (14 mA, 1.65 volts)

12 V

No tooth aligned

Figure 10-13  This is a view of a ­magnetoresistive wheel speed sensor.

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Controller

Controller

5 V reference Return signal (7 mA, 0.9 volt)

Figure 10-14  The magnetoresistive sensor will return a signal of 14 mA at 1.65 volts with a tooth aligned with the sensor head. With no tooth aligned, the return signal is 7 mA at 0.9 volt.

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Fast wheel

Slow wheel

Figure 10-15  A fast wheel will generate a rapid cycling or high frequency. A slow wheel will produce fewer cycles or a low frequency. B+

Cruise control TCC

Brake lights CHMSL ABS

Figure 10-16  Brake switch.

to the microprocessor when the brake pedal is depressed. This is a complex switch that contains two sets of contacts: one open circuit and one closed circuit (Figure 10-16). The normally open contacts in the brake switch close when the brake pedal is depressed. This sends B1 power to the stop lamp circuit, the center high-mounted stop lamp (CHMSL), and the ABS microprocessor. When the normally closed contacts open, they cancel the vehicle cruise control and torque converter lock-up features. The latest ABS units use a brake pedal position switch to determine how fast the brake pedal has been depressed. If a panic stop is anticipated, some ABS units can increase the amount of brake pressure applied to the brakes through the hydraulic modulator. The brake pedal position switch is also a critical component of vehicle stability control.

Pumps and Accumulators The last major components of an ABS are internal or external hydraulic pumps and accumulators. Many ABSs have pumps to supply their own brake boost pressure instead of vacuum boosters.

Caution Many magnetoresistive sensors have a mercury acceleration sensor internal to the sensor. Any sensor with mercury must be considered a hazardous material when stored or in use. It must be treated as hazardous waste when determined to be unserviceable.

High-Pressure Pumps and Accumulators.  Some ABS units boost pressure comes from a high-pressure electric pump. It charges the accumulator, with brake fluid from the reservoir. Anytime the accumulator pressure drops below a minimum point, a pressure switch grounds a power relay coil or sends a signal to the EBCM to command the pump on. This connects the high-pressure pump to the ignition B1 power. The ABS boost pressure operates the high-pressure pump when the key is turned on if the vehicle has not been started for a time and the pressure has bled below the minimum point. Low-Pressure Return Pumps.  An ABS without an accumulator or pressure switch but with an electrohydraulic unit that contains an electric motor is called a low-pressure system. The motor is connected to a low-pressure pump that quickly returns fluid to the master cylinder and the reservoir. On some systems, this pump is used to apply light pressure to an isolated hydraulic circuit of an individual wheel. This feature is used to correct

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traction problems during acceleration. If the vehicle is equipped with a lateral accelerometer, the ABS is programmed to eliminate fishtail during acceleration. It applies light brake pressure to the spinning drive wheel. Dynamic Rear Proportioning.  The DRP replaces the standard hydraulic proportioning valve found on many older vehicles. It is an electronic operation within the hydraulic control unit and is used on most late-model vehicles.The DRP uses active control and the existing ABS to regulate brake pressure to the base rear wheels. As with the hydraulic valve, this keeps most of the braking force on the front wheels during routine stops. The red brake warning light will illuminate if there is a hydraulic problem within the base brake system.

AUTHOR’s NOTE  The DRP is active for every situation that may cause a wheel locking condition. The engineers who designed the proportioning valve system had to assumptions based on vehicle loading and road conditions when they designed the proportioning valve. With dynamic rear proportioning the actual conditions can be read by the computer and the best outcome can be had based on these conditions.

Active brakes can warn the driver of an impending crash, or actually applying the brakes if necessary to avoid a crash.

Lamps and Communications The lamps are not essential to ABS operation; however, they are really the only contact between the vehicle’s electronic package and the operator. Communications, on the other hand, is essential to the electronic package because without communications between the various components there would be no operation. Warning Lamps.  Most people understand that the red brake warning lamp is used by the foundation brake system. This lamp indicates problems to the driver. It comes on when brake fluid levels are low and when the parking brakes are applied. This lamp also can be used as a brake pad wear indicator lamp. Some ABSs use the red warning lamp to indicate ABS problems when the amber ABS warning lamp or its circuit is nonoperational. The amber warning lamp is used in several situations: to indicate that the microprocessor is testing the system; to indicate ABS operation; and to alert the driver about a malfunction in the ABS. Some systems use a remote lamp driver to control the amber warning lamp. If the microprocessor is functional, it is able to command the remote lamp driver to turn the amber warning lamp off after the POST. If the microprocessor or its related remote lamp driver wiring is not functional, it is unable to turn off the amber warning light, so it remains on.

COMMUNICATIONS The majority of ABSs share data with other computers on the vehicle through the vehicles communication network. The ABS system communicates with other computers such as the ECM, BCM, and stability control system. This reduces the number of sensors needed and helps the vehicle to react as a system. An example of this sharing is the vehicle speed information. The ECM can share this information with the EBCM, eliminating the need for two separate sensors. The technician can communicate with all the computers in the network through the use of a scan tool. This allows the technician to retrieve codes and records but also to command functions, read data lists, and take data snapshots. Some ABSs can hold as many as six failure codes for up to 100 ignition cycles.

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Different carmakers use many variations in computer communication. The vehicle service information is still the best source for specific vehicle repair information. It is the best source of information for code retrieval, data list interpretation, and testing.

TRACTION CONTROL SYSTEM The TCS is an outgrowth of four-wheel four-channel ABSs. Most of the same components are used in both systems with the major changes being in the controller and its programming. The TCS also interfaces with the engine (PCM) and transmission (TCM) control modules to request that specific actions be taken. The TCS is designed to control wheel spin or positive wheel slip. If the vehicle is accelerated hard from a dead stop, the wheels tend to spin on the road surface assuming there is enough power available from the engine. This has led to some broken axles and other damage if the spinning wheel was on dirt and suddenly moved onto dry pavement. Although TCS can reduce wheel spin during hard acceleration, that is not its underlying purpose. It is designed to control wheel spin during snow, ice, wet pavement, and other road conditions. Going back to the discussion on isolation/dump valves, it was noted that the accumulator in that valve could apply some pressure to the wheel brakes to reduce wheel speed. The TCS has taken that a step further by using a hydraulic modulator modified from the one used strictly for the ABS. If a wheel sensor indicates that a drive wheel’s speed is greater than that of the other wheels, the TCS controller can request that the ECM reduce the ignition timing and or injector pulse width. If the wheel is still exhibiting a positive wheel spin, then the TCS controller will command the hydraulic modulator to apply hydraulic fluid to that wheel. In effect, the brakes are applied. Because of the gear setup in the vehicle’s differential, the power is transferred to the other drive wheel(s). When both or all four of the drive wheels approach the same speed, the TCS reduces or eliminates the pressure to the spinning wheel brakes. It can reapply the brakes if necessary or leave them off, depending on the wheel speed.

Shop Manual page 462 Before the days of traction control a driver with a manual transmission could start out in a gear higher than first on slippery pavement. This reduced the amount of torque at the wheels and may limit wheel spin. The TCS controller can limit torque applied by retarding timing and reducing injector pulse width, and with an automatic transmission shift to a higher gear ratio as needed.

AUTHOR’s NOTE  The TCS is an electronic version of the old, and still used, limited slip differential that was common on many production performance vehicles. This type of differential has some problems because of its mechanical nature, the locking clutches, and, in many cases, the type of lubricant. A differential without any provision for limited slip is called an “open differential.” With an open differential, if one wheel has no traction, then it spins and the other wheel simply sets still. TCS can apply the brakes to the spinning wheel and allow some torque to be transferred to the wheel with traction, allowing the vehicle to escape the slippery situation.

In the case of automatic transmissions, the TCS controller will signal the TCM to shift up to a higher gear, reducing the torque being supplied to the drive wheels. In either case, power is reduced to the drive wheels, and it is hoped the wheels can regain traction. It is possible that all three actions—engine reduction, higher gear ratio, and brake a­ pplication— may be required to control positive wheel slip. This is especially helpful in snow and mud conditions. The major differences between the ABS and the TCS are different hydraulic modulator and the controller. Most TCSs and ABSs use the same controller with more sophisticated programming (Figure 10-17).

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ABS unit

Figure 10-17  The ABS controller on this unit is mated to the hydraulic modulator.

AUTHOR’s NOTE  Educating the owner of the vehicle often becomes an important aspect of doing business. Sometimes senior citizens with a new vehicle may complain of a serious braking noise and pedal movement during hard braking or when braking on a gravel road surface. They may not be aware of exactly how an ABS works. After questioning the owner on exactly what is happening and a complete inspection of the brake system reveals no faults, it may be best to explain to the customer exactly how an ABS works. It is also wise to inform them that if they are in a dangerous situation when panic braking is needed, they should not release the brake pedal until the danger is gone or the vehicle is stopped.

The BPMV is the unit that houses the ABS and TCS control valves.

The Delphi DBC-7 is the oldest ABS/TCS system discussed in this chapter. It should be interesting to compare it to the Teves Mk60/70, and the Bosch ABS 9.0. Shop Manual page 242 Even though EBTCM is the name given to the electrohydraulic modulator with TCS, most in the field will continue to call the unit electrohydraulic modulator because TCS has been standard equipment for some time.

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DELPHI DBC-7 ABS The Delphi DBC-7 is used almost exclusively on General Motors vehicles. It is a nonintegral system that houses the valve body and controller into a single housing. The DBC-7 can be used on three- and four-channel ABS and can be adapted to TCS. The DBC-7 is lighter and less costly than its predecessors. The DBC-7 is a major change from the Delco-VI it replaced. The most obvious engineering change is the change from Delco VI is a motor pack hydraulic modulator back to the more standard modulator using solenoids The valves and pumps are in the valve block known as the brake pressure modulator valve (BPMV). The valve solenoids and controller are mounted to the valve body and are called the EBCM. If the system is fitted with TCS, this control unit is listed as the electronic brake traction control module (EBTCM). The ABS relay, which is mounted separately in the Delco-VI, is now mounted within the EBCM or EBTCM. Each of these two units can be replaced as separate assemblies if necessary. In cavity 11 of the EBCM (EBTCM) wiring harness, a small vent tube has been installed to stop buildup of pressure or vacuum between the controlling unit and the valve housing. In the BPMV are an inlet and an outlet valve for each brake hydraulic channel. Two accumulators are placed in the BPMV, one for each front/rear or diagonal hydraulic circuit. This is a total of eight valves and two accumulators for a four-channel system with six valves and two accumulators for a three-channel. Outlet valves are normally closed and inlets are normally open. The EBCM/EBTCM provides a ground to the solenoids to close the solenoid circuits. Four-channel systems are used on General Motors passenger cars equipped with the DBC-7 ABS. Each BPMV is connected to a separate brake line and the lines are color

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coded: L/R is purple, R/R is yellow, L/F is red, and the R/F is green. A brake pedal switch is used to signal that the brakes are applied. This signal is not needed for ABS functioning, but the signal will deactivate the TCS. Additional sensors are installed on some vehicles. One is an accelerometer sensor that measures the forward and reverse motions of the vehicle so the EBCM/ EBTCM can adjust brake pressure according to how fast the vehicle is decelerating. The sensor is provided with a 5-volt reference signal and returns a portion of the 5 volts to the EBCM/EBTCM. If the voltage is high, then the pressure to the front brake can be reduced. This helps prevent nose diving at the front of the vehicle and provides better vehicle stability and control. Like all ABSs wheel speed is sensed by speed sensors. Wheel sensors are used and may be integrated into the wheel bearing assembly (hub) or of the typical plug-in type. The integrated sensors provide a more concise signal that is read directly by the EBCM/ EBTCM instead of being converted from AC to DC like the ABS VI systems. Integrated WSSs are used on higher-end GM FWD vehicles (Figure 10-18). Neither type of sensor is adjustable and all have a fixed air gap when installed. The DBC-7 works like most ABSs in that it controls brake fluid pressure to a wheel(s) that is slowing faster than the other wheels. In the pressure hold phase, the inlet valve is closed to prevent further pressure buildup from the master cylinder and to hold the current brake line pressure. The pressure decrease phase opens the outlet valve to allow some fluid to flow from the affected brake line into the accumulator to relieve some of the pressure. This releases the brake and allows the wheel to turn faster. During pressure increase, the inlet valve is opened and the outlet valve closed, allowing master cylinder pressure to the affected brake line. The pump is switched on during the three phases to pump fluid from the accumulator back into the brake’s hydraulic system. This cycle is repeated as long as the pedal is depressed and the ABS is required. The DBC-7 uses dynamic rear proportioning (DRP) to control rear brake pressure during normal braking. This eliminates the mechanical/hydraulic proportioning valve and is much better at precise pressure control. The proportioning process is done by cycling the inlet and outlet valve(s) to the rear wheel(s) much the same as the ABS actions used to control wheel lockup. The DBC-7 has two possible traction control systems: enhanced traction system (ETS) and TCS. The TCS can control wheel slippage by signaling the PCM to reduce power and then applying brake pressure to the spinning wheel. This is a typical TCS operation using a program in the EBCM. The ETS can signal the PCM to reduce engine power output only by retarding spark timing, shutting down selected cylinders, leaning air-fuel mixture, reducing the throttle angle or upshifting the transmission. One or any combination of these five actions may be commanded by the PCM. Of note is the fact that no braking action is taken in the ETS to control wheel spin. If the EBCM senses wheel slip when the brakes are not applied, its first step is to request the PCM to reduce engine torque. The PCM can alter spark timing and open selected fuel injector circuits. The reduction in engine torque is signaled to the EBCM by the PCM. This signal is called the delivered torque signal.

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Dynamic rear ­proportioning replaces the old mechanical proportioning valves with ABS action to prevent rear wheel lock up during heavy braking.. Enhanced traction ­system can control wheel slippage in some cases by simply reducing the output torque of the engine by reducing ignition timing, cutting cylinders, reducing the throttle opening, or reducing fuel delivery...

ETS can also be called torque management.

PM wheel speed sensor

Figure 10-18  Shown is a GM hub-and-bearing assembly with an integrated PM wheel speed sensor.

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Figure 10-19  The traction control lights shown are typical of General Motors vehicles and are very similar in other vehicle brands.

A protocol is a computer language that modules use to communicate with each other.

If the wheel(s) continues to slip, the EBCM can apply the brakes to the affected wheel(s). This is done by closing the ABS inlet valve. The prime valve is opened and the pump is switched on to charge the accumulator. The EBCM then opens and closes the inlet and outlet valves to accomplish three phases: pressure hold, pressure increase, and pressure decrease. The different phases are cycled until the wheel slippage stops. The TCS has two dash-mounted lights and an audible warning (Figure 10-19). One light is the TRAC OFF. When this lamp is lit, it means the TCS programming has been deactivated because of a sensed malfunction. At the same time the EBCM requests the BCM to sound an alarm by using the radio. The TRACTION ACTIVE light is lit when the EBCM module senses wheel slippage and begins to apply the brakes in an attempt to regain traction. Another major change between the DBC-7 and previous GM ABSs is the use of Class 2 protocol. Class 2 protocol is a computer network language. Each wired-in module can share information by different pulse signals used to identify each module on the net. Class 2 is faster than the older electronic communication and operates at a higher voltage. The communication speed is 10,400 bits per second (bps) versus the old 8,192 bps. The DBC-7 operates on 7 volts instead of 5 volts. Although these changes do not seem significant on the surface, when the speed of electrons is approximately 186,000 miles per second it is a huge change in the amount of information that can be transferred. The system does require a scan tool capable of reading Class 2 data. Now the prevailing network communication type is CAN, although several networks still use Class 2 in their systems, but they have largely been replaced by CAN as far as real-time networking needs like VSC. Although the DBC-7 ABS used class 2 networking, Bosch 9.0 and Teves mk60/70 use CAN networking.

CAN Protocol The control area network (CAN) is the most common network communication type at this point, and it is incorporated into most all vehicles. CAN helps to save wiring and sensors by sharing information over the vehicle network and allowing multiple modules to communicate and work together. The CAN system uses either a single wire of a pair of wires to send messages to other computers (modules). CAN connects most all the modules in the vehicle. Since CAN is a recognized communication protocol (computer language), it can allow the use of generic modules that can be programmed to perform specific functions. There are two types of CAN. Low-speed CAN operates at 125 kb/s (kilobits per second) and is also known as ISO 11898-3. High-speed CAN, which is needed for “real time” computer interaction, is rated at

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1Mb/second. High-speed CAN is used for critically fast computation speeds like ABS and stability control operations. Compare this to the Class 2 discussion later in the chapter, which has a speed of 10.4kb/s, low-speed CAN is much faster than normal Class 2 systems. Some vehicles still use Class 2 for some functions, but CAN has been fairly dominant since 2008, especially when speed is a factor. With the increasing use of ABS/TCS, ARC, and electrical steering, that train of thinking is becoming to consider the vehicle as a system rather than a series of components with specific jobs. The entire vehicle is working and communicating together for the good of the driver.

Continental Teves Mk60/Mk70 The Teves Mk60/Mk70 is used on some compact cars for the ABS, TCS, and stability control systems. The wheel speed sensors are of the magnetoresistive type, and produce a square wave signal. The magnetoresistive wheel speed sensors are much more accurate at very low speeds. The hydraulic modulator controls brake pressures at all four wheels, including dynamic rear proportioning, which eliminates the need for separate proportioning valves. The system uses Electronically Variable Rear Proportioning (EVRP). During EVRP, the EBCM controls rear brake pressure through the solenoid valves during hard rear braking to prevent rear wheel lock up. The EBCM controls the system and supplies power to the control solenoids and hydraulic pump. The brake hydraulic modulator contains isolation and dump valves for all four wheels, and two traction control isolation/supply valves for the front wheels. (Stability control is discussed further in the next chapter.) The hydraulic modulator controls pressure to each wheel to prevent wheel lockup by reducing, holding, or increasing pressure. In this mode, the modulator cannot increase the pressure beyond that supplied from the master cylinder. The Continental Teves Mk60/Mk70 system has hydraulic brake assist that increases pressure to the brakes whenever a panic stop is detected through the brake pedal sensor. (The hydraulic assist system was explained in the chapter on power brakes.) Traction control is accomplished by monitoring the wheel that is spinning under acceleration. The ABS computer will first request that engine torque is reduced through the vehicle network. If the wheel continues to slip, the EBCM commands the pump motor to run and applies braking pressure through the appropriate valve to stop the wheel from spinning. AUTHOR’s NOTE  Up until about 1993–1994, the engine was engineered with fuel economy and emissions as the core with little regard to the transmission. Electronic engine controls and their maintenance were designed and performed with the same idea. A transmission was engineered based on how best to deliver engine power to the wheels and further the emission and economy goals of the engine. The engine and transmission were treated as separate stand-alone components. It became obvious during the 1990s that the vehicle could not meet government and consumer requirements without engineering these two major components into one system. By the early 2000s, the term powertrain became more commonplace because the engine and transmission had to function as one organized unit. For the repair technician, this meant that a drivability problem had to involve diagnosis of the system as opposed to one component. Today an incorrect shift point in the transmission may be directly linked to or caused by a malfunction of an engine control.

Bosch The Bosch ABS 9.0 is a four-channel ABS system. This system is capable of handling ABS, TCS, VSC, Hill start assist, DRP and brake assist. Bosch 9.0 also houses pressure sensors and some of the needed components to perform VSC duties. The Bosch 9.0 unit looks similar to earlier hydraulic modulators, but because of the introduction of rare earth

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magnets into the unit, it is approximately 30 percent smaller, and at the same time it is lighter. The hydraulic pump for the Bosch 9.0 system has nine pistons instead of two that were used on earlier systems, allowing it to move more fluid quicker.

Bosch ABS 9.0 Components A diagram of the Bosch 9.0 system is shown in Figure 10-20. Electronic Brake Control Module or EBCM is used to interpret inputs and command outputs from the ABS/TCS/ VSC system. It is usually mounted on the hydraulic modulator (GM calls this the brake pressure modulator valve or brake modulator). The hydraulic modulator contains four inlet and outlet valves (one for each wheel). The hydraulic modulator also has two traction/ stability control isolation valves and two traction/stability control supply valves. The hydraulic modulator maintains a diagonal split LF and RR circuits and RF and LR circuits that are separated hydraulically, just like a conventional braking system. The BCM monitors the brake pedal position sensor (BPP) and sends the information over the vehicle network to the EBCM. An internal brake pressure sensor tells the EBCM how hard the driver is pushing on the brake pedal. The ECM sends vehicle speed information to the brake control module, the BCM and the instrument cluster. The steering angle sensor sends information to the EBCM that will be used for VSC calculations. The TCM is also on the vehicle network and relays gear position information to the EBCM. Vehicle accelerometers are part of the inflatable restraint system, and are also used as part of the VSC system. The VSC system will be discussed more in depth in the next chapter. The wheel speed sensors are magnetoresistive sensors that use a 12-volt power supply from the EBCM to the sensors. As you recall, the magnetoresistive sensors are more accurate at low speeds, and can, in fact, produce a waveform from a stopped wheel. Bosch ABS 9.0 uses the same methodology as other ABS systems to control wheel skid: isolation (holding) of the wheel brake pressure; then, if the wheel continues to slow down, the pressure is reduced; and finally, when the wheel is turning at a speed near the other wheels, the pressure is allowed to increase. With traction control, there are two isolation/apply valves for the drive wheels, which allow the pump motor to apply one brake and isolate the other from pressure as often as necessary to control positive wheel spin.

Bosch POST Bosch ABS 9.0 does a power-on self-test POST when the key is first turned, and then an initialization test of all the electrical solenoids and motors as soon as one of the wheel speeds exceeds 10 mph. Instrument cluster

TCS/VSC on–off switch

BPP Sensor

Body control module (BCM)

Transmission control module (TCM)

Engine control module (ECM)

Electronic brakes control module (EBCM)

Hard wired circuits Network wiring

Power steering control module

LF/WSS

RF/WSS

LR/WSS

RR/WSS

Figure 10-20  A diagram for the Bosch 9.0 system.

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A sensor may measure electrical energy directly or convert a mechanical action into electrical energy. Signals may be analog or digital; digital signals have the advantage of having a consistent amplitude regardless of wheel speed. Frequency is the number of times a cycle occurs within one second. Duty cycle indicates the amount of time on versus time off. Actuators are normally used to change electrical energy into mechanical action. A controller is the computer module for a particular device, system, or group of systems. Multiplexing is the term applied to the communications on the vehicle computer system. More than one message can be sent at the same time. Control area network (CAN) is a popular communication protocol for vehicles. The hydraulic modulator is the actuator that directly controls brake fluid pressure during ­electronically controlled braking. Commands are electrical signals generated by the controller and sent to an actuator to perform an action. An ABS offers drivers a braking system that can help control and stabilize their vehicles. Integrated and nonintegrated ABSs usually indicate the placement of the hydraulic modulator in relation to the master cylinder and power booster. Four-wheel ABSs come in two configurations: three-channel and four-channel.

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Controllers may be known as electronic brake control module, controller antilock brake, or ­similar designations desired by the ABS manufacturers. An electrohydraulic unit is the combined assembly of a controller and hydraulic modulator. Permanent magnet sensors generate an ac voltage based on the speed of the wheel and are the most common wheel speed sensors. Magnetoresistive sensors have a low and a high voltage and current signal regardless of wheel speed. Wheel speed is calculated based on the frequency of change between waveform cycles generated by the magnetoresistive sensor. ABSs may be equipped with high-pressure pumps and accumulators. The mechanical proportioning valve has been replaced on many vehicles with electrically controlled proportioning programming known as dynamic rear proportioning. Common TCS/ABS components are WSS, ICU, and the mechanical/hydraulic service brake assemblies. The DBC-7 hydraulic modulator with TCS has two additional valves and an electronic brake traction control module. The DBC-7 uses integrated PM sensors for wheel speed. The DBC-7 ABS provides programming for dynamic rear proportioning, tire inflation monitoring system, and two TCS programs named enhanced traction system and traction control system. Class 2 wiring is used within the DBC-7 system for shared communications between networked controllers.

REVIEW QUESTIONS Short-Answer Essays 1. Describe the general operation of a magnetic reluctance (PM) wheel speed sensor. 2. Describe the general operation of a magnetoresistive wheel speed sensor. 3. Explain the job of wheel speed sensors in the ABS system. 4. Describe the construction differences between the integrated ABS and the nonintegrated ABS.

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5. Describe the difference in the DBC-7 without TCS and the DBC-7 with TCS. 6. What can the Bosch ABS 9.0 unit control as far as braking/stability control enhancements? 7. Explain why some ABS systems no longer use proportioning valves. 8. What is the advantage of vehicle networking? 9. What is the first thing the traction control can do to help eliminate positive wheel spin?

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Fill in the Blanks 1. If the EBCM senses wheel slip when the brakes are not applied, its first step is to request the PCM to reduce______________ _______________. 2. The DBC-7 operates on _______________ volts instead of _______________ volts. 3. High-speed CAN, which is needed for “real time” computer interaction is rated at _______________ 4. A slow wheel as monitored by the wheel speed sensor will produce a _______________frequency signal, whereas a faster wheel will cause a comparatively _______________ frequency. 5. The _______________ replaces the standard hydraulic proportioning valve found on many older vehicles. 6. The magnetoresistive sensor produces a _______________ signal and has its own power supply. The amplitude of the signal is constant. 7. Magnetic lines of force are called _______________ _______________. 8. The Continental Teves Mk60/Mk70 system has hydraulic brake assist that increases pressure to the brakes whenever a _______________ _______________ is detected through the brake pedal sensor. 9. The hydraulic pump for the Bosch 9.0 system has _______________ pistons instead of two that were used on earlier systems. 10. The TCS is designed to control wheel spin or _______________ wheel slip.

Multiple Choice 1. Technician A says with digital signals only the frequency changes. Technician B says an analog voltage signal is infinitely variable; in other words, it flows smoothly as it changes voltage levels. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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2. Sensors are being discussed. Technician A says that sensors are used to measure some sort of physical action and change it to an electrical signal. Technician B says that the simplest sensors are often on–off switches. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 3. Technician A says that an actuator converts mechanical action to electric energy. Technician B says that an actuator uses electric current to perform a mechanical action. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 4. Actuators and sensors are being discussed. Technician A says that a too low current may mean that an actuator or sensor is not functioning properly. Technician B says that the controller cannot monitor actuator and sensor operation electrically. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. Command signals are being discussed. Technician A says that automotive controllers (computers) are simple compared to those used at work or school. Technician B says that most automotive computers work without sharing information with other computers on the network. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 6. While discussing TCS as an outgrowth of fourwheel four-channel ABS, Technician A says most of the same components are used in both systems. Technician B says the TCS also interfaces with the engine (PCM) and transmission (TCM) control modules to request that specific actions be taken. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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7. Technician A says that an integrated ABS unit has many serviceable parts. Technician B says that the nonintegrated ABS has many serviceable parts. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

9. While discussing ABS brakes, Technician A says ABS is excellent in directional stability. Technician B says ABS is excellent in directional control. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

8. There are several different names in use for the ABS controller. All of the following names have been used except: A. BACU C. EBCM B. ICU D. CAB

10. Technician A says that PM generator (variable reluctance) sensor produces a digital signal. Technician B says that a PM generator used an electromagnet as part of the sensor. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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Upon completion and review of this chapter, you should be able to: ■■

Compare how fatality rates for miles traveled have been reduced.

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Explain the purpose of each of the ­stability control sensors. Describe active braking. Describe cruise control systems that ­utilize active braking. Explain the operation of a regenerative braking system on a hybrid vehicle.

Terms To Know Distronic

Pre-brake

Rolling diameter

INTRODUCTION The public and the federal governments have demanded more from vehicles and their manufacturers since the development of the automobile. First, we saw the demand for cleaner vehicles and the development of emission controls in the early 1960s. In the mid-1960s, safety belts became mandatory equipment in new vehicles. More fuel-efficient vehicles were mandated after the fuel shortages in the 1970s. In the 1980s we started to see fuel efficiency and performance go hand in hand as new fuel injection and ignition systems were developed. Next, the need for safer vehicles came to the forefront. We have seen the development of air bags, ABS and traction control system (TCS), and lately active braking systems and stability control. The automotive industry continues to develop new and innovative technology that few other industries can match. Of course, the automotive industry did have help from the development of faster computers that could meet the challenge of “real time” reaction and integrated networks inside the vehicle that allowed the ECM, BCM, ABS, and stability control (VSC) modules to react as one to prevent crashes. According to the National Highway Traffic Safety Administration (NHTSA), the fatality rate per 100 million miles traveled was 5.5 in 1966, 1.10 in 2011, 1.25 in 2016. The fatality rate would have been less, except for the fact that some people still do not use their safety belts or are doing something very unwise like texting or drinking while driving. The biggest cause of fatalities is driver inattention. By some estimates as many as 95 percent of all accidents are caused by driver inattention.

STABILITY CONTROL SYSTEMS History Shop Manual page 515

The first development on the road to stability control, as you have seen in this text, was antilock braking. As you probably recall from earlier chapters, the development of ABS

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came at a time when the prime concern was the loss of vehicle control because of the possibility of the rear wheels locking and causing a spin from which the driver could not correct, particularly on wet pavement. Many vehicles were transitioning to front-wheel drive, meaning that the front wheels did nearly all the braking. Compounding that problem was the fact that pickup trucks were gaining in popularity. Many of these trucks never hauled anything heavier than groceries, whereas many trucks were still in use by the construction, farming, and hauling industry. Work trucks were likely to be heavily loaded. This posed a huge problem for the designers, as the same truck might do both jobs. The original solution was a height-sensing proportioning valve intended to help compensate for heavy loads by measuring the sag on the rear springs because of loading. Rear-wheel antilock brakes were eventually established for full-size pickup trucks. These were relatively simple by today’s standards. The rear wheels were controlled as a pair; no matter which wheel was skidding, both rear wheels were treated in the same way. The way in which the rear brake pressure was modulated has not changed that much. This is the familiar isolation (when the brake pressure from the master cylinder was isolated) and not allowed to increase regardless of how much pressure was applied. If the wheel continued to slow down too fast (as reported by the wheel speed sensor), then the pressure was reduced to the rear wheels. This cycle could take place several times per second and greatly increased the safety of the vehicle. These early ABS systems were single-channel ABS. They controlled only the rear brakes, and then only as a pair.

Three- and Four-Channel ABS The next major development of the ABS system was the advent of three-channel and four-channel ABSs. Three-channel ABSs were the most common when ABS were first introduced in passenger cars. Both front wheels were controlled independently of each other, but the rear wheels were controlled as a pair. If one rear wheel started to lock up, then both rear wheels were modulated in the same manner. Finally, for stability control, four-channel ABS is the rule. All four wheels are controlled independently. ABS, as you recall, does not necessarily stop a vehicle faster but allows for control of the vehicle in a hard-braking situation. If the front wheels lock, the vehicle cannot be steered; if the rear wheels lock, then the vehicle tends to spin out of control (Figure 11-1).

ABS and Stability Control You could say that ABSs in themselves were a start of stability control, because if the vehicle remained drivable during a panic stop it is far less likely to crash. Development of stability control is the story of integration of several individual systems that have the ability to work together.

Figure 11-1  ABS brakes and stability control have saved countless accidents over the years.

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Traction Control Traction control was born out of the ABS system and appeared just a few years after ABS became common on most vehicles. Traction control did not require a large amount of hardware to accomplish; it required only a pump (if it was not already present) and a couple of valves. The rest was software enhancements. Traction control is basically the reverse of ABS; it looked for a wheel spinning too fast and then applied the brakes to slow it down (Figure 11-2). Wheels spinning because of a loss of traction is called positive wheel slip. Traction enhancements have been around for many years on rear-wheel drive vehicles as limited-slip differentials, although these new electronic systems are faster and do not have clutches to wear out or lubricant to change. Traction control also has one more development that is important; it was one of the first systems to interface with the ECM. The first response to a wheel slip is a torque reduction request from the EBCM whenever a wheel is spinning. This torque reduction usually comes about by a reduction in ignition timing and throttle control. Electronic throttle control allows the vehicle network to control the throttle position. If this does not correct the wheel slip, then the brake pressure modulator valve (BPMV) is commanded to apply brake pressure to the slipping wheel. The ECM can also tell the transmission to shift to a higher gear (also reducing torque) at the request of the ABS computer. It is important to note that on most vehicles, traction control is only effective at relatively low speeds, but some sports cars can have traction control at much high speeds. AUTHOR’s NOTE  Old-timers had their own way to get some traction whenever they were stuck in the mud or snow. On a vehicle with a conventional differential, if one wheel has no traction it will spin by itself and the vehicle will not move. Knowing this, they would apply the emergency brake slightly. Of course, this would apply the brakes on both wheels, but sometimes it was enough to slow the wheel with no traction just enough that the wheel with traction can pull the vehicle out of the slippery situation. Another technique was to start the vehicle out in a gear higher than first (with a manual transmission). This would reduce the torque applied to the spinning wheels. Today, the modern TCS works in the same ways as illustrated, just higher tech.

Figure 11-2  Positive wheel spin can be stopped with traction control.

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Figure 11-3  A typical steering angle sensor measures the driver’s intended direction.

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Figure 11-4  The actuator is solenoid used to control power steering fluid flow from the pump to the steering gear.

Computer-Controlled Hydraulic Steering/Electric Steering Electronic or electrically controlled steering began in the 1990s. The electric steering computer regulated the flow of pressurized power fluid to the steering gear. During lowspeed operation, full power steering flow was allowed for parking maneuvers. At highway speeds the power steering flow is cut back for better road feel. Full power steering pressure can be delivered during an emergency maneuver by utilizing the steering wheel angle sensor. The steering angle sensor for one of these hydraulic systems is located at the bottom of the steering column and measures steering rotation in both degree of turn and speed of steering wheel rotation (Figure 11-3). Using these data and other information such as VSS, the electric steering computer regulates the flow of pressurized power fluid to the steering gear using a solenoid mounted on the power steering pump (Figure 11-4). Other electrical steering assist can be done by attaching an electric motor to the steering shaft or gear that can apply force to the steering mechanism.

Shop Manual page 521

Electric Power Steering Electric power steering serves two purposes for automakers. The electric power steering uses no energy when not in use, such as when driving straight down the road, and, for systems that depend on computer control such as lane departure and steering a vehicle back into the correct lane. The electric steering effort is appropriate to the road speed; the same is true for the speed sensitive type hydraulic system, which also uses the VSS to determine road speed. There are three types of electrical power steering: the column mount, (Figure 11-5), the rack mount (Figure 11-6), and the pinion-mounted electric motor (Figure 11-7). The electrical power steering control module (PSCM) is connected with the vehicle’s network to share information with the other stability control components, such as driver input steering torque and steering wheel position and road speed from the ECM (Figure 11-8). The torque sensor is a dual sensor that is mounted on a torsion bar inside the steering column, which tells the VSC module how hard the driver is turning the steering wheel. The steering torque sensor produces two output signals from

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Steering column

Power steering motor and controller

Figure 11-5  A column style electric power steering system used on some GM vehicles. Similar systems were used on several different vehicles.

Figure 11-6  A rack-mounted motor style electric rack and pinion.

Electric motor

Steering angle and torque sensor

Pinion shaft

Steering shaft Power steering control module

Figure 11-7  A pinion-mounted electric power steering motor.

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Power steering control module

Electronic brakes control module

Power steering motor

Power steering torque sensor

Instrument cluster

Steering angle sensor

ECM Serial data

Figure 11-8  Electric power steering network of modules, inputs, and outputs.

about 0.25 volts to almost 5 volts. Output signal 1 voltage goes up and output signal 2 goes down during a right turn; during a left turn, output signal 1 goes down and output signal 2 goes up. In this way, the computer has two signals to check for validity of this important signal. The steering wheel position sensor is also used as an input to the stability control. Figure 11-9 shows a scan tool graph of a steering angle sensor as the wheel is turned to the left.

Tire Pressure Monitoring Systems Tire pressure monitoring systems (TPMS) have been around for the past several years on high-end vehicles and have been introduced into passenger vehicles. The system monitors and detects low tire pressure in the vehicle’s tires. The system has been designed to prevent a low tire from overheating and blowing out, which has been implicated in causing several roll-over crashes, particularly involving SUVs. Additionally, having tires with unequal pressures also affects vehicle handling. In order to maximize the effect of stability control and ABS braking, external factors such as tire pressures need to be at the correct pressures. Stability control is difficult enough while not adding the complication of underinflated tires. The direct TPMS operates by using transmitters in each wheel, which are generally located in the tire valve stems (Figure 11-10). A radio signal that contains tire pressure information is transmitted to the TPMS module. On some systems, the tire position must be relearned, if the tires are rotated. Some systems called indirect TPMS can 343.9 343.8 343.7 343.6 343.5 343.4 343.3 343.2 343.1

343.2

Figure 11-9  Steering angle sensor graph, wheel turned fully to the left.

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Figure 11-10  A typical tire pressure sensor.

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use the ABS wheel speed sensors to determine slightly different wheel speeds. A tire with low air pressure has a smaller rolling diameter than a wheel at proper inflation. Stability control is not a substitute for careful driving. Remind your customers that stability control is a driving aid; much like a rear-view mirror, just much higher tech.

You can think of ­stability control action like the way a ­bulldozer turns; one tread stops and pulls the bulldozer to the side with the stopped tread.

Stability Control Stability control is the controlled application and release of brakes at the correct time, independently of each other, to prevent an out of control vehicle during hard maneuvering. There are two common terms for loss of steering control through a corner: understeer and oversteer. AUTHOR’s NOTE  It is important to remember that no matter what kind of sophisticated braking or traction control system is present on a vehicle, worn out tires will defeat the ABS, TCS, and stability control systems every time.

Understeer Understeer, simply stated, means that the vehicle did not make it through a turn and went off the road on the outside of the turn. It appears almost as though the driver did not turn hard enough, but more than likely was driving too fast for weather conditions or the condition of the tires or vehicle and the front wheels lost traction (Figure 11-11). In an understeer situation, the inside rear-wheel brake can be applied by the stability control system to help pull the vehicle around the curve.

Oversteer Oversteer is the loss of traction at the rear wheels leading to a vehicle spin (Figure 11-12). Once again, the driver might have steered into the corner too hard, the rear tires might

Figure 11-11  Understeer means the vehicle is going to go off the road on the outside edge—usually because the front wheels have lost traction.

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Figure 11-12  Oversteer means the vehicle is going into a spin because the rear wheels have lost traction.

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be worn dangerously thin, or the driver might have been driving too fast for conditions. The outer-front-wheel brake is applied by the stability control system to help counter oversteer.

STABILITY CONTROL HARDWARE Steering Angle Sensor As was illustrated earlier, the steering angle sensor measures the actual direction the steering wheel turned, as well as how fast the wheel is turned. This information can be used by the electronic stability control (VSC) module and compared to the yaw sensor. (Figure 11-13).

Yaw Sensor The yaw sensor can measure the difference between the actual direction that the vehicle is traveling and the direction the driver is trying to steer the vehicle by way of the steering angle sensor. This difference is called the slip angle. The VSC computer then calculates the amount of steering correction needed. Some yaw sensors also contain lateral and longitudinal acceleration or “G”-sensors (Figure 11-14) that can measure side force the vehicle is under during a turn. The longitudinal acceleration sensor can determine the rate of acceleration and deceleration. Figure 11-15 is a screen shot from a scan tool showing the steering angle, yaw rate, and lateral and longitudinal acceleration. To understand yaw, imagine a pin through the roof of the car and into the pavement below; the yaw rate is the angle and speed that the vehicle is rotating around the pin through the center of the vehicle. Think of a vehicle sliding sideways down the road. The front of the vehicle is facing off the road and the vehicle is sliding down the roadway. The rate that the vehicle is spinning around its vertical axis is the yaw rate. The slip angle is the difference between the intended direction of travel and the desired direction of travel (Figure 11-16). Think of a vehicle that is drifting around a corner; the slip angle is desired during this kind of driving (Figure 11-17). The rear of the car sliding around in the corner is yaw.

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Beam-Type Hall-Effect Yaw Sensors The newest yaw sensors are beam-type Hall-effect sensors that receive a 5-volt signal from the EBCM and return some portion of that voltage as a signal. Usually the portion returned is 2.5 volts, representing a zero gravity force in a lateral direction. In other words, the vehicle is

Figure 11-13  A yaw rate sensor measures the actual turning rate of a vehicle.

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Figure 11-14  A G-sensor, also known as a lateral acceleration sensor, that works with the VSC. The G-Sensor measures the rate of acceleration and the direction of movement.

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2048 1792 1536 1280 1024 768 512 256 0

Yaw rate (hPa/m3/h) 50

16s 14s 12s 10s 8s

6s

4s 2s

2047.9 1791.9 1535.9 1279.9 1023.9 767.9 511.9 255.9 0

Lateral acceleration (m/s2) 512 448 384 320 256 192 128 64 0

3.6

16s 14s 12s 10s 8s

6s

4s 2s

Sterring angle sensor (°) 480.8

16s 14s 12s 10s 8s 6s 4s 2s Longitudinal acceleration (m/s2)

512 448 384 320 256 192 128 64 0

–2.0

16s 14s 12s 10s 8s 6s 4s 2s

Figure 11-15  A typical reading for a longitudinal and lateral accelerometer and yaw sensor.

Actual direction of travel

Slip angle Intended direction

Figure 11-16  Illustration of yaw and slip angle.

Figure 11-17  A vehicle drifting around a corner is illustrating yaw rate.

completely level and moving straight ahead or sitting still. The variation from 2.5 volts is interpreted by the EBCM as the actual motion of the vehicle. The beam-type Halleffect sensor produces an analog output signal that is interpreted by the VSC computer.

Hydraulic Modulator (BPMV) The hydraulic modulator, also called a brake pressure modulator valve (BPMV, Figure 11-18), is generally composed of a valve body that contains the control valves used to isolate, decrease, and increase pressure at the individual wheels that can control the application of brake pressure according to the demands placed on the vehicle by the driver, and the optimum corrections as calculated by the VSC computer. The hydraulic modulator can also contain a pump motor and, in many cases, the VSC module (EBCM) is part of the assembly.

Throttle Actuator Control The ECM has control of the throttle position on most late-model vehicles using the throttle actuator control (TAC) (Figure 11-19). The VSC module can request the ECM to find

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Figure 11-19  A throttle actuator control unit. Figure 11-18  The hydraulic modulator, also known as a BPMV, can apply or release pressure to any of the four brakes. Figure 11-20  The accelerator pedal position sensor is usually located on the accelerator pedal.

1 volt

Accelerator position Sensor 1

WOT

Closed

2.9 volts

Accelerator position Sensor 2

WOT

Voltage

3.1 volts

Voltage

Voltage

2 volts

Closed

3.8 volts

4 volts

Closed

Accelerator position Sensor 3

WOT

Figure 11-21  The accelerator pedal position is made up of three sensors in one housing.

the most appropriate throttle angle for vehicle control. The accelerator pedal position (APP) sensor (Figure 11-20) relays the driver’s demands for throttle to the ECM. The APP sensor has at least two and sometimes three separate sensors to make sure the signal is reliable (Figure 11-21). If the driver is requesting full throttle in a situation that is resulting in a wheel spin, the ECM can request that the throttle be backed down to an acceptable level regardless of the driver’s input. The VSC module and the ECM can keep track of the throttle position by using the throttle position sensor (TP sensor). The TP sensor has two sensors, each using at least two separate sensors (Figure 11-22). The ignition timing can also be retarded to remove some torque from the wheels when required.

Roll Control/Ride Control It would be simple to prevent a vehicle from rolling in a turn by making the suspension very stiff and lowering the vehicle, like road-racing vehicles. This is not acceptable to most drivers in their daily vehicle. Some systems incorporate a feature called automatic ride control (ARC). Automatic ride control works with the vehicles struts/shock absorbers to prevent roll in hard turns but can still provide a comfortable ride.

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Chapter 11 5V 4.17 V

4.02 V

4V

Voltage

TP sensor 2 3V

2V TP sensor 1 1V 0.86 V

0.93 V

100%

0% Throttle opening

Figure 11-22  Dual TP sensor voltage rates. (Note: There are several types of sensors; always use the chart for your specific vehicle.)

A separate ride control module controls the shock absorbers’ compression rate. These systems use hydraulic, pneumatic, or magnetic controls that can rapidly change the rate of the shocks. An air spring suspension (Figure 11-23) can control body roll and suspension rate, as well as control ride height. Some of the suspension control systems also have a control on the dash to change the overall feel of the suspension, such as sport and normal settings.

Figure 11-23  The air spring can be inflated or deflated to control body lean and ride height for better control and a better ride.

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Cadillac Magnetic Ride Control Cadillac and several other GM divisions have a magnetic suspension system that can alter the stiffness of the shock absorbers electrically and, therefore, the amount of body roll during hard cornering. The shock absorbers contain fluid called magneto-rheological fluid that stiffens when a magnetic field is exposed to it. The magnetic field can be changed at 1,000 times per second. The strength of the magnetic field can be changed by varying current flow (Figure 11-24). The ride height is constantly monitored by suspension position sensors, as shown in Figure 11-25.

VSC Computer and the Vehicle Network The VSC computer works in cooperation with the other computers in the vehicle network to provide stability control by commanding the appropriate brake pressures for ABS, TCS, and VSC purposes, as well as communicating with the instrument panel control module (IPC) and the ECM. The communication with the IPC tells the VSC module of the driver’s demands, such as turning the VSC off, and communicating messages to the IPC such as illumination of the “ABS” warning lamps, “TCS” active lamp and “VSC active” lamp depending on the application. The reason the warning lights are activated is to tell the driver that the situation is being corrected for them. The idea is that the driver may get too confident in their driving ability without the notifications. Through communication with the ECM, the VSC can request lower engine torque and/or reduced throttle angle to

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Rebound Direction F Cylinder of strut Piston rod

High pressure

Electromagnetic coil Magnetic flux lines Magnetic pole pieces Magnetically active regions

Suspension height sensor

Air spring Low pressure

Figure 11-24  The flow control valve can vary the magneto-rheological fluid’s viscosity by applying an electric field.

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Figure 11-25  Height sensor shown on rear wheel. Air shock on this vehicle is for load leveling the vehicle when trunk is loaded.

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ECM

IPC

VSC module

ARC

Figure 11-26  Vehicle stability control depends on the interaction of many control modules on the vehicle’s network.

help keep the vehicle under control. The ECM can also share information such as brake pedal position, throttle position sensor (TPS) and vehicle speed sensor (VSS) signals with the VSC and ARC computers (Figure 11-26).

ACTIVE BRAKING SYSTEMS

There are several types of active braking systems available such as Subaru’s “Eyesight” or Mercedes “Pre-brake that prepare the braking system for a sudden stops.

Distronic is the name that Mercedes gave their cruise control that has the ability to maintain a safe distance from other vehicles on the road ahead with no input from the driver.

Several new systems have been developed in recent years to add to the active braking systems that have been developed over the past several years. Many vehicles use a system with high-definition cameras that can scan the road ahead and warn the driver of a possible collision. Manufacturers have developed radar systems to warn drivers and can even apply the brakes to avoid a collision, if necessary. Radar cruise systems use active braking systems that utilize the cruise control not only to keep a set speed, but to maintain a safe distance to vehicles ahead. Active braking systems were also discussed in Chapter 6. Active braking systems will build increased pressure from the master cylinder in anticipation of a panic stop, when the danger of an impending crash is possible as measured by the vehicle’s short-range radar system (Figure 11-27). Some of these systems, like Mercedes Benz’s Pre-brake or Subaru’s Eyesight system, will prepare the brakes to apply only the necessary braking pressure when the driver responds, thus preventing a panic stop situation. If the driver does not apply the brakes after a warning, the system will do it for him or her to prevent an accident, or as the manufacturers say to “reduce the severity of an accident if it occurs.” Mercedes also has a cruise control system called Distronic. The Distronic is a cruise control system that can see drivers approximately 600 feet in front of the vehicle and apply the brakes if necessary to maintain a safe distance. Once the safe following distance is reestablished, the cruise control can accelerate the

Figure 11-27  An active brake warning system.

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vehicle back to its programmed speed. If the gap between vehicles is closing too fast, the Distronic cruise control can calculate the force needed to avoid the vehicle and apply just the force needed to stop the vehicle. Distronic cruise control can apply the brakes if the driver fails to respond to visual and audible warnings. The calculated brake force can stop the vehicle, but not too fast for drivers behind to be able to stop on their own.

REGENERATIVE BRAKING SYSTEMS Introduction The idea behind regenerative braking is to recover some of the energy that is lost as heat when the brakes are applied and the vehicle is stopped. Most hybrid and electric vehicles have a way to recover this lost energy as electrical power stored in the battery. The general idea is that part of the braking is actually accomplished by using generators attached to the wheels or engine that engage to slow the vehicle down during moderate stops. A hydraulic system is still needed for panic stops and to bring the vehicle to a complete stop. The amount of regenerative braking is tailored by the EBCM and depends on how much braking force is being demanded from the driver. The braking is done in a blended manner; some of the braking is done regeneratively, and some is done hydraulically. If braking is very heavy, then most of the braking will be done by the hydraulic brakes. If braking requested is very light, then most of the braking is done by the regeneration braking.

Prius The Toyota Prius uses two motor generators: MG1 and MG2. MG1 is driven by the gasoline engine and generates the power to charge the main storage battery. MG2 is generally used as an electric motor drive, but will act as a generator when the drive wheels are turning the generator. The Toyota Prius uses regenerative braking that begins as soon as the accelerator pedal is released by activating the motor/generator MG2, which is connected through the vehicle’s driveline. This allows the vehicle to recover about 30 percent of the energy previously lost as heat on braking. The motor generator produces alternating current, which is then transferred to the hybrid vehicle battery through an inverter. The inverter converts the AC voltage to DC. Direct current has to be used to recharge a battery. The power conserved depends on the state of charge of the battery and is controlled by the power management ECU. Speed downhill can be controlled by shifting the transmission into the “B” range when going downhill and can convert more energy to the battery as well. The hybrid Prius works with VSC in the same manner as nonhybrid vehicles do, through the hydraulic modulator.

Caution Make certain that all safety precautions are followed whenever working on or around a hybrid vehicle. Always disable the high-voltage system by removing the service plug or switching the service disconnect to “off.” Wear high-voltage gloves and shoes as prescribed by the manufacturer.

KIA Optima The KIA Optima uses active hydraulic brakes. The system uses a brake pedal position sensor to determine the amount of braking force needed. The braking control module blends the hydraulic braking with the regenerative braking to produce the total braking force required. The KIA Optima Hybrid uses a belt-driven starter generator (Figure 11-28) to help slow the vehicle during deceleration; hydraulic brakes are used to bring the vehicle to a complete stop and during hard braking. The starter generator has coolant circulating through it to keep it cool.

Chevrolet Volt The Chevrolet Volt uses one electric motor to drive the wheels. The gasoline engine is used only to charge the battery. Any time the accelerator pedal is released, the drive motor becomes a generator.

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Figure 11-28  A belt-driven starter generator can be used for regenerative braking by loading the engine on deceleration.

SUMMARY ■■

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Highway fatalities have been dropping due to vehicle safety improvements like ABS brakes and stability control. ABS was the starting point for traction control and stability control systems. The development of faster computers that could meet the challenge of “real time” reaction and computer networks inside the vehicle allowed the ECM, BCM, ABS, and stability control modules to react as one to prevent crashes. Stability control helps prevent oversteer and understeer. Understeer means that the vehicle did not make it through a turn and went off the road on the outside of the turn. Oversteer is the loss of traction at the rear wheels leading to a vehicle spin.

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Electronic/hydraulic and electric steering systems have been incorporated into the stability control systems. The steering angle, torque, and speed are valuable input to the stability control system. Tire pressure monitoring systems help owners maintain proper tire pressures, which increases safety, as well as the effectiveness of the stability control system. Active braking systems like Mercedes Benz’s Prebrake system will actually prepare the brakes to apply only the necessary braking pressure when the driver responds, thus preventing a panic stop. Smart cruise control systems have the ability to maintain distance behind the vehicle in front of them by applying the brakes as necessary to slow the vehicle. Hybrid vehicles utilize regenerative braking to help recharge the batteries.

REVIEW QUESTIONS Short-Answer Essays 1. Compare how fatality rates for miles traveled have been reduced. 2. Explain what brought on the development of ABS braking and why. 3. Explain how the rear wheels were controlled on the original rear-wheel antilock brakes such as RWAL or RABS.

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4. Explain the difference between three- and four-channel ABS brakes. 5. Explain what is meant by understeer. 6. Explain what is meant by the term oversteer. 7. Describe the first response to wheel slip by the traction control. 8. Explain how computer-controlled hydraulic steering works.

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9. Briefly explain how active braking systems operate. 10. Explain the use of a yaw sensor.

Fill in the Blanks 1. By some estimates, as many as _______________ percent of all accidents are caused by driver inattention. 2. Computer _______________ inside the vehicle allowed the ECM, BCM, ABS, and stability ­control (VSC) modules to react as one to prevent crashes. 3. Traction control is basically the _______________ of ABS. 4. The _______________ sensor is a dual sensor that is mounted on a torsion bar inside the steering column. 5. The Toyota Prius uses _______________ braking that begins as soon as the accelerator pedal is released by activating the motor/generator. 6. _______________ braking systems will build increased pressure from the master cylinder in the event of a panic stop. 7. The Toyota Prius uses two motor generators: _______________ and _______________. 8. The KIA Optima Hybrid uses a _______________ driven starter generator to help slow the vehicle during deceleration. 9. Electronic or electrically controlled steering began in the _______________. 10. Active ride control works with the vehicles struts/ shock absorbers to prevent _______________ roll _______________ in hard turns.

Multiple Choice 1. Technician A says that the ABS was the first step on the road to stability control systems. Technician B says that ABS brakes allow the driver to control the vehicle when braking. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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2. Technician A says that a direct TPMS sensor transmits a signal to the TPMS module concerning tire pressure. Technician B says that some TPMSs use temperature sensors to determine an overheating tire. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 3. Technician A says the steering torque sensor tells the VSC module how hard the driver is turning the steering wheel. Technician B says the steering wheel position sensor is also used as an input to the stability control. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 4. Technician A says an air spring suspension can control body roll. Technician B says an air spring suspension cannot be used to control ride height. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. While discussing the VSC module, Technician A says the VSC computer works in cooperation with the other computers in the vehicle network to provide stability control. Technician B says that the VSC module stands alone and does not need to communicate with the vehicle network. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 6. Technician A says that reducing torque to the wheels can help prevent loss of traction. Technician B says that starting out in a lower gear can reduce torque to the wheels. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 7. The Toyota Prius uses two electric motor generators: MG1 and MG2. Technician A says that MG1 is used as a generator when braking and on deceleration. Technician B says that MG2 is used as the main drive electric motor. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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8. Technician A says the TAC module has direct control of the throttle position. Technician B says that the ECM can command the TAC to find the best throttle position for the conditions. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

10. Technician A says that the yaw sensor measures the actual turning angle that the vehicle is traveling. Technician B says that the steering angle sensor measures the direction that the driver is trying to steer. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

9. Technician A says the Distronic system is a cruise control system. Technician B says the Distronic system can see drivers approximately 6,000 feet in front of the vehicle. A. A only C. Both A and B B. B only D. Neither A nor B

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Note: Terms are highlighted in bold, followed by Spanish translation in color. ABS  An ABS is a service brake system that modulates hydraulic pressure to one or more wheels as needed to keep those wheels from locking during braking. If the wheel locks during braking, steering control becomes very difficult. ABS allows the driver to maintain control of the vehicle during a panic stop. ABS  Un ABS es un sistema de servicio de frenos que modula la presión hidráulica a una o más ruedas según sea necesario para evitar que esas ruedas se enllaven durante el frenado. Si la rueda se enllava durante el frenado, el control de la dirección se vuelve muy dif ícil. El ABS premite al conductor mantener el control del vehículo durante una parada de emergencia. accumulator  A container that stores hydraulic fluid under pressure. It can be used as a fluid shock absorber or as an alternate pressure source. A spring or compressed gas behind a sealed diaphragm provides the accumulator pressure. In an ABS, the accumulator is a gas-filled chamber that acts as both a storage container for system fluid and a reserve pressure chamber to provide smooth antilock operation and dampen pressure pulses from the system pump. acumulador  Recipiente que contiene líquido hidráulico bajo presión. Se puede utilizar como líquido amortiguador o como fuente de presión alternativa. Un resorte o gas comprimido detrás de un diafragma sellado proporciona presión al acumulador. En un sistema ABS, el acumulador es una cámara llena de gas que actúa a la vez como recipiente de almacenamiento de líquido para el sistema y como cámara de reserva de presión para proporcionar una operación suave de antibloqueo y amortiguar los pulsos de presión que provienen de la bomba del sistema. active brakes  A brake system that warns the driver of an impending collision with a vehicle ahead. The system can also apply the brakes to slow the vehicle if the driver does not respond.

frenos activos  Sistema de frenos que advierte al conductor de una colisión inminente con un vehículo que se encuentra al frente. El sistema también puede activar los frenos para que se disminuya la velocidad del vehículo si el conductor no responde. active braking systems  Active braking systems can apply the brakes without the driver touching the brake pedal. Meant to be used during an emergency stop. sistemas de frenado activo  Los sistemas de frenado activo pueden accionar los frenos sin que el conductor toque los pedales de freno. Destinado para utilizarse durante una parada de emergencia. actuator(s)  Any device that receives an output signal or command from a computer and does something in response to the signal. impulsor  Cualquier dispositivo que reciba un comando o una señal de salida de un computador y haga algo como respuesta a dicha señal. adjustable pedal system (APS)  Mechanical devices capable of moving the brake, accelerator, and clutch pedal forward (up) and backward (down) to accommodate different drivers. Usually computer controlled based on the driver’s input. sistema de pedal adaptable (APS) Dispositivo mecánico capaz de mover los pedales del freno, el acelerador y el clutch o embrague hacia adelante (arriba) y hacia atrás (abajo) para acomodar a los diferentes conductores. Usualmente está controlado por una computadora en el mando de entrada del conductor. adsorption  The condensation of a gas on the surface of a solid. adsorción  La condensación de un gas en la superficie de un sólido. air brakes  Braking system used on large trucks that utilize air pressure instead of hydraulics to operate. frenos de aire  Sistema de frenado utilizado en grandes camiones que usa presión de aire en lugar de presión hidráulica para funcionar. 267

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ampere (A)  The unit for measuring electric current. One ampere equals a current flow of 6.241 × 1018 electrons per second. amperio (A)  Unidad de medida de la corriente ­eléctrica. Un amperio equivale a un flujo de ­corriente de 6,28 × 1018 ­electrones por segundo. analog  A signal that varies proportionally with the information that it measures. In a computer, an analog signal is voltage that fluctuates over a range from high to low. analógica  Señal que varía proporcionalmente con la información que mide. En un computador, una señal analógica es la tensión que fluctúa en un ­margen de alto a bajo. antilock brake control module (ABCM) The ­computer that controls the ABS operation. May be used on some systems for traction control. módulo de control antibloqueo de frenos (AC)  Computador que controla el funcionamiento de los frenos ABS. En algunos sistemas se puede utilizar para controlar la tracción. antilock brake system (ABS)  A service brake ­system that modulates hydraulic pressure to one or more wheels as needed to keep those wheels from locking during braking. An antilock brake system can improve vehicle control during hard ­braking and eliminate or reduce the tendency for the ­vehicle to skid. sistema antibloqueo de frenos (ABS)  Sistema de frenos de servicio que modula la presión hidráulica a una o más ruedas cuando es necesario para evitar que éstas se bloqueen al frenar. Un sistema antibloqueo de frenos puede mejorar el control del vehículo durante un frenado brusco y eliminar o reducir la tendencia del vehículo a patinar. aramid fibers  A family of synthetic materials that are stronger than steel but weigh little more than half what an equal volume of fiberglass weighs. fibras de aramida  Familia de materiales sintéticos más fuertes que el acero pero que pesan poco más de la mitad que un mismo volumen de fibra de vidrio. arcing  The process of grinding or forming drum brake linings to conform to the drum diameter and provide clearance where needed. formación de arco  Proceso de limar o formar los forros de frenos de tambor para que se adapten al diámetro del tambor y den tolerancia donde sea necesario.

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asbestos  The generic name for a silicate compound that is very resistant to heat and corrosion. Its excellent heat dissipation abilities and coefficient of friction make it ideal for automotive friction materials such as clutch and brake linings. Asbestos fibers are a serious health hazard if inhaled. amianto  Nombre genérico de un compuesto de silicatos muy resistente al calor y a la corrosión. Su excelente capacidad de disipación de calor y su coeficiente de fricción lo hacen ideal para materiales de fricción para automoción, como el embrague y los forros de frenos. Las fibras de amianto constituyen un serio peligro para la salud si se inhalan. asbestosis  A progressive and disabling lung disease caused by inhaling asbestos fibers over a long period of time. asbestosis  Enfermedad pulmonar progresiva que provoca la incapacidad de la persona a causa de la inhalación de fibras de amianto. aspect ratio  The ratio of the cross-sectional height to the cross-sectional width of a tire expressed as a percentage. relación entre dimensiones  Relación entre la altura y la anchura de la sección transversal de un neumático, expresada en un porcentaje. atmospheric pressure  The weight of the air that makes up the Earth’s atmosphere. presión atmosférica  Peso del aire que constituye la atmósfera de la Tierra. atmospheric suspended  A term that describes a power brake vacuum booster in which atmospheric pressure is present on both sides of the diaphragm when the brakes are released. An obsolete type of vacuum booster. de suspensión atmosférica  Término que describe un reforzador de vacío para frenos de potencia en el cual hay presión atmosférica a ambos lados del diafragma cuando se sueltan los frenos. Tipo ­obsoleto de reforzador de vacío. automatic ride control (ARC)  An electronically controlled suspension system designed to improve vehicle ride and increase vehicle stability. control automático del movimiento (ARC)  Sistema de suspensión controlado ­electrónicamente diseñado para mejorar el manejo y la estabilidad del vehículo. Automotive Friction Material Edge Code  A series of codes on the side of a brake lining (disc or drum)

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Glossary

that identifies the manufacturer, the lining material, and coefficient of friction. These codes are for lining identification and comparison; they do not indicate quality. Código de Borde para Material de Fricción en Automóviles  Serie de códigos situados en el lado de un forro de frenos (de disco o de tambor) que identifica el fabricante, el material del forro y el coeficiente de fricción. Estos códigos identifican y comparan los forros; no indican calidad. backing plate  The mounting surface for all other parts of a drum brake assembly except the drum. placa de refuerzo  Superficie en que se montan todas las partes de un freno de tambor, excepto el tambor. ball and ramp  A common kind of caliper-actuated parking brake. bola y rampa  Tipo común de freno de estacionamiento accionado por calibre. banjo fitting  A round, banjo-shaped tubing connector with a hollow bolt through its center that enables a brake line to be connected to a hydraulic component at a right angle. ajuste de banjo  Conector redondo, en forma de banjo, atravesado en el centro por un perno hueco, que permite conectar en ángulo recto una línea de frenos a un componente hidráulico. bearing cage  The steel component that holds the rollers together in a tapered roller bearing. jaula de cojinetes  Componente de acero que mantiene juntas las bolillas en un cojinete de bolillas cónicas. bearing cone  The inner race of a tapered roller bearing; usually an integral assembly with the rollers and the cage. cono del cojinete  Canaleta interior de un cojinete de bolillas cónicas; por lo general, conjunto integrado de bolillas y jaula. bearing cup  The outer race of a tapered roller bearing; usually pressed into the wheel hub. taza del cojinete  Canaleta exterior de un cojinete de bolillas cónicas; por lo general está comprimida en el buje de la rueda. belted bias ply tire  Tire construction that incorporates the belts used in radial ply tires with the older bias ply construction. neumático encintado de capas contrapuestas  Construcción de neumáticos que incorpora las cintas usadas en los neumáticos de

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capas radiales a la construcción más antigua de capas contrapuestas. bias ply tire  Tire construction in which the cords in the body plies of the carcass run from bead to bead at an angle from 26 to 38 degrees instead of 90 degrees as in a radial ply tire. neumático de capas contrapuestas Construcción de neumáticos en la cual los cables de las capas del cuerpo de la carcasa van de una a otra nervadura en un ángulo de 26 a 38 grados, en vez de uno de 90 grados como en los neumáticos radiales. bimetallic drum  A composite brake drum made of cast iron and aluminum. tambor bimetálico  Tambor de frenos hecho de hierro fundido y aluminio. binary system  The mathematical system that uses only the ­digits 0 and 1 to present information. sistema binario  Sistema matemático que utiliza sólo los dígitos 0 y 1 para presentar información. binder  Adhesive or glue used in brake linings to bond all the other materials together. aglomerante  Adhesivo o pegamento que se utiliza en los forros de frenos para unir todos los demás materiales. bit  A binary digit (0 or 1). Bit combinations are used to represent letters and numbers in digital computers. Eight bits equal one byte. bit  Dígito binario (0 o 1). Las combinaciones de bits se emplean para representar letras y números en los computadores digitales. Ocho bits equivalen a un byte. bleeding  A service procedure that removes air from the hydraulic system. extracción de vapor  Procedimiento de mantenimiento que extrae aire del sistema hidráulico. bonded brake linings  Bonded brake linings are attached to the steel backing with adhesive. revestimientos de freno unidos  Los revestimientos de freno unidos están pegados a la placa de resfuerzo de acero con remaches. bonded lining  Brake lining attached to the pad or shoe by high-strength, high-temperature adhesive. forro adherido  Forro de freno unido a la pastilla o zapata por un adhesivo muy fuerte, de alta temperatura. brake assisted (BA)  A sensor mounted on the vacuum brake booster to detect brake pedal motion and speed of motion for faster brake application.

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freno, asistido (BA)  Sensor instalado en el sistema booster del freno para detectar el movimiento del pedal y la velocidad del movimiento para una más rápida aplicación del freno. brake caliper  The part of a disc brake system that converts hydraulic pressure back to mechanical force that applies the pads to the rotor. The caliper is mounted on the suspension or axle housing and contains a hydraulic piston and the brake pads. calibre del freno  Parte de un sistema de frenos de disco que vuelve a convertir la presión hidráulica en fuerza mecánica que aplica las pastillas al rotor. El calibre va montado en el alojamiento del eje o la suspensión, y contiene un pistón hidráulico y las pastillas de freno. brake fade  The partial or total loss of braking power caused by excessive heat, which reduces friction between the brake linings and the rotors or drums. pérdida de freno  Pérdida parcial o total de la potencia de freno debido a un calor excesivo, el cual reduce la fricción entre los forros de los frenos y los rotores o tambores. brake pad  The part of a disc brake assembly that holds the lining friction material that is forced against the rotor to create friction to stop the vehicle. pastilla de freno  Parte de un conjunto de frenos de disco que aloja el material de fricción del forro que se fuerza contra el rotor para crear la fricción que detendrá el vehículo. brake pedal position (BPP) sensor  Sensor used to determine how fast and how far the brake pedal has been depressed. sensor de posición del pedal de freno (BPP)  Sensor utilizado para determinar cuán rápido y qué tanto se presiona el pedal de freno. brake pressure modulator valve (BPMV)  A valve assembly used in the Teves Mark 20 ABS to control braking of the wheels. Commonly referred to as the hydraulic modulator. válvula moduladora de la presión de los frenos (BPMV)  Válvula que se usa en el sistema de ABS del Teves Mark 20 para controlar el frenado de las ruedas. Comúnmente se le llama modulador hidráulico. brake shoes  The curved metal parts of a drum brake assembly that carry the friction material lining.

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zapatas de freno  Partes metálicas curvas de un conjunto de frenos de tambor que llevan el forro de material de fricción. buffer  An isolating circuit used to avoid interference between a driven circuit and its driver circuit. Also a storage device, or circuit, that compensates for a difference in the rate of data transmission. A buffer can absorb data transmitted faster than a receiving circuit or device can respond. separador de interferencias  Circuito aislante que se emplea para evitar posibles interferencias entre un circuito controlado y su circuito controlador. También un dispositivo, o circuito, de almacenamiento que compensa una diferencia en la velocidad de transmisión de datos. Un separador de interferencias puede absorber datos transmitidos más rápidamente de lo que puede responder un circuito o dispositivo receptor. bulkhead  Steel panel that separates the engine compartment from the passenger compartment. mampara  Panel de acero que separa el compartimiento del motor del compartimiento del pasajero. caliper  The major component of a disc brake system. It houses the piston(s) and supports the brake pads. calibre  Componente principal de un sistema de frenos de disco. Contiene el pistón (o pistones) y soporta las pastillas de freno. caliper support  The bracket or anchor that holds the brake caliper. soporte del calibre  Mordaza o ancla que aloja el calibre de freno. camber  The inward or outward tilt of the wheel measured from top to bottom and viewed from the front of the car. inclinación  Inclinación de la rueda hacia dentro o hacia fuera, medida de arriba abajo y vista desde la parte frontal del vehículo. cam-ground lining  A brake shoe lining that has been arced or formed so that it is thinner at the ends than at the center, and the lining surface is not a portion of a circle with a constant radius. forro elíptico  Forro de zapata de freno que se ha arqueado o formado de tal manera que es más delgado en los extremos que en el centro, y cuya superficie de recubrimiento no forma parte de un círculo de radio constante.

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carcass  The steel beads around the rim and layers of cords or plies that are bonded together to give a tire its shape and strength. carcasa  Nervaduras de acero alrededor de la llanta y las capas de cordones, o capas que están unidas para dar forma y resistencia a un neumático. casing  Layers of sidewall and undertread rubber added to a tire carcass. cubierta  Capas de caucho añadidas a la carcasa del neumático. caster  The backward or forward angle of the steering axis viewed from the side of the car. inclinación del eje  Inclinación hacia delante o hacia atrás del eje de dirección visto desde el costado del auto. center high-mounted stoplamp (CHMSL)  Stoplamp mounted above the taillamps or tailgate to aid in visibility. luz de freno central elevada (CHMSL)  Luz de freno colocada sobre las luces o la cajuela trasera para mejorar la visibilidad. central processing unit (CPU)  The calculating part of any computer that makes logical decisions by comparing conditioned input with data in memory. unidad central de proceso (UCP)  Parte de cálculo de un computador que llega a decisiones lógicas comparando los datos de entrada condicionados con los datos que tiene en la memoria. ceramic  Ceramic brake pads are made from ceramic and copper which make less noise and cause less damage to rotors than semimetallic pads. Cerámica  Los tacos cerámicos de freno están hechos de cerámica y cobre, los cuales hacen menos ruido y causan menos daño a los rotores en comparación a los tacos semi-metálicos. ceramic brake pads  Pads consisting of a combination of ceramic material and copper or some other metal fibers. cojines de freno de cerámica  Cojines que consisten en una combinación de materiales y del cobre de cerámica, o algunas otras fibras del metal. channel  Individual legs of the hydraulic system that relay pressure from the master cylinder to the wheel cylinder. canal  Terminales del sistema hidráulico que transmiten presión desde el cilindro maestro al cilindro de la rueda.

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check valve  Valve that allows fluid or air to flow in one direction but not in the opposite direction. válvula de control  Válvula que permite el paso de líquidos o aire en un sólo sentido contrario. chlorinated hydrocarbon solvents  A class of chemical compounds that contain various combinations of hydrogen, carbon, and chlorine atoms; best known as a class of cleaning solvents. solventes clorohidrocarbonados  Clase de compuestos químicos que contienen diferentes combinaciones de átomos de hidrógeno, carbono y cloro; más conocidos como un tipo de solventes limpiadores. class 2 wiring  A multiplexing network in which each wired-in module can share information through different pulse signals that are used to identify each module on the net. cableado clase 2  Red múltiple en la cual cada módulo conectado pueden compartir información mediante diferentes señales de pulsación que se usan para identificar cada módulo en la red. coefficient of friction  A numerical value that expresses the amount of friction between two objects, obtained by dividing tensile force (motion) by weight force. A coefficient of friction can be either static or kinetic. coeficiente de fricción  Valor numérico que expresa la cantidad de fricción que hay entre dos objetos, obtenido mediante la división de la fuerza de tracción (movimiento) por la del peso. Los coeficientes de fricción pueden ser estáticos o dinámicos. cold inflation pressure  The tire inflation pressure after a tire has been standing for 3 hours or driven less than 1 mile after standing for 3 hours. presión de inflado en frío  Presión de inflado del neumático después de haber estado en reposo durante tres horas o haber recorrido menos de una milla después del mismo tiempo de reposo. combination valve  A hydraulic control valve with two or three valve functions in one valve body. válvula de combinación  Válvula de control hidráulico con dos o tres funciones de paso en el mismo cuerpo de válvula. command  An electrical signal or output signal from a computer (controller) to an actuator. comando  Señal eléctrica o señal de salida de una computadora (servo-regulador) a un servo-motor.

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composite drum  A drum made of different materials, usually cast iron and steel or aluminum, to reduce weight. The friction surfaces and the hubs are cast iron, but supporting parts are made of lighter metal. tambor compuesto  Tambor hecho de diferentes materiales, normalmente de hierro fundido y acero o aluminio, para reducir su peso. Las superficies de fricción y los bujes son de hierro fundido, pero las partes de soporte se hacen de metal más ligero. composite rotor  A rotor made of different materials, usually cast iron and steel, to reduce weight. The friction surfaces and the hubs are cast iron, but supporting parts are made of lighter steel stampings. rotor compuesto  Rotor construido con diferentes materiales, normalmente hierro fundido y acero para reducir su peso. Las superficies de fricción y los bujes son de hierro fundido, pero las partes de soporte son estampaciones de acero más ligero. conduit  A flexible metal housing or jacket that houses the parking brake cables to protect them from dirt, rust, abrasion, and other damage. conducto  Alojamiento de metal flexible o forro que recubre los cables del freno de estacionamiento para protegerlos de la suciedad, el polvo, la abrasión y otros daños. control valve assembly  The block of metal that contains the hydraulic passages and electric solenoids used to direct brake fluid during an ABS event. conjunto de válvulas de control  Bloque metálico que contiene los pasos hidráulicos y los solenoides eléctricos que se usan para dirigir el líquido de frenos en un evento ABS. controller  A computer programmed to perform certain decisions based on sensor signals and issue electrical commands to actuators. servo-regulador  Computadora programada para tomar ciertas decisiones de acuerdo a señales de un sensor y envíar ordenes eléctricas a los servo-motores. controller antilock brake (CAB) module The computer that controls the ABS operation. controlador, antibloqueo de freno (CAB)  Computador que controla el funcionamiento de los frenos ABS.

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cup expander  A metal disc that bears against the inner sides of wheel cylinder seals to hold the seal lips against the cylinder bore when the brakes are released. This keeps air from entering the cylinder past the retracting pistons and seals. cubeta de expansión  Disco metálico que se ajusta a los costados internos de las juntas del cilindro de las ruedas para sujetar los bordes de la junta contra el hueco del cilindro al aplicar los frenos. Así se impide que el aire que entra en el cilindro pase más allá de los pistones retráctiles y las juntas. cup seal  A circular rubber seal with a depressed center section surrounded by a raised sealing lip to form a cup. Cup seals often are used on the front ends of hydraulic cylinder pistons because they seal high pressure in the forward direction of travel but not in the reverse. cubeta de obturación  Junta de goma circular con una sección central hundida rodeada por un borde de junta saliente que forma una copa. Las cubetas de obturación se suelen usar en los extremos frontales de los pistones de los cilindros hidráulicos porque impiden el paso de alta presión hacia delante pero no en el sentido contrario. curing agent  A class of materials used in brake linings to accelerate the chemical reaction of the binders and other materials. agente endurecedor  Una clase de material que se utiliza en los forros de frenos para acelerar la reacción química de los aglomerantes y otros materiales. cycle  The microprocessor action of turning solenoids on or off. ciclo  Acción del microprocesador al activar o desactivar los solenoides. Department of Transportation (DOT) The U.S. government executive department that establishes and enforces safety regulations for motor vehicles and for federal highway safety. Departamento de Transportes (DOT)  Departamento ejecutivo del Gobierno de los EE.UU. que establece y hace cumplir las normas de seguridad para los vehículos a motor y para la seguridad vial federal. diaphragm  A flexible membrane, usually made of rubber, that isolates two substances or areas from each other. A rubber diaphragm isolates brake fluid in the master cylinder reservoir from the air. A

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diaphragm separates the two chambers of a power brake vacuum booster. diafragma  Membrana flexible, por lo común de goma, que aísla una sustancia o una zona de otra. Un diafragma de goma aisla del aire el líquido de frenos en el depósito del cilindro maestro. Un diafragma separa las dos cámaras de un reforzador de vacío en frenos de potencia. digital  A signal that is either on or off and that is translated into the binary digits 0 and 1. In a computer, a digital signal is voltage that is either low or high or current flow that is on or off. digital  Señal que está activada o desactivada y que se traduce por los dígitos binarios cero y uno. En un computador, una señal digital es una tensión alta o baja, o un flujo de corriente que está abierto o cerrado. digitized  The process of converting an analog voltage signal to a digital equivalent that the computer can understand. digitalizado  Proceso de conversión de una señal de tensión analógica a una señal equivalente que el computador pueda entender. directional control  The ability to steer the automobile while stopping. control direccional  Capacidad de gobernar el automóvil al detenerlo. directional stability  The ability to maintain a straight line stopping action. estabilidad de dirección  Capacidad de conservar la línea recta al detener el vehículo. disc brake  A brake in which friction is generated by brake pads rubbing against the friction surfaces on both sides of a brake disc or rotor attached to the wheel. freno de disco  Freno en el que la fricción se genera al rozar las pastillas de freno contra las superficies de fricción a ambos lados de un disco o rotor de freno que está unido a la rueda. distronic  A cruise control system introduced by Mercedes-Benz that can see vehicles approximately 600 feet in front. Distronic  Un sistema de control de crucero introducido por Mercedes-Benz que puede ver vehículos a aproximadamente 600 pies en frente. double flare  A type of tubing flare connection in which the end of the tubing is flared out, then is formed back on to itself.

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doble ensanche  Tipo de conexión de tubos en la que el extremo del tubo se acampana y luego se vuelve a doblar. drum brake  A brake in which friction is generated by brake shoes rubbing against the inside surface of a brake drum attached to the wheel. freno de tambor  Freno en el que la fricción la generan zapatas que rozan contra la superficie interior de un tambor de freno unido a la rueda. drum-in-hat  A brake rotor that includes a small drum used only for the parking brake. tambor interno  Rotor de freno que incluye un pequeño tambor, el cual se usa únicamente para el freno de estacionamiento. drum web  The closed side of a brake drum. membrana del tambor  Lado cerrado de un tambor de freno. duo-servo brake  A drum brake that develops selfenergizing action on the primary shoe, which in turn applies servo action to the secondary shoe to increase its application force. Brake application force is interrelated for the primary and the ­secondary shoes. Also called a dual-servo or a fullservo brake. freno servoduo  Freno de tambor que desarrolla acción autónoma sobre la zapata primaria, que a su vez aplica servoacción a la zapata secundaria para aumentar su fuerza de aplicación. La fuerza de aplicación de freno es interrelacionada para las zapatas primarias y las secundarias. También se conoce como freno servo dual o totalmente asistido. duty cycle  The percentage of time that a solenoid is energized during one complete on–off cycle during pulse-width modulation. ciclo de trabajo  Porcentaje de tiempo que recibe energía un solenoide en lo que dura un ciclo completo de activación–­desactivación durante la modulación de amplitud de pulso. dynamic rear proportioning (DRP)  An electric valve within an ABS used to control fluid to the rear brake in an action similar to the mechanical or hydraulic proportioning valve. el proporciónar dinámico de la parte posterior  Una válvula eléctrica dentro de un ABS controlaba el líquido al freno posterior en la acción similar a la válvula mecánica/hidráulica que proporcionaba.

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dynamic rear proportioning and electronic brake distribution  Dynamic rear proportioning and electronic brake distribution are names for the electronic function of the proportioning valve by the ABS braking system. dosificación dinámica trasera y distribución electrónica de frenos  La dosificación dinámica trasera y la distribución electrónica del freno son nombres de la función electrónica de la válvula dosificadora por el sistema de frenos ABS. eccentric  Not round, or concentric. excéntrico  Que no es redondo ni concéntrico. electronic brake control module (EBCM)  A term used to designate an ABS control module or the ABS computer. módulo de control electrónico de freno (EBCM)  Término que se usa para designar un módulo de control ABS o una computadora ABS. electronic brake system (EBS)  A hydraulic modulator used in conjunction with the brake assist sensor. sistema de frenado electrónico (EBS) Modulador hidráulico que se usa en conjunto con el sensor de asistencia de frenado. electro-hydraulic brake (EHB)  An electrically controlled hydraulic braking system that is being used to combine ABS and TCS into one system. freno electrohidráulico  Sistema de control hidráulico controlado eléctricamente que se usa para combinar el ABS y el TCS en un sistema. electrohydraulic unit  The microprocessor and hydraulic unit are combined in one unit. unidad electrohidráulica Microprocesador y unidad hidráulica combinados en un solo elemento. electromagnetic induction  The generation of voltage in a conductor by relative motion between the conductor and a magnetic field. inducción electromagnética  Generación de tensión en un conductor mediante un movimiento relativo entre el conductor y un campo magnético. electromagnetic interference (EMI)  A magnetic force field that influences a signal being sent to the microprocessor. interferencia electromagnética (EMI)  Campo de fuerza magnética que influye en una señal enviada al microprocesador.

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electronic brake traction control module (EBTCM)  Computerized module that controls the traction and antilock brakes. módulo de control electrónico de tracción de frenos (EBTCM)  Módulo computarizado que controla la tracción y los frenos antibloqueo. electronic steering  Power steering that uses an electric motor for assist. dirección electrónica  Dirección asistida que utiliza un motor eléctrico. enhanced traction system (ETS)  A traction control system used with the DBC-7 ABS. sistema de tracción mejorada (ETS)  Sistema de control de tracción que se usa con el ABS del DBC-7. equalizer  Part of the parking brake linkage that balances application force and applies it equally to each wheel. The equalizer often contains the linkage adjustment point. compensador  Parte del acoplamiento del freno de estacionamiento que equilibra la fuerza ejercida y la aplica por igual en cada rueda. Con frecuencia, el compensador incluye el punto de ajuste del acoplamiento. erasable programmable read-only memory (EPROM)  Computer memory program circuits that can be erased and reprogrammed. Erasure is done by exposing the integrated circuit chip to ultraviolet light. memoria de sólo lectura borrable y programable (EPROM)  Circuitos de programa de memoria del computador que se pueden eliminar y reprogramar. La eliminación es posible exponiendo a la luz ultravioleta el chip de circuito integrado. federal motor vehicle safety standards (FMVSS)  U.S. government regulations that prescribe safety requirements for various vehicles, including passenger cars and light trucks. The FMVSS regulations are administered by the U.S. Department of Transportation (DOT). normas federales de seguridad de vehículos a motor (FMVSS)  Normas gubernamentales de EE.UU. que dictan los requisitos de seguridad para diversos vehículos, incluyendo los automóviles de pasajeros y los camiones ligeros. El Departamento de Transportes de los EE.UU. (DOT) es el que administra las normas FMVSS. filler  A class of materials used in brake linings to reduce noise and improve heat transfer.

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relleno  Tipo de material usado en los forros de frenos para reducir el ruido y mejorar la transferencia de calor. fittings  The term applied to all plumbing connections on the car or in the house. ajustes  Término aplicado a las conexiones de tuberías del auto o de la casa. fixed caliper brake  A brake caliper that is bolted to its support and does not move when the brakes are applied. A fixed caliper must have pistons on both the inboard and the outboard sides. freno de calibre fijo  Calibre de freno que se fija al soporte con un perno y no se mueve al aplicar los frenos. Un calibre fijo debe tener pistones tanto en el lado exterior como en el interior. fixed rotor  A rotor that has the hub and the rotor cast as a single part. rotor fijo  Rotor en el que el buje y el rotor forman una única pieza. fixed seal  A seal for a caliper piston that is installed in a groove in the caliper bore and that does not move with the piston. junta fija  Junta para un pistón de calibre que se instala en una hendidura del hueco del calibre y que no se mueve con el pistón. floating caliper  A caliper that is mounted to its support on two locating pins or guide pins. The caliper slides on the pin in a sleeve or bushing. Because of its flexibility, this kind of caliper is said to float on its guide pins. calibre flotante  Calibre que se monta al soporte mediante dos pasadores de posición o pasadores guía. El calibre se desliza dentro del pasador a través de un manguito o casquillo. Debido a su flexibilidad, se dice que este tipo de calibre flota en los pasadores guía. floating rotor  A rotor and hub assembly made of two separate parts. rotor flotante  Conjunto de rotor y buje en dos piezas distintas. flux lines  Lines of magnetism. líneas de flujo  Líneas de magnetismo. force  Power working against resistance to cause motion. fuerza  Energía que trabaja contra la resistencia para producir movimiento. free play  The distance the brake pedal moves before the master cylinder primary piston moves.

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holgura  Distancia recorre el pedal del freno antes de que se mueva el pistón primario del cilindro maestro. frequency  The number of times, or speed, at which an action occurs within a specified time interval. In electronics, frequency indicates the number of times that a signal occurs or repeats in cycles per second. Cycles per second are indicated by the symbol hertz (Hz). frecuencia  Número de veces, o velocidad, a la que ocurre una acción dentro de un intervalo de tiempo especificado. En electrónica, la frecuencia indica el número de veces que una señal se da o se repite en ciclos por segundo. Los ciclos por segundo se indican con el símbolo “herzios” (Hz). friction  The force that resists motion between the surfaces of two objects or forms of matter. fricción  Fuerza que se opone al movimiento entre las superficies de dos objetos o formas de materia. friction materials  Friction materials help provide the frictional stopping power, such as graphite, powdered metal, and nut shells. materiales de fricción  Los materiales de fricción ayudan a proporcionar la energía de frenado friccional, como el grafito, metal en polvo y cáscaras de nuez. friction modifier  A class of materials used in brake linings to modify the final coefficient of friction of the linings. modificador de rozamiento  Tipo de material usado en los forros de frenos para modificar el coeficiente final de fricción de las envolturas. fulcrum  The pivot point of a lever. punto de apoyo  Punto de apoyo de una palanca. gas fade  It is caused by hot gas and dust, which reduce between the brake shoe and drum or rotor and brake pad during prolonged hard braking. pérdida de gas  es causada debido al gas caliente y al polvo que se reducen entre la zapata del freno y el tambor o rotor, y la pastilla del freno durante un frenado fuerte prolongado. geometric centerline  A static dimension represented by a line through the center of the vehicle from front to rear. línea media geométrica  Dimensión estática representada por una línea en el centro del vehículo desde el frente hasta la parte de atrás.

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gross vehicle weight rating (GVWR)  Total weight of a vehicle plus its maximum rated payload. peso bruto del vehículo (GVWR)  Peso total de un vehículo más la carga de régimen máxima.

Hall-effect switch  A device that produces a voltage pulse dependent on the presence of a magnetic field. Hall-effect voltage varies as magnetic reluctance varies around a current-carrying semiconductor.

conmutador de efecto Hall  Aparato que produce una variación rápida de tensión dependiente de la presencia de un campo magnético. La tensión de efecto Hall varía al cambiar la resistencia magnética de alrededor de un semiconductor que lleva corriente.

height-sensing proportioning valve A proportioning valve in which hydraulic pressure is adjusted automatically according to the vertical movement of the chassis in relation to the rear axle during braking; sometimes also called a weightsensing proportioning valve.

válvula dosificadora de detección de altura  Válvula dosificadora en la que la presión hidráulica se ajusta automáticamente según el movimiento vertical del chasis en relación con el eje trasero durante el frenado; a veces también se la denomina válvula dosificadora de detección de peso.

hold-down springs  Small springs that hold drum brake shoes in position against the backing plate while providing flexibility for shoe application and release.

resortes de sujeción  Pequeños resortes que mantienen las zapatas de frenos de tambor en posición contra la placa de refuerzo, a la vez que dan flexibilidad para aplicar y soltar la zapata.

hydraulic modulator  The common term for an ABS computer-controlled set of valves used to control brake pressure to various wheels. modulador hidráulico  Término común para el conjunto de válvulas controladas por computadora del ABS que se usan para controlar la presión del frenado a las distintas ruedas.

hydraulic system mineral oil (HSMO)  A brake fluid made from a mineral oil base, used by a few European carmakers. DOT specifications do not apply to HSMO fluids, and HSMO fluids cannot be mixed with DOT fluids. aceite mineral del sistema hidráulico (HSMO)  Líquido de frenos a base de aceite mineral que utilizan algunos fabricantes de automóviles

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europeos. Las especificaciones de los líquidos DOT no se aplican a los líquidos HSMO, y éstos últimos no se pueden mezclar con los primeros. hydro-boost  A hydraulic power brake system that uses the power steering hydraulic system to provide boost for the brake system. reforzador hidráulico  Un sistema hidráulico de frenos de potencia que utiliza el sistema hidráulico de dirección de potencia para alimentar el sistema de frenado. hydroplane  The action of a tire rolling on a layer of water on the road surface instead of staying in contact with the pavement. Hydroplaning occurs when water cannot be displaced from between the tread and the road. aquaplaning  Acción de un neumático que rueda sobre una capa de agua sobre la superficie vial en lugar de mantenerse en contacto con el pavimento. El “aquaplaning” se produce cuando no se puede desplazar el agua entre los dibujos del neumático y la calle. hydroplaning  Hydroplaning is the sliding or skidding caused by the vehicle riding on a thin film of water, risking a serious loss of traction. Hydroplaning is aggravated by having worn tires and excessive speed. Hidroplaneo  El Hidroplaneo es el deslizamiento o resbalo causado por una fina capa de agua, arriesgándose a una grave pérdida de tracción. El hidroplaneo es agravado por el uso de llantas desgastadas y la excesiva velocidad. hygroscopic  The chemical property or characteristic of attracting and absorbing water, particularly out of the air. Polyglycol brake fluids are hygroscopic. higroscópico  Que posee la propiedad química o característica de atraer y absorber agua, en especial del aire. Los líquidos de frenos con poliglicol son higroscópicos. inertia  The tendency of an object in motion to keep moving and the tendency of an object at rest to remain at rest. inercia  Tendencia de un objeto en movimiento a seguir moviéndose y la de un objeto en reposo a permanecer en reposo. integrated ABS  An antilock brake system in which the ABS hydraulic components, the standard brake hydraulic components, and a hydraulic power booster are joined in a single, integrated hydraulic system.

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ABS integrados  Sistema antibloqueo de frenos en el que los componentes hidráulicos de los frenos ABS, los componentes hidráulicos de los frenos estándar y un reforzador hidráulico de potencia se unen en un único sistema hidráulico integrado. integrated circuit (IC)  A complete electronic circuit of many transistors and other devices, all formed on a single silicon semiconductor chip. circuito integrado (IC)  Completo circuito electrónico de muchos transistores y otros dispositivos, todos formados sobre un único chip semiconductor de siliconas. integrated control unit (ICU)  A controller for an ABS and TCS. integrado control unidad (ICU)  UN controlador por un ABS y TCS. intermediate lever  Part of the parking brake linkage under the vehicle that increases application force and works with the equalizer to apply it equally to each wheel. palanca intermedia  Parte del acoplamiento del freno de estacionamiento, situada debajo del vehículo, que aumenta la fuerza de aplicación y que trabaja con el compensador para aplicarla por igual a cada rueda. ISO fitting  A type of tubing flare connection in which a bubble-shaped end is formed on the tubing; also called a bubble flare. ensanche ISO  Tipo de conexión con ensanche del tubo en el cual un extremo toma forma de burbuja; también se le llama ensanche de burbuja. kinetic energy  The energy of mechanical work or motion. energía cinética  Energía del trabajo mecánico o movimiento. kinetic friction  Friction between two moving objects or between one moving object and a stationary surface. fricción cinética  Fricción entre dos objetos en movimiento, o entre uno en movimiento y una superficie estacionaria. lands  The raised surfaces on a valve spool. partes planas  Superficies elevadas en un carrete de válvula. lateral accelerometer  Vehicle sensor used to measure the speed of the vehicle’s lateral movement during operation. acelerómetro lateral  Un acelerómetro lateral es un sensor del vehículo usado para medir la velocidad

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del movimiento lateral del vehículo durante la operación. lathe-cut seal  A fixed seal for a caliper piston that has a square or irregular cross section; not round like an O-ring. junta torneada  Junta fija para un pistón de calibre que tiene una sección transversal cuadrada o irregular, no redonda como en un toroide. leading shoe  The first shoe in the direction of drum rotation in a leading-trailing brake. When the vehicle is going forward, the forward shoe is the leading shoe, but the leading shoe can be the front or the rear shoe depending on whether the drum is rotating forward or in reverse and whether the wheel cylinder is at the top or the bottom of the backing plate. The leading shoe is self-energizing. zapata tractora  Primera zapata en la dirección de giro del tambor en un freno de tracción-remolque. Cuando el vehículo avanza, la zapata delantera es la tractora, pero la zapata tractora puede ser la delantera o la trasera dependiendo de si el tambor está girando hacia delante o hacia atrás y de si el cilindro de la rueda está en la parte superior de la placa de refuerzo o en la inferior. La zapata tractora es autónoma en cuanto a energía. leading-trailing brake  A drum brake that develops self-­energizing action only on the leading shoe. Brake application force is separate for the leading and the trailing shoes. Also called a partial-servo or a nonservo brake. freno tracción-remolque  Freno de tambor que desarrolla una acción autónoma sólo sobre la zapata tractora. La fuerza de aplicación de freno es independiente para las zapatas tractoras y para las de remolque. También se conoce como freno parcialmente asistido o freno no asistido. leverage  The use of a lever and fulcrum to create a mechanical advantage, usually to increase force applied to an object. The brake pedal is the first point of leverage in a vehicle brake system. transmisión por palancas  Utilización de una palanca y un punto de apoyo para crear una ventaja mecánica, generalmente aumentar la fuerza que se aplica a un objeto. El pedal del freno es el primer punto de transmisión por palancas en un sistema de frenos de vehículos. lining fade  Brake fade because of a loss of brake lining coefficient of friction caused by excessive heat.

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pérdida por envolturas  Pérdida de frenado debido a una disminución del coeficiente de fricción de los forros de freno a causa de un calor excesivo. lockup  A condition in which a wheel stops rotating and skids on the road surface. bloqueo  Condición en la cual una rueda deja de girar y patina sobre la superficie vial. lockup or negative wheel slip  Lockup or negative wheel slip is a condition in which a wheel stops rotating and skids on the road surface. enllave o deslizamiento negativo de la rueda El enllave o deslizamiento negativo de la rueda es una condición en la cual una rueda deja de girar y se desliza sobre la superficie de la carretera. mass  The measure of the inertia of an object or form of matter or its resistance to acceleration. Also the molecular density of an object. masa  Medida de la inercia de un objeto o forma de materia, o su resistencia a la aceleración. También la densidad molecular de un objeto. master cylinder  The liquid-filled reservoir in the hydraulic brake system or clutch where hydraulic pressure is developed when the driver depresses a foot pedal. cilindro principal  El cilindro principal es el depósito llenado del líquido en el sistema de frenos hidráulico donde se desarrolla la presión hydráulica cuando el conductor presiona un pedal con su pie. mechanical advantage  Increase in force through the use of leverage, such as at the brake pedal. Ventaja Mecánica  Aumento de la fuerza a través del uso de apalancamiento, como en el pedal de freno. mechanical fade  Brake fade because of heat expansion of a brake drum away from the shoes and linings. Mechanical fade does not occur with disc brakes. pérdida mecánica de frenado  Pérdida de frenado debido a la dilatación térmica de un tambor de freno, que lo separa de las zapatas y los forros. La pérdida mecánica no se produce con los frenos de disco. metallic lining  Brake friction material made from powdered metal that is formed into blocks by heat and pressure. forro metálico  Material de fricción para frenos hecho de metal en polvo que se transforma en bloques por medio de calor y presión.

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metering valve  A hydraulic control valve used primarily with front disc brakes on RWD vehicles. The metering valve delays pressure application to the front brakes until the rear drum brakes have started to operate. válvula de dosificación  Válvula de control hidráulica que se usa principalmente con frenos delanteros de disco en vehículos RWD. La válvula de dosificación demora la aplicación de presión a los frenos delanteros hasta que hayan comenzado a funcionar los frenos traseros de tambor. microprocessor  A digital computer or processor built on a single integrated circuit chip. A microprocessor can perform functions of arithmetic logic and control logic. It is the basic building block of a microcomputer system. microprocesador  Computador digital o procesador construido sobre un único chip de circuitos integrados. Un microprocesador puede realizar funciones de lógica aritmética y lógica de control. Es el elemento básico de construcción de un sistema de microprocesador. mold-bonded lining  A pad assembly made by applying adhesive to the pad and then pouring the uncured lining material onto the pad in a mold. The assembly is cured at high temperature to fuse the lining and adhesive to the pad. forro adherido al molde  Conjunto de pastillas formado por la aplicación de adhesivo a las pastillas y vertiendo luego el material de envoltura no vulcanizado sobre éstas en un molde. El conjunto se vulcaniza a una temperatura elevada para fundir el forro y el adhesivo a la pastilla. momentum  The force of continuing motion. The momentum of a moving object equals its mass times its speed. impulsor  Fuerza de un movimiento continuo. El impulso de un objeto en movimiento es igual a la masa por la velocidad. multiplexing  The network used by multiple computers so that only one component is transmitting at a time. multiplexación  La red usada por las computadoras múltiples de modo que solamente una componente esté transmitiendo a la vez. National Highway Transportation and Safety Agency (NHTSA)  A federal agency assigned to develop regulations for highway safety including vehicle safety features.

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Agencia Nacional de Transporte y Seguridad en Carreteras (NHTSA)  Agencia federal asignada a desarrollar regulaciones para la seguridad en las carreteras incluyendo detalles de seguridad vehicular. negative wheel slip  Wheel lockup that occurs when too much braking force is applied to a wheel and the tire skids on the pavement. ABS controls negative wheel slip by modulating (decreasing and increasing) the hydraulic pressure to the wheel or wheels that is/are skidding. deslizamiento negativo de la rueda  Bloqueo de la rueda que tiene lugar cuando se aplica un frenado demasiado fuerte a la rueda y la llanta patina sobre el pavimento. Los frenos ABS controlan el deslizamiento negativo de la rueda regulando (aumentando y disminuyendo) la presión hidráulica de la rueda o las ruedas que patina/n. network  The channel through which several computers share information. red  Canal a través del cual diversos computadores comparten la información. nonintegrated ABS  An antilock brake system in which the ABS hydraulic components are attached to, but separate from, the normal brake hydraulic system and power booster. ABS no integrado  Sistema antibloqueo de frenos en el que los componentes hidráulicos del ABS se conectan, pero estando separados, al sistema hidráulico normal de frenos y al reforzador de potencia. O-ring  A circular rubber seal shaped like the letter “O.” toroide  Junta de goma circular con la forma de la letra “O.”

Occupational Safety and Health Administration (OSHA)  A division of the U.S. Department of Labor that establishes and enforces workplace safety regulations. Administración de Seguridad y Salud en el Trabajo (OSHA)  División del Departamento de trabajo de los EE.UU. que establece y hace cumplir las normas de seguridad en el lugar de trabajo. ohm  The unit used to measure the amount of electrical resistance in a circuit or an electrical device. One ohm is the amount of resistance present when one volt forces one ampere of current through a circuit or a device. Ohm is abbreviated with the Greek letter omega (Ω).

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ohmio  Unidad usada para medir la cantidad de resistencia eléctrica de un circuito o de un aparato eléctrico. Un ohmio es la cantidad de resistencia presente cuando un voltio hace pasar un amperio de corriente a través de un circuito o de un aparato. El ohmio se abrevia con la letra griega omega (Ω). Ohm’s law  The mathematical formula for the relationships between voltage, current, and resistance; often stated simply as E (voltage) = I (current) × R (resistance). ley de Ohm  Fórmula matemática que expresa las relaciones entre tensión, corriente y resistencia; frecuentemente se enuncia simplemente por E (tensión) = I (corriente) × R (resistencia). organic lining  Brake friction material made from nonmetallic fibers bonded together in a composite material. forro orgánico  Material de fricción del freno hecho de fibras no metálicas adheridas en un material compuesto. overload spring  Spring in the end of the cable in cable-operated adjusters that lets the cable move without breaking if the pawl or star wheel is jammed. resorte de sobrecarga  Resorte al final del cable de los reguladores operados por cables que permite que éste se mueva sin romperse si el trinquete o la rueda de estrella están agarrotados. P-metric system  The most common modern system to specify passenger car tire sizes. sistema métrico P  Sistema métrico más moderno y común para especificar el tamaño de los neumáticos de los automóviles. pad hardware  Miscellaneous small parts such as antirattle clips and support clips that hold brake pads in place and keep them from rattling. hardware de cojines  Piezas pequeñas surtidas, como grapas antiresonancia y grapas de apoyo que mantienen los cojines de los frenos en su lugar y evitan que suenen. pad wear indicators  Devices that warn the driver when disc brake linings have worn to the point where they need replacement. Wear indicators may be mechanical (audible) or electrical. indicadores del desgaste de los cojines Dispositivos que advierten al conductor de que los forros de los frenos de disco se han gastado tanto que es necesario cambiarlos. Los indicadores de desgaste pueden ser mecánicos (acústicos) o eléctricos.

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parking brake control  The pedal or lever used to apply the parking brakes. control del freno de estacionamiento Pedal o palanca que se usa para aplicar los frenos de estacionamiento. parking brakes  The braking system that is used to hold the vehicle stationary while parked. pawl  A hinged or pivoted component that engages a toothed wheel or rod to provide rotation or movement in one direction while preventing it in the opposite direction. trinquete  Componente articulado o embisagrado que se engrana a una rueda o varilla dentada para ofrecer rotación o movimiento en un sentido mientras que lo impide en el sentido contrario. permanent magnet (PM) generator  A reluctance sensor. A sensor that generates a voltage signal by moving a conductor through a permanent magnetic field. generador de magneto permanente (PM) Sensor de reluctancia. Sensor que genera una señal de tensión al mover un conductor a través de un campo magnético permanente. perpetual energy  Energy that can be produced or converted without using additional energy forever. energía perpetua  Energía que puede producirse/ convertise sin usar energía adicional. phenolic plastic  Plastic made primarily from phenol, a compound derived from benzene and also called carbolic acid. plástico fenólico  Plástico hecho principalmente de fenol, compuesto derivado del benceno, llamado también ácido carbólico. piston stop  A metal part on a brake backing plate that keeps the wheel cylinder pistons from moving completely out of the cylinder bore. tope de pistón  Parte metálica de la placa de refuerzo del freno que impide que los pistones del cilindro de la rueda se salgan del hueco del cilindro. polyglycol  A mixture of several alcohols. Polyalkylene-­glycol-ether brake fluids that meet specifications for DOT 3 and DOT 4 brake fluids. poliglicol  Mezcla de varios alcoholes. Líquidos de frenos de polialquilenglicoléter que están dentro de las especificaciones DOT 3 y DOT 4 para líquidos de frenos. positive wheel spin  The excessive wheel spin that occurs during acceleration as a wheel loses traction and spins on the pavement.

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deslizamiento positivo de la rueda  Giro excesivo de la rueda que se produce durante una aceleración cuando una rueda pierde tracción y gira sobre el pavimiento. pre-brake  A Mercedes-Benz system that will actually prepare the brakes to apply only the necessary braking pressure when the driver responds, thus preventing a panic stop. prefreno  Sistema de Mercedes-Benz que prepara los frenos para aplicar solo la presión de frenado necesaria una vez que responde el conductor, lo que previene frenadas intempestivas. pressure  Force exerted on a given unit of surface area. Pressure equals force divided by area and is measured in pounds per square inch (psi) or kilopascals (kPa). presión  Fuerza ejercida sobre una unidad de superficie ­determinada. La presión es igual a la fuerza dividida por el área y se mide en libras por pulgadas cuadradas (psi) o ­kilopascales (kPa). pressure differential  The difference between two pressures on two surfaces or in two separate areas. The pressures can be either pneumatic (air) or hydraulic. diferencial de presión  Diferencia entre dos presiones en dos superficies o áreas distintas. La presión puede ser neumática (aire) o hidráulica. pressure differential valve  A hydraulic valve that reacts to a difference in pressure between the halves of a split brake system. When a pressure differential exists, the valve moves a plunger to close the brake warning lamp switch. válvula de diferencial de presión Válvula hidráulica que reacciona ante una diferencia de presión entre las dos partes de un sistema de frenos dividido. Cuando hay una diferencia de presión, la válvula mueve un pistón que cierra el conmutador de la luz indicadora de freno. pressure-sensor base (PSB)  Has a pressure sensor located on each wheel and reads tire pressure directly. It is a software that measures tire pressure with on-wheel sensors and relays the pressure to an onboard computer. base de presión sensitiva  Software que mide la presión de las llantas con sensores en la rueda y transmite la presión a una computadora del vehículo. primary shoe  The leading shoe in a duo-servo brake. The primary shoe is self-energizing and

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applies servo action to the secondary shoe to increase its application force. Primary shoes have shorter linings than secondary shoes. zapata primaria  Zapata guía en un servofreno dual. La zapata primaria es autónoma y aplica una servoacción a la zapata secundaria para aumentar su fuerza de aplicación. Las zapatas primarias tienen forros más pequeños que las secundarias. proportioning valve  A hydraulic control valve that controls the pressure applied to rear drum brakes. A proportioning valve decreases the rate of pressure application above its split point as the brake pedal is applied harder. válvula de dosificación  Válvula de control hidráulico que controla la presión aplicada a los frenos de tambor traseros. Una válvula de dosificación disminuye la proporción de aplicación de presión por encima de su punto de separación cuando se presiona más fuerte el pedal del freno. protocol  A protocol is a computer language that modules use to communicate with each other. protocolo  Un protocolo es un lenguage de computadora que modula el uso para comunicarse mutuamente. quick take-up master cylinder  A dual master cylinder that supplies a large volume of fluid to the front disc brakes on initial brake application, which takes up the clearance of low-drag calipers. cilindro maestro de tensor rápido Cilindro maestro doble que proporciona una gran cantidad de líquido a los frenos de disco delanteros en la primera frenada, compensando la holgura de los calibres de baja resistencia. quick take-up valve  The part of the quick take-up master cylinder that controls fluid flow between the reservoir and the primary low-pressure chamber. válvula de tensor rápido  Parte del cilindro maestro del tensor rápido que controla el flujo de líquido entre el depósito y la cámara de baja presión primaria. radial ply tire  Tire construction in which the cords in the body plies of the carcass run at an angle of 90 degrees to the steel beads in the inner rim of the carcass. Each cord is parallel to the radius of the tire circle. neumático de capas radiales  Fabricación de neumáticos en los que los cordones de las capas del cuerpo de la carcasa se fijan con un ángulo de 90 grados a las nervaduras de acero en borde interior de la carcasa. Cada cordón es paralelo a los radios del círculo del neumático.

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reaction disc (or reaction plate and levers) The components in a vacuum power booster that provide pedal feel or feedback to the driver. disco de reacción (o placa y palancas)  Componentes de un reforzador de vacío que proporcionan sensaciones en el pedal o respuesta al conductor. rear wheel antilock (RWAL/RABS)  A two-wheel ABS used on the rear wheels of light-duty pickup trucks and some SUVs. One of the best known Kelsey–Hayes systems. antibloqueo de ruedas traseras (RWAL) Frenos ABS para dos ruedas utilizado en las ruedas traseras de camionetas ligeras y en algunos SUV. Uno de los sistemas de Kelsey–Hayes más conocidos. regenerative braking  Converting the energy (heat and mass) of a moving vehicle to stop that vehicle. frenar regenerador  El frenar regenerador está convirtiendo la energía (calor y masa) de un vehículo móvil para parar ese vehículo. relay  An electromagnetic switch that uses a small amount of current in one circuit to open or close a circuit with greater current flow. Relays are used as remotely controlled switches for circuits. relé  Un conmutador electromagnético que toma una pequeña cantidad de corriente de un circuito para abrir o cerrar otro con mayor flujo de corriente. Los relés se utilizan como conmutadores de control remoto para los circuitos. reluctor  A metal tooth ring used to influence the magnetic flux lines of the PM generator. reluctor  Anillo metálico dentado que se usa para influir en las líneas de flujo magnético del generador de PM. replenishing port  The rearward port in the master cylinder bore; also called other names. puerto de abastecimiento  Puerto situado más atrás en el hueco del cilindro maestro; también recibe otros nombres. reservoir  Storage tank for the master cylinder. depósito  Tanque de almacenamiento para el cilindro maestro. residual pressure check valves  Residual pressure check valves were once used to hold slight pressure on the drum brake pistons to maintain seal contact with the walls of the wheel cylinder. Cup expanders are used now. válvula de retención de presión residual  Las válvulas de retención de presión residual alguna vez fueron

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utilizadas para mantener una ligera presión sobre los pistones del tambor de frenos para mantener el contacto del sello con las paredes del cilindro de la rueda. Ahora su utilizan expansores de taza. return spring  A strong spring that retracts a drum brake shoe when hydraulic pressure is released. resorte de vuelta  Resorte fuerte que retrae una zapata de freno de tambor cuando se libera presión hidráulica. riveted lining  Brake lining attached to the pad or shoe by ­copper or aluminum rivets. forro remachado  Forro de freno unido a la pastilla o zapata por remaches de cobre o de aluminio. rolling diameter  The effective diameter of a tire when placed on the vehicle. It can vary with tire pressure. diámetro del elemento rodante  El diámetro efectivo de un neumático cuando se coloca en el vehículo. Puede variar con la presión. rolling resistance  The resistance of the vehicle’s weight and mass and the friction of all moving components to the movement of the vehicle. coeficiente de resistencia a la rodadura  Resistencia del peso y masa de un vehículo y de la fricción de todos los componentes movibles al movimiento del vehículo. rotor  The rotating part of a disc brake that is mounted on the wheel hub and contacted by the pads to develop friction to stop the car. Also called a disc. rotor  Parte giratoria de un freno de disco que va montada en el buje de la rueda y entra en contacto con las pastillas para causar el rozamiento que detiene el vehículo. También llamado disco. run-flat  A tire that can be run at reduced speed, even when flat. neumático runflat o antipinchazo  Neumático que se puede utilizar a velocidad reducida, aun después de haber sufrido un pinchazo. screw-and-nut  A common kind of caliper-actuated parking brake. tornillo y tuerca  Tipo común de freno de estacionamiento accionado por calibre. scrub radius  The distance from the tire contact patch centerline to the point where the steering axis intersects the road. radio de fricción  Distancia desde la línea central de la banda de rodadura del neumático hasta el punto en que el eje de dirección corta la vía.

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secondary shoe  The trailing shoe in a duo-servo brake. The secondary shoe receives servo action from the primary shoe to increase its application force. Secondary shoes provide the greater braking force in a duo-servo brake and have longer linings than primary shoes. zapata secundaria  Zapata de remolque en un servofreno dual. La zapata secundaria recibe acción asistida de la primaria para aumentar su fuerza de aplicación. Las zapatas secundarias proporcionan mayor potencia de frenado en un servofreno dual y tienen forros más grandes que las primarias. section width  The width of a tire across the widest point of its cross section, usually measured in millimeters. anchura de sección  Anchura de un neumático en el punto más amplio de su sección transversal; se suele medir en milímetros. self-adjusters  A cable, lever, screw, strut, or other linkage part that provides automatic shoe adjustment and proper lining-­­to-drum clearance as a drum brake lining wears. autoreguladores  Cable, palanca, tornillo, puntal u otro mecanismo de unión que proporciona un ajuste automático a la zapata y la holgura adecuada entre forro y tambor cuando se desgasta el forro de un freno de tambor. self-energizing operation  The action of a drum brake shoe when drum rotation increases the application force of the shoe by wedging it tightly against the drum. operación autoactivada  Acción de una zapata de freno de tambor cuando la rotación del tambor aumenta la fuerza de aplicación de la zapata al ajustarse como una cuña contra el tambor. semimetallic lining  Brake friction material made from a mixture of organic or synthetic fibers and certain metals; these linings do not contain asbestos. forro semimetálico  Material de fricción del freno hecho con una mezcla de fibras orgánicas o sintéticas y ciertos metales; estos forros no contienen amianto. service brakes  The disc or drum brakes operated by the driver to stop the vehicle. frenos de servicio  Frenos de disco o de tambor sobre los que actúa el conductor para detener el vehículo. servo action  The operation of a drum brake that uses the self-energizing operation of one shoe to apply mechanical force to the other shoe to assist its

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Glossary

application. Broadly, servo action is any mechanical multiplication of force. servoacción  Acción de un freno de tambor en el que una zapata actúa de forma autónoma al aplicar una fuerza mecánica a la otra zapata y ayudarla en su funcionamiento. Más ampliamente, una ser-voacción es cualquier multiplicación mecánica de una fuerza. setback  A difference in wheelbase from one side of a vehicle to the other. retroceso  Diferencia en la distancia entre ejes en un lado y otro del vehículo. shoe anchor  The large pin, or post, or block against which a drum brake shoe pivots or develops leverage. anclaje de zapata  Pasador grande, o poste, o bloque contra el que la zapata de un freno de tambor pivota o desarrolla transmisión por palancas. sliding caliper  A caliper that is mounted to its support on two fixed sliding surfaces or ways. The caliper slides on the rigid ways and does not have the flexibility of a floating caliper. calibre de desplazamiento  Calibre que se monta en el soporte sobre dos superficies o vías fijas de deslizamiento. El calibre se desliza por vías rígidas y no tiene la flexibilidad de un calibre flotante. slope  The numerical ratio or proportion of rear drum brake pressure to full system pressure that is applied through a proportioning valve. If half of the system pressure is applied to the rear brakes, the slope is 1:2 or 50 percent. atenuación diferencial  Razón numérica o proporción entre la presión del freno de tambor trasero y la presión total del sistema que se aplica a través de una válvula de dosificación. Si la mitad de la presión del sistema se aplica a los frenos traseros, la atenuación diferencial es 1:2 ó del 50 por ciento. solid rotor  A rotor that is a solid piece of metal with a friction surface on each side. rotor sólido  Rotor formado por una pieza sólida de metal con una superficie de fricción a cada lado. split point  The pressure at which a proportioning valve closes during brake application and reduces the rate at which further pressure is applied to rear drum brakes. punto de separación  Presión a la que la válvula de dosificación se cierra durante la aplicación de los frenos y se reduce la relación con la que se aplica más presión a los frenos de tambor traseros.

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spool valve  A cylindrical sliding valve that uses lands and valleys around its circumference to control the flow of hydraulic fluid through the valve body. válvula de carrete  Válvula cilíndrica de deslizamiento que usa partes planas y hundimientos en su circunferencia para controlar el flujo del líquido hidráulico a través del cuerpo de la válvula. square-cut piston seal  A fixed seal for a caliper piston that has a square cross section. junta cuadrada de pistón  Junta fija para un pistón de calibre con sección transversal cuadrada. star wheel  A small wheel that is part of a drum brake adjusting link. Turning the star wheel lengthens or shortens the adjuster link to position the shoes for proper lining-to-drum clearance. rueda en estrella  Rueda pequeña que forma parte de un acoplamiento de ajuste de un freno de tambor. Al hacer girar la rueda en estrella se alarga o acorta el acoplamiento para poner en posición las zapatas y conseguir una tolerancia conveniente entre forro y tambor. static friction  Friction between two stationary objects or surfaces. fricción estática  Fricción entre dos objetos o superficies estáticas. steering axis inclination (SAI)  The angle formed by the steering axis of a front wheel and a vertical line through the wheel when viewed from the front with the wheels straight ahead. inclinación del eje de dirección (SAI) Ángulo formado por el eje de dirección de una rueda delantera y una línea vertical que pasa por la rueda cuando se mira desde la parte delantera con las ruedas directamente hacia delante. steering knuckle  The outboard part of the front suspension that pivots on the ball joints and lets the wheels turn for steering control. Mangueta de Dirección  La parte externa de la suspensión delantera que pivota en las articulaciones esféricas y permite que las ruedas giren para controlar la dirección. steering wheel position sensor  Steering wheel position sensor determines which direction the driver is trying to steer. sensor de posición del volante  El sensor de posición del volante determina en qué dirección el conductor está intentando dirigirse.

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Glossary

stroke sensor  Stroke sensor informs the brake controller how fast and how much pressure the driver applied to the brakes. sensor de golpes  El sensor de golpes informa al controlador de freno qué tan rápido y cuánta presión el conductor aplicó a los frenos. stroke simulator  Stroke simulator provides brake pedal feedback to the driver. estimulador de golpes  El estimulador de golpes proporciona retroalimentación del pedal de frenos al conductor. Subaru’s “Eyesight” or Mercedes “Pre-brake” There are several types of active braking systems available such as Subaru’s “Eyesight” or Mercedes “Pre-brake that prepare the braking system for a sudden stop. These systems can actually apply the brakes to stop the vehicle or lessen the severity of a crash. “Acance de vista” del Subaru o “Pre-freno” del Mercedes  Hay varios tipos de sistemas de frenado activo disponibles, tales como el “Alcance de vista del subaru” o el “pre-freno” del Mercedes los cuales preparan el sistema de frenos para una parada repentina. Esos sistemas de hecho pueden accionar los frenos para detener el vehiculo o disminuir la severidad de un choque. swept area  The total area of the brake drum or rotor that contacts the friction surface of the brake lining. zona barrida  Área total del freno de tambor o del rotor que toca la superficie de fricción del forro del freno. synthetic lining  Brake friction materials made from nonorganic, nonmetallic, and nonasbestos materials; typically fiberglass and aramid fibers. forro sintético  Materiales de fricción de frenos hechos de materiales no orgánicos, no metálicos y sin amianto; por lo común, fibra de vidrio y fibras de aramida. table  The outer surface of a brake shoe to which the lining is attached. tabla  Superficie exterior de una zapata de freno a la que se une el forro. tandem  Two or more devices placed one behind the other in line. en serie  Dos o más dispositivos colocados en línea uno detrás de otro. tandem booster  A power brake vacuum booster with two small diaphragms in tandem to provide additive vacuum force.

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reforzador en serie  Reforzador de vacío para frenos con dos pequeños diafragmas en serie que proporcionan mas fuerza al vacío. tensile force  The moving force that slides or pulls an object over a surface. fuerza de tracción  Fuerza de movimiento que desliza o arrastra un objeto sobre una superficie. thermal energy  The energy of heat. energía térmica  Energía del calor. thrust angle  The angle between the geometric centerline and the thrust line of a vehicle. ángulo de empuje  El ángulo formado por la línea geométrica central y la línea de empuje de un vehículo. thrust line  The bisector of total toe on the rear wheels, or the direction in which the rear wheels are pointing. línea de empuje  Bisectriz de la separación total de las ruedas traseras, o la dirección en que señalan dichas ruedas. tire load range  The load-carrying capacity of a tire, expressed by the letters A through L. The load range letters replace the older method of rating tire strength by the number of plies used in its construction. límites de carga de neumáticos  Capacidad de carga de un neumático, expresada por letras de la A a la L. Las letras de los límites de carga reemplazan el método anterior de clasificar la resistencia de los neumáticos mediante el número de capas usadas en su construcción. tire pressure monitoring system (TPMS) A system of devices and software used to alert the driver of underinflated tire(s). sistema de supervisión de la presión del neumático (TPMS)  Un sistema de los dispositivos y del software que alerta el conductor de neumáticos inflados inferiores. toe angle  The difference in the distance between the centerlines of the tires on either axle (front or rear) measured at the front and rear of the tires and at spindle height. ángulo de separación  Diferencia de la distancia entre las líneas centrales de los neumáticos en cada eje (delantero o trasero) medida en las partes delantera y trasera de los neumáticos y a la altura del husillo. toe-out on turns (turning radius)  The difference between the angles of the front wheels in a turn.

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Glossary

divergencia en los giros (radio de giro) Diferencia entre los ángulos de las ruedas delanteras al girar. traction control systems  Traction control systems are designed to prevent wheel slip in low-traction situations by applying the brakes to the free spinning wheel. sistemas de control de tracción  Los sistemas de control de tracción están diseñados para prevenir el deslizamiento de las ruedas en situaciones de baja tracción al aplicar los frenos a la rueda giratoria libre. trailing shoe  The second shoe in the direction of drum rotation in a leading-trailing brake. When the vehicle is going forward, the rear shoe is the trailing shoe, but the trailing shoe can be the front or the rear shoe depending on whether the drum is rotating forward or in reverse and whether the wheel cylinder is at the top or the bottom of the backing plate. The trailing shoe is non-self-energizing, and drum rotation works against shoe application. zapata de remolque  Segunda zapata en la dirección de giro del tambor en un freno de tracciónremolque. Cuando el vehículo avanza, la zapata trasera es la remolcada, pero la zapata de remolque puede ser la delantera o la trasera dependiendo de si el tambor está girando hacia delante o hacia atrás y de si el cilindro de la rueda está en la parte superior de la placa de refuerzo o en la inferior. La zapata de remolque no es autónoma, y el giro del tambor funciona contra la aplicación de la zapata. tread  The layer of rubber on a tire that contacts the road and contains a distinctive pattern to provide traction. rodadura  Capa de goma de un neumático que está en contacto con la carretera y contiene un patrón distintivo que favorece la tracción. tread contact patch  The area of the tire tread that contacts the road; determined by tire section width, diameter, and inflation pressure. banda de rodadura  Superficie de la rodadura del neumático que se pone en contacto con la carretera; viene determinada por la anchura de la sección del neumático, el diámetro y la presión de inflado. tread wear indicator  A continuous bar that appears across a tire tread when the tread wears down to the last 322 ( 161 ) inch. When a tread wear indicator appears across two or more adjacent grooves, the tire should be replaced. indicador de desgaste de la rodadura  Barra continua que aparece transversalmente en la rodadura del

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neumático cuando ésta se desgasta más de 322 ( 161 ) pulgadas. Cuando aparece el indicador de desgaste de rodadura cruzando dos o más hendiduras adyacentes, se debe cambiar el neumático. unidirectional rotor  A rotor with cooling fins that are curved or formed at an angle to the hub center to increase cooling airflow. Because the fins work properly only when the rotor turns in one direction, unidirectional rotors cannot be interchanged from right to left on the car. rotor unidireccional  Rotor con álabes refrigerantes curvadas o formando un ángulo con el centro del buje para aumentar el flujo de aire de refrigeración. Como los álabes sólo funcionan adecuadamente cuando el rotor gira en una sola dirección, los rotores unidireccionales no se pueden intercambiar entre la derecha y la izquierda del auto. unidirectional tread pattern  A tire tread pattern that can be rotated only in one direction. Thus, leftand right-side tires with unidirectional tread cannot be interchanged. patrón de rodadura unidireccional  Patrón de rodadura de un neumático que se puede girar en una única dirección. Es decir, los neumáticos de la izquierda y de la derecha con rodadura unidireccional no se pueden intercambiar. uniform tire quality grading (UTQG) indicators  Letters and numbers molded into the sidewall of a tire to indicate relative tread life, wet weather traction, and heat resistance. indicadores del grado de calidad de neumáticos uniformes (UTQG)  Letras y números moldeados en los lados de un neumático para indicar la duración relativa de un neumático, la tracción en tiempo lluvioso y la resistencia al calor. vacuum  In automotive service, vacuum is generally considered to be air pressure lower than atmospheric pressure. A true vacuum is a complete absence of air. vacío  En relación con los automóviles, el vacío se suele considerar como una presión de aire menor que la atmosférica. Un vacío verdadero es la completa ausencia de aire. vacuum suspended  A term that describes a power brake vacuum booster in which vacuum is present on both sides of the diaphragm when the brakes are released. The most common kind of vacuum booster. de suspensión de vacío  Término que describe un reforzador de vacío para frenos en el que existe vacío

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a ambos lados del diafragma cuando se sueltan los frenos. El tipo más común de reforzador de vacío. valleys  The annular grooves or recessed areas between the lands of a valve spool. hundimientos  Hendiduras anulares o áreas ahuecadas entre las partes de una válvula de carrete. vehicle stability control  Vehicle stability control is an electronically assisted braking system that can selectively apply and release brakes during critical maneuvers to help the driver maintain control. control de estabilidad del vehiculo  El control de estabilidad del vehiculo es un sistema eléctronico de frenado asistido que puede accionar o liberar los frenos durante maniobras críticas para ayudar al conductor a mantener el control. vehicle stability system  The integration of electronically controlled steering, braking, and suspension systems that provide for enhanced vehicle control and safety. sistema de estabilidad vehicular  Integración de la dirección controlada electrónicamente, los frenos y el sistema de suspensión que proporciona un control mejorado de los vehículos y de la seguridad. vent port  The forward port in the master cylinder bore; also called by other names. válvula de ventilación  Válvula delantera de la parte interior del cilindro maestro; también recibe otros nombres. ventilated rotor  A rotor that has cooling fins cast between the braking surfaces to increase the cooling area of the rotor. rotor ventilado  Rotor que tiene álabes refrigerantes entre las superficies de frenado para aumentar la superficie refrigerante del rotor. voltage  The electromotive force that causes current to flow. The potential force that exists between two points when one is positively charged and the other is negatively charged. voltio  Unidad usada para medir la cantidad de fuerza o energía eléctrica. water fade  Brake fade that occurs when water is trapped between the brake linings and the drum or rotor and the coefficient of friction is reduced.

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pérdida de agua  Pérdida de frenado debido a que el agua queda atrapada entre los forros de los frenos y el tambor o el rotor, reduciéndose el coeficiente de rozamiento. web  The inner part of a brake shoe that is perpendicular to the table and to which all of the springs and other linkage parts attach. membrana  Parte interior de una zapata de freno perpendicular a la tabla y en la que se fijan todos los resortes y otras partes de acoplamiento. weight  The measure of the Earth’s gravitational force or pull on an object. peso  Medida de la fuerza de gravedad de la Tierra o de la atracción sobre un objeto. wheel cylinder  The hydraulic slave cylinder mounted on the backing plate of a drum brake assembly. The wheel cylinders convert hydraulic pressure from the master cylinder to mechanical force that applies the brake shoes. cilindro de la rueda  Cilindro hidráulico auxiliar montado en la placa de refuerzo de un conjunto de frenos de tambor. Los cilindros de la rueda convierten la presión hidráulica del cilindro maestro en la fuerza mecánica que se aplica a las zapatas de freno. wheel offset  The distance between the centerline of the rim and the mounting plane of the wheel. desajuste de la rueda  Distancia entre la línea central de la llanta y el plano de montaje de la rueda. wheel speed base  A software program in an ABS used to determine the inflation of a tire. base de velocidad de la rueda  Programa de software en un ABS que se usa para determinar la cantidad de aire de una llanta. wheel speed sensor  A sensor used to determine the rotating speed of a wheel. sensor de velocidad de las ruedas  Sensor utilizado para determinar la velocidad de rotación de una rueda. yaw  Swinging motion to the left or to the right of the vertical centerline or rotation around the vertical centerline. derrape  Movimiento de balanceo de izquierda a derecha de la línea central vertical o giro alrededor de dicha línea.

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Index

Note: Page numbers in bold print reference non-text material.

A ABSs. See Antilock brake systems (ABSs) Abutments. See Ways, sliding calipers Acceleration sensor, 239, 257 Accumulator, 138, 239–240, 267 See also Pumps and accumulators Active brakes, 267 Active braking systems, 13, 262, 262–263, 267 Actuator, 12, 229, 230, 267 Adjustable pedal system (APS), 267 Adsorption, 30, 267 Air brakes, 16–17, 17, 267 Air systems, 125, 126 Alignment wheel performance, 64–66, 65 ALNICO permanent magnet, 236 Ampere (A), 40, 267 Analog, 267 Analog signals, 228, 229, 236 Antilock brake control module (ABCM), 267 Antilock brake systems (ABSs), 2, 10, 232–240, 267 accumulators, 239–240 brands, 234 components, 235–240 Bosch 9.0 system, 246, 246 brake switch, 238–239 controllers, 235–236 lamps and communications, 240 magnetoresistive wheel speed sensors, 237–238, 238–239 pumps and accumulators, 239–240 wheel sensors, 236, 236–239 four-wheel, 234 hydraulic pressure control, 110–112 lamps communications, 240 warning, 240 pumps, 239–240 dynamic rear proportioning (DRP) value, 240 high-pressure, 239 low pressure return, 239–240 rear-wheel, 234 traction control systems, 241–242 types and general operations, 232–234 four-wheel ABS, 234, 235 integrated and nonintegrated ABS, 233, 233–234 rear-wheel ABS, 234 vehicle control, 232

See also Electronic brake system (EBS) Aramid fibers, 161, 267 ARC. See Automatic ride control (ARC) Arcing, 267 Arcing the brake shoe, 192 Asbestos, in brake linings, 31, 160–162, 268 Asbestosis, 268 Aspect ratio, 48, 268 Atmospheric pressure, 123, 123–124, 268 Atmospheric suspended vacuum booster, 130, 268 Automatic parking brake release, 214 Automatic ride control (ARC), 13, 259, 268 Automotive Friction Material Edge Code, 162, 162, 268 Automotive networking, 230, 231 Auxiliary drum parking brakes, 221, 222

B Backing plate, 186, 187, 190, 193, 193–194, 268 Ball-and-ramp caliper-actuated parking brakes, 223, 223–224, 268 Ball bearings, 56, 57, 58, 58 Banjo fittings, 104, 105, 268 Beam-type Hall-effect yaw sensors, 257–258 Bearing cage, 159, 268 Bearing cone, 159, 268 Bearing cup, 159, 268 Belted bias ply tires, 46, 47, 268 Bendix, 234 Bias ply tire, 46, 46, 268 Bimetallic drum, 268 Binary system, 268 Binders, 160, 268 Bit, 268 Bleeding, 71, 268 Boiling point, brake fluid, 69–70, 69 table Bonded brake linings, 268 Bonded linings, 164, 268 Bosch, 234, 245–246 Bosch POST, 246 Bosch 9.0 system, 246, 246 BPMV. See Brake pressure modulator valve (BPMV) BPP sensor. See Brake pedal position (BPP) sensor Brake assist (BA), vacuum booster, 143, 143, 269 Brake caliper, 167, 168, 269 Brake fade, 29–30, 149, 269 gas fade, 30 lining fade, 29 mechanical fade, 30 287

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288

Index

Brake fluid. See Hydraulic brake fluid Brake friction materials, 160–162, 191 attachment, 164, 164–165 selection, 162–164, 163 table types ceramic brake pads, 161–162 organic linings, 160 semimetallic linings, 160–161 synthetic linings, 161 Brake hoses, 99–101, 99–101 Brake lines, 6, 8–10, 95–106, 96 fittings, 101–105, 101–105 hoses, 99–101, 99–101 line and fitting precautions, 106 tubes or pipes, 96–99, 97–99 Brake pads, 159, 159–160, 269 Brake pad wear indicators, 112 Brake pedal and pushrod, 74, 74–75, 75 brake linkage free play, 75, 75 Brake pedal feel, 133–134 Brake pedal position (BPP) sensor, 115, 115, 269 Brake pressure modulator valve (BPMV), 242, 258, 259, 269 Brake shoes, 190, 190–193, 191, 269 Brake switch, 238–239, 239 Brake system braking dynamics, 24–25, 25 electric, 14, 14–15 electrical principles, 39–41 amperage, voltage, and resistance, 39–40 Ohm’s law, 40, 40–41 electronic, 12 energy, 22–24 inertia and momentum, 24 kinetic energy, mass, weight, and speed, 22–24, 23 friction principles brake fade, 29–30 brake friction materials, 30, 30–31 coefficient of friction, 27–29 friction and pressure, 26, 26 friction and surface area, 26, 26 kinetic and static friction, 25, 25–26 functions, 1 hydraulic pressure, 21, 21 hydraulic principles, 33–39 hydraulic surge, 14 operation/conventional system, 21, 21 overview, 2 antilock brake systems (ABSs), 12 hydraulic systems, 6–7, 6–8, 14 leverage and brake pedal design, 2–3, 3 parking brakes, 12 power boosters, 11, 11–12 service brake design, 3–6, 5–6 vacuum and air pressure principles, 39 weight transfer, 24, 25 Brake warning system. See Electrical warning system

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Braking dynamics, 24–25, 25 Breakaway condition for trailers, 15 Bubble flare. See Inverted double flare Buffer, 269 Bulkhead, 3, 269

C Cables, parking brakes, 215–216, 215–218 CAB module. See Controller antilock brake (CAB) module Cadillac magnetic ride control, 261, 261 Caliper, 5, 269 hydraulic pressure applications, 5 parts and operation, 167–169 body, 168, 168–169 dust boots, 172, 172 hydraulic passages and lines, 169, 169 pistons, 10–11, 11, 169, 169–170 piston seals, 170–172, 171 support, 168, 269 Caliper-actuated parking brakes ball-and-ramp operation, 223, 223–224 screw-and-nut operation, 222, 223 Camber, 58, 59, 59, 65, 269 Cam-ground lining, 192, 192, 269 Carbolic acid, 170 Carcass, tire, 46, 269 Cars active brake systems, 245 caliper pistons, 170 disc brake performance, 177 drum brakes, 4 load ratings, 48 P-metric system, 48 semimetallic linings, 161 steel rods, 216 tire construction, 46 tire-sizes, 47–48 tread design, 50–51 Casing, tire, 46, 269 Caster, 59, 59–60, 269 Center high-mounted stoplamp (CHMSL), 114–117, 118, 119, 269 Central processing unit (CPU), 269 Central-valve master cylinders, 91, 91–92 Ceramic brake pads, 31, 161–162, 269 Channel, 234, 241, 242, 251, 269 Check valve, 125, 269 Chevrolet volt, 263 Chlorinated hydrocarbon solvents, 270 CHMSL. See Center high-mounted stoplamp (CHMSL) Class 2 protocol, 244 Class 2 wiring, 270 Coefficient of friction, 27, 27–29, 29, 270 heat dissipation, 29 materials, 28

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Index surface finish, 28 temperature, 29 Cold inflation pressure, 49, 49, 270 Combination valve, 110, 111, 270 Commands, 232, 270 Communications, 240 Compensating port. See Replenishing port Composite drums, 190, 190, 270 Composite rotor, 157, 157, 270 Compression fittings, 104, 105 Computer-controlled hydraulic steering/electric steering, 253, 253 Conduit, 216, 270 Continental Teves Mk60/Mk70, 245 Continental Teves system, 220, 221, 245 Controlled area network (CAN), 231, 244–245 Controller, 230, 230, 270 Controller antilock brake (CAB) module, 235, 270 Control valve assembly, 270 Cup expander, 87, 88, 195, 195, 270 Cup seal, 80, 82, 82, 270 Curing agents, 160, 270 Cycle, 229, 229, 270

D Delco-Bosch, 234 Delivered torque signal, 243 Delphi DBC-7 ABS, 242–244, 243–244 Department of Transportation (DOT), 14, 270 Diagonally split hydraulic system, 76, 76 Diaphragm, 78, 128, 270 suspension, 130 Digital, 271 Digital signals, 227, 229 Directional control, 232, 271 Directional stability, 232, 271 Disc brakes, 4–6, 5–6, 148–179, 271 advantages and disadvantages, 149–154 brake servo action, 151–153, 152, 153 fade resistance, 149–150, 149–151 noise, 153–154, 154 parking brake, 154 self-adjustment, 151, 151 caliper parts and operation, 167–169 body, 168, 168–169 dust boots, 172, 172 hydraulic passages and lines, 169, 169 pistons, 169, 169–170 piston seals, 170–172, 171 construction, 154–167 brake pads, 159, 159–160 brake pad wear indicators, 165–167, 166–167 composite rotors, 157, 157 fixed and floating rotors, 156, 156–157 friction materials, 160–162, 163 table, 164

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pad-to-caliper attachment, 165, 165 rotors, hubs, and bearings, 155–156, 155–156, 159 solid and ventilated rotors, 157–158, 158 friction material attachment, 164, 164–165 friction material selection, 162–164, 163 table hydraulic pressure applications, 5 operation, 154 pad-to-caliper attachment, 165 performance disc brakes, 177–179 rear wheel disc brakes, 177, 177, 178 types, 172–177 fixed caliper, 173, 173–174, 174 floating caliper, 174–176, 175 sliding caliper, 176, 176–177 Distronic cruise control, 262–263 DOT. See Department of Transportation (DOT) DOT 3, DOT 4, and DOT 5, 69, 71–72 DOT 5 silicone fluid, 69 Double flare, 101, 103, 103 DRP valve. See Dynamic rear proportioning (DRP) valve Drum brakes, 4, 5, 182–208, 271 advantages and disadvantages, 182–186 fade resistance, 185–186, 185–186 lack of noise, 183–184 parking brake operation, 184 pulling and grabbing, 183 self-adjustment, 184–185 self-energizing and servo action, 203–205 backing plate, 193, 193–194 brake drums and hubs, 187–190, 188–189 solid cast-iron drums, 189, 189–190 steel and iron drums, 190, 190 brake shoes and linings, 190–193, 190–193 construction, 186–202, 187 designs, 202–207 duo-servo brakes, 202, 203, 206–207 leading-trailing brakes, 202, 202, 205–206, 206 self-energizing and servo actions, 202–205, 203–205 friction materials, 191 lining-to-drum fit, 192–193, 192–193 parking brake linkage, 202 return and hold-down springs, 195–196, 195–197 self-adjusters, 197–202 duo-servo star wheel adjusters, 197–199, 198–199 leading-trailing-shoe cam adjusters, 201, 201 leading-trailing-shoe ratchet adjusters, 200, 200–201 leading-trailing-shoe star wheel adjusters, 199 precautions, 201–202 self-energizing and servo action, 202–205 Drum-in-hat, 177, 177, 271 Drums solid cast-iron, 189, 189–190 steel and iron, 190, 190 Drum web, 188, 271 Dual-piston master cylinder, 78–79, 78–88, 81–87 construction, 78–79, 78–88, 81–87

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Index

Dual-piston master cylinder (continued) hydraulic brake assist, 83, 83–84 operation, 84–87, 84–87 portless master cylinder, 83, 83 ports, 80 reservoir, 78–80, 79 residual pressure check valve, 87, 88 Duo-servo brakes, 197–199, 202, 203, 206–207, 271 Duo-servo star wheel adjusters, 197–199, 198–199 Dust boots, caliper, 167, 172, 172 Duty cycle, 229, 271 Dynamic rear proportioning (DRP) valve, 10, 111, 240, 243, 271

E EBCM. See Electronic brake control module (EBCM) EBS. See Electronic brake system (EBS) EBTCM. See Electronic brake traction control module (EBTCM) Eccentric shaft, 222 EHB. See Electro-hydraulic brake (EHB) Electrical parking brake systems, 220, 221 Electrical warning system, 112–119 brake pad wear indicators, 112 electric parking brakes, 112 master cylinder fluid level switch, 113, 113–114 parking brake switch, 112 stoplamp bulbs, 115–119, 115–119 stoplamp switch and circuit, 114–115, 114–115 turn signal/brake lamp operation, lamp module control, 119, 119 Electric braking system (EBS), 14, 14–15, 227–247 components, 227–232 actuators, 229, 230 automotive networking, 230, 231 commands, 232 hydraulic modulator, 230, 231 sensors, 227, 228 signals, 228, 229 See also Antilock brake systems (ABSs) Electric power steering, 253–255, 254–255 Electric steering, 253, 253 Electro-hydraulic brake (EHB), 143–145, 144–145, 271 Electrohydraulic unit, 235, 271 Electromagnetic induction, 271 Electromagnetic interference (EMI), 271 Electronically variable rear proportioning (EVRP), 245 Electronic brake control module (EBCM), 235, 246, 271 Electronic brake distribution, 10, 271 Electronic brake system (EBS), 143, 271 Electronic brake traction control module (EBTCM), 242, 271 Electronic steering, 271 Emergency brakes, 12, 210 Energy, 31–32 perpetual, 32

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Enhanced traction system (ETS), 243, 271 Environment Protection Agency (EPA), 73 EPA. See Environment Protection Agency (EPA) Equalizer, 215, 215, 216, 272 Erasable programmable read-only memory (EPROM), 272 ETS. See Enhanced traction system (ETS) EVRP. See Electronically variable rear proportioning (EVRP) Eyesight system, 262

F Fade resistance, 149–150, 149–151, 185–186, 185–186 disc brake, 149–151, 150 drum brake, 185–186, 185–186 Failure warning lamp switch, 109–110, 110 Fast-fill and quick take-up master cylinders, 88–90 Federal Motor Vehicle Safety Standards (FMVSS), 4, 272 Fillers, 160, 272 Fittings, brake, 98, 100, 101–105, 101–105 Fixed caliper brake, 173, 173–174, 174, 272 Fixed rotor, 156, 156, 272 Fixed seals, 171, 173–174, 272 Floating calipers, 174–176, 175, 272 Floating rotors, 156, 156–157, 272 Flux lines, 236, 272 FMVSS. See Federal Motor Vehicle Safety Standards (FMVSS) Force, 3, 35–38, 272 Force multiplication, 123 Four-wheel antilock systems, 234, 235 Free play, 75, 75, 272 Frequency, 228, 272 Friction, 4, 272 principles, 25–31 coefficient of, 27–29 kinetic and static friction, 25, 25–26 and pressure, 26, 26 and surface area, 26, 26 Friction materials, brake, 30, 30–31 ceramic, 31 fully metallic, 31 nonmetallic, 31 semimetallic, 31 See also Brake friction materials Friction modifiers, 160, 272 Front-to-rear split hydraulic system, 76, 76 Front-wheel drive (FWD) cars, 159 Fulcrum, 3, 272 Fully metallic brake lining materials, 31 FWD cars, 55, 58, 107, 159, 161, 188, 192, 206

G Gas fade, 30, 150, 185, 272 General Motors four-channel system (cars), 242 PM wheel speed sensor, 243 traction control light, 244

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Index Geometric centerline, 61, 61, 272 Gross vehicle weight rating (GVWR), 45, 272 GVWR. See Gross vehicle weight rating (GVWR)

H Hall-effect switch, 272 Hardware, 105, 165, 257–262 Heat dissipation, 29 Height-sensing proportioning valve, 273 High-pressure pumps and accumulators, 239 Hold-down springs, 196, 196–197, 273 Hoses, brake, 99–101, 99–101 HSMO. See Hydraulic system mineral oil (HSMO) Hubless rotor. See Floating rotors Hubs, rotor, 155–156 Hybrid master cylinders brake lines and hoses, 8–10, 10 pressure control valves, 10 wheel cylinders and caliper pistons, 10–11, 11 Hybrid vehicles, 263 Hydraulic advantage, 123 Hydraulic brake fluid, 68–74 boiling point, 69–70, 69 table, 70, 71 contaminated fluid problems, 73–74 DOT 5 silicone fluid, 69 fluid compatibility, 72 hydraulic system mineral oil fluids, 72 precautions, 73 requirements, 71 storage and handling, 72–73 synthetic fluids, 71–72 Hydraulic channels, 242 3(three) channel, 242 4(four) channel, 242 Hydraulic modulator, 230, 231, 273 Hydraulic power brakes, 137–145, 138, 140–143 hydro-boost operation, 138–142, 140–142 hydro-boost principles, 138, 138–139 vacuum booster with brake assist, 143, 143 Hydraulic pressure, 21, 21 control with ABS, 110–112 Hydraulic principles, 33–39 and brake system engineering, 39 fluids apply pressure to transmit and increase force, 35–38, 35–38 fluids cannot be compressed, 34, 34 fluids can transmit movement, 34, 34–35, 35 Hydraulic surge, 14 Hydraulic system mineral oil (HSMO), 72, 273 Hydraulic systems, 6–7 master cylinder, 6, 6–7 split systems, 7, 7, 8 Hydro-boost, 138, 273 operation, 138–142, 140–142 brakes being released, 140, 141 brakes holding, 139–140

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brakes not applied, 139, 140 moderate brake application, 139, 141 reserve brake application, 142, 142 principles, 138, 138–139 Hydroplane, 273 Hydroplaning, 273 Hygroscopic, 69, 72, 73, 273

I IC. See Integrated circuit (IC) ICU. See Integrated control unit (ICU) Independent parking brakes, 210 Inertia, 24, 32, 273 Intake manifold systems, 125, 126 Integrated ABS, 233, 233, 273 Integrated circuit (IC), 238, 273 Integrated control unit (ICU), 235, 273 Intermediate lever, 219, 273 International Standards Organization (ISO), 95 Inverted double flare, 98, 98, 104 Inverted flare, 102, 104 IPC. See Panel control module (IPC) ISO. See International Standards Organization (ISO) ISO flare, 98, 98 fittings, 103–104, 104 Isolation/dump valve, 234, 235, 241

K Kelsey-Hayes, 234 KIA Optima, 263, 264 Kinetic energy, 22–24, 23, 273 Kinetic friction, 25, 25–26, 273

L Lamps and communications, 240 communications, 240, 261 warning lamps, 240, 261 Lands, 139, 273 LAP flare. See Inverted flare Lateral accelerometer, 13, 240, 273 Lathe-cut seals, 170, 273 Laws of motion, 32–33, 33 Leading shoe, 202, 273 Leading-trailing brakes, 202, 202, 205–206, 206, 274 Leading-trailing-shoe cam adjusters, 201, 201 Leading-trailing-shoe ratchet adjusters, 200, 200–201 Leading-trailing-shoe star wheel adjusters, 199 Leverage, 123, 274 and brake pedal design, 2–3, 3 Levers, parking brakes, 213 Light trucks. See Trucks Lining, brake shoe, 192–193, 192–193 Lining fade, 29, 185, 274 Lining-to-drum fit, 192–193, 192–193 Linkage, parking brake, 202

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292

Index

Load, 237 Lockup slip, 12 See also Negative wheel slip Lockup, wheel, 12, 274 Loughead (Lockheed), Malcolm, 6 Low-drag caliper seals, 172 Low pressure area, 84 Low-pressure return pumps, 239–240 Low-profile tires, 48–50, 49

M Magnetoresistive wheel speed sensors, 237–238, 238, 245 brake switch, 238–239, 239 Magneto-rheological fluid, 261 Mass, 22–24, 23, 274 Master cylinder fluid level switch, 113, 113–114 Master cylinders, 6, 6–7, 34, 274 central valve, 91, 91 dual-piston, 78–88, 79, 84 external hydraulic leak, 87 fast fill and quick take-up, 88–90, 89 split system, 7 See also Dual-piston master cylinder Materials, 28 Mechanical advantage, 37, 123, 274 Mechanical fade, 30, 185, 274 Metallic linings, 161, 274 Metering valve, 106–107, 107, 274 Microprocessor, 235, 237, 239, 240, 274 permanent magnet generators, 236, 236 Mold-bonded linings, 164, 274 Momentum, 24, 274 Motion, laws of, 32–33, 33 Multiplexing, 274

N National Highway Transportation and Safety Administration (NHTSA), 53, 274 Negative wheel slip, 12, 232, 274 Network, 230, 240, 261–262, 274 Newton’s laws of motion, 32–33, 33 NHTSA. See National Highway Transportation and Safety Administration (NHTSA) Noise, disc brake, 153–154, 154 Nonintegrated ABS, 233–234, 274 Nonmetallic brake lining materials, 31 Nonservo brakes. See Partial-servo brakes

O Occupational Safety and Health Administration (OSHA), 275 Ohm (Ω), 40, 275 Ohm, Georg Simon, 41 Ohm’s law, 40, 40–41, 275 One-shot adjuster, 201 Organic disc pad linings, 163

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Organic lining, 160, 275 O-rings, 78, 275 Overload spring, 199, 275 Oversteer, stability control systems, 256, 256–257 Ozone, 100

P Pad hardware, 165, 165, 275 Pad-to-caliper attachment, 165, 165 Pad wear indicators, 275 Panel control module (IPC), 261 Parking brake control, 212–214, 275 Parking brakes, 2, 12, 210–224, 211–212, 275 controls-levers and pedals, 212, 212–214, 214 automatic parking brake release, 214 levers, 213 pedals, 213, 214 electrical, 221 electronic parking brakes, auto-hold, 218, 218 linkage, 202, 215–220 cables, 215–216, 215–218 equalizers and adjusters, 219 levers, 219 rods, 216 operation, 210–212 disc brakes, 154 drum brakes, 186 rear disc, 221–224 auxiliary drum parking brakes, 221, 222 caliper-actuated parking brakes, 222–223, 222–224 rear drum, 219–220, 219–220 Parking brake switch, 113 Partial-servo brakes, 202 Pascal, Blaise, 39 Pascal’s law, 39 Passenger cars. See Cars Pawl, 197, 275 Pedal force, 122 Pedal position sensor, 259, 263 Pedals, 212–214, 214 Performance brakes, 177–179 tires, 64 wheel alignment, 64–66, 65 Permanent magnet (PM) generators, 236, 237, 275 Perpetual energy, 32, 275 Phenol. See Carbolic acid Phenolic plastic, 170, 171, 275 Piston seals, calipers, 170–172, 171 Piston stops, 194, 275 Plate-and-lever boosters, 135, 135 PM. See Permanent magnet (PM) generators P-metric system, 48, 275 PM generators. See Permanent magnet (PM) generators Polyglycol, 69, 275 Portless master cylinder, 83, 83

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Index Positive wheel slip, 241, 275 Positive wheel spin, 12 See also Wheel spin POST program. See Power on system test (POST) program Power boosters, 11, 11–12, 123 Power brake systems, 122–145 electro-hydraulic brake (EHB), 143–145, 144–145 hydraulically-assisted power brakes, 137–145, 138, 139, 140–143 hydro-boost operation, 138–142, 140–142 increase in braking power, 122–123 tandem, boosters, 135–137, 136–137 vacuum and air systems for power boosters, 125–127, 126–127 vacuum power boosters, 128–137, 129, 131–137 vacuum principles, 123–125, 124 Power on system test (POST) program, 236 Power steering control module (PSCM), 253 Pre-brake, 262, 275 Pressure, 7, 275 Pressure control valves, 10 Pressure differential valve, 109–110, 110, 124, 275 Pressure-sensor base (PSB), 53, 276 Primary shoe, 204, 205, 276 Program, 69, 230, 234, 235, 236, 240, 241, 244, 263 Proportioning valve, 108–109, 108–109, 276 Protocol, 276 PSB. See Pressure-sensor base (PSB) Pumps and accumulators, 239–240 dynamic rear proportioning (DRP) value, 240 high-pressure, 239 low pressure return, 239–240 Pushrod. See Brake pedal and pushrod

Q Quick take-up master cylinder, 88, 89, 276 Quick take-up valve, 89, 276

R RABS. See Rear antilock brake system (RABS) Radial ply tire, 46, 47, 276 Radial runout, 63, 63 Raymond Company, 32 Reaction disc, 134, 276 Reaction-disc booster, 134, 134–135 Reaction plate-and-lever booster, 135 Reaction plate and levers, 134 See also Reaction disc Reaction retainer, diaphragm, 130 Rear antilock brake system (RABS), 234, 276 Rear wheel antilock (RWAL) system, 234, 235, 276 Rear wheel disc brakes, 177, 177, 178 Rear-wheel drive (RWD) vehicles, 159 Regenerative braking systems, 2, 263–264 Relay, 239, 242, 276 Reluctance sensor, 237

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Reluctor, 236, 276 Replenishing port, 80, 276 Reservoir, 78–80, 79, 276 Residual pressure check valve, 87, 88, 276 Return springs, 195–196, 195–196, 276 Reverse braking, 15–16, 15–16 Ride control, 259–260, 260, 261 Rim width, 54, 54–55 Riveted linings, 164, 276 Rods, parking brakes, 216 Roll control/ride control, 259–260, 260 Rolling diameter, 256, 276 Rolling resistance, 26, 276 Root cause, 50 Rotor, disc brake, 154, 155–159, 276 composite, 157, 157 fixed, 156, 156 floating, 156, 156–157 solid, 157, 158 unidirectional, 158 ventilated, 158, 158 Run-flat tires, 51–53, 277 RWAL/RABS, 234 RWAL system. See Rear wheel antilock (RWAL) system

S SAE flare fittings, 102–103, 103 SAI. See Steering axis inclination (SAI) Screw-and-nut caliper-actuated parking brakes, 222, 223, 277 Scrub radius, 55, 56, 277 Seamless tubing, 96 Secondary shoe, 204, 205, 277 Second class lever, 3 Section width, 47, 277 Self-adjusters, 197–202, 277 duo-servo star wheel adjusters, 197–199, 197–199 leading-trailing-shoe cam adjusters, 201, 201 leading-trailing-shoe ratchet adjusters, 200, 200–201 leading-trailing-shoe star wheel adjusters, 199 precautions, 201–202 Self-adjustment disc brake, 151, 151 drum brake, 184–185 Self-energizing operation, 183, 277 and brake design, 202–205 drum brakes, 183, 183, 184 Self-sealing tires, 51–52 Semimetallic linings, 31, 160–161, 277 Sensors, 227, 228 beam-type Hall-effect yaw sensors, 257–258 steering angle sensor, 257, 257 wheel sensors, 236–239, 237 Service brake design, 2, 3–6, 178 disc brakes, 4–6, 6 drum brakes, 4, 5

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Index

Servo action, 277 and brake design, 202–205 disc brakes, 151–153, 152, 153 drum brakes, 183, 183, 184 Setback, 61–62, 62, 277 Shoe anchors, 193–194, 277 Side-to-side, 63 Signals, 228, 229 Silencer, 125 Sintering, 31 Sliding calipers, 176, 176–177, 277 Slope, 109, 277 Solenoid, 123, 143, 220, 229, 230, 245, 253 Solenoid valves, 233, 245 reversing, 15, 16 Solid cast-iron drums, 189, 189–190 Solid rotor, 157, 158, 277 Speed, 22–24, 23 wheel sensors, 12 Split hydraulic system operation, 76–77, 77 Split point, 109, 277 Split system, 7, 7, 8 Spool valve, 138, 277 Square-cut piston seal, 170, 277 Stability control hardware beam-type Hall-effect yaw sensors, 257–258 hydraulic modulator, 258, 259 roll control/ride control, 259–260, 260 steering angle sensor, 257, 257 throttle actuator control (TAC), 258–259, 259–260 VSC computer and vehicle network, 261–262, 262 Stability control systems and ABSs, 251 computer-controlled hydraulic steering/electric steering, 253, 253 electric steering, 253, 253 history, 250–251 oversteer, 256, 256–257 three- and four-channel ABS, 251, 251 tire pressure monitoring systems (TPMS), 255, 255–256 traction control, 252, 252 understeer, 256, 256 Standard flare, 102 Star wheel, 197–199, 277 Static friction, 25, 26, 277 Steel and iron drums, 190, 190 Steering angle sensor, 257, 257 Steering axis inclination (SAI), 60, 60, 277 Steering knuckle, 168–169, 278 Steering wheel position sensor, 13, 278 Stoplamp bulbs, 115–119, 115–119 Stoplamp switch and circuit, 114–115, 114–115 Straight roller bearings, 58, 58 Stroke sensor, 7, 8, 278 Stroke simulator, 278 Sumitomo ABS, 234

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Surface finish, 28 Swept area, 278 disc brake, 149, 150, 185, 185 drum brake, 185 Synthetic fluids, 71–72 Synthetic linings, 161, 278

T Table, brake shoe, 190, 190, 278 TAC. See Throttle actuator control (TAC) Tandem, 136, 278 Tandem boosters, 135–137, 136–137 Tapered roller bearing, 56, 57, 57–58, 58 TCSs. See Traction control systems (TCSs) Temperature, 29 Tensile force, 27, 278 Thermal energy, 26, 278 Throttle actuator control (TAC), 12, 258–259, 259–260 Thrust angle, 61, 61, 278 Thrust line, 61, 278 Tire load range, 48, 278 Tire pressure monitoring systems (TPMS), 53, 54, 278 direct, 255, 255 indirect, 255–256 rolling diameter, 256 Tires, 45–54 carmaker’s recommendations, 45, 45 construction, 46–47, 46–47 inflation monitoring, 45 performance, 64 run-flat, 51–53 self-sealing, 51–52 size, 47–48, 48 specifications, 48 tread design, 50–51, 51 Toe angle, 60, 60, 278 Toe-out on turns, 61, 61, 278 Toyota Prius, 263 TPMS. See Tire pressure monitoring systems (TPMS) Traction control systems (TCSs), 12–13, 241–242, 278 ABS controller, 242 air spring, 260, 260 Continental Teves Mk60/Mk70, 245 stability control systems, 252, 252 wheel slip, 241 wheel spin control strategies, 241 See also Electronic brake system (EBS) Trailer brakes, 13–17 breakaway condition, 15 electric brakes, 14, 14–15 hydraulic surge, 14 reverse braking, 15–16, 15–16 Trailing shoe, 204, 278 Tread contact patch, 62, 62, 279 Tread, tire, 46, 279 Tread wear indicator, 51, 51, 279

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Index Trucks caliper piston, 174 disc brakes, 6 drum brakes, 6, 205 linkage rod, 216 load range, 48 power boosters, 11 semimetallic linings, 161 tire construction, 46 wheel bearings, 56–58 Tubing, 96–99, 99 installation, 98–99, 99 sizes, 97, 97 Turning radius, 61, 61 Two-piece rotor, 156

U Understeer, stability control systems, 256, 256 Unidirectional rotor, 158, 279 Unidirectional tread pattern, 51, 279 Uniform tire quality grading (UTQG) indicators, 50, 51, 279 UTQG indicators. See Uniform tire quality grading (UTQG) indicators

V Vacuum, 39, 123–125, 279 Vacuum and air systems for power boosters, 125–127 air systems, 125, 126 intake manifold systems, 125, 126 vacuum check valves, 127, 127 Vacuum booster, 128–137 brake assist, 143, 143 brake pedal feel, 133–134 construction, 128–130, 129 diaphragm suspension, 130 operation, 130–133 brakes being released, 132, 133 brakes holding, 131–132, 133 brakes not applied, 130, 132 full brake application, 133 moderate brake application, 131, 132 plate-and-lever booster, 135, 135 reaction-disc booster, 134, 134–135 types of vacuum boosters, 130–133, 131–133 general types, 130, 131 operation, 130–133, 131–132 Vacuum check valves, 127, 127 Vacuum principles, 123–125, 124 Vacuum reservoir, 125, 126 Vacuum suspended vacuum booster, 125, 130, 279 Valleys, 139, 279 Valves, 106–112 combination valve, 110, 111 metering valve, 106–107, 107

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295

pressure differential valve, 109–110, 110 proportioning valve, 108–109 Vehicle control. See Antilock brake systems (ABSs) Vehicle network, 261–262, 262 Vehicle stability control (VSC), 12, 13, 279 computer and vehicle network, 261–262, 262 Vehicle stability system, 279 Ventilated rotor, 158, 158, 279 Vent port, 80, 279 Volt (V), 40 Voltage, 40, 279

W Warning lamps, 112–119, 240, 261 Water fade, 150 Ways, sliding calipers, 176 Web, brake shoe, 190, 279 Weight, 22–24, 23, 279 Wheel fundamentals, 58–62, 59–62 performance, 64 Wheel alignment, 58–62 camber, 59, 59 caster, 59, 59–60 effects on braking, 62–63 performance, 64–66, 65 setback, 61–62, 62 steering axis inclination, 60, 60 thrust angle, 61, 61 toe-out on turns, 61, 61 Wheel bearings, 56–58, 57, 58, 159, 159 Wheel cylinders, 10–11, 11, 194, 194–195, 195, 279 Wheel effects on braking, 54–56 rim width, 54, 54–55 wheel offset, 55–56, 55–56 Wheel lockup. See Negative wheel slip Wheel offset, 55–56, 55–56, 280 Wheel sensors, 236–239, 237 magnetoresistive sensors, 237–238, 238 speed, 12 Wheel slip, 244 negative, 232 positive, 241 Wheel-speed base (WSB), 53, 280 Wheel speed sensors (WSS), 13, 280 Wheel spin, 12 Wheel spin control strategies, 241 Work, 31–32 WSB. See Wheel-speed base (WSB)

Y Yaw, 13, 280 Yaw sensor, 13, 257–258, 257–258

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Automotive Brake systems

7

Shop Manual

Ken Pickerill SE/Author/Author, Title, 5th Edition   ISBN -978-X-XXX-XXXXX-X  ©2014  Designer: XXX Text & Cover printer: Transcon-Beauceville   Binding: PB   Trim: 8.5" x 10.875"   CMYK

Shop Manual For Automotive Brake Systems

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Shop Manual For Automotive Brake Systems

Seventh Edition Ken Pickerill

Australia • Brazil • Mexico • Singapore • United Kingdom • United States

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Today’s Technician: Automotive Brake

© 2019, 2015 Cengage Learning, Inc.

­Systems, Seventh Edition

Unless otherwise noted, all content is © Cengage.

Ken Pickerill

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Cengage is a leading provider of customized learning solutions with employees residing in nearly 40 different countries and sales in more than 125 countries around the world. Find your local representative at www.cengage.com. Cengage products are represented in Canada by Nelson Education, Ltd. To learn more about Cengage platforms and services, visit www.cengage.com. Purchase any of our products at your local college store or at our preferred online store www.cengagebrain.com.

Notice to the Reader Publisher does not warrant or guarantee any of the products described herein or perform any independent analysis in connection with any of the product information contained herein. Publisher does not assume, and expressly disclaims, any obligation to obtain and include information other than that provided to it by the manufacturer. The reader is expressly warned to consider and adopt all safety precautions that might be indicated by the activities described herein and to avoid all potential hazards. By following the instructions contained herein, the reader willingly assumes all risks in connection with such instructions. The publisher makes no representations or warranties of any kind, including but not limited to, the warranties of fitness for particular purpose or merchantability, nor are any such representations implied with respect to the material set forth herein, and the publisher takes no responsibility with respect to such material. The publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or part, from the readers’ use of, or reliance upon, this material.

Printed in the United States of America Print Number: 01  Print Year: 2018

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Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x Chapter 1  Brake Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Introduction 1 • Brake System Safety Regulations 9 • Brake Warnings and Cautions 11 • Asbestos Health Issues 11 • Chemical Safety 14 • Safety and Environmental Agencies 16 • Hazardous Communications 17 • Handling of Hazardous Waste 20 • Air Bag Safety 22 • Fire Control 24 • Technician Training and Certifications 25 • ASE-Style Review Questions 26 • Job Sheets 27 Chapter 2  Brake Service Tools and Equipment . . . . . . . . . . . . . . . . 45 Fasteners 45 • Measuring Systems 46 • Measuring Tools 49 • Selection, Storage, and Care of Tools 59 • Common Hand Tools 61 • Special Brake Tools 63 • Power Tools 66 • Brake Lathes 70 • Lifting Tools 71 • Hoist Safety 71 • Pressure Bleeders 74 • Cleaning Equipment and Containment Systems 76 • Cleaning Equipment Safety 79 • Brake Lubricants 81 • Electronic Test Equipment 82 • Electrical Principles 85 • Service Information 87 • Summary 90 • ASE-Style Review Questions 90 • Job Sheets 93 Chapter 3  Related Systems Service . . . . . . . . . . . . . . . . . . . . . . . . . 97 Isolating Brake Problems 97 • Tire and Wheel Service 98 • Tapered Roller Bearing Service 105 • Wheel Alignment, Steering, and Suspension Inspection 118 • ASE-Style Review Questions 122 • ASE Challenge Questions 123 • Job Sheets 125 Chapter 4  Master Cylinder and Brake Fluid Service . . . . . . . . . . . 133 Brake System Road Test 133 • Brake Pedal Mechanical Check 135 • Pedal Travel and Force Test 135 • Pedal Free Play Inspection and Adjustment 136 • Brake Fluid Precautions 141  • Master Cylinder Fluid Service 143 • Checking ABS Fluid Level 148 • Master Cylinder Test and Inspection 148 • Integral and Non-Integral ABS Systems 152 • Master Cylinder Reservoir Removal and Replacement 154 • Rebuilding the Master Cylinder 156 • Bench Bleeding Master Cylinders 157 • Installing a Non-Integral ABS Master Cylinder 161 • Master Cylinder Bleeding on the Vehicle 162 • Hydraulic System Bleeding 163 • Brake Fluid Replacement: Flushing and Refilling the Hydraulic System 180 • ASE-Style Review Questions 182 • Ase Challenge Questions 183 • Job Sheets 185 Chapter 5  Hydraulic Line, Valve, and Switch Service . . . . . . . . . . . 199 Introduction 199 • Re-Centering a Pressure Differential Valve (Failure Warning Lamp Switch) 200 • Brake Line, Fitting, and Hose Service 201 • Servicing Hydraulic System Valves 214 • Brake Electrical and Electronic Component Service 216 • Stop Lamp Testing and Switch Adjustment 217 • ASE-Style Review Questions 228 • Ase Challenge Questions 229 • Job Sheets 231

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vi

Chapter 6  Power Brake Service . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 Types of Power Brake Systems 247 • Vacuum Booster Testing and Diagnosis 249 • Brake Pedal Checks 253 • Vacuum Booster Removal and Installation 256 • Booster Overhaul 260  • Vacuum Booster Pushrod Length Check 260 • Adjusting the Booster Pushrod on a Honda 263 • Hydro-Boost Power Brakes 265 • Servicing the Hydro-Boost 269 • Hydro-Boost Air Bleeding 269 • Servicing Vacuum Boosters on Vehicles with Vehicle Stability Control 270 • Servicing an Electrohydraulic Power Booster System 271 • ASE-Style Review Questions 274 • Ase Challenge Questions 275 • Job Sheets 277 Chapter 7  Disc Brake Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 Service Precautions 285 • Diagnosing Disc Brake Problems 286 • Inspecting Brake Pads 287 • Disc Brake Service Operations 290 • Brake Pad Replacement for Floating or Sliding Calipers 292 • Disc Brake Cleaning 303 • Brake Caliper Service 307 • Rotor Service 322 • Refinishing Brake Rotors 332 • Rear Disc Brake Inspection and Replacement 347 • ASE-Style Review Questions 353 • Ase Challenge Questions 354 • Job Sheets 355 Chapter 8  Drum Brake Service . . . . . . . . . . . . . . . . . . . . . . . . . . . 373 Service Precautions 373 • Diagnosing Drum Brake Problems 374 • Drum Brake Service Operations 377 • Brake Drum Removal 377 • Drum Brake Cleaning 383 • Drum Brake Assembly Inspection 385 • Drum Brake Disassembly 389 • Wheel Cylinder Service 395  • Drum Brake Reassembly 397 • Brake Adjustment 403 • Brake Drum Service 409 • Refinishing Brake Drums 415 • ASE-Style Review Questions 423 • Ase Challenge Questions 424 • Job Sheets 425 Chapter 9  Parking Brake Service . . . . . . . . . . . . . . . . . . . . . . . . . . 435 Parking Brake Tests 435 • Cable and Linkage Adjustment 440 • Cable and Linkage Repair and Replacement 446 • Parking Brake Lamp Switch Test 450 • Electric Parking Brake Service 451 • ASE-Style Review Questions 455 • Ase Challenge Questions 456 • Job Sheets 457 Chapter 10  Electrical Braking Systems Service . . . . . . . . . . . . . . . 461 Introduction 461 • Brake System Troubleshooting 462 • ABS Hydraulic System Service 465  • General ABS Troubleshooting 469 • Diagnostic Strategy 470 • Switch Testing 477  • ABS Component Replacement 486 • Testing Specific Manufacturers’ Systems 490 • Delphi DBC-7 491 • Bosch ABS 9.0 495 • ASE-Style Review Questions 499 • Ase Challenge Questions  500 • Job Sheets 503 Chapter 11  Advanced Braking Systems . . . . . . . . . . . . . . . . . . . . . 515 Stability Control Systems 515 • Stability Control and the Vehicle Network 517 • System Component Service 518 • Brake Warning Indicators 520 • Active Cruise Control 525 • Regenerative Braking Systems 525 • Ase-Style Review Questions 527 • Ase Challenge Questions 528 • Job Sheets 529 APPENDIX Ase Practice Examination . . . . . . . . . . . . . . . . . . . . . . . . . 539

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 544 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554

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Photo Sequences

1. Using Eye Wash 7 2. Typical Procedures for Wet-Cleaning the Brakes 80 3. Removing and Installing a Bearing Race 111 4. Typical Procedure for Adjusting Tapered Roller Bearings 119 5. Typical Procedure for Filling a Master Cylinder Reservoir 145 6. Typical Procedure for Bench Bleeding a Master Cylinder 158 7. Typical Procedure for Manually Bleeding a Disc Brake Caliper 170 8. Typical Procedure for Fabricating and Replacing a Brake Line 207 9. Soldering Two Copper Wires Together 225 10. Typical Procedure for Vacuum Booster Testing 252 11. Typical Procedure for Replacing a Vacuum Booster 257 12. Typical Procedure for Replacing Brake Pads 293 13. Typical Procedure for Rebuilding a Disc Brake Caliper 308 14. Mounting a Floating Rotor (Drum) on a Brake Lathe 337 15. Typical Procedure for On-Vehicle Brake Lathe 344 16. Typical Procedure for Overhauling a Rear Brake Caliper 348 17. Typical Procedure for Removing a Brake Drum from a Rear Axle 381 18. Typical Procedure for Disassembling a Drum Brake 391 19. Typical Procedure for Installing a Drum Brake Assembly 398 20. Mounting a One-Piece Disc/Hub (Drum/Hub) on a Brake Lathe 417 21. Typical Procedure for Inspecting and Adjusting Rear Drum Parking Brakes 442 22. Setting an Oscilloscope for Use 482 23. Pump and Motor Removal 487 24. Typical Procedure for Using a Scan Tool on the Delphi Dbc-7492

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Job Sheets

1. Shop Safety Survey 2. Working in a Safe Shop Environment 3. Working Safely Around Air Bags 4. High Voltage Hazards in Today’s Vehicles 5. Hybrid High Voltage and Brake System Pressure Hazards 6. Material Data Safety Sheet Usage 7. Fire Extinguisher Care and Use 8. Preparing the Vehicle for Service and Customer 9. Linear Measurement Practice 10. Vehicle Service Data 11. Remove and Install a Wheel Assembly on a Vehicle 12. Remove, Repack, and Install an Inner Wheel Bearing 13. Inspecting and Replacing Wheel Studs 14. Brake Fluid 15. Checking a Master Cylinder for Leaks and Proper Operation 16. Replace a Master Cylinder on a Non-Integrated Abs System 17. Manually Bleeding a Brake System 18. Pressure Bleed a Brake System 19. Vacuum Bleed a Brake System 20. Checking Brake Pedal Height and Free Play 21. Identifying Brake Problems and Concerns 22. Diagnosing Pressure Problems 23. Inspecting and Diagnosing Brake Lines and Hoses 24. Constructing an ISO Fitting 25. Replace a Brake Hose 26. Check Operation of the Brake Stop Lamp System 27. Identifying/Inspecting Booster Components 28. Vacuum Booster Testing and Diagnosis 29. Replace a Vacuum Booster 30. Diagnosing Disc Brake Problems 31. Replace Brake Pads 32. Measuring Rotor Runout 33. Machining Brake Rotors Off-Vehicle 34. Machining Brake Rotors On-Vehicle 35. Properly Burnishing Brake Pads After Replacement 36. Diagnosing Drum Brake Problems 37. Replace Brake Shoes

27 29 31 33 35 37 39 41 93 95 125 127 129 185 187 189 191 193 195 197 231 235 237 241 243 245 277 279 281 355 357 361 363 367 371 425 427

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38. Machining Brake Drums 39. Adjusting Parking Brake Cables 40. Testing Parking Brake Warning Light Circuit 41. Brakes/Abs/Stability Control Warning Lamps Check 42. Use Scan Tool to Scan Abs for Codes 43. Testing an Abs Wheel Speed Sensor 44. Replace an Abs Wheel Speed Sensor 45. Diagnosing Abnormal Pedal Feel in an Electronically Controlled Brake System 46. Electronic Brake Control Diagnosis 47. Perform Stability System Tests with a Scan Tool 48. Describe a Regenerative Braking System 49. Diagnose Vehicle Braking Concerns Caused by Vehicle Modifications

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PREFACE

The Today’s Technician™ series features textbooks and digital learning solutions that cover all mechanical and electrical systems of automobiles and light trucks. The content corresponds to the 2017 ASE Education Foundation program accreditation requirements. They are specifically correlated to the Task Lists contained in each level of program accreditation; Maintenance and Light Repair (MLR), Automotive Service Technology (AST), and Master Service Technology (MAST). Additional titles include remedial skills and theories common to all of the certification areas and advanced or specific subject areas that reflect the latest technological trends. Today’s Technician: Automotive Electricity & Electronics, 7e is designed to give students a chance to develop the same skills and gain the same knowledge that today’s successful technician has. This edition also reflects the most recent changes in the guidelines established by the ASE Education Foundation. The purpose of the ASE Education Foundation program accreditation is to evaluate technician training programs against standards developed by the automotive industry and recommend qualifying programs for accreditation. Programs can earn accreditation upon the recommendation of ASE Education Foundation. These national standards reflect the skills that students must master. ASE Education Foundation accreditation ensures that certified training programs meet or exceed industry-recognized, uniform standards of excellence.

HIGHLIGHTS OF THIS NEW EDITION—CLASSROOM MANUAL The text and figures of this edition are updated to show modern brake technology and its applications, including the integration of stability control and active braking systems. The Classroom Manual covers the complete mechanical-hydraulic automotive braking theories. It introduces the reader to basic brake systems as well as advanced electronics utilized in stability control systems. The following chapters cover basic brake physics theories: discussion of newer components and materials, including a section on electric parking brakes, and any braking functions required for passenger cars and light trucks. The reader is introduced to fundamental information on trailer brakes, DOT requirements for trailer brakes, and a brief introduction to air brakes. Chapter 10, Electrical Braking Systems (EBS), simplifies the discussion on traditional antilock brake systems (ABS) while retaining the information for a complete understanding of ABS. Included in this chapter is a detailed discussion of electro-hydraulic brakes, including the Teves Mk60/70, Delphi DBC-7 and the newer Bosch 9.0 are introduced in Chapter 10. Advanced Braking Systems, Chapter 11, goes more into stability control and its relationship with some of the ancillary systems that work with stability control. This chapter also explains some of the ancillary systems that make stability control work more effectively, such as electro-hydraulic and fully electric steering, and tire pressure monitoring systems. The very latest technologies, such as active braking and intelligent cruise control systems, are introduced. Lastly, the chapter examines regenerative braking systems in use on the latest hybrid vehicles in production today. The Classroom Manual guides the reader from traditional hydraulic brake to the brake system of the future. x

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HIGHLIGHTS OF THIS NEW EDITION—SHOP MANUAL Safety information remains in the first chapter of the Shop Manual, placing this critical subject next to the tasks to be accomplished. Chapter 2, Brake Service Tools and Equipment, covers basic tools with more information on brake special tools and equipment. Figures and technical information have been added to cover the use of common shop tools such as on-car brake lathes. Some of the safety information that is pertinent to a particular piece of equipment is still in the chapter, so safety issues are presented just prior to the operation of the equipment. In keeping with typical shop diagnostic procedures and curriculum sequence, Chapter 3 retains the information on related systems that may have a direct impact on the braking system. Updated information on diagnosing electric parking brakes and electric braking systems has been added to this edition. To clarify the diagnosis and repair procedures for electric braking, three major ABS/TCS brands, Delphi DBC-7 and Bosch ABS 9.0 and Teves Mk 60/70, are retained for discussion instead of an individual discussion on all industry ABS offerings. This helps the reader better understand the technical diagnosing and repairing for all ABS/ TCS. This edition of the Shop Manual will guide the student/technician through all the basic tasks in brake system repair and presents a look into the near-term future of electric brakes and vehicle stability systems. The Shop Manual has several additions in the Advanced Braking Systems chapter, Chapter 11. This chapter deals with the diagnosis and repair of stability control systems and the surrounding technologies, such as electric steering, tire pressure monitoring systems, active braking, and intelligent cruise control.

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xii

SHOP MANUAL To stress the importance of safe work habits, the Shop Manual also dedicates one full chapter to safety. Other important features of this manual include: 1

C h a p Te R

feTy BRake Sa

Basic Tools Lists ls

Basic Too le to: g should be ab s or ts for workin s chapter, you Safety glasse requiremen review of thi ety saf and n the tio t ■ Lis goggles Upon comple fluid. d methods with brake os tor an est pira ed asb Res ne of the ■ Explain the hazards working HEPA ■ Describe ing a safe Vacuum with for maintain filter materials. with solarea. ety concerns issues tem saf sys ety the saf ean in e t-cl We ■ Expla s. discuss som er chemical ide ■ List and eration in the vents and oth Carbon monox h vehicle op ns of the dealing wit neral functio system t ge ven of s the in cie ■ Expla tal agen en nm shop. er(s) se ish viro sen ngu en mmon Fire exti safety and Canada. e of the co States and ■ Explain som wer us the United rking with po s of hazardo ple rules for wo nci pri ■ Discuss the Master Cy nt in equipment. tions. linder an and equipme communica d Brake ety concerns per clothing Fluid Se ■ Wear pro e of the saf rvice and air ke ■ Discuss som bra ck p. a sho remove ed with antilo iat to p oc ste ass first aid the in s. pla tem Ex ■ eyes. bag sys d the an m g fro s inin t chemical hnician tra governmen ■ Discuss tec purpose for and . ■ Explain the rformance certification of brake pe regulations standards. tion (OSHA) Administra ow tal Canada Terms To kn osgene Environmen Ph n tal Protectio tal inflatable Asbestos Environmen Supplemen A) tem (SIRS) Agency (EP restraint sys Asbestosis Figure 4-2 ures (EP) ced thylene Ch Pro for n r eck roe nte ctio ing hlo stop lamp Extra Tetrac Canadian Ce Health op era le tio hic n. al BR tor Ve roethane AK Occupation Federal Mo 1,1,1-Trichlo (CCOHS) E pEDAl Mndards (FMVSS) and Safety roethylene fety Sta EChAn et hlo Sa Tric Ch ec iCAl Ch us noxide king the brak ial safety data she EC Carbon mo eter shootin on Klace Hazardoation rkp pedal mec Wo WhethMa hanical op orm hydrocarbg. S) er(M yoSD Materials Inf u do Chlorinated test, check th it as pa anderation is an im fetofy th ese points ation rt Sa t al ts po ee Classroom ven rta Sh e sol brake syste nt ■ Ch Occupof pedal op Manual ec m road te part of brake tro eration: page 74 t of (w k for frictionHe alth st or durin ub and Departmen ith th noise by T)e engi g a system le(DO on pr ati es ne ort sin lea running g and Transp k return

Performance-Based Objectives These objectives define the contents of the chapter and define what the student should have learned on completion of the chapter.

■

Move

s with no

re for powe r brakes). leasing the brake pe Be ise

lag or no

Each chapter begins with a list of the basic tools needed to perform the tasks included in the chapter.

t also

the brake da bu sure the is wearing . peda ov l, severaan l times N peda an IO peCT dal m ounting pa l from side ttoonsid at the technici is lifmon smhn eestec ooici lye.wh INTRO■DU thly and rts. olves no Chec Exce e here

inv k stop lam ivetag injpury side mov keeping the shop ld adssvan operataiosaf d ent in Htectioancofrom anem e. The twofo are n by dicaavo Personal pro avepin wo er rk depr n equipment te iding estec singtio check th rn l pro eakee g therkwo na and resta od chance of s wo rso pe at e nd lea th ng e fitby e ari making and ch tim sinag go rs lam is we re theme t will provid vishtitoea leased (F ployees ps sel or lig br sto ntetha him ak g pl igh tin ig uip pedal seve ch t. It is im er emure 4-2), in practices tim andeeq is protec ha oth th the ral times e po all pe n clu rta se da the ding the ntdis vee,to have4 l is presse s tho . tocu nosse te th R er d th th clean and saf ird apt an E at e ch or center d go off som T ury. This ignition in ru Aorpinj —high nts n before e vehicles equipp ideh accC . ed with lig -mounted— the brake rsonal safety lamps wi hting mod overallpand pe ll operate. ules EDA

Special To

ols

Coworker

1

R linDE viCE ER CY luiD SER T S A l F TRAv M E E K l A A nD FOR R Air inD CE TEST n the B hydraulic A us system ually

Terms To Know List Terms in this list are also defined in the Glossary at the end of the manual.

ed ■ Ble r cylin lyze the cond . maste system ck the cessary. Ana id from its Che 4_hr_133ned 198.ind l as rake flu and fil vehi cl135e’s b a tion of nce. ra appea l ABS Integra Know ing To s l bleed Term Manua ing ABS bleed ch tegral en B Non-in w ing re ed sc er re ble su Bleed es g Pr in bleed Brake g in ed ble Gravity

Special Tools Lists Whenever a special tool is required to complete a task, it is listed in the margin next to the procedure.

rep

64540_ch0

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er tomet Refrac ty c gravi Specifi ing ed le b Surge ing bleed Vacuum

system a brake presof nents of TEST compo b the system r and D lic A au ro O dr linde can r hy TEM R e lines the master cy anged or d othe der an E SYS ch r or brak ter cylin aster cylinde which is why linings are correcte d BRAK as m e or be ds ly, th the m conditions, ate safe s must brake pa eaks in g To oper k properly. L us operatin henever the ny problem A w ro or ce: must w cause dange be inspected or braking. rforman o d pe t p e us an sure em m mplains of or brak s cause lic syst cause po ed tire at n fl ca hydrau customer co n -i at over the a tions th wer. If ated, or when tely. g condi der-infl ia aking po ll to one followin immed pu more br ched, un for the quires may grab or mismat , re Check n e cl or hi es ve ms. W loaded side, the brak e proble ing. ■ Tir to heavily l brak ing. A back or side unequa vehicle load ont to al fr qu om ne l fr ■ U unequa load is side.

8.indd

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solves th e problem causes most lowtem, inco pedal prob s. Low pe rrec dal als lems, brake shoe t pushrod length adjustmen o can be caused by and bleeding s, or a dr thse syste um brake t, a service a aseic Tool W m sh 4.indd 1 hen a gi brake that leak inBth 1-04 oe r_00 ven amou adjuster an’saulic sysexceed a 64540_ch01_h cidr is out of technihy th nt at of is sp not woan force is rkding. Basic adsejut stment, wo about 2.5 ecified maximum able to: applied to leak s rn r e peda tool inches (6 be distance. foth l ld er d we ou l, brake pe n shop to 4u m linis m fications shm) wh Th ter cy aximum da caap en ter,foyo n be m0aspo Special To t a10 d l sp Cleal tratve und inInth unds (445 anve wrlenmchust speec etra ols Fathis ch ■ ve arele)akofagforceed ecifiFlca view of ilure to tionun is no not rN . cle service er fo tshi ed and re measure test exhaust brak Brake peda rmally def e ec cylindinform inioen.ne is applied. The boostas ment. Us r pletion l effort m at te em m er pr st co et exact spec e a brake st a m essut re gauge dd ese five pr Upon anwi rakethsy ll Te b ipe re ■ en su da fe lt in an in der mrt l ef ocedures sa apfo Tape meas gauge to lincorrect pe orm a air entr ure pedal : meaas ■ Perf da 1. Tuernbra suterer cy am Service ma ofke Aeden rcdeerapplied l travel or force pairs. th justgi cyfolin place drive. nual ms in rese ssarfy.th ne. On re to the pe and re the master cerve vacu proble as ne ve ovse wi dal with hi se m cle ed no Re r um r’s le g ■ is exhaus chthb vacun. repai 2. an ■ Dia Inuf aclltuthre d en sta um b an te as d d e sis e brake pe tio m an from th t, .pump th linkag e la lay to3. Hook booster.cylinder e instal e nc peeda orug free p the lip dofrag, dal effort befga ter e l a th pedal . mas g seque in l until all e tape m the digsta e brakice b auon brake th cations leedin ea vererhov hicle line fro pin , ncte specifi ■ Osu l ifi raul peda r cym (Fcigve ereth th ur hyedto r stop ec as ya e e pe rd oo m 4sp th p p da sti y 3). a ed l to caeteste for ge of the ede som gnose al caused b ck on erct need vehicles■inLoth inio akeicpeda ■ Dia g ns wh stru ped een.l rim (F br erform d einof l an plac ul atio an dra or hard lems and p hyur a fo tarm in e 4-4). Yo d measure ke ig pe e ra b m ic b ea rv ro e su p u can use se l der sh th re. id leve ia and flu der flu airs.

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138

Chapter 4

SERviCE Tip  The vehicle’s brake light switch must be activated any time the brake pedal is moved downward any amount. There is “no free play” allowed with regard to the brake light switch.

Author’s Notes

AuThOR’S nOTE The following procedure is based on a Honda S2000. Other vehicles have similar procedures. Many vehicles do not have an adjustment for pedal height.

This feature includes simple explanations, stories, or examples of complex topics. These are included to help students understand difficult concepts.

Adjusting pedal height 252

One to adjust the brake pedal height and free play follows. Disconnect and loosen Cha ptemethod r6

the brake pedal position switch until it is no longer touching the brake pedal lever (Figure 4-7, A and B). Gain clear access to the floorboard by lifting the carpet and the CE(Figure insulator 4-8C). Measure the pedal height, (Figure 4-8), from the right center of 10

PhOTO SEqUEN

Typical Pro theced brake pad to the floorboard. In the case of this Honda, the pedal height should ure Caution For vaccleared uum oster Tes be 179 mm or 7 ¹/₆ inches). IfBo necessary to adjust ting the pedal height, loosen the locknuts, and If the switch is not adjusted correctly, the brakes will drag. This may cause heat problems with the friction materials and poor braking performance.

turn the pushrod to obtain the correct measurement (Figure 4-9). With the correct height obtained, hold the pushrod in place while tightening the locknut to 15 Nm (11 ft. lb.). Install the brake pedal position switch until its plunger is against the pedal lever and completely pushed into the switch (Figure 4-10). Unscrew the switch until there is 0.3 mm (0.01 inch) between the switch’s threaded end and the mounting pad. Connect the switch to its electrical harness. Have an assistant check the brake lights as the brake pedal is depressed and released.

Photo Sequences Many procedures are illustrated in detailed Photo Sequences. These photographs show the students what to expect when they perform particular procedures. They also familiarize students with a system or type of equipment that the school might not have.

Adjusting pedal Free play Using the same Honda vehicle as the example, the pedal free play is checked and adjusted

P10-1 With the engin idling, attach a vacu gauge to an intake in ethe manner. The engine should be off. Push on the brake by hand while um P10manifoldfollowing 2 Disconnect the port. Any reading below 14 in. Hg of from the intake mani vacuum hose that runs vacuum may indic P10-3 If you do not ate an fold to the booster engine problem. feel a quickly place your thumb over it befor andPushrod step 2, shut off the engin strong vacuum in e e, remove the hose engine stalls. You and see if it is colla should feel strong the , psed, crimped, or vacuum. clogged. Replace it ifLocknut needed. (A) Brake switch

Lift floor mat

(C) Measuring point (B) Pedal bracket

(E) Pedal height

P10-4 To test the operation of the vacu check valve, shut P10-5 Remove the off the engine and um check valve from the Standard pedal height wait for 5 minutes. Apply the booster. (with carpet P10-removed): 6 Test the check power assist on at brakes. There should be valve by blowing into least one pedal strok 179 mm in.) intak(7e mani the fold end of there is no power e. If assist on the first Figure 4-7 Remove the pedal be a complete block the valve. There should appli the check valve is catio position switch Figure 4-8 Remove the floor mat and a portion n, or stop lamp age of of airflow. leaking. switch from the pedal bracket. the carpet to gain clear access to the floorboard.

replace th e the wiring parking brake sw Hydrau itch. If th harness lic Line, 1/31/18 10:33 AM between e Valve, an the body lamp is still off, d Switc find and control co h Service Brake Fl repair th mputer uid leve 223 e op an en circui d the sw l Switch With the itch. t in Test ig to alert th nition on and th e brake flu e driver of a low-f into the id level sw reservoi itch clos r body; ot luid condition in for both ed, the br hers are types. ake warni attached the master cylin ng lam Begin by de to the re P10-7 Apply vacu en servoir ca r. Some switche p lights suring th theum to the ig boos s are built ni p. Test pr at ter tio end the valve. Vacuum thP10of e flu8idChec on and ob inciples should be nblock le at k ve the th boos ed. l serve thperfo If you do is at or ter air control valve not get the state resule switc are simila h. ne e by rming ts w in ar If r a step ar P10brake th 6 th 9 Turn the front whee finkdvalve e la7,mp th of the ning lamdrag e fu replace the chec test. With the ll m an.d repa and step whee ls by hand and note p. ar ls vehic en k If le the raise on amount go out, d off theitfloor, ir the sh is , discthe th is ort circ brake es To verif replace th litpump pedal to exha onnect th e reseofrvdrag oir.that Turnpresent. ual e sw vacu e um w twter.een th ust resid thet be from iri boos the switc y that the warni ui itc ng conn h. If the e switch ng h ec lamp do and the lamp do float or remove lamp will light es not go tor lamp. w es not lig th out, ht with th e cap with an hen the fluid leve and the integral lamp. If l is low, m e switch sw ci cl rc an itc osed, ch uit contin As a fin eck for an h and let the flo ually depress wire betw al check, discon uity is good, re at op dr en op ci pl . ne rcuit betw If the ee ace the sw If it does n the two term ct the wiring ha een the itch. rness fro inal switch not, find m the sw 64540_ch06_hr_2 compute and repa s in the harness 47-284.indd itch, and 252 r. co ir the op connect en circui nnector. The w a ju ar t betwee n the sw ning lamp shou mper electric ld itch and al wirin the body light. g Repai 1/31/18 8:57 control Wire siz AM r e is determ drop allo ined by th w e amount or in met ed. Wire size is of cu rrent, th specified ric crosse leng in se tor. A 20 gauge is ctional area. Th either the Amer th of the circuit, e higher much sm ican Wir and the When the voltage alle e wiring di replacing a wire r than a 12 gaug number in AWG Gauge (AWG) syst agrams or , the corr e. the smal prevent ler the co em ect size An America chafing or in parts books. wire mus nducn wire Each ha t be used to splice damage gauge (A rness to aw as show WG n on appl wires. Ro ire, and use insu the insulation du or wire must be system for ) is a e ic sin flux he specifying la to ab tin ld vi le g se bratio tape cure wire size clea does acid (conductor -based flu ns the connectio or heat-shrink n. Always use ro ly in place to cross-secti complet sin flux tubing to n during x. Apply on ely sold ing heat cover all solderin by a serie al area) seal unde seal the wiring g withou to shrin splices or er s an k t rground numbers; of gauge electrical d connections. U tubing causes th eroding the mat bare the lower Many el erial as the numb e tubing tility com supply ca ectrical er, to make th pa bl sy co es ni stem re ntract an . es used he the wire cro the larger ese d at-shrin ss section shorts or repairs in a way pairs require re k tubing . placing gr that does to damaged with man ounds in the re no t in crea pa w y accessib factors influenci ired area. Severa se the resistanc ires. It is import Caution ility of th ng the ch e in the an l methods t to circuit or ew oice requirem are used Never rep lead to ents. Th iring, the type of . These factors to repair lace a wi e three m in re with one of ost com conductor and siz clude the type of damaged wire 1. Wrapp mon repa size. Using a smaller repair re e of wire ing the da ir qu m ne ire m et ed is damag d aged insu hods are: rect size the incored, and ed co th la uld tio an e circuit d th cause nw 2. Crimpi repeated ng the co e wiring is unha ith electrical tape failure an d 3. Solder rmed) damage nnections (in cases to ing splic with a so where th cle electr the vehies e insulatio lder-less ical syste connecto When de n m. r ciding w connectio here to ns cut a da of each ot . As a rule, do Rosin flu maged w x solder not her. Use ire, avoi is solder us a wire of have two splices d points ed Crimping close to the sam trical rep for elec. e size or or connections other sp A solder airs. tors . So w la lic le ith rg es ss er in or co than the me man 1. ufacture nnection uses a wire bein 5 inches (40 mm repairs. rs re com g replaced ) Crimping Heat-shrin . selfsealin quire the use of pressed junction k g solder to connec se plastic tub tubing is less conn lf-sealing sold t two co ing that er ections shrinks in is an acce less connections nducdiameter ptable w on wh en al exposed l ay to splic to heat. e wire,

64540_ch04_hr_133-198.indd 138

Margin Notes The most important terms to know are highlighted and defined in the margin. Common trade jargon also appears in the margins and gives some of the common terms used for components. This feature helps students understand and speak the language of the trade, especially when conversing with an experienced technician.

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Master

Lower l the peda

d Service

ake Flui

r and Br

Cylinde

139

Pedal lever

(A) ) (0.01 in.

0.3 mm

Pushrod

Raise pedal

the d turn locknut an or Loosen the longer Figure 4-9 to make the rod vement rod sh mo pu the the pending on shorter de needed.

knut hin its loc switch wit ned. The cleartai 0 Turn the Figure 4-1 per clearance is ob mm (0.01 0.3 until the pros switch should be ance on thi int A. inch) at po (C) Locknuts

dal Brake pe pad

Power Brake Service

y Pedal pla 1–5 mm Vacuum booster

Service Tips Whenever a shortcut or special procedure is appropriate, it is described in the text. Generally, these tips describe common procedures used by experienced technicians.

136

271

Check valve

free the pedal n C 1 Check tur Figure 4-1 tment is needed, ved. hie jus play. If ad per free play is ac n. tio pro era op until the stop lamp’s Check the

rement is measu e is felt. Th to 3/16 inch) ch resistanc in iff e /6 st a (1 the brak before to 5 mm cknut on rdal travels ould be 1 mm ing the lo play is co ce the pe d sh e l free play by loosen ion until the free the distan dal foot pad an th g ay k pl rin ec e su Brake peda table on rech e fre mea rect ake pe adjust th e appropriate di ent is made and at the br is not adjus m th is taken 11). If necessar y, st in ju . h e switc 4all vehicles ter the ad k switch (Figure turning th the locknut af kage, chec Vacuum l lin ondthis itch an 6-26 Figure pe l swbooster daThe ake peda source hose to tighten htened. br et e rg th fo system. VSA a of t part Honda is tig no h on . rect. Do ter the locknut is l stop lamp switc g pedal free play Figure 6-28 Do not remove the check valve from this af hanica adjustin free play type of booster. Remove the hose from the check valve has a mec necessar y after If the car instead. it if st ju ad n and Electrical ch operatio s mp Swit connectors 300 Serie Stop la e Chrysler th 10 ng on 20 Adjusti Figure 6-27 Before removing the is based ebooster ur ed oc electrical ESP the of pr all g fasteners, disconnect in w The follo on the booster and master cylinder. TE connectors R’S nO AuThO m vehicle. ping its Magnu battery. Remove the windshield wiper module and componen dfrom by warts an the adjusted negative cable lly could be s are usua p switch p lamp switchecylinder. to gain access to the booster. lam p nt co acts a stobooster to sto the master remove and e, the ns timat day’s connectio e itches or Disconnect the electrical ever, bend  At one forms th lines. ternal sw brake How Tip from in the in . damage or E at nt up not iC Do th re booster. ed the or Rv cylinder backplunger lin l e diffe senscheck valve Move the master SE using athe ake peda ur or fiv the from the up doclenot but to fovalve, s areremove of the br ) hi nt to gethoseun vacuum ith check ve w ) Disconnect the e CM mou PP m its (E nal stems. So Control Module Pedal Position (B unctio6-28). Figure from the booster multif mputer sy ne ake e many co e (BCM) or Engi is named the Br P switch. the BPthat that serv nsorsteeringaccolumn, the ensure l Modulin orvearound cording to The sethe ntro l. Co working Before tra dy WARNiNG e lamps Bo tent of brakto bag air the e ex disarm th d properly e an Failure . at n discharge had time to has sitio bag systempo ill oper air w M BC Chapter 4 e injury. serious system could result Switch.inTh sufficient time has elapsed for the air Tape measure Move inside the passenger compartment, and, if lamp switch (Figure 6-29). The switch bags to disarm, disconnect and remove the stop Caution the booster. Use a screwdriver to of n installatio upon will be replaced with a new one and slide the pushrod from the pedal Before even beginremove the retaining clip from the booster pushrod, ning to work on a mounting nuts, and remove the four booster’s the Remove 6-29). Figure to pin (refer back d 139 hybrid effortor electric Brake r_133-198 the.indengine compartment. from booster ch04_h gaugemake certain 64540_ a new booster seal is present on the pedalvehicle, Before installing the new booster, ensure that that you are aware of the bulkthrough place into Unapplied booster the Slide 6-30). (Figure the procedure to disbulkhead side of the booster pedal brakepushrod ons. Position the booster able the high voltage head and tighten the four mounting nuts to specificati lamp a tape measure 4-4 Use Figurestop Install and adjust the new supply system power or over the pedal pin and install a new retaining clip. distance to service all theaccording yardstick to measure a reconnect and booster the onto cylinder switch. Under the hood, install the master Brake pedal pedal to the steering wheel. the from Connect ts. information. gauge effort other removed componen and electrical connections. Install the wiper module vehicle. test4-3the the brake pedal effort gauge on the brake pedal. Install Figure the battery and road

1/31/18

SERviCiNG AN ELECTROhYDRAULiC POWER BOOSTER SYSTEM

gasoline vehicles, use an electric brake Hybrid vehicles, as well as some conventional unit Figure 6-31) used to pressurize booster pump (often referred to as a hydraulic power which has the master cylinder system, booster hydraulic a in use brake fluid for

References to the Classroom Manual

10:33 AM

Cautions and Warnings Cautions appear throughout the text to alert the reader to potentially hazardous materials or unsafe conditions. Warnings advise the student of things that can go wrong if instructions are not followed or if an incorrect part or tool is used.

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Figure 4-5 Apply the specified amount of pedal force.

References to the appropriate page in the Classroom Manual appear whenever necessary. Although the chapters of the two manuals are synchronized, material covered in other chapters of the Classroom Manual may be fundamental to the topic discussed in the Shop Manual.

4. Apply the brake pedal until the specified test force registers on the brake effort gauge (Figure 4-5).

pedal

hisSERviCE Tip  Before starting any diagnosis, refer to the vehicle’s service for examtory if available. Note any recent history pertaining to this repair order, accurate quick, a to way the point may repair brake recent A low. ple, brake pedal diagnosis. The increased 5. Note the change in pedal position on the tape measure or yardstick. service distance should not exceed the maximum specification listed in the vehicle adjustmanual. If it does, look for a leak in the hydraulic system and check pushrod also can brake parking adjusted poorly a or adjusters, shoe bad shoes, Worn ment. cause excessive pedal travel.

pEDAl FREE plAY inSpECTiOn AnD ADJuSTMEnT Classroom Manual page 75

pushrod and the Brake pedal free play is the clearance between the brake pedal or booster must exist so that primary piston in the master cylinder. A specific amount of free play so that pedal and released is pedal the when the primary piston is not partially applied

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140

Chapter 4

Stoplamp switch Stoplamp switch mou nting bracket

Brake pedal lever

Figure 4-12 Pull before installa the switch plunger all the tion way out and not release . The pedal should be lock ed d until the swit ch is installed. down

Use a brake pedal for a depressor depressor to hold the brake pedal ). Rotate the down (check stop lamp sw and pull rea the alig rward on the itch approxim sw ately 30 degree nment machine hand force only, pull the itch. It should separate s counterclock from its mo switch plung should be hea wise unt (Figure er out to its rd as the plu 4-12). Using ful ng ly er ext ratchets out. Ensure the bra ended positi on. Low clic ke ped al is down as switch’s index ks far as it will key to the no go and is firm switch about tch in the bra ly held in pla 30 deg cket and pu ce. Align the sh the switc Apply foot for rees clockwise until it loc h int o pla ks. ce ce. Rotate the to the brake to gently ris pedal and rem e until it sto ove the pedal ps. Using gen stops movin depressor. All tle hand for g. This will ow the pedal ce, pull up on ratchet the adjustment switch plung the brake ped is initially che er to the cor al until it cke pedal is dep rect position ressed and rel d by having an assistant . The switch observe the eased. Howe where the cru brake lights ver, the final ise as the brake check requir at a safe speed. control can be safely use es a d. During the road test on Once the sys road test, eng a tem is stabilize should turn age the cruise road off. If not, the d, depress the control n the switch brake slightl must be che y. The cruise cked and rea djusted as nee control ded. CuSTOMER CARE A cus tom his or her car is through the er’s only contact, literal ly, with the bra mance by “pe brake pedal. dal feel.” It is Customers ten ke always a goo brake pedal d to judge bra system in d idea to eva before startin ke perforluate the fee g any brake pedal feel sho l and action job. Then wh uld be notic of the en you delive eably impro brake pedal r the ved action is air in the system . The biggest cause of spo finished job, lot to ensure , so careful ble ngy or low customer con eding of the fidence. system will do a

Caution

Do not release the brake pedal by pul ing the depress lor and letting the out pedal slam up to its sto The stop lamp p. switch will not adjust properly and may be damaged.

Customer Care This feature highlights those little things a technician can do or say to enhance customer relations.

Brake peda

l position

Switch Many late-m odel vehicle s use a BPP sen the brake ped sor to inform al the body con supplies a 5-v position (Figure 4-13). trol module Th olt reference (BCM) of signal and gro e BPP sensor is a poten tiometer. Th und to the sen e BC sor and the sensor suppli M es an

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Name ______

____________

____________

DIAGNOSIN

G DRUm BR

________

Drum Brake

Date ______ ___

________

AkE PROB Upon comple LEmS tio ing, grabbing, n of this job sheet, you will be able dragging or to pedal pulsat ion problems diagnose poor stopping, ASE Educa tion Founda . noise, pulltion Correlat This job she ion et addresses the following C.4. MLR task: Inspect wheel needed. (P-2) cylinders for leaks and proper operat ion; remove This job she et addresses and replace as the following AST/MAST C.1. Diagnose po tasks: or pulsation con stopping, noise, vibrat ion, pulling, cerns; determ grabbi C.5. ine necessary Inspect wheel action. (P-1) ng, dragging or pedal and replace cylinders for leaks and proper operat as needed. (Pion; remove 2) Tools and Ma terials • Basic hand tools Protective Clo Goggles or saf thing ety glasses wit h side shield Describe the s vehicle being worked on: Year ______ ________ Ma ke _________ Engine type _____ Model and size ___ ____________ ____________ __ VIN ______ Procedure ____________ ________ ____________ ____________ _________ 1. Begin the inspection of the unusual wear drum brake or improper sys inflation. Wh tem by checking the tire at did you fin s for excessive d? or 2. Wheels for bent

or warped rim

s. What did

3. Wheel bea rin

gs for loosen

4. Suspensio n

ess or wear.

system for wo

5. Brake flu id lev

rn or broken

el in the ma

ster cylinder.

Service

425

JO 1/31B /18 Sh 10:33 EE AM T

36

Job Sheets Located at the end of each chapter, the Job Sheets provide a format for students to perform procedures covered in the chapter. A reference to the ASE Education Foundation task addressed by the procedure is included on the Job Sheet.

you find?

What did you

find?

components. Wh

What did you

at did you fin

d?

find?

6. Signs of leakag at each wheel e at the master cylinder, . What did you in brake line s or hoses, at find? all con

nections, and

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Ase Challenge Questions Each technical chapter ends with five ASE challenge questions. These are not mere review questions; rather, they test the students’ ability to apply general knowledge to the contents of the chapter.

Case Studies Each chapter ends with a Case Study describing a particular vehicle problem and the logical steps a technician might use to solve the problem. These studies focus on system diagnosis skills and help students gain familiarity with the process.

Ase–Style Review Questions Each chapter contains ASE-style review questions that reflect the performance objectives listed at the beginning of the chapter. These questions can be used to review the chapter as well as to prepare for the ASE certification exam.

424

Chapter 8

can be used S depth gauge B says n A says a tire . Technician 4. Technicia ng thickness e, lini lath a re lining thickon asu um m me to cify a minim unting a dru spe mo to s g s ker sin above the unt ) ma cus most car or 0.75 mm ece drum mo 1. While dis says a two-pi inch (0.030 in. t rivet head. Who is cones. ness of 1/32 Technician A ses d or spherical ed above the clo ter or with tapere or cen le arb is e tab m e lath sho the ece dru says a one-pi d cone and B correct? Technician B spring-loade C. Both A and adaptarbor with a cup-shaped on the lathe nor B A. A only by two large ce D. Neither A pla in ed clamp y onl B t? B. rec hn cor . Tec ician B ers. Who is ng discussed C. Both A and se inders are bei inder may4cau 5. Wheel cyl nor B 99s that A. A only king wheel cyl lea D. Neither A a say t e tha s icia ic A say rv n B k. Tec s Sehn nA B. B only grab orSloc eel cylystem the wheel to kinpag sed. Technicia inside the wh g nd cus dis fou e ng ke for Brasee se bra ms are bei ssl or pneca dam ered a cause drums may cau is 2. Brake dru Electri t is not consid t? ing d spots in the inder dust boo eel cylinder. Who is correc says that har s that chatter hnician B say wh Who A and B replacing the chattering. Tec fluid-soaked brake pads. th Bo C. by ot n is B y s usually caused nor onl A. A ral year D. Neither A mve B is correct? yother co e lastB.se B eonl C. Both A and ithin th bec om an to display B w nor t A il er A. A only u ld ly D. Nehith icles b has actual actually to strument y e of ve B. Bponl ority t p,anel d lights ar ch. Most in ster that cut menbits am s e st e mkeajlath ruting s an clu n gthbra uld r or swit ing l ile dis ugesho er osin heofinthe mes a cluster is ting stcus e gabit Ttip ti u cut so h . y n cl p Warn 3.mWh T t . o se an shs the etwork en ciapnicAalsay y nded ops. M anrou or hile a n n B saysgafrslig stru hni ty omhtly ve cia airl sh own time w rogrammed otihni pwil in The in bleTec m in theor esha re Tec ad t to rp. el tha re p d m au t ea raz the dru t pan s reisduce be re irec n th ove into a dgro servic odube le ocan otral rumen anspi elp o also need to stke cut hWh on. in a, rati m h y bit ope at r ic lt d l te h bra ia il al pu erratic ged, w spec noisytoand uster w on seri se nt out ilt is exchan strument cl based arcau t? rebu ts, s e serecn Both A and B the in C. elemen cluster adcor y bee yditionally, ced. la B re mmon p nor onl d al re A A A er A.red. has any co lways make s D. Neith been m ai e as p h ar A re sh d. ed. A ce yit Bnonl being ze s in use ation is use icle concern ation, li B.d o system h rm rm reinitia e latest e right info air for the ve service info th f o at th ost ific rep lt the latest ing. Ip M to verify th e spec st su ICe T n for th repairs, con diagnostic te SeRv s necessary r rmatio is alway service info show up fo r up-to-date it t u b eck in to ulletins fo ch eg b to s em sure ice b er syst al serv the new and technic , ry low recalls at a ve be okay, to tivating ABS ac ng appeared g to a slow of the in ythi ng m er ni co ev ai d d y compl inspected, vement an tool an of r D ne an U pa ST e sc ere e ow on dr y akes w with th read th e source CaSe e shop ere made, br the vehicle e technician had to be th oblem. th to in w pr th V with checks e BPM e came e while e same tivated an to A vehicl l the normal the ABS ac t out to driv cided that th e still had th the technici amiAl at an de be cont an told e vehicl speed. r the fact th ok an assist cian finally ator, th lp. The forem t appear to replaced fo ni to ul ch pt an od te ce ci no m e ex e he e d e techni rmal. Th an for pensiv they di e shoes wer s here: Start stop. Th ng looked no acing the ex shop forem en though th help. ev e When pl o lesson ever ythi lem. After re d to go to th the drums, placement. There are tw hen you need re ce w de the prob int he deci and resurfa t of needing ed normally. technician s po in rm ed oe is po rfo nc th sh e pe rie th At the rear vehicle ore expe worn to sreplace any way or achined, the to ask a m h a cu id m in m wit be afra nated drums were p4ro2b3le rtant to ask ydo not e ickeing and th basics, and g Saebrvra it is impo nician B sa e ke in th ra ss B ith ys h w dismcu NS e ru n A sa ilD ng the rs. Tec eSTIO 3. Wh , Technicia blem occu done duri W qU tomer when a pro k what was AM as RevIe tly ssed. to e ac cu t B 1/31/18 10:16 l t? is ex st an y d ec u T port A and corr eing -7 m aSe-S B BS is b elphi DBC in sit is im ice. Wbhraokeis lathe, i-C. Both A nor x D g an A rv on a sem stdru appro of. Neither leedin ys that the three times ol f la b o e g d k D nin 1. Bra nician A sa rakes bleSd at a scan to espe- achining a . A in le spee ondly a series . BS w ar n B N ys th 424 d h em, henrm A usesAa sp ialyn B makes diameter ia ice b b er A Tec r_373-434.ind 64540_ch08_h n B sa e servUEnSicTiaIO BS syst6. W m at the am n. Te chnic can sthonician e th loec . hBnoicn final druys anicA havIE e, of fluid T Wceq m. TBec lered . Tech e n A sa th malfunctio lamp also rp b rv th 0 V t se to 5 n en E 1 in u o. BS d Bw arning uirded obtae chnicia E R sequ be reqke am ect?mately A L rumlafo e to ? rr er Y rg an ts ct st co T an cu A KE 4. T als asshaoe adju. Who is corre might a brae w dB allow ASE-S t? p sig n C.e BreodthBR A n B or hBo is remalolyveif the er brake replapceardking . Both A ansh hroBis correc lam that th m. W A and thberleA ying to ci C ff th no V wasin the . Both ks oB . SNpeiro AW says ore tr DB or B PalM g C l slack an A either 1. Bef nician A bac ths eup in only N er A n al in A . n -l . g D si Ain an B . Neith o m-to Tech ian B take . co d D oneclyt? tw ru t d n an e A rr ly ly e A A oifnth ic of th prese B. B on A s e . at er ar B A th Techn ble. Who is only C. Both et r as ys nodes ng iam ca bleAco n A sa . t,Bth B. B onelyd atter as lo . ouer brake trth Nei d. hnicia t is corrBec . le nec on ot m ltDip 7.uT gro only t do n imensi en mu n men ician A mmon A. A adjust n an axle se e discard d iameters o 2. Wh look for:der, Technat a co t o ly d o n o , th n n o b s S li ti ton AB heel cy connec . drum not exceed at the drum me. Who is B. B o kind the pis on this fact sa th do ng a .wa wbea e ti ys ey th eh . ec sa y it th ed A tl fluid plien circbuas linder en insp ician B e exac o nder e w ees.l cy 8 2. Wh liquid brake Bh. ee Techn les must b dB anl cy 1/31/1 th signhal Who is ax th A an finds uilds the w ot w builltdage given C. Bo nor B b n lo re-vo the ebosiogt.nals. ect? and re ian B doesC. und inolt ther A rr ag co fohigh-v ic D. Nei n is h s ly B ec es n . e T n D o d b A. A damp must und th A an rums o if only C. Bo nly nor B new d fing comp at t? B. B o ther A o th ys that correc D. Nei n A sa the rustpro ician B says ia ly all n ic h o n it rw move move Tech echn A. A re ca . T re 8 a to e. to n the ned nly oes o surfac be cleaned e. Who is s ea o sh ve m cl B o ru . ke B ed rfac ust e bra nician A m heel. th su m th s m m g o m fr w ru stin d 49s, 9 Tech the dru e star hed d e the nd en adr_ju 1-51 refinis articles from dB g4.ibrake ay from th to just forc en3. Wh0_ch10d_h st46in p cy th A an r aw dis 54lf-a ju 64se metal g leve is best poli er without C. Bo or B t? justin it d er A n st ec -a ju ys rr lf d co se B sa lf-a . Neith n se D ia e h ic th ly gs wit B A on Techn eel against in d . n t? an li A ec h rr h th A icate a ly kes wit star w . Who is co C. Bo nor B at bra der end ind that if . B on A it B th g er ys in th gag n A sa wheel cylin ician B says re D. Nei hnicia n e only mo heel 9. Tec wear at th ition. Tech A. A e and e is worn corthe to more wear cond er vo brake installed in nly orn at says that th B w B. B o e al o-s ly norm e bad hnician A echnician may b n a du o ar es g o gs in sh linin o is . Tec d drum. T e lin the B h , n m gs o d er W in ru . th an n li m n eo 4. D ect? th A of the out-of-rou tapered dru B than th ho is corr C. Bo areas A nor W m is a m is an either rectly. N B . proble the proble d D A an at turn only th th re o A n B . ys B . A ke sa C nor or bro g to one t? nly ther A weak correc llin B. B o D. Nei ys that drag or pu problems only e d n A sa p A. A hnicia cause brake at the sam or an ino dis c ar which ec m T . ru ly n 10 to ys th king plate ed can r sa th gs te B n e B. B o at ri n sp diam ic ian B ys th nicia a loose bac rrect? h sa m u ec A T n im is co side. d by dB nic ian e ma x the d. Te ch cause . Who th A an 5. Te ch sion is th refinishe iame ter is can be self-adjuster not C. Bo or B dimen ms c an b e dis c ard d n and e er A n ensio erativ Neith . D the dru the drum we ar dim ter. Who is only at le A e . th ab m A w ia lo says gd um al nly hinin B. B o ma xim w able mac dB lo th A an the al ? C. Bo nor B A ct er e th corr D. Nei only A. A nly B. B o

LENG ASE ChAL

E qUESTION

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AM

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xvii Disc Brake Service

___

Name ___________________________________

Date _________________

DIAGNOSING DISC BRAkE PROBLEMS

355

Job Sheets

JOB ShEE T

30

Located at the end of each chapter, the Job Sheets provide a format for students to perform procedures covered in the chapter. A reference to the ASE Education Foundation task addressed by the procedure is included on the Job Sheet.

be able to diagnose poor stopping, noise, Upon completion of this job sheet, you will n problems. pulling, grabbing, dragging, or pedal pulsatio ASE Education Foundation Correlation AST task: This job sheet addresses the following AST/M pulling, grabbing, dragging, Diagnose poor stopping, noise, vibration, D.1. y action. (P-1) or pulsation concerns; determine necessar Tools and Materials Basic hand tools

Protective Clothing Goggles or safety glasses with side shields

Describe the vehicle being worked on: _ Model ______________ VIN ______________ Year _______________ Make ______________ Engine type and size _______________ Procedure

e or system by checking the tires for excessiv 1. Begin the inspection of the disc brake did you find? unusual wear or improper inflation. What ___ ___________________________________ ___________________________________

did you find? 2. Wheels for bent or warped wheels. What ___ ___________________________________ ___________________________________ find? you did What wear. or ss 3. Wheel bearings for loosene ___ ___________________________________ ___________________________________ components. What did you find? 4. Suspension system for worn or broken ___ ___________________________________ ___________________________________

. What did you find? 5. Brake fluid level in the master cylinder ___ ___________________________________ ___________________________________ and , in brake lines or hoses, at all connections, 6. Signs of leakage at the master cylinder you find? at each wheel. What didAp pe nd ix ___ ___________________________________ ___________________________________ As e pr Ac tic e check and travel e excessiv for ex Am in At io n brake pedal, 7. Road test the vehicle. As you apply the sponginess. What did you find? _______________________________ _______ _______ _______ _______ ______________ linings, but 1. Tech nicia the obvious sounds of grinding pads or pad A says not fornnoises, thatjust 8. Listen if the master cylin der did you find?6. A vehi What and rattles. push rod ical clanks, is adju mechan cle drifts_______ sted clunks, too long, the brakes migh ___ t while driving. _______ to the righ t ______________ not be able ______________ Technicia to fully _______ n A says that a crimped apply. _______ ______________ Technicia n B says that if line to the left the master cylinder push whe el caliper coul bad a d for be check the rod applied, caus are is when e. Technician B says that adjusted brakes the too to one side short, the vehicle If brak 9.the may es mighpulls fluid interior or brake t drag of that of greasethe the . signs Who for righ check is t Also corr brak wheel. ect? e one hose at caliper could be dampads. or damage . Whodisbrake A.orAloose only correct? rotor. Check for distorted aged have contaminated the pads C.and Both A and B A. A only B. B only C. Both A and B D. Neither A nor B B. B only 2. While discussing mas D. Neither A nor B ter cylinders, Technicia nA says normal brake linin 7. Technician A says serv g wear causes a slight ice information circuit drop in fluid level. Technicia diagram s or sche matics make it easy to n B says a sure sign of identify combrake fluid contamination mon circuit problems with mineral oil is the . Technician B says if seve 02/02/18 swelling of the master ral circu its fail at the same time cylinder cover diaphrag , check for a common m. .indd 355is correct? power or ground conn 64540_ch07_hr_285-372Who ection. Who is correct? A. A only A. A only C. Both A and B C. Both A and B B. B only B. B only D. Neither A nor B D. Neither A nor B 3. Technician A says that 8. Technician A says that master cylinder leaks there is a vacuum chec can be internal or external k valve in line between man . Technician B says that ifold vacuum source a leaking master cylinder and the booster. Technicia will remove paint from n B says this check the area below the mas valv e is to allow air pressure ter cylinder. Who is into the booster durcorrect? ing wide-open throttle operation of the engine. Who is correct? A. A only C. Both A and B A. A only B. B only C. Both A and B D. Neither A nor B B. B only 4. While discussing brak D. Neither A nor B e lines, Technician A says that copper tubing can 9. Dru m brak es are being discussed. Tech be used for brake lines . nician A Technician B says that says that a grabbing brak brake lines can use doub e could be traced to a leflare or an ISO flare fittin leaking axle seal. Tech gs. Who is correct? nician B says that a leak ing wheel cylinder can also A. A only cause drum brake grab C. Both A and B bing. Who is correct? B. B only D. Neither A nor B A. A only C. Both A and B 5. Technician A says to replace a double-flare B. B only fitting with an ISO-type fittin D. Neither A nor B g as new brake lines are required. Technician B 10. Befo re tryin g to remove a brake drum says that flexible brake for service, hoses allow movement Technician A uses the of components. Who self-adjuster to back off is correct? the brake shoes. Technicia n B adjusts the parking brake cable to remove A. A only the slack . Who is corr C. Both A and B ect? A. A only B. B only C. Both A and B D. Neither A nor B B. B only D. Neither A nor B

Ase Practice Examination A 50-question ASE practice exam, located in the Appendix, is included to test students on the content of the complete Shop Manual.

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CLASSROOM MANUAL Features of the Classroom Manual include the following: C h a pT eR 1

BRake SyST

Cognitive Objectives

Terms To Know List A list of key terms appears in the beginning of the chapter. Students will see these terms discussed in the chapter. Definitions can also be found in the Glossary at the end of the manual.

and review of this chapter, you should be able List and descr to: ibe the opera tion of the basic parts of ■ Descr a brake system ibe the use of . ■ Descr valves and lin ibe the opera to direct and es tion of the bra control the hy system during ke draulic fluid. and after peda l application. ■ Discus s the purpose ■ Discus of brake po s the increasin boosters and g use of disc the parking bra wer brakes instea ke. ■ Discus d of drum bra s the general op kes. ■ Descr eration of ele ibe a typical bra tronic and act cive braking sys ke hydraulic system. tems. ■ Discus s the general operation of tra brakes and air iler brakes. Terms To know Active braking Friction Actuators Service brakes Fulcrum Air brakes Steering whee Lateral acccel l position Antilock brake ero me ter system (ABS) sensor Leverage Automatic rid e control Str ok e sen sor Lockup (ARC) Stroke simula Master cylind tor Bulkhead er Traction-contro Negative whee Caliper l system (TCS) l slip Ve hic le stability co Parking brakes Disc brake ntrol (VS C) Positive whee Drum brake l spin Wh ee l cyl inder Pressure Force Wheel speed Regenerative sensors braking Yaw ■

INTRODUCT

4

The most important terms to know are highlighted and defined in the margin. Common trade jargon also appears in the margin and gives some of the common terms used for components. This helps students understand and speak the language of the trade, especially when conversing with an experienced technician.

ION

verage

of le The brake system inciples d applied same pr is one of the mo e pa heel. The rce of the brak functions: d little st impo oked fo nt wsyssetem sprta mph an early e on nth 20 d de s to oo a veh ph icle. It nt that aw crea 1 of 10 m tir tire on tions in es meahas four basic Chapter 1. It must slo a solid installa l with speeds ic l of at da e m id pe e a moervin d wel d pneu gak the outs w m veh either od n br 2. Ittomu es .worke and beyond) an e using akicle k in storbri ngtira e.veh iles wer w internalat w The iclesetobracesto 0 mph (3p. fe automob obiles. 3. It thto solid muthste ho century, um brakes. A acting brakes rforman ed on autom ldighe peicle th a veh r tie sta tr t-liv twen ortio narydewhofenthesto ding dr fic. H 4. It allo rnal-con the driveline trafws were sh st deca pped dir al-e. xpan es. Exte akes ion brect al confir hten or intern motor vehicl um located on wagon akes d of the trol du g ma kage tig brrin earlybrakinound a dr me um By the en acting band soxim If the bra rs and lin s Model T g. ar ve on le d ; ed ie ke tr er sys on erte tr famou l wrapp or at the cent w do ’s ia es es rd er no ternal-c tem ak at Fo injured orexkil op eramte properly d on band br tion e en ingan , the e brakes ndin ing accide paled with fricch anchored at on rvic ver ission. an smsse er brak he sedri skilled expex isnic s wh nd lined nt.baTe ngersn highld e trdanpa rce. Tvic ert a ba s be he nd r brian cau bel servo have inside thkectiveness whe cou aking foo ser s. Two the heel fo rk wse a drume theeibra echanica band sys the e fe that bra of um m tem y to th ef the ce do e dr r d for mu can on e th ie t ke st pl sav orsystem byound th be hig is the hlyal nds lose tern In th ws ill Friction tion between ar pre tin al, s. band ap exteernlive arn abou ith an in g gthe u chleapter, we w the band le cosen bas or ceptsakes, yothi ntractin ake te resists mo s of two stubrdy o action starnrtalou ng internalic con ce barnd the surfa forms of matter. loptsse associdrum br and par ofrvall were a si brakes, either exte an ke sys oblems u study fficult to deve onbra tem pr n yo s. objects or n er Band tio he th ac external rvo d. O ry di ed. W

spee is ve ed. Se n with need force is brake shoes. It rce is thus need and high drum loss of frictio expanded too d d of ake fo e forces mage an overheated an and reduced action higher br ab at high brak ater da d g w in an um d at e, dr an rt e gr erhe brak if the clude di the brak drum ov to lock to make band brakes in these brakes om band and 1 the stan of fr became 1950s, es ak ated with the tendency es also suffer br the late d -drum ak bands an rnal band br shoe-and ing brakes until ng di te an In rnal-exp e used as park much. e s. force. ved, inte wer s were th braking um brakes evol band brakes by the late 1920 ng shoe ge er ting As dr -expandi vers and linka g -contrac brakes were ov 1/31/18 10:3 al rn internal 9 AM te es with hanically by le A were amon dard. Ex days as service ak br el um ec err erg Mod on low 920s, dr ated m but thei e mid-1 es were oper 1921 Duesenb ted to appear th. Ford th By e es star Plymou Brakes. rly drum brak rs such as th ic brak me the Drum ca ar. Hydraul x, which beca rule. Ea luxury odel ye brakes . t Si general 3). Expensive 1938 m 1lic drum Chr ysler’s Ligh through the e  au ur dr ig hy es (F with brak have l 0s ca to 92 ni st -1 mid mecha the fir rs in the er, used d use of priced ca pany, howev increase The four Com for the ) Motor reasons ones: (1 e time o major cally-applied rce at the sam e the tw e er ni ha mak g fo re w the mec ount of brakin djustment to Te The as the -a R’S NO d brakes over w re am O al e nt m tic Th ac aU e sa plie consta e ever pr apply th almost lically ap . akes wer hydrau ver seemed to ges required nical br at high speeds ka ne ha lin ec e m ak brakes ed br ly reason (2) the be travel ble because k at all. The on and couldn't the flexi r h or er than te brake w ads were roug e strong rred with grea ro at th be mad ct cu fa es could oblems that oc er. With hydrau ak br pr fast drum cars d ge t ith ka an os l w ea m fu r fo s used ated br power em s e in oe st rd or sh sy im e da m el g t in d brak ns. This fety Stan rd brak obiles go The rigi ake desig ired as autom ned the standa otor Vehicle Sa made front at earlier br requ es remai g of Federal M mance tests th irst century, ak bands of rces that were br ty-f fo perfor el drum ith the comin braking the twen . ur-whe specific to pass 1960s. W nning of and light trucks ation, fo lic actu iddle and late e systems had en at the begi rs akes of m ak many ca s. Ev of 70 s rcraft br el 19 ai into the 105 in 1967, br e he d from plying pressure le in th on the rear w ) pe ru SS l lo V ra ve M (F e de e gene used by ap er k th el hub ill w st or es he es e w w ak brak the akes disc br brakes ar ive disc brakes, disc br r attached to , drum to automot t” however Modern iginally as “spo a spinning ro braking s. A : ke es ra Disc Brak t forces two Disc B ar II. Known or posite sides of W system tha on opposite ds on op World ds brake pa spinning rotor brake pa to two es of a

a brake brake is A drum friction is in which by brake generated bing against 64533_ch01_h oes rub sh 1-019.indsu r_00 ce of a d rfa 1 the inside attached to um brake dr l. the whee

sid vehicle to stop the

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eNTalS

Upon comple tion

These objectives outline the chapter’s contents and identify what students should know and be able to do upon completion of the chapter. Each topic is divided into small units to promote easier understanding and learning.

Margin Notes

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Related Systems:

ons

ings, and Suspensi

Tires, Wheels, Bear

45

in proper lems if they are not create braking prob e systems and the e components can ionships between brak springs. Any of thes relat key the ines chapter outl working order. This ings, and suspensions. els, tires, wheel bear related systems of whe

talS tIre Fundamen

perof weight, size, and many vehicle factors tires neered in relation to tread design of the truction, size, and Brake systems are engi the tires and the factors are the cons een e thes betw ng lable Amo . avai formance be ld expected to be ion shou els frict or whe ion tract at all four and the amount of performance, tires most reliable brake road. For the best and and tread pattern. size, , tion truc identical in cons

Shop Manual page 98

on mendations information placard since 1968 have a tire The tire informaand light trucks built ment (Figure 3-1). Most passenger cars e the glove compart recommended insid any or r, and pilla size tire door a door, on a inal equipment and manufacturer’s orig inflation pressures, Gross vehicle weight tion placard lists the d cold front and rear are engilists the recommende WR). Brake systems rating (GVWR) is the optional sizes. It also e ard. cle weight rating (GV plac vehi s the on gros d total weight of a vehicl rear liste s and pressure sizes maximum front and e tire som the of plus its maximum rated with rear t efficiently the front and at tires and els payload, including pasneered to work mos ance sports rent sized whe diffe form ll -per fuel insta s full high and of aker rs ge senge A few carm a small percenta inally tice is reserved for tank. on the road are orig vehicles, but this prac percent of the vehicles turers may 911. More than 99 Although manufac cars like the Porsche inal e size at each corner. orig t sam fron the of the tires than r rear that are large fitted with wheels and the at ing brak sizes to tire tion can lead two optional aker’s recommenda recommend one or variation from the carm systems. equipment size, a large uce with other vehicle front to rear may prod from ter 2lems, as well as problems eters approb diam Ch e tire t in e than thos 22 eme differenc the concep s much largerysi GY andals eR cs,sign eN For example, an extr sTeM phnsor d sensors of ABSs. Tireor “laspee ” of spee s in el ws whe d-se sY the e from es cle als rk anrd come l aK te vehi d sign ncipl wolarge cura pri do inac uce to few unequal speeBR y a prod ica ilit to may are ab er ctr ing ele cles mak y is sthe if all four tires the vehi erg exist work accord lem energy, and prob ce. En sam recommendedl by scieen systemrol ule.phThis mod ysical brake energy, heat Al ABS cont rt of or the s. s. chanical basic par’s y, me to the PCM of y is aufac energtion recomml enda ergman otive system To slow and stop a enthe ture ms : chemica us forms in all autom er. for r oth ilia or smaller than an y through many fam energy to most obvio to heat energ er, they of physical among the s one form y of motion energy are anoth tem convert kinetic energ e form of energy to the ge an A brake sys kes ch change on icle, the bra y. g veh ytion. When the brakes or resis energ vinoF hIStor by drivers to using tance BIt amo lot of using is the easaing was ion of fric of rel 70s, plicat ultthere Kinetic energy ical have enough uced in theres the apwere introd firstrk. han driving” to “they don’t Work is the when energy of mec . When radial tiresdo funny wo le “feels ing from aren. Complaints ranged from a brand-new vehic energy. work or motion the new desig to remove radial tires resisstroy deard die-h rs even went so far as ate or crethis tire overc e toame radia of the air in them.” Some drive r cylinder is also ste thil s timfile cteristics ssi have at ma chara r e today ble of majo Th o Two tires er. po r-proto anoth is im nverted int and to install bias tires. 's and fuel mileamge.onLowe ased e formrinfla increIt ” brake pedal is co mechaniOR ride NOTe ted. fro ther ed unde aUTh g the ert earin of nv “app y to tance: a much smoo co tires erg about the mechanical en ents be , it can erted back comm nv ver the co of we er most Ho lat the eliminated s happens: er bore. It is one place thi y in the master cylind erg hydraulic en the wheels. cal energy at

carmakers’ recom

starts, d automobile , and spee ergy n. When an s, Weight of kinetic en rk or motio ergy, Mas chanical wo e at The amount

Kinetic en

Cross-References to the Shop Manual References to the appropriate page in the Shop Manual appear whenever necessary. Although the chapters of the two manuals are synchronized, material covered in other chapters of the Shop Manual may be fundamental to the topic discussed in the Classroom Manual.

Author’s Notes This feature includes simple explanations, stories, or examples of complex topics. These are included to help students understand difficult concepts.

the rat y of me y is at work. speed, and y is the energ kinetic energ ss (weight), Kinetic energ , and stops, vehicle’s ma decelerates mined by a ter objects on de accelerates, is ibe nt y mome ly to descr aand lists at work at an changinisg.located on the driver door interchangeab same. Mass is a me the can be used ed is This placard spe3-1 eight” Figure “winflati asurement on pressure. are not technically which d me an a cold ” is and ass size ht tire ed “m recom terms to a two terms ject. Weig e ob The mend the sho t an ke bu , up m a steel bra of the Earth s that make the surface of molecule l objects have mass, fro ing too deeply into the measure of the number Related Sys out go ss. Al t and Mass is the tems: Tires, surement of springs.lec ressor. With an object y on that ma s in an objec re Wheels, Be y of the inertia of mo Anule an air comp ect of gravit of these commo in its eff er arings, and or air mb the tter the nu of ma ponents can1/31/18 9:44 AM to the working Suspensions ject and the or form of t ober. create brakin draulic fluid the greater Thigh ss of thaord is cha t. pter outlines g problems if quart of hy the marel be said that r resistance to also is we can ate ate it t’s gre d cs, jec sys the they are not it the key relationsh the s are, of is that ob tems ofthi ce of physi wh t ule acceleration; en ing in eel jec lec of sci nk proper s, ob ips mo tire sity an bet den s, ween brake sys lar 45 mass of rstood by mplex the 67.indd molecu .wheel bearings, and de co the ther_044-0 rth un re on Ea y tem be 64533_ch03_h mo vit the s and the the suspensions. gra d weight can the launch pad, on an object. The effect of een mass an 2-2). Its on dense it is. ss (Figure ference betw out 1,000,000 pounds tIre ightle nd amentalS The basic dif y, it is weFu ighs ab Earth’s gravit , which we the a ttle s de ha tsi shu ed ou ce Brake system it, spa but spe arey,eng ttle is in orb etic enserg ine bedcal forte kin incu itu When the shu same, however. relation to ma nce. Am obgject canere speed const ma ny vehicle fac the these y movingon weight and and of an mass stays tors of weigh the amount of tra factors are the construct d effects of etic energy ine t, size, and per kin mb e co ion, size, and Th ctio e t. n or friction Th road. For the n weigh tread design expected to be bes simple: r effect tha Shop Manual of the tires available bet identical in con t and most reliable brake much greate formula, which is quite ween the tire performance s page 98 struction, siz thi th s and the wi , ed tire e, lat and tread pat s at all four wh ter eel n. s should be carmakers’ 2 recommen mv 5 Ek dations Most passen ger cars and 29.9 light trucks bu a door, on a do ilt since 1968 or pillar, or ins have a tire inf tio ide n ere the glove com placard lists wh ormation pla partment (Fi card on optional sizes. the manufacturer’s origin gure 3-1). Th unds po in al equipment It ht) e tire inform also lists the eig tire size and ma rec ur xim m 5 mass (w om ho r um me nded cold fro front and rea any recomme amiles pe in ) eed r nt gro nded (sp and neered to wo ss vehicle we rear inflation v 5 velocity s rk most pressures, and 2,000 ight rating (GVWR). ciently wit foot-pound ighhs the A few carma pheffi Brake system c energy in ). One we tire sizes and ker (m s ins s Ek 5 kineti ur are ho tall eng pre r dif pe veh ssu ifer res icle ent sized wh listed on the Gross vehicle 30 miles s, but this practic eels and weight placard. traveling at car e is reserved rating (GVWR) like).the Porsch res 2-3 for a small per tires at the front and rea o cars, both pounds (Figu is the e 911. More r of some total weight of centage of hig Consider tw 00 4,0 fitt s ed tha igh a wit n we 99 percent of h-performanc h wheels and other plus its maximu vehicle the tire e spo veh s of m rated rts pounds; the recommend icles on the roa payload, inclu one or two opt the same size at each cor d are ding originally ner. Although ional tire sizes equipment siz sengers and full pasmanufacturers at the rear tha e, a large variati fuel tank. 1/31/18 t9:42 may areAMlarger tha problems, as on from the car n the front ori well as proble ginal ms with other maker’s recommendation For example, can veh lead to brakin icle systems. unequal speed an extreme difference in g tire diameter sig s from front recommended nals from the wheel speed to rea sensors of AB by the vehicle d 22 Ss. Tires much r may produce to the PCM or ma r_020-043.ind larger than tho the ABS contro ker may produce inaccu 64533_ch02_h rate vehicle spe se or smaller tha l module. Th is same proble ed-sensor sig n the manufac nals m exists if all turer’s recom four tires are mendations. larger

45

A Bit of History

a BIt oF

This feature gives the student a sense of the evolution of the automobile. This feature not only contains nice-to-know information, but also should spark some interest in the subject matter.

hIStory When radial tire s the new design. were first introduced in the 70s, there was Com a lot of resista air in them.” Som plaints ranged from “fee nce by drivers ls funny when e drivers even to driving” to “the and to install went so far as y don’t have eno using bias tires. Two ugh major characteri to remove radial tires from tance: a much a brand-new veh stics of the rad smoother ride icle ial tire overcame and eliminated mo st of the comme increased fuel mileage. Low this die-hard resi er-profile tires nts about the stires “appearing of underinflated.” today have also

Figure 3-1 This recommended placard is located on the driv tire size and cold er doo inflation pressure r and lists .

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92

Chapter 4

In most instances, only one dual-piston cylinder is used with some type of split system. However, some race crews opt for two identical single-piston master cylinders. The two master cylinders act like a split hydraulic system in that one master cylinder serves the front wheels, whereas the other serves the rear wheels. The master cylinders are applied by one brake pedal acting through a balance bar between the pedal lever and the two push-rods. Some race units are equipped with a brake power booster, and others are not. In this case, it is more an issue of weight than of driver endurance. Of primary importance to race vehicle braking is the type of brake fluid used. On short tracks with a lot of braking, the boiling point of the fluid can be reached quickly and may be sustained for long periods. Brake fluids developed for racing purposes generally have the same chemical properties as conventional fluids, but they have much higher boiling points. Castrol offers a blend of polyglycol ester of dimethyl silane, ethylene polyglycols, and oxidation inhibitors. This blend has a dry boiling point of 4508F(2328C) and helps prevent fluid contamination during operation. Another brand, GS610, offers a fluid with a dry boiling point of 6108F(3218C). There are several manufacturers and suppliers of racing brake components. Brembo is one of the larger manufacturers of racing components, and some of its products are now being installed on some production performance vehicles.

Summary Each chapter concludes with summary statements that contain the important topics of the chapter. These are designed to help the reader review the contents.

Review Questions Short-answer essay, fill in the blank, and multiple-choice questions follow each chapter. These questions are designed to accurately assess the student’s competence in the stated objectives at the beginning of the chapter.

sUMMARY Brake fluid specifications are defined by SAE hydraulic systems. Each of the two pistons in the Standard J1703 and FMVSS 116. master cylinder has a cup, a return spring, and a Fluids are assigned DOT numbers: DOT 3, DOT 4, seal. ■ During application, the piston and cup force fluid DOT 5, DOT 3/4, and DOT 5.1. ■ Always use fluid with the DOT number recomahead of the piston to activate the brakes. ■ During release, the return spring returns the mended by the specific carmaker. ■ Never use DOT 5 fluid in an ABS or mix with any piston. ■ Fluid from the reservoir flows from the reservoir other brake fluid. ■ HSMO fluids are very rare and should never be through the replenishing port around the piston used in brake systems designed for DOT fluids. cup. ■ The brake pedal assembly is a lever that increases ■ Excess fluid in front of the piston flows back into 93 pedal force to the master cylinder. the reservoir through theuivent d ports. ake Fl master d Br ■ The brake pedal lever is attached to a pushrod, ■ Quick take-up fast-fill cylinders have a rs anor r Cylinde te as M which transmits force to the master cylinder pistons. step bore, which is a larger diameter bore for the ■ A front-to-rear split hydraulic system has two masrear section of the primary piston. ■ Quick take-up master cylinders have a valve that ter cylinder circuits. One is connected to the front rts: a provides rapid filling spool area brakes and the other to the rear brakes. o mainofpathe low-pressure _. reservoir. r has twpiston ____the ■ A diagonally split hydraulic system is one in which thedeprimary from cylin ______ aster of __ m s __ a N he d T IO 8. left to valves in sT cylinder circuit is connected to the ■ __ Some ABS master cylinders have check one master ___ an E ed U nt __ Q ve __ e covers arto reduce REVIEW front and right rear brakes and the other circuit__is____ as or pistons the heads and pedal caofpsthe _____ piston cylinder and__ ________ ter vibration _ __wear. - rear brakes. cup connected to the right front comleft 9. All mas __ t reand ________ reservoir. no __ is ay id a t ss E ■ The master cylinder master useisa replenishake flu has two main parts: a reser-preven ■ Portless s in the cylinders do notde r DOT 5 br turer. level drop cylinbetween n why the flow voir andan a uf cylinder body. Fluid can the reserac is the fluid ing or vent port. 1. Explai the rear of e one at the ake fluid y atarea by any m t ofa br mblthe in se can be separate piece or cast as one voir and ahead of the master cylinder th as po d mended■ The reservoir an on ng , st ston _ piston. e boili he pi pi T th __ _ . __ __ hy 10 __ __ w n __ machined into the with the cylinder. pistons of__a__ valve ____ by means __ DOT 5 2. Explai piece the ______ to mix has der is thepistons when the master cylinder t. master cylinder two separate pismaster e cylincylinder od idea import■anA dual-piston front of th is not a gopressure hy itproviding 4. for two independent is at rest. T n wtons n O ai io D pl at d Ex in 3. ntam DOT 3 an e fluid co fluids with gn of brak e a sure si an ge s Choice 4. Describ eral oil. -play is lin de r ch ee fr Multiple m as te r cy e pe da l to l linkage with min th says th e ake peda A on br e an hy rc ci w fo n th is ni ca l 1. Te ch ni 5. Explai . ’s m echa an B says y. lic system th e dr iv er es su re . Te ch ni ci ba ck to necessar 64533_ch04_hr_068-094.indd 92 drau r. hy an ge d au lic pr n the split site master cylinde d how it is ch dr W ho is is hy . re es 6. Explai an pres su el br ak e a compo cup seal hy dr au lic l fo rce at th e w he 7. Describ a master cylinder ni ca e ha ib ec cr m es 8. D the A and B bottom of C. Both co rrec t? used. B rts in the do er A nor are the po servoir, and what D. Neith . A only 9. What A re r de lin r ra te fo as id m master cy ly p flu t ke-u B. B on at if ng the righ a quick ta they do? ys choosi the simple idea th ntage of cian A sa n the adva on DOT 2. Techni 10. Explai e is based ust be better, and cl hi ve c specifi T4m hicle man cylinder. good, DO ys most ve DOT 3 is . Technician B sa Who is correct? ill 4. 5 better st commend DOT A and B re linder is e Blanks C. Both ufacturers master cy a Fill in th B k take-up sign that creates er A nor ic th qu ly ei or N on . ill de D A. A 1. A fast-f by the dual bore ake _____ br __ of d __ t ly ie in __ tif on po iden B. B or ____ cony boiling g. _______ ys the dr of new, un ________ _____ of the castin cian A sa ng point flu __ 3. Techni e minimum boili polyglycol lyalkylene _ for ys ________ po sa e B th ar s is an nici ey do fluid ______ 4 fluid fluid. Tech ch means that th is and DOT s, called ________ ed 3 at T in O hi m D w ta re ho 2. c, er mixtu groscopi the air. W glycol-eth ids are hy vapor from rb water ids short. not abso OT 4 flu r, D ai d e and B an th A 3 OT from C. Both correct? e both D _______ nor B 3. Becaus _______ ________ ly capped. Neither A on . ly A __ D ht . __ A tig __ __ ners ep contai ly tly under e re boiling on gh tu B sli ra always ke _ B. pe __ ak __ -tem ________ slightly spongy br ake fluid ys a high e fluid __ a cian A sa ent that br id also 4. Silicon which can cause 4. Techni e only requirem e flu says brak and must t is th B in pressure, an po ci _ . t. Techni oration ________ pedal feel must mee freezing and evap w temperatures. ry ______ st s have a ve s at lo must resi ycol fluid osity test sc vi c ifi 5. Polygl pass spec ect? _______ A and B shelf life. rr ________ C. Both Who is co _____ -to- oldest split B ________ e er A nor th ly ei N on . 6. The __ split system is th D A. A hydraulic ly _ on B. B ________ system. a ______ cars have te-model 7. Most la aulic system. split hydr ■

■

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SUPPLEMENTS Instructor Resources The Today’s Technician series offers a robust set of instructor resources, available online at Cengage’s Instructor Resource Center and on DVD. The following tools have been provided to meet any instructor’s classroom preparation needs: ■■ An Instructor’s Guide provides lecture outlines, teaching tips, and complete answers to end-of-chapter questions. ■■ Power Point presentations include images, videos, and animations that coincide with each chapter’s content coverage. ■■ Cengage Learning Testing Powered by Cognero® delivers hundreds of test questions in a flexible, online system. You can choose to author, edit, and manage test bank content from multiple Cengage Learning solutions and deliver tests from your LMS, or you can simply download editable Word documents from the DVD or Instructor Resource Center. ■■ An Image Gallery includes photos and illustrations from the text. ■■ The Job Sheets from the Shop Manual are provided in Word format. ■■ End-of-Chapter Review Questions are also provided in Word format, with a separate set of text rejoinders available for instructors’ reference. ■■ To complete this powerful suite of planning tools, a pair of correlation guides map this edition’s content to the NATEF tasks and to the previous edition.

MindTap for Today’s Technician: Automotive Brake Systems, 7e MindTap is a personalized teaching experience with relevant assignments that guide students to analyze, apply, and improve thinking, allowing you to measure skills and outcomes with ease. ■■ Personalized Teaching: Becomes yours with a Learning Path that is built with key student objectives. Control what students see and when they see it. Use it as-is or match to your syllabus exactly—hide, rearrange, add, and create your own content. ■■ Guide Students: A unique learning path of relevant readings, multimedia, and activities that move students up the learning taxonomy from basic knowledge and comprehension to analysis and application. ■■ Promote Better Outcomes: Empower instructors and motivate students with analytics and reports that provide a snapshot of class progress, time in course, engagement and completion rates.

REVIEWERS The author and publisher would like to extend special thanks to the following instructors for reviewing the draft manuscript: Rodney Batch University of Northwestern Ohio Lima, OH

Larry Stanley Arizona Western College Yuma, AZ

Christopher J. Marker University of Northwestern Ohio Lima, OH

Claude F. Townsend Oakland Community College Bloomfield Hills, MI

Tim Pifer Midlands Technical College Columbia, SC

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Chapter 1

Brake Safety

Upon completion and review of this chapter, you should be able to: ■■

■■

Explain the need and methods for maintaining a safe working area. List and discuss some safety issues dealing with vehicle operation in the shop.

■■ ■■ ■■

■■

Explain some of the commonsense rules for working with power equipment.

■■

■■

Wear proper clothing and equipment in a shop.

■■

■■

Explain the first aid step to remove chemicals from the eyes.

■■

■■

Explain the purpose for government regulations of brake performance and standards.

■■

List the safety requirements for working with brake fluid. Describe the hazards of asbestos materials. Explain the safety concerns with solvents and other chemicals. Explain the general functions of the safety and environmental agencies of the United States and Canada. Discuss the principles of hazardous communications. Discuss some of the safety concerns associated with antilock brake and air bag systems. Discuss technician training and certification.

Basic Tools Safety glasses or goggles Respirator Vacuum with HEPA filter Wet-clean system Carbon monoxide vent system Fire extinguisher(s)

Terms To Know Asbestos Asbestosis Canadian Center for Occupational Health and Safety (CCOHS) Carbon monoxide Chlorinated hydrocarbon solvents Department of Transportation (DOT)

Environmental Canada Environmental Protection Agency (EPA) Extraction Procedures (EP) Federal Motor Vehicle Safety Standards (FMVSS) Material safety data sheet (MSDS) Occupational Safety and Health

Administration (OSHA) Phosgene Supplemental inflatable restraint system (SIRS) Tetrachloroethylene 1,1,1-Trichloroethane Trichloroethylene Workplace Hazardous Materials Information Sheet

INTRODUCTION Personal protection from injury involves not only what the technician is wearing, but also making and keeping the work area safe. The twofold advantage here is if one technician is protecting himself by wearing personal protection equipment and keeping the shop clean and safe, then all the other employees or visitors stand a good chance of avoiding accidents or injury. This chapter discusses those practices and equipment that will provide overall and personal safety. 1

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Housekeeping

Some oil dry or absorbent ­compounds have to be treated as hazardous waste after being used. They should not be thrown in the trash bin.

Good housekeeping is a safety issue. A cluttered shop is a dangerous shop. Each employee is responsible for keeping the work area and the rest of the shop clean and safe. All surfaces must be kept clean, dry, and orderly. Any oil, coolant, or grease on the floor can cause slips that could result in injury. Use commercial oil absorbent to clean up oil or brake fluid spills (Figure 1-1). Oily rags must be stored in a sealed metal container until disposed of properly. Keep all water off the floor; remember that water is a conductor of electricity. A serious shock hazard will result if a live wire falls into a puddle in which a person is standing. When a vehicle is raised with a hand-operated jack, always set the car down on safety stands and remove the jack (Figure 1-2). Do not leave the jack handle sticking out from under the car where someone can trip over it.

Figure 1-1  Use a commercial absorbent to soak up a spill.

Figure 1-2  Support a vehicle on safety stands such as these and move the jack out of the way.

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3

Creepers also must be used and stored safely. When not in use, stand the creeper on end against a wall. Pushing it completely under the vehicle gets it out of the way, but it is easy to forget that it is there and drive over it after the job is completed. Air hoses and power extension cords should be neatly coiled and hung. Do not leave a tangled mess in walkways or on the shop floor. Check air hoses and power cords for signs of damage. A leaking or bulging air hose should be immediately disconnected and replaced. Power cords should be inspected before each use and replaced if frayed or damaged. Keep all exits open. A blocked exit violates fire codes and leaves the shop liable to legal action if people become trapped in a fire or dangerous situation. Memorize the route to the nearest exit in case of a fire or hazardous material spill.

Vehicle Operation WARNING:  Use extra caution when moving a vehicle that requires brake repairs. The brakes may be poor or completely inoperative. Damage to the vehicle or shop or injury to yourself or others could result.

Test the brakes on the car to make sure they work before you start the engine. Push the car into the shop if it has a complete brake failure. After completing a brake repair and before moving the vehicle, always check the service brakes. There have been several small but embarrassing and expensive incidents where brakes were replaced but not seated. The first time the brakes were applied, there were no brakes. When new brake pads are installed in a disc brake system, always apply the brakes several times to move the brake pads out against the rotor before putting the vehicle into gear. It will take a few seconds to get pedal back to normal after replacing the pads. Be very careful when driving a car in the shop. Be watchful of other workers or customers. Drive slowly and carefully, and get someone to act as a guide if visibility is blocked. Leave a window cranked down so instructions from someone outside the car can be heard. Once the car is in the service area, place the automatic transmission shift lever in PARK. If the car has a manual transmission, put it in reverse gear with the engine off. Engage the parking brake by pulling the lever or setting the parking brake pedal. The engine must often be operated in the shop to check for problems and to check your repairs. Several safety precautions should be followed when working on a running engine: ■■ ■■

■■ ■■ ■■

It is a good idea to never reach inside the vehicle to start a vehicle in the shop. There have been several instances in which technicians have started a car that immediately “took off” and crashed through a garage door, walls, and even people! Do not be that technician! Always get inside the vehicle to start the engine.

Use wheel blocks to block the front and back of one of the wheels (Figure 1-3). Never get under a car when someone else is working on it or when the engine is running. Do not stand in front of or behind an automobile when the engine is running. Be careful of hot manifolds and moving engine parts if working under the hood. Many cars use electric cooling fans. Keep hands, tools, and test equipment clear of electric fans because they can start up at any time, even when the engine is not running.

Carbon Monoxide Running an engine inside a shop can be very hazardous. Engine exhaust contains large amounts of carbon monoxide, a deadly gas that is odorless and colorless. Carbon monoxide poisoning begins with headaches and drowsiness. High exposure can lead to coma and death. Never run an engine in the shop without properly venting the exhaust fumes to the outside or to a dedicated ventilation system for exhaust gas (Figure 1-4), and make sure the ventilation system is working properly.

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Chapter 1

Wheel blocks

Figure 1-3  Block at least one wheel both in front and behind before raising the other end of the vehicle.

Figure 1-4  When running an engine in a shop, always connect the exhaust to the ventilation system.

The most easily prevented injury is an eye injury—always wear safety glasses in the shop.

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Housekeeping and Brake Dust There are special tools and equipment designed to be used to collect and contain brake dust. This special equipment is discussed in detail in Chapter 2 of this manual, but some common sense should always be used when working on and around vehicles undergoing brake service. The first and probably most critical is to never use compressed air to blow dust from the braking components. This, obviously, moves and suspends the dust in the air. Use only the equipment or their equivalents listed in Chapter 3 to clean the brake components and surrounding area. A second commonsense rule is the wearing of safety glasses and gloves. As discussed earlier in this chapter, brake fluid and cleaning solvents are hazardous materials and can cause injuries. If a vacuum cleaner is not available to clean the floor around the work area, mop the floor with water. When the mop is rinsed, the rinse water and the material it collects must be stored and treated as hazardous waste. This may seem to present some work problems, but like many things in the automotive repair business it must be done to protect the employees, the environment, and the community in general. Smokers or persons with some type of respiratory problems must be considered when dealing with brake

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Brake Safety

dust. Even with so-called clean air, those individuals may suffer an extreme reaction to what we technicians consider everyday conditions. A technician should make every attempt to prevent the spread of brake dust while working on a vehicle.

Eye and Face Protection The most frequent causes of eye injuries are flying objects, corrosive chemical splash, dangerous light rays, and poisonous gas or fumes. WARNING:  Grinding and cutting tools can be dangerous, even to a person not in the immediate area of the work. Ensure that the area is cleared of personnel as much as possible before metal-shaping work.

The best way to prevent eye injuries is to wear the correct type of eye protection. When you are performing jobs such as grinding metal, cutting metal, or driving a punch or chisel, the eyes are at risk from flying objects. Occupational safety glasses (Figure 1-5) are the best protection against flying objects. These safety glasses are especially designed to provide the most protection. The glass or plastic lens provides maximum protection against an impact to the eye. The frames are constructed to prevent the lens from being pushed out of the frame during impact. They must have side shields to prevent objects from entering the eye from the side. They are available in prescriptions for people who need corrective lenses.

CAUTION Do not use compressed air to clean brake components. Brake dust will be present and can be blown into the eyes, embedded into the skin, and, at least, will contaminate the surrounding air. Use only authorized lowpressure washers or vacuum-cleaner-type equipment.

WARNING: Wear occupational safety glasses when working in the shop, e­ specially when performing any grinding or cutting operations. Ordinary ­prescription dress glasses are made to standards that provide impact protection, but the impact ­ ccupational protection and the frame strength of dress glasses are much lower than o safety glasses.

The face shield (Figure 1-6) provides protection for the entire face and is a good choice when the danger is from flying objects or splashing liquids. Goggles can be used for nearly every type of eye hazard, and they can be used over ordinary dress glasses. Goggles have another advantage over occupational safety glasses because they fit against the head, which allows them to distribute an impact better. Clear-cover goggles provide protection against flying objects or liquid splash. Some goggles have vents and baffles on top to prevent harmful vapors or fumes from getting into the eyes. When you wear goggles, do not over tighten the straps. They need only be taut enough to hold the goggles in

Figure 1-5  Occupational safety glasses provide protection from flying objects that ordinary eyeglasses do not.

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Figure 1-6  A face shield protects your entire face.

place. As with all other clothing, they have to be worn for a while for you to adapt to their weight and viewing area. When taking off goggles or a face shield, close the eyes. Small particles of sharp metal may have attached themselves to the outside of the goggles or face shield and may drop into the eyes.

Initial First Aid Most shops and all schools require an accident report to be completed and filed.

Make sure the location and contents of the shop’s first aid kit are known. There should be eyewash solution or eyewash stations in the shop so the eyes can be rinsed thoroughly should hydraulic fluid, battery acid, asbestos dust, or other irritants enter them (Figure 1-7). See Photo Sequence 1 for details. After eye washing, seek medical attention. Find out if there is a resident nurse in the shop or at the school, and locate the nurse’s office. If there are specific first aid rules in the school or shop, find out what they are and abide by them. In a school, a report is required to be filed for any injuries to a student.

Figure 1-7  An eyewash solution will flush contaminants from your eyes.

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If someone is overcome by carbon monoxide, move the person to fresh air immediately. Rinse burns immediately in cold water or apply an ice pack. To stop bleeding from a deep cut or puncture wound, apply pressure on or around the wound and get medical help. Never move someone you suspect has broken bones or a back injury unless the person is in danger from another hazard such as fire or carbon monoxide gas. Call for medical assistance.

Hand Protection Hands are one of the most frequently injured parts of the body. This fact is not surprising when you think of how often the hands are used doing automotive repair. There are two parts to protecting the hands. One is to keep hands out of dangerous areas. Rotating parts, such as the belts on the front of an engine, are hand danger areas. Make an effort to keep the hands out of those areas as much as possible.

Photo Sequence 1

Using Eye Wash

P1-1  Remove the eyewash bottle from the wall holder. The injured person may require assistance. P1-3  Tilt the head back and over so the injured eye is lower than the other eye. P1-2  Open the bottle. Attempt not to touch the mouth of the bottle once it is opened. The injured person may require assistance.

P1-4  Pour the water so the flow goes from the nose bridge, over the eye, and down the cheek. Keep both eyes open and looking upward during the flushing. The injured person may require assistance.

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P1-5  The injured eye should be examined by an ophthalmologist for injuries that may not be immediately apparent.

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The second part of hand safety is to wear hand protection when necessary. Special protective gloves are available for many jobs that require hand protection. There are heavy work gloves for metal working, rubber gloves for electrical shock protection, and nitrile gloves for handling used oil, brake fluid, and chemicals such as those used to clean parts. Always use the correct type of gloves for the hand hazards in the work area. Do not wear a wristwatch or jewelry while working. Watches can get caught in rotating machinery. Necklaces or rings can get caught in machinery or provide a path for an electrical shock. Long hair can get caught in rotating machinery. Many serious injuries have been caused by the hair pulling the face into a rotating part. Always tie up long hair or wear a hat over it. Always wear safety shoes in the shop. Safety shoes have metal or fiberglass protection over the toe to prevent an injury if a heavy object falls on your foot. Safety shoes should at least have oil-resistant soles that grip slippery floors better than casual dress shoes.

Lifting and Carrying If you lose control of a lifted object, do not attempt to catch it. Step back and let the object drop.

The back is one of the most often injured parts of the body. The most common kind of back injury at work is caused by improper lifting. Not all back injuries are caused by lifting too much weight but by lifting relatively small, light objects. The problem occurs while lifting the object and twisting the body or lifting when the load is unbalanced. Most back injuries can be prevented by following these 10 simple rules: 1. Do not lift any heavy object by yourself. Get someone to share the load or get some equipment such as a chain hoist to do the lifting. 2. Study the load before you attempt to lift it. Use your head before you use your back. 3. Place your body close to the object as shown in Figure 1-8. Keep your legs close to the load and positioned for good balance. 4. Bend your legs, not your back. 5. Get a strong grip on the object with your hands. 6. Lift with your legs, keeping your back as straight as possible. 7. Keep the load close to your body as you lift it up. 8. Keep a tight grip on the object and do not try to change your grip while lifting.

Straight back Position body over load Keep back as erect as possible

Use leg muscles

Weight close to body

Legs bent

Figure 1-8  Keep your back straight and bend your legs to lift heavy objects safely.

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9. Do not twist your body to change direction. Move your feet in the new direction. 10. When you are ready to set the load down, do not bend forward. Keep the load close to your body and lower it by bending your legs. When placing the object on a shelf, place the edge of the load on the surface of the shelf and slide it forward. When setting an object on the floor, lower it by bending your knees and keeping your back straight. Bending forward strains your back muscles. Having the body out of position can lead to painful injury even if nothing is being lifted. The most common muscle sprain or injury happens when the person is lifting a small weight but the body is twisted off center.

BRAKE SYSTEM SAFETY REGULATIONS In the United States, brake systems are regulated by Part 571 of the Federal Motor Vehicle Safety Standards (FMVSS). These regulations are established and enforced by the U.S. Department of Transportation (DOT). The standards that relate to brake ­systems are: ■■ ■■ ■■ ■■ ■■ ■■ ■■

FMVSS 105 Hydraulic Brake Systems FMVSS 106 Brake Hoses FMVSS 108 Lamps, Reflective Devices, and Associated Equipment FMVSS 116 Motor Vehicle Brake Fluids FMVSS 121 Air Brake Systems FMVSS 122 Motorcycle Brake Systems FMVSS 211 Wheel Nuts, Wheel Discs, and Hub Caps

Many U.S. states and Canadian provinces also have regulations that govern the brakes’ safety, condition, and operation. Several of the federal standards apply to specific components included in this text. General performance requirements for service brakes and parking brake systems are governed by FMVSS 105. This standard became effective in 1967, was revised significantly in 1976, and has undergone several smaller changes since then. FMVSS 105 spells out the “requirements for hydraulic service brake and associated parking brake systems to ensure safe braking performance under normal and emergency conditions for passenger cars, multipurpose passenger vehicles, trucks, and buses with hydraulic service brakes.” FMVSS 105 does not prescribe the design of brake systems; it establishes brake performance requirements. By so doing, however, it also establishes the baseline for system safety. The standard regulates four major features of brake systems: instrument panel warning lamps, the fluid reservoir and its labeling, automatic adjustment, and mechanically operated friction parking brakes. Although FMVSS does not dictate brake system hardware and design, one of its first major effects that car owners saw was the introduction of dual-chamber master cylinders and split hydraulic systems on 1967 model-year cars. Also, the increased performance requirements in the 1976 revision made it impractical to use drum brakes on the front wheels of cars. The standard did not specify front disc brakes, but discs were the most practical way to meet the performance requirements. Brake systems are not designed just to meet minimum legal standards, however. They are designed in relation to the performance and intended use of a vehicle. Trucks have larger brakes than passenger cars, for example, to stop a vehicle with a heavier payload. A high-performance car will have high-performance brakes, but an economy compact car will not. Every vehicle has a brake system that meets motor vehicle safety requirements and matches the performance capabilities and intended use of that vehicle. Thus, brake systems reflect both safety regulations and sound engineering practices.

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Department of Transportation (DOT) is the U.S. government executive department that establishes and enforces safety regulations for motor vehicles and for federal highway safety and oversees, inspects, and regulates all interstate transportation including road, rail, and water facilities; commercial operators training/ certification; and commercial vehicles. They are assisted by state-funded transportation departments.

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57 feet at 30 mph 216 feet at 60 mph

Figure 1-9  One of the 18 stages of the brake performance test in FMVSS 105 requires 1 stop from 30 mph in 57 feet or less and 1 stop from 60 mph in 216 feet or less.

Brake Performance Test The brake performance test of FMVSS 105 defines the minimum requirements for the hydraulic brake system on any vehicle driven on the highway. The technician should know a bit about the performance test, not for the sake of being able to quote government regulations, but because parts of the test define the kind of performance a brake system should deliver after the vehicle is serviced. The brake performance test is divided into eighteen stages and begins with a new set of brakes on a test vehicle. The first stage of testing is discussed as an example of the other 17. The first stage is to install the test instruments on the vehicle and verify that they operate correctly. The vehicle then goes through what is called the “first effectiveness test.” This test is performed with fresh brake linings before they have had a chance to burnish in. The vehicle makes 6 stops from 30 mph and 6 stops from 60 mph. At least one of the stops from 30 mph must be made in 57 feet or less, and one stop from 60 mph must be in 216 feet or less (Figure 1-9). These stopping distances and stopping distances in other stages of the test are absolute requirements for any vehicle of any size and weight. Remember that FMVSS 105 defines minimum brake performance. It is up to the engineers to design the vehicle and the brake system to meet the performance standards. While the governments set the minimal rules and regulations for design and manufacturing, the technician should understand the ramifications if a brake system is not returned to its designed capability. Failure to follow correct repair procedures could cause a vehicle accident, resulting in damage, injuries, and lawsuits. It takes less time to do it right rather than to take a shortcut that saves time and labor in the short term but may result in much greater loss of time and money later.

Brake Service Laws and Regulations After new vehicles are first sold, the responsibility for maintaining safe brake operation falls on the vehicle owners. The owners, in turn, rely on service technicians to keep the brakes in proper operating condition. Many states and provinces have laws that govern brake system operation and brake service. Some states require periodic vehicle safety inspection, either every year or every 2 years. These safety inspections usually include at least an inspection of brake components. Some also include dynamic stopping tests, done on a brake system analyzer or on a measured course. If a vehicle fails any part of the safety inspection, its registration cannot be renewed until all defects are fixed. Some states require that a vehicle that has failed a brake test or inspection or that has been cited for unsafe brakes by a police officer can only be repaired at a state-authorized repair facility. In addition, some states, provinces, counties, or cities have regulations for the licensing or certification of brake service technicians. Some areas conduct their own certification programs; others rely on Automotive Service Excellence (ASE) certification in brake

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service. ASE is a nonprofit organization that technically certifies automotive technicians with a series of standardized written tests. Automotive business leaders, technicians, and educators select and write the test questions. Working in an area that has brake service regulations, the technician will find that safety is not only good common sense, it is good business. Service technicians who pass all certification requirements for brake systems will get more of the service business, have more secure employment, and earn higher wages. In addition, any technician who provides high-quality brake service can take satisfaction in knowing that he or she is contributing to driving safety.

BRAKE WARNINGS AND CAUTIONS At the beginning of many manufacturers’ service manuals and at appropriate points throughout the manuals are various cautions and warnings to alert the technician to some dangers inherent in brake repair. Some of the most common manufacturers’ warnings and cautions are paraphrased and listed in Table 1-1. Within this text and the Classroom Manual, there are also warnings and cautions pertaining to servicing brake systems. To prevent damage both to the vehicle and vehicle equipment and possible injury, it is imperative that the technician adhere to the information contained in the alert messages. As you read and study further chapters, you will become more conversant with the warnings and cautions and why they are necessary.

ASBESTOS HEALTH ISSUES One of the greatest safety concerns in any shop doing brake service is personnel exposure to asbestos dust. Exposure to asbestos was a greater problem in automotive service many years ago than it is today. Avoiding asbestos exposure and asbestos safety are still equally important today. However, it is important to note that imported brake shoes do not have the same restrictions as those made in the United States. Asbestos is a silicate compound that is very resistant to heat and corrosion. Its excellent heat dissipation abilities and coefficient of friction make it ideal for automotive friction materials such as clutch and brake linings. Unfortunately, asbestos has other characteristics that make it an extreme health hazard.

It is hard to imagine, but even though asbestos has been removed from most brake linings, there are no regulations that require that imported brake parts be free of asbestos. Also, even if there is no asbestos, some of the compounds that replaced it are also hazardous to your health. Treat all brake lining dust as hazardous.

TABLE 1-1  A SAMPLE OF BRAKE WARNINGS AND CAUTIONS. OTHER COMPONENTS AND SUBSYSTEMS OF THE BRAKE SYSTEM WILL ALSO HAVE SPECIFIC ALERT MESSAGES SIMILAR TO THOSE LISTED HERE.

Pertaining to brake fluids:

 CAUTION: Brake fluid is corrosive to body finish. Do not allow fluid to spill onto the paint or components. The fluid will damage the finish and possibly damage some components.

 

 WARNING:  Brake fluid can damage the eyes and skin. Wear safety glasses and chemical-resistant gloves

 

 WARNING:  Never mix different types of brake fluids unless specifically authorized by the vehicle manufac-

when handling brake fluid. Damage to the eyes or skin can be caused by direct contact with brake fluids.

turer. Mixing different types of brake fluid may result in a loss of braking ability and cause damage or injury.

Pertaining to disc brake calipers:

 

WARNING:  Do not hang the caliper from its brake hose. Damage to the hose could occur that may result in

 

WARNING:  Do not use a sharp object to remove the caliper seal. Scratches or nicks could prevent proper

poor braking ability. Damage or injuries could result.

sealing around the piston. Damage to the caliper bore or the piston could result.

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Asbestos contains millions of small, linked fibers that give it both strength and flexibility. Because asbestos does not deteriorate or decompose naturally, inhaling asbestos fibers lodges them in the respiratory passages and the lungs. Once inhaled, these fibers are in place forever. Even moderate quantities of inhaled asbestos fibers can lead to serious diseases. The most serious are asbestosis and lung cancer. Asbestosis is a progressive lung disease caused by asbestos fibers continually lodging in the lungs and inflaming the lung air sacs. The inflammation of asbestosis can heal, but it leaves scar tissue in the lungs that thickens the air sacs and makes it increasingly more difficult for oxygen to enter the bloodstream. Over a period of years, breathing becomes increasingly more difficult. Once started, asbestosis is irreversible. Lung cancer is the most deadly of any asbestos-related disease. Asbestos exposure combined with other respiratory irritations, such as tobacco smoke, can accelerate the development of cancer and produce more severe effects. It is possible for a person to develop both asbestosis and lung cancer from severe asbestos exposure. Heavy exposure to asbestos also can lead to other cancers of the respiratory and digestive systems.

A BIT OF HISTORY The Occupational Safety and Health Act (OSHA), which regulates workers safety, was passed into federal law in 1970.

Occupational Safety and Health Administration (OSHA) is a division of the U.S. Department of Labor that establishes and enforces workplace safety regulations.

Environmental Protection Agency (EPA) is the U.S. government executive department that establishes and enforces regulations to protect and preserve the physical environment through the control of hazardous materials and waste, including landfills. It is best known for regulations relating to air quality. Many times OSHA and EPA authority overlap in large incidents.

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Asbestos Control Laws and Regulations Regulations of the U.S. Occupational Safety and Health Administration (OSHA) control asbestos exposure and handling of materials that contain asbestos. OSHA regulations state that fibers of 5 microns or larger are hazardous. These regulations further say that no worker can be exposed to more than 0.1 fiber per cubic centimeter of air during an 8-hour period. That is an extremely small exposure to an extremely small amount of material. However, these low exposure limits can be maintained in a brake service shop through the proper use of brake cleaning equipment and respiratory safety devices. A respirator designed specifically for protection against asbestos inhalation is your best personal protection. The respirator shown in Figure 1-10 is approved by the National Institute for Occupational Safety and Health (NIOSH) and has replaceable filters for maximum protection. A brake dust vacuum cleaning enclosure (Figure 1-11) and a brake washing system will keep asbestos dust within safe limits for the entire shop area. Along with OSHA, the U.S. Environmental Protection Agency (EPA) regulates some aspects of asbestos safety. EPA regulations are concerned primarily with handling and disposal of asbestos waste. These regulations state that any waste material containing more than 1 percent asbestos must be disposed of by rigidly controlled methods that do not endanger public health. Technicians’ concern with asbestos safety does not end with prescribed cleaning of brake systems and respiratory safety. They must dispose of cleaning residue according to EPA regulations. Because brake dust may contain more than 1 percent asbestos, any vacuum cleaner bags, filters, and cloths used to wipe up brake dust must be sealed in double plastic bags or a similar non-permeable container. The bag or container must then be labeled with an asbestos exposure warning, similar to the following: In most areas of the country, it is acceptable to turn over properly contained asbestos residue to local sanitation agencies for burial in a landfill. This eliminates the hazard of airborne fibers. Local asbestos disposal regulations may vary, however, and some may require additional special handling. It is the technician’s responsibility to know the local regulations and to ensure that they are observed in the workplace.

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CAUTION

Breathe air in

Cartridge

Hazardous Materials. This container holds asbestos fibers. Avoid creating dust when moving or opening. Breathing protection should be worn when unsealing/sealing container. Asbestos fibers are hazardous and can cause cancer and lung disease.

Air out

Figure 1-10  This NIOSH-approved filter-type respirator is ideal for brake work.

Glovebag collection system

HEPA vacuum cleaner

Figure 1-11  This full-enclosure asbestos vacuum system traps brake dust and helps keep the shop’s air free of dust.

A BIT OF HISTORY Health concerns were good reasons to remove asbestos from brake linings, but there was an equally good engineering reason. Modern brake friction materials work better than asbestos. Asbestos was still common in some friction materials in the early 1990s, but higher temperatures of smaller disc brakes caused the asbestos pads to wear faster than was acceptable. Moreover, even the best asbestos material will start to glaze at temperatures as low as 2508F (1228C). Modern semi-metallic and organic linings are safer, and they also provide better braking performance than asbestos did.

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AUTHOR’S NOTE  All containers in which you store hazardous material or waste must be labeled as to contents. The text can be handwritten or printed with other methods as long as it cannot be easily wiped off or will not fade during the time the container is used for this purpose.

Additional Respiratory Safety Concern for the health hazards of asbestos exposure has led to a reduction of its use in automotive components. For many years, asbestos has been eliminated from the brake linings of new cars and light trucks sold in North America and from replacement brake linings made in the United States and Canada. These restrictions do not apply, however, to replacement brake linings manufactured outside North America and imported into the United States or Canada. Furthermore, the asbestos content of imported brake linings may not be identified clearly on packaging. As asbestos content was reduced in brake linings, other materials took its place. Today, many brake linings are made primarily of organic or semi-metallic compounds. As with asbestos, however, these materials wear and create airborne dust. Semi-metallic brake linings, for example, may contain copper or iron compounds, and these materials become part of the brake dust. Although exposure to these metals may not be as hazardous as asbestos exposure, it cannot be good for a person to inhale copper or iron dust. For all of these reasons, proper use of brake cleaning equipment and respiratory safety devices is as important today as it has ever been. Do not think for a moment that the reduced use of asbestos in automotive materials has reduced the requirements for safe material handling. All personnel must take the proper steps to protect themselves and create a safe work environment. Most new automotive cleaning solvents no longer contain chlorine. Chlorine is suspected of causing damage to the ozone layer and is banned from common use by the EPA.

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Chemical Safety Asbestos is not the only hazardous material found in auto service facilities. Solvents, cleaners, brake fluids, gasoline, oils, and other chemicals all present hazards if not handled properly. They may be flammable, emit harmful vapors, or be irritating to the eyes or skin.

Brake Cleaning Solvents One reason liquid solvents were developed for brake cleaning was to reduce the hazard of blowing off brake assemblies with compressed air and creating clouds of airborne fibers and dust. Wetting the dirt and dust residue on the brakes with solvent keeps the toxic materials out of the air. Always work with cleaning solvents in a well-ventilated area that is free of sparks or flames. The fumes from aerosol cleaners and open part washers are heavier than air and will settle to the lower part of the work area such as below floor-level dynamometers and alignment pits. Solvent vapors may also be harmful if inhaled, particularly in large quantities for prolonged periods. If necessary, use a respirator to prevent inhaling the vapors. Chlorinated hydrocarbon solvents may be absorbed through the skin with toxic effects. Always wear gloves when using any cleaning solvent. The best first aid for skin and eye contamination is flushing with large amounts of water and contacting medical personnel. Inhalation exposure requires quick removal to clean air and medical attention. Although they are a lesser health hazard than asbestos, various cleaning solvents used on brake systems must be handled with specific precautions. Among the most significant

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15

Figure 1-12  This aerosol brake cleaner contains tetrachloroethylene. You should know and practice the safe use of all solvents in the shop.

from a safety standpoint are those that contain chlorinated hydrocarbon solvents such as 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene (Figure 1-12). These are all colorless solvents with a strong odor of ether or chloroform. The vapors from these solvents can cause drowsiness or loss of consciousness. Very high levels of exposure, even for a short time, may be fatal. Although these hydrocarbon solvents are not flammable, they decompose when exposed to flame and release toxic gases such as phosgene, carbon monoxide, and hydrogen chloride. This family of chlorinated hydrocarbon solvents reacts in the atmosphere and depletes the Earth’s ozone layer. Their manufacture has been restricted since January 1, 1996. Other solvents such as hexane, heptane, and xylene are replacing chlorinated hydrocarbons in brake cleaners (Figure 1-13). Hexane and heptane are flammable, however, so all fire safety precautions must be observed when using these solvents.

Causes and Effects of Chemical Poisoning A person may be exposed to chemical health hazards in three ways: by ingestion, by inhalation, and by contact with the skin. Material safety data sheets (MSDS), discussed in more detail in subsequent paragraphs, describe any poisoning hazards and how to counteract poisonous effects. An MSDS for every solvent used in the shop should be readily available to every worker. Obviously, swallowing any solvent—even soap—can be hazardous, but this does not happen very often. Solvents also can be ingested by a smoker who lights a cigarette while working with the solvent. Solvents must always be handled carefully and kept in properly labeled containers. When not in use, the containers must be stored away from untrained personnel and children. Contact with solvents occurs most often through inhalation or absorption through the skin. Inhalation has the more immediate effect. Absorption can be just as dangerous; however, its effects may not be noticeable for several days after exposure.

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Chlorinated hydrocarbon solvents are a class of chemical compounds that contain various combinations of hydrogen, carbon, and chlorine atoms. 1,1,1Trichloroethane is a chlorinated cleaning solvent often used in aerosol brake cleaners. Trichloroethylene is a chlorinated toxic cleaning solvent often used in aerosol brake cleaner and as an insecticide fumigant. Phosgene is a poisonous gas that is formed when certain other gases are exposed to flame; it is also known as mustard gas, the principal poison gas used in World War I.

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Figure 1-13 Nonchlorinated cleaning solvents also require specific handling and safety precautions.

Current OSHA standards for exposure to airborne trichloroethylene say that more than 100 parts per million (ppm) in the air during 8 hours is dangerous. To give you an idea of how small the allowable exposure is, 100 ppm equal 0.0001 percent. WARNING  Always wear nitrile gloves when working with chemicals. Exposure can lead to skin injuries and, sometimes, ingestion through the skin into the bloodstream. Serious injury could result.

There is no current standard for physical contact with these solvents, but the immediate effect is the removal of natural skin oils, which causes drying of the skin and redness and irritation. Prolonged skin contact with solvent can have the same effects as inhalation. Exposure to chlorinated hydrocarbons and other solvents by any means can cause nausea, drowsiness, headache, dizziness, and eventually unconsciousness. Prolonged exposure can lead to liver and kidney damage.

SAFETY AND ENVIRONMENTAL AGENCIES Environment Protection Agency The EPA is a federal agency charged with instituting and enforcing regulations that assist in protecting the environment. It was formed in the early 1970s to reduce air pollution caused

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by vehicle and manufacturing emissions. Inherent within that charter was the control and disposal of waste products from almost all businesses, including the local automotive repair shop and individuals. The main concern of the EPA is the storage and disposal of hazardous waste from major manufacturers, plants, the local garbage dump, and everything in between. Although its formation met with much resistance, the results some 50 years later are cleaner air and less ground and water pollution. Unless something changes, the agency will be in operation for the foreseeable future. The EPA’s website is http://www.epa.gov.

Occupational Safety and Health Administration (OSHA) OSHA was formed to help protect employees and, ultimately, employers. It has the legal authority to inspect businesses and ensure that working areas are safe for the employees. Some safety concerns of utmost interest are the control of chemicals within the workplace, the equipment/facility in which to store or use those chemicals, the equipment and tools used within the facility, and the general working environment. It should be noted that since the formation of OSHA, accidents resulting from unsafe working environments have been reduced, with an increase in production associated with lowered loss of man-hours and fewer accidents. A suggested website for OSHA is https://www.osha.gov/SLTC/index.html.

Environmental Canada Environmental Canada is the Canadian version of the U.S. EPA. It has requirements that relate to Canada’s more northern environment and citizens. Within its organization are subagencies, such as the Canadian Environmental Assessment Agency, which may not be directly related to sub-agencies of the U.S. EPA. As far as the automotive industry is concerned, however, the legal and environmental control requirements are almost exactly the same. Section 7 of the Canadian Environmental Protection Act specifically covers the Canadian automotive industry. The website best suited for information on this agency is http://www.ec.gc.ca.

Canadian Center for Occupational Health and Safety (CCOHS) The Canadian Center for Occupational Health and Safety (CCOHS) is similar to the U.S. OSHA with a similar mandate, responsibility, and authority. It performs inspections, determines administrative fines, files criminal charges, and directs training programs in much the same manner as the U.S. OSHA does. The website is http://www.ccohs.ca/. It should be noted that each of the four agencies listed operates “over border” because many pollutants tend to cross borders. Automotive manufacturing, vehicle repair, and vehicle operation are shared by the United States and Canada and many associated problems are the result of actions in one country affecting the environment of its neighbor. Each of the listed websites has a large amount of information pertaining to almost any environmental and safety issue.

HAZARDOUS COMMUNICATIONS Each of the agencies noted in the last section enforces what are known as right-to-know laws or hazardous communications. Basically, right-to-know requires the employer to notify employees of dangerous materials that are housed or used on-site. They also require the initial training of new employees; annual (or more often) refresher training of all employers; and employer-designated personnel with specific authority to train, maintain records, and, in some instances, act as first responders to fires or accidents. Of direct interest to all employees are the three main informational documents pertaining to on-site chemicals. Important information about such materials is contained in material safety data sheets (MSDS), which are multiple-page information sheets (Figure 1-14). The MSDS

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HEXANE ======================================================= MSDS Safety Information ======================================================= Ingredients ======================================================= Name: HEXANE (N_HEXANE) % Wt: >97 OSHA PEL: 500 PPM ACGIH TLV: 50 PPM EPA Rpt Qty: 1 LB DOT Rpt Qty: 1 LB ======================================================= Health Hazards Data ======================================================= LD50 LC50 Mixture: LD50:(ORAL,RAT) 28.7 KG/MG Route Of Entry Inds _ Inhalation: YES Skin: YES Ingestion: YES Carcinogenicity Inds _ NTP: NO IARC: NO OSHA: NO Effects of Exposure: ACUTE:INHALATION AND INGESTION ARE HARMFUL AND MAY BE FATAL. INHALATION AND INGESTION MAY CAUSE HEADACHE, NAUSEA, VOMITING, DIZZINESS, IRRITATION OF RESPIRATORY TRACT, GASTROINTESTINAL IRRITATION AND UNCONSCIOUSNESS. CONTACT W/SKIN AND EYES MAY CAUSE IRRITATION. PROLONGED SKIN MAY RESULT IN DERMATITIS (EFTS OF OVEREXP) Signs And Symptions Of Overexposure: HLTH HAZ:CHRONIC:MAY INCLUDE CENTRAL NERVOUS SYSTEM DEPRESSION. Medical Cond Aggravated By Exposure: NONE IDENTIFIED. First Aid: CALL A PHYSICIAN. INGEST:DO NOT INDUCE VOMITING. INHAL:REMOVE TO FRESH AIR. IF NOT BREATHING, GIVE ARTIFICIAL RESPIRATION. IF BREATHING IS DIFFICULT, GIVE OXYGEN. EYES:IMMED FLUSH W/PLENTY OF WATER FOR AT LEAST 15 MINS. SKIN:IMMED FLUSH W/P LENTY OF WATER FOR AT LEAST 15 MINS WHILE REMOVING CONTAMD CLTHG & SHOES. WASH CLOTHING BEFORE REUSE. ======================================================= Handling and Disposal ======================================================= Spill Release Procedures: WEAR NIOSH/MSHA SCBA & FULL PROT CLTHG. SHUT OFF IGNIT SOURCES:NO FLAMES, SMKNG/FLAMES IN AREA. STOP LEAK IF YOU CAN DO SO W/OUT HARM. USE WATER SPRAY TO REDUCE VAPS. TAKE UP W/SAND OR OTHER NON_COMBUST MATL & PLACE INTO CNTNR FOR LATER (SU PDAT) Neutralizing Agent: NONE SPECIFIED BY MANUFACTURER. Waste Disposal Methods: DISPOSE IN ACCORDANCE WITH ALL APPLICABLE FEDERAL, STATE AND LOCAL ENVIRONMENTAL REGULATIONS. EPA HAZARDOUS WASTE NUMBER:D001 (IGNITABLE WASTE). Handling And Storage Precautions: BOND AND GROUND CONTAINERS WHEN TRANSFERRING LIQUID. KEEP CONTAINER TIGHTLY CLOSED. Other Precautions: USE GENERAL OR LOCAL EXHAUST VENTILATION TO MEET TLVREQUIREMENTS. STORAGE COLOR CODE RED (FLAMMABLE). ======================================================= Fire and Explosion Hazard Information ======================================================= Flash Point Method: CC Flash Point Text: _9F,_23C Lower Limits: 1.2% Upper Limits: 77.7% Extinguishing Media: USE ALCOHOL FOAM, DRY CHEMICAL OR CARBON DIOXIDE. (WATER MAY BE INEFFECTIVE.) Fire Fighting Procedures: USE NIOSH/MSHA APPROVED SCBA & FULL PROTECTIVE EQUIPMENT (FP N). Unusual Fire/Explosion Hazard: VAP MAY FORM ALONG SURFS TO DIST IGNIT SOURCES & FLASH BACK. CONT W/STRONG OXIDIZERS MAY CAUSE FIRE. TOX GASES PRDCED MAY INCL:CARBON MONOXIDE, CARBON DIOXIDE. =======================================================

Figure 1-14  The MSDS for any chemical lists physical and chemical properties and all necessary safety ­information.

The Canadian equivalent of the MSDS is the Workplace Hazardous Materials Information Sheet

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is issued by the manufacturer of the material. It provides detailed information on hazardous materials, including dangerous ingredients, corrosiveness, reactivity, toxicity, fire and explosion data, health hazards, spill and leak procedures, and special precautions. Federal law requires that an MSDS be available for each hazardous material in the workplace. They are sometimes posted in the shop or available in the office. An employee must have access to all MSDS documents pertaining to his or her work area. The MSDS often states recommended uses for the material and lists specific handling instructions and safety precautions that must be observed. Emergency treatments for accidental ingestion, inhalation, and eye and skin contact are given when applicable. Guidelines for cleaning up spills or responding to other emergencies are included. The Canadian equivalent of the MSDS is the Workplace Hazardous Materials Information Sheet. The employer is responsible for obtaining all MSDS for the hazardous materials in the shop and for making this information available to all employees. The employer must also

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provide formal training on the safe handling of all hazardous materials and must update this training yearly. Containers storing potentially hazardous materials must be properly labeled with regard to health, fire, reactivity, and handling hazards (Figure 1-15). The simplest way to ensure compliance is to keep materials in their original containers. If a chemical is moved into another container, it is the responsibility of the shop to see that the container is the proper type and is correctly labeled. Do not use materials in unmarked containers. They may not be what they appear to be, or they may be contaminated. Every employer also must maintain documentation on all hazardous materials used in the shop. The employer must provide proof of training programs, keep records of all accidents or spills, and satisfy all employee requests to review MSDS. Even if a hazardous material is phased out of use, the MSDS must be kept on file for 30 years. OSHA and other regulatory agencies are quite serious when it comes to employee safety and hazardous materials. Each employee should be too. During the workday, a technician may use any number of materials that can be hazardous. For example, there are solvents, brake cleaners, and brake fluids. The storage containers for these and all other hazardous materials must have a label that should be read before using them (see Figure 1-15). Figure 1-16 shows a typical container label. The label must identify the hazardous chemicals in the product and tell what the specific hazards are. For example, the label

Figure 1-15  Chemical storage cabinets must be labeled as to contents and fire hazards.

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Figure 1-16  The label on a can of brake fluid lists hazards, warnings, and first-aid information.

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Oily Rags

Figure 1-17  Hazardous waste materials must be stored in clearly labeled safety containers until they can be disposed of properly.

would tell the technician that the material might be poisonous or flammable and list what precautions should be taken. There might be a warning to wear eye protection or to use the material in a well-ventilated area. First-aid information is also provided on the label. Unlabeled materials can be very dangerous. Many people have been injured when they did not know what was in a container. There may be times when a material from a labeled container is placed into another container. Always make a label for the new container that describes the contents. Other persons may use the container or material. Many of the waste materials from shop use are also considered hazardous (Figure 1-17). Dirty solvent, used engine coolant, used batteries, used engine oil, and vacuum cleaner bags with brake dust are just a few examples of shop hazardous waste. Never throw these materials in the trash or pour them down a drain. They could end up in a place where they could injure someone. Federal laws regulate how hazardous waste materials should be handled. Automotive shops usually have contracts with companies to pick up these materials and dispose of them properly.

HANDLING OF HAZARDOUS WASTE When the shop is finished using a hazardous material, it becomes hazardous waste. The EPA defines hazardous waste as solid or liquid materials that have one or more of the following characteristics: ■■ Ignitability. This characteristic applies to liquids with flash points below 1408F or solids that can spontaneously ignite. ■■ Corrosivity. Materials that dissolve metals or other materials or burn the skin on contact are considered corrosive. ■■ Reactivity. Reactive materials include those that react violently with water or other materials. They may release cyanide gas, hydrogen sulfide gas, or similar gases when exposed to low-pH acid solutions. They may also generate toxic or flammable vapors. ■■ Extraction Procedures (EP) toxicity. Materials that leach one or more heavy metals in concentrations greater than 100 times primary drinking water standard concentrations are considered toxic. A complete list of hazardous wastes may be found at the EPA or CCOHS websites. When handling any hazardous waste material, always wear the safety equipment specified in the MSDS. In many cases, this includes full eye protection, chemical-resistant gloves, and a respirator (Figure 1-18).

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Figure 1-18  Wear proper safety equipment when handling hazardous materials such as cleaning solvents.

Cleaning Equipment Safety Parts cleaning is an important part of any brake repair job. Be careful when using solvents. Most are toxic, caustic, and flammable. Avoid placing bare hands in solvent; wear protective gloves, if necessary. Read all manufacturer’s precautions and instructions and material safety data sheets (MSDS) before using. Do not use gasoline to clean components. This practice is very dangerous. Gasoline vaporizes at such a rate that it can form a flammable mixture with air at temperatures as low as 2508F. Gasoline also is dangerous if it gets on the skin because the chemicals in gasoline can be absorbed through the skin and get into your body. WARNING:  Never work with gasoline in a closed area. One experienced technician was working on a carburetor in his home garage. After leaving for awhile to go shopping, he re-entered the garage through a door between the kitchen and garage. When he flipped the light switch on, an explosion demolished the kitchen and garage. He was killed instantly. An investigation found that he apparently left a gasoline container open and the vapors filled the two-car garage sufficiently to ignite from a small electrical spark. Even a small amount of gasoline or other flammable liquid can produce enough vapors to cause lots of ­damage and injuries.

Small cleaning jobs are often done with aerosol cleaners. These spray cans contain chemicals that break down dirt and grease and allow them to be removed. Always read the warnings on the can and follow them. Wear eye protection, proper gloves, and a shop coat to prevent exposure to the skin or eyes. Always do the cleaning in a well-ventilated area.

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A

B

C

Figure 1-19  To relieve high ABS pressures, (A) disconnect the battery negative cable, (B) be sure the ignition is off, and (C) pump the brake pedal 25–50 times until you feel a definite increase in pedal firmness.

Many of the solvents used in solvent cleaning tanks are flammable. Be careful to prevent an open flame around the solvent tank. Never mix solvents. One could vaporize and act as a fuse to ignite the others. Wear neoprene gloves when washing parts. Some solvents can be absorbed through the skin and into the body. This is especially true if there is a cut on your hand. Do not blow compressed air onto the hands if they get wet with solvent, as this can cause the solvent to go through your skin. Wipe up spilled solvents promptly, and store all rags in closed, properly marked metal containers. Store all solvents either in their original containers or in approved, properly labeled containers. Finally, when using a commercial parts washer, be sure to close the lid when the job is finished.

Antilock Brake Hydraulic Pressure Safety Many ABSs generate extremely high brake fluid pressures that range from 2,000 to 3,000 psi. Failure to fully depressurize the hydraulic accumulator of an ABS before servicing any part of the system could cause severe personal injury from high-pressure brake fluid escaping from a service connection. Follow the exact shop manual procedure for the vehicle being serviced. A typical depressurizing procedure follows, with complete details in Chapter 10. 1. Disconnect the negative (−), or ground, battery cable (Figure 1-19A). 2. Be sure the ignition key is off (Figure 1-19B). 3. Pump the brake pedal at least 25 to 50 times, using about 50 pounds of pedal force (Figure 1-19C). 4. Continue pumping until you feel a definite increase in pedal firmness. Pump the pedal a few more times to ensure complete relief of hydraulic pressure from the system. 5. Proceed with system service.

AIR BAG SAFETY   WARNING:  Late-model cars and light trucks have supplemental inflatable restraint systems (SIRSs), known as air bags. To avoid accidental deployment of the air bag and possible injury or vehicle damage, always disconnect the battery ground (negative) cable, then the positive battery cable, and wait a minimum of 20 minutes before working near any of the impact sensors, steering column, or instrument panel. Do not use any powered electrical test equipment on any of the air bag system wires or tamper with them in any way unless specifically directed by the instructor or supervisor. Do not use memory saver devices unless the air bag system is disabled.

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Most vehicles built since the early 1990s have a supplemental inflatable restraint ­system (SIRS), more commonly called an air bag. This system is designed to protect the driver and other passengers from injury in case of a collision. The system consists of an air bag module in the center of the steering wheel, another in the right side of the instrument panel, and possibly others in the side panels and headrests. When working on brake system components under the instrument panel or near any of the air bag sensors or actuators, it is a good idea to deactivate the air bag system as described in the warning above. Exact procedures may vary from one vehicle to another, so consult the specific vehicle service manual for details. Automotive manufacturers have installed side and headrest air bags in many of the 2000 and later model vehicles. Some side bags are in the doors, whereas others are in the side of the seat backrest. They are protection during a side impact. The headrest bags are designed to reduce head and neck injuries during a collision from the rear. It is an accepted fact that SIRSs of this type can be dangerous to automotive and emergency technicians. The newest SIRSs are disarmed in a manner similar to that for driver and passenger bags. Always consult the service manual before beginning work in or around any SIRS components.

Hybrid Vehicle Electrical Hazards WARNING:  Hybrids have very high voltage systems that can kill you if they are mishandled! Do not attempt to service a hybrid vehicle until you have been trained and understand the proper procedures necessary to keep you safe!

Every manufacturer is using high voltage for their hybrid and electric vehicles (EV). It is important to know what the proper procedures are for disarming the high voltage system to prevent electrocution and or property damage. It is beyond the scope of this text to describe every manufacturer’s specific safety precautions, so never ever attempt ANY repair on a hybrid vehicle until you know the proper procedures through training. Generally, orange wiring and conduit identify the high voltage system (Figure 1-20). It is also important to know that some hybrids will restart on their own if the battery is low and the key is in (or near, in the case of a smart key) the ignition. Imagine what would happen if you had your hands around a rotating part if the engine started.

Figure 1-20  The Chevrolet Volt has high voltage wiring identified by orange insulation and conduit.

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FIRE CONTROL There are four general classifications of fires and a type of fire extinguisher to match the burning materials (Figure 1-21). Each class of fire is matched with a type of fire extinguisher containing the best material for controlling or extinguishing that fire. The automotive repair shop is normally in danger of fire from fuel, mostly gasoline, or from electrical fires. Electrical fires can sometimes be easily extinguished by disconnecting the battery, but do not go in harm’s way trying to do this. Fuel fires will continue to burn as long as there is fuel. One thing not to use on fuel fires is spraying water. That will only spread the fuel and the fire. A Class B or a multiple-purpose fire extinguisher is the best tool for stopping a fuel fire. Most automotive shops have multiple-purpose-type extinguishers because they will work on different types of fire. The first thing that should be done when a fire is discovered is to sound the alarm, then locate and remove the extinguisher from its mount. Using a fire extinguisher is fairly simple provided that the employer and employee have done their routine checks. Each fire extinguisher in the shop must have a tag where the date and time of inspection have

Class

A

Fires

Class of Fire

Typical Fuel Involved

Type of Extinguisher

For Ordinary Combustibles Put out a Class A fire by lowering its temperature or by coating the burning combustibles.

Wood Paper Cloth Rubber Plastics Rubbish Upholstery

Water*1 Foam* Multipurpose dry chemical4

For Flammable Liquids Put out a Class B fire by smothering it. Use an extinguisher that gives a blanketing, flame-interrupting effect; cover whole flaming liquid surface.

Gasoline Oil Grease Paint Lighter fluid

Foam* Carbon dioxide5 Halogenated agent6 Standard dry chemical2 Purple K dry chemical3 Multipurpose dry chemical4

For Electrical Equipment Put out a Class C fire by shutting off power as quickly as possible and by always using a nonconducting extinguishing agent to prevent electric shock.

Motors Appliances Wiring Fuse boxes Switchboards

Carbon dioxide5 Halogenated agent6 Standard dry chemical2 Purple K dry chemical3 Multipurpose dry chemical4

For Combustible Metals Put out a Class D fire of metal chips, turnings, or shavings by smothering or coating with a specially designed extinguishing agent.

Aluminum Magnesium Potassium Sodium Titanium Zirconium

Dry powder extinguishers and agents only

(green)

Class

B

Fires

(red)

Class

C

Fires

(blue)

Class

D (yellow)

Fires

*Catridge-operated water, foam, and soda-acid types of extinguishers are no longer manufactured. These extinguishers should be removed from service when they become due for their next hydrostatic prerssure test. Notes: (1) Freezes in low temperatures unless treated with antifreeze solution, usually weighs over 20 pounds (9 kg), and is heavier than any other extinguisher mentioned. (2) Also called ordinary or regular dry chemical (sodium bicarbonate). (3) Has the greatest initial fire-stopping power of the extinguishers mentioned for class B fires. Be sure to clean residue immediately after using the extinguishers so sprayed surfaces will not be damaged (potassium bicarbonate). (4) The only extinguishers that fight A, B, and C classes of fires. However, they should not be used on fires in liquefied fat or oil of appreciable depth. Be sure to clean residue immediately after using the extinguisher so sprayed surfaces will not be damaged (ammonium phosphates). (5) Use with caution in unventilated, confined spaces. (6) May cause injury to the operator if the extinguishing agent (a gas) or the gases produced when the agent is applied to a fire is inhaled.

Figure 1-21  Class B- and C-type fires present the greatest fire concern in an automotive shop. A multiple-purpose fire extinguisher will work on each type.

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been completed. This inspection is performed and the tag initialed each month. Usually the local fire marshal will conduct an annual inspection visit of each facility, and this is one of the things that will be checked. Before placing the fire extinguisher into action, check the small gauge near the handle. The needle should be in the green zone. If it is not, then the extinguisher is no longer charged and will not function. When fighting a fire with an extinguisher, make sure that you have an exit to your back, so you can escape if necessary. Pull the pin on the extinguisher, and aim at the base of the fire. Sweep from side to side. Stay upwind of the fire if you are outside. Exercise extreme caution when fighting a fire. If at any point it appears out of control, immediately evacuate the building or area and allow the first responders to control the situation.

TECHNICIAN TRAINING AND CERTIFICATIONS Technician training can start as early as the early teens, helping family or friends repair personal vehicles. In many ways, this is one of the best ways to start a career in automotive service. Back in the good old days, before electronics, a person who was known for working on his or her personal vehicle and keeping it operational could get a job in almost any automotive repair center. With the highly sophisticated vehicles of today, that backyard experience does not count for much with today’s service managers. It is almost imperative that any person who desires to be an automotive service technician to receive formal training. This training may start in high school and continue through a postsecondary technical school or college. A diploma or degree from a postsecondary school will get an applicant a job, but the training will not stop there. All dealerships and most independent shops will require additional training throughout the technician’s career. Before selecting a postsecondary automotive program, check out its job placement program. A job placement in the 90th percentile level means the employers served by that program trust the content of the program and the instructors. Based on this trust won over many years, they will hire graduates, knowing that the new employees have the will and knowledge to be successful. Another key to proving success is completing certification programs for the technician. The most well known for automotive technicians is the Automotive Institute for Excellence (ASE), Figure 1-22. This is a nonprofit organization that conducts semiannual written tests on the 8 system areas of the vehicle. More information can be gained through its website at https://www.ase.com/Home.aspx. ASE has a sub-agency named the National Automotive Technician Education Foundation (NATEF). NATEF certifies automotive training programs ranging from high school to postsecondary and manufacturer-specific schools. Another thing to consider during postsecondary program selection may be: Is it NATEF certified?

Figure 1-22  ASE-certified technicians may wear these shoulder patches.

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ASE-STYLE REVIEW QUESTIONS 1. Technician A says always checks air hoses and power cords for signs of damage before use. Technician B says to immediately disconnect and replace a leaking or bulging air hose. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 2. While discussing safety glasses, Technician A says, as with all other clothing, they must be worn for awhile for you to adapt to their weight and viewing area. Technician B says when taking off goggles or a face shield, close the eyes. Small particles of sharp metal may have attached themselves to the outside of the goggles or face shield and may drop into the eyes. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 3. Technician A says basically, right-to-know requires the employer to notify employees of insurance benefits. Technician B says they also require the initial training of new employees only. A. A only C. Both A and B B. B only D. Neither A nor B 4. While discussing Material Safety Data Sheets (MSDS), Technician A says the MSDS is issued by the manufacturer, and it provides detailed information on hazardous materials. Technician B says federal law requires that an MSDS is available for most hazardous material in the workplace. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. Always work with cleaning solvents in a well-­ ventilated area that is free of sparks or flames. Technician B says that chlorinated hydrocarbons can be absorbed through the skin with toxic effects. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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6. Some states require periodic vehicle safety inspection. These safety inspections usually include at least an inspection of brake components. How often are these inspections performed? A. Every 3 years C. Every 5 years B. Either every year D. Vehicles picked at or every 2 years random 7. Technician A says the most frequent kind of back injury at work is caused by improper lifting. Technician B says not all back injuries are caused by lifting too much weight but by lifting relatively small, light objects. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 8. Occupational Safety and Health Administration (OSHA) is a division of the U.S. Department of Labor that establishes and enforces A. Workplace safety C. Hiring practices regulations legislation B. Automotive brakD. Manufacturing ing safety quality standards regulations 9. Technician A says liquid solvents were developed for brake cleaning to reduce the hazard of cleaning off brake assemblies. Technician B says blowing off brake assemblies with compressed air is an acceptable practice. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 10. A person may be exposed to chemical health hazards in which of the following ways? A. Ingestion C. Contact with the skin B. Inhalation D. All the above

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Name ______________________________________

Date _________________

SHOP SAFETY SURVEY As a professional technician, safety should be one of your first concerns. This job sheet will increase your awareness of shop safety rules and safety equipment. As you survey your shop area and answer the following questions, you will learn how to evaluate the safeness of your workplace.

27

JOB SHEET

1

ASE Education Foundation Correlation This job sheet addresses the following RST Shop and Personal Safety tasks: Task #1 Identify general shop safety rules and procedures. Task #6 Identify marked safety areas. Task #8 Identify the location and use of eye wash stations. Task #10 Comply with the required use of safety glasses, ear protection, gloves, and shoes during lab or shop activities. Task #11 Identify and wear appropriate clothing for lab or shop activities. Task #12 Secure hair and jewelry for lab or shop activities. Tools and Materials Copy of the shop rules from the instructor Procedure Your instructor will review your progress throughout this worksheet and should sign off the sheet when you complete it. 1. Are there safety areas marked around grinders and other machinery? h Yes h No 2. Have your instructor provide you with a copy of the shop rules and procedures. Have you read and understood the shop rules? h Yes h No 3. Before you begin to evaluate your work area, evaluate yourself. Are you dressed to work safely? h Yes h No If not, what is wrong?_________________________________________________________ 4. Are your safety glasses OSHA approved? h Yes h No Do they have side protection shields? h Yes h No 5. Look around the shop, and note any area that poses a potential safety hazard or is an area that you should be aware of.    Any true hazards should be brought to the attention of the instructor immediately. 6. What is the air line pressure in the shop? _______________ psi What should it be? _______________ psi 7. Where is the first aid kit(s) kept in the work area?  

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Chapter 1

8. Ask the instructor to show the location of and demonstrate the use of the eyewash station. Where is it, and when should it be used?   9. What is the shop’s procedure for dealing with an accident?    10. Explain how to secure hair and jewelry while working in the shop.   11. List the phone numbers that should be called in the case of an emergency.  Problems Encountered    Instructor’s Response   

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Brake Safety

Name ______________________________________

Date _________________

WORKING IN A SAFE SHOP ENVIRONMENT Upon completion of this job sheet, you will know how to work safely in the shop and about the technicians’ environment. You will also learn about the two basic tools a technician uses, which are hoists and the floor jack.

29

JOB SHEET

2

ASE Education Foundation Correlation This job sheet addresses the following RST Shop and Personal Safety tasks: Task #2 Utilize safe procedures for handling of tools and equipment. Task #3 Identify and use proper placement of floor jacks and jack stands. Task #4 Identify and use proper procedures for safe lift operation. Task #5 Utilize proper ventilation procedures for working within the lab or shop area. Task #9 Identify the location of the posted evacuation routes. Tools and Materials Vehicle for hoist and jack stand demonstration Service information Describe the vehicle used: Make _____________________ Model _____________________ Year _____________________ Procedure 1. Are the shop emergency escape routes clearly marked? h Yes h No 2. Have your instructor demonstrate the exhaust gas ventilation system in the shop. Explain the importance of the ventilation system.   3. What types of hoists are used in the shop?   4. Find the location of the correct lifting points for the vehicle supplied by the instructor. Draw a simple figure showing the location of these lifting points. 5. Ask your instructor to demonstrate the proper use of the hoist. Summarize the proper use of the hoist.    

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Chapter 1

6. Demonstrate the proper use of jack stands with the help of your instructor. Summarize the proper use of jack stands. ________________________________ Problems Encountered    Instructor’s Comments   

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Brake Safety

Name ______________________________________

Date _________________

WORKING SAFELY AROUND AIR BAGS Upon completion of this job sheet, you should be able to work safely around and with air bag systems.

31

JOB SHEET

3

ASE Education Foundation Correlation This job sheet addresses the following RST Shop and Personal Safety tasks: Task #13 Demonstrate awareness of the safety aspects of supplemental restraint systems (SRS), electronic brake control systems, and hybrid vehicle high voltage circuits. Tools and Materials A vehicle(s) with air bag Safety glasses, goggles Service information appropriate to vehicle(s) used Describe the vehicle used: Year _____________________ Make _____________________ Model _____________________ VIN ____________________________ Engine type and size _____________________________ Procedure 1. Locate the information about the air bag system in the service information. How are the critical parts of the system identified in the vehicle?   2. List the main components of the air bag system and describe their location.    3. There are some very important guidelines to follow when working with and around air bag systems. Look through the service information to find the answers to the questions and fill in the blanks with the correct words. A. Wear _______________ when servicing an air bag system and when handling an air bag module. B. Wait at least _______________ minutes after disconnecting the battery before beginning any service. The reserve _______________ module is capable of storing enough energy to deploy the air bag for up to _______________ minutes after battery voltage is lost. C. Never carry an air bag module by its _______________ or _______________, and, when carrying it, always face the trim and air bag _______________ from your body. When placing a module on a bench, always face the trim and air bag _______________. D. Deployed air bags may have a powdery residue on them. _______________ is produced by the deployment reaction and is converted to _______________ when it comes in contact with the moisture in the atmosphere. Although it is unlikely that harmful chemicals will still be on the bag, it is wise to wear ______________ and _______________ when handling a deployed air bag. Immediately wash your hands after handling a deployed air bag.

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Chapter 1

E. A live air bag must be _______________ before it is disposed. A deployed air bag should be disposed of in a manner consistent with the _______________ and manufacturer’s procedures. F. Never use a battery- or AC-powered _______________, _______________, or any other type of test equipment in the system unless the manufacturer specifically says to. Never probe with a _______________ for voltage. 4. Explain how an air bag sensor should be handled before it is installed on the vehicle.    Problems Encountered    Instructor’s Response   

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Brake Safety

Name ______________________________________ 

Date _________________

HIGH VOLTAGE HAZARDS IN TODAY’S VEHICLES Upon completion of this job sheet, you will be able to describe some of the necessary precautions to take while performing work around high voltage hazards such as high intensity discharge (HID) headlamps and ignition systems

33

JOB SHEET

4

ASE Education Foundation Correlation This job sheet addresses the following RST Shop and Personal Safety task: Task # 14 Demonstrate awareness of the safety aspects of high voltage circuits (such as HID lamps, ignition systems, injection systems, etc.). Tools and Materials Service information for HID headlamps. Describe the vehicle used: Year _____________________ Make _____________________ Model _____________________ Engine type and size _____________________ Describe general operating condition: ________________________________________________________________________________ Procedure HID Headlamp Precautions 1. List three precautions a technician should observe when working with HID headlamp systems.    2. How many volts are necessary to initiate and maintain the arc inside the bulb of this HID system?   3. A technician must never probe with a test lamp between the HID ballast and the bulb. Explain why.   High Voltage Ignition System Precautions 4. High voltage ignition systems can cause serious injury, especially for those who have heart problems. Name at least three precautions to take when working around high voltage ignition systems.    

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34

Chapter 1

Problems Encountered    Instructor’s Comments   

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Brake Safety

Name ______________________________________

Date _________________

HYBRID HIGH VOLTAGE AND BRAKE SYSTEM PRESSURE HAZARDS

35

JOB SHEET

5

Upon completion of this job sheet, you will be able to describe some of the necessary precautions to take in performing work around high voltage hazards such as hybrid vehicles, as well as high-pressure hazards of some braking control systems. ASE Education Foundation Correlation This job sheet addresses the following RST Shop and Personal Safety tasks: Task # 13 Demonstrate awareness of the safety aspects of supplemental restraint systems (SRS), electronic brake control systems, and hybrid vehicle high voltage circuits. Tools and Materials Appropriate service information AUTHOR’S NOTE:   According to the vehicles’ manufacturers, a technician should not work on hybrid vehicles without taking specific training that is beyond the scope of this job sheet. This job sheet assumes that the student will be ­accessing information only, not actually working on live high voltage vehicles. Protective Gear Goggles or safety glasses with side shields High voltage gloves with properly inspected liners Orange traffic cones to warn others in the shop of a high voltage hazard Describe the vehicle selected: Year _____________________ Make _____________________ Model _____________________ Engine type and size _____________________ Describe general operating condition: ________________________________________________________________________________ Procedure Hybrid High Voltage Hazards 1. Special gloves with liners are to be inspected before each use when working on a hybrid vehicle. A. How should the integrity of the gloves be checked?   B. How often should the gloves be tested (at a lab) for recertification? 

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Chapter 1

C. What precautions must be taken when storing the gloves?   D. When must the gloves be worn?    2. What color are the high voltage cables on hybrid vehicles?  3. What must be done BEFORE disconnecting the main voltage supply cable?    4. Describe the safety basis of the “one hand rule.”    5. Explain the procedure to disable high voltage on the vehicle you selected.    6. Explain the procedure to test for high voltage to ensure that the main voltage is disconnected.    High Pressure Braking System Hazards 7. Note: Many vehicles have a high-pressure accumulator or a high-pressure pump in their braking systems. Opening one of these systems can be hazardous because of the high pressures involved. Research the vehicle you have been assigned and describe the procedure that must be followed BEFORE opening the hydraulic braking system.    Problems Encountered    Instructor’s Comments   

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Brake Safety

Name ______________________________________

Date _________________

37

JOB SHEET

6

MATERIAL DATA SAFETY SHEET USAGE Upon completion of this job sheet, the student will be able to locate the MSDS folder and describe the use of an MSDS sheet on the job site. ASE Education Foundation Correlation This job sheet addresses the following RST Shop and Personal Safety tasks: Task # 15 Locate and demonstrate knowledge of material safety data sheets (MSDS). Tools and Materials Selection of chemicals from the shop MSDS sheets Locate the MSDS folder in the shop. It should be in a prominent location. Did you have any problems finding the folder?  Procedure

Task Completed

1. Pick a common chemical from your tool room such as brake cleaner. Locate the chemical in the MSDS folder.

h

2. What is the flash point of the chemical? ________________________________________ 3. Briefly describe why the flash point is important.   4. What is the first aid if the chemical is ingested?   5. Can this chemical be absorbed through the skin?  

h h

h

h

6. What are the signs of exposure to the chemical you selected?  

h

7. What are the health hazards of the chemical?  

h

8. What is the first-aid procedure for exposure?  

h

9. What are the recommendations for protective clothing?  

h

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Chapter 1

Problems Encountered    Instructor’s Comments   

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Brake Safety

Name ______________________________________ 

Date _________________

FIRE EXTINGUISHER CARE AND USE Upon completion of this job sheet, you will be able to demonstrate knowledge of the procedures for using fire extinguishers and other fire safety equipment, and identify the location of fire extinguishers in the shop.

39

JOB SHEET

7

ASE Education Foundation Correlation This job sheet addresses the following RST Shop and Personal Safety task: Task # 7 Identify the location and the types of fire extinguishers and other fire safety equipment; demonstrate knowledge of the procedures for using fire extinguishers and other fire safety equipment. Procedure NOTE: Never fight a fire that is out of control or too large. Call the fire department immediately! 1. Identify the location of the fire extinguishers in the shop, and list them below.   2. Have the fire extinguishers been inspected recently? (Look for a dated tag.)   3. What types of fires are the shop’s fire extinguishers rated to fight?   4. What types of fires should not be used with the shop’s extinguishers?   5. One way to remember the operation of a fire extinguisher is to remember the term PASS. Describe the meaning of PASS below. A. P B. A C. S D. S Problems Encountered    Instructor’s Comments   

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Brake Safety

Name ______________________________________

Date _________________

PREPARING THE VEHICLE FOR SERVICE AND CUSTOMER Upon completion of this job sheet, you will be able to prepare a service work order based on customer input, vehicle information, and service history. The student will also be able to describe the appropriate steps to take to protect the vehicle and deliver the vehicle to the customer after the repair.

41

JOB SHEET

8

ASE Education Foundation Correlation This job sheet addresses the following RST Preparing a Vehicle for Service tasks: Task #1 Identify information needed and the service requested on a repair order. Task #2 Identify purpose and demonstrate proper use of fender covers, mats. Task #3 Demonstrate use of the three Cs (concern, cause, and correction). Task #4 Review vehicle service history. Task #5 Complete work order to include customer information, vehicle-identifying information, customer concern, related service history, cause, and correction. This job sheet addresses the following RST Vehicle for Customer task: Task #1 Ensure vehicle is prepared to return to customer per school/company policy (floor mats, steering wheel cover, etc.). Tools and Materials An assigned vehicle or the vehicle of your choice Service work order or computer-based shop management package Parts and Labor Guide Work Order Source: Describe the system used to complete the work order. If a paper repair order is being used, describe the source.   Procedure

Task Completed

1. Prepare the shop management software for entering a new work order or obtain a blank paper work order. Describe the type of repair order you are going to use.  

h

2. Enter customer information, including name, address, and phone numbers onto the work order.

h

3. Locate and record the vehicle’s VIN. Where did you find the VIN?_______________ 4. Enter the necessary vehicle information, including year, make, model, engine type and size, transmission type, license number, and odometer reading.

h

5. Does the VIN verify that the information about the vehicle is correct?_______________ 6. Normally, you would interview the customer to identify his or her concerns. However, to complete this job sheet, assume the only concern is that the customer wishes to have the front brake pads replaced. Also, assume no additional work is required to do this. Add this service to the work order.

h

7. Prepare the vehicle for entering the service department. Add floor mats, seat covers, and steering wheel covers to the vehicle.

h

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Chapter 1

8. The history of service to the vehicle can often help diagnose problems as well as indicate possible premature part failure. Gathering this information from the customer can provide some of this information. For this job sheet, assume the vehicle has not had a similar problem and was not recently involved in a collision. Service history is further obtained by searching files for previous service. Often this search is done by customer name, VIN, and license number. Check the files for any related service work.

Task Completed h

9. Search for technical service bulletins on this vehicle that may relate to the customer’s concern. Did you find any? If so, record the reference numbers here.  

h

10. Based on the customer’s concern, service history, TSBs, and your knowledge, what is the likely cause of this concern?  

h

11. Enter this information onto the work order.

h

12. Prepare to make a repair cost estimate for the customer. Identify all parts that may need to be replaced to correct the concern. List these here.  

h

13. Describe the task(s) that will be necessary to replace the part.  

h

14. Using the parts and labor guide, locate the cost of the parts that will be replaced and enter the cost of each item onto the work order at the appropriate place for creating an estimate. If the valve or cam cover is leaking, what part will need to be replaced? 

h

15. Now, locate the flat rate time for work required to correct the concern. List each task with its flat rate time.  

h

16. Multiply the time for each task by the shop’s hourly rate and enter the cost of each item onto the work order at the appropriate place for creating an estimate. Ask your instructor what shop labor rate to use and record it here.

h

 17. Many shops have a standard amount they charge each customer for shop supplies and waste disposal. For this job sheet, use an amount of $10 for shop supplies.

h

18. Add the total costs and insert the sum as the subtotal of the estimate.

h

19. Taxes must be included in the estimate. What is the sales tax rate and does it apply to both parts and labor, or just one of these?  

h

20. Enter the appropriate amount of taxes to the estimate, then add this to the subtotal. The end result is the estimate to give the customer.

h

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Brake Safety

21. By law, how accurate must your estimate be?  

h

22. Generally speaking, the work order is complete and is ready for the customer’s signature. However, some businesses require additional information; make sure you enter that information to the work order. On the work order, there is a legal statement that defines what the customer is agreeing to. Briefly describe the contents of that statement. 

h

23. Now that the vehicle service is complete and the vehicle is ready to be returned to the customer, what are the appropriate steps to take to deliver the vehicle to the customer? What would you do to make the delivery special? What should not happen when the vehicle is delivered to the customer?  

h

43

Problems Encountered    Instructor’s Comments   

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Chapter 2

Brake Service Tools and Equipment

Upon completion and review of this chapter you should be able to: ■■

■■

■■ ■■

List the basic units of measure for length and volume in the metric and U.S. customary systems. Identify and use the major measuring tools and instruments used in brake service work. Explain how to measure with both an inside and outside micrometer. Identify and describe the purpose and use of hand tools commonly found in a service technician’s toolbox.

■■

Identify and describe the purpose and use of special tools used for brake service.

■■

Identify and describe the purpose and use of commonly used power tools.

■■

Identify and use the electrical test tools used in ABS diagnostic work.

■■

Describe asbestos containment equipment commonly used in the shop.

■■

Select and retrieve service information.

Terms To Know Auto ranging

High impedance

Brush hone

International System of Units or metric system

Cylinder hone Digital storage oscilloscope (DSO) Digital multimeter (DMM) Force High-efficiency particulate air (HEPA) filter

Linear Multiple Parallel circuit Pascal Reamer Scan tool

Series circuit Series-parallel circuit Stem unit Submultiple Technical Service Bulletin (TSB) Tubing bender Tubing cutter Vernier scale

Caution Some U.S. customary and metric fasteners may appear to be exactly the same and to require the same wrench. Even bolt head markings can be misleading when identifying metric or standard sizes. An example is a fastener requiring a 1/2-inch wrench and a fastener requiring a 13-mm wrench. Although the wrench may appear to fit, it does not fit tightly enough to prevent damage to the fastener’s head and perhaps some skinned knuckles. Always make sure you use the correct tool for the job.

FASTENERS Although not truly tools, nuts and bolts and other fasteners are part of everyday automotive work, and the technician must understand their characteristics and grading system. Figure 2-1 identifies U.S. customary and metric fastener dimensions and terminology. Figure 2-2 shows the Society of Automotive Engineers (SAE) grade and strength markings for bolts used in automotive and other industrial assemblies. Metric fastener strength ratings are indicated by numbers embossed in the head of the bolt or nut. The most common metric fastener grades for automotive use are 9.8 and 10.9. Service information lists important fastener information. Using an incorrect fastener or a fastener of poor quality can result in dangerous failures and personal injury.

45

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46

Chapter 2 E

B H

C

F

D H = Head D = Length (millimeters) E = Thread pitch (distance crest to crest in millimeters) F = Nominal diameter (millimeters)

A A = Length (inches) B = Thread pitch (threads per inch) C = Nominal diameter (inches) U.S. Customary

Metric

Figure 2-1  The basic dimensions of an automotive fastener are length, diameter, and thread.

SAE Grade Markings DEFINITION

No lines: unmarked indeterminate quality SAE grades 0-1-2

3 Lines: common commercial quality automotive and AN bolts SAE grade 5

4 Lines: medium commercial quality automotive and AN bolts SAE grade 6

5 Lines: rarely used SAE grade 7

6 Lines: best commercial quality NAS and aircraft screws SAE grade 8

MATERIAL

Low carbon steel

Medium carbon steel, tem-pered

Medium carbon steel, quenched and tempered

Medium carbon alloy steel

Medium carbon alloy steel, quenched and tempered

TENSILE STRENGTH

65,000 psi

120,000 psi

140,000 psi

140,000 psi

150,000 psi

Figure 2-2  Lines on bolt heads indicate the relative strength of SAE inch-sized fasteners.

MEASURING SYSTEMS Older vehicles will still require standard sizes of sockets and wrenches, but metric sizes are the norm for vehicles manufactured in the last several years.

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Two different measurement systems are currently used in the United States and Canada: the U.S. customary system and the International System of Units or metric system. Note the speedometer markings on your personal vehicle. They are in miles per hour and kilometers per hour. Most vehicles manufactured in the United States as well as those imported from Europe and Asia use metric-sized nuts and bolts. Vehicle specifications and tightening torque are normally listed in both metric and customary units, so tools such as micrometers and torque wrenches can be based on either system.

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47

Brake Service Tools and Equipment

U.S. Customary System In the U.S. customary system, the basic unit of linear measurement is the inch. The inch can be divided into fractions, such as those used to designate wrench or socket sizes (¼, 5 , ½, 9 , and so on). 16 16 For component size and tolerance measurements, the inch is commonly divided into tenths, hundredths, thousandths, and even ten-thousandths. When an inch is divided in this way, the measurement is written with a decimal point. A single digit to the right of the decimal point indicates tenths of an inch (0.1 in.). Tenths of an inch can be further divided by ten into hundredths of an inch, which is written using two digits to the right of the decimal point (0.01 in.). The division after hundredths is thousandths (0.001 in.), followed by ten-thousandths (0.0001 in.). The following paragraphs summarize metric units of linear measurement, as well as metric volume, weight, pressure, torque, and temperature measurement units that may be encountered in brake service.

International System of Units or metric system is the modern international metric system used by the automotive industry and other industries. Linear means in a straight line.

Metric System The metric system has a basic unit for every kind of measurement. The most common metric units used in automotive service are: ■■ ■■ ■■ ■■ ■■

■■

Linear measurement: the meter (m) Volume measurement: the cubic meter (m 3 ), cubic centimeter (cc) or liter (l) Weight: the kilogram (kg) Pressure: the pascal (Pa) Torque: the newton-meter (Nm), or the older units of kilogram-meters or kilogramcentimeters (kg-m or kg-cm) Temperature: degrees Celsius (Technically, the basis for metric temperature units is the kelvin, but it is not used for everyday measurements.)

The basic metric units are called stem units. For large measurements, any metric stem unit is multiplied one or more times by 10. For small measurements, any stem unit is divided one or more times by 10. Units larger than the stem units are called multiples; units smaller than the stem units are called submultiples. Multiples and submultiples are indicated by prefixes written or abbreviated in front of the stem units. The most common metric prefixes for automotive measurements are listed in Table 2-1:

Linear.  The metric base unit for linear measurement is the meter, which is about 39 inches (Figure 2-3). For distance measurement on the road, the common unit is

A stem unit is any metric unit to which a prefix can. be added to indicate larger or smaller measurements to some power of 10. Multiple refers to the metric measurement unit that is larger than the stem unit through multiplying by a power of 10. Submultiple is the metric measurement unit that is smaller than the stem unit through dividing by a power of 10.

TABLE 2-1  METRIC PREFIXES FOR COMMON AUTOMOTIVE MEASUREMENTS.

MULTIPLE

PREFIX

ABBREVIATION

3 1,000

kilo

k

3 1,000,000

mega

M

SUBMULTIPLE

PREFIX

ABBREVIATION

3 0.01

centi

c

3 0.001

milli

m

3 0.000001

micro

µ

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48

Chapter 2 Yardstick 1

10

2

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35

20

30

40

50

60

70

80

90

Meterstick

Figure 2-3  A meter is approximately 39 3/8 inches.

Caution Never use a metric wrench or socket on a U.S. customary bolt or nut or an inchsized wrench on a metric fastener. The wrench or socket will always be slightly oversized and will slip off or damage the fastener.

the kilometer (1,000), which is abbreviated km. For smaller measurements, the meter is divided by 10 into submultiples. The most common measurements for automotive work are: ■■ One-hundredth of a meter (0.01 m), or a centimeter (cm) ■■ One-thousandth of a meter (0.001 m), or a millimeter (mm) The millimeter is the most common metric measurement used in automotive work. Metric wrenches are sized by millimeter: for example, 10 mm, 12 mm, and so on. The exact conversion factors for kilometers, centimeters, and millimeters into customary units are: Kilometer (km) 3 0.621377 5 miles 6093 3 miles 5 kilometers (km) ■■ Centimeters ( cm ) 3 0.3937 5 inches ■■ 2.540 3 inches 5 centimeters ( cm ) ■■ Millimeters ( mm ) 3 0.03937 5 inches ■■ 25.400 3 inches 5 millimeters (mm) ■■ ■■

Volume.  Although the cubic meter ( m 3 ) is the base metric unit for volume, the more accustomed is the common unit used for fluid volume: the liter. The liter is not an official metric unit, but it is recognized as a volume of 1 cubic decimeter (1/10 m 3 ) for liquids. The liter also is often divided into submultiples of one-thousandth, or cubic centimeters. The official abbreviation for the cubic centimeters is cm 3, but the auto industry has used “cc” for so long that either is acceptable. The cubic centimeter also equals 1 milliliter (ml), which may be seen occasionally in fluid measurements. The common conversion factors for liters into quarts and gallons (Figure 2-4) are:

Liter (1) 3 0.946 5 quart ■■ 1.057 3 quart 5 liter (1) ■■ Liter (1) 3 0.26418 5 gallon ■■ 3.7854 3 gallon 5 liter (1) ■■

1 liter (1.057 quart)

1 quart (0.946 liter)

1 gallon (4 quarts) (3.78 liters)

Figure 2-4  A liter is slightly larger in volume than a U.S. quart.

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49

Weight.  The metric base unit for weight is the kilogram (kg), but the kilogram itself is a multiple of a stem unit: the gram. A gram is a very small unit, so the kilogram—1,000 grams—is common in automotive work. The exact conversion factors for kilograms into pounds are: Kilogram ( kg ) 3 2.2046 5 pounds ■■ 0.4536 3 pounds 5 kilogram ( kg ) ■■

Pressure.  Many different units are used for pressure measurement, but the customary pressure unit most used in automotive service is pounds-per-square-inch (psi). Older metric specifications usually also were written in units of force divided by area, such as kilograms-per-square-centimeter ( kg-cm 2 ). The SI metric pressure unit, however, is the pascal (Pa). The basic pascal unit is very small, so pressure is usually expressed in thousands of pascal, or kilopascals (kPa). The conversion factors are: ■■

Kilopascals ( kPa ) 3 0.145 5 psi

■■

6.895 3 psi 5 kilopascals ( kPa )

Torque.  Customary units for torque measurement are compound units of force times distance: foot-pounds and inch-pounds. Since 1971, may be the metric base unit has been the newton-meter (Nm), but older metric specifications may be given in kilogram-meters (kg-m) or kilogram-centimeters (kg-cm). The conversion factors for newton-meters to foot-pounds and inch-pounds are: Newton-meter  ( Nm ) 3 0.737 5 foot-pounds 1.356 3 foot-pounds 5 newton-meter ( Nm ) ■■ Newton-meter  ( Nm ) 3 0.089 5 inch-pounds ■■ 0.113 3 inch-pounds 5 newton-meter ( Nm ) ■■

■■

Temperature.  The zero-point of the metric Celsius temperature scale is the freezing point of water. The boiling point of water is 100 degrees Celsius (1008C ). In the customary Fahrenheit scale, the freezing and boiling points of water are 32 degrees Fahrenheit and 212 degrees Fahrenheit, respectively. Therefore, the conversion factors require both subtraction and multiplication or division:

The measurement, ­pascal, is derived from Blaise Pascal, who researched and formulated the theories of hydraulics.

Most torque wrenches used in the United States are calibrated in foot-pounds or inch-pounds. Most have U.S. customary and metric markings or settings.

8F 2 32 3 5/9 5 Celsius (8C), or ■■ 8F 2 32 4 1.8 5 Celsius ( 8C) ■■ (1.8 3 8C ) 1 32 5 Fahrenheit ( 8F ) ■■

MEASURING TOOLS Many of the procedures for brake service require exact measurements of parts and clearances. Accurate measurements require precision measuring tools capable of measuring to the thousandth of an inch and smaller. For example, the acceptable lateral runout of a brake rotor may be as little as 0.004 inch (0.1 mm). The minimum acceptable thickness variation may be as small as 0.0005 inch (0.01 mm). Tools for measuring such small increments are delicate instruments and should be handled with great care. Never strike, pry, drop, or force these tools. Clean them before and after every use. As with all tools, measuring tools should be used only for the purposes for which they were designed. Some instruments are not accurate enough for very precise measurements; others are too accurate to be practical for less critical measurements.

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Chapter 2

All measuring tools should be calibrated or checked periodically against known good equipment or tool standards. This ensures that they work properly and give accurate measurements. Many different measuring devices are used by automotive technicians. The following sections cover those commonly used to service brake systems.

Steel Ruler or Tape Measure A steel ruler or tape measure is needed to measure brake pedal travel. Although a drum micrometer (described later) is necessary to accurately measure drum diameter, a ruler or tape measure can be used for a quick check.

Micrometers Micrometers are used to measure the outside diameter of an object or the inside diameter of a bore or drum. An outside micrometer has a fixed anvil and a movable spindle in a C-shaped frame (Figure 2-5). Figure 2-5 also shows an inside micrometer that may be used to measure a cylinder bore. Measurement gradations are on the fixed sleeve or body and on the movable thimble. Any micrometer has an accurately ground screw thread that is rotated in a fixed nut to change the distance between two measuring surfaces. Turning the thimble of an outside micrometer moves the spindle in and out toward the anvil. The screw thread of a decimalinch micrometer has 40 threads per inch. One revolution of the thimble moves the spindle 1/40, or 0.025 inch. Similarly, the lines on the fixed sleeve correspond to the micrometer screw threads. Each line represents 1/40, or 0.025 inch. Every fourth line is numbered to indicate hundreds of thousandths (Figure 2-6). Line 1 equals 0.100; line 2 equals 0.200; Sleeve

Lock nut

Thimble

Spindle

Lock screw for rod

Ratchet

Anvil

Thimble Anvil

5

.1 0

10

5 10

.1 0

Rod point Insert rod here Short handle

Frame

Body

Figure 2-5  Major parts of an outside micrometer (left) and an inside micrometer (right).

Sleeve Thimble Spindle

0

1

5

0

Figure 2-6  Readings on a micrometer graduated in thousandths of an inch.

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Brake Service Tools and Equipment Slip back and forth over object

Rock from side to side

51

Sleeve Thimble

1

.1 0

0

5

5

10

0

Reading 0.178 inch

Figure 2-8  Reading a micrometer graduated in thousandths of an inch (0.178 in.). Figure 2-7  Slide the micrometer over the part being measured so that it drags just slightly. Rock micrometer slightly and close the thimble gently.

line 3 equals 0.300, and so on. The beveled edge of the movable thimble has 25 lines, each representing 0.001. Turning the thimble from one line to another moves the spindle in or out 0.001 inch To measure a small object with an outside micrometer, open the jaws and slip the object between the spindle and the anvil. Hold the object against the anvil and lightly turn the thimble so that the object just fits between the spindle and the anvil (Figure 2-7). Do not overtighten the thimble. The object should slide between spindle and anvil with very slight resistance. To read a micrometer graduated in thousandths of an inch, multiply the number of vertical divisions on the spindle by 0.025, and then add the number of thousandths shown by the line on the thimble that matches with the horizontal line on the spindle. Figure 2-8 shows the following measurement: Line 1 on the spindle equals 0.100. Three more lines on the spindle equal 3 3 0.025 or 0.075. Line 3 on the thimble coincides with the horizontal line on the spindle, which equals 3 3 0.001 or 0.003. The micrometer reading is 0.178. Some micrometers have even finer gradations on the sleeve to give readings in ten-­ thousandths of an inch. These gradations are 10 division marks on the sleeve that occupy the same space as nine divisions on the thimble (Figure 2-9). The difference between one space on the fixed sleeve and one space on the movable thimble is 0.1 of a thimble division, or 0.0001. To read this micrometer, first take the reading in thousandths and then see which line on the fine scale of the sleeve matches a line on the thimble. If it is line 1, add 0.0001 to the thimble reading; if it is line 2, add 0.0002, and so on. Figure 2-9 shows the following measurement: Line 2 on the sleeve equals 0.200. Two more lines on the spindle equal 2 3 0.025 or 0.050. The longitudinal line on the sleeve is between the 0 and 1 on the thimble, indicating that a ten-thousandth measurement must be read from the vernier. Line 7 on the vernier coincides with a line on the thimble: 7 3 0.0001 or 0.0007. The micrometer reading is 0.2507.

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Chapter 2 Sleeve

Finer gradation

Thimble

Thimble

0

1

2

0

5

5

30

0 20

10

0

1

2

5

25

Reading 5.78 mm

Figure 2-10  Reading a micrometer graduated in hundredths of a millimeter (5.78 mm).

0 Figure 2-9  Readings on a micrometer graduated in ten-thousandths of an inch (0.2507 in.).

Metric micrometers have a spindle screw thread pitch of 0.5 mm so that each full turn of the thimble moves the spindle 0.5 mm. The longitudinal line on the sleeve is graduated from 0 to 25 mm and marked in 1.0 and 0.5 mm increments (Figure 2-10). The beveled edge of the thimble has 50 divisions, and every fifth line is numbered. A full turn of the thimble moves the spindle 0.5 mm, so each thimble gradation equals 1/50 of 0.5, or 0.01 mm. To read a metric micrometer, add the mm reading from the sleeve to the reading in hundredths of a mm on the thimble. Figure 2-10 shows the following measurement: Line 5 on the spindle equals 5.0 mm. One more half-mm line on the spindle equals 0.05 mm. Line 28 on the thimble is on the longitudinal line of the spindle (each line is 0.01 mm): 28 3 0.01 5 0.28 mm. The micrometer reading is 5.78 mm. Outside micrometers come in many different sizes, but the measurement range of the spindle is usually just 1 inch or 25 mm. That is, a 4-inch micrometer measures from 3 to 4 inches. Special micrometers are made for measuring brake rotor thickness. The throats on these micrometers are deeper than on standard micrometers to allow for the diameter of the rotor. The anvil and spindle of a rotor micrometer are usually pointed to allow measurements at the deepest points of any grooves in the rotor. To measure a large object such as a brake rotor, slide the micrometer over the object and lightly tighten the thimble while continuing to slide the micrometer across the object When you feel a light drag, rock the micrometer slightly to be sure it is contacting the object squarely. Then tighten the locknut (if equipped) and take the reading. A micrometer is a precision instrument. Observe these precautions when using one: ■■ ■■ ■■

■■

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Be sure the anvil is clean before measuring any item. Always hold the part being measured squarely between the anvil and the spindle. Do not overtighten the thimble, which could damage the micrometer or the part being measured, or both. If the micrometer has a torque-limiting ratchet, use it to tighten the thimble.

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Figure 2-11  Use a micrometer depth gauge to measure lining thickness precisely.

Depth Gauges A depth gauge is used to check the lining thickness of drum brake shoes (Figure 2-11). A depth gauge is graduated and read like a micrometer. Both customary inch and metric models are available.

Drum Micrometer A drum micrometer is a single-purpose instrument, used to measure the inside diameter of a brake drum (Figure 2-12). A drum micrometer has a movable arm on a shaft. The arm moves along a shaft that has both USC and metric measurement markings. The fixed arm or base has an anvil that fits against the inside of the drum. The movable arm is held in place by a small set screw that follows a narrow groove along the shaft. To use a drum micrometer of this type, slide the moveable arm toward the anvil end so the micrometer will fit into the drum. Place the anvil against one side of the drum about midway of the friction area and slide the other arm until its measuring point touches the

Some of the older drum micrometers can be difficult to set up and read. The newest drum micrometers available are electronic digital types.

Figure 2-12  An electronic drum micrometer is easy to use, is accurate, and can, at the press of a button, convert from USC to metric or vice versa.

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Chapter 2

other side of the drum at about the same place on the friction area. Gently lock the movable arm in place with the screw and try to slide one end of the micrometer around the inside of the drum. If properly positioned, the micrometer end cannot be moved easily. Look at the inner side of the movable arm where it fits around the shaft. Record the largest measurement visible. Either USC or the metric measurement may be used based on the drum specifications available. Metric drum micrometers work the same way except that the shaft is graduated in 1 cm major increments, and the lock screws fit in notches every 2 mm. Electronic drum micrometers are available at a reasonable cost. They are much easier to use, are extremely accurate, and metric or USC measurements can be selected.

SERVICE TIP  Handle precision measuring tools gently and store them properly. Micrometers should be checked for accuracy before use and at specified intervals. Standards are used to measure the tool’s accuracy (Figure 2-13).

Figure 2-13  The tool in the center is a micrometer standard used to check the accuracy of outside micrometers and dial calipers.

Vernier Calipers

A vernier scale is a fine auxiliary scale that indicates fractional parts of a larger scale.

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Vernier calipers (Figure 2-14) can take both inside and outside measurements, and vernier depth and height gauges are made with scales for measurements to 0.001 inch or 0.02 mm. On a 25-division vernier caliper that measures thousandths of an inch, the bar is graduated in 40 units of 0.025 inch. Each fourth gradation shows tenths of an inch. The 25 divisions on the movable vernier plate occupy the same space as 24 divisions on the bar. Since one division on the bar equals 0.025 inch, 24 divisions equal 0.600 inch (24 3 0.025 5 0.600). The 25 divisions on the movable plate also equal 0.600 inch, so each division equals 1/25, or 0.024 inch. Therefore, the difference between each mark on the bar and on the plate is 0.001 inch. To read a 25-division vernier scale, count the number of inches, tenths (0.100), and fortieths (0.025) that the 0 mark on the plate is from the 0 mark on the bar. Then add the number of thousandths shown by the line on the plate that exactly matches a line on the bar. The example in Figure 2-15 shows a reading of 1.000 inch, plus 0.400, plus 0.025, or 1.425 inches. The eleventh line on the plate matches a line on the bar, so add 0.011 to 1.425 for an exact reading of 1.436 inches. On a 25-division metric vernier, the gradations on the movable plate are 1 50 , or 0.02 mm. The bar is graduated in centimeters, millimeters, and one-half (0.5) millimeters.

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Figure 2-14  The vernier caliper can make inside and outside measurements.

1

2 1

2

4

0

7

6

5

5

10

8

9

15

20

1

3

4

5

25

English measurement, reading 1.436 inches

Figure 2-15  Typical decimal-inch measurement on a 25-division vernier scale.

The example in Figure 2-16 shows a reading of 4.00 cm (40.0 mm), plus 1.00 mm, plus 0.50 mm, or 41.50 mm.

Dial Indicators Dial indicators are the most common measurement device used with automotive disc brakes. Various kinds of dial indicators can be used to measure hole depth, surface smoothness, and out-of-round and runout of cylinders and rotating parts. They are usually used to check measurement variations rather than single linear measurements. In brake service,

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Chapter 2

4

5

0

5

10

15

20

25

Metric measurement, reading 41.60 mm

Figure 2-16  Typical metric measurement on a 25-division vernier scale.

the most common use of a dial indicator is to measure the runout in a disc brake rotor (Figure 2-17). Dial indicators have a plunger and a precision gear mechanism to turn a pointer on a dial. Most are graduated in thousandths (0.001) or ten-thousandths (0.0001) of an inch, or hundredths (0.01) or thousandths (0.001) of a millimeter. Continuous dial indicators read in one direction from the zero point (Figure 2-18). Balanced dial

Figure 2-17  Use a dial indicator to measure rotor runout.

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Brake Service Tools and Equipment

0

9

1

8 7

.0001" - .025"

6

1 2

2

3

3

1 2 3

.0001" - .025"

4

4

5

0

5

4

Figure 2-18  Dial indicators are either continuous reading (left) or balanced reading (right).

indicators read in both directions, plus and minus, from zero (Figure 2-18). Dial indicators come with various mounting fixtures to hold them for different jobs. On most indicators, the dial is turned to align the zero point with the pointer and then locked in place before starting a measurement. Pointer movement then indicates the variation from zero.

Feeler Gauges A feeler gauge is a thin strip of metal of a known thickness. A feeler gauge set is a collection of these strips, each with a different thickness (Figure 2-19). A steel feeler gauge set usually contains strips of 0.002-inch to 0.010-inch thicknesses (in increments of 0.001 inch) and strips of 0.012-inch to 0.024-inch thicknesses (in increments of 0.002 inch). Feeler gauges are used to check piston to wheel cylinder bore, drum to brake shoe, and other types of small clearances down to the thousandths of an inch. Metric feeler gauges are usually graduated in increments of 0.05 mm. Nonmetallic feeler gauges may be used to set older wheel speed sensors’ air gap.

Brake Shoe Adjusting Gauge (Calipers)

Feeler gauges

0.016

0.0 14 0.0 12

0.020

0.025

0.03

0.0

35

0

A brake shoe adjusting gauge is an inside-outside measuring device (Figure 2-20). This gauge is often called a brake shoe caliper. During drum brake service, the inside part of the gauge is placed inside a newly machined drum and expanded to fit the drum diameter. The lock screw is then tightened and the gauge moved to the brake shoes installed on the backing plate. The brake shoes are then adjusted until the outside part of the gauge just slips over them. This provides a rough adjustment of the brake shoes. Final adjustment must still be done after the drum is installed, but the brake shoe gauge makes the job faster.

The brake shoe adjusting gauge is particularly helpful on brake systems that require the drum to be removed for brake adjustment.

8 00 0. 006 0. 04 0.0 2 0.0001 0.0 0.001 0.001 0.002

Figure 2-19  Feeler gauges are available in both decimal-inch and metric gradations.

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Chapter 2

1. Set to Drum Diameter

2. Find Correct Brake Shoe Diameter

Figure 2-20  A brake shoe adjusting gauge is used for preliminary shoe adjustment. In this illustration, it is the only adjustment for the GM truck parking brake.

SERVICE TIP  A noncontact pyrometer is an infrared thermometer that you simply aim at an object to read its temperature. You can use a pyrometer to check brake temperatures on a car with a brake-pull problem. Drive the car and stop it with moderately hard braking effort and immediately measure drum or rotor temperature from front to rear or side to side. If rotor or drum temperatures differ significantly, caliper pistons may be sticking or a problem may exist with the pads or shoes. Temperature changes are a result of pressure and force applied.

Pressure Tools The brake system can be diagnosed using pressure testers or gauges. This is especially true for electronic braking systems in which a failure in one valve, line, or other hydraulic can result in a diagnostic trouble code (DTC) being set. The fault may be traced down by using brake pressure gauges tapped into various places and comparing the pressure generated against the specifications or against like components such as one wheel brake against another. Figure 2-21 shows a typical kit sold as a master cylinder pressure gauge set. It can be used in areas of the system other than the master cylinder if a very high pressure gauge is included with the kit and the appropriate adapter is available. This type of kit may be most valuable on comeback jobs in which the problem is hard to trace. Connecting the gauge(s) into a master cylinder outlet immediately determines if the cylinder is generating the same pressure by each piston. The same connection can isolate a bad proportioning valve built into or directly attached to the master cylinder. Moving the gauge(s) to a frame-mounted proportioning valve can help determine if that valve is functioning properly. Locating the connection at the caliper end of the two front brake hoses can help the technician diagnose the proper application or release of the fluid to each wheel. If the pressure in one wheel fails to increase with the matching wheel, then there is probably a blockage in the hose. A blockage may also be identified if the two pressures do not decrease the same amount when the brakes are released.

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Figure 2-21  Typical kit sold as a master cylinder pressure gauge set.

WARNING  Ensure that the connection of the gauge to the system is tight and leak-free. Wear safety glasses when using pressure gauges for diagnosing and testing. Apply just enough force to the brake pedal to charge the system and check for leaks. If leak-free, apply normal pedal pressure. When possible, do not get in the same plane as the gauge or system connection. Brake systems generate high, dangerous pressures and leaking fluid could be injected into the flesh or eye over a distance of several feet.

SELECTION, STORAGE, AND CARE OF TOOLS Brake system service requires a wide variety of tools. Many of these tools are the common hand and power tools used in all types of automotive service. Other tools are more specialized and are used only for specific brake system testing and repair. Measuring tools are particularly important in brake service work. Brake service involves the precision measurement of rotors, brake drums, and other components where measurements as small as one ten-thousandth of an inch (0.0001 in.) can determine the serviceability of a part. To work quickly, safely, and efficiently, the right tools for the job must be available. Professional service technicians use quality tools and keep them clean, organized, and within reach. Any tool should feel comfortable and balanced, and the tool’s finish should be smooth for easy cleaning. A roll cabinet (Figure 2-22), tool chest, and smaller tote tray are standard items used to store and carry the tool set. Store cutting tools such as files, chisels, and drills in separate drawers to avoid damaging the cutting edges. Keep the most frequently used tools at hand, and keep tool sets such as wrenches, sockets, and drill bits together. Leaving a tool on a workbench is the first step in losing it. Make a habit to return frequently used tools, such as screwdrivers, to the tool chest or tote tray after each use. Keep delicate measuring tools, such as micrometers, in their protective cases and store in a clean, dry area. After each use, clean the tool using a lightly oiled lint-free cloth.

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The best method of tracking tools is the use of tool control equipment. The equipment may be a cheap socket rail and wrench holder to expensive full-blown versions sold by tool manufacturers with perfect cutouts for each tool in the box. Most technicians find something in the middle to control their tools.

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Figure 2-22  A typical tool set for an experienced technician.

Common tools are usually the technician’s personal set. Many technicians are buying expensive diagnostic tools and equipment formerly purchased by the shop.

SERVICE TIP  A few years back an at-work survey was taken by several a­ gencies concerned with technician efficiency and time management. About 100 experienced technicians were observed during their normal work day and their actions were noted in regard to their productivity. It was found that the average technician lost 20 minutes a day looking for his or her personal tools. Doesn’t sound like much until the loss of profits to the technician and business is calculated. Consider the technician is making $20 per hour flat rate. Twenty minutes a day equals 1.6 hours weekly, 6.6 hours monthly, 75 hours annually (11 1/2 months). That is about a $1,500 loss to the technician without even considering the 75 hours that could have been spent on other jobs and maybe reaping even more salary. Of course, the shop lost 75 hours of labor income also.

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COMMON HAND TOOLS Both basic and specialized brake tools are discussed in the following paragraphs.

Wrenches To work on late-model brake systems, metric wrenches are needed. Metric wrenches are sized in increments of 1 mm. Wrenches are either boxed or open ended. A box wrench (Figure 2-23) completely encircles a nut or bolt head. It is less likely to slip and cause damage or injury. But when clearances are very tight, it may not be possible to place a box wrench around the nut or bolt. Open-end wrenches may help solve the problem of tight clearances. They have open, squared ends and grasp only two of the nut’s four or six flats (Figure 2-24). Open-end wrenches are more likely to slip than box wrenches but may be the only alternative in a tight spot. An open-end wrench is normally the best tool for turning the nut down before final tightening or for holding a bolt head. To reduce cost and storage space, a set of combination wrenches that have an openend wrench on one end and a box wrench on the other is desirable. Both ends are sized the same and can be used interchangeably on the same nut or bolt.

Caution Do not use an openend wrench on a bleeder screw. The awkward locations of many bleeder screws almost ensure that an open-end wrench will slip and round off the screw shoulders. Avoid using a twelvepoint box wrench on a bleeder screw; use a six-point bleeder valve wrench whenever possible.

Flare-Nut (Line) and Bleeder Screw Wrenches Flare-nut wrenches (Figure 2-25) should be used to loosen or tighten brake line or tubing fittings. Using open-end wrenches on these fittings will tend to round the corners of the nut, which are typically made of soft metal and can distort easily. Flare-nut wrenches surround the nut and provide a better grip on the fitting. A section is cut out so that the wrench can be slipped around the brake line and dropped over the flare nut. Once loosened, an open-end wrench can be used to complete the removal. Special bleeder valve wrenches often are used to open bleeder screws (Figure 2-26). Bleeder valve wrenches are small, six-point box wrenches with strangely offset handles for access to bleeder screws in awkward locations. The six-point box end grips the screw more securely than a twelve-point box wrench can and avoids damage to the screw.

Square head bolt 5/8 in

ch

Hex head bolt

⅝ inch

⅝ inch

5/8 in

ch

Figure 2-23  Assorted box-end wrenches.

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Figure 2-24  An open-end wrench grips only two flanks (sides) of a nut or bolt head.

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Chapter 2

Figure 2-25  Use flare-nut (line) wrenches, not open-end, to loosen tube fittings (flare nuts).

Figure 2-26  Brake bleeder valve wrenches are used to get into the awkward locations of many bleeder screws.

SERVICE TIP  Torque wrenches must be handled carefully and must be properly stored. Torque wrenches should be backed down (set) to zero before storing. The wrench’s calibration can be knocked off by rough handling. Torque wrenches should be recalibrated about every 12 months.

Torque Wrenches Caution Use a torque wrench for tightening purposes only. Do not use this tool to break nuts or bolts loose. Some torque wrenches will break if used to break fasteners loose.

Torque wrenches measure the torque, or twisting force, applied to a fastener. Many fasteners such as caliper mounting bolts, bleeder screws, and brake hose-to-caliper fasteners must be tightened to a torque specification that is expressed in footpounds or newton-meters. Some bleeder screws may require an inch-pound torque wrench. Torque wrenches are available with 1/4-inch, 3/8-inch, and 1/2-inch drives in manual and electronic version. Common torque wrench designs include the dial type (Figure 2-27), the beam and break-over types (Figure 2-28), and the electronic digital-readout type. These all have a scale that measures turning effort as the fastener is tightened. With a break-over torque wrench, the desired torque is dialed in. The wrench then makes an audible click when you have reached the correct force.

Figure 2-27  Dial-type torque wrench.

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Figure 2-28  Beam-type torque wrench (top), breakover torque wrench (center), and an electronic torque wrench (bottom).

SPECIAL BRAKE TOOLS Many tools are designed for a specific purpose. Car manufacturers and specialty tool companies work together to design and manufacture special tools required to repair cars. Most special tools for brake service are listed in carmakers’ service information. Special tools needed for routine brake service procedures are discussed in this Shop Manual. Following are brief descriptions of some of the special tools used in brake service.

Hold-Down Spring and Return Spring Tools Brake shoe return springs used on drum brakes are very strong and require special tools for removal and installation. Although mass retailers offer some brake tools, they are designed for the do-it-yourself vehicle owner. The tools are excellent for that use but tend to fail quickly under typical shop operations. Most return spring tools have special sockets and hooks to release and install the spring ends. Some are built like pliers (Figure 2-29). Hold-down springs for brake shoes are much lighter than return springs, and many such springs can be released and installed by hand. A hold-down spring tool looks like a cross between a screwdriver and a nut driver. A specially shaped end grips and rotates the spring retaining washer.

Drum Brake Adjusting Tools Although almost all drum brakes built in the last 50 years have some kind of self-adjuster, the brake shoes still require an initial adjustment after they are installed. The star wheel adjusters of many drum brakes can be adjusted with a flat-blade screwdriver. Brake adjusting spoons (see Figure 2-29) and wire hooks designed for this specific purpose can make the job faster and easier, however.

Boot Drivers, Rings, and Pliers Dust boots attach between the caliper bodies and pistons of disc brakes to keep dirt and moisture out of the caliper bores. A special driver (Figure 2-30) is used to install a dust boot with a metal ring that fits tightly on the caliper body. The circular driver is centered on the boot placed against the caliper and then hit with a hammer to drive the boot into place. Other kinds of dust boots fit into a groove in the caliper bore before the piston is

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Chapter 2

Spoon

Retaining spring tools Wheel cylinder clamp

Retaining spring pliers

Return spring tool

Figure 2-29  Special brake tools include adjusting spoons for drum brakes (top), wheel cylinder clamps (top center), brake spring pliers (bottom center), and return spring tools (bottom).

Dust boot installer

Dust boot pliers

Figure 2-30  This driver and special pliers are used to install dust boots on calipers.

installed. Special rings or pliers (see Figure 2-30) are then needed to expand the opening in the dust boot and let the piston slide through it for installation.

Caliper Piston Removal Tools A caliper piston can usually be slid or twisted out of its bore by hand. Rust and corrosion (especially where road salt is used in the winter) can make piston removal difficult. One simple tool that helps with the job is a set of special pliers that grip the inside of the piston and let you move it by hand with more force (Figure 2-31). These special pliers work well on pistons that are only mildly stuck. For a severely stuck caliper piston, a hydraulic piston remover can be used. This tool requires that the caliper be removed from the car and installed in a holding fixture. A hydraulic line is connected to the caliper inlet and a hand-operated pump is used to apply up to 1,000 psi of pressure to loosen the piston. Because of the danger of spraying brake fluid, always wear eye protection when using this equipment. There are some special ratchet-type tools used to compress the caliper piston back into its bore (Figure 2-32). This is necessary to provide room for new pads to fit over

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Figure 2-31  These special pliers are used to remove pistons from calipers.

65

Figure 2-32  This tool is very useful for winding (screwing) in the caliper on a rear disc caliper. It may also be used to push the piston in on the standard front disc calipers.

the rotor. The tool can be used to compress front pistons, but it is especially good on rear disc calipers because many of them ratchet outward as their self-adjusting mechanism. Chapter 7 on disc brake service contains specific procedures and safety precautions for using compressed air to remove a caliper piston. Follow the instructions and observe the required precautions in Chapter 7 to prevent injury and damage to vehicle parts.

Brake Cylinder Hones Cylinder hones (Figure 2-33) are used to clean light rust, corrosion, pits, and built-up residue from the bores of master cylinders, wheel cylinders, and calipers. A hone can be a very useful—sometimes necessary—tool when you have to overhaul a cylinder. A hone removes material, makes the bore bigger, and must be used accordingly. A hone will not, however, save a cylinder with severe rust or corrosion. Another kind of hone is the brush hone. It has abrasive balls attached to flexible metal brushes that are, in turn, mounted on the hone’s flexible shaft. In use, centrifugal force moves the abrasive balls outward against the cylinder walls; tension adjustment is not required. A brush hone provides a superior surface finish and is less likely to remove too much metal as is a stone hone. Ideally, hones are used only on larger brake components. Generally, a damaged caliper, wheel cylinder, or master cylinder on a light vehicle is replaced rather than rebuilt. Larger vehicles, having much larger components, can be honed and rebuilt cheaper. It is desirable to use only the brush-type hone because less material is removed. The stone-type hones should be used only when absolutely necessary, and, even then, the technician must consider the ramifications of making the cylinder bore and pistons larger. Even a small change of a few thousandths of an inch in bore and piston diameters will alter the vehicle’s braking characteristics to some extent. It is recommended that no more than one pass be made in a cast-iron brake component. Aluminum wheel cylinder bores should never be honed. Either kind of hone must be lubricated with brake fluid during use. Do not use a petroleum-based lubricant. After honing a cylinder, flush it thoroughly with denatured alcohol to remove all abrasives and dirt.

Figure 2-33  Adjustable brake cylinder hone.

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Brake pedal effort gauge

Figure 2-34  A brake pedal effort gauge measures the force applied to the brake pedal.

Brake Pedal Effort Gauge The brake pedal effort, or force, gauge (Figure 2-34) is used more and more often to test and service modern brake systems. Some carmakers specify the use of this gauge when checking brake pedal travel and effort or when adjusting the parking brakes. The assembly has a hydraulic plunger and gauge that measures the force applied by your foot in pounds or in metric newtons. The gauge assembly is mounted on a steel bracket that can be attached to a brake pedal.

Tubing Tools Caution Do not attempt to hand bend a pipe or tubing. In most cases the bend will crimp and weaken the pipe or tubing material, split the material, or block the pipe or tubing.

The rigid brake lines or pipes of the hydraulic system are made of steel tubing to withstand high pressure and to resist damage from vibration, corrosion, and work hardening. Although copper is flexible and easy to work with, copper tubing cannot be used for brake lines because it cannot withstand high pressure and is susceptible to breaking due to vibration. Rigid brake lines often can be purchased in preformed lengths to fit specific locations on specific vehicles. Straight brake lines can be purchased in many lengths and several diameters and bent to fit specific vehicle locations. Even with prefabricated lines available, there may be occasions to cut and bend steel lines and form flared ends for installation. The common tools should include: ■■ ■■ ■■ ■■

A tubing cutter and reamer Tubing bender A double flaring tool for SAE flares An ISO flaring tool for European-style ISO flares

A tubing cutter is used to cut a pipe or hose at a flat angle. A pipe reamer is used to smooth the interior where the cutter broke through the metal. A tubing bender is a collection of interchangeable curved sections used to bend a pipe to the correct radii without crimping. The curved sections must fit the pipe’s outside diameter. Figure 2-35 shows some of these tubing tools. Their uses are explained in detail in Chapter 5 of this manual, along with the subjects of forming and installing brake lines.

POWER TOOLS Power tools, whether electric or pneumatic (air), save time and energy. Stationary power tools such as bench grinders, brake lathes, and air compressors are part of the shop equipment. The next section outlines some of the necessary inspection and use of power tools.

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Figure 2-35  A tubing cutter, tubing bender, and flaring tools are used to create brake lines.

General Safety Guidelines Portable power tools are powered by electricity or air (pneumatic). Never operate a power tool without being properly trained in its use. Always use a tool for the job it was designed to do and keep all guards in place and in working order. Follow these general safety practices with all power tools: 1. Always wear the proper eye and ear protection. Gloves and a face shield are required when operating air chisels or air hammers. WARNING  Do not use electric power tools while standing on a damp floor or ground. Even a properly grounded tool could cause a shock if an easier path to ground is available to the electrical current.

2. All electrical tools, unless they are the double-insulated type, must be grounded. Replace damaged or frayed power cords (Figure 2-36), and do not use a two-prong electrical adapter to plug in a three-prong, grounded piece of equipment. Never use a grounded piece of equipment that has the third ground plug removed. 3. Never try to make adjustments to, lubricate, or clean a power tool while it is running or plugged in. Keep all guards in place and in working order. 4. Be sure pneumatic tools and lines are attached properly. 5. Turn off and unplug all portable power tools when not in use, and return all equipment to its proper place. When operating stationary power tools such as brake lathes and grinders: 1. Always wear eye and ear protection. 2. Make sure that all others are clear of the power tool before turning on the power. Damaged cord

Missing ground terminal

Defective

Correct

Figure 2-36  Replace damaged power cords, and do not use an electric plug with the third grounding terminal removed.

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Caution When cleaning and drying bearings of any type with compressed air, ensure that the bearing cannot spin. The bearing can spin at high speed and disintegrate, causing damage.

Caution Do not use an impact wrench to tighten critical fasteners or parts that may be damaged by the hammering force of a wrench.

3. Be sure all machine safety guards are in the correct position before starting the machine. 4. The user should start the power tool and remain with it until it is turned off and it has come to a complete stop. 5. Stay clear of power tools being operated by others. 6. Do not talk to or distract someone who is using a power tool. 7. Do not operate any machine without receiving instructions on the correct operating procedures. Read the owner’s manual to learn the proper applications of a tool and its limitations. Make sure all guards and shields are in place. Remove all key and adjusting wrenches before turning the tool on. 8. Give the machinery your full attention. Do not look away or talk to fellow students or workers. Keep the work area clean and well lighted. Never work in a damp or wet location. 9. Do not abuse electrical cords by yanking them from receptacles or running over them with vehicles or equipment. 10. Inspect equipment for any defects before using it. Make all adjustments before turning on the power. Whenever safety devices are removed to make adjustments, change blades or adapters or make repairs, turn off and unplug the tool. Lock and tag the main switch, or keep the disconnected power cord in view at all times. 11. Always wait for the machine to reach full operating speed before applying work. 12. Do not leave the power tool until it has come to a complete stop. Allow a minimum of 4 inches between hands and any blades, cutters, or other moving parts. Do not overreach; be sure to keep the proper footing and balance at all times.

Compressed Air Safety Compressed air is used in most shops to inflate tires, operate air tools, and blow dry parts. An air compressor in the shop sends air under pressure through air lines to flexible air hoses. Badly worn air hoses will burst under pressure. The fittings on the ends of an air hose are attached with special crimped connectors that can withstand several hundred pounds of pressure. Air hose fittings should never be attached with hose clamps. Replace worn hoses to prevent accidents. The discharge of high-pressure air through a blowgun nozzle can injure the face or body. Never pull the trigger when the gun is pointed directly toward anyone. Be sure that an air nozzle used for cleaning has a safety tip that limits air outlet pressure to 30 pounds per square inch (psi) when the nozzle tip is blocked or dead ended (Figure 2-37). This type of nozzle is commonly referred to as an OSHA-approved nozzle. Air pressure regulator with outlet pressure less than 30 psi Safety blow gun with pressure relief device

Figure 2-37  The nozzle to the left is the most common in an automotive shop. It is also known as an OSHA air nozzle.

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When an air nozzle is used to clean parts, direct the airflow away from yourself and other personnel. Never use an air nozzle to dust off clothing or hair. Wear safety glasses when working with pneumatic equipment. Do not look into the discharge nozzle while trying to find out if the nozzle is clogged. Check hose connections before turning on the air. When turning air on or off, hold the air hose nozzle to prevent it from whipping. WARNING  Never blow brake dust off a part with compressed air. The dust contains particles that could enter the lungs. WARNING  Make sure you know how to operate a power tool before using it. Carelessness or mishandling of power tools can cause serious injury.

Impact Wrenches An impact wrench (Figure 2-38) hammers or impacts a nut or bolt to loosen or tighten it. Removing wheel nuts from wheels is a common job for an impact wrench. Light-duty impact wrenches are available in three drive sizes: 1 4 inch, 3 8 inch, and 1 2 inch; and two heavy-duty sizes: 3 4 inch and 1 inch. Sockets for use with an impact wrench are special heavy, hardened sockets to withstand the blows of the impact hammer. Sockets for an ordinary hand ratchet or breaker bar must not be used with an impact wrench because they may shatter and cause damage or injury. Many technicians use torque sticks to install wheel assemblies quickly. Do not use torque sticks on other assemblies or to remove fasteners.

Air Ratchet Air ratchets are used for general disassembly or reassembly work. Because they turn sockets without a jarring impact force, air ratchets can be used on most parts and with ordinary sockets. Air ratchets typically have a 3 8 -inch drive (Figure 2-39). Air ratchets are not torque sensitive. After snugging a fastener down with an air ratchet, a wrench must be used to set the final fastener tightness. WARNING  Always maintain control of air ratchets. When a fastener begins to torque down, the ratchet will attempt to rotate itself instead of the fastener. Fingers can be mashed or cut, and damage to the component or fastener may occur.

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Caution The chrome plating on a standard socket will chip if used on an impact wrench. The chip can embed itself in the skin causing a very painful and sometimes serious wound. If embedded in the eye, the chrome can cause very serious eye infection and possibly some vision loss.

Caution Brake lathes have extreme turning torque when in operation. Keep the hands and clothing away from the work being machined and away from the rotating arbor. The brake lathe can quickly pull clothing and limbs into the rotating components, and the only option is to shut the lathe down immediately. Serious injury can result from clothing caught in the lathe’s action.

Figure 2-38  An impact wrench is a high-torque power wrench that loosens and removes fasteners by hammering them.

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Figure 2-39  An air ratchet speeds fastener removal and installation.

BRAKE LATHES Brake lathes are special power tools used only for brake service. They are used to turn and resurface brake rotors and drums (Figure 2-40). Turning involves cutting away very small amounts of metal to restore the surface of the rotor or drum. The traditional brake lathe is an assembly mounted on a stand or workbench. This so-called bench lathe requires that the drum or rotor be removed from the vehicle and mounted on the lathe for service. No person should ever operate a power tool without proper training. Training may consist of reading a pamphlet or attending formal classes. When assigned to use a machine, notify the supervisor or instructor if training has not been received. As the drum or rotor is turned on the lathe spindle, a carbide steel cutting bit is passed over the drum or rotor friction surface to remove a small amount of metal. The cutting bit is mounted rigidly on a lathe fixture for precise control as it passes across the friction surface. Obviously a brake drum must be removed from its axle or spindle to turn it on a lathe. The friction surface of a rotor is exposed, however, when the wheel, tire, and caliper are removed. Then it is possible to apply a cutting tool to the rotor friction surface without removing the rotor from the car. With the universal adoption of disc brakes, on-car brake lathes were developed for rotor service.

Figure 2-40  A typical bench brake lathe for machining (turning) drums and rotors.

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Figure 2-41  A typical on-car lathe for turning disc brake rotors.

An on-car lathe is bolted to the vehicle suspension or mounted on a rigid stand to provide a stable mounting point for the cutting tool (Figure 2-41). The rotor may be turned either by the vehicle engine and drive train (for a front-wheel-drive car) or by an electric motor and drive attachment on the lathe. As the rotor is turned, the lathe cutting tool is moved across both surfaces of the rotor to refinish it. An on-car lathe not only has the obvious advantage of speed, it rotates the rotor on the vehicle wheel bearings and hub so that these sources of runout or wobble are compensated for during the refinishing operation. Most drum and rotor lathes include attachments for applying a final surface finish to the rotor or for grinding hard spots on drums. Chapter 7 covers disc brake rotors servicing and machining, and Chapter 8 covers drum brakes.

LIFTING TOOLS Lifting tools are necessary for most brake service procedures and are usually provided by the shop. Correct operating and safety procedures should always be followed when using lifting tools.

Jacks Jacks are used to raise a vehicle off the ground. Two basic kinds of jacks are found in most shops: hydraulic and pneumatic. The most popular jack is the hydraulic floor jack, which is classified by the weight it can lift: 1 1 2 tons, 2 1 2 tons, or more. A hydraulic floor jack is operated by pumping the handle up and down. A pneumatic portable floor jack operates on compressed air from the shop’s air supply.

Safety Stands Whenever a vehicle is raised by a jack, it must be supported by safety stands (Figure 2-42). Never work under a car with only a jack supporting it; always use safety stands. The hydraulic seals of a floor jack can let go and allow the vehicle to drop. Check in the vehicle service information for the proper locations for positioning the jack and the safety stands. Always follow the guidelines for each vehicle.

HOIST SAFETY Most brake service requires that the vehicle be raised off the floor. If an automobile were to fall from the hoist, the person working underneath would be seriously injured. Great care must be taken in using hoists or lifts. Always make sure the vehicle is properly placed

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Caution When using any lift for the first time, learn the control operation by raising and lowering it without a vehicle in place.

Figure 2-42  Always use safety stands to support a car after it has been raised with a floor jack.

on the hoist (lift) before raising it, and always use the safety locks to prevent the lift from coming down unexpectedly. Hoists use electricity, hydraulics, or compressed air for power. There are several styles of hoists. The single-post lift is simple to operate and can be adjusted quickly for any size vehicle by swinging the four large pads under the vehicle frame. The large center post, however, makes working on the middle of the vehicle difficult. To work on the center of the vehicle, a twin-post lift can be used (Figure 2-43). Its two posts lift the vehicle by its two sides.

Figure 2-43  A twin-post hoist provides good access to undercar components as well as to the brakes.

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WARNING  Refer to service information before lifting any vehicle to identify the proper locations for lifting. Failure to use the correct lifting points is dangerous and may cause damage or injury.

To ensure safe operation of a hydraulic lift, follow these ten guidelines: 1. Inspect each lift daily. 2. Never operate a lift if it does not work properly or if it has broken or damaged parts. 3. Never overload a lift. The rate capacity of the lift is listed on the manufacturer’s nameplate. Never exceed that rating. 4. Always make sure the vehicle is properly positioned before making the lift. Refer to service information before lifting any vehicle to identify the proper lifting points (Figure 2-44). 5. Never raise a vehicle with someone in it. 6. Always keep the lift clean and clear of obstructions. 7. Before moving a vehicle over a lift, position the arms and supports to allow for free movement of the vehicle over the lift. Never drive over or hit the lift arms, adapters, or supports because this may damage the vehicle or the lift. 8. If the vehicle being lifted is equipped with some form of air suspension, turn off the air suspension system. The switch is typically located in the trunk. 9. Carefully load the vehicle onto the lift, and align the lift arms and contact pads with the specified lift points on the vehicle. Raise the lift until it barely supports the vehicle, then check the contact area of the lift. 10. Always lock the lift into position while working under the raised vehicle. 11. Before lowering the lift, make sure all tools and other equipment are removed from under the vehicle. Also make sure no one is standing under or near the vehicle as it descends.

All lifts or hoists have automatic locking devices. After lifting the vehicle to the correct working height, set the locks before beginning work.

Do not lift or support on track bar Drive-on hoist

Frame-contact hoist

Twin-post hoist

Unibody Car

Drive-on hoist

Twin-post suspension hoist

Frame-engaging hoist

Frame Car

Figure 2-44  If there is any doubt about the vehicle’s lift points, consult service information.

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Caution Do not depress the brake pedal when pressure brake bleeding equipment is being used. This could damage seals and piston cups within the brake system.

When used correctly, a hydraulic lift (hoist) is the safest, most convenient lifting tool. It allows the technician to raise the vehicle high enough to work comfortably and quickly.

SERVICE TIP  Place only DOT 4 brake fluid in the new fluid reservoir. DOT 4 can be used to replace DOT 3 in all standard hydraulic brake systems, but DOT 3 should not be used to replace DOT 4. Synthetic brake fluids may be used in place of either DOT 3 or DOT 4, but most customers and shops are not willing to pay the extra cost of synthetics. Never use silicone-based brake fluid in a machine used to service DOT 3 or DOT 4 systems. If the shop does enough silicone-based systems, then separate machines are required or just use the manual method to bleed or flush the brake system.

Various safety features prevent a hydraulic lift from dropping if a seal does leak or if air pressure is lost. Before lifting a vehicle, make sure the vehicle is properly placed on the lift, and always use the safety locks to prevent the lift from coming down unexpectedly. Always refer to the shop information before lifting any vehicle to identify the proper locations for lifting. When using any lift for the first time, learn the control operation by raising and lowering it without a vehicle in place.

PRESSURE BLEEDERS Pressure bleeding is a fast and efficient way to bleed a brake system for two reasons. First, the master cylinder does not have to be refilled several times, and second, the job can be done by one person. A pressure bleeder is a tank separated into two sections by a flexible diaphragm. The top section is filled with brake fluid. Compressed air is fed into the bottom section, and as the air pushes on the diaphragm, the brake fluid above it also is pressurized. A pressure bleeder is normally pressurized to about 30 psi. Higher pressures should be avoided because fluid may be forced rapidly through the hydraulic system, causing a swirling or surging action. This, in turn, may actually create air pockets in the lines and valves and make bleeding difficult. A supply hose runs from the top of the tank to the master cylinder. The hose is connected to the master cylinder by an adapter fitting that fits over the reservoir, taking the place of the reservoir cap. These adapters exist in different shapes for the different types of reservoirs, including the plastic reservoirs on some of the newer vehicles. The pressurized brake fluid flows into the master cylinder and out through the brake lines, quickly forcing air out of the lines. Because most brake fluids (except for silicone) tend to absorb moisture from the air, always keep containers tightly capped. It is better to buy smaller containers of brake fluid and keep them sealed until needed. Taking these steps to minimize water in the brake fluid will help reduce corrosion and keep the brake fluid boiling point high throughout the hydraulic system. Another type of bleeder uses a hand-operated pump either to inject fluid into the system or to suck fluid from the system. The equipment known as the Phoenix Injector can be used to bleed all wheels or individual wheels as required (Figure 2-45). The unit comes in a basic kit with additional adaptors available as accessories.

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Bleed screw

75

Hose to fluid container

Brake fluid Caliper

Master cylinder

Figure 2-45  A Phoenix Injector™ set up to inject fluid through the brake system.

WARNING  Do not use the same pressure bleeder for silicone-based and ­ lycol-based brake fluids. The wrong type of fluid could be introduced into a g ­system and cause extensive damage and possible injury.

One new piece of equipment is a powered brake flusher/bleeder (Figure 2-46). It is capable of bleeding one wheel, a combination of wheels, or the entire brake system at once. The machine will work with antilock brake systems as well as standard systems. Most brake flushers like the one shown in Figure 2-46 have a fill line for the master cylinder which has a quick-release non-leak connector. It is attached to one of several adapters available that fit onto the master cylinder. There are four hoses that can be attached to the brake bleeder screws. There are two rear hoses and two front hoses. Another hose that may be available is labeled “vacuum,” which can be used to bleed a hydraulic clutch control or empty the master cylinder. The last 2 feet of each hose is clear plastic so the retrieved fluid can be observed. The machine operates on standard household 120-volts AC or may be attached to the vehicle’s battery. At bottom center is the reservoir for waste brake fluid with a new fluid container protruding from the top of the machine housing. When the waste container is emptied, the used brake fluid must be treated as a hazardous waste. The machine is simple to use. For a full system flush, select and install the correct adapter to the master cylinder. Connect the fill hose to the adapter. Add enough fluid to the machines’ reservoir to complete the current job. Usually a pint or two will be sufficient to flush most light trucks and passenger cars. Connect the two rear hoses to each of the rear wheel bleeder screws. Loosen the bleeder screws. Repeat this procedure for the two front hoses. Switch the machine on and select “Fluid Exchange” or “Bleed/Flush” dependent upon the machine being used. The machine will pressurize the system. Ensure there are no leaks at the master cylinder adapter. If a leak is present, shut down the machine and readjust the adapter onto the master cylinder.

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Figure 2-46  This brake flusher/bleeder can flush an entire system or just one wheel, easier, safer, and cleaner.

Caution

Do not leave excess brake fluid in the reservoir for more than a day or two and only with the filler cap installed tight. Put just enough brake fluid in the reservoir estimated to complete the current job. The fluid can become contaminated within a couple of days even in a “sealed” container.

Once the system is pressurized, the vacuum side of the machine will begin to draw old fluid from the wheel brakes. Observe the clear plastic portion of the rear hoses (the rears seem to clear first). When clean, clear brake fluid is observed, close that bleeder screw, but do not disconnect the hose. Once all hoses show clear fluid and all bleeder screws are closed, shut down the machine and disconnect and store all hoses. Remove the master cylinder adapter and install the master cylinder cap. The entire process takes about 10 minutes with little wasted fluid and results in a very clean work area with no spilled brake fluid to wipe up. Other tools used in brake bleeding operations include a large rubber syringe, used to remove fluid from the master cylinder on some systems; master cylinder bleeder tubes, used to return fluid to the master cylinder reservoir from the outlet ports during bench bleeding; and assorted line and port plugs, used to close lines and valves temporarily during service and keep out dirt and moisture.

CLEANING EQUIPMENT AND CONTAINMENT SYSTEMS The following systems and methods are used to safely contain brake dust in the workplace.

Negative-Pressure Enclosure and HEPA Vacuum Systems In a negative-pressure enclosure, brake system cleaning and inspection are performed inside a tightly sealed protective enclosure that covers and contains the brake assembly (Figure 2-47). The enclosure prevents the release of asbestos fibers into the air. The enclosure is designed so you can clearly see the work in progress. It has impermeable sleeves and gloves that let you perform the brake cleaning and inspection. Examine the condition of the enclosure and its sleeves before beginning work. Inspect the enclosure for leaks and a tight seal.

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Glovebag collection system

HEPA vacuum cleaner

Figure 2-47  This negative-pressure enclosure is used to contain brake dust during cleaning.

A high-efficiency particulate air (HEPA) filter vacuum keeps the enclosure under negative pressure as work is done. Because particles cannot escape the enclosure, compressed air can be used to remove dust, dirt, and potential asbestos fibers from brake parts. The HEPA vacuum also can be used to loosen the asbestos-containing residue from the brake parts. Once the asbestos is loose, draw it out of the enclosure with the vacuum port. The dust is then trapped in the vacuum cleaner filter. When the vacuum cleaner filter is full, spray it with a fine mist of water, then remove it and place it immediately in an impermeable container. Label the container as follows:  his container holds asbestos fiber. Avoid creating dust when removing it. Asbestos T fibers can cause cancer and lung disease. Asbestos waste must be collected, recycled, and disposed of in sealed impermeable bags or other closed, impermeable containers. Any spills or release of asbestos-containing waste material from inside the enclosure or vacuum hose or vacuum filter should be cleaned up immediately using vacuuming or wet-cleaning methods. Review the asbestos safety instructions in Chapter 1 of this Shop Manual.

Low-Pressure Wet-Cleaning Systems Low-pressure wet-cleaning systems wash dirt from the brake assembly and catch the contaminated cleaning agent in a basin (Figure 2-48). The reservoir contains water with an organic solvent or wetting agent. To prevent any asbestos-containing brake dust from becoming airborne, control the flow of liquid so that the brake assembly is gently flooded. You can use the cleaning liquid to wet a brake drum and backing plate before the drum is removed. After the drum is removed, thoroughly wet the wheel hub and the back of the assembly to suppress dust. Wash the brake backing plate, brake shoes, and brake parts used to attach the brake shoes before removing the old shoes. Some wet-cleaning equipment uses a filter. When the filter is full, first spray it with a fine mist of water, then remove the filter and place it in an impermeable container. Label and dispose of the container as described earlier.

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A high-efficiency ­particulate air (HEPA) filter is the filter that removes the smallest particulates from the air.

A HEPA filter can clean large volumes of air.

Caution Never clean brake dust with compressed air in the open shop, even if you are wearing a respirator. Asbestos fibers will be suspended in the air. Wet-cleaning tools are probably the most common brake cleaners used in the typical shop. These are cheap and easy to use, and the waste can be stored fairly easily and safely.

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Figure 2-48  Shown is a heated, low-pressure aqueous brake washer. It has a filter to trap the brake dust. The filter must be treated as hazardous waste when it is filled.

Wet-Cleaning Tools and Equipment The wet-cleaning method of containing asbestos dust is the simplest and easiest to use, but it must be done correctly to provide protection. First, thoroughly wet the brake parts using a spray bottle, hose nozzle, or other implement that creates a fine mist of water or cleaning solution. Once the components are completely wet, wipe them clean with a cloth. Place the cloth in a correctly labeled, impermeable container, and properly dispose of it. The cloth can also be professionally laundered by a service equipped to handle asbestosladen materials and can then be reused.

SERVICE TIP:  Do not be tempted to remove fingerprints and small grease spots from the friction material on brake pads or shoes with aerosol brake cleaner. Aerosol cleaners are petroleum products and will contaminate the friction materials. You can remove small dirt spots by lightly sanding them with medium sandpaper and wiping them off with denatured alcohol and a clean cloth.

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Figure 2-49  Always use a vacuum cleaner with a HEPA filter to clean the shop. This cleaner also works well in cleaning brake parts.

Cleaning with Wet-Cleaning Equipment Photo Sequence 2 shows how to use wet-cleaning equipment to clean a drum brake assembly.

Vacuum Cleaning Equipment Several types of vacuum cleaning systems are available to control asbestos in the shop. The vacuum system must have a HEPA filter to handle asbestos dust (Figure 2-49). A generalpurpose shop vacuum is not an acceptable substitute for a special brake vacuum cleaner with a HEPA filter. After vacuum cleaning, wipe any remaining dust from components with a damp cloth. Because they contain asbestos fibers, the vacuum cleaner bags and cloths used in asbestos cleanup are classified as hazardous material. Such hazardous material must be disposed of in accordance with OSHA regulations. Always wear your respirator when removing vacuum cleaner bags or handling asbestos-contaminated waste. Seal the cleaner bags and cloths in heavy plastic bags. Label and dispose of the container as described previously.

CLEANING EQUIPMENT SAFETY Parts cleaning is an important part of any brake repair job. You must often clean parts to find problems and measure for wear. Brake parts cleaning must always be done with approved equipment because of the danger of asbestos exposure.

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Photo Sequence 2 Typical Procedures for Wet-Cleaning the Brakes

P2-1 After removing the wheel assembly, position the cleaner so the run-off waste is captured in the cleaner.

P2-2 Use the wet brush to remove any brake dust from the outside of the drum. This brush is not used to clean mud or accumulated dirt from the drum. If mud is present, use a dry brush to remove it.

P2-3 Remove the drum and use the wet brush to clean the inside of the drum. Once clean, set the drum to the side.

P2-4 Use the wet brush to wash the brake components free of dust. Ensure the waste material/liquid is draining into the cleaner’s tub.

P2-5 Once the brake has been disassembled, wash the individual parts separately, holding them so the waste drains into the tub. Lay the parts on rags or a table for drying.

P2-6 After cleaning the various individual parts, complete the cleaning by washing down the backing plate.

P2-7 After cleaning is complete, check the cleaner’s waste filter and replace it if necessary. The full filter must be treated as hazardous waste and disposed of accordingly.

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Be careful when using solvents. Most are toxic, caustic, and flammable. Avoid placing your hands in solvent; wear protective gloves, if necessary. Read all manufacturer’s precautions and instructions and the Material Safety Data Sheet before using. Do not use gasoline to clean components. This practice is very dangerous. Gasoline vaporizes at such a rate that it can form a flammable mixture with air at temperatures as low as 2508F. Gasoline also is dangerous if it gets on your skin because the chemicals in gasoline can be absorbed through the skin and get into your body. Small cleaning jobs are often done with aerosol cleaners. These spray cans contain chemicals that break down dirt and grease and allow them to be removed. Do not throw empty spray containers in the trash without punching a hole in the side. If the Environmental Protection Agency inspector finds an undamaged can in the trash, she will test it for pressure. A few hours in the warm sun will build enough pressure in the can to get a warning or a citation from the inspector. Always read the warnings on the can and follow them. Wear eye protection, proper gloves, and a shop coat to prevent exposure to your skin or eyes. Always do your cleaning in a well-ventilated area. Many of the solvents used in solvent cleaning tanks are flammable. Be careful to prevent an open flame around the solvent tank. Never mix solvents. One could vaporize and act as a fuse to ignite the others. Wear neoprene gloves when washing parts. Some solvents can be absorbed through the skin and into your body. This is especially true if you have a cut on your hand. Do not blow compressed air on your hands if they get wet with solvent, as this can cause the solvent to go through your skin. Wipe up spilled solvents promptly, and store all rags in closed, properly marked metal containers. Store all solvents either in their original containers or in approved, properly labeled containers. Finally, when using a commercial parts washer, be sure to close the lid when you are finished.

SERVICE TIP  After resurfacing disc brake rotors, some technicians like to clean those rotors with aerosol brake cleaner. However, this type of solvent does not remove small particles of iron and abrasive material as well as detergent and hot water do, and it is not recommended by most carmakers. Washing the rotors with soap and water is the preferred cleaning method. Besides, brake cleaner is more expensive than soap and water.

BRAKE LUBRICANTS Special lubricants are used in brake service to aid assembly and to help prevent corrosion and mechanical seizure.

Assembly Fluid If hydraulic parts such as cylinders and calipers are overhauled, assembly fluid will help to install pistons past seals or to install piston seals into bores. Brake fluid can be used as an assembly lubricant, but special assembly fluid has a higher viscosity than brake fluid. The higher viscosity provides better lubrication and lets the fluid remain on the part until it is installed and put into service.

Brake Grease Brake grease is applied to the shoe support pads on backing plates and to moving caliper parts on disc brakes. Brake grease has a melting point above 5008F (2608C) and contains

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As with brake fluid, brake assembly lubricants should be stored in tightly capped, dry containers.

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solid lubricants that will remain in place even if the temperature rises above the grease melting point. Brake grease often can be identified by its light color (almost white). Wheel bearing grease or chassis grease should not be used in place of brake grease because when the grease is heated by brake operation, it may run onto the pads and linings and ruin them.

Rubber Lubricants Some master cylinder overhaul kits contain a small package of nonpetroleum grease for application to the rubber boot of the cylinder where the pushrod enters. This special grease should be used only on rubber boots of cylinders. Do not use it in place of assembly fluid or brake grease.

Wheel Bearing Grease Brake service often includes repacking front or rear wheel bearings. Although some multipurpose greases can be used for both chassis lubrication and wheel bearings, you must be sure that whatever grease you use is identified as suitable for wheel bearing lubrication. All greases are made from oils blended with thickening agents so that the grease will stick to the surfaces to be lubricated. Greases are identified by the National Lubricating Grease Institute (NLGI) number and by the kinds of thickeners and additives that the grease contains. The higher the NLGI number, the higher viscosity (thicker) the grease is. Almost all wheel bearing and chassis greases are NLGI number 2 greases. Most wheel bearing grease uses a lithium-based thickener for temperature resistance. Molybdenum disulfide is another common additive that improves the antiseize properties of wheel bearing grease. There is no way to tell what kind of grease was used previously on a wheel bearing. Therefore, clean away all old grease thoroughly when repacking wheel bearings and use only new grease that meets the vehicle maker’s specifications for wheel bearing service. SERVICE TIP  Ford Motor Company specifically prohibits the use of any petroleum-based brake grease on all of its cars and light trucks built since the early 1980s. Petroleum-based grease may damage the EPDM rubber parts used in Ford’s disc brakes. Ford specifies silicone grease that meets Ford specification ESEM1C171-A for all disc and drum brakes on its vehicles. Other manufacturers have followed this requirement in recent years. Check the service information.

ELECTRONIC TEST EQUIPMENT With the increasing use of ABSs, electronic controls have become part of the brake systems being serviced. For troubleshooting these systems, two basic pieces of electrical test equipment are needed—a circuit tester and a digital multimeter.

CUSTOMER CARE:  One of those little things that irritate customers during repair is having to reset the radio, power seat, CD player, and other electronic devices because the vehicle battery was disconnected. Before disconnecting the battery, connect a memory-saver battery so all of the memories are preserved. If working in an air bag area requiring a NO-POWER condition, advise the customer that you will note the radio and some presets, but ones such as the power seat memory will be lost. Most customers will understand and appreciate your thoughtfulness.

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Circuit Testers Circuit testers, or test lights, are used to identify shorted and open electrical circuits. Test light.  The most common test light, or probe light, looks like an ice pick. Its handle is transparent and contains a light bulb. A probe extends from one end of the handle and a wire and clip extend from the other end. When the clip is attached to a ground and the probe is touched to a live connector, the bulb in the handle lights up. If the bulb does not light, voltage is not available at the connector (Figure 2-50). The test light also can be reversed by connecting its wire to a voltage source and touching the probe to a possible ground. If the bulb lights, the circuit is complete, and you have found an electrical ground. Note that only the presence of voltage is shown, not the amount. LED Test Light.  A test light made with a light-emitting diode (LED) provides higher resistance than an incandescent lamp and is suitable for use on an electronic circuit (Figure 2-51). An LED test light is used in the same way as an incandescent probe light.

83

Caution Do not use a test light to test the lowcurrent circuits of an electronic control system. The incandescent lamp bulb may draw too much current and damage the electronic integrated circuits. Always test electronic circuits with a highimpedance digital voltmeter.

Self-Powered Test Light.  A self-powered test light is called a continuity tester. It is used with the power off in the circuit being tested. It looks like a regular test light, except that it has a small internal battery. When the clip is attached to one terminal of a component and the probe is touched to the other, the bulb will light if the circuit is complete. If an open circuit exists, the bulb will not light.

Multimeters The multimeter is one of the most versatile tools for diagnosing electrical and electronic systems. The most common multimeter is the volt, ohm, and milliamp meter (Figure 2-52).

Test Light

Continuity Light

Figure 2-50  A test light and a self-powered test light (continuity tester) are common electrical troubleshooting tools.

Figure 2-51  LED test lights such as this one are recommended for use on low-power electronic circuits instead of a test light.

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Figure 2-52  A digital multimeter (DMM) should always be used to check electronic circuits.

Auto ranging is a feature of an electrical test meter that lets it shift automatically from one measurement range to another for a given value such as voltage or resistance.

Such a meter is referred to as a digital volt-ohmmeter (DVOM), or a digital multimeter. Regardless of the name, this type of multimeter tests voltage, resistance, and current. As the name indicates, multimeters are multifunctional. Most measure direct current (DC) and alternating current (AC) amperes (A), volts (V), and ohms (Ω). More advanced multimeters may also test engine revolutions per minute (rpm), ignition dwell, diode connections, distributor conditions, frequency, and even temperature. Many electronic tests require very precise voltage measurement. Digital multimeters provide this accuracy by measuring volts, ohms, or amperes in tenths, hundredths, or thousandths of a unit. Several test ranges are usually provided for each of these functions. Some meters have multiple test ranges that must be manually selected. Others are auto ranging. A typical multimeter may have 18 test ranges. It may measure DC voltage readings as small as 1/10 millivolt (0.0001 volt) or as high as 1,000 volts. SERVICE TIP  When measuring a circuit for electrical values, pay attention to the small-scale indicator in one corner of the display screen. If there is no electrical value present in the circuit, many DMMs will display some numerical value that could be interpreted as the actual reading. But further observance of the display will show a scale that is not in the range the technician expected. For instance, when checking a circuit for 12 volts on an auto ranging meter a display of 2.03 may be shown. Checking the scale shows that the meter is actually reading 2.03 mV. This usually means that the correct voltage is not present and the meter is really showing some sort of background reading. The same applies to current and resistance measurements.

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Brake Service Tools and Equipment

Figure 2-53  Scan tools are essential for complete testing and bleeding of ABS control systems. A typical scan tool and accessories.

Digital meters have a high impedance—high input resistance—of at least 10 megohms (10 million ohms). Metered voltage for resistance tests is below 5 volts, reducing the risk of damage to sensitive components and computer circuits.

High impedance is high input resistance ­provided by a digital meter.

Scan Tools Scan tools (Figure 2-53) are essential for servicing most modern brake systems. The scan tool plugs into the brake system control computer and allows the reading of stored or current DTCs and system operating data that help pinpoint system problems. The scan tool is also essential for bleeding most ABS systems. The scan tool operates all the internal valves in the brake modulator so that any trapped air can be removed during an automated bleeding sequence. Many scan tools also can activate system functions to test individual components or to record a snapshot of the system in operation during a test drive.

Scan tools allow the technician to interface with the vehicle computer network.

Graphing Meters Graphing meters are commonly known as scopes or oscilloscopes. They are electronic diagnostic instruments that can graph the flow of electrical values and come in different sizes and capabilities. The digital storage oscilloscope (DSO) was at one time the most elaborate, most expensive, and a large-size unit. The typical DSO is shown in Figure 2-54. It is a small hand-held unit capable of displaying four traces or graphs at once. Each trace can be attached to a different electrical device so comparisons can be viewed simultaneously. Similar DSOs are available from most of the major vehicle tool vendors.

A digital storage ­oscilloscope is used to analyze electrical waveforms in minute detail.

ELECTRICAL PRINCIPLES Modern electronic braking systems rely on electronic actuation and control, but modern brake systems also use simple electrical circuits for basic system status checks and safety functions. For example, an electrical circuit is energized if the parking brake is applied or

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Figure 2-54  A four-trace DSO can graph and store various electronic operations by measuring volts, amperes, and resistance all at the same time for comparison data.

Electric circuits can be series circuits, parallel circuits, or series-parallel circuits.

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if fluid level in the master cylinder reservoir falls below a certain point. All of these circuits are tied into one or more brake system warning lamps on the instrument panel. When a problem exists, the warning lamp lights to alert the driver. Some vehicles with electronic instrument panels flash a written message instead of lighting a warning lamp. However, the basic circuit operation is essentially the same between the instrument panel and the warning circuit switch. Brake stop lamp circuits to the rear stop lamps and the center high-mounted brake lamp are energized when the brake pedal is depressed. These lamps warn other motorists that the brakes on the vehicle in front of them have been applied. Although most circuits involved in brake stop lamp and warning lamp operation are simple circuits, the increased use of electrical equipment on modern vehicles may make them more difficult to find and trace. Always work from the service information electrical schematics and follow the principles of electrical troubleshooting outlined later. In a vehicle electrical system, electric power flows from a power source to a load device and then back to the source of power to form a complete circuit. In addition to the power source and loads, most automotive circuits contain circuit control and protection components (Figure 2-55). The vehicle battery and alternator are the power sources that provide power for all electric circuits during startup or alternator failure. During normal operation, the alternator assumes that responsibility of providing the vehicle with electrical power. Circuit protection devices include items such as fuses, circuit breakers, and fusible links. They provide overload protection for the circuit. Circuit controllers such as switches or relays are used to control the power within a circuit. They open and close the circuit. Circuit loads may be lamps, motors, or solenoids.

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Brake Service Tools and Equipment Lamp

Lamp

87

Lamp

Fuse

Switch

Switch

+

−

+

− Battery

Battery

Figure 2-55  An electrical circuit consists of a power source (battery), a control device (switch), circuit protection (fuse), and one or more load devices (lamp).

Switch

Figure 2-56  A series circuit has the loads connected one after another with the power source.

Resistor

R1

+

Lamp

R2

R3

− Battery

Figure 2-57  A parallel circuit has several alternative (parallel) loads connected to the power source.

Switch

Lamp

+

Lamp

− Battery

Figure 2-58  A series–parallel circuit has one or more loads in series with the parallel branches and with the power source.

Series Circuit In a series circuit, the electrical load devices are connected to form one current path to and from the power source. Series circuit voltage is shared by all the components proportionally to the resistance of each. Current flows through every component in series and remains constant throughout the circuit (Figure 2-56).

Parallel Circuit In a parallel circuit, the electrical loads are connected to form more than one current path to and from the power source. Voltage is equal for each parallel current path, and current varies proportionally to the resistance of each parallel branch (Figure 2-57).

Series-Parallel Circuits A series-parallel circuit consists of some loads in parallel with each other and one or more loads in series with the power source and with the parallel branches (Figure 2-58).

SERVICE INFORMATION Service information is essential for safe, complete brake service. It is needed to obtain specifications on torque values and critical measurements such as drum and rotor discard limits. Service information also provides drawings and photographs that show where and

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Good service information, paper or computerized, is the best single all-around tool a technician can use. This applies to new technicians on their first day as well as technicians nearing retirement.

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how to perform service procedures on a particular vehicle. Tools or instruments are listed and illustrated when they are required. Precautions are given to prevent injury or damage to parts. Most automobile manufacturers rely on the Internet to supply service information to their technicians. The Internet can provide the best, most up-to-date and complete information for those vehicles. Several independent publishers reproduce carmakers’ information in aftermarket manuals and information systems. Brake parts manufacturers also often publish service information and service literature independently of vehicle manufacturers. The most common service information today is the computerized version. Paper manuals are expensive and take up a lot of storage space, a lot of different ones are required, and they are easily damaged. Computerized information offers a quick, easy method to extract specific data and usually need only a computer terminal with Internet connection. The Internet data bank is updated continually in most cases. The major vendors are Snap-on, Mitchell, and Alldata. Each offers a version of the same thing: a comprehensive data bank covering almost all years and models of vehicles back to about 1983. In addition, the more sophisticated systems can display labor times and parts. Some even offer Internet order capability so the technician can determine what part is needed and immediately order it online from a local parts vendor. Most can be tied into the service repair order and accounting programs, so, in theory at least, there is no paperwork involved. Everything from the opening of the repair order through the payment by the customer is done via the shop’s computer internal network. Although the information from different publishers varies in presentation and arrangement of topics, all service information is easy to use after a technician is familiar with their organization. Most information is divided into several sections, each of which covers different systems of the vehicle. Each section includes diagnostic, service, and overhaul procedures and has an index indicating specific areas of information.

Repair Order

Technical Service Bulletins are released by the manufacturer to advise technicians of common fixes for difficult repairs that have been discovered after regular service information has been printed. This is not the same as a recall, but should be considered repair advice for vehicles in service.

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The repair order (Figure 2-59) is a legal document and must be completed on a vehicle being repaired on the premises or on the road under the auspices of the business license. There are a few items that the technician or service manager should insist on with regard to a repair order. If the work is being performed free or at a reduced rate for a person or institution, make sure the order is completed in the same manner as a routine “for-hire” order. The only difference should be the cost of the repair, usually paid by the vehicle owner. A completely “free” repair still legally obligates the shop and employees the same as a regular customer-pay work order. The second occurrence is as rare as the free work, but both happen now and then. If during the course of the repair something is found to need service and the customer refuses to approve the work, make sure it is stated on the work order and the customer signs that the service is refused. This is especially critical if the refused service pertains to some safety aspects of vehicle operation such as bald tires or completely worn brakes. It is one thing for a customer to refuse an oil change, which may cause the shop to buy an engine. But refusal to replace the bald tire, which causes a death or injury and the shop being sued for all costs, is an entirely different matter. Ensure that the customer signs the note indicating the repair was refused. Usually repair orders are opened, completed, and paid in a routine manner. A typical repair order that has been started is shown in Figure 2-59. The repair history, the vehicle identification, and the customer’s complaint have been inserted. At this point, the technician would research the shop’s database of related Technical Service Bulletins (TSB), warranties, recalls, and, possible repair and service diagnosis. After the repair is accomplished, parts, labor, and the total cost of the repair will be added. A copy will be kept on file at the shop and a copy will be given to the customer.

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Brake Service Tools and Equipment JACK’S SHOP

Customer Information Company ______________________________ MAKE SURE YOU HAVE Name _________________________________ ALL OF THE Address CUSTOMER’S CONTACT _______________________________ INFORMATION!! ______________________________________ City __________________________________ State _________ Zip code ________________ Home: (_____) _________________ Work: (_____) _________________ Cell: (_____) _________________ Other: ( ) Description of Service

REPAIR ORDER

1234TODAY’S Some Street DATE Sometown, AA 98765 (555)123-7890

12345

DATE __ /__/___

Vehicle Information Year: _____________ Make: __________________________________ YOU MUST HAVE COMPLETE Model: __________________________________ AND ACCURATE INFORMATION Color: __________________________________ IN ORDER TO PROPERLY VIN: __________________________________ REPAIR THE VEHICLE! Engine: _________________________________ License Number: _____________ ST ________ Odometer reading: Repair Estimate

_______________________________________________Total Parts:

THIS IS ONE OF THE MOST IMPORTANT SPACES YOU NEED TO FILL IN! EXPLAIN WHAT THE CUSTOMER WANTS AND/OR WHY THE VEHICLE HAS BEEN BROUGHT INTO THE SHOP.

Time

Price

R&R Right Front Strut R&R Air Filter

2.3 0.1

138.00 6.00

STANDARD TIME FOR EACH SERVICE

______________

Total Labor: ______________ IN MOST______________ STATES, YOUR Other charges: ESTIMATE MUST BE Initial estimate: ______________ WITHIN 10% OF THE Estimate given by: FINAL YOUR Date BILL. TAKE Time TIME AND GIVE AS Phone: __________ __________ ACCURATE AN ESTIMATE In person __________ __________ AS YOU CAN! Additional authorized amount: __________ Revised estimate: ______________ Authorization given by: Date Time Phone: __________ __________

Services

EACH SERVICE PERFORMED

89

HOURLY LABOR RATE MULTIPLIED BY TIME

Totals Date completed ___/___/___ Tech _______________

Services

144.00

Part #

Description

Qty.

Price Ext. Price

Parts

80.42

JE8538 RE4949 XX3344z

Strut assembly Air filter Shop supplies

1 1 1

73.47 73.47 6.95 6.95 10.00 10.00

Shop supplies

10.00

Sub total

234.42

WHAT THETax CUSTOMER PAYS 6%

14.07

THIS INFORMATION NEEDS TO BE COMPLETE FOR ACCURATE BILLING AND FOR INVENTORY MAINTENANCE.

Total

$

248.49

Figure 2-59  This repair shows a recent history (top) and the customer’s complaint (center).

Throughout this book, the reader is told to refer to the appropriate service information to find the correct procedures and specifications. Although the brake systems of all automobiles work in much the same way, there are many variations in design, particularly for ABS and vehicle stability systems. Each design has its own repair and diagnostic procedures. Always follow the recommendations of the manufacturer to identify and repair problems. Make using vehicle service information a habit. The benefits include increased productivity, less rework, and safer working conditions.

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Chapter 2

SUMMARY ■■

■■

■■

■■

■■

■■

■■

■■

■■

■■

■■

■■

■■

Fasteners must be replaced with the same type fastener removed. The USC unit of measurement is the inch. The metric unit of measurement is the meter. Precision measuring tools include outside and inside micrometers, rule, depth micrometers, and rotor and drum micrometers. Rotor and drum micrometers are specially designed to make measuring rotors and drums quick and accurate. Vernier calipers and dial indicators may be used to measure rotors, drums, and inside measurement of calipers and wheel cylinders. Brake adjusting tools provide a quick, accurate way to initially adjust drum brakes before installing the drum. Hand tools should always be stored clean after each job. Common hand tools for brake repair are the same ones used in other vehicle repairs. Flare-nut or line wrenches and bleeder wrenches are critical hand tools for brake repairs. Special brake tools include spring tools, adjusting tools, boot or seal removers or drivers, and hones. Tubing tools are required to cut and form steel brake lines. Power tools used in brake repairs are typically the same ones used in other automotive repairs. Brake lathes are power-driven machining tools used to resurface rotors and drums.

■■

■■

■■

■■

■■

■■

■■

■■

■■

■■

■■

■■

Brake lathes may be bench-mounted or portable on-the-car types. Lifting tools include typical automotive lifts and floor jacks. Pressure bleeders make one-person brake bleeding easier and help prevent running the master cylinder during the bleeding process. Pressure bleeders create a pressure within the master cylinder reservoir that forces brake fluid past the piston cups. Vacuum bleeders apply a vacuum (suction) at the output end of the brake hydraulic system to pull fluid and air from the system. Brake cleaning systems are designed to create minimum dust and to capture the brake residue from cleaning. Brake cleaning systems may be completely sealed or use low-pressure solvent and a capture container. Brake lubricants are specifically formulated to resist heat, dust, and brake fluid contamination. Scan tools are used to diagnose some electrical or electronic faults with the brake system, particularly antilock brakes. DSOs show graphs or traces of electrical values as they actually occur. The principles of electricity within a brake system include current, voltage, resistance, conductors, power source, and load. Brake repair or informational data may be on paper or in computerized format.

ASE-STYLE REVIEW QUESTIONS 1. Technician A says metric fastener strength ratings are indicated by numbers embossed in the head of the bolt or nut. Technician B says the most common metric fastener grades for automotive use are 6.2 and 7.1. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 2. Technician A says that two different measurement systems are currently used in the United States and Canada. Technician B says these are the U.S. customary system and the International System of Units or metric system. A. A only C. Both A and B B. B only D. Neither A nor B

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3. Technician A says the basic metric units are called stem units. Technician B says for large measurements, any metric stem unit is divided one or more times by 10. For small measurements, any stem unit is multiplied one or more times by 10. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

4. Technician A says the cubic meter ( m 3 ) is the base metric unit for volume in the metric system. Technician B says the more accustomed is the common unit used for fluid volume: the liter. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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Brake Service Tools and Equipment

91

5. Technician A says the zero-point of the metric Celsius temperature scale is the freezing point of water. Technician B says the boiling point of water is 212 degrees Celsius (2128C). Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

9. Technician A says the metric pressure unit is the Pascal (Pa). Technician B says the basic Pascal unit is very large, so pressure is usually expressed in thousandths of a Pascal. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

6. Technician A says that a flare-nut wrench should be used on a line fitting to prevent damage. Technician B says once the fitting is loosened, an open-end wrench can be used to complete the removal. A. A only C. Both A and B B. B only D. Neither A nor B

10. Technician A says outside micrometers come in many different sizes, but the measurement range of the spindle is usually just 1 inch or 25 mm. Technician B says that means a 4-inch micrometer measures from 3 to 4 inches. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

7. While discussing brake cylinder honing, Technician A says It is recommended that no more than three passes be made in a cast-iron brake component. Technician B says aluminum wheel cylinder bores should never be honed. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 8. Technician A says sockets for use with an impact wrench are special heavy, hardened sockets to withstand the blows of the impact hammer. Technician B says sockets for an ordinary hand ratchet or breaker bar must not be used with an impact wrench because they may shatter and cause damage or injury. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

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Brake Service Tools and Equipment

Name ______________________________________ 

Date _________________

LINEAR MEASUREMENT PRACTICE ASE Education Foundation Correlation

93

JOB SHEET

9

This job sheet addresses the following RST Tools and Equipment tasks: Task #1 Identify tools and their usage in automotive applications. Task #2 Identify standard and metric designation. Task #3 Demonstrate safe handling and use of appropriate tools. Task #4 Demonstrate proper cleaning, storage, and maintenance of tools and equipment. Task #5 Demonstrate proper use of precision measuring tools (i.e., micrometer, dial-­indicator, dial-caliper). This job sheet addresses the following MLR task: B.1. Describe proper brake pedal height, travel, and feel. (P-1) This job sheet addresses the following AST/MAST task: B.2. Measure brake pedal height, travel, and free play (as applicable); determine needed action. (P-1) Tools and Materials • Vehicle • Rule • Micrometer Describe the vehicle being worked on: Year _____________________ Make _____________________ Model ______________________ VIN _____________________________ Engine type and size _____________________________ Procedure

Task Completed

NOTE TO INSTRUCTORS: Other devices may be used to check the student’s skill with measuring instruments. 1. Consult with the instructor for the use of a vehicle or other device to be measured with a rule.

h

  WARNING Ensure that wheel blocks are placed in front of and behind at least one wheel and the parking brake is set. Damage or injury could occur if the vehicle should move when the clutch is disengaged, or the automatic transmission is not in “PARK.” 2. Use a ruler to determine the following brake pedal heights. If vehicle has a manual transmission, the clutch pedal can also be used for the same measurements for additional practice. Engine off.

h

Brake pedal topmost height from floor  Brake pedal height at brake engagement (free play)  Brake pedal height at full brake application  If power assisted, pump pedal several times and measure pedal height from floor with full brake application  If power assist, start the engine  Brake pedal topmost height from floor  Brake pedal height at brake engagement (free play)  Brake pedal height at full brake application 

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Optional. Based on your training to this point, have you determined if a defect exists as shown by your measurements and observations? If so, what? Wrong guesses count as two (2) answers.    3. Measure a brake rotor or similar device for thickness using a brake micrometer. Specify the measurement units and then convert to other measurement units, that is, metric to U.S. customary. Make the measurements at least at six different points around the device. 1 __________ 2 __________ 3 __________ 4 __________ 5 __________ 6 __________ 7 __________ 8 __________ 9 __________ 10 __________ 11 __________ 12 __________ Optional. Based on your training to this point, have you determined if a defect exists as shown by your measurements and observation? If so, what? Wrong guesses count as two (2) answers.    4. INSTRUCTORS: Additional space is provided for more measurements if deemed necessary. 1 _______________ 2 _______________ 3 _______________ 4 _______________ 5 _______________ 6 _______________ 7 _______________ 8 _______________ 9 _______________ 10 _______________ 11 _______________ 12 _______________ 1 _______________ 2 _______________ 3 _______________ 4 _______________ 5 _______________ 6 _______________ 7 _______________ 8 _______________ 9 _______________ 10 _______________ 11 _______________ 12 _______________ 5. Clean the area and store the tools.

h

Problems Encountered    Instructor’s Response   

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Brake Service Tools and Equipment

Name ______________________________________ 

Date _________________

VEHICLE SERVICE DATA ASE Education Foundation Correlation

95

JOB SHEET

10

This job sheet addresses the following MLR task: C.1. Remove, clean, and inspect brake drum; measure brake drum diameter; determine serviceability. (P-1) This job sheet addresses the following AST/MAST task: C.2. Remove, clean, and inspect brake drum; measure brake drum diameter; determine serviceability. ( ) Tools and Materials • Vehicle or brake drum(s) (number instructor choice) • Brake drum caliper (manual or electronic) • Service information (paper or computerized) Describe the vehicle being worked on: Year _____________________Make _____________________Model _____________________ VIN __________________Engine type and size __________________ Procedure 1. Use paper or computerized service information database to collect the following service information. Drum discard diameter _______________ Drum discard diameter _______________ Drum discard diameter _______________ Drum discard diameter _______________ 2. Use the brake drum diameter to measure each drum’s diameter. Drum diameter _______________ Drum diameter _______________ Drum diameter _______________ Drum diameter _______________ 3. Compare the measurements against the specifications. Determine if the drum(s) are serviceable. Drum diameter Yes _______________No _______________ Drum diameter Yes _______________No _______________ Drum diameter Yes _______________No _______________ Drum diameter Yes _______________No _______________

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4. Of the serviceable drum(s), state the amount of metal that can be removed during machining and still retain serviceability. Drum _______________ Drum _______________ Drum _______________ Drum _______________ Problems Encountered    Instructor’s Response   

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Chapter 3

RELATED SYSTEMS SERVICE

Upon completion and review of this chapter, you should be able to: ■■ ■■ ■■ ■■

Isolate brake problems from those originating in other systems. Check and inspect tires and inflate them to proper pressures. Install tires and wheels and torque wheel nuts or bolts to specifications.

■■

Troubleshoot braking problems related to wheel bearings.

■■

Remove, clean, inspect, lubricate, reinstall, and adjust tapered roller wheel bearings.

■■

Inspect steering suspension and wheel alignment for possible causes of braking problems.

Check radial and lateral runout of wheels and tires and correct if possible.

Basic Tools Basic technician’s tool set Service information

Terms To Know Bearing driver Bearing packer Brinelling

Etching Galling Hydroplane

Road force balancers Wear-indicating ball joint

ISOLATING BRAKE PROBLEMS There are times when what appears to be a brake problem is actually a problem caused by a defect in a related system. Problems of this type are usually caused by tires or alignment. However, damaged or worn components in the steering or suspension may create problems in several systems. Experienced technicians can quickly locate the root cause using their experience and a good working knowledge of the systems involved. The first step is to listen to what the customer is saying. Ask questions on when, what, where, and what conditions. The second step is to road test the vehicle if the problem is not obvious. Before road testing the vehicle, conduct a visible inspection of the outside of the vehicle and perform some basic operational checks inside the vehicle. Make the following checks: ■■ Do the tires appear to be properly inflated? ■■ Do all tires have acceptable tread? ■■ Check the steering wheel for looseness or free play. ■■ Check the brake pedal with the engine off and operating. ■■ Does the vehicle appear to be safe for a road test? Conduct the road test on a smooth level road with minimum traffic if possible. Listen, feel, and observe for any of the following: ■■ Noise, binding, or jerking of the steering wheel ■■ Pulling or drifting to one side when the vehicle is moving ■■ Pulling or drifting as the brakes are applied lightly and then firmly ■■ Movement of the steering wheel or brake pedal during braking ■■ Noise when the brakes are applied

Special Tools Tire gauge Tread depth gauge

97

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Chapter 3

After completing the road test, use the following guidelines to separate actual brake problems from those caused by the related systems: Symptom

Cause in order of probability

Steering wheel movement/binding

Steering mechanism, wheel bearing

Pull/drift to one side, brake off

Tire inflation, alignment, dragging brake shoes/pads, wheel bearing

Pulling/drifting, brake applied

Brake inoperative one side, excessive ­positive camber

Steering wheel/brake pedal movement

Brake rotor/drum, wheel bearing, tire tread

Noise, brakes applied

Brakes pads/shoe, wheel bearing, suspension problems

Although the guidelines are general in nature, they provide a starting point for the diagnosis. Usually when a customer complains of a brake problem, it is a brake problem, but the technician must be aware of contributing causes that affect braking action. One of the most common causes is a simple lack of maintenance by the owner.

TIRE AND WHEEL SERVICE Tire and wheel problems can reduce the effectiveness of even the best brake service and, in some cases, affect the operation of the brakes themselves. The tire and wheel problems that can affect brake performance the most are tire condition, inflation pressure, and tire and wheel installation methods. The following sections explain the inspection and service procedures for troubleshooting and fixing brake problems associated with wheels and tires.

Tire and Wheel Inspection Tires that are badly worn, mismatched in size or tread condition, or incorrectly inflated can cause brake problems. Simple inspection and checking with a pressure and a depth gauge can diagnose many of these problems. SERVICE TIP  At times a pull to one side may develop after a tire rotation. If the tires are inflated properly, this may be caused by a problem in the steel belt causing a “tire pull.” Swap the two front tires side to side, and road test the vehicle. In a few instances, it may be necessary to “un-rotate” the tires or install two new tires on the front. Some road force balancers can determine the amount and direction a tire will pull by loading it during balancing the tire/wheel assembly.

Tire Inflation.  Improper inflation is the most common tire problem, and under-inflation is far more common than over-inflation. Do not rely on visual inspection to determine if a tire is inflated properly; use a pressure gauge. Over-inflation and under-inflation will both change the tire contact patch and affect brake performance. Unequal inflation from side to side can cause brake pull. Several myths and misunderstandings work against proper tire maintenance. One myth that has persisted for decades is that the sidewalls of radial ply tires are supposed to bulge. That may have been the case in the late 1960s when radials were built with higher, 78- and 80-series profiles and ran at 32-psi pressure. Today, with higher-pressure

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Related Systems Service

LF

RF

LF

RF

LR

RR

LR

RR

RWD and 4WD

99

FWD

Figure 3-1  These tire rotation patterns are recommended by most carmakers and by the Rubber Manufacturers Association.

50-, 60-, and 70-series low-profile radials, that old myth is just an excuse to ignore proper inflation pressure. A low-profile radial ply tire can be 10 pounds to 20 pounds underinflated before it will show a noticeable bulge in its sidewall. Another equally old myth is that radial tires should only be switched front to rear on the same side of the car. Manufacturing technology in the 1960s and 1970s was not what it is today. Tire molds were not as precise, and radial plies were known to acquire a rotational set or direction. In the late 1960s and early 1970s, many carmakers did recommend keeping radials continuously on the same side of the car. That has not been the case for years, however, except for high-performance directional tires. Follow the rotation patterns in current tire service manuals and owner’s manuals (Figure 3-1). Problems caused by under-inflation and lack of rotation can be compounded on tires with a mud-and-snow tread design. When a tread block hits the pavement during braking, it has the same effect as a pencil eraser hitting a sheet of paper. The rubber wears at an angle. If the tires are not rotated to reverse the direction of wear, the wear becomes excessive and leads to chunking. Under-inflation increases this kind of wear because the rubber tends to dig into the pavement more. Mismatched Tires and Tire Wear.  Equal braking performance at each wheel requires that the tires at all four wheels be the same type, size, and condition. Tires of different size, construction, or tread design will have different traction characteristics. Unequal tire diameters on the same axle can cause the vehicle to pull during braking and to wander under other driving conditions. Tire diameter can be measured when troubleshooting brake problems by placing a straightedge horizontally across the wheel and tire at the wheel center point. Then place smaller straightedges across the tread, perpendicular to the tire sidewall. A better, more accurate method is to measure the circumference of the tire, inflated and loaded, using a tape measure (Figure 3-2). This is also the rolling circumference. The best way to eliminate tire differences as a cause of brake problems is to mount identical tires on all four wheels. If this is not possible, tires of the same size and tread condition should be paired on each axle. All modern car and light truck tires have tread wear indicators that appear as continuous

Incorrectly sized tires can cause engine, vehicle, and electronic braking system problems. In some cases, a new calibration can be programmed into the control modules to correct the wheel speed readings for the tire size.

bars across the tread when the tread wears down to the last 2/32 (1/16) inch (Figure 3-3). When a tread wear indicator appears across two or more adjacent grooves, the tire should be replaced. A tread depth can be used to measure with a tire tread gauge. Although 2/32 inch is the minimum safe tread depth, a tire should be replaced before it wears to this

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Chapter 3 Tire circumference (distance around tire)

Wear-indicator bars

Figure 3-2  A method to determine the rolling circumference of an inflated and loaded tire.

Special Tools Lift or jack with stands, Impact tools, Torque wrench

Conditions

Figure 3-3  When wear-indicator bars appear across several tread grooves, the tire is ready for replacement.

point to ensure vehicle safety and proper braking performance. Tire wear can be due to several causes (Figure 3-4). Uneven braking also can result from variations in tread pattern and condition from side to side and from front to rear. Dry and wet pavement will affect braking performance based on tread condition. A slick tire may have a high coefficient of friction on dry pavement and good stopping power. On wet pavement, the same slick tire will hydroplane on a layer of water trapped between the tread and the pavement. Hydroplaning occurs when the tire is lifted from the road surface by the water on the road. Consider that a water skier skis on top of the water, but he or she cannot ski through the water. Because liquid cannot be

Rapid wear at shoulders

Rapid wear at center

Underinflation or lack of rotation

Overinflation or lack of rotation

Cracked treads

Wear on one edge

Feathered edge

Bald spots

Excessive camber

Incorrect toe

Unbalanced wheel

Scalloped wear

Effect

Causes

Lack of rotation of tires or worn or out-ofalignment suspension

Underinflation or excessive speed

Or tire defect

Corrections

Adjust pressure to specifications. When tires are cool, rotate tires.

Adjust camber to specs

Adjust toe to specs

Dynamic or static balance wheels

Rotate tires and inspect suspension

Figure 3-4  Tire wear may be caused by several problems related to the suspension and steering system and lack of preventive maintenance.

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compressed, the water on the road acts the same as the water acts on water skis, lifting the tire and eliminating friction. It must be remembered that new tires with good tread may also hydroplane if the tread is not formed to shed or direct water from under the tire. The traction and braking performance are then the opposite of what they are on dry pavement.

Tire and Wheel Installation Two factors of tire and wheel installation that affect braking are the wheel nut or bolt torque and the sequence in which the wheel nuts or bolts are tightened. If wheel nuts or bolts are overtightened or tightened unevenly or in the wrong sequence, the brake drum or rotor can be distorted. This distortion creates runout in the drum or rotor that, in turn, causes pedal pulsation and uneven brake application. To install a tire and wheel, be sure that the mounting surfaces of the wheel and the brake drum or rotor are free of dirt, rust, burrs, or any condition that could prevent proper installation and create wheel runout. Clean the wheel, drum, or rotor with a wire brush if necessary. Lift the wheel straight onto the drum or rotor, being careful not to damage the threads on the studs. Then install the nuts or bolts. Do not use any lubricant or antiseize compound on wheel nut or bolt threads. Lubricants and anti-seize compounds will increase the torque applied to the nuts or bolts and result in overtightening.

Special Tools Lift or jack with stands Dial indicator

SERVICE TIP  There is a special tool available that will reduce cleaning time and efficiency. It is a drill-driven wire brush that fits over the wheel stud and cleans the hub and/or rotor area directly around the stud. It is also used to clean the remainder area of the hub and/or rotor.

Every vehicle manufacturer specifies torque values for wheel nuts and bolts. For most passenger cars, these range from 50 foot-pounds to 100 foot-pounds. Specifications for individual vehicles can be found in tire service manuals and owner’s manuals. Again, these are dry specifications, without any lubricant or anti-seize compound. An impact wrench can be used to remove a wheel from a vehicle but should not be used to reinstall the wheel unless a torque stick is used. Wheel nuts and bolts should always be installed with a torque wrench or with a specified torque stick used with an impact wrench (Figure 3-5). A torque stick is an extension for an impact wrench that includes the correct size socket for the wheel nut and that acts as a torsion bar to limit the

Figure 3-5  A torque stick can be used with an impact wrench for correctly applying torque to lug nuts. Torque sticks are color coded as to socket size and torque limit. Never use a torque stick to loosen fasteners.

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1

1

3 3

4

4

5

2

2

Four-nut wheel

Five-nut wheel

1

3

6

5

4

2

Six-nut wheel

Figure 3-6  Wheel nut tightening patterns.

Caution A torque stick that is used to remove fasteners can shatter. The splinters can embed in the shin or eyes and cause serious injury. Never use a torque stick to loosen fasteners.

torque applied by the impact wrench. Torque sticks come in sets that contain several sticks with specific torque ratings. Do not use a torque stick to remove a wheel nut or bolt. The sequence in which the wheel nuts are tightened is as important as the torque value. All tightening sequences are crisscross patterns in which the nuts or bolts are tightened alternately from one side of the wheel to the other (Figure 3-6). Of equal importance, the nuts or bolts should not be tightened to the final torque value in one step. They should be tightened in three or four stages to one-half, three-quarters, and full torque. Then they should be retightened to the final value a second time in the specified sequence. SERVICE TIP  Most torque sticks (sockets) will not work correctly unless the impact wrench can produce at least 250 foot-pounds of torque. The wrench must have an air pressure supply of at least 120 psi. Still, the best method to torque lug nuts is a socket driven by a hand-operated torque wrench.

Checking Tire and Wheel Runout Tire and wheel runout can be factors in troubleshooting braking performance. Excessive radial runout can prevent a tire from maintaining uniform traction, which can cause braking force to vary as the tire rotates. Excessive lateral runout can cause the contact patch to shift as the tire rotates and can contribute to uneven braking. When measuring radial or lateral runout, measure at the tire first because this will indicate the total runout of both the wheel and the tire. If runout at the tire is out of limits, then measure at the wheel to isolate the problem to either the wheel or the tire or to runout that have accumulated in one direction during mounting. Before measuring runout, be sure the wheel bearings are not loose or excessively worn. Some technicians prefer to tighten the bearings of a tapered roller bearing (usually

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found on older rear wheel drive vehicles on the front) temporarily while measuring runout or to measure runout with the tire and wheel mounted on a wheel balancer to eliminate the wheel bearings as a cause of runout. If measuring runout with the wheel and tire mounted on the vehicle, be sure the wheel nuts are tightened properly as explained previously. Finally, drive the vehicle for several miles to warm the tires and eliminate any flat spots that may have developed from sitting stationary. A special dial indicator with a small roller on the end is the best tool to use for measuring tire runout. The roller keeps the indicator from catching on the tread or uneven spots on the wheel or tire. Measure radial runout first (Figure 3-7), then lateral runout (Figure 3-8), as follows: SERVICE TIP  Another reason to tighten the lug nuts in sequence and torque stages is to draw the wheel flat against the rotor or hub or axle flange. Tightening one or two nuts on one side will cock the wheel and the other nuts will probably torque but not bring the wheel flat. The result is a loose tire and wheel assembly that will be very noticeable within a mile of driving. This will result in an unhappy customer and possibly some damaged studs, nuts, and/or wheel. It may also damage the reputations and profits of both the technician and the shop.

1. Raise the vehicle on a hoist and support it safely so that the wheels can turn freely. 2. Position the pointer of the dial indicator against the center tire tread where it can contact a uniform section of tread around the circumference (see Figure 3-7A). 3. Rotate the tire until you get the lowest reading on the dial indicator. Then set the indicator to zero. 4. Rotate the tire until you get the highest reading on the dial indicator. This is the total radial runout of the tire and the wheel, and it should not exceed 0.060 inch (1.5 mm). Mark the location on the tire. If radial runout is excessive, proceed to check the runout of the wheel alone. If radial runout is within limits, proceed to step 8 and check lateral runout. 5. To check the radial runout of the wheel alone, reposition the dial indicator pointer to the inside of the rim flange (see Figure 3-7B). 6. Rotate the wheel until you get the lowest reading on the dial indicator. Then set the indicator to zero. 7. Rotate the wheel until you get the highest reading on the dial indicator. This is the radial runout of the wheel, and it should not exceed 0.040 inch (1.0 mm) for a steel wheel or 0.030 inch (0.75 mm) for an alloy wheel. Mark the location on the wheel. 8. Measure lateral runout of the wheel and tire by repositioning the dial indicator plunger to the tire sidewall, just below the wear rib on the sidewall (see Figure 3-8A). Do not place the pointer against the wear rib because any damage or wear on this area will cause a false measurement.

Excessive radial runout can cause a wheel to jump up and down or hop, whereas radial runout causes a wheel to wobble from side to side.

SERVICE TIP  If you are troubleshooting a low-pedal complaint on a rearwheel drive (RWD) vehicle with rear disc brakes, do not overlook rear axle runout as a possible cause. Excessive lateral runout in an axle flange can become rotor runout that knocks the caliper piston farther back in its bore. The pedal then must travel farther to take up the extra pad-to-rotor clearance. Although this was a common problem on old Corvettes with Delco Moraine fixed-caliper rear discs, the problem still shows now and then.

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Chapter 3 Check wheel radial runout here (wheel only)

Check total radial runout here (wheel and tire) A

B

Figure 3-7  Radial runout check. Note this dial indicator does not have the roller point, so the wheel must be rotated slowly. The duct tape shown is smooth and works well with a non-roller type dial indicator.

A

Check wheel lateral runout here (wheel only)

B Check total lateral runout here (tire and wheel)

Figure 3-8  Lateral runout check. Note this dial indicator does not have the roller point, so the wheel must be rotated slowly to prevent dragging the point and getting an incorrect measurement.

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SERVICE TIP  Place masking tape, aligned with the center tread, around the circumference of the tire. The tape will help prevent the tip of the dial indicator from hanging on the tread and provide a more accurate reading.

9. Rotate the tire until you get the lowest reading on the dial indicator. Then set the indicator to zero. 10. Rotate the tire until you get the highest reading on the dial indicator. This is the total lateral runout of the tire and the wheel, and it should not exceed 0.080 inch (2.0 mm). Mark the location on the tire. If lateral runout is excessive, proceed to check the runout of the wheel alone. 11. To check the lateral runout of the wheel alone, reposition the dial indicator pointer to the side of the rim flange as shown in (Figure 3-8B). 12. Rotate the wheel until you get the lowest reading on the dial indicator. Then set the indicator to zero. 13. Rotate the wheel until you get the highest reading on the dial indicator. This is the lateral runout of the wheel, and it should not exceed 0.045 inch (1.15 mm) for a steel wheel or 0.030 inch (0.75 mm) for an alloy wheel. Mark the location on the wheel.

Caution Too much torque on the lug nuts can warp (bend) a brake rotor. It is critical that lug nuts are torqued correctly. Over torque may damage the rotor beyond repair.

SERVICE TIP  The sealed, preloaded, zero-clearance front wheel bearings on late-model cars require little or no toe-in. This lack of toe-in is great to reduce rolling resistance and improve fuel economy, but bearings with no end play cannot absorb small amounts of hub and rotor runout. This makes rotor runout and thickness measurements very critical on these cars.

Radial runout is more often a cause of braking problems than is lateral runout, but neither should be overlooked. Runout often can be reduced, if not eliminated altogether, by repositioning the tire on the rim. When measuring runout, mark the locations of maximum radial and lateral runout for both the wheel and the tire. Excessive runout can be reduced by remounting the tire so that the points of maximum runout are opposite each other. Rebalancing will be required if the tire is remounted on the wheel. Repositioning the tire and wheel assembly on the brake drum or rotor also may help to reduce runout. Radial runout also may be reduced by shaving the tire on a tire truing machine.

Road Force Balancing Some tires also may have abnormally stiff sections in their sidewalls and areas of the tread. These stiff sections keep a tire from rolling concentrically and uniformly when loaded. Although this condition is hard to detect when vehicle weight is unloaded from the tire and wheel, some wheel balancers have the capability to load the tire and identify hard spots and stiff areas. These balancers are called road force balancers (Figure 3-9). Road force balancers can detect lateral rolling forces in tires that result in a tire pull, as well as radial and lateral runout. The road force balancer can suggest the best possible wheel to rim match when mounting or balancing a tire or wheel.

Road force ­balancers simulate the actual loads experienced by the tires on the road for a better balance. These balancers can also help diagnose run-out problems with wheels and tires.

TAPERED ROLLER BEARING SERVICE The wheels and axles of late-model cars and light trucks are supported by tapered roller bearings, straight roller bearings, or ball bearings. Straight roller bearings and ball bearings do not require periodic service or adjustment. They are replaced only when defective,

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Figure 3-9  A road force balancer can determine how a tire will perform on the road under load. Figure 3-10  Although many technicians prefer to use hand packing, this bearing packer is easy to use and less messy.

Certain bearing ­services are usually included as part of the brake service.

Classroom Manual page 56

and the procedures are outside the scope of a brake service text. Details on this service may be found in Cengage Learning’s Today’s Technician: Automotive Suspension & Steering. Some vehicles have sealed double-row ball bearings or tapered roller bearings in an assembly that includes the wheel hub, the bearing races, and a mounting flange. They may be used at the front drive axles on FWD cars or on nondriving wheels. These are nonserviceable, nonadjustable assemblies that must be replaced if damaged or defective. Tapered roller bearings are used on the front or rear nondrive wheels of many vehicles. Tapered roller bearings must be cleaned and repacked with grease periodically and then adjusted (Figure 3-10). These bearing services are usually part of a complete brake job. If the bearings are too tight, the hub and brake assembly may overheat with accompanying problems that include brake fade. If wheel bearings are too loose with too much end play, wheel runout may be excessive.

Tapered Roller Bearing Troubleshooting Bearings rarely fail suddenly. Rather, they deteriorate slowly from dirt, lack of lubrication, and improper adjustment. Bearing wear and failure are almost always accompanied by noise. Start diagnosing possible wheel bearing problems by raising the vehicle on a hoist so that the wheels can turn freely. Rotate the wheel and listen to the sounds of brake drag and bearing rotation. If the brakes are dragging slightly, they will produce a high-pitched

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swishing sound. Bearing noise will be a lower-pitched rumble. Bearing sounds should be uniform through the wheel revolutions. An uneven rumble or a grinding sound indicates possible bearing problems. If a bearing is unusually noisy, roughness can usually be felt as the wheel is rotated. Hold onto the wheel lightly; listen for a low-frequency rumbling sound and feel for rough and uneven rotation as the wheel turns. Compare left and right wheels to determine whether a problem may exist. Without rotating the wheel, try to move it in and out on the spindle and note the amount of axial movement. Worn or damaged bearings or bearings that need adjustment will have a noticeable amount of end play. Also grasp the top and bottom of the tire and try to wobble the wheel and tire back and forth. There should be little or no wobble in a properly adjusted bearing that is in good condition. SERVICE TIP  You can use a noncontact pyrometer or infrared thermometer to solve a wheel bearing problem on a car with sealed wheel bearings. Drive the car for several miles at highway speeds and immediately use the pyrometer to measure wheel temperatures from side to side. If one wheel is hotter than the other, take a close look at the sealed wheel bearing on that side. The same kind of test can help you pinpoint constant velocity (CV) joint problems on FWD cars and dragging brakes on any vehicle.

Sealed wheel bearings cannot be adjusted. If they show any axial movement, the bearing assembly must be replaced. Measure bearing end play precisely with a dial indicator placed against the wheel hub (Figure 3-11). Install the rotor and lug nuts for the measurement. (If the lug nuts are conical, it will be necessary to use a regular nut for this purpose.) Set the indicator to zero, move the wheel in and out on the spindle, and note the reading. Tapered roller bearings can have 0.001 inch to 0.005 inch (0.025 mm to 0.127 mm) of end play. Check the vehicle manufacturer’s specifications for the exact amount of allowable end play. Attach dial indicator clamp to suspension component Lug nuts @ 108 Nm (11.0 kgf-m, 79.6 lb.-ft)

Dial indicator plunger contacting hub surface

Figure 3-11  Notice that the lug nuts are on and torqued. Also note where the plunger of the dial indicator is placed.

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Finally, inspect the wheel and the brake drum or rotor for grease being expelled through a leaking seal. Bearing grease can contaminate brake linings, and a leaking grease seal can let dirt into the bearing. A leaking seal must be replaced, but the bearings also must be cleaned, inspected, and repacked to be sure they have not been damaged.

Bearing Service Guidelines The procedures to remove, clean, lubricate (repack), and install tapered roller bearings are basically the same for servicing a used bearing or installing a new one. The outer races or cups are pressed into the hub and must be driven or pressed out when installing a new bearing. A bearing and its outer race must be replaced as a set. Installing a new bearing in a used race will cause an uneven wear pattern that will lead to premature bearing wear or failure. The procedure to replace the bearing races is detailed in photo sequence 3. When installing a new bearing, leave the bearing in its protective packaging until it is time to lubricate it. Be sure the hands are clean before handling a bearing. Some technicians prefer to apply a light film of motor oil to their fingers before handling a bearing. This prevents acid from their fingers from damaging the bearing. Whether repacking and reinstalling a used bearing or installing a new one, always install a new grease seal. Seals wear with age and can be damaged during bearing removal. A new seal ensures that bearing grease stays in the hub where it belongs, not on the brake linings. A new seal also ensures that dirt and moisture stay out of the bearing. If the brake shoes or pads are contaminated the pads must be replaced. A leaking grease seal will cause the brakes to grab on application, as will differential lubricant and brake fluid.

Special Tools Lift or jack with stands Impact tools Cotter pin puller Seal puller Brass punch

Tapered Roller Bearing Removal With drum brakes, you can leave the tire and wheel on the drum to remove the bearing if you wish. The drum and bearing are easier to handle with the weight of the wheel and tire removed, however. With disc brakes, the wheel and tire must be removed for access to remove the caliper (Figure 3-12). Remove inner and outer tapered roller bearings as follows: 1. Raise the vehicle on a hoist and support it safely so that the wheels can be removed. 2. Remove the wheel cover, if so equipped, and remove the wheel and tire from the drum or rotor. Grease seal Inner bearing cone Outer bearing cone Spindle

Thrust washer

Cotter pin

Nut lock Grease cap

Brake caliper

Rotor and hub parts

Figure 3-12  Typical hub and tapered roller bearing assembly.

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3. If the axle has disc brakes, remove the brake caliper as explained in Chapter 7 of this Shop Manual and suspend it out of the way. Do not support the caliper by the brake hose. 4. Pull the dust cap from the center of the hub to expose the bearing nut (Figure 3-13). 5. Remove the cotter pin and nut lock. 6. Loosen and remove the adjusting nut (sometimes called the axle nut). 7. Lift the outer bearing and thrust washer from the hub and set them aside for cleaning. 8. Place the thumb of one hand over the thrust washer outboard of the outer bearing and carefully slide the drum or rotor off the spindle. Support the drum or rotor with both hands so that it does not drag on the spindle as you remove it. If a brake drum catches on the shoes, reinstall the adjusting nut and back off the brake adjustment as explained in Chapter 8 of this Shop Manual. Then remove the drum. 9. Set the drum or rotor on a clean work surface with the inboard side down. 10. Remove the inner bearing and grease seal in one of the following ways: A. Turn the drum or rotor over, hook the claw of a seal puller against the inside of the grease seal, and lever the seal out of the hub. A small prybar can also be used to remove the seal. B. Raise the drum or rotor on suitable blocks so that the inside of the hub is 1 inch to 2 inches off the bench. Then insert a large, nonmetallic drift punch through the outer bearing diameter and place it against the inner race of the inner bearing (Figure 3-14). Tap the bearing at several locations around its circumference until the bearing and seal are driven from the hub. 11. Set the inner bearing aside for cleaning or replacement. 12. If a new bearing is to be installed, remove the race by inserting a large drift punch through the opposite side of the hub and placing it against the inner edge of the race. Strike the punch with a hammer at several locations around the circumference of the race until the race is driven from the hub. A bearing race can be removed from a hub using a press and suitable adapters.

Figure 3-13  Removing the grease cap using grease cap pliers.

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Figure 3-14  Removing a bearing race from a hub.

SERVICE TIP  There is an easy way to remove the inner bearing and seal on hubs with an internal bore large enough to let the adjusting nut slide through. Use this method only if the bearing is being replaced. After removing the outer bearing and thrust washer, screw the adjust nut onto the spindle several turns. Grip the hub, slide it toward the outer end of the spindle, and then jerk it outward and downward. The adjusting nut will pull the inner bearing and seal from the hub. Remember, use this method only if the bearing is being replaced. Regardless of the reason for removing the seal, it must be replaced once removed.

Special Tools Parts washer Cloths

Caution Do not spin the bearings with compressed air during cleaning. High-speed rotation of an unlubricated bearing will damage it. Compressed air also can dislodge bearings from the cage and cause additional damage or injury.

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Tapered Roller Bearing Cleaning and Inspection After the bearings are removed from the hub, wipe the old grease off the spindle and out of the center cavity of the hub with clean, lint-free shop cloths or paper towels. Examine the old grease for metal particles from the bearings or their races. Any sign of metal particles in the grease is a clue to inspect the bearings very closely for wear and damage. Also inspect the old grease for dirt, rust, and signs of moisture that could indicate a leaking grease seal. If the outer races for the bearings are still installed in the hub, wipe old grease off them with a clean, lint-free shop cloth and inspect them closely for wear or damage (Figure 3-15). Also wipe as much of the old grease as possible from the bearings with a clean, lint-free shop cloth or paper towel and inspect them similarly for wear or damage. If the race seems to have a faint bluish tint to part or all of the bearing contact surface, it could be a sign of overheating. Inspect each of the bearing’s rollers closely to determine if one or more roller shows heat or other damage. Inspect the grease removed from the bearings for metal particles, rust, and dirt. Turn the rollers in the cage, and listen and feel for roughness. The following are common bearing defects: ■■ Galling. Galling is indicated by metal transfer or smears on the ends of the rollers and is caused by overloading, lubricant failure, or overheating. Overheating is usually the result of adjustment that is too tight.

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Photo Sequence 3

Removing and Installing a Bearing Race

P3-1  Shown in the inner bearing race. Note the depth of the race inside the hub.

P3-2  Flip the hub over. Position the punch through the cavity and against the edge of the race.

P3-3  Strike the punch with medium force. Move the punch tip around the edge of the race to help keep the race even in the bore during removal.

P3-4  Observe the area where the race was removed from and ensure there is no damage from the punch or from the race spinning in its seat.

P3-5  Fit the race in as far as possible with hand force. Align the driver over and into the race.

P3-6  Use moderate hammer force to drive the race in place. When the race bottoms in the cavity, it will be noticeable because a different sound will come from the hammer and the driver.

P3-7 Check to ensure the race is completely in place. The space between the race and outer edge of the hub should be close to where the old race was positioned.

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Chapter 3 Tapered Roller Bearing Diagnosis Consider the following factors when diagnosing bearing condition: 1. General condition of all parts during disassembly and inspection. 2. Classify the failure with the aid of the illustrations. 3. Determine the cause. 4. Make all repairs following recommended procedures.

Abrasive Step Wear

Galling

Bent Cage

Pattern on roller ends caused by fine abrasives. Clean all parts and housing; check seals and bearings and replace if leaking, rough, or noisy.

Metal smears on roller ends due to overheating, lubricant failure, or overload. Replace bearing, check seals, and check for proper lubrication.

Cage damaged due to improper handling or tool usage. Replace bearing.

Abrasive Roller Wear

Etching

Bent Cage

Pattern on races and rollers caused by fine abrasives. Clean all parts and housings; check seals and bearings and replace if leaking, rough, or noisy.

Bearing surfaces appear gray or grayish black in color with related etching away of material, usually at roller spacing. Replace bearings, check seals, and check for proper lubrication.

Cage damaged due to improper handling or tool usage. Replace bearing.

Indentations Surface depressions on race and rollers caused by hard particles of foreign material. Clean all parts and housings. Check seals and replace bearings if rough or noisy.

Good Bearing

Misalignment Outer race misalignment due to foreign object. Clean related parts and replace bearing. Make sure races are properly sealed.

Figure 3-15  Good and bad bearings.

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Figure 3-16  A good bearing and race (right) and a damaged race and bearing (left).

Etching. Etching is a condition that results in a grayish-black bearing surface and is caused by insufficient or incorrect lubricant. ■■ Brinelling. Brinelling occurs when the surface is broken down or indented and is caused by impact loading, usually because the adjustment is too loose. ■■ Abrasive wear. Abrasive wear results in scratched rollers and is caused by dirty or contaminated bearing lubricant. Clean the bearings in a parts washer, using clean petroleum-based solvent. Rotate the bearings in the cage as you clean them and remove old grease with a stiff-bristled brush. Wash each bearing separately and if being reused keep them sorted to be sure they are reinstalled in the same hubs from which they were removed. After cleaning, flush all of the cleaning solvent from the bearings with a non-­ petroleum-based brake-cleaning solvent. Let the bearings dry in the air for a few minutes and then blow any remaining solvent from the bearings and cages with low-pressure compressed air. Direct the air through the bearing from side to side, along the axis of the rollers. Do not spin the bearings with compressed air. All solvent must be removed from the bearing for the new solvent to adhere to the bearing components. Carefully inspect the bearings after cleaning. Turn each roller completely around and check the surface. Carefully inspect each of the races also. Figure 3-16 shows a good bearing and some common bearing problems. If the roller or race shows signs of any of the conditions shown in Figure 3-15 or if unsure of the bearing condition in any way, replace the bearing. A replacement bearing contains inner and outer races and the rollers in their cage. Always compare the old parts with their replacements to be sure the items are correct. ■■

Special Tool Bearing packer

Tapered Roller Bearing Lubrication Tapered roller bearings must be lubricated or packed with grease made especially for wheel bearing use. Disc brakes cause wheel bearings to run at higher temperatures than do drum brakes, and many wheel bearing greases are labeled for use with disc brakes. Always use the type of grease specified by the vehicle manufacturer. Because wheel bearing grease must operate at higher temperatures than chassis grease, it contains oils and other lubricants that have been made particularly heavy with thickening agents. Different grease manufacturers use different thickening agents and other additives, so it is best to avoid mixing greases by removing all of the old grease before repacking a bearing.

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SERVICE TIP  There is a myth that grease must completely fill the interior of the hub and the dust cap. This is wrong because the grease will expand when it heats up during normal vehicle operation. Excessive grease will force past the seal and once the seal is violated, a permanent leak will be present. A film of grease should be applied to the bearing races and only about one-quarter of the dust cup should be filled. No extra grease should be placed in the hub cavity.

Wheel bearing grease seal may be called a “grease seal,” “wheel bearing seal,” or a “lip seal.”

Tapered roller bearings can be packed with grease most efficiently and thoroughly with a bearing packer (Figure 3-17). This packer uses a grease gun to insert the grease. Place the bearing in the packer with the taper pointing down, and screw the cone down on the bearing. Apply a hand-operated grease gun to the fitting on the center shaft of the packer and force grease into the bearing and out around the rollers in the cage. Do not use a pneumatic grease gun to avoid spraying grease out of the bearing. Some bearing packers contain a supply of grease. Pushing on the cone handle forces the bearing down into the packer and lubricant in the tool is forced into the bearing. Hand packing is still the preferred packing technique among many technicians because the new grease can be seen moving through the bearing. If a bearing packer is unavailable, force grease by hand through the large end of the bearing and around the rollers. Rotate the bearing several times while packing it by hand to ensure that grease is forced completely around each roller (Figure 3-18). Finish by spreading an even film of grease around the outside of all the rollers. After packing the bearings, set them aside on a clean sheet of lint-free paper until they are ready for installation. Before installing the bearings and the hub, inspect the spindle for wear or damage. Remove any burrs with a fine file or emery cloth. Spread a light coating of bearing grease around the entire spindle. Also spread fresh grease inside the hub to a level just below the bearing races. Applying grease to the spindle and hub, even to nonbearing surfaces, will protect against rust and other moisture damage. Grease on the bearing surfaces of the spindle also lets the inner bearing races creep slightly on the spindle and distribute the bearing load uniformly. Be careful to keep grease off the braking surfaces of the drum or rotor.

Figure 3-17  A typical wheel bearing packer.

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Figure 3-18  Packing bearings by hand.

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Tapered Roller Bearing Installation and Adjustment Bearing adjustment procedures are the same whether a used bearing is being repacked and reinstalled or a bearing is being replaced. If replacing a bearing, however, a new race in the hub must be installed in the hub. Install and adjust tapered roller bearings as follows: 1. If the old bearing race has been removed from the drum, install a new one as follows: A. Apply a thin film of grease to the back of the race and to the bore in the hub to aid installation. B. Position the race squarely at the end of the bore and use a bearing driver (Figure 3-19) or a suitably sized socket and a hammer to drive the race into the hub. But care must be taken to ensure the socket fits the outer edge of the race. C. Be sure the tool contacts the outer edge of the race squarely. D. Listen for a change in the hammer sound as the race is seated in the hub. 2. Place the drum or rotor with the outer side down on a workbench. 3. Apply a light coat of grease to the outer race for the inner bearing. Then insert the freshly packed bearing into the race. 4. Place a new grease seal into the inner bore of the hub with the lip pointing inward (Figure 3-20). 5. Drive the seal into place with a seal driver until the outer surface of the seal is flush with the hub (Figure 3-21). 6. Apply a thin film of bearing grease to the lip of the seal to protect it during installation on the spindle. 7. Turn the hub over and apply a light coat of grease to the outer race for the outer bearing. Then insert the freshly packed bearing into the race. 8. Install the rotor or drum carefully onto the spindle in a straight line, and be careful not to hit the inner bearing on the spindle threads. 9. Support the rotor or drum with one hand, and install the outer bearing and thrust washer into the hub. 10. Install the bearing adjusting nut finger tight against the thrust washer (Figure 3-22).

A bearing driver is a special tool to install a bearing race into a hub.

Special Tools Seal driver Bearing driver

Figure 3-19  Bearing driver used to install a new bearing race.

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Figure 3-20  The grease seal lip must face inward in the hub when installed.

Figure 3-21  Install a new grease seal with the proper size driver.

Figure 3-22  Install the adjusting (spindle or axle) nut finger tight.

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11. Rotate the drum or rotor by hand, and lightly tighten the adjusting nut by hand to seat the bearings. Then adjust the bearings by one of the following methods (Figure 3-23): A. Rotate the drum or rotor, and lightly snug up the adjusting nut with a wrench to seat the bearings. Then back off the nut one-quarter to one-half turn or until it is just loose while continuing to rotate the drum or rotor. Tighten the nut by hand to a snug fit and lock it as described later. This is a method used by experienced technicians. Beginners should use method B or C. B. Rotate the drum or rotor, and tighten the adjusting nut with a torque wrench to the torque specified by the carmaker, which is usually 12 foot-pounds to 25 foot-pounds. Then back off the nut one-third turn and retorque it to the value specified by the carmaker while continuing to rotate the drum or rotor. Final torque is usually 10 to 15 inch-pounds. Lock the adjusting nut as described below. C. To adjust bearing end play with a dial indicator, rotate the drum or rotor and tighten the adjusting nut with a torque wrench to 12 foot-pounds to 25 footpounds. Then back off the nut one-quarter to one-half turn or until it is just loose. Mount a dial indicator on the drum or rotor with its pointer against the spindle. Move the drum or rotor in and out, and note the indicator reading. Turn the adjusting nut as necessary to obtain the specified end play, which is usually 0.001 inch to 0.005 inch (0.025 mm to 0.125 mm). Lock the adjusting nut as described below.

Classroom Manual page 57

12. Install the nut lock over the top of the bearing adjusting nut so that the slots in the nut lock align with the cotter pin hole in the spindle (Figure 3-24).

1. Hand spin the wheel. 2. Tighten the nut to 16 Nm (12 ft.-lb) to fully seat the bearings—this overcomes any burrs on threads. 3. Back off the nut until just loose.

4. Hand "snug up" the nut.

Bend end of cotter pin legs flat against nut. Cut off extra length.

5. Loosen the nut until a hole in the spindle lines up with a slot in the nut. Insert cotter pin. 6. When the bearing is properly adjusted there will be from 0.03 to 13 mm (0.001" to 0.005") of end play.

Figure 3-23  Typical bearing adjustment specifications.

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1

2

3

4

With hub rotating tighten adjusting nut to 17–25 ft.-lb

Back adjusting nut off 1/2 turn

Tighten adjusting nut to specifications

Install retainer and a new cotter pin

Figure 3-24  Typical spindle nut, nut lock, and cotter pin installation.

13. Install a new cotter pin through the spindle and nut lock and bend its ends to secure it. Reinstall the dust cap in the hub. 14. If the axle has drum brakes that were backed off to allow removal of the drum, readjust the brakes as explained in Chapter 8 of this Shop Manual. 15. If the axle has disc brakes, reinstall the caliper as explained in Chapter 7 of this Shop Manual. 16. Reinstall the wheel and tire and lower the vehicle to the ground. 17. Pump the brake pedal several times to reset the disc brake pads. Photo Sequence 4 outlines the key points of bearing adjustment and provides additional details.

SERVICE TIP  A quick way to isolate a brake problem from related components or systems is to ask the customer if the pull happens all the time or just during braking. If it occurs only during braking, then the fault is very probably in the braking system. Pull that is present at all times does not completely rule out the brakes, but the fault will most often be found in a related component or system.

WHEEL ALIGNMENT, STEERING, AND SUSPENSION INSPECTION Problems in the steering and suspension systems that affect braking usually are related to a pull to one side or the other. And braking problems related to steering, suspension, and wheel alignment usually involve front-end components. Components that are damaged, worn, or otherwise loose make it hard to maintain directional stability. When braking forces are applied to loose parts, the pulling reaction often becomes more apparent. Noises that occur when the brakes are applied can indicate suspension problems, loose or missing bushings, or worn parts. Repairing steering and suspension problems and correcting wheel alignment are beyond the scope of brake service, but brake system troubleshooting often includes inspection of these other undercar systems. For a thorough inspection, raise the vehicle on a hoist so that the wheels hang freely. Before lifting the vehicle, however, inspect the suspension as it sits on the shop floor. Look for any noticeable sagging or uneven ride height from side to side or front to rear. This condition often is a sign of broken or weak springs or other suspension parts. Examine the front and rear wheels as the vehicle weight is on them and look for any apparently

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Photo Sequence 4

Typical Procedure for Adjusting Tapered Roller Bearings

P4-1 Always make sure the car is positioned safely on a lift before working on the vehicle.

P4-2 Remove the dust cap from the wheel hub.

P4-3 Remove the cotter pin and nut lock from the bearing adjusting nut.

P4-4 Tighten the bearing adjusting nut to 17–25 foot-pounds.

P4-5 Loosen the bearing adjusting nut one-half turn.

P4-6 Rotate the wheel while tightening the bearing adjusting nut to specification.

P4-7 Position the adjusting nut lock over the adjusting nut so the slots are aligned with the holes in the nut and spindle.

P4-8 Install a new cotter pin and bend the ends around the retainer flange.

P4-9 Install the dust cap and be sure the hub rotates freely.

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extreme camber angles or toe angles. Look at each wheel by itself and compare right to left sides, front and rear. Raise the vehicle on a hoist so that the wheels hang freely and inspect the tie rod ends and shock absorbers for looseness. Also check steering idler arms and pitman arms for looseness and worn or damaged bushings. Inspect shock absorbers and struts for fluid leakage, and check all the mounting fasteners for looseness. Grab the front tires by the treads, and try to move the toe in and out. There should be no noticeable movement without some movement on the companion wheel. Then try to move the steering linkage up and down while watching the front wheel toe angle. Toe angle should not change, and there should be no noticeable looseness in the steering linkage. Loose steering linkage can make it impossible to adjust the toe angle. Looseness in the linkage can cause enough toe angle change during acceleration and braking to cause a pull. Similarly, loose control arm or strut bushings may cause caster or camber angles to change during acceleration, braking, and cornering, which can cause or contribute to a brake pull.

SERVICE TIP  When troubleshooting a problem of steering shimmy while braking on a car with four-wheel disc brakes, do not overlook the rear rotors as a possible cause. Severe runout and rear end shimmy can be felt through the steering wheel. If the front rotors check out within specs for runout and parallelism, take some close measurements on the rear rotors. Install good sealing plugs at the proportioning valve rear brake outlets or at the ends of the line or hose leading to the rear brake calipers or cylinders. This prevents fluid from entering the rear brakes. Do not clamp brake hoses. Clamping could damage the interior lining of the hose. Test stop the vehicle. If the steering shimmy goes away, suspect the rear rotors as the cause.

Ball Joint Inspection A wear-indicating ball joint is a ball joint with a visual indicator to show the amount of wear on the joint.

Special Tools Jack Prybar

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Many cars have wear-indicating ball joints. These ball joints must be inspected with the vehicle weight resting on the joints. Some vehicles have ball joints on which the grease fitting recedes into the housing as the joint wears. Replace the ball joint if the shoulder of the fitting is flush with or receded into the ball joint housing (Figure 3-25). On other wear-indicating ball joints, try to wiggle the fitting by hand. If the fitting moves at all, replace the ball joint. If a vehicle does not have wear-indicating ball joints, check the joints with the vehicle weight removed from them. Most of the wear will occur on the load-carrying joint, which must be unloaded to check it for looseness. If the spring is between the frame and a lower control arm, raise the vehicle on a jack and support the lower control arm as far outboard as possible. If the spring is between the frame and an upper control arm or if the vehicle has MacPherson struts, raise the vehicle on a jack and support the vehicle inboard of the lower control arm. With the vehicle supported as required, grasp the tire at the top and bottom, and try to rock it in and out. Watch the ball joint, or have an assistant watch it, for signs of radial (in-and-out) play. Then place a prybar under the tire and try to lever it up and down while watching for axial (up-and-down) play. If radial or axial play of the load-carrying ball joint exceeds specifications, replace the ball joint. Replace a non-load-carrying ball joint if it is loose in any way.

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New

Wear surfaces

When ball joint wear causes wear indicator shoulder to recede within the socket housing, replacement is required.

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Sintered iron bearing

0.050"

Rubber pressure ring

Figure 3-25  Typical wear-indicating ball joint.

Wheel Alignment Inspection If inspection of the steering and suspension reveals any looseness or if ball joints are replaced, it is a very good idea to check wheel alignment on an alignment rack, using alignment equipment. Pay close attention to the caster and camber variations from side to side. Front wheel caster and camber are often used to keep a vehicle from pulling to one side or the other. Some carmakers specify different caster angles for right and left front wheels to compensate for a pull caused by the crown of the road. Road crown causes a pull to the right so if different caster angles are used from right to left, the right front wheel will have more positive caster to create a slight caster lead and compensate to the left. Different camber angles from right to left also can compensate for road crown pull, but because of the effects on tire wear, camber variations are not used as often as caster variations. Excessive ball joint wear is sometimes felt as a bump or heard as a popping sound as the brakes are applied.

SERVICE TIP  When you are troubleshooting a brake pull problem and cannot pinpoint the cause, try driving the car in reverse and applying the brakes. If the car pulls in opposite directions while braking in forward and reverse (for example, pulls left when going forward and pulls right in reverse), look closely for loose or broken suspension and steering components such as ball joints and tie rod ends.

AUTHOR’S NOTE  Camber and toe angles are considered as “tire wear angles” in that incorrect camber or toe angles will wear the tire life substantially. Caster, unless it is way out of specifications, will not cause a tire to wear improperly.

Braking problems can arise when caster or camber angles are significantly different from right to left. In such cases, the vehicle will tend to pull toward the side with the more negative caster or the more positive camber. A pull caused by extreme caster or camber

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variations may be more noticeable under braking than under acceleration or cruising because of the torque reaction forces imposed on the wheel while braking. Excessive vehicle setback also may contribute to brake pull problems. Setback cannot be adjusted. It is set up by the vehicle designers and manufacturing process. When troubleshooting a complaint of brake pull, do not overlook the caster and camber angles and the setback measurement. If the wheel alignment may be contributing to a brake problem, realignment to manufacturer’s specifications is a good investment.

AUTHOR’S NOTE Many customers think that an alignment will correct wheel shimmy/vibration problems. As technicians, we know that lateral or radial runout cannot be corrected by an alignment. This is another good reason to make sure the customer’s complaint is thoroughly understood before work is performed.

CASE STUDY Most race cars are set up with the right rear tire larger than the left rear tire. On a sprint car, the size differential is really obvious; but even with tires of the same size specification, manufacturing variations create slight size differences. Racers use this advantage to improve traction in corners, particularly on oval tracks. The racers call this selective tire sizing “stagger.” What works well on the race track, however, does not always work well on the highway.

Case Study The Cadillac Fleetwood Brougham had some weird drivability symptoms that included an accelerator pedal that became hard to press at about 45 mph to 50 mph. The cruise control would shut off all by itself at about the same speed. The vehicle had ABS and traction control system (TCS), and the tech working on the problem thought the TCS might be involved. She road tested the car with a scan tool connected and monitored the wheel speeds on the ABS and TCS data stream. As the car accelerated, the left rear wheel gradually went faster than the other three wheels and faster than the car speedometer. At 45 mph to 50 mph (the problem speed), the left rear wheel was 3 mph to 4 mph faster. The tech questioned the car owner and learned that the left rear tire had been replaced recently. The original tire suffered a sidewall blowout. The other three tires on the car had only about 20,000 miles on them, so they were not replaced. It seemed strange but just a 3 mph or 4 mph difference in driving wheel speed caused the TCS to kick in at moderate cruising speed in a straight line. Rotating the new tire to the front eliminated the tire stagger and solved the problem.

ASE-STYLE REVIEW QUESTIONS 1. Technician A says there are times when what appears to be a brake problem is actually a problem caused by a defect in a related system. Technician B says problems of this type are usually caused by tires or alignment. A. A only C. Both A and B B. B only D. Neither A nor B

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2. The tire and wheel problems that can affect brake performance the most are: A. Tire condition B. Inflation pressure C. Tire and wheel installation methods D. All the above

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3. Technician A says that if wheel nuts or bolts are overtightened, tightened unevenly, or in the wrong sequence, the brake drum or rotor can be distorted. Technician B says this distortion creates runout in the drum or rotor that, in turn, causes pedal pulsation and uneven brake application. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 4. Technician A says excessive lateral runout can prevent a tire from maintaining uniform traction, which can cause braking force to vary as the tire rotates. Technician B says excessive lateral runout can cause the contact patch to shift as the tire rotates and can contribute to uneven braking. A. A only C. Both A and B B. B only D. Neither A nor B 5. Technician A says problems in the steering and suspension systems can affect braking performance. Technician B says these problems are usually are related to a loss of traction. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 6. These alignment angles are often used to keep a vehicle from pulling to one side or the other: A. Toe and caster B. Camber and toe C. Rear caster and rear toe D. Front wheel caster and camber

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7. Technician A says if the brake shoes or pads are contaminated, the pads must be thoroughly cleaned. Technician B says a leaking grease seal will cause the brakes to grab on application, as will differential lubricant and brake fluid. A. A only C. Both A and B B. B only D. Neither A nor B 8. Tapered roller bearings can have an end play measurement from: A. 0.01 inch to 0.05 inch (0.25 mm to 1.27 mm) B. 0.1 inch to 0.5 inch (2.5 mm to 12.7 mm) C. 0.0001 inch to 0.0005 inch (0.0025 mm to 0.0127 mm) D. 0.001 inch to 0.005 inch (0.025 mm to 0.127 mm) 9. Technician A says braking problems can arise when caster or camber angles are significantly different from right to left. Technician B says in such cases, the vehicle will tend to pull toward the side with the more negative caster or the more positive camber. C. Both A and B A. A only B. B only D. Neither A nor B 10. Technician A says problems caused by underinflation and lack of rotation can be compounded on tires with a mud-and-snow tread design. Technician B says when a tread block hits the pavement during braking, it has the same effect as a pencil eraser hitting a sheet of paper. The rubber wears at an angle. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

ASE Challenge Questions 1. Technician A says a pull caused by extreme caster or camber variations may be more noticeable under braking. Technician B says the problem will be more noticeable under acceleration or cruising. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 2. Technician A says tires that are badly worn, mismatched in size or tread condition, or incorrectly inflated can cause brake problems. Technician B says simple inspection and checking with a pressure and a depth gauge can diagnose many tire problems. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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3. Technician A says low-profile radial ply tire can be 20 pounds to 30 pounds underinflated before it will show a noticeable bulge in its sidewall. Technician B says an old myth is that radial tires should only be switched front to rear on the same side of the car. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

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4. Technician A says rely on visual inspection to determine if a tire is inflated properly. Overinflation and under-inflation will both change the tire contact patch and affect brake performance. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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5. Technician A says equal braking performance at each wheel requires that the tires at all four wheels be the same type, size, and condition. Technician B says tires of different size, construction, or tread design will have different traction characteristics. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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Date _________________

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REMOVE AND INSTALL A WHEEL ASSEMBLY ON A VEHICLE Upon completion of this job sheet, you will be able to remove and install a wheel assembly on a vehicle. ASE Education Foundation Correlation This job sheet addresses the following AST/MAST task: A.4.

Install wheel and torque lug nuts. (P-1)

Tools and Materials • Service manual, paper or computerized • Impact wrench with impact socket • Torque stick (socket) or torque wrench (recommended) • Lift or jack and safety stands Procedure

Task Completed

1. Determine the following information from the service manual and VIN. Vehicle Make _______________ Model _______________ Year _______________ Lug nut torque  ABS Cautions, if equipped   2. Lift the vehicle until the tire is free of the floor. 3. Inspect the hub cap or center piece to determine if it is held on by the lug nuts. If not, use a hub cap hammer or wide blade screwdriver to remove the hub cap or center piece. 4. Select the correct size impact socket, and fit it to the impact wrench. Ensure the impact wrench is set for the correct rotation direction. 5. Remove the lug nuts in a staggered manner. When the last lug nut is set to be removed, place one hand at the top of the wheel assembly to prevent the assembly from flipping from the lug nut studs.

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6. Grip the tire at about the 3 and 9 o’clock position and lower the assembly to the floor.

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7. Inspect the lug nut stud threads for any damage. If damage is apparent, consult with the instructor.

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8. Place the wheel assembly near and below the vehicle hub. Grip the tire at about the 3 and 9 o’clock position and lift the assembly with the legs to the hub and slide it into the studs. Balance the assembly on the studs with one hand until at least one lug nut is started onto the stud.

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NOTE: If the center piece or hub cap is secured by the lug nuts, place the cap or center in place before screwing on the first lug nut. 9. Screw each of the lug nuts several turns onto the studs.

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10. Use a ratchet and socket or hand to screw each of the lug nuts as far as possible onto the studs. Ensure the wheel is flat against the rotor or drum.

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11. Torque to specifications. Torque the lug nuts in a diamond pattern. The torque can be applied in two ways. A ½-drive impact wrench with the correct torque stick (socket) may tighten the lug nuts, but the recommended method is to use a standard torque wrench.

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WARNING  Ensure the impact wrench is strong enough to create the correct torque and the compressed air is of sufficient pressure. A typical torque stick requires a wrench capable of 250 foot-pounds of torque at 120 psi of air pressure. Use of weak or insufficient wrenches or low air pressure will prevent the correct torque being applied to the lug nuts. This could lead to the loss of a wheel during vehicle operation and cause damage and/or injury.

Task Completed

12. With the lug nut torqued and hub cap or center piece in place, lower the vehicle to the floor.

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13. Ensure vehicle is prepared to return to customer per school/company policy (floor mats, steering wheel cover, etc.).

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Problems Encountered    Instructor’s Response   

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Caution Bend at the knees, not the back, as the assembly is lowered. Keep the back as straight as possible during this maneuver.

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REMOVE, REPACK, AND INSTALL AN INNER WHEEL BEARING Upon completion and review of this job sheet, you should be able to remove, repack, and install an inner wheel bearing and seal. ASE Education Foundation Correlation This job sheet addresses the following AST/MAST task: F.2. Remove, clean, inspect, repack, and install wheel bearings; replace seals; install hub and adjust bearings. (P-2) F.6. Replace wheel bearing and race. (P-3) Tools and Materials • Service manual • Impact tools • Bearing packer • Seal remover • Seal driver • Lift or jacks with stands • Hub with inner bearing and seal installed • Blocking materials • Parts washer • New bearing and race • Drift and bearing race installer Describe the vehicle being worked on: Year _____________________ Make _____________________ Model ______________________ VIN _____________________________ Engine type and size _____________________________ ABS ________________________ yes ________________________ no ______________________ If yes, type  NOTE: This job sheet assumes the hub is removed from the vehicle and the outer bearing removed. Procedure

Task Completed

1. Place the hub with the inner side facing up. If necessary, use blocks so clearance is available between the hub and bench.

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2. Use the seal remover to force the seal from its cavity.

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3. Remove the inner bearing.

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4. Wash the bearing and hub cavity using a parts washer.

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WARNING  Do not allow the bearing to spin when using compressed air as a drying agent. Serious injury could result if the bearing comes apart. 5. Use reduced-pressure compressed air to dry the bearing. Use a catch basin to collect the cleaner and waste.

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6. Using the appropriate service manual procedure, remove the bearing race. (Make sure you are wearing your safety glasses.)

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7. Using the correct bearing race installer, replace the race.

Task Completed

Results   8. Place the bearing, small end down, into the bearing packer.

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9. Force the grease into the bearing until clean ribbons of grease are visible at the top of the rollers.

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10. Smear a light coat of grease on the outer sides of the rollers.

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11. Install the bearing, small end first, into the cleaned and dried hub cavity.

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12. Place the grease seal, lip first, over the cavity.

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13. Hold the seal in place with the seal driver while using the hammer to drive the seal in place.

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14. Drive the seal in until it is flush with the edge of the hub.

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15. Use your fingers to rotate the bearing within the hub. If it moves freely, the task is complete. Results   Problems Encountered    Instructor’s Response   

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INSPECTING AND REPLACING WHEEL STUDS Upon completion of this job sheet, you will be able to inspect and replace wheel studs in axle flanges, brake rotors, and drums. ASE Education Foundation Correlation This job sheet addresses the following AST task: F.7.

Inspect and replace wheel studs. (P-1)

This job sheet addresses the following MAST task: F.8.

Inspect and replace wheel studs. (P-1)

Tools and Materials • Bushing tool • Hammer • Punch set • Thread chaser Protective Clothing Goggles or safety glasses with side shields Describe the vehicle being worked on: Year _____________________ Make _____________________ Model _____________________ VIN _____________________ Tire size __________________ Wheel diameter _____________ Procedure

Task Completed

1. Determine the proper lift points for the vehicle. Describe them here:   2. Raise the vehicle. Make sure it is high enough to remove the wheel assembly. Once it is in position, place safety stands under the vehicle or set the mechanical lock on the lift.

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3. Remove the lug nuts and the tire and wheel assembly.

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4. Are any wheel studs broken or missing? Yes _________________ No ________________ Explain:   5. Carefully inspect the condition of the wheel stud and lug nut threads. Describe their condition.   6. If the lug nuts are severely damaged, both the lug nut and the associated wheel stud should be replaced. If the lug nut threads are slightly damaged, they can be cleaned and corrected with a thread chaser. What size chaser would you use in the lug nuts of this vehicle? 

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7. If a wheel stud needs to be replaced, the procedure to do so varies with the component the stud is installed in. The studs can be pressed into the axle flange, rotor, or drum. Where are the studs installed on this vehicle?  

Task Completed

8. If the wheel studs are installed in the axle flange, they can typically be loosened by tapping the outer end of the stud with a hammer and punch. Attempt to do this and describe what happened.   9. If the stud did not loosen with the tapping, use a bushing press to press the stud out of the flange.

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10. Removing a stud from a drum or rotor can be more difficult, depending on how the stud is retained. Carefully study the drums and/or rotors, and describe how the studs are retained.   11. If the stud is held by swaging, the raised metal around the base of the stud must be removed with a special cutting tool.

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12. After the retaining metal has been removed, the stud can be tapped or pressed. Make sure you use the correct tools and don’t damage or distort the drum or rotor. Describe any difficulties you had in doing this.   13. Before installing a new stud, make sure it is the same diameter and length as the original one and has the same length of serrations.

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14. Install the new stud into its bore.

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15. Place several flat washers over the stud threads.

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16. Install and tighten a lug nut, with its flat side against the flat washers, onto the stud. The stud will be pulled into position as the lug nut is tightened.

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17. Loosen the lug nut and remove the washers. Check to make sure the stud is fully seated.

h

18. Before installing the wheel and tire assembly, make sure the tire is inflated to the recommended inflation. What is that inflation?   19. Install the wheel assembly onto the vehicle and start each of the lug nuts.

h

20. Hand tighten each lug nut so that the wheel is fully seated against the hub. Then tighten the lug nuts to specifications and in a staggered or star pattern. The order you used to tighten the lug nuts was:  The recommended torque spec is: 

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Problems Encountered    Instructor’s Response   

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Upon completion and review of this chapter, you should be able to: ■■

Perform a safe brake system test drive.

■■

■■

Diagnose problems in the brake pedal linkage and repair as necessary. Adjust pedal free play to manufacturer’s specifications.

■■

■■

■■

Diagnose poor stopping, brake drag, or hard pedal caused by master cylinder problems and perform needed repairs. Check the master cylinder fluid level and fill as necessary. Analyze the condition of a vehicle’s brake fluid from its appearance.

■■

■■ ■■

■■

Inspect a master cylinder for leaks and defects. Test a master cylinder for leakage and air entrapment and determine needed repairs.

Basic Tools Basic technician’s tool set Clean shop towel Flare-nut wrench

Remove and replace a master cylinder and bench bleed the master cylinder before installation. Overhaul a master cylinder. Locate the hydraulic bleeding sequence and instructions for a specific vehicle in service information. Bleed and flush the brake hydraulic system.

Terms To Know Bench bleeding Bleeder screw Brake bleeding Gravity bleeding

Integral ABS Manual bleeding Non-integral ABS Pressure bleeding

Refractometer Specific gravity Surge bleeding Vacuum bleeding

BRAKE SYSTEM ROAD TEST To operate safely, the master cylinder and other hydraulic components of a brake system must work properly. Leaks in the master cylinder or brake lines can rob the system of pressure and cause dangerous operating conditions, which is why the master cylinder and hydraulic system must be inspected whenever the brake pads or linings are changed or when a customer complains of poor braking. Any problems must be corrected immediately. Check for the following conditions that can cause poor brake performance: ■■ Tire problems. Worn, mismatched, under-inflated, or over-inflated tires cause unequal braking. ■■ Unequal vehicle loading. A heavily loaded vehicle requires more braking power. If the load is unequal from front to back or side to side, the brakes may grab or pull to one side.

133

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Wheel misalignment. Wheels that are out of alignment may cause problems that appear to be related to the brakes. For example, tires with excessively unequal camber or caster settings pull to one side.

WARNING  Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to this precaution could lead to serious personal injury and vehicle damage. Refer to Chapter 3 for a pre-operation inspection checklist before moving onto a roadway.

If the tires are in good shape and the wheel alignment and vehicle loading do not appear to be the problem, proceed with a brake system road test. Follow these guidelines when road testing a vehicle for brake problems: ■■

■■

■■

The brake light is red in color and is usually one of the largest warning lights on the instrument panel.

Test drive the vehicle on a dry, clean, relatively smooth roadway or parking lot. Roads that are wet or slick or that have loose gravel surfaces will not allow all wheels to grip the road equally. In many cases, loose gravel roads may cause the ABS to function. Rough roads can cause the wheels to bounce and lose contact with the road surface. Avoid crowned roadways. They can throw the weight of the vehicle to one side, which will give an inaccurate indication of brake performance. First test the vehicle at low speeds. Use both light and fairly heavy pedal pressure. If the system can safely handle it, test the vehicle at higher speeds. Avoid locking the brakes and skidding the tires.

Check the brake warning lamp on the instrument panel. Depending on the model of the vehicle, it should light either when the ignition switch is in the start position and go off when the ignition returns to the run position with engine running or come on as the engine starts and stay on for a few seconds afterward (Figure 4-1). If the brake warning lamp stays on when the engine is running, verify that the parking brake is fully released. If it is, the problem may be a low brake fluid level in the master cylinder. Most vehicles have a separate master cylinder fluid level warning lamp. If either warning lamp remains on, check the fluid level in the master cylinder reservoir. Listen for unusual brake noise during the test drive. Are there squeals or grinding? Do the brakes grab or pull to one side? Does the brake pedal feel spongy or hard when applied? Do the brakes release promptly when the brake pedal is released?

Figure 4-1  Depending on the model of the vehicle, the bulb test for the red brake lamp and amber ABS lamp may come on at key on, start or immediately after starting.

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135

Figure 4-2  Checking stop lamp operation.

BRAKE PEDAL MECHANICAL CHECK Checking the brake pedal mechanical operation is an important part of brake troubleshooting. Whether you do it as part of the brake system road test or during a system leak test, check these points of pedal operation: ■■ Check for friction and noise by pressing and releasing the brake pedal several times (with the engine running for power brakes). Be sure the pedal moves smoothly and returns with no lag or noise. ■■ Move the brake pedal from side to side. Excessive side movement indicates worn pedal mounting parts. ■■ Check stop lamp operation by depressing and releasing the brake pedal several times. Have a coworker check that the lamps light each time the pedal is pressed and go off each time it is released (Figure 4-2), including the third or center—high-mounted— stoplight. It is important to note that some vehicles equipped with lighting modules have to have the ignition in run before the brake lamps will operate.

Classroom Manual page 74

Special Tools Coworker

PEDAL TRAVEL AND FORCE TEST Air in the hydraulic system causes most low-pedal problems, and bleeding the system usually solves the problems. Low pedal also can be caused by a leak in the hydraulic system, incorrect pushrod length adjustment, a service brake that is out of adjustment, worn brake shoes, or a drum brake shoe adjuster that is not working. When a given amount of force is applied to the pedal, brake pedal travel must not exceed a specified maximum distance. This maximum travel specification is normally about 2.5 inches (64 mm) when 100 pounds (445 N) of force is applied. The exact specifications can be found in the vehicle service information. Failure to exhaust brake boost pressure will result in an incorrect pedal travel or force measurement. Use a brake pedal effort gauge to measure force applied to the pedal with these five procedures:

Special Tools Brake pedal effort gauge Tape measure Service manual

1. Turn off the engine. On vehicles with vacuum assist, pump the pedal until all reserve vacuum is exhausted from the booster. 2. Install the brake pedal effort gauge on the brake pedal (Figure 4-3). 3. Hook the lip of the tape measure over the top edge of the brake pedal and measure the distance from the pedal to the steering wheel rim (Figure 4-4). You can use a yardstick on some vehicles in place of a tape measure.

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Chapter 4 Tape measure

Brake effort pedal gauge Unapplied brake pedal

Brake pedal effort gauge

Figure 4-4  Use a tape measure or a yardstick to measure the distance from the pedal to the steering wheel.

Figure 4-3  Install the brake pedal effort gauge on the brake pedal.

Figure 4-5  Apply the specified amount of pedal force.

4. Apply the brake pedal until the specified test force registers on the brake pedal effort gauge (Figure 4-5). SERVICE TIP   Before starting any diagnosis, refer to the vehicle’s service history if available. Note any recent history pertaining to this repair order, for example, brake pedal low. A recent brake repair may point the way to a quick, accurate diagnosis.

5. Note the change in pedal position on the tape measure or yardstick. The increased distance should not exceed the maximum specification listed in the vehicle service manual. If it does, look for a leak in the hydraulic system and check pushrod adjustment. Worn shoes, bad shoe adjusters, or a poorly adjusted parking brake also can cause excessive pedal travel.

PEDAL FREE PLAY INSPECTION AND ADJUSTMENT Classroom Manual page 75

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Brake pedal free play is the clearance between the brake pedal or booster pushrod and the primary piston in the master cylinder. A specific amount of free play must exist so that the primary piston is not partially applied when the pedal is released and so that pedal

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travel is not excessive. Free play at the primary piston is usually only a small fraction of an inch or a few millimeters. The pedal ratio multiplies this free play to about ⅛ inch to ¼ inch at the pedal (Figure 4-6). Too much free play causes the pedal to travel too far before moving the pistons far enough to develop full pressure in the master cylinder. Excessive free play can severely reduce braking performance and create an unsafe condition.

137

Special Tools Trap measure of rule Service information

SERVICE TIP   Some vehicles require an adjustment of the booster pushrod when the booster is replaced. Some require the booster pushrod be adjusted before adjusting the pedal pushrod, or vice versa. It is important to check both pushrods if the booster is replaced. The manufacturer will have specific instructions in its service information.

Too little free play causes the pedal to maintain contact with the primary piston. This can cause the piston cup to block the vent port and maintain pressure in the lines when the pedal is released. Unreleased pressure can cause the brakes to drag, overheat, fade, and wear prematurely. Additionally, with the piston cup blocking the vent port, each stroke of the pedal draws fluid from the low-pressure area behind the piston into the highpressure area in front of the piston as the pedal is released. Eventually, enough fluid pressure can accumulate ahead of the piston to lock the brakes. Check pedal free play by pumping the brake pedal with the engine off to exhaust vacuum in the booster. Place a ruler against the car floor, in line with the arc of pedal travel. Then press the pedal by hand and measure the amount of travel before looseness in the linkage—the free play—is taken up. Take the measurement at the top or bottom of the pedal, whichever provides the most accurate view. Refer to vehicle specifications for the exact amount of free play to be provided. Adjust the free play by lengthening or shortening the pushrod. On most vehicles, loosen the locknut on the pushrod at the pedal and rotate the pushrod while rechecking free play measurement. Tighten the locknut when adjustment is correct. Free play at pushrod inch (1.5 mm)

Pedal free play to inch (3 to 6 mm)

Figure 4-6  The pedal ratio multiplies free play at the master cylinder several times at the pedal.

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SERVICE TIP   The vehicle’s brake light switch must be activated any time the brake pedal is moved downward any amount. There is “no free play” allowed with regard to the brake light switch.

AUTHOR’S NOTE  The following procedure is based on a Honda S2000. Other vehicles have similar procedures. Many vehicles do not have an adjustment for pedal height.

Adjusting Pedal Height

Caution If the switch is not adjusted correctly, the brakes will drag. This may cause heat problems with the friction materials and poor braking performance.

One method to adjust the brake pedal height and free play follows. Disconnect and loosen the brake pedal position switch until it is no longer touching the brake pedal lever (Figure 4-7, A and B). Gain clear access to the floorboard by lifting the carpet and the insulator (Figure 4-8C). Measure the pedal height, (Figure 4-8), from the right center of the brake pad to the cleared floorboard. In the case of this Honda, the pedal height should be 179 mm or 7 ¹/₆ inches). If necessary to adjust the pedal height, loosen the locknuts, and turn the pushrod to obtain the correct measurement (Figure 4-9). With the correct height obtained, hold the pushrod in place while tightening the locknut to 15 Nm (11 ft. lb.). Install the brake pedal position switch until its plunger is against the pedal lever and completely pushed into the switch (Figure 4-10). Unscrew the switch until there is 0.3 mm (0.01 inch) between the switch’s threaded end and the mounting pad. Connect the switch to its electrical harness. Have an assistant check the brake lights as the brake pedal is depressed and released.

Adjusting Pedal Free Play Using the same Honda vehicle as the example, the pedal free play is checked and adjusted in the following manner. The engine should be off. Push on the brake by hand while Pushrod Locknut (A) Brake switch

Lift floor mat

(C) Measuring point (B) Pedal bracket

Figure 4-7  Remove the pedal position switch or stop lamp switch from the pedal bracket.

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(E) Pedal height Standard pedal height (with carpet removed): 179 mm (7 in.)

Figure 4-8  Remove the floor mat and a portion of the carpet to gain clear access to the floorboard.

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139

Pedal lever

Pushrod

(A) 0.3 mm (0.01 in.)

Raise the pedal

Figure 4-9  Loosen the locknut and turn the pushrod to make the rod longer or shorter depending on the movement needed.

Figure 4-10  Turn the switch within its locknut until the proper clearance is obtained. The clearance on this switch should be 0.3 mm (0.01 inch) at point A.

(C) Locknuts

Brake pedal pad Pedal play 1–5 mm

Figure 4-11  Check the pedal free play. If adjustment is needed, turn C until the proper free play is achieved. Check the stop lamp’s operation.

measuring the distance the pedal travels before a stiff resistance is felt. This measurement is taken at the brake pedal foot pad and should be 1 mm to 5 mm (1/6 inch to 3/16 inch) (Figure 4-11). If necessary, adjust the free play by loosening the locknut on the brake pedal switch and turning the switch in the appropriate direction until the free play is correct. Do not forget to tighten the locknut after the adjustment is made and recheck the free play after the locknut is tightened. If the car has a mechanical stop lamp switch on the brake pedal linkage, check switch operation and adjust it if necessary after adjusting pedal free play.

Brake pedal free play is not adjustable on all vehicles.

Adjusting the Stop lamp Switch AUTHOR’S NOTE  The following procedure is based on 2010 Chrysler 300 Series and Magnum vehicle.

SERVICE TIP   At one time, a stop lamp switch could be adjusted by warping its mount to get the plunger lined up. However, today’s stop lamp switches are usually multifunctional units with up to four or five different internal switches or contacts that serve many computer systems. Some vehicles are using a sensor that informs the Body Control Module (BCM) or Engine Control Module (ECM) of the brake pedal position and extent of travel. The sensor is named the Brake Pedal Position (BPP) Switch. The BCM will operate the brake lamps according to the BPP switch.

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Chapter 4 Stoplamp switch

Stoplamp switch mounting bracket

Brake pedal lever

Figure 4-12  Pull the switch plunger all the way out before installation. The pedal should be locked down and not released until the switch is installed.

Use a brake pedal depressor to hold the brake pedal down (check the alignment machine for a depressor). Rotate the stop lamp switch approximately 30 degrees counterclockwise and pull rearward on the switch. It should separate from its mount (Figure 4-12). Using hand force only, pull the switch plunger out to its fully extended position. Low clicks should be heard as the plunger ratchets out. Ensure the brake pedal is down as far as it will go and is firmly held in place. Align the switch’s index key to the notch in the bracket and push the switch into place. Rotate the switch about 30 degrees clockwise until it locks. Apply foot force to the brake pedal and remove the pedal depressor. Allow the pedal to gently rise until it stops. Using gentle hand force, pull up on the brake pedal until it stops moving. This will ratchet the switch plunger to the correct position. The switch adjustment is initially checked by having an assistant observe the brake lights as the brake pedal is depressed and released. However, the final check requires a road test on a road where the cruise control can be safely used. During the road test, engage the cruise control at a safe speed. Once the system is stabilized, depress the brake slightly. The cruise control should turn off. If not, then the switch must be checked and readjusted as needed.

Caution Do not release the brake pedal by pulling the depressor out and letting the pedal slam up to its stop. The stop lamp switch will not adjust properly and may be damaged.

CUSTOMER CARE  A customer’s only contact, literally, with the brake system in his or her car is through the brake pedal. Customers tend to judge brake performance by “pedal feel.” It is always a good idea to evaluate the feel and action of the brake pedal before starting any brake job. Then when you deliver the finished job, pedal feel should be noticeably improved. The biggest cause of spongy or low brake pedal action is air in the system, so careful bleeding of the system will do a lot to ensure customer confidence.

Brake Pedal Position Switch Many late-model vehicles use a BPP sensor to inform the body control module (BCM) of the brake pedal position (Figure 4-13). The BPP sensor is a potentiometer. The BCM supplies a 5-volt reference signal and ground to the sensor and the sensor supplies an

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Left rear brake lamp power output

Right rear brake lamp power output

5V

Signal

A

Ground

Switched 12V relay power from BCM

141

BCM

B

Brake pedal position sensor C Left rear brake lamp

B+

Right rear brake lamp

30 CHMSL relay 87

86

Fuse

Center high mount stop lamp

ECM

TCM

G301

Figure 4-13  A typical BCM controlled stop lamp circuit.

analog signal back to the BCM. The BCM supplies power to the brake lamps directly, while the BCM controls a relay to operate the high-mounted stop lamp. If the BCM or BPP sensor is replaced, the brake pedal position must be calibrated to insure the brake lamps, cruise control, and/or torque converter clutch will operate properly.

Typical Procedure for Calibrating a GM Brake Pedal Position Sensor

1. The vehicle is parked and the parking brake is applied. 2. Install a scan tool and clear codes from the BCM. 3. Go to the Vehicle Control Systems menu. 4. Select module set-up. 5. Select BCM. 6. Follow Brake Pedal Position Calibration instructions. Use care not to apply the brake pedal during the calibration, or the calibration will have to be redone. 7. Test brake lamp operation.

BRAKE FLUID PRECAUTIONS The specifications of all automotive brake fluids are defined by SAE Standard J1703 and Federal Motor Vehicle Safety Standard (FMVSS) 116. Fluids classified according to FMVSS 116 are assigned U.S. Department of Transportation (DOT) numbers: DOT 3, DOT 4,

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Classroom Manual page 69

and DOT 5. Basically, the higher the DOT number, the more rigorous the specifications for the fluid. Review Chapter 4 of the Classroom Manual for a detailed explanation of brake fluid specifications. Choosing the right fluid for a specific vehicle is not the simple idea that if DOT 3 is good, DOT 4 must be better, and DOT 5 better still. Domestic carmakers all specify DOT 3 fluid for their vehicles, but Ford calls for a heavy-duty variation that meets the basic specifications for DOT 3 but has the higher boiling point of DOT 4. Import manufacturers are about equally divided between DOT 3 and DOT 4. DOT 5 fluids are all silicone based because only silicone fluid can meet the DOT 5 specifications. However, no vehicle manufacturer recommends DOT 5 fluid for use in its brake systems, particularly in antilock brake systems. Although all three fluid grades are compatible in certain aspects, they do not combine if mixed together in a system. DOT 5 in particular should never be mixed with or used to replace other types of brake fluids. Therefore, the best general rule is to use the fluid type recommended by the carmaker and do not mix fluid types in a system.

Caution DOT 5.1 and DOT 5.1 long-life brake fluids are not siliconebased fluids. Do not mix or replace DOT 5 fluid with DOT 5.1 or DOT 5.1 long-life fluids. Damage to the brake system and possible injury could occur due to damage to brake system components.

Caution When working with brake fluid, do not contaminate it with petroleum-based fluids, water, or any other liquid. Keep dirt, dust, or any other solid contaminant away from the fluid. Contaminated fluid may cause system failure.

SERVICE TIP   If the vehicle is still under manufacturer warranty or covered by an extended warranty, check with the warranty writer or agent to determine if the use of synthetic brake fluids violates the warranty terms. Some warranties are very specific about repair or replacement parts and fluids.

The DOT rating is found on the brake fluid container (Figure 4-14). The vehicle service manual and owner’s manual specify what rating is correct for the car. Do not use a brake fluid with a lower DOT rating than specified by the manufacturer. The lower-rated fluid could boil and cause a loss of brake effectiveness. DOT 3/4 and DOT 5.1 synthetic brake fluids should be stored in the same manner as other brake fluids and can be mixed or used to replace DOT 3 or DOT 4 fluids. Refer to the manufacturer or service manual to see if synthetic fluids can be used in the vehicle being repaired.

Figure 4-14  The brake fluid DOT number is found on every brake fluid container.

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WARNING  Brake fluid can cause permanent eye damage. Always wear eye protection when handling brake fluid. If you get brake fluid in your eye, see a doctor immediately. WARNING  Brake fluid will irritate your skin. If fluid gets on your skin, wash the area thoroughly with soap and water. WARNING  Brake fluid is a toxic and hazardous material. Dispose of used brake fluid in accordance with local regulations and EPA guidelines. Do not pour used brake fluid down a wastewater drain or mix it with other chemicals awaiting disposal. DOT 5 SILICONE FLUID DOT 5 silicone fluid does not absorb water and has a very high boiling point. It is noncorrosive to hydraulic system components, and it does not damage paint as does polyglycol fluid. DOT 5 fluid has other characteristics that are not so beneficial. DOT 5 silicone fluid has a lower specific gravity than polyglycol fluid. If the two types are mixed, they do not blend; the silicone fluid separates and floats on top of the polyglycol fluid. Silicone fluid compresses slightly under pressure, which can cause a slightly spongy brake pedal feel. Silicone fluid also attracts and retains air more than polyglycol fluid does, which makes brake bleeding harder; it tends to outgas slightly just below its boiling point; and it tends to aerate from prolonged vibration. DOT 5 fluid has other problems with seal wear and water accumulation and separation in the system. All of these factors mean that DOT 5 silicone fluid should never be used in an ABS. The best practice is to use a single, high-quality brand of brake fluid of the DOT type specified for a particular vehicle. Avoid mixing fluids whenever possible. WARNING     DOT 5 should never be mixed with or used to replace DOT 3, DOT 4, or DOT 3/4, or DOT 5.1 fluids because of their chemical incompatibility. They will not mix and silicone can damage seals designed for polyglycol liquids.

MASTER CYLINDER FLUID SERVICE Brake fluid service procedures are the most basic—but among the most important—brake system services. The following paragraphs provide instructions for checking the master cylinder fluid level and adding fluid to the system. Later sections of this chapter contain procedures for bench bleeding a master cylinder. Complete system bleeding instructions and fluid flushing and filling instructions are discussed later.

Checking Master Cylinder Fluid Level and Condition Master cylinder fluid level and fluid condition should be inspected at least twice a year as part of a vehicle preventive maintenance schedule. If the car has a translucent fluid reservoir, general fluid level can be checked every time the motor oil is checked or changed. Although normal brake lining wear causes a slight drop in fluid level, an abnormally low level in either chamber—especially an empty reservoir—usually means that there is a leak in the system. When checking the fluid in the master cylinder, look for two things. First, be sure that the reservoir is filled to the correct level. A two-piece master cylinder with a plastic reservoir usually has graduated markings to indicate the correct fluid level (Figure 4-15). The markings may be on the outside of the reservoir if the reservoir is translucent, or they

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Caution Never mix glycolbased and siliconebased fluids because the mixture could cause a loss of brake efficiency and possible injury.

Caution Always store brake fluid in clean, dry containers. Brake fluid is hygroscopic; it will attract moisture and must be kept away from dampness in a tightly sealed container. When water enters brake fluid, it lowers the boiling point. Never reuse brake fluid.

Caution DOT 3 and DOT 4 polyglycol fluids have a very short storage life. As soon as a container of DOT 3 or DOT 4 fluid is opened, it should be used completely because it immediately starts to absorb moisture from the air.

Caution Do not spill glycolbased brake fluid on painted surfaces. Glycol-based fluids damage a painted surface. Always flush any spilled fluid immediately with cold water.

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Caution DOT 5.1 and DOT 5.1 long-life brake fluids are not siliconebased fluids. Do not mix or replace DOT 5 fluid with DOT 5.1 or DOT 5.1 long-life fluids. Damage to the brake system and possible injury could occur due to damage to brake system components. Classroom Manual: page 80

Special Tools Brake fluid Cloths

Layering or separation of fluids occurs when a lightweight fluid separates and floats on top of heavier fluids. Mix oil and water and the oil will sink to the bottom.

MAX MIN

Figure 4-15  Most translucent reservoirs have markings for the minimum and maximum fluid levels (arrows).

may be inside if the reservoir is opaque. Fill the reservoir to the FULL mark or equivalent. If the master cylinder has a one-piece cast body with an integral reservoir, fluid level may not be marked in the reservoir. In this case, fill the reservoir to ¼ inch (6 mm) from the top. If the reservoir is mounted at an angle on the master cylinder, measure fluid level at the point closest to the reservoir rim (Figure 4-16). Some composite master cylinders have opaque plastic reservoirs (Figure 4-17). Remove the reservoir caps or covers to check fluid level, it should be level with the indicator inside. Do not overfill any reservoir and use only the type of fluid specified by the vehicle maker. For 90 percent of vehicles, this will be DOT 3 or DOT 4 fluid. Photo Sequence 5 shows the procedure for filling the master cylinder reservoir. The second thing the brake fluid is checked for concerns contamination. Most DOT 3 and DOT 4 fluids are clear or light amber when fresh, and, ideally, fluid in service should retain most of its original appearance. Fluid in good condition should be clear and transparent, although some darkening is allowable. Any of the following conditions may indicate the need for flushing and refilling the system or for more serious service: 1 – 4 inch

Fill to bottom of ring

Level Cylinder 1 – 8 inch

Tilted Cylinder

Figure 4-16  Check fluid level at the point closest to the reservoir rim if the master cylinder is tilted. Fluid level is usually higher for a tilted reservoir.

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Figure 4-17  Checking fluid level in an opaque plastic reservoir.

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145

Photo Sequence 5

Typical Procedure for Filling a Master Cylinder Reservoir

P5-3  Check that the vent is open. Some have a hole in the cover, some have a passage. The vent allows the fluid level to change without building a vacuum.

P5-1  Thoroughly clean the reservoir cover before removing it to prevent dirt from entering the reservoir body.

P5-2  Remove the reservoir cover and the diaphragm.

P5-4  Inspect the diaphragm for holes, tears, and other damage. If the diaphragm is swelled, the brake system fluid has been contaminated.

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P5-5  Check the brake fluid level and its appearance. The fluid level should be within 1/4 inch of the top of the reservoir or at the reservoir’s (FULL or MAX) level marking. The fluid should be clean, with no rust or other contamination. Note the level of fluid in each section of the reservoir for diagnostic purposes.

P5-6  Fill the reservoir with the recommended brake fluid. The wrong type of brake fluid, contaminated fluid, water, or mineral oil may cause the brake fluid to boil or the rubber components in the system to deteriorate.

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SERVICE TIP   Phoenix Systems offers a set of test strips to check the contamination (Figure 4-18). This strip is not a moisture or pH test but tests for copper instead. A strip is dipped into the fluid in the reservoir and the color change is compared to a supplied test chart. This is almost a fail-safe method of field testing the brake fluid and making a service recommendation to the customer.

Figure 4-18  Test strips for determining if the brake fluid is contaminated.

Caution Be careful to avoid spraying brake fluid. To protect your face, never bend directly over the reservoir. Wear eye protection.

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If the vehicle’s brake fluid is contaminated with mineral oil (power steering fluid, engine oil, and transmission fluid) the rubber parts of the system will have to be replaced. The mineral oil will swell the seals, and render them useless. A sure sign of this is the swelling of the master cylinder cover diaphragm. If the diaphragm is swollen, or the customer tells you that the system has been contaminated, all rubber parts, and any part that has rubber internal seals of the braking system will have to be replaced. The steel lines must be flushed. This includes the calipers and/or wheel cylinders, rubber brake lines, master cylinder, and hydraulic modulator. Do not try to save any seal containing parts; there is a very good chance they will fail. On some antilock brake systems, the system must be depressurized before adding brake fluid. When depressurized, fluid level may rise slightly, giving a more accurate level reading. ■■ Swelling of the master cylinder cover diaphragm. A vehicle that shows signs of swelling of the rubber diaphragm in the cap of the master cylinder is an indication of mineral oil contamination of the brake fluid. ■■ Cloudy fluid. Cloudiness usually indicates moisture contamination. ■■ Dark brown or murky fluid, not transparent. Very dark fluid usually indicates excessive contamination by rust and dirt. ■■ Layering or separation. These conditions indicate a mixture of two fluids that have not blended together. The contaminating fluid may be oil or some other petroleumbased product, or it may be DOT 5 silicone fluid. ■■ Layering or separation accompanied by cloudy or murky color and deteriorated rubber parts. This condition almost always indicates oil contamination. In this case, the system must be flushed thoroughly and all seals and other rubber parts replaced. The following conditions may also be seen when checking fluid in the master cylinder. These conditions by themselves do not always indicate a need for master cylinder service: ■■ Unequal fluid levels in the master cylinder reservoir chambers on front disc and rear drum systems may result as fluid moves from the reservoir into the calipers

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■■

■■

■■

147

to compensate for normal lining wear. On the other hand, if the system is diagonally split, the volumes should be close to equal. Fill both chambers to the full marks. A slight squirt of brake fluid from one or both master cylinder reservoir chambers when the brake pedal is applied is normal. It is caused by fluid moving through the reservoir vent ports as the master cylinder pistons move forward in the bore. Light fluid turbulence in the reservoir when the brake pedal is released is the result of brake fluid returning to the master cylinder after the brakes have been released. A slight trace of brake fluid on the booster shell below the master cylinder mounting flange is normal. It results from the lubricating action of the master cylinder wiping seal.

CUSTOMER CARE  Remind your customers to check the brake fluid level in their master cylinder reservoirs periodically, particularly on older vehicles that may develop slow leaks. Leaking fluid is a sign of trouble. Emphasize that service is needed whenever this problem is noticed.

SERVICE TIP   If the reservoir is more than half-full, do not top of the master cylinder unless it has just been serviced. If this chamber of the reservoir is more than half empty, do not add brake fluid until the wear on the disc brake pads is checked. Adding brake fluid and then servicing the disc brakes could result in brake fluid being sprayed past the reservoir cover and damaging the vehicle’s finish.

Checking Boiling Point and Water Content A simple instrument called a refractometer can be used for a quick check of brake fluid water content and boiling point. A refractometer works by measuring the way light is bent or refracted as it passes through a liquid. A refractometer works on the principle that different liquids have different specific gravities, and liquids of different specific gravities will refract or bend light waves at different angles. As brake fluid absorbs water, its specific gravity changes. Water refracts light in a specific way. A brake fluid refractometer is graduated so that the specific gravity is correlated to the water content of the fluid and the resulting change in boiling point. To use the refractometer, place a couple drops of fluid on the sample window, close the cover, point the instrument toward a light source, and focus the eyepiece. Light shining through the fluid sample will refract or bend and indicate a line across the measuring scale. SAE tests have shown that the average 1-year-old car contains 2 percent water in its brake fluid. This occurs just through the normal hygroscopic attraction of polyglycol fluids for water. As little as 4 percent water content can cut the boiling point of DOT 3 fluid in half. Checking brake fluid with a refractometer can often be the deciding point on whether complete flushing and refilling of the hydraulic system should be recommended.

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Special Tools  Refractometer Service information

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CHECKING ABS FLUID LEVEL A refractometer is a test instrument that measures the deflection or bending of a beam of light.

Some older ABSs have an electrohydraulic booster that shares the reservoir with the master cylinder. Some require the system accumulator to be charged, whereas others require it to be discharged before checking fluid level. Teves supplies ABS components to several vehicle manufacturers, including Ford and General Motors. However, most modern vehicles with ABS require no special procedures to check the fluid, with a few exceptions.

Ford Depressurization is not needed on most late model Ford products. The fluid level should be at the MAX mark on the master cylinder reservoir. This system uses DOT 3 brake fluid. Specific gravity is the weight of a volume of any liquid divided by the weight of an equal volume of water at equal temperature and pressure.

General Motors Most GM vehicles with antilock brakes do not require depressurization with one exception. The Kelsey-Hayes EBC 440 ABS system used on some full-size trucks requires the brake system to be depressurized, but the depressurization occurs automatically after the key is turned to the off position (without stopping in the accessory position) and not applying the brake pedal. After one to three minutes, the system will depressurize, and the fluid level can then be checked. WARNING  Never open or loosen a brake line serving the ABS controls or modules without ensuring that the pressure has been released. Opening a pressurized line could result in injury. See service information before servicing any ABS system.

MASTER CYLINDER TEST AND INSPECTION Classroom Manual page 78

Special Tools Brake fluid Service manual Coworker Rule

Check for cracks in the master cylinder housing. Look for drops of brake fluid around the master cylinder. A slight dampness in the area surrounding the master cylinder is normal and is usually no reason for concern. However, if a reservoir chamber is cracked, it may be completely empty and the surrounding area may be dry. This is because the fluid drained very quickly and has had time to evaporate or wash away. But with only one-half of the brake system operational, the BRAKE warning lamp should be lit and a test drive should reveal the loss of braking power. Refill the master cylinder reservoir section that is empty and apply the brakes several times. Wait 5 to 10 minutes and check for leakage or fluid level drop in the reservoir. Although brake pedal response and reservoir fluid levels are strong indicators of problems with the master cylinder or hydraulic system, other tests can be performed to help pinpoint the problem.

Hydraulic System Inspection If the master cylinder does not appear to be leaking, raise the vehicle on a lift and inspect all brake lines, hoses, and connections (Figure 4-19). Look for brake fluid on the floor under the vehicle and at the wheels. Brake lines must not be kinked, dented, or otherwise damaged, and there should be no leakage. Brake hoses should be flexible and free of leaks, cuts, cracks, and bulges. Drum brake backing plates and disc brake calipers should be free of brake fluid and grease. Any parts attached to them should be tight.

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(A)

(B)

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(C)

Figure 4-19  Inspect the hydraulic system for leaks at these and other points: (A) brake lines and hoses, (B) drum brake backing plates, and (C) disc brake calipers.

SERVICE TIPS   Wagner Brake Products sells a set of test strips used to indicate the amount of moisture content in DOT 3 or DOT 4 brake fluid. The product is called Wet Check and works in less than 1 minute. Dip the end of the strip into the brake fluid and watch the color. The shade of color indicates the amount of moisture (water) in the fluid. Snap-on Tools has an instrument that will boil the water and alert the technician to contaminated fluid.

Testing the Hydraulic System for Trapped Air The following test requires a helper to pump the brake pedal while the reaction of fluid in the master cylinder is observed (Figure 4-20): 1. Top off the master cylinder reservoir with fresh brake fluid. 2. Loosely place the gasket and cover on the master cylinder. Do not tighten the cover. 3. Have the coworker rapidly pump the brake pedal approximately 20 times. The brake pedal should be held down on the last application. 4. Remove the master cylinder cover and observe the fluid in the reservoirs. 5. Have the coworker release the brake pedal quickly. If air is trapped in the system, pumping the brake pedal will compress it. When the brake pedal is released, the compressed air will expand. This will push brake fluid back into the master cylinder with enough force to produce bubbling or even a small geyser. 6. If air is found in the system, bleed or flush the brake system following the service manual recommended sequence.

Paint missing from the booster or vehicle finish below the ­driver’s end of the master cylinder ­indicates an external leak. The master ­cylinder should be replaced. If brake fluid has been pulled into the brake booster, it may also have to be replaced.

Checking Master Cylinder Fluid Level and Condition Hydraulic brake system leaks can be internal or external. Most internal leaks are actually fluid bypassing the cups in the master cylinder. If the cups lose their ability to seal the pistons, brake fluid leaks past the cups, and the pistons cannot develop system pressure. Internal and external rubber parts wear with use or can deteriorate with age or fluid contamination. Moisture or dirt in the hydraulic system can cause corrosion or deposits to form in the bore, resulting in the wear of the cylinder bore or its parts. Although internal leaks do not cause a loss of brake fluid, they can result in a loss of brake performance. This internal leakage, or fluid bypassing back to the reservoir, is the cause of many softpedal or no-pedal complaints and can be hard to pinpoint. When external leaks occur, the system loses fluid. External leaks are caused by cracks or breaks in master cylinder

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Chapter 4 Air may be indicated by spongy pedal, low pedal, or bottoming pedal. 1

Check fluid level, replenish if necessary.

2 Replace cap loosely atop cylinder.

3 ...rapidly pumps 20 times and holds.

One technician watches the cylinder while the other

5

4

Release pedal quickly and observe fluid.

Remove cap.

6 Look for geyser or squirt in either reservoir.

RESULTS: Geyser from reservoir: Indicates air trapped in the system. It is compressed by pumping and causes a squirt when released. (If pedal is low, rear brake misadjustment can also cause a geyser.) Action: Bleed the affected system or systems. If one reservoir only, you need not bleed the other.

Figure 4-20  This quick test will help to determine which half of the brake system may have air trapped in it.

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Applied brake pedal Ruler

1

2

3

4

1-inch distance

Floor Power brakes

Figure 4-21  With the brakes applied, the distance from the pedal to the floor should be about 1 inch for power brakes.

Caution reservoirs, loose system connections, damaged seals, or leaking brake lines or hoses. Check for a brake fluid leak as follows: 1. Run the engine at idle with the transmission in neutral. 2. Depress the brake pedal and hold it down with a constant foot pressure. The pedal should remain firm, and the foot pad should be at least 1 inch from the floor (Figure 4-21). 3. Hold the pedal depressed with medium foot pressure for about 15 seconds to make sure that the pedal does not drop under steady pressure. If the pedal drops under steady pressure, the master cylinder or a brake line or hose may be leaking. Inspect the system as described later in this chapter. If the inspection reveals no external leakage, but the pedal still drops under steady pressure, check for fluid bypassing the piston cups inside the master cylinder as explained under Internal Leak Test (Fluid Bypass Test).

Internal Leak Test (Fluid Bypass Test) If the primary piston cup seal is leaking, the fluid will bypass the seal and move between the vent and replenishing ports for that reservoir or, in some cases, between reservoirs. If no sign of external leakage exists, but the BRAKE warning lamp is lit, the master cylinder may be bypassing or losing pressure internally. Another sign of internal leakage, or bypassing, is a fluid level that rises slightly in one or both reservoirs when pressure is held on the brake pedal. Test for fluid bypassing the piston cups as follows: 1. Remove the master cylinder cover and be sure the reservoirs are at least half full. 2. Watch the fluid levels in the reservoirs while a coworker slowly presses the brake pedal and then quickly releases it. 3. If fluid level rises slightly under steady pressure, the piston cups are probably leaking. Fluid level rising in one reservoir and falling in the other as the brake pedal is pressed and released also can indicate that fluid is bypassing the piston cups. 4. Replace or rebuild the master cylinder if it is bypassing fluid internally. Another quick test for internal leakage or bypassing is to hold pressure on the brake pedal for about 1 minute. If the pedal drops but no sign of external leakage exists, fluid is probably bypassing the piston cups.

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This test may result in brake fluid bubbling or spraying out of the master cylinder reservoir. Wear safety goggles. Cover the master cylinder reservoirs with clear plastic wrap or other suitable cover to keep brake fluid off the paint. An external leak may give a hint of its location by looking at which master cylinder reservoir section is low. Remember that each section of the reservoir serves two wheels. Depending on the type of brake system split, the leak can be confined to the front or rear, or a diagonal pair of wheels. Many times internal leakage in the master cylinder can be diagnosed by a symptom of a pedal that goes to the floor when pressure has been applied for a few seconds, such as when sitting at a stop light.

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Test for Open Vent Ports Test for open vent ports in the master cylinder as follows:

SERVICE TIP   The most common customer complaint that indicates an internal master cylinder leak is: “The brakes stop well, but while I am sitting at a stoplight the pedal slowly drops.” To the technician this means that the fluid ahead of one of the master cylinder pistons is leaking past the piston seal and returning to the reservoir. Double-check before replacing the master cylinder.

1. Remove the cover from the master cylinder. While a coworker pumps the brake pedal, observe the fluid reservoirs. A small ripple or geyser should be seen in the reservoirs as the brakes are applied. 2. If there is no turbulence, loosen the bolts securing the master cylinder to the vacuum booster about ⅛ inch to ¼ inch and pull the cylinder forward, away from the booster. Hold it in this position and repeat step 1. 3. If turbulence (indicating compensation) now occurs, adjust the brake pedal pushrod length. If turbulence still does not occur, replace the master cylinder. Turbulence can be seen only in the front (secondary) reservoir of a quick take-up master cylinder. If turbulence does not occur in the master cylinder during the preceding steps, the pistons are probably restricting the vent ports, meaning that the pushrod is not allowing the pistons to return to the fully released positions. In most cases if this occurs, the output pushrod of the power brake booster requires adjustment. Refer to Chapter 6, Power Brake Service, for booster pushrod adjustment instructions.

Quick Take-Up Valve Test Classroom Manual page 88. This is a quick, accurate test that can be used after a master cylinder or booster replacement to confirm pushrod placement.

The quick take-up valve is used in quick take-up master cylinders with low-drag disc brakes to provide a high volume of fluid on the first pedal stroke. This action takes up the slack in low-drag caliper pistons. No direct test method exists for a quick take-up valve, but excessive pedal travel on the first stroke may indicate that fluid is bypassing the valve. If this symptom exists, check for a damaged or unseated valve. If the pedal returns slowly when the brakes are released, the quick take-up valve may be clogged so that fluid flow from the cylinder to the reservoir is delayed.

INTEGRAL AND NON-INTEGRAL ABS SYSTEMS The vast majority of vehicles today are equipped with ABS. The difference in master ­cylinder removal is whether the ABS system is an integral ABS or non-integral ABS. A hydraulic modulator from a non-integral ABS is shown in Figure 4-22. The master cylinder from the non-integral ABS is shown in Figure 4-23. The integral systems have the ABS master cylinder, hydraulic modulator, and hydraulic booster built together as an assembly Figure 4-24. Many of the integral units use brake fluid under pressure and a pump to provide power assisted braking (so no vacuum booster is present). The nonintegral unit generally has a vacuum booster and conventional master cylinder with a separate hydraulic modulator. More on these in Chapter 10.

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Figure 4-22  ABS Hydraulic Modulator.

Cap and connector Fluid reservoir

Solenoid valve connector

Pressure warning switch

Solenoid valve block

Hydraulic pump

Figure 4-24  Non-Integrated ABS systems include the hydraulic ­modulator and master cylinder into one unit. Figure 4-23  Master cylinder.

Some manufacturers called the non-integral ABS an “add-on” ABS because the system used a basic brake system with ABS hardware “added.”

Removing a Master Cylinder (without Integral ABS)

The hydraulic modulator is often called the brake pressure modulator valve or BPMV.

Remove the master cylinder from the vehicle as follows: 1. Disconnect the battery ground (negative) cable. 2. Relieve any residual vacuum by pumping the pedal 15 to 20 times until you feel a change in pedal effort. 3. Use a shop towel to remove any loose dirt or grease around the master cylinder that could work its way into open lines or the vacuum booster unit. 4. Unplug the electrical connector from the fluid level sensor, if equipped.

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Chapter 4 Vacuum booster Master cylinder

Fluid level sensor

Nuts Brake lines

Figure 4-25  Remove the mounting nuts and disconnect the brake lines and any electrical connectors to remove the master cylinder.

Special Tools Hand Tools Catch basin Cloths After exhausting the booster, the brake pedal should become very firm even with a malfunctioning master cylinder.

Caution Do not drip brake fluid onto the vehicle paint while removing the master cylinder. Paint damage will occur.

5. Place a container under the master cylinder to catch any brake fluid that leaks from the outlet ports when the lines are disconnected. 6. Use a flare-nut wrench to disconnect each brake line fitting from the master cylinder. Plug the end of each line as it is disconnected to keep dirt out of the line and to prevent excessive brake fluid loss. 7. Remove the nuts attaching the master cylinder to the vacuum booster unit (Figure 4-25). 8. Lift the master cylinder out of the vehicle. It may be necessary to insert a small prybar between the booster and the master cylinder to free the master cylinder. Before removing the master cylinder from some vehicles, the proportioning valve must be slid off of the master cylinder mounting studs. On some vehicles, the vacuum valve from the booster must be removed, and the pressure warning switch connector must be disconnected before removing the master cylinder. 9. Clean the master cylinder and vacuum booster contact surfaces with a clean shop towel. See Chapter 10 for more information on removing the modulator and master cylinder assembly.

MASTER CYLINDER RESERVOIR REMOVAL AND REPLACEMENT SERVICE TIP   Some newer reservoirs are held to the master cylinder with a fastener (Figure 4-26). The fastener is usually below and to one side of the reservoir. Before trying to pry or pull the reservoir from the cylinder, ensure that this fastener(s) is removed or damage to the reservoir may occur. Remember to reinstall the fastener(s) after the reservoir is installed again.

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Reservoir fastener

Figure 4-26  Before removing the reservoir, make sure there is no fastener of some sort holding it in place.

To remove a plastic reservoir without damaging it, secure the master cylinder in a vise. Clamp on the metal cylinder body flange to avoid damaging the cylinder body. Insert a prybar between the reservoir and cylinder body and push the reservoir body away from the cylinder (Figure 4-27). When the reservoir is free, remove and discard the rubber grommets that seal the reservoir to the cylinder body. Make sure the reservoir is not cracked or deformed. Replace it if it is. WARNING     Never use the old grommets when replacing the master cylinder reservoir. A leak may occur and cause a loss or a severe reduction in braking.

If the reservoir is serviceable, clean it with denatured alcohol and dry it with clean, unlubricated compressed air. Using clean brake fluid, lubricate the new grommets and the bayonets on the bottom of the reservoir. To reinstall the reservoir, place the reservoir top down on a hard, flat surface, such as a workbench. Start the cylinder body onto the reservoir at an angle, working the lip of the reservoir bayonets completely through the grommets until seated. Using a steady downward force and a smooth rocking motion, press the cylinder body onto the reservoir (Figure 4-28).

Classroom Manual page 84

Special Tools Small prybar Vise

Caution Always clean around any lines or covers before removing or loosening them. Dirt and other contaminants will void the warranty and may damage the system components.

Master cylinder body

Figure 4-27  Carefully pry the reservoir off the master cylinder with a prybar or large screwdriver.

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Cylinder body

Grommets

Reservoir

Place reservoir top down on a hard, flat surface

Figure 4-28  Install new grommets on the cylinder and carefully push the reservoir onto the cylinder. Lubricate the grommets with brake fluid to aid assembly.

REBUILDING THE MASTER CYLINDER Special Tools Stone or brush hone Brake fluid Electric drill Service manual

The rebuilding bench or table must be kept clean and a catch basin must be readily available during rebuilding of the master cylinder.

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Rebuilding a master cylinder involves the following major steps: ■■ Draining the reservoirs ■■ Disassembling the unit completely ■■ Inspecting all parts, including the cylinder bore ■■ Replacing all rubber seals (cups) and O-rings ■■ Reassembling the unit with new seals and O-rings The rebuild kit for the master cylinder usually contains all replaceable seals, O-rings, and retainer clips (Figure 4-29). Other components such as the reservoir body, external valves, and fluid sensors are replaced only if they are faulty. See Chapter 5, Hydraulic Line, Valve, and Switch Service, for details on testing these sensors and valves. The information presented is just for general information because master cylinders on passenger cars and light trucks are almost never rebuilt. Usually it is cheaper and much faster to replace the master cylinder. Another consideration is the fact that most modern master cylinders are made of anodized aluminum. If the cylinder is pitted, which is often the case; the master cylinder cannot be honed. However, there are times when it may be cheaper to rebuild the master cylinder, such as on some medium trucks and equipment. The process is fairly simple: Remove, clean, disassemble, inspect, and clean the interior and parts and reassemble with new components. Like all rebuilding operations, use a clean work area and follow the instructions in the service manual.

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Figure 4-29  Typical master cylinder rebuild kit.

BENCH BLEEDING MASTER CYLINDERS To remove all air from a new or rebuilt master cylinder, bench bleed it before installing it on the vehicle. Bench bleeding reduces the possibility of air getting into the brake lines. Proper bench bleeding is particularly important with dual-piston cylinders, tandem chamber reservoirs, and master cylinders that mount on an angle other than horizontal. WARNING  Avoid spraying brake fluid or making it bubble violently during the bench-bleeding procedure. Do not hold your face directly above the reservoirs. Wear safety goggles or a face shield.

Bench bleeding involves mounting the master cylinder in a vise and forcing all air out of the unit. The most popular bench-bleeding technique involves installing lengths of tubing to the cylinder outlet ports and feeding the tubing back into the reservoir (Figure 4-30). Bench-bleeding kits are available that contain assorted fittings and tubing that will fit most vehicles. A kit can also be made using brake lines or hoses and fittings. Always make sure the tube nuts are tightened securely to guard against air being drawn into the master cylinder on the return stroke. Pump the cylinder pistons manually to recirculate fluid back to the reservoir in a closed loop until all air bubbles to the surface. The procedure for bench bleeding the master cylinder is shown in Photo Sequence 6.

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Bench bleedingis a process that attempts to remove most of the air from a master cylinder before it is installed on the vehicle. This helps prevent the introduction of air into the rest of the brake system by trying to bled the master cylinder on the car.

Caution Do not clean master cylinder parts with gasoline, kerosene, solvent, or other petroleum products. Damage to rubber seals and O-rings will result.

Special Tools Brake bleeder kit, syringe, or Phoenix Injector™ Vise Cloths Catch basin

Caution

Figure 4-30  Bench bleeding a master cylinder with bleeding tubes.

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Do not remove protective shipping seals, covers, or plugs before preparing to bleed the new master cylinder. Dirt and other contaminants may enter and damage the system components or void warranty.

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Master Cylinder Bench Bleeding by Syringe Another bench-bleeding technique for the master cylinder uses a special bleeding syringe to draw fluid out of the reservoir, remove air from it, and inject the fluid back into the unit (Figure 4-31):

Photo Sequence 6

Typical Procedure for Bench Bleeding a Master Cylinder

P6-1  Mount the master cylinder firmly in a vise, but do not apply excessive pressure to the casting. Position the master cylinder so the bore is horizontal. When possible, clamp the master cylinder by its mounting lug.

P6-2  Hoses from a master cylinder bleeder kit are installed. These particular hoses have check valves built into them to prevent air from being drawn back into the master cylinder.

P6-3  Position the hoses into the chambers of the master cylinder.

P6-4  Fill the reservoirs with fresh brake fluid until the level is above the ends of the tubes.

P6-5  Using a wooden dowel or a Phillips screwdriver, slowly push on the master cylinder pistons until both are completely bottomed out in their bore.

P6-6  Watch for bubbles to appear at the tube ends immersed in the fluid. Slowly release the cylinder piston and allow it to return to its original position. On quick take-up master cylinders, wait 15 seconds before pushing in the piston again. On other units, repeat the stroke as soon as the piston returns to its original position. Slow piston return is normal for some master cylinders.

P6-7  Pump the cylinder piston until no bubbles appear in the fluid. Light tapping on the body may help to dislodge trapped air bubbles.

P6-8  Remove the tubes from the outlet ports and plug the openings with temporary plugs or your fingers. Keep the ports covered until you install the master cylinder on the vehicle.

P6-9  Install the master cylinder on the vehicle. Attach the lines, but do not tighten the tube connections.

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Photo Sequence 6 (continued)

P6-10  Place rags under the fittings to absorb any fluid that is expelled. Have an assistant slowly depress the brake pedal several times to force out any air that might be trapped in the connections. Loosen the nuts slightly before each pedal depression and tighten them before releasing the pedal.

P6-11  When there are no air bubbles in the fluid, tighten the connections to the manufacturer’s specifications. Make sure the master cylinder reservoirs are adequately filled with brake fluid.

P6-12  After reinstalling the master cylinder, bleed the entire brake system on the vehicle.

AUTHOR’S NOTE  Figure 4-31 shows the bleeding process using a syringe. The old-fashioned syringe still works, but newer tools are available such as the Phoenix Injector. It can be used to perform bench bleeding of the master cylinder as well as for bleeding the rest of the braking system. The Phoenix Injector is shown in Figures 4-47 and 4-48.

SERVICE TIP   Master cylinders fed by remote reservoirs should be bled on the vehicle. If the reservoir can be easily removed and controlled, it may be easier and cleaner to move the master cylinder and reservoir to the vise for bench bleeding. Do not disconnect the reservoir after bleeding is completed. If the procedure must be done on the vehicle, use rags or other material to capture any leaking brake fluid. The bleeder hose in this case is routed back into the remote reservoir.

1. Plug the outlet ports of the master cylinder. Carefully mount it in a vise with the pushrod end slightly elevated (Figure 4-31, Item 1). Do not clamp the cylinder by the bore or exert pressure on a plastic reservoir. 2. Pour brake fluid into the master cylinder until it is half full. 3. Remove a plug from one outlet port so you can use the syringe to draw fluid out of the cylinder. 4. Depress the syringe plunger completely and place its rubber tip firmly against the outlet port to seal it. 5. Slowly pull back on the plunger to draw fluid out of the cylinder. Fill the syringe body about one-half full (Figure 4-31, Item 2).

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6. Point the tip of the syringe upward. Slowly depress the plunger until all air is expelled (Figure 4-31, Item 3). 7. Place the tip of the syringe (with fluid) firmly against the same outlet and slowly depress the plunger to inject the fluid back into the cylinder (Figure 4-31, Item 4). Air bubbles should appear in the reservoir.

4

1

2 5

6

3

Figure 4-31  You can bench bleed a master cylinder with a special syringe as shown in these six steps. When possible, clamp the cylinder by its mounting lug.

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SERVICE TIP   The pump stroke should not exceed 1 inch in travel. This will help prevent bottoming the pistons and possibly “rolling” the piston cups over. On a step bore (quick take-up) master cylinder wait 20 seconds between strokes allowing any trapped air to return to the reservoir.

8. When these bubbles stop, remove the syringe and plug the outlet. Repeat this procedure at the other outlet. Plug all outlets tightly. 9. With the pushrod end tilted downward slightly, re-clamp the master cylinder in the vise. 10. Slowly slide the master cylinder pushrod back and forth about ⅛ inch until you see no air bubbles in the reservoirs (Figure 4-31, Item 5). 11. Remount the master cylinder with the pushrod end up (Figure 4-31, Item 6). Fill the syringe with brake fluid and expel the air as in step 6. 12. Remove one outlet plug at a time and repeat step 6 and step 7. The master cylinder is now completely bled. If the pedal stays low after thorough bleeding of the master cylinder and the system, check the adjustment of the rear drum brakes, if equipped. Inoperative self-adjusters and poor adjustment of the rear brakes when serviced are leading causes of low-pedal problems.

INSTALLING A NON-INTEGRAL ABS MASTER CYLINDER After bench bleeding a master cylinder, install it as follows:

1. Install the master cylinder onto the vacuum booster studs. 2. Start each brake line fitting into the master cylinder port but do not tighten. 3. Install the retaining nuts and torque to specifications. 4. Unplug each outlet port and use a flare-nut wrench to install the brake line fitting. Tighten securely (Figure 4-32). 5. Reconnect the wiring harness connector to the brake fluid level sensor connector, if equipped. 6. Reconnect the battery ground (negative) cable. 7. Bleed the system.

Figure 4-32  Use tubing wrenches to connect the brake line fittings to the master cylinder.

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SERVICE TIP   Keep the plugs in the master cylinder’s outlets until it is time to connect the brake tubing (lines) to the cylinder. This will reduce the chance of air entering the system. This eliminates the on-car bleeding steps P6-10 and P6-11 shown in Photo Sequence 6 and allowing immediate system bleeding after the master cylinder is installed on the vehicle.

Pushrod Adjustment Proper adjustment of the master cylinder pushrod is essential for safe and correct brake operation. If the pushrod is too long, the master cylinder piston will restrict the vent ports. This can prevent hydraulic pressure from being released and can result in brake drag. If the pushrod is too short, the brake pedal will be low and the pedal stroke length will be reduced, which can result in a loss of braking power. When the brakes are applied with a short pushrod, groaning noises may be heard from the vacuum booster. If a problem with pushrod length or adjustment is suspected, perform the “Test for Open Vent Ports” presented earlier in this chapter. If fluid does not spurt from the vent ports when the brake pedal is released, the pushrod may be holding the master cylinder pistons in positions that partially restrict the ports. In a vacuum power brake system, the pushrod is part of the booster and is matched to the booster during assembly. It is normally adjusted only when the vacuum booster or the master cylinder is serviced. Vacuum booster pushrod length is usually checked with a gauge. Because pushrod length is most often checked and adjusted as part of vacuum booster overhaul or replacement, procedures are included in Chapter 6, Power Brake Service. Checking and adjusting brake pedal free play as explained earlier in this chapter also will help to ensure proper master cylinder piston travel.

SERVICE TIP   Do not rush to condemn the master cylinder as the cause of a low brake pedal. Bench bleeding the master cylinder before installation and careful bleeding of the entire system are important to ensure proper pedal height.

MASTER CYLINDER BLEEDING ON THE VEHICLE

Special Tool Hand Tools

Caution Ensure that the fitting is not cross-threaded when reconnecting. This could damage the fitting, the component, or both.

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Whenever possible, bleed the master cylinder on the bench before installing it on the vehicle. Bleeding the cylinder after installing it on the car removes any final air bubbles in the outlet ports or air that may enter the fittings when they are connected. Fluid pressure to bleed the master cylinder can be supplied by a pressure bleeder or by having a coworker press the brake pedal. Because the master cylinder is the highest point of the hydraulic system and because air rises, bleed the master cylinder before bleeding any of the wheel brakes. WARNING     Brake fluid can be irritating to the skin and eyes. In case of contact, wash skin with soap and water or rinse eyes thoroughly with water.

On-Vehicle Bleeding Modern master cylinders do not have bleeder screws, but trapped air can be removed at the outlet ports by loosening the line fittings and applying fluid pressure. Usually the master cylinder is bled on the vehicle after a thorough bench bleeding.

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Figure 4-33  Loosen one of the two brake lines as the brake pedal is being depressed. Tighten it back before the pedal is released. Do one line at a time.

1. Discharge the power booster, if equipped, by pumping the pedal with the engine off until it becomes hard. 2. Fill the master cylinder with fresh brake fluid and ensure that it stays at least half full during the bleeding procedure. 3. Using a flare-nut wrench, loosen the forward or highest line fitting on the master cylinder outlet ports (Figure 4-33). 4. Apply fluid pressure with a pressure bleeder or by having a coworker press and hold the brake pedal. 5. Hold a clean rag or a container under the fitting to catch fluid that escapes. 6. While maintaining fluid pressure, tighten the fitting. 7. Repeat step 3 through step 6 until no air escapes from the fitting along with the fluid. Then repeat these steps at each remaining fitting on the master cylinder, working from the highest to the lowest.

Special Tools Hand Tools Cloths

Caution

HYDRAULIC SYSTEM BLEEDING Brake bleeding is the process of removing air from the hydraulic lines by opening a bleeder port at each wheel and sometimes elsewhere in the system. These ports are sealed with bleeder screws that are opened to allow fluid and air to escape the system (Figure 4-34). Bleeder screws are located at high points throughout the brake system (Figure 4-35). A bleeder screw is normally installed in each drum brake wheel cylinder and in each disc brake caliper. Some bleeder screws have a threaded passage and a protective dust cap screw that must be removed before a drain hose can be installed on the bleeder screw.

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Prevent brake fluid from coming in contact with the vehicle’s finish. Brake fluid damages paint and finish immediately on contact. If fluid contacts the finish, wash area thoroughly with running water and soap if possible.

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Master cylinder

Bleeder screw Bleeder screw

Wheel cylinder

Figure 4-34  Bleeder screws, such as this one on a disc brake caliper, are also installed on wheel cylinders and some ABS hydraulic modulators.

Caliper

Figure 4-35  Bleeder screws are located at the highest points on calipers and wheel cylinders.

If air is trapped in the system, the brake pedal will be low and feel spongy when first applied. Rapidly pumping the pedal several times will compress much of the air and cause the pedal to rise and become firmer. As soon as pressure is released from the pedal, the air will expand again, and the pedal will return to its spongy and low condition. Upward bends in the brake tubing as it is routed through the vehicle chassis also can trap air in the system (Figure 4-36). This condition makes bleeding the system even more important and often more difficult. All of the air must be removed from the system to ensure proper brake operation and pedal feel. SERVICE TIP   Brakes dragging? Check the fluid level in the master cylinder. Overfilling the reservoir can prevent fluid from returning completely from the brake lines. The excess fluid in the lines then maintains slight pressure on the brakes and causes drag and overheating. The fluid level should not be above the MAX line in the reservoir.

Master cylinder

Bleeder screw

Caliper

Air pockets Bleeder screw

Combination valve

Wheel cylinder

Figure 4-36  Bends in brake hoses and tubing can trap air and make bleeding more difficult. All air must be removed for proper operation.

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SERVICE TIP   Bleeding the brakes or master cylinder that are mounted at an angle can be best done by lifting the rear of the vehicle until the master cylinder is horizontal or as near as possible. This will help prevent air bubbles from being trapped in the forward end of the master cylinder.

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SERVICE TIP   Russell Performance Products makes a special tool used for one-person brake bleeding. The Speed Bleeder has a built-in check valve and replaces the standard brake bleeder screw. Loosen the Speed Bleeder one quarter turn and pump the brake pedal. When that wheel is bled, close the bleeder and move to the next wheel. Do not remove the Speed Bleeder. The customer gets the tool along with the brake repairs.

The brake pedal symptoms of a system that contains air can be similar to the pedal symptoms caused by drum brakes that need adjustment. A low pedal caused by misadjusted drum brakes, however, will become firm after two or three applications and will not have the spongy feeling caused by air in the system. See Testing the Hydraulic System for Trapped Air covered earlier in this chapter. AUTHOR’S NOTE  The term brake lines usually means the steel tubing and the hydraulic system in general. However, the brake’s hydraulic circuit includes both the steel tubing and the flexible hoses at each wheel. Brake lines should not be used when referring to the steel tubing alone. Chapter 5 covers brake lines, but the information is separated into notes on tubing and hoses.

SERVICE TIP   Bleeding or flushing? Bleeding is the removal of air from the brake system, and not all of the wheels are necessarily bled. Flushing, on the other hand, is the complete replacement of all system brake fluid with new fluid. Generally speaking, if only two wheels receive new brake pads/shoe, then only those two wheels are bled. However, installed brake fluid has a service life of about 24 months to 30 months in a typical light vehicle. If the fluid is aged or appears to be contaminated, it is probably best to flush the system. A complete flush should add no more than 10 minutes to the job, and a charge for the flushing may be added to the repair order. Newer flushing equipment can do the total flush faster than two wheels can be bled manually. Consult the service writer/manager and the customer for guidance.

Overall Brake Bleeding Sequences Bleeding may be performed on all or just part of the hydraulic system. As explained earlier in this chapter a master cylinder usually is bled on the bench before it is installed on the car. Then, final bleeding can be performed at the master cylinder fittings or bleeder screws to remove any air trapped in the connections. If brake pedal and master cylinder operation is normal after these procedures, it may not be necessary to bleed the wheel brakes. Depending on where the hydraulic system was opened to air, bleeding may be needed at all four wheels and the master cylinder; or it might be needed only at two wheels. If all

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fittings are disconnected from a dual-reservoir master cylinder, or if air was introduced into the system through low fluid level in both cylinder reservoirs, bleeding is required at the master cylinder and all four wheels. If the tubes for one set of wheels are disconnected at the master cylinder, or if air entered through a low fluid level in only the reservoir for that set of wheels, only those wheels and lines need to be bled. If there is any doubt about air in the system, however, the entire system should be bled. Air rises, certainly, so if an entire brake system is to be bled, it is bled starting at the highest point in the system. An overall brake bleeding sequence would be: ■■ Master cylinder ■■ Combination valve (if equipped) ■■ Wheel cylinders and/or brake calipers. Whether bleeding the complete system or just part of it, the first step is to fill the master cylinder with fresh fluid. Being careful not to let dirt or other contamination enter the reservoir, remove the cap or cover and fill the reservoir to the specified level with fresh fluid. If fluid in the reservoir falls below the level of the compensating and replenishing ports, air will enter the system. If this happens, bleeding steps must be repeated to ensure that all air is removed. General practice with any type of bleeding is to slip a hose over the end of the bleeder screw. Place the free end of the hose into a jar half filled with brake fluid. Always keep the end of the hose submerged in brake fluid. This prevents air from being drawn back into the system and lets you observe when air bubbles stop flowing from the bleeder to indicate that air has been removed from that portion of the system.

Freeing a Frozen Bleeder Screw When opening or removing a bleeder screw, use a special six-sided bleeder screw box wrench of the correct size. The shoulders of a bleeder screw are easily rounded if the wrong tool is used. Do not exert too much force on the screw. It is possible to break off the small screw in the housing. Fixing this problem requires drilling and tapping so avoid it by working carefully. If drilling and tapping are not possible, the entire cylinder or caliper must be replaced. Before performing cylinder or caliper service, always check the bleeder screw to see if it can be loosened. If the caliper or cylinder is serviceable but the bleeder screw is frozen, one of the following methods may free it. Use a special wrench to exert pressure on the screw by striking it with a hammer. The shock to the screw from the hammer blows and the tension against it may free the screw. Apply a few drops of penetrating oil around the screw threads. Let the oil soak in for a few minutes, and try again to turn the screw. WARNING     Never apply heat to a closed brake system. The fluid could boil, generating great pressure and rupturing the weakest point. Serious injury could occur. If heat must be used, remove the pistons and brake lines so the heat can dissipate through the openings. SERVICE TIP   When troubleshooting a problem of brake drag, overheating, or premature wear, connect a pressure gauge to the bleeder port on each caliper and wheel cylinder in turn. When the brakes are applied, pressure should rise quickly and drop just as quickly when the brakes are released. Other than that, any residual pressure in one brake line usually indicates a restricted tube or hose. Inspect all the brake lines for that wheel closely.

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As a last resort, if a replacement component is not readily available, use a welding torch to heat the housing around the screw to a dull red. When the caliper or cylinder body is hot, apply pressure to the screw with the correct size wrench. When using this method, be sure to remove the rubber and plastic parts in the caliper or cylinder to prevent heat damage. This method is best done with the caliper or cylinder removed from the vehicle and clamped in a bench vise. If heat must be applied to brake parts while on the vehicle, remove any adjacent brake hoses or cover them with wet cloths to protect them from heat. If a frozen bleeder screw is heated with the caliper or cylinder clamped in a vise, position the bleeder screw downward. Any residual fluid in the bore will then run into the screw threads as they are heated and help to free the screw.

Wheel Brake Bleeding Sequences All vehicle manufacturers recommend a specific sequence in which to bleed the wheel brakes. These recommendations can be found in vehicle service information and in aftermarket brake service information. Before bleeding the wheel brakes on any vehicle, refer to these recommendations and follow them during the bleeding procedure. If the manufacturer’s recommendations are not available, the following sequence will work on most vehicles: ■■ Master cylinder ■■ Right rear ■■ Left rear ■■ Right front ■■ Left front This sequence is based on the principle of starting at the highest point in the system and working downward, then starting at the wheel farthest from the master cylinder and working to the closest. A few more general rules also are worth remembering. If the brake system is split between the front and rear wheels, the rear wheels (which are farthest from the master cylinder) usually are bled first. If the brake system is split diagonally, the most common sequence is: RR, LF, LR, RF (Figure 4-37). This sequence also applies to most systems with a quick take-up master cylinder. If you bleed a quick take-up system in any other sequence, you may chase air throughout the system. Exceptions to the general rules exist, however. Chrysler, for example, recommends bleeding both rear brakes before the front brakes, regardless of how the hydraulic system is split. If a caliper has two bleeder screws, one higher than the other, bleed the lower one first. These instructions may seem contrary to the general rule of bleeding the system from the highest points downward. In the case of calipers and dual wheel cylinders with upper and lower bleeder screws, starting at the lower bleeders will remove air trapped in the lower parts of the assembly. Any air remaining will rise to the top, where it can be removed by a final bleeding step at the upper bleeder for an individual wheel brake assembly. Remember, some older vehicles have a metering valve. The metering valve can be opened by pressing or pulling the stem of a metering valve to lock it open when using a pressure bleeder. Many valves require a special clip to hold the metering valve stem open while bleeding the front brakes (Figure 4-38). Six methods are commonly used for brake bleeding:

1. Manual bleeding 2. Pressure bleeding 3. Vacuum bleeding 4. Gravity bleeding 5. Surge bleeding 6. Reverse fluid injection bleeding

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Caution On some vehicles, it is possible to install a right-hand caliper on the left-side wheel and vice versa. If you inadvertently do this, the bleeder screw will be located at the bottom of the caliper bore. This low position makes it impossible to bleed all air out of the system.

Caution Do not spill any brake fluid on the car finish. If you do, flush it immediately with water. Clean dirt away from the master cylinder reservoir cap or cover before opening it. Do not let contamination enter the hydraulic system.

Caution When bleeding the individual wheel cylinders or calipers always check for the proper bleeding sequence from the manufacturer. It was once taught that the technician bleed wheels in the order of RR, LR, RF, LF but this not true for all brake systems now.

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Caution Vehicles with ABSs often require special bleeding procedures or additional steps for the following general procedures. If air is tapped in the ABS hydraulic modulator, the modulator may have to be activated with the scan tools to completely bleed the system. Generally speaking, vehicles with a hydraulic modulator are bled using the pressure bleeder at the master cylinder and wheels, then a scan tool is used to activate the HCU valves and solenoids in order to remove any trapped air in the HCU, then the brake bleeding sequence is repeated. Failure to follow these special instructions may result in damage to ABS components or incomplete bleeding of the system. Refer to Chapter 10.

Manual bleeding requires no Special Tools or equipment.

1

Left rear 3

Right front 4

Left front 2

Figure 4-37  Use this bleeding sequence if the manufacturer does not use a recommended procedure.

The following sections explain the advantages and disadvantages of these six methods and contain procedures for their use.

Manual Bleeding Manual bleeding uses the brake pedal and master cylinder as a hydraulic pump to expel air and brake fluid from the system when a bleeder screw is opened. Manual bleeding is a two-person operation: one person pumps the brake pedal, and the other opens and closes the bleeder screws. Manual bleeding requires a bleeder screw wrench of the correct size, a container partially full of fresh brake fluid, a length of clean plastic tubing that fits over the top of the bleeder screws, and several clean shop cloths. During manual bleeding, the brake pedal must be applied slowly and steadily (Figure 4-39). Rapidly pumping the pedal will churn air in the system and make it harder to expel. Bleed the system as follows: SERVICE TIP   Some ABS systems require the use of a special automated bleeding procedure available using an appropriate scan tool.

1. Check the fluid level in the master cylinder reservoir, and be sure that both sections are full. Recheck the fluid level after bleeding each wheel brake and refill as necessary. If the level drops below the ports, air will enter the system. Be sure that the reservoir cover or cap is installed securely during bleeding. 2. Discharge the vacuum or hydraulic pressure reserve in the booster by pumping the brake pedal with the ignition off until the pedal becomes hard.

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Metering valve bleeding tool

Compress tool by squeezing.

Install on stem and release.

Figure 4-38  Typical example of tools used to hold metering valves open during bleeding.

3. Using a clean shop cloth, wipe dirt away from the bleeder screw on the first wheel in the recommended sequence. 4. Fit the plastic hose over the top of the bleeder screw and submerge the other end in the container of fresh brake fluid.

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Press slowly on brake pedal.

Hose attached to bleeder screw

Brake fluid Watch for bubbles

Figure 4-39  Basic setup for manual brake bleeding.

Special Tools Brake fluid Cloths Catch basin Brake bleeder kit or tubing and transparent container Hand tools

5. Loosen the bleeder one-half to one turn and have your assistant press the brake pedal slowly and steadily and hold it to the floor. Observe air bubbles flowing from the hose into the fluid container. 6. Tighten the bleeder screw and have your assistant slowly release the brake pedal. 7. Repeat step 5 and step 6 until no more air flows from the tubing into the brake fluid container. 8. Check the fluid level in the master cylinder and add fluid if necessary. Then proceed to the next wheel in the bleeding sequence. Repeat the bleeding sequence as necessary until the brake pedal is consistently firm. Check the fluid level a final time and install the reservoir cover or cap. If you have trouble getting all of the air out of a disc brake caliper, tap the caliper lightly but firmly with a hammer to loosen trapped air bubbles and let them rise to the bleeder screw (Figure 4-40). Photo Sequence 7 shows the proper way to bleed a disc brake caliper manually. The steps shown apply to one bleeder screw and should be repeated at all other bleed points.

Photo Sequence 7 Typical Procedure for Manually Bleeding a Disc Brake Caliper

P7-1  Be sure the master cylinder reservoir is filled with clean brake fluid. Recheck it often to replace fluid lost during the bleeding process.

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P7-2  Attach a bleeder hose to the bleeder screw.

P7-3  Place the other end of the hose in a capture container partially filled with brake fluid. Be sure that the free end of the hose is submerged in brake fluid. This helps to show air bubbles as they come out of the system and prevents air from being accidentally sucked into the system through the bleeder screw.

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Photo Sequence 7 (CONTINUED)

P7-6  Observe the fluid coming through the hose and into the bleeder hose and into the container. There should be bubbles at first. P7-4  Have an assistant apply moderate (40–50 pounds), steady pressure on the brake pedal and hold it down.

P7-5  Open the bleeder screw.

P7-7  When the fluid is clear and free of air bubbles, close the bleeder screw.

P7-8  Have your assistant release the brake pedal. Wait 15 seconds and repeat step 2 and step 3 until no bubbles are seen when the bleeder screw is opened. Close the bleeder screw at that wheel and move to the next wheel in the bleeding sequence. Bleed all four wheels in the same manner.

P7-9  When the entire system has been bled, turn on the ignition switch.

P7-10  Check the pedal for sponginess.

P7-11  Check the brake warning lamp for an indication for unbalanced pressure. Repeat the bleeding procedure to correct the problem.

P7-12  Top off the master cylinder reservoir to the proper fill level.

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Air bubbles

Figure 4-40  You can tap a caliper with a hammer to loosen air bubbles and let them rise to the bleeder screw.

Special Tools Pressure bleeder Tubing and transparent container Cloths

Caution Prevent brake fluid from coming in contact with the vehicle’s finish. Brake fluid damages paint and finish immediately on contact. If fluid contacts finish, wash area thoroughly with running water using soap if possible.

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Manual Bleeding with Check Valve Bleeder Hose.  Bleeding hoses are available with a one-way check valve that only lets fluid flow out of the bleeder screw, not in the reverse direction. This bleeder hose keeps air from being drawn back into the system when the brake pedal is released.

Pressure Bleeding Pressure bleeding requires special equipment to force brake fluid through the system. Pressure bleeding has two advantages over manual bleeding. It is faster because the master cylinder does not have to be refilled several times, and the job can be done by one person. Therefore, pressure bleeding is the method most often used in the brake service profession. Figure 4-41 shows the basic equipment and setup for pressure bleeding. WARNING     Do not depress the brake pedal when pressure brake bleeding equipment is being used. This could damage seals and piston cups within the brake system.

Older pressure bleeders are small tanks that contain brake fluid that is pressurized by compressed air (Figure 4-42). A hose from the pressure bleeder is connected to the master cylinder by an adapter fitting that fits over the reservoir in place of the reservoir cap. Adapters exist in different configurations for different types of reservoirs. One-piece cylinders with integral reservoirs generally use a flat plate adapter. Some plastic reservoirs require adapters that seal around the ports in the bottom of the reservoir (Figure 4-43).

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Rear brake

Master cylinder

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Hose attached to bleeder screw

Fluid supply valve

Brake fluid

Pressure bleeder tank

Valve stem

Boot

Push in

Pull out Special tool Holding Metering Valve Open

Figure 4-41  Basic setup for pressure brake bleeding. Pressure gauge Fluid control valve

To adapter

Fluid

Air Internal diaphragm

Air inlet

Figure 4-42  The lower chamber is compressed air; the upper chamber holds brake fluid. The chambers are separated by a flexible, air-tight diaphragm.

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Figure 4-43  Many different adapters are needed to properly pressure bleed the various master cylinder configurations.

Pressure Bleeding Vehicles with a Metering Valve The hydraulic pressure generated by manual bleeding is enough to open the metering or combination valve and let fluid flow to the front disc brakes. When pressure bleeding, the metering valve must be held open manually because the pressure bleeder works with pressure in the range where a metering valve is normally closed. To hold the metering valve open, either push the valve stem in or pull it out, depending on the valve type. Figures 4-38 and Figures 4-41, shown earlier, illustrate several kinds of metering valve tools and ways to open the valve for bleeding. On some combination valves, such as those used by GM, loosen a valve mounting bolt and slide the valve tool under the bolt head. Move the end of the tool toward the valve body until it depresses the metering valve stem. Then tighten the mounting bolt to hold the tool in place. Other valves have a stem that must be held outward by a spring clip tool. The stem on still other valves must be held in by hand when the front brakes are bled. WARNING   Wear safety glasses and/or face protection when using brake fluid. Injuries to the face and/or eyes could occur from spilled or splashed brake fluid.

In addition to a pressure bleeder with the right adapter and a metering valve tool (if required), pressure bleeding requires a bleeder screw wrench of the correct size, a container partially full of fresh brake fluid, a length of clean plastic tubing that fits over the top of the bleeder screws, and several clean shop cloths. Bleed the system as follows: 1. Fill the pressure bleeder with the type of fluid specified by the vehicle manufacturer. Then charge the bleeder with 30 psi of compressed air according to the equipment instructions. (Some late-model systems require a minimum of 30 psi to pressure bleed the system.) 2. Clean the top of the master cylinder, remove the reservoir cover, and fill the reservoir about half full of fresh brake fluid. 3. Install the adapter on the reservoir and connect the fluid supply hose from the pressure bleeder to the adapter. 4. If required, install the correct override tool on the metering valve.

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5. Open the fluid supply valve on the pressure bleeder to let pressurized fluid flow to the reservoir. Check the adapter and all hose connections for leaks and tighten if necessary. 6. Using a clean shop cloth, wipe dirt away from the bleeder screw on the first wheel in the recommended sequence. 7. Fit the plastic hose over the top of the bleeder screw, and submerge the other end in the container of fresh brake fluid. 8. Loosen the bleeder one-half to one turn, and observe air bubbles flowing from the hose into the fluid container. 9. Tighten the bleeder screw when clean fluid without any air bubbles flows into the container. 10. Repeat step 6 through step 9 at the next wheel in the bleeding sequence. Continue until the last brake in the sequence is bled. Repeat the bleeding sequence as necessary until the brake pedal is consistently firm. 11. Remove the metering valve override tool. 12. Close the fluid supply valve on the pressure bleeder. 13. Wrap the end of the fluid hose at the master cylinder adapter with a clean cloth, and disconnect the hose from the adapter. 14. Remove the adapter from the master cylinder, and be sure the reservoir is filled to the correct level. Install the reservoir cover or cap.

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Caution Always clean around any lines or covers before removing or loosening them. Dirt and other contaminants will void the warranty and may damage system components.

Vacuum Bleeding Vacuum bleeding is an alternative to pressure bleeding and is preferred by some technicians. As is pressure bleeding, vacuum bleeding is a one-person operation. Depending on the type of equipment, however, the master cylinder may require refilling during the bleeding operation. Two basic types of vacuum bleeding equipment are available: the hand-operated vacuum pump and the system operated by compressed air. A hand-operated vacuum pump used for brake bleeding is the same kind of vacuum pump used to test and service fuel systems and emission control devices. The pump holds a small cup that contains fresh brake fluid, and a length of plastic tubing connects the pump to the bleeder screw (Figure 4-44). Vacuum bleed a brake system as follows: 1. Check the fluid level in the master cylinder reservoir, and be sure that both sections are full. Recheck the fluid level after bleeding each wheel brake, and refill as necessary. If the level drops below the ports, air will enter the system. Be sure that the reservoir cover or cap is installed securely during bleeding. 2. Install the small fluid container on the vacuum pump according to the equipment instructions. Be sure all connections are tight so that the pump cannot draw air past the fluid container.

Special Tools Vacuum bleeder kit Cloths

Connect to bleeder screw Hand-operated vacuum pump

Jar adapter

Figure 4-44  The same type of hand-operated vacuum pump used for engine service can be used to bleed brakes with suitable adapters.

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3. Fill the small container about half full of fresh brake fluid. Be sure the short hose inside the container is submerged in fluid so that air cannot flow back into the brake system. 4. Using a clean shop cloth, wipe dirt away from the bleeder screw on the first wheel in the recommended sequence. 5. Fit the plastic hose from the vacuum pump over the top of the bleeder screw, and operate the pump handle 10 to 15 times to create a vacuum in the container. 6. Using the correct bleeder screw wrench, loosen the bleeder one-half to three-­ quarters turn. Observe fluid with air bubbles flowing into the fluid container on the pump. 7. After evacuating about 1 inch of fluid into the container, tighten the bleeder screw. 8. Repeat step 5 through step 7 until no more air flows into the brake fluid container. Remove old fluid from the pump container as necessary during the bleeding procedure. 9. Check the fluid level in the master cylinder, and add fluid if necessary. Then proceed to the next wheel in the bleeding sequence. Repeat the bleeding sequence as necessary until the brake pedal is consistently firm. Check the fluid level a final time, and install the reservoir cover or cap.

Special Tools Four sets of tubing and transparent containers

Some vacuum bleeding equipment that uses compressed air may include a fresh fluid container that attaches to the master cylinder reservoir with an adapter similar to the type used with a pressure bleeder. This eliminates the need to refill the reservoir repeatedly during bleeding. A compressed air vacuum pump uses airflow through a venturi to create a vacuum in a chamber connected to the throat of the venturi. This process is called air-aspirated vacuum. The vacuum pump is connected to the compressed air supply during bleeding, or it may be charged with reserve vacuum and disconnected from the air supply for use. To use vacuum bleeding equipment (Figure 4-45), fill the master cylinder, or connect the fresh fluid container to the master cylinder according to the equipment instructions. Then connect the vacuum pump to the first wheel in the recommended bleeding sequence. Open the wheel bleeder screw and the vacuum valve, and let fluid flow from the wheel brake into the pump container until it is free of air bubbles. Close the bleeder screw, and move the vacuum pump to the next wheel in sequence. Repeat the bleeding sequence as necessary until the brake pedal is consistently firm and no more air flows from any wheel brake. Remove old fluid from the pump container as necessary during the bleeding procedure. Check the fluid level in the master cylinder a final time, and install the reservoir cover or cap. When this type of vacuum bleeding equipment is used, it is common to see bubbles or foam in the fluid drawn from the brake system. Air is drawn into the evacuated fluid, past the threads of the bleeder screw. The air mixes with the fluid being drawn out of the system and flows to the vacuum bleeder (Figure 4-46). This does not affect the bleeding operation and does not indicate continuous air in the system. Vacuum bleeding with either a hand-operated pump or a compressed-air system generally does not require overriding the metering valve. Check the equipment operating instructions, however, to verify the exact requirements.

Gravity Bleeding Gravity bleeding is letting nature take its course in brake bleeding. Atmospheric pressure on the surface of the fluid in the reservoir eventually forces the fluid through the brake system and out the open bleeder screws. Gravity bleeding is the simplest and

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Airflow creates low pressure at this point.

Airflow

Airflow

Leave cap off. Atmospheric pressure helps push fluid out.

Shop air source

Airflow

Fluid flow Interior under low pressure

Figure 4-45  A typical vacuum bleeding setup.

Vacuum draws foamy fluid into bleed canister.

Bleed screw

Air drawn past threads

Fluid mixed with air Fluid from wheel circuit

Figure 4-46  Air entering via the bleeder screw threads will not affect the bleeding process.

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slowest way to bleed a brake system. It also can be the most effective on some systems. Gravity bleeding works best on a system that does not have a combination valve or a proportioning valve that requires bleeding. Gravity bleeding cannot be used on a system that contains a residual pressure check valve or any other valve that isolates any part of the system at low pressure. Gravity bleeding also may be difficult on a system with high points in the lines that can trap air. Before using the gravity bleeding method, the master cylinder should be thoroughly bench bled and then bled again after it is installed on the vehicle. Gravity bleeding requires that all bleeder screws on the wheel brakes be open at the same time. Install lengths of clean plastic tubing on all bleeder screws and immerse the other end of each hose in a container of clean fluid before opening the bleeder screws. If all bleeder screws were opened to the air, air might be drawn back into the system because the total area of the bleeder openings may be greater than the area of the compensating ports through which fluid must flow to the master cylinder. Fill the master cylinder reservoir with fresh fluid before starting the bleeding process, and check it periodically during gravity bleeding. Open each bleeder screw approximately one turn, and verify that fluid starts to flow from each tube. Check the fluid level in the master cylinder periodically during bleeding. If fluid falls below the master cylinder ports, you will have to start the bleeding process all over again. Gravity bleeding can take an hour or more to completely purge the system of air. When fluid flowing from the bleeder screws is clear and free of air bubbles, close the bleeder screws, disconnect the tubing, and check the master cylinder fluid level. Add fluid as required.

Surge Bleeding Surge bleeding is a supplementary procedure that can be used to remove air pockets that resist other bleeding methods. Surge bleeding is a variation of manual bleeding in which a coworker pumps the brake pedal rapidly to create turbulence in the system. Surge bleeding should not be used as the only bleeding procedure for a brake system. The agitation will often dislodge air trapped in pockets in the system. The steps for surge bleeding are basically the same as for manual bleeding with one exception. After connecting plastic tubing to a wheel bleeder screw and immersing the tubing in a container of fresh fluid, open the bleeder screw about one full turn. Then, with the bleeder open, have a coworker pump the brake pedal rapidly several times. Watch for surges of air bubbles to flow from the tubing into the fluid container. Finally, have the coworker hold the pedal to the floor when you close the bleeder screw. Repeat the surge bleeding procedure at each wheel several times and then let the system stabilize for 5 to 10 minutes. Follow the surge bleeding with any of the other bleeding procedures explained previously.

Other Bleeding Equipment As mentioned in Chapter 3 of the Shop Manual, one style of brake bleeding equipment can pressure or vacuum the system. Figure 4-47 shows a typical hookup to pressure bleed the brake system with a Phoenix Injector. The injector fluid source (which may be a regular container of brake fluid) has been filled with the correct brake fluid and the injector system bled. The master cylinder has sufficient fluid to seal the port(s) when the injector is removed. Note the capture container attached to the wheel cylinder/caliper bleeder screw. Open the bleeder screw enough to allow fluid to flow from the cylinder/caliper. Support the container in some way to prevent tipping or spillage, or have a second technician hold it, and open and close the bleeder screw. Insert the nozzle of the injector into the appropriate replenishment port of the master cylinder firmly enough to seal the

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Figure 4-47  A pressure bleeding system.

connection. Pump the handle to force fluid from the source through the injector and throughout the brake system. Repeat until clear, air-free brake fluid is forced from the bleeder screw. Tighten the bleeder screw before moving the injector or capture container. Repeat with the other wheels until the complete system is bled. Remove the injector completely after the last wheel is bled, and fill the master cylinder to the proper level. A modified version of this setup could be used to bench bleed the master cylinder on or off the vehicle. Figure 4-48 shows a typical installation of the Phoenix Injector set up to suction (vacuum) bleed a brake system. In this setup, the injector uses the brake system as the source fluid and pumps the fluid from the open bleeder screw into a capture container. The master cylinder has to be monitored and kept full at all times in this procedure. Ensure that the bleeder screw is closed before disconnecting the injector. Repeat with each wheel brake until all show clear, air-free fluid from the cylinder/caliper. Fill the master cylinder to the proper level if needed.

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Special Tools Flushing requires the same special tools as bleeding. The tools depend on the type of bleeding method used.

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Master cylinder

Bleed screw

Hose to fluid container

Brake fluid Caliper

Figure 4-48  A vacuum (suction) bleeding system.

SERVICE TIP   Two good reasons for periodic flushing and refilling of the brake hydraulic system are:

1. Flushing the system and refilling with fresh fluid keeps sediment out of ABS valves. 2. Flushing and refilling the system also keeps that sediment out of the self-­ adjusting parking brake mechanisms on rear-wheel disc brakes.

BRAKE FLUID REPLACEMENT: FLUSHING AND REFILLING THE HYDRAULIC SYSTEM Manufacturers are about evenly divided on whether or not the brake system should be flushed periodically and refilled with fresh fluid. DOT 3 and DOT 4 fluids absorb moisture from the atmosphere. Most vehicles will contain about 2 percent water in their brake fluid after just 1 year of service. As little as 6 percent moisture in the brake fluid can cut the fluid boiling point in half. These facts may be very good arguments for periodically flushing and refilling the brake hydraulic system. Some vehicle manufacturers recommend periodic fluid changes and some do not. Change intervals vary from as often as every 12 months or 15,000 miles to as infrequently as every 60,000 miles. Perhaps the best policy is to check the condition of the fluid with available test strips.

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If this service is offered, however, there are a few general points to remember. All brake systems accumulate sludge over some period of time. Flushing the system can remove this sludge; but once it has been disturbed, make sure to get all of it out of the system. Stirring up sludge from the master cylinder reservoir may cause it to get into ABS valves and pumps if the sludge is not out of the system.

SERVICE TIP   Flush a brake system by draining the old fluid and adding denatured or isopropyl alcohol to the system. Continue to add alcohol until the system is clean. Flush out the alcohol with new brake fluid until all of the alcohol is removed.

Brake hoses for disc brakes usually enter the caliper near the top of the caliper body. The bleeder valve also is located at the top of the caliper bore. (It has to be because air rises.) If sludge accumulates in the caliper bore, it collects at the bottom. A quick, superficial bleeding of the caliper just passes a few ounces of fluid across the top of the bore. It does not flush out the sludge and all the old fluid. To flush a caliper thoroughly, pump several ounces of fluid through it. On some vehicles, it may be advisable to remove the caliper from its mounts and retract the piston to force out all the old fluid. Then reinstall it and thoroughly flush it with fresh fluid. Flushing is done at each bleeder screw in the same manner as bleeding. Open the bleeder screw approximately one-and-a half turns and force fluid through the system until the fluid emerges clear and uncontaminated. Do this at each bleeder screw in the system. After all lines have been flushed, bleed the system using one of the bleeding procedures explained previously.

CUSTOMER CARE  A little customer education can go a long way toward safer driving. Explain to your customers the importance of following their vehicle maintenance schedules for brake hydraulic system flushing and refilling. Refilling the system with fresh fluid is cheap insurance against hydraulic failure due to sludge, dirt, and moisture in the system.

CASE STUDY A customer complained of excessive pedal travel on a 10-year-old domestic sedan. The master cylinder reservoir was full. A test drive confirmed the condition. The car was placed on the lift. Lines and hoses were in good condition and leak-free at all connections. The wheels were pulled and the caliper and wheel cylinders were inspected for leakage. All checked out okay. The technician then suspected problems with the master cylinder or an improperly adjusted pushrod. The first problem was more likely, and a fluid bypass test confirmed the problem. The technician watched the fluid levels in the reservoirs while a helper pressed the brake pedal slowly and then released it quickly. The level in one reservoir rose, whereas the level in the other reservoir dropped. But the total level remained the same. A leaking primary piston cup seal was allowing the fluid to bypass the seal and move between reservoirs. The technician replaced the master cylinder, and the problem was solved.

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ASE-STYLE REVIEW QUESTIONS 1. Technician A says if the tires are in good shape and the wheel alignment and vehicle loading do not appear to be the problem, proceed with a brake system road test. Technician B says test drive the vehicle on a wet, heavily crowned road to really test brake operation. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

6. Hydraulic brake system leaks can be internal or external. Technician A says most internal leaks are actually fluid bypassing the cups in the master cylinder. Technician B says that if the cups lose their ability to seal the pistons, brake fluid leaks past the cups and the pistons cannot develop system pressure. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

2. During a road test, it is important to check for which of the following: A. Listen for unusual brake noise. B. Determine if the brakes grab or pull to one side. C. Determine if the brake pedal feel spongy or hard when applied. D. All of the above

7. Technician A says to remove all air from a new or rebuilt master cylinder (with an attached reservoir), bled only after installing it on the vehicle. Technician B says bench bleeding a master cylinder reduces the possibility of air getting into the brake lines. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

3. Technician A says brake pedal free play is the clearance between the brake pedal or booster pushrod and the secondary piston in the master cylinder. Technician B says a specific amount of free play must exist so that the primary piston is not partially applied when the pedal is released and so that pedal travel is not excessive. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 4. Technician A says if the pushrod is too long, the master cylinder piston will restrict the vent ports. Technician B says this can prevent hydraulic pressure from being released and can result in brake drag. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. Technician A says that brake fluid contaminated with mineral oil will swell brake system seals and render them useless. Technician B says a sure sign of this is the swelling of the master cylinder cover diaphragm. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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8. While discussing the rebuilding of master cylinders, Technician A says usually it is cheaper and much faster to replace the master cylinder. Technician B says another consideration is the fact that most modern master cylinders are made of anodized aluminum and cannot be honed if pitted. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 9. Technician A says if air is trapped in the brake system, the brake pedal will be low and feel spongy when first applied. Technician B says slowly pumping the pedal several times will ­compress much of the air and cause the pedal to fall and become even more spongy. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 10. Technician A says manual brake bleeding uses the brake pedal and master cylinder as a hydraulic pump to expel air and brake fluid from the system when a bleeder screw is opened. Technician B says manual bleeding is a two-person operation: one person pumps the brake pedal, and the other opens and closes the bleeder screws. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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ASE Challenge Questions 1. While discussing bleeding the braking system, Technician A says the first step is to fill the master cylinder with fresh fluid. Technician B says when the fluid in the reservoir falls below the level of the compensating and replenishing ports, air will be able to leave the system. Who is correct? A. A only B. B only

C. Both+P A and B D. Neither A nor B

2. Technician A says general practice with any type of bleeding is to slip a hose over the end of the bleeder screw. Technician B says place the free end of the hose into a jar half filled with brake fluid. Who is correct? A. A only B. B only

C. Both A and B D. Neither A nor B

4. Technician A says too much free play causes the pedal to travel too far before moving the pistons far enough to develop full pressure in the master cylinder. Technician B says excessive free play can severely reduce braking performance and create an unsafe condition. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. Technician A says DOT 3 fluids are all silicone based because only silicone fluid can meet the DOT 3 specifications. Technician B says no vehicle manufacturer recommends DOT 3 fluid for use in its brake systems, particularly in antilock brake systems. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

3. While discussing brake pedal travel, Technician A says the maximum travel specification is normally about 4 inches (101.6mm) when 100 pounds (445 N) of force is applied. The exact specifications can be found in the vehicle service information. Technician B says exhausting brake boost pressure will result in an incorrect pedal travel or force measurement. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

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Master Cylinder and Brake Fluid Service

Name ______________________________________

Date ________________

185

JOB SHEET

14

BRAKE FLUID ASE Education Foundation Correlation This job sheet addresses the following MLR tasks: B.4. Select, handle, store, and fill brake fluids to proper level; use proper fluid type per manufacturer specification. (P-1) B.7.

Test brake fluid for contamination. (P-1)

This job sheet addresses the following AST/MAST tasks: B.9. Select, handle, store, and fill brake fluids to proper level; use proper fluid type per manufacturer specification. (P-1) B.13.

Test brake fluid for contamination. (P-1)

Tools and Materials • MSDS • Brake fluid containers • Brake fluid test strips or electronic meter Describe the vehicle being worked on: Year _______________ Make _______________ Model _______________ VIN _______________ Engine type and size _______________ Procedure 1. On the vehicle selected, determine the proper fluid type. List the type here. 

Task Completed

2. Describe the fluid level and visual condition of the fluid in the vehicle.   3. Was there a special procedure used to determine the fluid level, such as discharging the accumulator?  Types and characteristics of brake fluid 1. Select containers of DOT 3, DOT 4, DOT 5, DOT 3/4, and DOT 5.1 (if possible). 2. Locate MSDS for DOT 3, DOT 4, DOT 5, DOT 3/4, and DOT 5.1 (if possible).

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3. Determine and list the boiling point and hygroscopic properties of each type of fluid listed. DOT 3  DOT 4  DOT 5 0  DOT 3/4  DOT 5.1  4. Determine and list the general and specific hazards of each fluid. DOT 3 

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DOT 4  DOT 5  DOT 3/4  DOT 5.1  5. Describe the first-aid measures for each fluid. DOT 3  DOT 4  DOT 5  DOT 3/4  DOT 5.1  6. Explain the general storage limitations and procedures for each fluid. DOT 3  DOT 4  DOT 5  DOT 3/4  DOT 5.1  7. Using a brake fluid test strip or meter, test the brake fluid for contamination. Explain your findings.    8. Explain how you could determine if the brake fluid was contaminated without using a test strip or meter.    Problems Encountered    Instructor’s Response   

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Master Cylinder and Brake Fluid Service

Name ______________________________________

Date ________________

CHECKING A MASTER CYLINDER FOR LEAKS AND PROPER OPERATION

187

JOB SHEET

15

Upon completion of this job sheet, you will be able to check a master cylinder for internal and external leaks and for proper operation. ASE Education Foundation Correlation This job sheet addresses the following MLR task: B.2.

Check master cylinder for external leaks and proper operation. (P-1)

This job sheet addresses the following AST/MAST task: Check master cylinder for internal/external leaks and proper B.3.  operation; determine needed action. (P-1) Tools and Materials • Basic hand tools Protective Clothing • Goggles or safety glasses with side shields Describe the vehicle being worked on: Year _______________ Make _______________ Model _______________ VIN _____________ Engine type and size  Procedure 1. Check the fluid level in the master cylinder reservoir and, if necessary, add fluid to correct the level. What type of fluid is recommended for this vehicle? __________________________________________________________________________ 2. Carefully check the condition of the fluid. The fluid should be clear and transparent, although some darkening is acceptable. Describe your findings, and state what is indicated by the condition of the fluid. __________________________________________________________________________ __________________________________________________________________________ 3. Check for unequal fluid levels in the master cylinder reservoir chambers. Describe your findings. __________________________________________________________________________ __________________________________________________________________________ 4. Check for evidence of leaks or cracks in the master cylinder housing. Describe your findings. __________________________________________________________________________ __________________________________________________________________________ 5. If the master cylinder does not appear to be leaking, raise the vehicle on a lift and inspect all brake lines, hoses, and connections. Look for brake fluid on the floor under the vehicle and at the wheels. Describe your findings. __________________________________________________________________________ __________________________________________________________________________

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6. Check the brake lines for kinks, dents, or other damage. Also check for signs of leakage. Describe your findings.

Task Completed

__________________________________________________________________________ __________________________________________________________________________ 7. Check the brake hoses. They should be flexible and free of leaks, cuts, cracks, and bulges. Describe your findings. __________________________________________________________________________ __________________________________________________________________________ 8. Inspect the backing plates for fluid and grease. Describe your findings. Also make sure all parts attached to the plates are securely fastened. __________________________________________________________________________ __________________________________________________________________________ 9. To determine whether or not the brake system has an external leak, run the engine at idle with the transmission in neutral.

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10. Depress the brake pedal, and hold it down with a constant foot pressure. The pedal should remain firm, and the pedal should be at least 2 inches from the floor for manual brakes and 1 inch for power brakes without ABS.

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11. Hold the pedal depressed with medium foot pressure for about 15 seconds to make sure that the pedal does not drop under steady pressure. If the pedal drops under steady pressure, the master cylinder or a brake line or hose may be leaking.

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12. If there appears to be no external leak but the BRAKE warning lamp is lit, the master cylinder may be bypassing or losing pressure internally.

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13. To check for an internal master cylinder leak, remove the master cylinder cover and be sure the reservoirs are at least half full.

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14. Watch the fluid levels in the reservoirs as an assistant slowly presses the brake pedal and then quickly releases it.

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15. If fluid level rises slightly under steady pressure, the piston cups are probably leaking. Fluid level rising in one reservoir and falling in the other as the brake pedal is pressed and is released also can indicate that fluid is bypassing the piston cups. Describe your findings. __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________

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Name ______________________________________

Date ________________

189

JOB SHEET

16

REPLACE A MASTER CYLINDER ON A NON-INTEGRATED ABS SYSTEM Upon completion of this job sheet, you should be able to replace a master cylinder. ASE Education Foundation Correlation This job sheet addresses the following AST/MAST task: B.4. Remove, bench bleed, and reinstall master cylinder. (P-1) Tools and Materials • Safety glasses • Hand tools • Cloths • Fender cover Describe the vehicle being worked on: Year _____________________ Make _____________________ Model _____________________ VIN _____________________________ Engine type and size _____________________________

Caution Wear safety glasses or face protection when using brake fluid. Injuries to the face or eyes could occur from spilled or splashed brake fluid.

Procedure WARNING     Always clean around any lines or covers before removing or loosening them. Dirt and other contaminants will void the warranty and may damage the system components. WARNING     Do not remove protective shipping seals, covers, or plugs before installing the device. Dirt and other contaminants may enter and damage the system components or void warranty. WARNING     Prevent brake fluid from coming in contact with the vehicle’s finish. Brake fluid damages paint and finish immediately on contact. If fluid contacts finish, wash area thoroughly with running water and soap if possible. 1. List the service data. Power assisted? _______________ Type _______________ Master cylinder mounting fasteners torque _______________ Does the service manual specify procedures for checking or adjusting the brake pushrod? If yes, outline the procedures and tools. _______________

Caution Ensure the fitting is not cross-threaded when reconnecting. This could damage the fitting, the ­component, or both.

Caution Do not use paints, lubricants, or ­corrosion inhibitors or fasteners unless specified by the ­manufacturer. Add-on coating of any type may affect clamping or damage the fastener(s).

2. Explain why this master cylinder is being replaced. _________________________________________________________________________ 3. Place a fender cover over the vehicle. Place cloths under the master cylinder.

Task Completed

4. Remove the brake lines from the master cylinder.

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5. Remove the master cylinder fasteners and the master cylinder.

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6. Remove the reservoir from the master cylinder, and install it on the new one if necessary.

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7. Refer to Job Sheet 15 for bench bleeding the master cylinder.

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8. Install the master cylinder to the cowl or power booster.

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9. Connect the brake lines to the master cylinder. Do not completely tighten the lines at this time.

Task Completed h

10. Have a coworker slowly depress the brake pedal while step 10 through step 12 are being accomplished.

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11. Loosen the rear brake line slightly. Check the fluid for air. Tighten the brake line before the pedal achieves the halfway point.

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12. Loosen the front brake line and repeat step 10. 13. Have the coworker release the pedal. 14. Repeat step 9 through step 13 once or twice more to ensure the master cylinder is clear of air. 15. Operate the brake pedal to full brake with the engine off and on (if power assisted). 16. Does the brake pedal have the correct feel? Are the brakes operative?

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17. If either answer to step 16 is no, determine the needed repairs or actions. Consult the instructor.

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18. When the repair is complete, clean the area, store the tools, and complete the repair order.

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Problems Encountered    Instructor’s Response   

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Caution Use the correct fastener torque and tightening sequence when installing components. Incorrect torque or sequencing could damage the fastener(s) or components).

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Master Cylinder and Brake Fluid Service

Name ______________________________________

Date _________________

191

JOB SHEET

17

MANUALLY BLEEDING A BRAKE SYSTEM Upon completion of this job sheet, you will be able to bleed/flush a brake system using manual procedures. ASE Education Foundation Correlation This job sheet addresses the following MLR task: B.6.

Bleed and/or flush brake system. (P-1)

This job sheet addresses the following AST/MAST task: B.12.

Bleed and/or flush brake system. (P-1)

Tools and Materials • Service manual, paper or computerized • Appropriate type of brake fluid • Appropriate line wrenches • Flexible hose about 18 inches long • Clear capture container • Lift or jack and safety stands • Coworker Procedure 1. Determine the following information from the service manual. Year ___________________ Make ___________________ Model ___________________ Type of split system  Bleeder screw torque  Brake fluid type  Bleeding sequence  ABS cautions, if equipped 

Caution If the vehicle is raised on a lift with the coworker inside, ensure the vehicle is well balanced, pads are placed correctly, and the manual locks are engaged when the vehicle is at working height. If a jack and jack stands are used, ensure both are placed correctly. Failure to follow safety procedures and proper use of lifting equipment could result in damage or injury.

2. Check the brake fluid level and top off as needed.

Task Completed h

3. Lift the vehicle until the wheels are free of the floor. Install jack stands if needed.

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4. Remove the rubber dust cap from the first wheel to be bled. Check with service information for the proper bleeding sequence.

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5. Ensure the capture container is about ¼ full of clean brake fluid appropriate to the vehicle being serviced.

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6. Connect one end of the flexible hose onto the bleeder screw. Insert the other end into the fluid in the container.

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7. Place the line wrench on the bleeder screw and ask the coworker to pump the pedal several times and then hold the brake pedal down.

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8. After the coworker has the brake pedal depressed, open the bleeder screw one complete turn. Observe the container for air bubbles.

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9. When alerted by the coworker that the pedal is on the floor, close the bleeder screw and ask the assistant to pump up the pedal again.

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10. Repeat step 8. 11. Are air bubbles still visible in the container as the fluid is expelled from the system? If yes, repeat steps 8 and 9 until the expelled fluid is clear of air. Once air is cleared, continue with steps 8 and 9 until clear, new fluid is expelled.

Task Completed h

12. Remember to check and top off the fluid level often.

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13. Does expelled brake fluid appear to be new fluid? If yes, go to step 13. If not, go back to steps 8 and 9.

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14. Disconnect the hose from the bleeder screw and install the dust cap.

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15. Check the fluid level in the master cylinder reservoir. Is the reservoir dry? If so, top off and go back to step 4 and repeat the process with the wheel(s) that have been bled. If not, top off and go to step 15.

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16. Connect the hose and capture container to the next wheel in the sequence.

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17. Follow steps 4–14 to bleed this wheel.

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18. Continue to bleed each wheel in sequence.

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Problems Encountered    Instructor’s Response   

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Name ______________________________________ Date _________________

193

JOB SHEET

18

PRESSURE BLEED A BRAKE SYSTEM Upon completion of this job sheet, you will be able to bleed/flush a brake system using an air-operated pressure bleeder. ASE Education Foundation Correlation This job sheet addresses the following MLR task: B.6.

Bleed and/or flush brake system. (P-1)

This job sheet addresses the following AST/MAST task: B.12.

Bleed and/or flush brake system. (P-1)

Tools and Materials • Service manual, paper or computerized • Appropriate type of brake fluid • Appropriate line wrenches • Flexible hose about 18 inches long • Clear capture container • Lift or jack and safety stands • Air-operated brake bleeder Procedure 1. Determine the following information from the service manual. Year _____________________ Make _____________________ Model ________________ Type of split system  Bleeder screw torque  Brake fluid type  Bleeding sequence 

Caution If the vehicle is raised on a lift, ensure the vehicle is well balanced, pads are placed correctly, and the manual locks are engaged when the vehicle is at working height. If a jack and jack stands are used, ensure both are placed correctly. Failure to follow safety procedures and proper use of lifting equipment could result in damage or injury.

Brake bleeder operating air pressure  ABS cautions, if equipped  NOTE: The procedures in this job sheet are based on a compressed air brake pressure bleeder. If another type of pressure bleeder is used, substitute that equipment manufacturer’s instructions for the procedures listed here.

Task Completed

2. Ensure the lower chamber is at zero air pressure. Remove the top and fill the upper chamber with the appropriate brake fluid.

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3. Pressurize the bleeder’s lower chamber with the proper air pressure.

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4. Select the master cylinder/bleeder adapter kit and install the kit onto the master cylinder.

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5. Connect the bleeder’s outlet hose to the adapter.

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6. Turn on the bleeder hydraulic outlet valve. Check the adapter kit for leaks at the master cylinder.

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7. Lift the vehicle until the wheels are free of the floor. Install jack stands if needed.

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8. Remove the rubber dust cap from the first wheel to be bled. Check with service information on the proper bleeding sequence.

Task Completed h

9. Ensure the capture container is about ¼ full of clean brake fluid appropriate to the vehicle being serviced.

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10. Connect one end of the flexible hose onto the bleeder screw. Insert the other end into the fluid in the container.

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11. Place the line wrench on the bleeder screw.

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12. Open the bleeder screw one complete turn. Observe the container for air bubbles.

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13. Continue to observe the container for air bubbles and new fluid. When the air is cleared and new fluid is being expelled, close the bleeder screw.

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14. Disconnect the hose from the bleeder screw and install the dust cap.

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15. Connect the hose and capture container to the next wheel in the sequence.

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16. Follow steps 10–15 to bleed this wheel.

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17. Continue to bleed each wheel in sequence.

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18. After the last wheel is bled, lower the vehicle to the floor.

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19. Turn off the bleeder valve.

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20. Exhaust the air pressure in the lower chamber until the gauge reads zero pressure.

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21. Place some rags under the master cylinder. Disconnect the bleeder’s hose and remove the adapter kit from the master cylinder.

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22. Remove the rags and, if necessary, clean any spilled brake fluid from the vehicle.

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23. Clean and store the brake bleeder.

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Problems Encountered    Instructor’s Response   

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Caution Before adding fluid to the brake bleeder, ensure the air pressure in the lower chamber has been exhausted down to zero. Eye and skin injuries could result if the upper chamber is opened with air pressure present in the lower chamber.

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Name ______________________________________ 

Date _________________

195

JOB SHEET

19

VACUUM BLEED A BRAKE SYSTEM Upon completion of this job sheet, you will be able to bleed/flush a brake system using a suction/vacuum bleeder. ASE Education Foundation Correlation This job sheet addresses the following MLR task: B.6.

Bleed and/or flush brake system. (P-1)

This job sheet addresses the following AST/MAST task: B.12.

Bleed and/or flush brake system. (P-1)

Tools and Materials • Service information, paper or computerized • Appropriate type of brake fluid • Appropriate line wrenches • Flexible hose about 18 inches long • Clear capture container • Lift or jack and safety stands • Brake suction equipment NOTE: For this job sheet, a typical hand-operated vacuum pump with capture container is used. Other suction equipment will be used in a similar manner. Procedure 1. Determine the following information from the service manual. Vehicle make __________________ Model ___________________ Year _______________ Type of split system  Bleeder screw torque 

Caution If the vehicle is raised on a lift, ensure the vehicle is well balanced, pads are placed correctly, and the manual locks are engaged when the vehicle is at working height. If a jack and jack stands are used, ensure both are placed correctly. Failure to follow safety procedures and proper use of lifting equipment could result in damage or injury.

Brake fluid type  Bleeding sequence  Brake bleeder operating air pressure  ABS cautions, if equipped 

Task Completed

2. Set up the suction equipment. Check its operation by placing a finger over the hose that goes to the bleeder screw and pump the handle. A vacuum should be felt.

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3. Lift the vehicle until the wheels are free of the floor. Install jack stands if needed.

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4. Remove the rubber dust cap from the first wheel to be bled. Check service information for the proper bleeding sequence.

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5. Connect the input (vacuum) end of the vacuum pump onto the bleeder screw.

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6. Place the line wrench on the bleeder screw.

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7. Open the bleeder screw one complete turn.

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8. Operate the vacuum pump until fluid flows into the capture container. Observe the container for air bubbles and new fluid.

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9. Continue to operate the pump until the expelled fluid is clear of air and new fluid is being expelled.

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10. Close the bleeder screw and disconnect the hose. Install the dust cap. 11. Lower the vehicle if necessary and check the fluid level in the master cylinder reservoir. If the reservoir is dry, then top off and return to the wheel(s) already bled and repeat steps 4–8 on each wheel. If the reservoir is not dry, top off as needed.

Task Completed h

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12. Connect the hose and capture container to the next wheel in the sequence.

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13. Follow steps 4–9 to bleed this wheel and check the brake fluid.

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14. Continue to bleed each wheel in sequence.

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15. After the last wheel is bled, lower the vehicle to the floor.

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Problems Encountered    Instructor’s Response   

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Master Cylinder and Brake Fluid Service

Name ______________________________________ 

Date _________________

197

JOB SHEET

20

Checking Brake Pedal Height and Free Play Upon completion of this job sheet, you will be able to accurately determine proper brake pedal height and free play. ASE Education Foundation Correlation This job sheet addresses the following MLR task: B.1.

Describe proper brake pedal height, travel, and feel. (P-1)

This job sheet addresses the following AST/MAST task: Measure brake pedal height, travel, and free play (as applicable); B.2.  determine needed action. (P-1) Tools and Materials • Service information • Brake pedal force gauge • Tape measure Task Completed

Procedure Determining brake pedal free play 1. The engine should be off. Push on the brake by hand while measuring the distance the pedal travels before a stiff resistance is felt. Record your reading here  . 2. Obtain the specification for pedal free play (if it is adjustable). Record them here. 

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3. Using service information, briefly describe the procedure to adjust pedal free play.  Determining brake pedal travel 1. Find the specification for the amount of brake pedal travel and the amount of force to be applied and record them here.  2. Exhaust all the vacuum from the power booster. Turn the key off and pump the brake pedal until the pedal becomes firm.

h

3. Place the brake pedal effort gauge on the brake pedal. Hook the tape measure on the back of the brake pedal and past the steering wheel. Apply the required force to the brake pedal as read by the pedal force gauge while looking at the tape measure at the bottom of the steering wheel to read the amount of travel.

h

4. What is your diagnosis of the brake pedal free play and the brake pedal travel on this vehicle?   

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Problems Encountered    Instructor’s Response   

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Hydraulic Line, Valve, and Switch Service

Upon completion and review of this chapter, you should be able to: ■■

Inspect brake lines and fittings for leaks, dents, kinks, rust, cracks, or wear.

■■

Tighten loose fittings and supports.

■■

Inspect brake hoses for leaks, kinks, cracks, bulging, or wear.

■■

Remove and replace double flare and ISO brake lines, hoses, fittings, and supports.

■■

■■

■■

Fabricate replacement brake tubing, including the forming of double inverted flare or ISO flare ends and correct bends to fit the vehicle chassis. Diagnose poor stopping and brake pull or grab conditions caused by problems in the brake lines or brake hoses and perform needed repairs. Reset a pressure differential valve (warning lamp switch).

■■

■■

■■ ■■ ■■ ■■ ■■ ■■

Diagnose poor stopping and brake pull or grab conditions caused by problems in the hydraulic system valves and perform needed repairs. Inspect, test, and replace metering valves, proportioning valves, pressure differential valves, and combination valves.

Basic Tools Cloths Tubing with transparent container

Diagnose electrical problems in circuits for brake system switches and sensors. Test, adjust, repair, or replace the brake stop lamp switch and wiring. Inspect, test, and replace the brake warning lamp, switch, and wiring. Test and repair the parking brake indicator lamps, switches, and wiring. Inspect, test, and replace the master cylinder fluid level sensor or switch. Repair electrical wiring and connectors.

Terms To Know American wire gauge (AWG) Heat-shrink tubing

Rosin flux solder Solder-less connector

Splice clip

INTRODUCTION All hydraulic systems need lines and hoses to contain the fluid. All hydraulic systems require valves to control and direct the fluid if work is to be done in an efficient manner. Take the dam across a river, for instance. The dam is, in fact, a valve that controls water flow, reducing flooding below the dam and directing flow through causeways to drive electric turbines. Releasing the water completely at one time would only destroy the electric plant and the surrounding areas. The hydraulic brake system shares some of the same concerns with regard to fluid containment and direction. Without the proper lines and hoses, the brake fluid would just “flood,” and there would be no braking effect. If control valves were present, there would be uneven or no braking effect at all, which brings up the problems associated with the old mechanical brake system. Over the last 100 years, hydraulic brake systems have been improved to be almost fail-safe. But those lines, hoses, and valves require some services during the life of the vehicle, even if the only reason is 199

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old age. This chapter outlines some of those common services. Some valves have been computerized, and, where appropriate, those valves are discussed in Chapter 10, Electronic Braking Systems.

RE-CENTERING A PRESSURE DIFFERENTIAL VALVE (FAILURE WARNING LAMP SWITCH)

Special Tools Cloths Tubing with transparent container

Classroom Manual page 109

As was covered in the Classroom Manual, the job of the pressure differential valve is to detect a leak in the braking system. After bleeding or flushing and refilling some brake systems, the pressure differential valve (or warning lamp switch) may be actuated and the warning lamp may be lit. Opening a bleeder screw creates a pressure differential between the two halves of the hydraulic system. This pressure differential has the same effect as a leak, and the valve piston moves toward the low-pressure side to close the lamp circuit. On late model vehicles the function of the pressure differential valve has been taken over by the hydraulic modulator of the ABS braking system. We are including this description here because there are still many vehicles on the road with these pressure differential valves in use. The piston in this type of valve (or switch) should re-center automatically with no special action required. Occasionally, however, the piston may stick at one side of its bore or the other and leave the lamp lit. If the lamp is lit with the ignition on, apply the brakes rapidly with moderate to heavy force two or three times. Hydraulic pressure usually frees a stuck piston, and the springs will re-center it. If the valve does not free itself, try opening the bleeder on the opposite side while having an assistant slowly depress the brake pedal. If necessary, alternate side to side a few times to see if the valve will free itself. If not, then the valve may need to be replaced. When trying to re-center the piston in this type of valve, the piston often goes over center in the opposite direction. This causes the lamp to turn off momentarily and then relight. If this happens, open a bleeder screw on the opposite side of the hydraulic system and repeat the procedure. Keep going from one side to the other bleeding the brakes. Two or three tries may be needed to get the piston properly centered. A solution to this problem is the use of a two-piston valve (Figure 5-1). Switch terminal

From master cylinder

From master cylinder

To front wheel

To rear wheels

Centering spring

Pistons

To front wheel

Centering spring

Figure 5-1  Pressure differential valve (warning lamp switch) with two pistons.

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BRAKE LINE, FITTING, AND HOSE SERVICE Special Tools SERVICE TIP  As mentioned in Chapter 5 of the Classroom Manual, there is a copper-nickel alloy brake tubing that meets SAE Standard J1047 and ISO 4038. It can be serviced in the same manner as the more common steel tubing.

Cloths Brake pedal depressor

Hydraulic system lines are made of steel tubing and rubber hoses. Rigid hydraulic lines are made of double-wall, welded steel tubing that is coated to resist corrosion. Brake hoses must be free to flex and move as the wheel moves up and down or turns. Brake hoses also must be able to withstand the high pressures within the system. Exposure to the elements, road salts in winter, salt air, water, and contaminants in the system all contribute to rusting and corrosion of brake fittings, lines, and hardware.

Brake Line Inspection All carmakers include brake line inspection on their vehicle maintenance schedules. Most manufacturers recommend inspecting brake hoses twice a year, but it is good practice to check them whenever the vehicle is getting lubrication service. Steel brake lines and fittings should be checked for damage and leakage once a year or whenever the vehicle gets brake service. Brake line inspection is more than a quick glance to see if all the parts are in place. Physical damage may be apparent from the outside, but wear and deterioration also can occur inside tubing and hoses. To inspect brake lines thoroughly, be sure to cover the points described in the following paragraphs.

SERVICE TIP  Very small leaks at brake line fittings that appear only under pressure can be hard to find. Often, pressure must be applied for a long time before seepage appears. Lift the vehicle and clean each valve and line connection. This will make it easier to spot a leak. To help pinpoint such a problem, apply the brakes with a brake pedal depressor used for wheel alignment. A brake pedal depressor is a long bar with a twist stop that rests against the driver’s seat. Place the end of the bar on the brake pedal, and apply as much hand and arm force as possible. With the force applied, slide the twist lock against the forward edge of the seat and slowly release the force. The lock will hold the pedal applied. A brake pedal depressor is usually found in the area of the wheel alignment bay. Leave the depressor applied for several hours and then check for small leaks. When using this test method, however, remove the stop lamp fuse to keep from discharging the battery.

Tubing Inspection.  Steel tubing is more durable than rubber hoses, but it can suffer rust, corrosion, impact damage, and cracking. Water trapped around brake tubes, fittings, and mounting clips can rust and corrode steel tubing. Corrosion can be particularly severe in areas that use a lot of salt to melt ice on the roads during the winter. Mounting clips are necessary to hold brake lines to the body or frame, but they can trap salt water and hide severe corrosion. Therefore, inspect all mounting points closely. Missing mounting clips can cause other problems. If brake tubing is not mounted securely, vibration can cause the tubing to fracture and leak. Brake tubing that hangs below

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Figure 5-2  Inspect brake tubing for damage such as kinks, rust, abrasion, and looseness. All bends should be smooth and without kinks.

the body or frame can be snagged and torn loose. Inspect all brake tubing for damage and looseness (Figure 5-2). Also look for empty screw holes or scuff marks on body and frame parts that indicate missing clips. Brake tubing can be damaged by objects thrown up by the tires, particularly if the vehicle is used off-road. Road impact damage is far less common; however, than impact damage caused by improperly installed towing chains or improper placement of a floor jack or lift. Inspect brake tubing for dents, kinks, and cracks caused by careless service practices. Hose Inspection.  Damage to the outside of a brake hose is easier to spot than internal damage or deterioration. Inspect brake hoses for abrasion caused by rubbing against chassis parts and for cracks at stress points, particularly near fittings. Look for fluid seepage indicated by softness in the hose accompanied by a dark stain on the outer surface. Look at each hose closely for general damage and deterioration such as cracks, soft or spongy feel or appearance, stains, blisters, and abrasions. Extreme rust between the clamp and hose or a crimped clamp could pinch the hose. To check for internal hose damage, have a coworker pump the brakes while feeling the hose for swelling or bulging as pressure is applied internally (Figure 5-3). Have the

Master cylinder

Fluid flow

Caliper

Blockage Fluid flow

Master cylinder

Caliper

Blockage Blister

Leakage stains

Figure 5-3  Possible internal defects in a brake hose.

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coworker apply and release the brakes, then quickly spin the wheel. If the brake at any wheel seems to drag after pressure is released, the brake hose may be restricted internally. No conclusive way exists to inspect or test for internal restriction, but replacing a hose if a brake has these symptoms can be good insurance. Finally, inspect the mounting clips, brackets, and fittings where hoses are connected to rigid brake lines. Replace any missing clips and be sure that the hoses are not kinked or twisted. At the front brakes, rotate the steering from lock to lock and verify that the brake hoses do not rub on chassis parts or twist and kink when the wheels turn.

Brake Hose Removal and Replacement

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Special Tool Cloths

Special Tools Brake pressure gauge(s) Cloths Service information

AUTHOR’S NOTE  A replacement brake hose must be the same length as the original one. A hose that is too long may rub on the chassis. A hose that is too short may break when the movable component reaches the limits of its travel. Some hoses may appear to be too short if the vehicle is lifted and the suspension extends to its maximum. Check the hose length closely in this instance.

SERVICE TIP  Make sure the hose is not twisted between the frame or body anchor and the point of attachment to the disc brake caliper. Sometimes during a rush job or do-it-yourself job, the hose gets twisted and is not noticed. This damages the hose, particularly during turns when it gets stretched because the twist makes the hose a little too short. Over a fairly short period of time, this breaks the inner lining and causes a “check-valve” condition.

Hose Removal.  Some brake hoses have a swivel fitting at one end and a fixed fitting that cannot be rotated at the other (Figure 5-4). Disconnect the swivel fitting first on this type of hose. Other hoses have a fixed male fitting on one end and a fixed female fitting on the other. The female end of such a hose is connected to a flare nut on a rigid brake tube; disconnect this end first. If the hose has a banjo fitting on one end—usually for connection to a caliper—disconnect the banjo fitting first (Figure 5-5), then the other end of the hose. Occasionally, some caliper fittings and hoses have left-hand threads. Sometimes the left-hand fasteners are noted with a slash through the flat surfaces of the nut or bolt.

Sealing washers

Banjo bolt Hose with banjo fitting

Fluid

Figure 5-4  Typical brake hose end fittings.

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Figure 5-5  Note the sealing washers on this banjo fitting.

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Chapter 5 Flare-nut wrench

Brake pipe

Brake hose To caliper

Figure 5-6  Use a flare-nut (line) wrench to disconnect the brake line (tubing) from the hose.

Follow these guidelines to remove a brake hose: 1. Clean dirt away from the fittings at each end of the hose to keep it from entering the system. 2. Use a flare-nut wrench to disconnect the flare nut from the female end of the hose (Figure 5-6) or loosen and disconnect the swivel end of the hose. When loosening one fitting at the end of a hose, hold the mating half of the fitting with another flarenut wrench, which will make fitting removal easier and prevent damage to mounting brackets and clips. 3. Remove the hose retaining clip from the mounting bracket with a pair of pliers. 4. Separate the hose from the mounting bracket and any other clips used to hold it in place. 5. Use a flare-nut wrench to disconnect the other end of the hose from the caliper or wheel cylinder. 6. If a replacement hose is not going to be installed immediately, cap or plug open fittings on the vehicle to keep dirt out of the system. Hose Installation.  When installing a brake hose, be sure the new hose is the correct length and determine whether or not the right-hand and left-hand hoses are the same or different. Route the new hose in the same location as the original, and provide ¾ inch to 1 inch of clearance between the hose and suspension and wheel parts in all positions. If the original hose had special mounting clips or brackets, the replacement should have the same.

SERVICE TIP  A piece of rubber can break partly loose inside a brake hose and act as a check valve to trap pressure at the brake. If you suspect that a dragging brake is caused by a “check-valved” hose, open the bleeder screw and turn the wheel by hand. If the brake changes from locked up to free, the hose is probably the culprit. To confirm the diagnosis, install a pressure gauge in place of the bleeder screw, pump up the brakes and release the pedal. If the brake locks again and a pressure reading stays on the gauge after the pedal is released, loosen the fitting that connects the brake pipe to the hose. If the brake does not loosen and the gauge pressure does not drop to zero, the hose is retaining the pressure. Replace it.

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WARNING  Ensure that the fitting is not cross-threaded when reconnecting. This could damage the fitting or the component, or both.

Follow these guidelines to install a brake hose: 1. If the hose has a fixed male end, install it into the wheel cylinder or caliper first. If the connection requires a copper gasket, install a new one. 2. If one end of the hose has a banjo fitting for attachment to a caliper, install the banjo bolt and a new copper gasket on each side of the fitting shown earlier in Figure 5-5. Leave the banjo bolt loose at this time; tighten it after connecting and securing the other end of the hose. 3. Route the hose through any support devices and install any required locating clips. 4. Insert the free end of the hose through the mounting bracket. 5. Depending on hose design, connect the flare nut on the steel brake line to the female end of the hose or connect the swivel end of the hose to the mating fitting. 6. Use a flare-nut wrench to tighten the fitting and hold the hose with another flarenut wrench to keep it from twisting (see Figure 5-6). Check the colored stripe or the raised rib on the outside of the hose to verify that the hose has not twisted during installation. 7. Install the retaining clip to hold the hose to its mounting bracket (Figure 5-7). Install any other clips as required. 8. If the banjo bolt was left loose in step 2, position the banjo fitting to provide the best hose position and tighten the bolt. After installing the new brake hose, check the hose and line connections for leaks and tighten if needed. Check for clearance during suspension rebound and while turning the wheels. If any contact occurs, reposition the hose, adjusting only the female end or the swivel end. When removing a banjo fitting, check it for sealing washers. If equipped with washers, it is recommended to replace them.

Caution Always clean around any lines or covers before removing or loosening them. Dirt and other contaminants will void the warranty and may damage system components.

Special Tools Hand tools Cloths

Brake pipe

Brake hose clip

Figure 5-7  The locking clip is tapped into place with a small hammer.

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Caution

SERVICE TIP  Some brake hoses are not DOT approved. Check with your supervisor or parts vendor as to the hose warranty or desirability of using nonapproved hose.

Always replace brake hoses in axle sets. This will eliminate brake malfunctions caused by bad hoses and help in diagnosing ongoing brake problems.

Brake Tubing Removal and Replacement

Caution Never use low-­ pressure hydraulic hoses or oil hoses as replacements for brake hoses. These components cannot withstand the high pressure of the brake system. Fluid leakage, line rupture, and system failure can result.

Removing and replacing a length of brake tubing looks like a straightforward job, but the following guidelines will make the task easier. Start by cleaning dirt away from the fittings at each end of the tubing. Do not remove the tubing mounting clamps yet. Leaving them in place will keep the tubing from moving around and make it easier to disconnect the fittings. Use a flare-nut wrench to disconnect the fittings at each end of the tubing. If the tubing is attached to a hose, use another flare-nut wrench to hold the hose fitting. If the tubing is attached to a rigidly mounted junction block or cylinder, a second wrench is not needed. If replacement tubing is not going to be installed immediately, cap or plug open fittings on the vehicle to keep dirt out of the system. Remove the mounting clips from the chassis and remove the brake tubing. Inspect the clips and their screws to determine if they are reusable. If they are not, install new ones. If the brake tubing has any protective shields installed around it, save them also for installation with the new tubing. If you must fabricate a new section of tubing, save the old section for a bending guide. To install a length of brake tubing, position it on the chassis and install the mounting clips loosely. Leaving the new tubing slightly loose will help to align the tube fittings. Next, use the appropriate flare-nut wrenches to connect the fittings at both ends of the tubing. Tighten the fittings securely and then tighten the mounting clips.

Fabricating Brake Tubing Brake pipes or tubes are normally 3/16-inch double-wall steel tubing. Stock brake tubing is available in various lengths with ends pre-flared and flare nuts installed (Figure 5-8).

Figure 5-8  Prefabricated brake lines come in various lengths with the fittings installed and the ends already flared.

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207

Always use prefabricated tubing whenever possible. If original equipment tubing that is formed to the required bends for a specific vehicle is available, it may be your best choice from a time and overall cost basis. Lacking a preformed original equipment manufacturer (OEM) tube, a straight section of brake tubing of the proper length is your next best choice. It may be necessary in many cases, however, to fabricate a replacement brake line from bulk tubing. The following sections explain how to cut and bend tubing and how to form the required flared ends. Photo Sequence 8 shows the basic steps of cutting and bending tubing and forming an SAE double flare on the tubing ends.

SERVICE TIP  Install the fittings onto the tubing before flaring the ends. Many feet of tubing have been wasted over the years because the fitting will not fit over a finished flare.

Special Tools Hand tools Cloths

8 Typical Procedure for Fabricating and Replacing a Brake Line Photo Sequence

Figure P8-1  Be sure to use the recommended bulk 3/16-inch double-wall steel brake tubing and the correct size and type of tube nuts.

Figure P8-4  Clean any burrs after cutting.

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Figure P8-2  To determine the correct length, measure the removed tube with a string and add about 1/8 inch for each flare.

Figure P8-5  Place the tube nut in the correct direction.

Figure P8-3  Cut the tubing to the required length with a tubing cutter.

Figure P8-6  Place the tubing in the flaring bar with the end protruding slightly above the face of the bar. Use the adapter shown in P 5-8 to set the correct length of the protruding portion.

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Photo Sequence 8 (CONTINUED)

Figure P8-7  Firmly clamp the tube in the bar so the force exerted during flaring does not push the tubing down through the bar.

Figure P8-8  Place the adapter (anvil) in place over the tube opening to form the first stage of the flare.

Figure P8-9  Tighten down the flaring clamp.

Figure P8-10  Loosen the flaring clamp, remove the adapter (anvil), and check to see that the end of the tubing is properly belled.

Figure P8-11  Install the cone onto the tube opening and retighten the flaring clamp.

Figure P8-12  The cone completes the double flare by holding the tubing back on itself. This doubles its thickness and creates two sealing surfaces.

Figure P8-13  Bend the replacement tube to match the original tube using a tubing bender.

Figure P8-14  Clean the brake tubing by flushing it with clean brake fluid.

Figure P8-15  Install the replacement brake tube, maintaining adequate clearance to metal edges and moving or vibrating parts.

Figure P8-16  Install the brake tube and tighten the tube nuts to shop manual ­specifications with an inch-pound torque wrench.

Figure P8-17  Bleed the lines.

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Cutting Tubing.  Bulk tubing comes in large rolls. To form a replacement length of tubing, a section must be cut from a roll as follows: 1. Determine the exact length of replacement tubing needed; add 1 8 inch for each flare that is to be made. Measure the old tubing as accurately as possible. Use a string, if necessary, as shown in Photo Sequence 8. 2. Hold the free outer end of the tubing against a flat surface with one hand and unroll the roll in a straight line with the other hand (Figure 5-9). Do not lay the roll flat and pull one end; this will twist and kink the tubing. 3. Mark the tubing at the point to be cut and place a tubing cutter on the tubing. Tighten the cutter until the cutting wheel contacts the tubing at the marked point. 4. Turn the cutter around the tubing toward the open side of the cutter jaws. After each revolution, tighten the cutter slightly until the cut is made. 5. Ream the cut end of the tubing with a reaming tool (usually attached to the cutter) to remove burrs and sharp edges. Hold the end downward so that metal chips fall out. Ream only enough to remove burrs; then blow compressed air through the tubing to be sure all chips are removed. Bending Tubing.  Whether a replacement brake tube is a straight length of pre-flared tubing or made from bulk material, it is usually necessary to bend the new line to match the old one. Steel tubing can be bent by hand to form gentle curves. For large-radius bends on small diameter tubing, a bending spring can be used. Slip the coil spring over the tubing and bend it slowly by hand (Figure 5-10). Bend the tubing slightly further than required and back off to the desired angle. This releases spring tension in the bender so it can be easily removed. A bending spring can be used more easily before the tubing ends are flared. To use a bending spring on flared tubing, you must use an oversize spring that will slip over the flares. Bending may be more difficult because of the looseness of the spring.

209

Special Tool Tubing cutter

Caution Double-wall steel brake tubing is the only type of tubing approved for brake lines. Never use copper tubing or any other tubing material as a replacement; it cannot withstand the high pressure or the vibrations to which a brake line is exposed. Fluid leakage and system failure can result.

Caution Do not use a hacksaw to cut tubing. The uneven pressure of the blade will distort the tubing end, and the teeth will leave a jagged edge that cannot be flared properly.

Spring-type bender

Unroll

Slip over-tubing

Hold here

Bending the tube

Figure 5-9  Unroll the desired length of tubing from the bulk roll in this manner.

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Figure 5-10  Large-radius bends on small-diameter brake tubing can be made with a bending spring.

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Caution Do not try to bend tubing into a tight curve by hand; you will usually kink the tubing. Because a kink in a brake tube weakens the line, never use a kinked tube. To avoid kinking, use a bending tool. Several types are available.

Special Tool Tubing flare kit

Caution Never use copper fuel line fittings as a replacement for steel brake line fittings. Copper cannot withstand the high pressure or the vibrations to which a brake line is exposed. Fluid leakage and system failure can result.

Figure 5-11  One type of tube bending tool that will form tight radius bends on steel tubing.

On larger diameter tubing, or where tighter bends are needed, use a lever-type or gear-type bender (Figure 5-11). Slip the bender over the tubing at the exact point the bend is required. If bending the tubing near an end that is to be flared, leave about 1½ inches of straight tubing at the end. After the tubing is bent to the proper shape, assemble the flare nuts on the tubing before flaring the tube ends. Once the ends are flared, the flare nuts will not fit over the end of the tubing. Observe these additional guidelines when bending and fabricating tubing: 1. Avoid straight lengths, or runs, of tubing from fitting to fitting. They are hard to install and subject to vibration damage. 2. Ensure that the required clips and brackets will fit a replacement length of tubing, especially on long sections. 3. Bend tubing to provide necessary clearance around exhaust components and suspension parts. 4. Be sure that tubing ends align with the fittings on mating components before mounting the tubing securely. 5. When installing tubing, connect the longest straight section first.

Flare Fittings After tubing is cut and bent to fit, flares must be formed on unfinished ends. Both the SAE and the International Standards Organization (ISO) were formed to research and establish automotive standards and improvements, and both organizations have established brake tubing flare standards: SAE 45-degree double flares and ISO flares or bubble flares (Figure 5-12). These flares and their fittings are not interchangeable. Be sure to form the proper type of flare required by the vehicle system. Always place the flare nut on the tubing with the threads facing the end of the tube before forming the flare. Flare nuts do not usually corrode or rust, but the tubing that passes through them may. If the line corrodes and freezes to the nut, the line will twist when trying to loosen the nut with a flare-nut wrench. To free a flare nut frozen to the line, apply penetrating oil to the connection. The connection can be heated with a torch if all plastic and rubber parts are removed from the immediate area. Using a pencil-thin flame, apply heat to all sides of the flare nut, never to the line. When the steel nut begins to glow from the heat, try to loosen the nut with the flare wrench. If the nut cannot be freed, cut the line. The component to which the line is connected may be reusable. If heat is used to free a frozen flare nut, the entire length of tubing should be replaced. Always use the correct size of flare-nut wrench when tightening or loosening hydraulic fittings. When loosening or tightening a nut on a fitting or a union, use two wrenches: one to turn the nut and one to hold the fitting or union (Figure 5-13). When connecting

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Hydraulic Line, Valve, and Switch Service 45° Inverted double flare

ISO flare

211

Brake pipe

Fitting Always use two line wrenches (flare-nut wrenches)

Steel tube Double Flare

Chamfer-type ISO Flaring

Figure 5-12  The two common flare types used on brake tubing. The 45-degree inverted double flare uses fractional inch-size fittings. The ISO flare uses metric fittings. See Figures 5-8 and 5-22 for more detailed drawings of the angles and fitting surfaces.

Figure 5-13  Use flare-nut (line) wrenches to loosen line fittings.

a tube to a hose, a tube connector, or a brake cylinder, use an inch-pound torque wrench to tighten the tube fitting nut to specifications. On fittings requiring gaskets, always install new copper gaskets. Used gaskets have taken a set and will not seal properly if reinstalled. Special tools are required to flare tubing, and the tools for SAE and ISO flares are different. The following sections provide more instructions for forming SAE and ISO flares. Observe these precautions about flaring and installing brake line fittings. Forming an SAE 45-Degree Double Flare.  A double flare is made in two stages using a special flaring tool. A typical flaring tool consists of a flaring bar and a flaring clamp. The double flaring process is shown in Figure 5-14 and demonstrated in Photo Sequence 8. The angle of the flare and the nut is 45 degrees, whereas the angle of the seat is 42 degrees. When the nut is tightened into the fitting, the difference in angles—called an interference angle—causes both the seat and the flared end of the tubing to wedge together. When correctly assembled, brake lines connected with flare fittings provide joints that can withstand high hydraulic pressure.

Flaring bar

Caution

43° 47°

Twice actual wall thickness ± .005 inch

Radius .030 inch/.050 inch

Tube size Double lap flare

Figure 5-14  The two steps for forming a double flare, the flaring tools, and the dimensions of a double 45-degree flare are shown.

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Tubing bender

Tubing flare kit

89° 91°

Tube I.D. ± .010 inch – .020 inch

Step 2

Special Tool

Special Tool

Flaring cone Adapter

Step 1

Caution Never use sphericalsleeve compression fittings in brake lines. Spherical compression fittings are lowpressure fittings. They will fail and leak under the high pressures and vibrations of a brake hydraulic system.

Do not interchange metric and inch-size fittings. They have different threads and cannot be mixed. Do not interchange ISO flare nuts with SAE inch-size flare nuts. Either of these conditions can cause fluid leakage and system failure.

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Follow these guidelines to form an SAE 45-degree double flare: 1. Select the forming die from the flaring kit that matches the inside diameter of the tubing. 2. Be sure the flare nut is installed on the tubing; then clamp the tubing in the correct opening in the flaring bar with the end of the tube extending from the tapered side of the bar the same distance as the thickness of the ring on the forming die. 3. Place the pin of the forming die into the tube and place the flaring clamp over the die and around the flaring bar. 4. Tighten the flaring clamp until the cone-shaped anvil contacts the die. Continue to tighten the clamp until the forming die contacts the flaring bar. 5. Loosen the clamp and remove the forming die. The end of the tubing should be mushroomed as shown in Figure 5-14. 6. Place the cone-shaped anvil of the clamp into the mushroomed end of the tubing. Be careful to center the tip of the cone and verify that it is touching the inside diameter of the tubing evenly. If the cone is not centered properly before tightening the clamp, the flare will be distorted. 7. Tighten the clamp steadily until the lip formed in the first step completely contacts the inner surface of the tubing. 8. Loosen and remove the clamp, and remove the tubing from the flaring bar. Inspect the flare to be sure it has the correct shape as shown in Figure 5-14 If it is formed unevenly or cracked, you must cut off the end of the tubing and start over again. SERVICE TIP  NAPA and other part and tool suppliers sell an ISO flaring tool that looks very similar to the one used for SAE flares. Do not use the wrong forming die or clamp. Use only the die and clamp included with the respective tools. The angle of the die and the diameter of the clamp are not the same between the SAE and ISO tools. Using the wrong die or clamp results in a waste of time and wasted tubing.

Classroom Manual page 109

Forming an ISO Flare.  An ISO flare or bubble flare has several advantages. When tightened, the shoulder of the nut bottoms in the body of the part to create uniform pressure on the tube flare. In addition, the design is not subject to overtightening. Simply tighten the nut firmly on the seat to produce the correct sealing pressure. Figure 5-15 shows the parts of the special tool used to make an ISO flare. Form an ISO flare as follows: 1. Cut the tubing to length, and install the fittings before forming the flare. Flaring tool body

Collet Brake tube

Clamp nut

Forming mandrel

Forcing screw

Figure 5-15  The special flaring tool used to form an ISO flare.

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2. Clamp the ISO flaring tool in a bench vise. Select the proper size collet and forming mandrel for the diameter of steel tubing being used. Insert the mandrel into the body of the flaring tool. Hold the mandrel in place with your finger and thread in the forcing screw until it contacts and begins moving the mandrel (Figure 5-16). After contact is felt, turn the forcing screw back one full turn. 3. Slide the clamping nut over the tubing and insert the tubing into the correct collet. Leave about ¾ inch of tubing extending out of the collet (Figure 5-17). 4. Insert the assembly into the tool body so that the end of the tubing contacts the forming mandrel. Tighten the clamping nut into the tool body very tightly to prevent the tubing from being pushed out during the forming process. 5. Using a wrench, turn in the forcing screw until it bottoms out. Do not overtighten the screw or the flare may be oversized. 6. Back the clamping nut out of the flaring tool body and disassemble the clamping nut and collet assembly. 7. Inspect the flare to be sure it has the correct shape (Figure 5-18). If it is formed unevenly or cracked, you must cut off the end of the tubing and start over again.

Forming mandrel

Clamping nut

Forcing screw

Collet

Flaring tool body

Brake pipe

Figure 5-16  Insert the correct size mandrel against the forcing screw in the flaring tool body.

Figure 5-17  Slide the brake tube (pipe) through the clamping nut and collet.

ISO flare

Tubing seat

Figure 5-18  The completed ISO flare.

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SERVICING HYDRAULIC SYSTEM VALVES Metering valves, proportioning valves, and combination valves were used by auto manufacturers to regulate pressures within the system. Valves were usually mounted on or near the master cylinder. Not all types of valves are used on all vehicles, so check the vehicle service information for the exact type and location of hydraulic valves. All valves in the hydraulic system should be inspected whenever brake work is performed or a problem exists in the system. Uneven braking or premature wear of pad or shoe lining may indicate a faulty metering, proportioning, or combination valve. SERVICE TIP  Most vehicles equipped with ABS or other electronic braking systems no longer use mechanical or hydraulic valves. Instead they use the hydraulic modulator operating on computer commands to control the brake pressures to the different wheels. This includes the metering and height-sensing proportioning pressures and the activation of the warning lamp. Control is more precise and quicker and some parts that could fail from damage, corrosion, or lack of maintenance are eliminated. Testing and service of the hydraulic modulator is covered in Chapter 10.

Metering Valves Inspect the metering valve (Figure 5-19) whenever the brakes are serviced. Fluid leakage inside the boot on the end of the valve means the valve is defective and should be replaced. A small amount of moisture inside the boot does not necessarily indicate a bad valve. When using a pressure bleeder, the metering valve will have to be disabled with a special tool, such as the one shown in Figure 5-20. Metering valves are not adjustable or repairable. If a valve is defective, replace it. Always be sure to mount the new valve in the same position as the old valve. A faulty metering valve can allow the front brakes to apply prematurely and possibly lock, especially on wet pavement. Premature front pad wear or a tendency for front brakes to lock may indicate a bad metering valve. If a metering valve problem is suspected, have a coworker apply the brakes gradually while watching and feeling in the valve stem. It should move as pressure increases in the system. If it does not, replace the valve. Body

Line connections

Stem

Figure 5-19  Whether it is an individual part or part of a combination valve, inspect the metering valve during every brake job.

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Metering value bleeding tool

Compress tool by squeezing

Install on stem and release.

Figure 5-20  Special tools to disable the meter valve for pressure bleeding.

The metering valve operation can be checked with a pressure bleeder. Charge the bleeder tank with compressed air to about 40 psi, and connect it to the master cylinder, as explained earlier in this chapter. Do not override the metering valve manually or with a special tool. Pressurize the hydraulic system with the pressure bleeder and open a front bleeder screw. If fluid flows at pressure from the bleeder, the metering valve is not closing at the right pressure and must be replaced.

Proportioning Valves Proportioning valve designs and locations vary more than those of metering valves. Older proportioning valves may be a single valve installed in a line to the rear drum brakes. Some master cylinders have two proportioning valves built into the master cylinder body. Some dual proportioning valves are separate assemblies, installed in the brake lines near the master cylinder (Figure 5-21). Many proportioning valves are part of a combination valve. Regardless of the design and location, all proportioning valves work in basically the same way. If rear drum brakes lock up during moderate-to-hard braking and all other possible causes of lockup, such as brake shoe contamination, have been eliminated, the proportioning valve is the likely problem. If the valve is leaking, replace or service it. In many cases, the valve cannot be disassembled and serviced; it must be replaced.

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Chapter 5 From master cylinder To rear brakes

To front brakes

Dual proportioning valve

Figure 5-21  A separate dual proportioning valve. Switch terminal

From master cylinder

To front wheel

From master cylinder

Boot To rear wheels Metering valve stem

Piston Metering To front valve seal wheel

Valve stem

Proportioning piston

Figure 5-22  Inspect a combination valve whenever the brakes are serviced.

Combination Valves Inspect a combination valve whenever the brakes are serviced. If there is leakage around the large nut on the proportioning end, the valve is defective and must be replaced. A small amount of moisture inside the boot or a slight dampness around the large nut does not indicate a defective valve. Combination valves are nonadjustable and nonrepairable. If a valve is defective in any way, it must be replaced (Figure 5-22).

BRAKE ELECTRICAL AND ELECTRONIC COMPONENT SERVICE

Classroom Manual Page 112

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Most electrical components in the brake system are switches and sensors that warn of hydraulic system problems. Because of their relationship with the hydraulic system, it is appropriate to include them in this chapter with hydraulic control valves. Stop lamps are the most basic part of the brake electrical system, so the sections on brake electrical components begin with stop lamp diagnosis and service. The following sections also cover: ■■ Brake system warning lamps (failure indicators) ■■ Parking brake indicator lamps ■■ Master cylinder fluid level switches (sensors) ■■ Basic wiring and connector repairs

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Logical Electrical Troubleshooting To isolate and repair an electrical problem, a logical troubleshooting procedure must be followed. Service information circuit diagrams or schematics make it easy to identify common circuit problems, which will help narrow the problem to a specific area. If several circuits fail at the same time, check for a common power or ground connection. If part of a circuit fails, check the connections between the functioning areas of the circuit and the failed areas. Also remember that a problem in one system could result in a symptom in another system. Proceed as follows to troubleshoot an electrical problem: 1. Verify the problem. Review the work order, operate the system, and list symptoms in order to check the accuracy and completeness of the owner’s complaint. If the problem is intermittent, try to re-create the problem. 2. Determine the possible causes of failure. Refer to the circuit diagram for clues to the problem. Locating and identifying the circuit components may help determine where the problem is. 3. Determine if the problem is located in a parallel circuit or the parallel portion of a series-parallel. If it is, check the other matching components wired parallel to the failed component; for example, one head lamp is inoperative. If one head lamp works, then the switch, fuse, relay, and most of the wiring are good. The same diagnostic observation can be applied to almost all exterior light circuits and many of the other parallel and series-parallel circuits on the vehicle. 4. Identify the faulty circuit by studying the circuit diagram to determine circuit operation for the problem circuit. You should have enough information to narrow the failure to one component or one portion of the circuit. 5. Locate the failed component or element. Service information procedures or diagnostic charts give a step-by-step approach to diagnosing a symptom. The test procedures are given in numerical sequence and should be followed in that order. 6. Make the repair and verify that the repair is complete by operating the system. Refer to Chapter 2 in this Shop Manual for an explanation of common electrical troubleshooting equipment. Many of the procedures in the following sections require the use of a digital multimeter (DMM) or a digital volt-ohmmeter (DVOM), a probe light, and some jumper wires.

Special Tool Service information and/or vehicle wiring diagram

Special Tools Vehicle wiring diagram Multimeter

STOP LAMP TESTING AND SWITCH ADJUSTMENT AUTHOR’S NOTE  On most older vehicles (1998 and earlier) and a few newer ones, the stop lamp switch is located in the “hot,” or positive, side of the stop lamp circuit. Closing the switch connects the lights to battery power. Modern electrical circuits may have the same switch acting as a grounding sensor in that when closed it completes a circuit in a lighting module, which then completes the stop lamp circuit. Diagnosing these computerized lighting circuits can be confusing to older technicians (and some new ones). The following section deals with stop lamp switch testing in general. The testing tools and diagnostic procedures may be different for the computerized version and even between different models from the same manufacturer, however. Many newer SUVs and light trucks are equipped with computer-controlled trailer light circuits. Always consult the service information and study the wiring diagrams and system description carefully. That is the only way to properly perform diagnostics on the new lighting systems.

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SERVICE TIP  The CHMSL on many vehicles is wired directly from the brake lamp switch to the lamp itself, whereas the two lower brake lamps are wired through the turn signal switch. If the CHMSL is lit when the brake pedal is depressed but the two lower lamps do not light, then the problem is most commonly found in the turn signal switch. Even if the turn signals work correctly, the switch cannot be ruled out as the brake lamp fault.

Caution Do not use a jumper wire until it has been absolutely determined that the stop lamp switch is not a sensor for a lighting module. Consult the wiring diagram and system description carefully. If the switch is acting as a sensor, use the service information directions and a DMM to test the switch and circuit. Use of improper test tools or jumpers can do serious damage to electronic circuits.

If one stop lamp lights but the other does not, it shows there is electric power through the fuses and switches to the rear of the car. In this case, the problem is usually a burned-out bulb. Occasionally, an open circuit may exist in the branch of the circuit to one of the stop lamps, but this is much less common. If the bulb is not burned out, but will not light when installed, use a DMM or probe light to pinpoint the open circuit. If all stop lamps do not light, check the circuit fuse. If the fuse is okay, check the bulbs. Occasionally, multiple lamp bulbs may fail at the same time. If the fuse and bulbs are okay, continue with the tests outlined next. Two other common problems with stop lamp circuits are that the lamps do not light at all or they are lit continuously. Lamps that do not light indicate an open-circuit problem. Lamps that are lit continuously indicate a short-circuit problem. Begin troubleshooting either condition by observing the stop lamps with the brakes applied and released. If the stop lamps do not light at all, check the following points: 1. Check the fuse first. 2. Locate the switch under the instrument panel or under the hood. 3. Disconnect the harness connect. Use a voltmeter or test light to determine if electric power is available on one side of the harness. 4. If power is present, connect a jumper wire between the two terminals of the connector. 5. Check the stop lamps; they should light. If they light, replace or adjust the switch. If the lamps do not light, continue testing for an open circuit condition between the switch and the lamps. If the stop lamps are lit continuously, check the following points: 1. Locate the switch under the instrument panel or under the hood. 2. Disconnect the harness connector and check the stop lamps. If the lamps are still lit, locate and repair the short circuit to battery voltage in the wiring harness. If the lamps turn off, adjust or replace the switch. Since the introduction of split hydraulic systems in 1967, almost all cars and trucks have had mechanical stop lamp switches operated by the brake pedal lever. Three basic adjustment methods exist for mechanical stop lamp switches: 1. If the switch has a threaded shank and locknut, disconnect the electrical connector and loosen the locknut. Then connect an ohmmeter or a self-powered test light to the switch. Screw the switch in or out of its mounting bracket until the ohmmeter or the test light indicates continuity with the brake pedal pressed about ½ inch. Tighten the locknut and reconnect the electrical harness. 2. If the switch is adjusted with a spacer or feeler gauge, loosen the switch mounting screw. Press the brake pedal and let it return freely. Then place the spacer gauge between the pedal arm and the switch plunger. Slide the switch toward the pedal arm until the plunger bottoms on the gauge. Tighten the mounting screw, remove the spacer, and check stop lamp operation.

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3. If the switch has an automatic adjustment mechanism, insert the switch body in its mounting clip on the brake pedal bracket and press it in until it is fully seated. Then pull back on the brake pedal to adjust the switch position. The switch click as it ratchets back in its mount. Repeat this step until the switch no longer clicks in its mounting clip. Finally, check stop lamp operation to be sure they go on and off correctly.

AUTHOR’S NOTE  A procedure for adjusting the type of stop switch noted in step 3 can be found in Chapter 4 of this text in discussing the adjustment of the brake pedal free play section.

Computer-Controlled Turn and Stop Lamps Most late-model vehicles are equipped with computer-controlled brake and stop lamp circuits. Figure 5-23 shows some common names for the module that controls the lighting function. The turn signal and brake lamp switches are used as inputs to a module that delivers power to the respective bulbs, as was detailed in the Classroom Manual’s Chapter 5. The module that controls the stop and turn signals usually controls most of the exterior lighting. Diagnosing the computer-controlled systems is straightforward, but somewhat different than diagnosing traditional electrical system problems. Look at the stop lamp and turn signal DTC chart for the Ford Flex (Figure 5-24). Although the exterior lighting system of this vehicle has codes for most of the circuits and GM

Body Control Module (BCM)

Toyota

Flasher Relay

Honda

MICU

Ford

Smart Junction Block (SJB)

Chrysler

Totally Integrated Power Module (TIPM)

219

Many stop lamps and parking lamps share the same bulb. The bulb has two filaments that can operate independently. The brake light filament is brighter than the parking lamp filament.

Special Tools Multimeter Vehicle wiring diagram

Special Tools Multimeter Vehicle wiring diagram

Figure 5-23  Modules that control exterior lighting by manufacturer.

B106E

Smart Junction block has temporarily disabled an output because of high current flow

B106F

Smart Junction block has permanently disabled an output because of high current flow

B1578

Park Lamp circuit short to ground

B2044

Left rear stop lamp circuit short to ground

B2045

Left rear stop lamp circuit open

B2046

Right rear stop lamp circuit short to ground

B2047

Right rear stop lamp circuit open

B2048

Left rear turn lamp circuit short to ground

B2050

Right rear turn lamp circuit short to ground

Figure 5-24  A partial listing of exterior lighting DTCs for a Ford Flex.

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switches used in the exterior lighting circuit, our focus is on the codes for opens and shorts in the turn-signals and brake lamps. The output of the lighting module is monitored for current flow. If there is no current flow, then the module knows that there is an open in a particular circuit. If there is excessive current flow in a monitored circuit, then the code for a short to ground is set. There are three levels of codes set for a short to ground. For instance, if a short to ground is detected in the left rear brake lamp circuit, the module immediately shuts down the current to that circuit and a code B2044 is set in memory. The next time the brake lamp is needed, the module allows current to flow, but if a short is detected, the circuit is shut down again. Depending on the amount of current flow, and how often the short occurs, the module may temporarily shut down the circuit. This sets a B106E code in memory. In order for the module to supply power to the left rear brake lamp, the short must be repaired and the self-test for the module must be successfully run. The B106E code can then be reset. If the code B106F is set, the short has been severe enough that the module has sustained damage. This code cannot be cleared from the module memory, and the module will have to be replaced. Obviously, the short must be located and repaired anytime these codes set to prevent further expense to the customer. Replacing Stop Lamp Bulbs.  Some taillamp and stop lamp bulbs can be replaced without removing the lens assembly. Remove the bulb and socket by twisting the socket slightly and pulling it out of the lens assembly (Figure 5-25). Push in on a brass base bulb and turn it counterclockwise. Plastic base bulbs are pulled straight out. When the lugs align with the channels of the socket, pull the bulb out to remove it. On other vehicles, the complete taillamp lens assembly must be removed for access to the bulbs. Figure 5-26 shows how a typical lens assembly mounts to the vehicle body. It is normally held in position by several nuts or special screws.

Brake Warning Lamp Circuit Troubleshooting The brake warning lamp on most vehicles performs multiple warning functions. Several circuits will cause the brake warning icon to illuminate (Figure 5-27). Typically, this lamp lights when: SERVICE TIP  If only the amber ABS warning light is lit, then the problem is in the ABS system. If both brake warning lights (red and amber) are lit, the problem is probably in some shared component. If only the red is lit, then the trouble is usually within the service or parking brake system.

Taillight assembly Light socket

Bulb Connector

Figure 5-25  Taillamp with removable socket.

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Figure 5-26  Many vehicles require the complete rear lamp assembly to be removed to replace a lamp.

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Instrument Panel Cluster (IPC) Instrument cluster Schematics in I/P, Gages and Console

IGN

Class 2 Serial Data

Class 2 (EBCM)

Brake

P

!

Logic

10 C2 A39

Body Control Module (BCM)

Class 2 Serial Data Park Brake Switch Signal C1

Brake Fluid Level Sensor Signal

A31

A45

A

A Park Brake Switch

Brake Fluid Level Switch

G105

Figure 5-27  A typical brake warning system with the IPC on the vehicle network.

If equipped, low pad sensors are grounded. The parking brake is applied. ■■ When the brake fluid level is low. ■■ As a circuit test while the ignition is first turned on. Additionally, on some vehicles with ABSs, the control module turns on the red brake warning lamp if it finds a problem in the amber warning lamp circuit. The instrument panel cluster illuminates the brake warning lamp light briefly when the ignition switch is turned on. On vehicles with daytime running lamps, the parking brake switch completes ground to the stop lamp through a diode in the daytime running lamp module. On some vehicles, the parking brake switch is an input to the body control module that controls the daytime running lamps. The brake fluid level switch closes to light the brake warning lamp when the brake fluid in one of the two reservoirs falls below switch level. This can be caused by a leak in one of the brake lines or by simply neglecting to top up the fluid level. Operational Check.  Check the basic operation of the brake warning lamp as follows: 1. Turn the ignition switch to the start position or a point halfway between on and start. The warning lamp should light. 2. Release the ignition switch to the run position. With the parking brake off, the warning lamp should turn off. On some vehicles, the lamp may stay lit for a few seconds with the ignition on and then go off. ■■ ■■

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Special Tools Multimeter Vehicle wiring diagram

Special Tools Solderless connectors crimping/crimping pliers

3. With the ignition on, apply the parking brake. The warning lamp should light. 4. Release the parking brake. The warning lamp should turn off. If the warning lamp operates as described in these four steps, the system is working properly. If the warning lamp stays lit with the ignition on and the parking brake off, the following problems may be present: ■■ ■■ ■■ ■■

Low fluid level in the master cylinder reservoir Low pad sensor(s) grounded Parking brake not fully released or parking brake switch shorted or grounded ABS problem

Circuit Troubleshooting.  As always, the vehicle service information should be the first source of information for electrical troubleshooting. Figure 5-27 is a typical brake warning lamp circuit. Besides checking the switches, check the power fuse in the fuse block and the individual grounds for each circuit branch. It is highly unlikely that all the indicators on the instrument panel would fail at the same time. If other indicators are not operating properly, check the fuses first. Next, check for voltage at the last common connection. If no voltage is present here, trace the circuit back to the battery. If voltage is found at the common connection, test each branch of the circuit in the same manner.

Instrument Clusters on the Vehicle Network Modern vehicles have their instrument clusters on the vehicle network. The network shares instructions and data from the other modules via serial data. This eliminates many of the wiring connectors used in the past, and with fewer wiring connectors and less wiring, there are generally fewer problems. Refer back to Figure 5-27. As you can see, the low fluid level switch and the brake light switch are inputs to the body control module (BCM). The BCM sends a serial data message to the instrument panel to illuminate the BRAKE icon on the dash. The brake warning lamp can usually be commanded on by a scan tool as well to help in diagnosis.

Low Brake Pad Warning Lamp Caution Do not use a jumper wire until it has been absolutely determined that the warning switch is not a sensor for a lighting module. Consult the wiring diagram and system description carefully. If the switch is acting as a sensor, use the service information directions and a DMM to test the switch and circuit. Use of improper test tools or jumpers can do serious damage to electronic circuits.

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Low pad sensors activate the brake warning light when the pad(s) become worn enough to be replaced. Before testing this circuit, ensure that the parking brake is off and the brake fluid is at the proper level. Determine if there is a sensor at each wheel or only at the two front wheels. It may be possible to disconnect the wiring without removing the wheel assembly. If not, lift and support the front axle of the vehicle and remove all affected wheels. Disconnect the sensor wiring at the wheel and switch the ignition on, engine off. If the light remains on, switch the ignition off and connect the wiring. Repeat with the other wheels until either the warning light goes off with the ignition on, engine off or it is determined that the circuit is bad or the pads need replacing. Many times the act of removing the wheels and inspecting the brake pads will determine that the system is working correctly.

Parking Brake Switch Test If the brake warning lamp does not light with the ignition on and the parking brake applied but otherwise works properly, a problem exists with the parking brake switch or circuit. To check the parking brake switch and its wiring, locate the switch on the pedal, lever, or handle and disconnect it with the ignition off. If the switch connector has a single wire, connect a jumper from that wire to ground. If the switch connector has two wires, connect a jumper between the two wires in the connector. Turn the ignition on and check the brake warning lamp. If the lamp is lit,

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replace the parking brake switch. If the lamp is still off, find and repair the open circuit in the wiring harness between the body control computer and the switch.

Brake Fluid Level Switch Test With the ignition on and the brake fluid level switch closed, the brake warning lamp lights to alert the driver of a low-fluid condition in the master cylinder. Some switches are built into the reservoir body; others are attached to the reservoir cap. Test principles are similar for both types. Begin by ensuring that the fluid level is at or near the full mark on the reservoir. Turn the ignition on and observe the warning lamp. If it is lit, disconnect the wiring connector at the switch. If the lamp then goes out, replace the switch. If the lamp does not go out, find and repair the short circuit between the switch and the lamp. To verify that the warning lamp will light when the fluid level is low, manually depress the switch float or remove the cap with an integral switch and let the float drop. If the lamp does not light with the switch closed, check for an open circuit between the switch and the lamp. If circuit continuity is good, replace the switch. As a final check, disconnect the wiring harness from the switch, and connect a jumper wire between the two terminals in the harness connector. The warning lamp should light. If it does not, find and repair the open circuit between the switch and the body control computer.

Electrical Wiring Repair Wire size is determined by the amount of current, the length of the circuit, and the voltage drop allowed. Wire size is specified in either the American Wire Gauge (AWG) system or in metric cross-sectional area. The higher the number in AWG the smaller the conductor. A 20 gauge is much smaller than a 12 gauge. When replacing a wire, the correct size wire must be used as shown on applicable wiring diagrams or in parts books. Each harness or wire must be held securely in place to prevent chafing or damage to the insulation due to vibration. Always use rosin flux solder to splice a wire, and use insulating tape or heat-shrink tubing to cover all splices or bare wires. Rosin flux cleans the connection during soldering without eroding the material as does acid-based flux. Applying heat to shrink tubing causes the tubing to contract and completely seal the wiring and connections. Utility companies used heat-shrink tubing to seal underground electrical supply cables. Many electrical system repairs require replacing damaged wires. It is important to make these repairs in a way that does not increase the resistance in the circuit or lead to shorts or grounds in the repaired area. Several methods are used to repair damaged wire with many factors influencing the choice. These factors include the type of repair required accessibility of the wiring, the type of conductor and size of wire needed, and the circuit requirements. The three most common repair methods are: 1. Wrapping the damaged insulation with electrical tape (in cases where the insulation is damaged and the wiring is unharmed) 2. Crimping the connections with a solder-less connector 3. Soldering splices When deciding where to cut a damaged wire, avoid points close to other splices or connections. As a rule, do not have two splices or connections within 1.5 inches (40 mm) of each other. Use a wire of the same size or larger than the wire being replaced. Crimping.  A solderless connection uses a compressed junction to connect two conductors. Some manufacturers require the use of self-sealing solderless connections on all repairs. Crimping selfsealing solder less connections is an acceptable way to splice wire,

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An American wire gauge (AWG) is a system for specifying wire size (conductor cross-sectional area) by a series of gauge numbers; the lower the number, the larger the wire cross section.

Caution Never replace a wire with one of a smaller size. Using the incorrect size could cause repeated failure and damage to the vehicle electrical system. Rosin flux solder is solder used for electrical repairs. Heat-shrink tubing is plastic tubing that shrinks in diameter when exposed to heat.

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because the connector has self-sealing epoxy that seals the connection against dirt and moisture. Do not use a non-sealing solderless connector for wiring repairs. To make a splice using a solderless connector:

A Solderless ­connector is a quick and easy way to slice two wires together.

1. Strip enough insulation from the end of the wire to allow it to completely penetrate the solder-less connector. 2. Position the wire in the connector and crimp the connector (Figure 5-28). To ensure a good crimp, place the open area of the connector facing toward the anvil. Make certain you compress the wire under the crimp. 3. Insert the stripped end of the other wire into the connector and crimp it in the same way. 4. Use a heat gun to seal the solder-less connector. The heat will melt the epoxy in the connector and seal the connection. The tap splice connector is another style of crimping connector. As shown (Figure 5-29), this connector allows for adding an additional circuit to an existing wire without stripping the wires. This type of splice connection should be considered a temporary fix. As the figure shows, there are a lot of places in the splice for contaminants to get into and add resistance to the current flow. However, many DIYs use this type of splice to connect a trailer electrical wiring to the vehicle harness in probably the worst place to ever use this splice: under the rear of the vehicle, exposed to every road hazard and to shorting when the boat trailer is backed into the water. The good part about this DIY work is that sooner or later the vehicle will show up at the shop to get the lights and other Conductor

Final Crimp Flattened

Upper jaw

Terminal tabs

Turned in Anvil

Compressed conductor

Figure 5-28  Crimping a solderless connector.

New wire

Hot wire

New wire

Tab Hot wire

A

Hinged cover

B

Plastic cover C

D

Figure 5-29  Using a tap connector to splice one wire to another. (A) Place wires in position in the connector, (B) close the connector around the wires, (C) use pliers to force the tab into the conductors, and (D) close the hinged covers.

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electrical problems repaired. A good starting point when a vehicle shows up for lighting or electrical problems is to check for a trailer hitch and then to check for the connection under the vehicle where the trailer’s harness is connected. As an aside, if a vehicle is presented for electrical problems and there are aftermarket accessories installed, those items should be the first things to check. Soldering.  Soldering is the best way to splice wires if performed properly. Photo Sequence 9 shows a typical soldering procedure. A splice clip is a special connector used with solder to create a good connection. The splice clip differs from a solderless connector in that it does not have insulation. The hole is used for applying the solder (Figure 5-30). A second way to solder wire uses a wire joint instead of a splice clip. Begin by removing about 1 inch of insulation from the wire ends. Join the wires using one of the techniques shown in Figure 5-31. Heat the twisted connection with the soldering iron and apply solder to the wires. Do not apply the solder directly to the iron. Heat the wire and allow the solder to flow onto it (Figure 5-32). Insulate the soldered connection with heatshrink tubing.

Caution

Electrical Connector Repair It is important to inspect the condition of the connectors when diagnosing electrical problems. Check connectors for cracks or signs of overheating and for contacts that are bent, scorched, corroded, or missing. If any of these problems are present, the connector should be replaced. Molded Connectors.  Molded connectors (Figure 5-33) are one-piece connectors that cannot be separated. If the connector is damaged, it must be cut out and a new connector spliced in wire by wire. This can be a time-consuming job, so work carefully around these connectors to avoid damaging them.

Do not use acid-core solder for electrical repairs. The acid will corrode the wire and increase its resistance.

Hard-Shell Connectors.  Hard-shell connectors allow removing the terminals for repair. Use a pick or special tool to depress the locking tang of the connector (Figure 5-34). Pull the lead back to release the locking tang from the connector. Remove the pick and pull the lead completely out of the connector. Repair the terminal using the same procedure as for repairing copper wire.

Photo Sequence 9 Soldering Two Copper Wires Together

P9-1  Tools required to solder copper wire: 100-watt soldering iron, 60/40 rosin core solder, crimping tool, splice clip, heat-shrink tube, heating gun, and safety glasses.

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P9-2  Disconnect the fuse that powers the circuit being repaired. Note: If the circuit is not protected by a fuse, disconnect the ground lead of the battery.

P9-3  Cut out the damaged wire.

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Photo Sequence 9 (CONTINUED)

P9-4  Using the correct size stripper, remove about ½ inch of insulation from both wires.

P9-5  Now remove about ½ inch of the insulation from both ends of the replacement wire. The length of the replacement wire should be slightly longer than the length of the wire removed.

P9-6  Select the proper splice clip to hold the splice.

P9-7  Slide the correct size and length of heatshrink tube over the open ends of the wire.

P9-8  Overlap the two splice ends and center the splice clip around the wires, making sure the wires extend beyond the splice clip in both directions.

P9-9  Crimp the splice clip place.

P9-10  Heat the splice clip with the soldering iron when applying solder to the opening of the clip. Do not apply solder to the iron. The iron should be 180 degrees away from the opening of the clip.

P9-11  After the solder cools, slide the heatshrink tube over the splice.

P9-12  Heat the tube with the hot air gun until it shrinks around the splice. Do not overheat the heat shrink tube.

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Rosin-core solder

Figure 5-30  Using a splice clip to join wires. Western union

Pigtail 1

Stripped wires

Twist

Insulation 2

Wrap tightly

T-Type Wrap tightly Wrap tightly 3

Completed splice

Figure 5-31  Twist wires together in one of these ways before soldering them.

Rosin-core solder

Joint

Soldering iron

Figure 5-32  Heat the rolled joint with the soldering iron, and let the heat draw solder into the joint. Do not apply solder directly to the iron.

Figure 5-33  Typical molded connector.

Push narrow pick between terminal and connector body

Figure 5-34  Depress the locking tang to remove the terminal from a hard-shell connector.

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CASE STUDY A customer complained that the stoplights would light when the right turn signal was switched on. The obvious problem seemed to be a short-to-power in the turn signal switch. Testing, replacing, and testing again did not solve the problem. After several hours of frustration, studying diagrams, Technical Service Bulletins (TSBs), and all other information he could find, the technician decided to just pull the wiring harness running from the column to the different circuits. A thorough inspection of the individual wires indicated that someone had stripped three wires apparently looking for a power source. Two of the wires were adjacent to each other and burn marks highlighted the point of contact between the two lighting circuits. A little tape and heat-shrink and almost $500 in labor fixed the problem.

ASE-STYLE REVIEW QUESTIONS 1. While discussing the brake hose removal and installation, Technician A says some brake hoses have a swivel fitting at one end and a fixed fitting that cannot be rotated. Technician B says disconnect the swivel fitting first on this type of hose system. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

5. Technician A says an ISO flare or bubble flare has several advantages. Technician B says when tightened, the shoulder of the nut bottoms in the body of the part to create uniform pressure on the tube flare. In addition, the design is not subject to overtightening Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

2. While discussing the fabrication of a new brake line, Technician A says the angle of the flare and the nut is 45 degrees. Technician B says the angle of the tubing seat is also 45 degrees. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

6. While discussing computer controlled turn and stop lamp systems; Technician A says If there is excessive current flow, then the module knows that there is an open in a particular circuit. Technician B says if there is no current flow in a monitored circuit, then the code for a short to ground is set. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

3. While discussing spherical compression fittings Technician A says spherical compression fittings are low-pressure fittings. Technician B says spherical compression fittings will leak under high pressure. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 4. Technician A says that copper-nickel alloy tubing requires special tools and processes for flaring. Technician B says that ISO and SAE flares are interchangeable. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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7. Technician A says service information schematic diagrams can make troubleshooting electrical problems easier. Technician B says if several circuits fail at the same time, check for a common ground or power circuit. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 8. Technician A says the higher the number in AWG the smaller the conductor. Technician B says a 20-gauge wire is much larger than a 12-gauge wire. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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9. Technician A says that the brake system warning lamp can be activated by different switches such as the parking brake switch or the low fluid level switch in the master cylinder reservoir. Technician B says that the brake system warning lamp should light briefly when the ignition is turned on. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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1 0. Technician A says late-model vehicles are equipped with computer-controlled brake and stop lamp circuits. Technician B says on some vehicles the turn signal and brake lamp switches are inputs to a module that delivers power to the respective bulbs. Who is correct? A. A only B. B only

C. Both A and B D. Neither A nor B

ASE CHALLENGE QUESTIONS 1. Technician A says crimping self-sealing solderless connections is an acceptable way to splice wire because the connector has self-sealing epoxy that seals the connection against dirt and moisture. Technician B says do not have two splices or connections within 1.5 inches (40 mm) of each other. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

4. Technician A says that the modern instrument cluster communicates with the modules on the vehicles network to illuminate the brake warning lamps. Technician B says that the BCM commands the instrument panel to turn the brake warning lamp on using serial data. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

2. Technician A says molded connectors are onepiece connectors that cannot be separated. Technician B says if the connector is damaged, it must be cut out and the wires spliced together without a connector. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

5. Brake warning lights are being discussed. Technician A says that all electrical connections should be soldered during repairs. Technician B says that having the emergency brake applied should turn on the amber (ABS) light. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

3. Technician A says that acid core solder was best for use on electrical wiring. Technician B says that rosin core solder is best for electrical work. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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Name ______________________________________ 

Date _________________

IDENTIFYING BRAKE PROBLEMS AND CONCERNS Upon completion of this job sheet, you will be able to define brake system problems or concerns prior to diagnosing or testing the systems, along with proper road-testing procedures.

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ASE Education Foundation Correlation This job sheet addresses the following MLR task: A.2. Describe the procedure for performing a road test to check brake system operation, including an anti-lock brake system (ABS). (P-1) This job sheet addresses the following AST/MAST tasks: A.1.

Identify and interpret brake system concerns; determine needed action. (P-1)

A.3. Describe the procedure for performing a road test to check brake system operation, including an anti-lock brake system (ABS). (P-1) Protective Clothing Goggles or safety glasses with side shields Describe the vehicle being worked on: Year _____________________ Make _____________________ Model _____________________ VIN __________________ Engine type and size __________________ Procedure Before the test drive, perform the following checks. 1. Check the brake fluid level and condition, if the fluid level is low; inspect the braking system for leaks before test driving the vehicle. Is the fluid level low? Does the brake fluid appear to be contaminated?   2. Inspect the tires. Are the tires in good shape? Are there any obvious alignment or vehicle-loading concerns?   3. Start the engine and check the feel of the brake pedal. Does the brake pedal feel spongy or hard when applied? When the brake pedal is released, do the brakes release promptly?   4. Are there any warning lamps on? Describe your findings below.   5. Are there any ABS trouble codes set?  

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WARNING  Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to this precaution could lead to serious personal injury and vehicle damage. Never try to read a scan tool while driving a vehicle. ■■

■■

■■

■■

Test drive the vehicle on a dry, clean, relatively smooth roadway or parking lot. Roads that are wet or slick or that have loose gravel surfaces will not allow all wheels to grip the road equally. In many cases, loose gravel roads may cause the ABS to function. Rough roads can cause the wheels to bounce and lose contact with the road surface. Avoid crowned roadways. They can throw the weight of the vehicle to one side, which will give an inaccurate indication of brake performance. First test the vehicle at low speeds. Use both light and fairly heavy pedal pressure. If the system can safely handle it, test the vehicle at higher speeds. Avoid locking the brakes and skidding the tires. Pay attention to other drivers on the road; avoid a heavy application of the brakes in traffic.

6. Take the vehicle for a safe road test, and pay strict attention to how the brakes operate in all conditions (partial application, moderate application, and hard application). Describe your results here.   7. Were there any unusual noises when the brakes were applied? If so, describe them and when they occurred.   8. Describe how the pedal felt when it was applied.   9. Did the vehicle tend to pull to one side when the brakes were applied? Explain.   10. Did the brakes seem to drag? Explain.   11. Turn off the engine and pump the brakes several times. What happened?   12. Does the ABS system appear to be operating normally?  

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13. Summarize your findings in detail; include both improper and proper system operation.   14. Based on the above, what are your suspicions and conclusions?   Problems Encountered    Instructor’s Comments   

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DIAGNOSING PRESSURE PROBLEMS Upon completion of this job sheet, you will be able to correctly diagnose pressure problems in the brake system.

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ASE Education Foundation Correlation This job sheet addresses the following AST/MAST task: B.1. Diagnose pressure concerns in the brake system using hydraulic principles (Pascal’s Law). (P-1) Tools and Materials • Service information Protective Clothing • Goggles or safety glasses with side shields Describe the vehicle being worked on: Year _____________________ Make _____________________ Model ______________________ VIN _____________________________ Engine type and size _____________________________ Procedure 1. Visually inspect the entire hydraulic system for signs of leakage and/or damage; record your results.   2. Explain how force is multiplied in a hydraulic system.  3. Explain how air in a brake system will keep the brakes from operating properly in terms of Pascal’s Law.   4. Explain how a leak in the system affects the brake pedal in terms of Pascal’s Law.    5. Use Pascal’s Law to describe why the brake pedal has to move further than the caliper pistons in the braking system.    6. Use Pascal’s Law to describe why the front caliper pistons are larger than the rear caliper pistons.   

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Problems Encountered    Instructor’s Comments   

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INSPECTING AND DIAGNOSING BRAKE LINES AND HOSES Upon completion of this job sheet, you should be able to inspect and diagnose brake lines, hoses, and connecting fittings. ASE Education Foundation Correlation This job sheet addresses the following MLR task: B.3. Inspect brake lines, flexible hoses, and fittings for leaks, dents, kinks, rust, cracks, bulging, wear, and loose fittings/supports. (P-1) This job sheet addresses the following AST/MAST tasks: B.5. Diagnose poor stopping, pulling or dragging concerns caused by malfunctions in the hydraulic system; determine needed action. (P-3) B.6. Inspect brake lines, flexible hoses, and fittings for leaks, dents, kinks, rust, cracks, bulging, wear, and loose fittings/supports; determine needed action. (P-1) Tools and Materials • Basic hand tools Describe the vehicle being worked on: Year _____________________ Make _____________________ Model _____________________ VIN _____________________________ Engine type and size _____________________________ ABS _______________________ YES ______________________ NO ______________________ Procedure

Task Completed

1. Brake inspection, engine compartment area components.  

h

2. Inspect all lines to the vacuum (hydro-boost) booster unit, if equipped, for crimps, damage, or leaks. Record your findings.  

h

3. Inspect the master cylinder for leaks or damage to the cap, the outlet fittings, and the mounting to the booster or fire wall. Record your findings and suggested repairs.  

h

4. If any brake hydraulic valves are visible, inspect them for leaks or damage. Record your findings and suggested repairs.  

h

5. Lift the vehicle to gain access to the undercarriage.

h

6. Inspect the valve(s) located in the area of the left rear engine compartment for leaks or damage. Valves are normally mounted below the master cylinder on the frame. Record your findings and suggested repairs.  

h

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7. Inspect the steel lines from the valve to each of the front wheels for leaks or damage. Record your findings and suggested repairs.  

Task Completed

h

8. It may be necessary to remove the wheel assembly to inspect the front hoses. If so, perform step 8 through step 12 before inspecting the front brake hoses.

h

9. Inspect the hoses from the steel lines to the caliper or wheel cylinder and their fittings for leaks or damage. Record your findings and suggested repairs.  

h

10. Inspect the steel lines from the valves to the rear wheels for damage or leaks. Is there more than one steel line?  

h

11. At which point on the vehicle does the steel line(s) connect to a brake hose(s)?  

h

12. Inspect the hose(s) and the fittings from the steel line to the caliper or wheel cylinder or differential for leaks or damage. Record your findings and suggested repairs.  

h

13. Describe an internal defect in the brake hose that may cause a vehicle to pull to one side which may not be obvious under visual inspection.  

h

14. If the vehicle has a solid rear axle, inspect the steel lines from the hose connection to each rear caliper or wheel cylinder for leaks or damage. Record your findings and suggested repairs.  

h

15. If the wheels must be removed to inspect the front brake hoses, remove the wheels at this point and perform step 8. Record your findings and suggested repairs.  

h

16. Was any damage noted on the undercarriage that may affect the brake lines or hoses at a future time? If yes, note the damage and suggested repairs to possibly prevent future line or hose damage.  

h

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Problems Encountered    Instructor’s Response   

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Date _________________

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CONSTRUCTING AN ISO FITTING Upon completion of this job sheet, you should be able to construct an ISO flare fitting. ASE Education Foundation Correlation This job sheet addresses the following AST/MAST task: B.8. Fabricate brake lines using proper material and flaring procedures (double flare and ISO types).(P-2) Tools and Materials • Basic hand tools • ISO flaring tool including tubing cutter Describe the vehicle being worked on: Year _____________________ Make _____________________ Model ____________________ VIN _____________________________ Engine type and size ____________________________ Procedure

Task Completed

1. Secure the tubing (steel line) and mark the exact length plus 1/8 inch. What is the total length to be used? What is the inside diameter of the tubing?  

h

2. Install the tubing cutter square and tighten the blade to the tubing. Do not overtighten.

h

3. Rotate the cutter completely around the tube. Adjust the cutter blade to a deeper depth during each rotation.

h

4. Repeat step 4 until the tubing is cut through.

h

5. Using the reamer on the tubing cutter, clean and square the end of the tubing to be flared.

h

6. Slide the flare nut over the tubing, ensuring it is facing in the right direction.

h

7. Clamp the ISO flaring tool in a bench vise.

h

8. Select the collet and mandrel for the size of tubing to be flared.

h

9. Install the mandrel into the body of the flaring tool and tighten the forcing nut until the mandrel begins to move.

h

10. Back off the forcing screw one full turn.

h

11. Slide the clamping nut over the tubing followed by the correct collet. About ¾ inch should be exposed after the collet.

h

12. Insert the tubing and collet into the flaring tool body until the tubing bottoms against the mandrel.

h

13. Hold the tubing in place as the collet is slid into place and the clamping nut is threaded.

h

14. Tighten the clamping nut very tightly to hold the tubing in place during the process.

h

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15. Using a wrench, tighten the forcing screw until the mandrel bottoms. Do not overtighten.

Task Completed h

16. Loosen the clamping nut and remove the collet and tubing from the flaring tool.

h

17. Inspect the ISO flare for any cracks or deformities. Record your findings and any suggested repairs.  

h

Problems Encountered    Instructor’s Response   

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REPLACE A BRAKE HOSE Upon completion of this job sheet, you should be able to replace a brake hose. ASE Education Foundation Correlation This job sheet addresses the following AST/MAST task: B.7.

Replace brake lines, hoses, fittings and supports. (P-2)

Tools and Materials Basic hand tools Describe the vehicle being worked on: Year _____________________ Make _____________________ Model ______________________ VIN _____________________________ Engine type and size ____________________________ ABS _______________________ YES ______________________ NO ______________________ Procedure

Task Completed

1. Lift the vehicle, if necessary, and remove the left front tire and wheel assembly. Different wheels may be selected.

h

2. Explain why (or what circumstances would cause) this brake hose needs to be replaced.   NOTE: This job sheet uses a front disc brake hose as an example. Other brake hoses are replaced in a similar manner. 3. Does this brake hose use banjo-type fittings at either end? If so, adjust your tool choice to perform the following steps.  

h

4. Use flare-nut (line) wrenches to disconnect the hose from the steel line on or near the vehicle frame. Plug the steel line. What size wrench was used?  

h

5. Use a small prybar or pliers to remove the hose retainer at the frame. What tool was used and how was the procedure performed?  

h

6. Use a flare-nut (line) wrench to disconnect the hose from the caliper.

h

7. Remove any washer present and plug the caliper port.

h

8. Select the proper length and diameter hose. Ensure that the hose meets the manufacturer’s specifications.

h

9. Slide the washer, if any, over the caliper end of the new hose.

h

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10. Remove the caliper plug and thread the hose into the port. Tighten to torque specifications. What is the torque specification on this fitting?  

Task Completed

11. Install the frame end of the hose through its mount and install the hose retainer.

h

12. Align and thread the flare nut on the steel line into the hose end. Tighten to specification. What is the torque specification on this fitting and which wrenches were used to tighten the fitting?  

h

13. Use job sheet 16, 17, or 18 to bleed the brake system. Which job sheet was utilized and why was it selected?  

h

14. Install the tire and wheel assembly. What is the torque specification on the lug nuts?  

h

15. Lower the vehicle and road test.

h

h

Problems Encountered    Instructor’s Response   

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CHECK OPERATION OF THE BRAKE STOP LAMP SYSTEM Upon completion of this job sheet, you should be able to diagnose a brake lamp system. ASE Education Foundation Correlation This job sheet addresses the following AST/MAST task: F.5.

Check operation of the brake stoplight system. (P-1)

Tools and Materials Basic hand tools Service Information Scan tool Testlamp Describe the vehicle being worked on: Year _____________________ Make _____________________ Model _____________________ VIN _____________________________ Engine type and size ____________________________ Procedure

Task Completed

1. Using service information look-up and print out a wiring diagram.

h

2. If the system has a lighting module, are codes available for the exterior lighting system?  

h

3. Describe the operation of the brake lamp system. Include the use of any modules, relays, or switches.  

h

4. Using the wiring diagram, explain where you would start diagnosis if only the left side brake lamp was inoperative.  

h

5. Using the wiring diagram, explain how you would diagnose the system if only the third brake lamp was operational.  

h

6. Explain the replacement of the brake lamp switch.  

h

Explain the adjustment of the brake lamp switch.   7. Does the brake lamp switch need to be recalibrated/relearned after replacement? If so briefly explain the process below.  

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Chapter 6

Power Brake Service

Upon completion and review of this chapter, you should be able to: ■■ ■■

■■

■■ ■■

Diagnose vacuum power booster problems. Test pedal free play with and without the engine running to check power booster operation. Check vacuum supply to a vacuum booster using a vacuum gauge. Inspect a vacuum power booster for vacuum leaks. Inspect the vacuum check valve for proper operation.

■■

■■

■■ ■■ ■■ ■■

Remove and install a vacuum booster and properly adjust the pedal linkage and pushrod. Disassemble, repair, and adjust a vacuum booster as required to restore proper operation.

Basic Tools Basic technician’s tool set Flare-nut wrench Vacuum gauge

Inspect and test a hydro-boost and accumulator for leaks and proper operation. Adjust or replace components on a hydro-boost system as needed. Flush and bleed a hydro-boost system. Test an electrohydraulic brake system.

Terms To Know Pressure differential

Vacuum suspended

TYPES OF POWER BRAKE SYSTEMS Two types of power brake systems are used on most late-model vehicles: vacuum-boost systems and hydraulic-boost systems. Both systems multiply the force exerted on the master cylinder piston by the driver. This increases the hydraulic pressure delivered to the wheel cylinder and caliper pistons, resulting in increased stopping performance. Vacuum boosters (Figure 6-1) use engine vacuum to produce boost pressure. Hydroboost power systems (Figure 6-2) use hydraulic pressure from the vehicle power steering pump. Other hydraulic-boost power brake systems use brake fluid under high pressure to provide booster pressure. Power brakes are simply conventional brakes with an added power booster. When troubleshooting and servicing power brake systems, however, keep the two systems separate. Check for faults in the master cylinder and hydraulic system first. As with conventional brakes, a spongy pedal in a power brake system is caused by air in the hydraulic lines. Brake grab may be caused by grease on the brake linings. Check out all basic brake components before moving on to the power-assist system. Except for the master cylinder pushrod adjustment, vacuum and hydraulic powerassist units are not adjusted in normal service. If the booster is suspect, it is removed and replaced with a new or rebuilt unit, or it can be rebuilt in the shop. Overhaul kits are available.

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Figure 6-1  Typical power brake vacuum booster with master cylinder attached.

Figure 6-2  Hydro-boost power brake booster.

Vacuum-Boost Systems

Classroom Manual page 123

Regardless of type or operation, technicians refer to power brake boosters as the brake booster.

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Vacuum boosters (Figure 6-3) generate their application energy through the pressure differential between engine vacuum and atmospheric pressure. A flexible diaphragm and a power piston use this energy to provide brake assistance. Modern vacuum boosters are vacuum-suspended units. This means the booster diaphragm is suspended in a vacuum on both sides when the brakes are not applied. When the brake pedal is pressed, an air control valve attached to the brake pedal pushrod opens. This valve admits atmospheric pressure to the back of the diaphragm. Atmospheric pressure forces the diaphragm forward where it increases the amount of force applied to the pushrod and master cylinder piston. Vacuum boosters can have one or two diaphragms, but most are single-diaphragm units. Single-diaphragm boosters are larger in diameter than dual-diaphragm vacuum boosters or tandem boosters. Tandem boosters allow more surface area to be contained in a smaller package, as explained in the Classroom Manual. All vacuum boosters have vacuum check valves. The check valve is located between the engine manifold and the booster. Vacuum can reach the booster through the one-way check valve, but it cannot leak back past the valve. As a result, vacuum is maintained inside the booster even after the engine is turned off.

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Vacuum check valve

Air valve

Floating control valve

Boot

Filter

Pedal pushrod Silencer Air passage

Figure 6-3  Vacuum power brake booster with master cylinder attached.

Hydraulically assisted power brakes Diesel engines and some gasoline engine installations do not produce enough intake manifold vacuum to operate a power brake booster. Hybrid vehicles may operate a significant amount of time on electric power, so there will not be any engine vacuum available at that time. One way to handle a lack of vacuum or low-vacuum conditions is to eliminate vacuum as a power source and use hydraulic power instead. The three kinds of hydraulic boosters are as follows: A mechanical hydraulic power-assist system operated with pressure from the power steering pump. This unit is a Bendix design called hydro-boost. An electrohydraulic power-assist system with an independent hydraulic power source driven by an electric motor. These units are often seen on vehicles with integrated ABS braking systems. The controller, master cylinder, pump, and reservoir are included in a single unit (Figure 6-4). On some vehicles, the reservoir and pump are located remotely. A block diagram of hydraulic booster operation is shown in (Figure 6-5).

Classroom Manual page 137

VACUUM BOOSTER TESTING AND DIAGNOSIS Vacuum boosters are usually trouble free, and many last the lifetime of a vehicle. An operational check and inspection of the vacuum booster are simple operations, however, and should be part of every brake service job.

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Figure 6-4  A hydraulic brake booster/ABS unit that uses pressurized brake fluid for boost.

Reservoir Hydrulic pump and accumulator

To calipers

To calipers

Master cylinder

Figure 6-5  Simplified diagram of a hydraulic brake booster. Note that control valves are not shown.

SERVICE TIP  Do not overlook the brake vacuum booster as the cause of drivability and comfort complaints. A leak in the booster vacuum hose or at the point that the hose connects to the manifold or the booster can cause a rough idle, misfire, hesitation, or surge. Depending on the size of the hole and the point where the hose connects to the manifold, the leak can affect the air-fuel mixture to one cylinder or several cylinders. Complaints about the air-conditioning system may also be a clue. If the air-conditioning plenum uses vacuum diaphragms to move the air delivery doors, the owner may complain that the air conditioner changes to full heat on the windshield when he or she drives up a long hill or accelerates.

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Any condition that reduces the amount of vacuum the engine generates will affect power brake performance. These conditions include vacuum leaks, faulty valves, and improper valve timing. An engine rebuilt with a high-performance camshaft may also produce lower vacuum. When investigating poor brake performance, check engine vacuum before inspecting the vacuum booster system. In most systems, at least 14 in. Hg of vacuum is required for proper power brake operation. Insufficient manifold vacuum, leaking or collapsed vacuum lines, punctured diaphragms, or leaky piston seals can cause weak booster operation. A steady hiss when the brake is held down indicates a leak that also can cause poor booster operation. Hard brake pedal is usually the first signal that the booster is failing. If the brakes do not release completely, they may have a tight or misaligned connection between the booster pushrod and the brake pedal linkage. If the pedal-to-booster linkage appears in good condition, loosen the connection between the master cylinder and the brake booster. If the brakes release, the trouble is in the power unit or the booster pushrod is too long. A piston, diaphragm, or bellows return spring may be broken. If the brakes do not release when the master cylinder is loosened from the booster, one or more brake lines may be restricted, or a problem may exist in the brake hydraulic circuit. If the brakes grab, look for common causes such as greasy linings, contaminated ­lining, or scored drums before checking out the booster. If the problem is in the booster, it may be a damaged reaction control. The reaction control assembly is a diaphragm, spring, and valving that tends to resist pedal action. This feature gives brake pedal feel to the driver.

251

Special Tool Vacuum gauge/pump

At times a leak in the vacuum booster may affect engine operation.

Basic Vacuum-Boost Operational Test Conduct a basic operating test of the vacuum booster as follows: Turn off the engine. Repeatedly pump the brake pedal to remove all residual vacuum from the booster. Hold the brake pedal down firmly and start the engine. If the system is working correctly, the pedal should move downward slightly and then stop. Only a small amount of pressure should be needed to hold down the pedal. If the results described in step 4 are not achieved do the following tests.

Vacuum Supply Tests If the booster is giving weak braking assistance or no assistance at all, a problem may exist with the vacuum supply to the unit. Vacuum boost efficiency is affected by loose or kinked vacuum lines and clogged air intake filters. Another cause may be the check valve, which retains vacuum in the booster when the engine is off. You can check this valve with a vacuum gauge to determine if it is restricted or stuck open or closed. Photo Sequence 10 shows the details. A vacuum supply hose that is restricted but not completely blocked will allow a normal reading on a vacuum gauge but will delay the buildup of full vacuum in the booster; that is, it can reduce the volume of vacuum for rapid, repeated brake applications. Check for a restricted vacuum hose by disconnecting it from the booster with the engine running. If the engine does not stumble suddenly and almost stall, the hose is probably restricted. Install a new hose and recheck booster operation. Also, if the vacuum hose contains a vacuum filter and the filter is clogged, the same kind of delayed vacuum application symptoms may occur. Photo Sequence 10 shows a typical procedure for vacuum booster testing.

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Photo Sequence 10

Typical Procedure for Vacuum Booster Testing

P10-1  With the engine idling, attach a vacuum gauge to an intake manifold port. Any reading below 14 in. Hg of vacuum may indicate an engine problem.

P10-2  Disconnect the vacuum hose that runs from the intake manifold to the booster and quickly place your thumb over it before the engine stalls. You should feel strong vacuum.

P10-3  If you do not feel a strong vacuum in step 2, shut off the engine, remove the hose, and see if it is collapsed, crimped, or clogged. Replace it if needed.

P10-4  To test the operation of the vacuum check valve, shut off the engine and wait for 5 minutes. Apply the brakes. There should be power assist on at least one pedal stroke. If there is no power assist on the first application, the check valve is leaking.

P10-5  Remove the check valve from the booster.

P10-6  Test the check valve by blowing into the intake manifold end of the valve. There should be a complete blockage of airflow.

P10-7  Apply vacuum to the booster end of the valve. Vacuum should be blocked. If you do not get the state results in step 6 and step 7, replace the check valve.

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P10-8  Check the booster air control valve by performing a brake drag test. With the wheels of the vehicle raised off the floor, pump the brake pedal to exhaust residual vacuum from the booster.

P10-9  Turn the front wheels by hand and note the amount of drag that is present.

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Photo Sequence 10 (continued)

P10-10  Start the engine and allow it to run for 1 minute and then shut it off.

P10-11  Turn the front wheels by hand again. If drag has increased, this indicates that the booster control valve is faulty and is allowing air to enter the unit with the brakes unapplied. Replace or rebuild the booster.

If the vacuum booster seems to have a normal vacuum supply but the brakes take more effort than normal to apply, the booster may have an internal vacuum leak. Check for this by starting the engine and letting it idle to develop normal vacuum at the booster. Then roll up the windows to reduce outside noise and slowly but firmly apply the brakes. Listen to the engine. If it stumbles or runs roughly, and a hissing sound increases around the pedal pushrod, the booster has an internal leak in the diaphragm. Do not mistake normal booster breathing for a vacuum leak. When the pedal is pressed, air rushing through the filter in the rubber boot of the booster input pushrod causes a slight breathing sound, which is normal. A diaphragm vacuum leak will cause a louder, continuing hiss.

Fluid Loss Test If the fluid level in the master cylinder reservoir level is low but there is no sign of an external leak, remove the vacuum hose from the intake manifold to the booster. Inspect it carefully for signs of brake fluid. If evidence of brake fluid is found, the master cylinder secondary seal may be leaking. If so, the master cylinder and the brake booster will require rebuilding or replacement. See Chapter 4, Master Cylinder and Brake Fluid Service, for details on rebuilding the master cylinder.

BRAKE PEDAL CHECKS The brake pedal must be adjusted properly for correct power-assist operation. In addition to the mechanical checks and brake travel check presented in Chapter 4, Master Cylinder and Brake Fluid Service, you should also check pedal free play and pedal height settings. Excessive play or low pedal height may limit the amount of power assist generated by the vacuum booster.

Pedal Free Play Inspection Pedal free play is the first easy movement of the brake pedal before the braking action begins to engage. Pedal free play should be only about 1/16 inch to 3/16 inch in most cases.

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Figure 6-6  Checking pedal free play by hand rather than with your foot will give you a more precise measurement.

To determine the amount of free play present, gently press the pedal down by hand until you feel an increase in effort (Figure 6-6). Hold a ruler alongside the pedal to measure the amount of free play. On many vehicles with stability control, the brake pedal position sensor must be calibrated when the position of the sensor is changed or the part is replaced.

Special Tool Ruler

Pedal Height Adjustment Brake pedal height specifications are listed in most vehicle service manuals. Typical heights range from 6 inches to 7 inches. Most pedal height measurements are taken from the floor mat to the base of the pedal, but in some cases the measurement is taken from a special point below the floor mat (Figure 6-7) Before adjusting pedal height, loosen the brake switch locknut and back off the brake switch until it no longer touches the brake pedal. Then use pliers to screw the pushrod in or out as needed (Figure 6-8). Pushrod Locknut Lift floor mat

Bulkhead

Pedal up Pedal down

Pushrod locknut Serrations for pliers

Measuring point (cutout) Pedal play Pedal travel

Figure 6-7  Pedal height is measured on some cars from a specific spot on the floor.

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Pushrod (counterclockwise to lower the pedal)

Figure 6-8  Pedal height is adjusted on most vehicles by shortening or lengthening the pushrod.

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Plunger

Pad Locknut

Brake pedal

0.3–1.0 mm (0.012–0.039 in.)

Figure 6-9  Typical stop lamp switch adjustment.

When the proper pedal height is set, adjust the stop lamp switch as required. Figure 6-9 is an example of one stop lamp switch adjustment method. After adjusting pedal height, check for proper stop lamp and cruise control operation. Be sure that the stop lamps are off with the brakes released and on with the brakes applied. Test drive the vehicle and verify that the cruise control disengages when the brake pedal is pressed. Refer to Chapter 5 of this Shop Manual for more information on stop lamp and other brake pedal switch adjustments. Vehicles that use a module to control the exterior lamps have to have the brake pedal position sensor reinitialized for proper operation after replacement of the switch or after service involving the switch. The general procedure to recalibrate a brake pedal position sensor on a GM vehicle follows. Make sure to follow the specific procedure for the vehicle being worked on. The brake pedal position sensor may need to be calibrated if the sensor itself is replaced or if the electronic brake control module, ECM, or BCM is replaced (depending on application.) It is important to note that the brakes should not be applied while performing the calibration. If the brake is applied you will have to redo the calibration. Following are the steps to calibrate:

1. Apply the parking brake. 2. Place the vehicle in Park. 3. Install the appropriate scan tool. 4. Clear BCM codes. 5. Select the Module Diagnostics Menu. 6. Go to BCM menu item. 7. Select Configuration/Reset Functions menu item. 8. Select the Brake Pedal Position Sensor Learn procedure and follow the directions displayed on the screen to configure the BCM. 9. Next, navigate to the Configuration menu of the ECM. 10. Select the Learn Functions menu. Select the Brake Pedal Position Sensor Learn procedure and follow the directions displayed on the screen to configure the sensor for the ECM.

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Chapter 6

VACUUM BOOSTER REMOVAL AND INSTALLATION Classroom Manual page 128

Special Tool Cloths

Follow these general steps to remove and replace a typical vacuum booster (Figure 6-10). Detailed steps will vary from one vehicle to another, but most removal and installation procedures follow this basic sequence. Photo Sequence 11 illustrates the basic steps. WARNING  Wear safety glasses or face protection when using brake fluid. Injuries to the face or eyes could occur from spilled or splashed brake fluid.

Booster Removal To remove a vacuum booster:

1. Set the parking brake and disconnect the battery ground (negative) cable. 2. Disconnect the vacuum hose at the booster check valve. 3. Remove all fasteners securing the master cylinder. 4. Pull the master cylinder back from the booster, taking care not to crimp a brake line. There is usually enough movement in the lines to allow this. If not, the lines must be disconnected and master cylinder outlets plugged.

Figure 6-10  Many times there are wiring harnesses and other components that must be moved or shifted to gain access to the booster fasteners and make room to extract the booster from the vehicle.

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Photo Sequence 11

Typical Procedure for Replacing a Vacuum Booster

P11-1   The master cylinder and booster may be easy or difficult to access depending on the components in the surrounding area.

P11-2  With the surrounding components removed or shifted to the side, the master cylinder fasteners can be accessed.

P11-3  Once the fasteners are removed, pull the master cylinder back from the booster. Take care to prevent damage to the brake lines.

P11-4  Many times some lower portion of the dash must be removed to gain access to the brake pedal. If the technician is tall or heavily built, it may be easier to work in this area with the front seat removed.

P11-5  On many vehicles, it is necessary to remove the stop lamp switch to prevent damage to it.

P11-6  The spring clip retaining the pushrod to the pedal can usually be unlocked and removed with a small pocket flat-tip screwdriver.

P11-7  The mounting nuts for the booster are sometimes far up on the bulkhead. Usually a ratchet, socket, and universal and a short extension will be needed.

P11-8  Once the fasteners are removed, the booster can be pulled away from the bulkhead and from the engine compartment.

P11-9  Slide the new booster into place on the bulkhead. If available, have an assistant hold the booster in place until the four fasteners under the dash have been started on the studs.

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Photo Sequence 11 (continued)

P11-10  Tighten the four booster fasteners to specifications.

P11-13  Install and clean the under-dash panels and any other components that were removed for access to the brake pedal.

Caution Always clean around any lines or covers before removing or loosening them. Dirt and other contaminants will void the warranty and may damage the system components.

P11-11  Connect the pushrod to the pedal and install the retaining clip. Replace the clip if so directed by the service information.

P11-14  Position the master cylinder and tighten the fasteners to specification. Check the brake lines for possible bends or kinks.

P11-12  Install the stop lamp switch and reconnect its electrical harness.

P11-15  Install all of the components that were removed for access to the master cylinder and booster.

5. With the master cylinder removed, move inside the vehicle and disconnect the stop lamp switch wiring connector from the switch (Figure 6-11). 6. Remove the switch from its mounting pin. 7. Remove the nuts fastening the vacuum booster to the passenger compartment side of the bulkhead. 8. Slide the booster pushrod and bushing off the brake pedal pin (Figure 6-12). 9. Return to the engine compartment and clear the area around the booster. This may require removing a vacuum reservoir or manifold (Figure 6-13), moving a wiring harness, or removing the transmission shift cable and bracket. 10. When the area is cleared of obstacles, move the booster forward so that its studs clear the engine compartment bulkhead. 11. Lift the booster out of the engine compartment. CUSTOMER CARE  The placement of most vacuum boosters requires the technician to work in a tight space in the hood hinge area. This places the technician’s belt buckle and clothing in closer contact with the vehicle’s panels than with other repairs. Slide the belt buckle around to the side. Use a fender cover during this repair to protect the finish and other items found in and around the booster location.

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Stoplamp switch Wiring connector

Brake pedal arm pin

Brake pedal lever

Pushrod Clip

Figure 6-11  Disconnecting the stop lamp switch connector.

Figure 6-12  The retaining clip holding the pushrod to the brake pedal has to be replaced if it is ever removed. The removal damages the spring action of the clip.

Figure 6-13  During the removal or shifting of the components, take care not to damage any of the electrical devices or braces.

Booster Installation Check the booster pushrod length as described later in this chapter under “Vacuum Booster Pushrod Length Check.” Install the vacuum booster following these 11 general steps:

1. Line up the brake support bracket from inside the vehicle. 2. Have a coworker set the booster in position on the engine compartment bulkhead. 3. Thread the nuts onto the studs from inside the vehicle. 4. Reinstall the pushrod onto the brake pedal pin using a new pushrod bushing. 5. Tighten the booster retaining nuts to the specified torque. 6. Reinstall the stop lamp switch on the pedal pin. Reconnect the electrical connector to the switch body. 7. Return to the engine compartment and reposition and install the wiring harness, transmission shift cable, and vacuum manifold. 8. Connect the manifold vacuum hose to the booster check valve. 9. Reinstall the master cylinder, connect all brake lines, and bleed the system of all air. 10. On a vehicle with a manual transmission or cruise control, adjust the manual shift linkage and cruise control dump valve. 11. Reconnect the battery and test drive the vehicle to be sure the booster is operating properly.

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Caution Ensure that the fitting is not cross-threaded when reconnecting the vacuum booster. Cross-threading could damage the fitting, the component, or both.

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Caution The return spring in the booster is strong, and the booster should not be separated unless it is mounted in a clamptype holding device. Damage and injury could result if the spring is released suddenly and without control.

Classroom Manual

page 128

Special Tool Booster-holding fixture

Then hold the 17 in. Hg to 20 in. Hg of vacuum and have a coworker apply and hold the brake pedal for 30 seconds. Vacuum should drop to no less than 6 in. Hg when the brakes are first applied and should leak down no more than another 2 in. Hg during 30 seconds.

BOOSTER OVERHAUL With a proper overhaul kit, a typical tandem booster can be overhauled (Figure 6-14) by following manufacturer’s instructions. Detailed steps will vary from one vehicle to another, but most overhaul procedures follow a basic sequence.

SERVICE TIP  You can make some quick tests of a vacuum booster with a handheld vacuum pump. Start by disconnecting the booster vacuum hose from the intake manifold and connect your vacuum pump to the hose. Apply 17 in. Hg to 20 in. Hg of vacuum. The gauge reading on the pump should hold steady. If it drops, the booster or the hose is leaking.

On passenger cars and light trucks, vacuum boosters are usually not overhauled but instead are replaced. Like the master cylinder, however, there may be a reason to actually overhaul a vacuum booster. This type of repair will be few and far between in most shops. Should it be necessary to overhaul a vacuum booster, ensure that service information is present and that the instructions are followed exactly. There are some repairs that can be performed on a hydraulic booster like the one used in hydro-boost systems, but these repairs usually consist of just replacing some seals instead of an overhaul.

VACUUM BOOSTER PUSHROD LENGTH CHECK Proper adjustment of the master cylinder pushrod is essential for the safe operation of vacuum power brake systems. If the pushrod is too long, the master cylinder piston will block the compensating port, preventing the hydraulic pressure from being released and resulting in brake drag. If the pushrod is too short, the brake pedal will be low and the pedal stroke length will be reduced, resulting in a loss of braking power. When the brakes are applied with a short pushrod, groaning noises may be heard from the booster. During assembly, the pushrod is matched to the booster. It is normally adjusted only when the vacuum booster or the master cylinder is serviced. The pushrod length is checked by observing fluid action at the master cylinder compensating ports when the brakes are applied. Remove the master cylinder cover and have an assistant apply the brake pedal. Observe the fluid reservoirs. A small ripple or geyser in the reservoirs should be visible as the brakes are applied. If there is no turbulence, loosen the bolts securing the master cylinder to the booster about ⅛ inch to ¼ inch and pull the cylinder forward, away from the booster. Hold it in this position and have the assistant apply the brakes again. If turbulence (indicating compensation) now occurs, the brake pedal pushrod or the booster pushrod needs adjustment. Booster pushrod adjustment is usually checked with a gauge, which measures from the end of the pushrod to the booster shell. Two basic gauge designs are used: Bendix and Delco-Moraine (Delphi Chassis). Be certain the pushrod is properly seated in the booster when making the gauge check.

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Power Brake Service Primary support plate Primary diaphragm

261

Secondary piston bearing

Diaphragm retainer Silencer Rear housing Power piston bearing Silencer Boot

Grommet Secondary support plate Vacuum check valve

Secondary diaphragm Housing divider

Front housing seal

Piston rod

Power Pedal piston pushrod

Return spring

Front housing

Reaction retainer

Filter

Figure 6-14  Typical tandem-diaphragm vacuum booster.

SERVICE TIP  The vacuum boosters are usually replaced rather than rebuilt in the shop. This saves time and money for the shop and the customer. However, replacement costs for larger vehicles may be expensive, and, therefore, it may be more feasible economically to rebuild.

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Chapter 6

Special Tool Bendix pushrod gauge

Classroom Manual page 128

Bendix Pushrod Gauge Check Bendix vacuum boosters are used on most Ford brake systems, as well as on vehicles from other manufacturers. Check and adjust pushrod length as follows with the booster installed on the vehicle and vacuum applied: 1. Disconnect the master cylinder from the vacuum booster housing, leaving the brake lines connected. Secure or tie up the master cylinder to prevent the lines from being damaged. 2. Start the engine and let it run at idle. 3. Place the gauge over the pushrod and apply a force of about 5 pounds to the pushrod (Figure 6-15). The gauge should bottom against the booster housing. 4. If the required force is more or less than 5 pounds, hold the pushrod with a pair of pliers and turn the self-locking adjusting nut with a wrench until the proper 5 pounds of preload exists when the gauge contacts the pushrod. 5. Reinstall the master cylinder. 6. Remove the reservoir cover and observe the fluid as your assistant applies and releases the brake pedal. If the fluid level does not change, the pushrod is too long. Disassemble and readjust the rod length.

Delco-Moraine Pushrod Gauge Check On most Delco-Moraine (or Delphi Chassis) brake systems, used primarily by GM, the master cylinder pushrod length is fixed. If the pushrod length needs to be adjusted after master cylinder or booster service, an adjustable pushrod must be installed. Check the pushrod length with the booster on or off the vehicle as follows:

Special Tool Delco-Moraine pushrod gauge

1. With the pushrod fully seated in the booster, place the go/no-go gauge over the pushrod (Figure 6-16). 2. Slide the gauge from side to side to check the pushrod length. The pushrod should just touch the longer, no-go, area and just miss the shorter, go, area. 3. If the pushrod is not within the limits of the gauge, replace the original pushrod with an adjustable one. Adjust the new pushrod to the correct height.

Adjust the pushrod screw to provide a slight pressure of approximately 5 pounds against the gauge Pushrod

Gauge

Figure 6-15  Bendix pushrod adjustment gauge.

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Gauge

Pushrod

GO NO GO

Figure 6-16  Delco-Moraine pushrod adjustment gauge.

4. Install the vacuum booster and check the adjustment. The master cylinder compensating port should be open with the engine running and the brake pedal released. Without proper pushrod clearance, the master cylinder can be held partially applied and cause the brakes to drag. Adjust the pushrod or shim the master cylinder away from the booster with cork gasket material.

ADJUSTING THE BOOSTER PUSHROD ON A HONDA If necessary, remove the master cylinder from the vehicle. Install the special tool onto the master cylinder (Figure 6-17). Use the adjusting nut to move the tool’s center shaft until it contacts the primary piston of the master cylinder. Install the special tool onto the booster without moving the center shaft. Use the master cylinder attaching nuts to hold the tool in place. Tee in a vacuum gauge into the engine or booster vacuum line. Operate the engine to a continuous 20 in. Hg (66 kPa) during the adjustment phase (Figure 6-18). With the tool in place and sufficient vacuum supplied, use a feeler gauge to measure the gap between the adjusting nut and the gauge body (Figure 6-19). If the gap is not between 0 mm and 0.4 mm (0 inch and 0.02 inch), then the pushrod must be adjusted. Locate the locknut on the pedal pushrod (opposite side of the booster) and turn the adjusting nut until the correct clearance is obtained (Figure 6-20). If the booster is off the vehicle, the length of the pushrod can be checked and adjusted as needed (Figure 6-21). SERVICE TIP  You can check master cylinder pushrod clearance by putting a small ball of putty or modeling clay on the end of the pushrod from the vacuum booster and then bolting the master cylinder to the booster. Then remove the master cylinder and measure the putty or clay thickness and compare to manufacturer’s specifications if available. It is usually about 0.015 inch of clearance.

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Chapter 6 Vacuum gauge Special tool 07JAG-SD40100

Adjusting nut

Figure 6-17  Install Honda’s special tool, 07JAG-SD40100, into the master cylinder. Special tool

Figure 6-18  Tee a vacuum gauge into the engine or booster hose and run the engine at a speed that will provide 20 in. Hg (66 kPa) of vacuum.

0–0.4 mm (0–0.02 in.)

Locknut

Feeler gauge

Figure 6-19  Measure the gap between the adjusting nut and the tool body.

Figure 6-20  Loosen the locknut and turn the adjuster to gain the proper clearance.

116 mm (4.6 in.)

Figure 6-21  If the booster has not been installed on the vehicle yet, measure the pushrod length and adjust as needed. This procedure will not work with the booster installed on the vehicle.

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SERVICE TIP  If the engine cannot achieve 20 in. Hg (66kPa) of vacuum, disconnect the vacuum line from the engine, and with an appropriate adapters), attach a hand-operated vacuum pump. Operate the hand pump until 20 in. Hg (66 kPa) of vacuum is achieved. Observe the gauge to ensure that the vacuum is holding. If vacuum cannot be maintained, then there is a problem with the pump connection or the diaphragm in the booster.

HYDRO-BOOST POWER BRAKES A hydro-boost power brake system consists of the booster assembly, the accumulator, and the power steering fluid circuit (including the pump and reservoir). The hydro-boost is mounted in the engine compartment the same as a vacuum booster (Figure 6-22). The pedal pushrod is connected at the booster input rod end. The master cylinder is bolted to the other end of the hydro-boost and is operated by a pushrod projecting from the booster cylinder bore. Power steering fluid is delivered to the booster from the power steering pump at 100 psi to 150 psi (Figure 6-23). The flow of fluid inside the booster is controlled by a hollowcenter spool valve. The fluid presses against the rear of the power piston, increasing the application force. When the brake pedal is released, pressure in the power cavity is released. A return spring pushes the power piston back to the unapplied position. The hydro-boost accumulator holds a charge of pressurized fluid as a reserve if fluid flow from the steering pump is lost or reduced. Inside the accumulator, the fluid compresses an internal piston and spring or a gas charge. If steering fluid pressure is lost, the force of the compressed spring or gas charge forces the pressurized fluid out of the accumulator to assist in applying the brakes. Depending on the system, one to three power applications are possible after power steering fluid pressure is lost.

Hydro-Boost System Inspection Before any detailed testing of hydro-boost components, check basic engine conditions and power steering operation that could affect hydro-boost performance. If both brake application and steering require more than normal effort, the cause is probably related to fluid pressure and delivery.

265

Special Tool Lift or jack with stands

Caution When using a jack, always block the wheels that remain on the floor. The vehicle and jack could roll causing damage to the vehicle and/or jack.

Caution Use the recommended power steering fluid in the boost system circuit of a hydro-boost system. The proper fluid is essential to system operation. Do not mix brake fluid with power steering or other hydraulic fluids. The use of improper fluids will damage the gaskets, O-rings, and other seals. Keep dirt out of the hydroboost system.

Hydro-boost

Fire wall

Master cylinder

Figure 6-22  Typical hydro-boost installation.

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Chapter 6 Power steering gear High-pressure lines

Return lines

Hydro-boost Power steering pump

Figure 6-23  The hydro-boost system shares hydraulic power with the power steering system.

Caution Always clean around any lines or covers before removing or loosening them. Dirt or other contaminants will void the warranty and may damage the system components.

Caution Do not hold the steering at full lock for more than 5 seconds when testing system pressure. System damage may result from prolonged high-pressure operation.

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Follow these steps to inspect the hydro-boost system: 1. Inspect fluid level in the power steering pump. Some pump reservoirs have dipsticks marked to check the fluid only when at normal operating temperature. Others have dipsticks with fluid level markings for both warm and cool fluid. Follow the carmaker’s instructions to check fluid level accurately, and use only the type of fluid specified for the vehicle. 2. Also inspect the condition of the power steering fluid. If it is dirty or smells burned or appears to be contaminated in any way, flush and refill the power steering system before proceeding further. 3. Inspect the condition of the power steering pump drive belt and replace it if it is cracked, glazed, grease soaked, or otherwise badly worn. Be sure that a serpentine belt is installed properly and correctly positioned on the belt tensioner. 4. Inspect all hoses and steel lines in both the hydro-boost system and the power steering system for leakage. 5. To verify a leak, have a coworker run the engine at fast idle and alternately apply the brakes and turn the steering from lock to lock. These actions develop high pressure and will force fluid from small leaks. Tighten connections or replace lines and hoses as required. 6. If leakage is found around the pump, clean and tighten all fittings and bolts. If the leak continues, rebuild or replace the pump. Figure 6-24 shows common leak locations in a power steering pump and in a steering gear. 7. Check brake fluid level in the master cylinder and add fluid if necessary. If air has entered the brake system and given the pedal a spongy feel, it will be difficult or impossible to troubleshoot hydro-boost operation accurately. Bleed the brake system if air has entered the lines and cylinders.

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267

Return tube fitting

Housing seal Power steering pump

Pressure and return lines

Ball seat leak

Drive shaft seal

Housing plug seal

Pinion seal

Outer rack seal

Inner rack seal

Rack and pinion steering gear

Figure 6-24  Possible leakage points in a power steering pump and steering gear.

8. Check engine idle speed and adjust it if necessary. Also check for engine speed control by the powertrain control module (PCM) as the steering is turned to full lock. If the engine does not drive the power steering pump at the required speed, the pump will not develop full pressure.

SERVICE TIP  Many vehicles have a power steering switch mounted either on the pump’s outlet or in the high-pressure line. This switch sends a signal to the vehicle’s engine controller under full-lock steering or when the power steering pressure reaches a preset limit. Failure of this switch could cause engine stalling or low idle during maneuvers like parking. If there is a problem with steering pump speed or output during high-pressure tests, check the power steering switch.

Power Steering Operation and Hydro-Boost Service The hydro-boost system requires a continuous supply of power steering fluid at the proper pressure and volume from the power steering pump. In addition to the inspection of power steering components listed previously, you may need to test the pressure developed by the pump. If so, follow the instructions of the pressure-test equipment manufacturers. Power steering pressures are listed in vehicle service manuals. The power steering pump should not be operated without fluid in the reservoir. The pump bearings and seals can be damaged. If the pump has failed, check the fluid carefully for abrasive dirt and metal particles that can damage the hydro-boost. If you find such particles in the fluid from any source, flush the system thoroughly. Depending on the

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Chapter 6 Housing seal

Return port fitting seal Spool valve seal Piston seal leak

Input seal leak

Accumulator cap seal

Figure 6-25  Possible leakage points in a hydro-boost booster.

severity of the contamination, you may need to remove the booster and disassemble it to clean it completely. Also, flush the power steering and hydro-boost lines thoroughly to remove particulate contamination.

Booster Fluid Leakage

Special Tool Power steering pressure gauge

Figure 6-25 shows possible leakage points at seals in the hydro-boost. If the booster is leaking at any of these points, it is often most practical to replace the booster with a new or rebuilt unit. All of these seals can be replaced individually, however, with seal repair kits. Most require that the booster be removed from the vehicle and disassembled. The spool valve plug seal and the accumulator seal can be replaced with the booster installed in the vehicle if component access permits. If leakage appears around the return port fitting, torque the fitting to 7 foot-pounds (10 Nm). If leakage continues, replace the O-ring under the fitting.

Basic Operational Test Check hydro-boost basic operation in two steps as follows: 1. With the engine off, pump the brake pedal repeatedly to bleed off the residual hydraulic pressure stored in the accumulator. 2. Hold firm pressure on the brake pedal and start the engine. The brake pedal should move downward and then push up against your foot.

Accumulator Test WARNING  Block the wheels when power testing the brakes. If the foot slips from the pedal or the brakes fail, injury could occur.

Test accumulator operation as follows: 1. With the engine running, rotate the steering wheel until it stops and hold it in that position for no more than 5 seconds. 2. Return the steering wheel to the center position and shut off the engine. 3. Pump the brake pedal. You should feel two to three power-assisted strokes.

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4. Now repeat step 1 and step 2. This will pressurize the accumulator. 5. Turn the engine off and wait 1 hour and then pump the brake pedal. There should be one or two power-assisted strokes. Bad valves are the most common accumulator problem. If the valves are leaking, the accumulator may hold a charge for only a short period or may fail to hold a charge at all. In either case, the booster must be disassembled and the valves replaced.

Noise Troubleshooting Because hydro-boost is part of another major system in the vehicle—the power steering system—problems in the steering system can affect the booster, and a problem in the booster can affect the steering. Certain noises often occur with the hydro-boost system and may be the cause for customer complaint. Some noises are normal and usually occur for a short time. Other noises are a sign of wear in the system or the presence of air in either the hydro-boost or the steering system.

SERVICING THE HYDRO-BOOST The hydro-boost can be overhauled or rebuilt in the field. Repair kits and service parts are available. In many cases, however, it is more practical to replace the booster with a new or rebuilt unit.

Booster Removal Remove a hydro-boost by following these general steps. Details will vary for different vehicle installations. WARNING  When fully charged, the accumulator holds more than 1,000 psi of hydraulic pressure. Before removing the hydro-boost, discharge the accumulator by firmly applying the brake pedal at least six times with the engine off. Pedal application force should increase as the accumulator discharges. Failure to discharge the accumulator could cause serious injury.

Classroom Manual page 137

Special Tools Vise Torque wrench

1. Before removing a hydro-boost from a vehicle, turn the engine off and pump the brake pedal several times to exhaust accumulator pressure. 2. Disconnect the master cylinder from the booster, but leave the service brake hydraulic lines connected to the master cylinder. 3. Carefully lay the master cylinder aside, being careful not to kink or bend the steel tubing. Support the master cylinder from a secure point on the vehicle with wire or rope. Do not support the master cylinder on the brake lines. 4. Disconnect the hydraulic hoses from the booster ports. Plug all tubes and the booster ports to prevent fluid loss and system contamination. 5. Detach the pedal pushrod from the brake pedal. Remove the nuts and bolts from the booster support bracket and remove the booster from the vehicle.

HYDRO-BOOST AIR BLEEDING Whenever the hydro-boost or power steering components are removed and reinstalled, the hydraulic system must be bled of all air. Air also can enter the hydro-boost system if the power steering fluid level drops below the minimum safe level in the pump reservoir, and air can be drawn into the fluid through loose fittings in hydraulic lines and hoses.

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Check the steering fluid for signs of air. Aerated fluid looks milky. The level in the steering fluid reservoir will also rise when the engine is turned off if air has been compressed in the fluid. If the fluid has air in it that cannot be purged using the following procedure, the problem may lie in the steering system pump. Refer to the vehicle service manual for further troubleshooting instructions on the power steering system. 1. Fill the power steering pump reservoir to the full mark and allow it to sit undisturbed for several minutes. 2. Start the engine and run it for approximately 1 minute. 3. Stop the engine and recheck the fluid level. Repeat step 1 and step 2 until the level stabilizes at the full mark. 4. Raise the front of the vehicle on a hoist or safety stands. 5. Turn the wheels from lock to lock. Check and add fluid if needed. 6. Lower the vehicle and start the engine. 7. Apply the brake pedal several times when turning the steering wheel from lock to lock. 8. Turn off the engine and pump the brake pedal five or six times. 9. Recheck the fluid level. If the steering fluid is extremely foamy, allow the vehicle to stand for at least 10 minutes with the engine off. Then repeat step 7 through step 9 until fluid in the pump reservoir is clear and free of air bubbles.

SERVICING VACUUM BOOSTERS ON VEHICLES WITH VEHICLE STABILITY CONTROL Special Tools Lift or jack with stands Large catch basin Sufficient power steering fluid Classroom Manual page 143

Vehicles manufactured after 2012 are equipped with Vehicle Stability Control (VSC). Some vehicles with vehicle stability control retain a vacuum booster. These boosters can often modify the amount of boost pressure in the event of a stability control assisted stop. In most cases, diagnosing and/or replacing the boosters follows the same procedures for a typical booster except for some additional steps. Most of those additional steps concern the electronics associated with VSC. This section highlights some of those steps. As always, the best guide is service information. AUTHOR’S NOTE  There are several names used for stability systems. Honda has the VSA, and Chrysler has the Electronic Stability Program (ESP). For consistency, this book has focused on the name Vehicle Stability Control or (VSC). Please note that almost every manufacturer has a different name for similar systems.

A Honda vacuum booster is shown in Figure 6-26. This booster is common to the standard, ABS, and VSC systems, and it is not particularly difficult to replace. The Chrysler booster shown in Figure 6-27 is more representative of the booster configuration used with newer ABS and VSC systems. As mentioned before, some VSC systems have no vacuum booster at all. Instead, they use the computer-controlled hydraulic modulator as a booster. The testing of the vacuum booster is done in the same manner as testing a typical vacuum booster. With the engine off, pump the brake pedal several times until it is firm and high. Hold the pedal down and start the engine. The pedal should fall away, stopping about 2 inches from the floorboard. If it does not respond accordingly, refer back to the vacuum booster testing and follow those guidelines. The following procedure is typical of a Chrysler booster replacement. Always look up the correct procedure for the vehicle you are working on in service information. Replacing the vacuum booster in a VSC requires some additional steps. Disconnect and isolate the

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Check valve

Figure 6-26  The booster on this Honda is part of a VSA system.

Vacuum source hose

Figure 6-28  Do not remove the check valve from this type of booster. Remove the hose from the check valve instead. Electrical connectors

Figure 6-27  Before removing the booster fasteners, disconnect all of the ESP electrical connectors on the booster and master cylinder.

negative cable from the battery. Remove the windshield wiper module and components to gain access to the booster. Disconnect the electrical connections at the booster and remove the master cylinder. Move the master cylinder back from the booster. Do not bend or damage the brake lines. Disconnect the vacuum hose from the check valve, but do not remove the check valve from the booster Figure 6-28). WARNING  Before working in or around the steering column, ensure that the air bag system has had time to discharge. Failure to properly disarm the air bag system could result in serious injury.

Move inside the passenger compartment, and, if sufficient time has elapsed for the air bags to disarm, disconnect and remove the stop lamp switch (Figure 6-29). The switch will be replaced with a new one upon installation of the booster. Use a screwdriver to remove the retaining clip from the booster pushrod, and slide the pushrod from the pedal pin (refer back to Figure 6-29). Remove the booster’s four mounting nuts, and remove the booster from the engine compartment. Before installing the new booster, ensure that a new booster seal is present on the bulkhead side of the booster (Figure 6-30). Slide the booster into place through the bulkhead and tighten the four mounting nuts to specifications. Position the booster pushrod over the pedal pin and install a new retaining clip. Install and adjust the new stop lamp switch. Under the hood, install the master cylinder onto the booster and reconnect all electrical connections. Install the wiper module and other removed components. Connect the battery and road test the vehicle.

Caution Before even beginning to work on a hybrid or electric vehicle, make certain that you are aware of the procedure to disable the high voltage power supply system according to service information.

SERVICING AN ELECTROHYDRAULIC POWER BOOSTER SYSTEM Hybrid vehicles, as well as some conventional gasoline vehicles, use an electric brake booster pump (often referred to as a hydraulic power unit Figure 6-31) used to pressurize brake fluid for use in a hydraulic booster system, which has the master cylinder

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Stoplamp switch

Engine bulkhead

Stoplamp switch mounting bracket

Booster seal Brake pedal lever

Nuts (4)

Figure 6-29  Remove the stop lamp switch, the pushrod retaining clip, and the pushrod from the pedal.

Clip

Figure 6-30  Always install a new booster seal before positioning the new booster in place on the bulkhead. Reverse the removal procedures to complete the installation. Brake pedal connection

Hydraulic connections Hydraulic booster section

Brake fluid reservoir

Accumulator

Figure 6-31  A hydraulic power unit for a late model import. The unit pressurizes brake fluid to provide boost for the power brakes.

Master cylinder section

Figure 6-32  Drawing of a brake actuator unit that utilizes an electrohydraulic booster. Note the combination of the hydraulic booster with the master cylinder.

incorporated into the design called a hydraulic actuator (Figure 6-32). The hydraulic power unit uses three pressure sensors. The pressure sensors allow the vehicle stability control module to monitor the brake systems operation. The sensors measure pressure inside the high-pressure accumulator, booster pressure and pedal simulator pressure. The pedal simulator is used to maintain proper brake pedal feel for the driver. Whenever a hydraulic power unit is replaced, the pressure sensors must be recalibrated. The master cylinder incorporates a hydraulic booster assembly (referred to in this example as a brake actuation unit). The brake actuation unit works with the hydraulic power unit and an electronic stability control (ESC) module to provide for ABS, traction control, and vehicle stability control. The reservoir provides brake fluid for the entire system. A brake pedal travel sensor is used to determine the proper brake pedal action.

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Servicing the Brake Actuation Unit The brake actuator replacement procedure is much like a conventional vacuum booster. 1. The hybrid high voltage system MUST be disabled. (See appropriate service information to determine this procedure as necessary.) 2. The 12-volt power supply negative ground is disconnected. 3. The low fluid level sensor is disconnected. 4. Remove the brake fluid from the reservoir (with a turkey baster). 5. The brake lines are disconnected, making note of their location. 6. Disconnect the brake lever. 7. Remove the four attaching nuts. 8. Carefully remove the brake actuator assembly. 9. On reinstallation, reverse the procedure. 10. Bleed the brake system using the scan tool to set the hydraulic unit to “air bleed mode.” 11. Check brake pedal height and free play. 12. Recalibrate the brake pedal travel sensor with the scan tool. 13. Test drive the vehicle and check for proper operation.

Recalibration of the Brake Pressure Sensors Recalibration of the brake pressure sensors must be done whenever the electronic brake control module (EBCM) or the brake pressure modulator valve assembly is replaced. The calibration is essential because the BPMV needs to know how much pressure needs to be applied to the braking systems. The pressure is measured by the brake pressure sensors. The Brake Pressure Sensor Calibration procedure can be completed with a scan tool using the following steps:

1. Apply the parking brake, or place the transmission in Park. 2. Make sure not to apply the brake pedal 3. Install the scan tool to the DLC. 4. Turn the ignition on and the engine off 5. On the scan tool, Select “Brake Pressure Sensor Calibration” in the EBCM Configuration/Reset Functions list. 6. Follow the scan tool directions to calibrate the sensors. 7. Clear any DTCs that might have set.

CASE STUDY A technician was working with a vehicle in the shop that seemed to have a problem with the stop lamps. The repair order stated that “stop lamps stay on all the time.” When the technician pulled the vehicle into the shop and verified that the stoplights were staying on, but after a few seconds with the engine off, the lights went out. The technician was puzzled, wondering what would cause this to happen? The technician started the vehicle, and the stop lamps came back on and stayed on till the engine was turned off again. The technician listened carefully and could hear a faint hissing sound from the brake pedal area with the engine running. After a few seconds, the hissing stopped when the engine was turned off. The technician then watched the brake pedal very carefully—with the engine started, the pedal dropped very slightly, not enough to apply the brakes, but just enough to activate the stop lamps. The technician decided to investigate the brake vacuum booster. On disassembly, it was found that the power valve inside the booster was damaged and causing a slight application of the brake pedal under full vacuum, but with the engine shut off, the vacuum between the chambers would eventually equalize and the pedal would return to its normal position.

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ASE-STYLE REVIEW QUESTIONS 1. Technician A says that if a vacuum booster is in good condition, starting the engine after the vacuum is exhausted should cause the brake pedal to drop slightly under foot pressure. Technician B says that the pedal should pulsate lightly after it drops. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 2. While discussing low brake fluid levels with no sign of an external leak, Technician A says to remove the vacuum hose from the intake manifold to the booster and to inspect it carefully for signs of brake fluid. Technician B says that if evidence of brake fluid is found, the master cylinder primary seal may be leaking. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 3. Technician A says a vacuum booster can have an internal vacuum leak. Technician B says an internal vacuum leak may cause the engine to stumble when the brake is applied, along with a hissing sound around the pedal pushrod area. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 4. While discussing checking the hydro-boost operation, Technician A says to start the engine and pump the brake pedal repeatedly to bleed off the residual pressure in the accumulator to begin testing. Technician B says the brake pedal should fall away under firm pressure on the pedal. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. Technician A says that the tandem-diaphragm booster will have no loss of boost even if one diaphragm is leaking. Technician B says tandem boosters allow more surface area for booster operation. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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6. Technician A says that the check valve in the booster is used to keep atmospheric air pressure from leaking from the booster when the brakes are applied. Technician B says that the check valve is used to keep vacuum from being lost from the booster when the engine is turned off. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 7. Technician A says that whenever a hydro-boost is serviced, the power steering system must be bled if the booster has been disconnected. Technician B says that power steering fluid and brake fluid are interchangeable in the hydro-boost system in small amounts. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 8. While discussing the adjustment of the master cylinder pushrod on a Honda, Technician A says never remove the master cylinder from the vehicle to install the special tool. Technician B says a feeler gauge is used to measure the gap between the adjusting nut and the gauge body. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 9. Technician A says hybrid vehicles can use an electric brake booster pump used to pressurize brake fluid for use in a hydraulic booster system. Technician B says whenever a hydraulic power unit is replaced the pressure sensors must be recalibrated. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 10. Technician A says that the accumulator of a hydro-boost system holds more than 1,000 psi of hydraulic pressure. Technician B says before removing the hydro-boost, discharge the accumulator by firmly applying the brake pedal twice with the engine off. Who is correct? A. A only B. B only

C. Both A and B D. Neither A nor B

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ASE CHALLENGE QUESTIONS 1. Replacement of a hydraulic brake actuator is being discussed. Technician A says the brake actuator replacement procedure is much like a conventional vacuum booster. Technician B says that checking a vacuum booster on a vehicle with stability control is the same as checking a vacuum booster without stability control. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 2. While discussing a Chrysler vehicle equipped with a Vacuum booster and VSC, Technician A says testing a vacuum booster on these vehicles requires a scan tool and a vacuum gauge. Technician B says care must be taken to prevent damage to the stop lamp switch on these vehicles. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

4. Technician A says a vacuum brake booster needs at least 10 in. Hg of vacuum for proper operation. Technician B says that faulty valve timing, vacuum leaks, or an aftermarket camshaft can contribute to poor booster operation. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. Technician A says that a vehicle with hydro-boost may have a hard pedal if the pressure switch is open. Technician B says that a hydro-boost system may lose boost if the drive belt is slick or loose. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

3. A vehicle has no brake boost until the engine has run for a few seconds, Technician A says that the vacuum check valve is leaking. Technician B says that the engine is just worn out and cannot hold a vacuum during shutdown. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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Name ______________________________________ 

Date __________________

Identifying/Inspecting Booster Components Upon completion of this job sheet, you should be able to identify components of any booster system. This job sheet was specifically added to cover hydraulic systems but will work for vacuum boosters as well.

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27

ASE Education Foundation Correlation This job sheet addresses the following MLR/AST/MAST task: E.2. Identify components of the brake power assist system (vacuum and hydraulic); check vacuum supply (manifold or auxiliary pump) to vacuum-type power booster. (P-1) This job sheet addresses the following AST/MAST task: E.4. Inspect and test hydraulically assisted power brake system for leaks and proper operation; determine needed action. (P-3) Tools and Materials Basic hand tools Service information Describe the vehicle being worked on: Year _____________________ Make _____________________ Model _____________________ VIN _____________________________ Engine type and size ____________________________ Type of booster utilized  Procedure 1. Using service information, identify the type of booster that this vehicle utilizes.  2. Are there any special precautions regarding this system, such as accumulator service?   3. Draw a simple diagram of this system and label all the major components with a brief description of what each component does.   4. Again, utilizing service information, detail the steps necessary to test this system’s operation, including any special tools needed.    For Hydraulic Boosters 5. On a hydraulic booster, briefly explain how you would test the booster for proper operation.  

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6. On a hydraulic booster, inspect the booster for hydraulic leaks and report your findings here.   For any Booster 7. Based on your observations what is the condition of the booster system? Are repairs indicated? If so what are they?   

Problems Encountered    Instructor’s Response   

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Date __________________

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28

VACUUM BOOSTER TESTING AND DIAGNOSIS Upon completion of this job sheet, you should be able to properly test and diagnose a vacuum booster system. ASE Education Foundation Correlation This job sheet addresses the following MLR/AST/MAST task: E.2. Identify components of the brake power assist system (vacuum and hydraulic); check vacuum supply (manifold or auxiliary pump) to vacuum-type power booster. (P-1) This job sheet addresses the following AST/MAST task: E.3. Inspect vacuum-type power booster unit for leaks; inspect the check-valve for proper operation; determine needed action. (P-1) Tools and Materials Basic hand tools Describe the vehicle being worked on: Year _____________________ Make _____________________ Model _____________________ VIN _____________________________Engine type and size _____________________________ Procedure Vacuum booster testing

Task Completed

1. Inspect the vacuum booster for obvious damage. Describe any damage to the booster, master cylinder, and lines or hoses.  

h

2. With the engine off, pump the pedal several times to exhaust the power booster reserve. Does the pedal feel become firm and high?  

h

3. With the pedal depressed, start the engine. What pedal action was observed? How much clearance is now available between the pedal and the floorboard?  

h

4. Release the pedal, pause for a few seconds, and then reapply the brakes. What is the pedal feel at this point? How much clearance is between the pedal and the floorboard? Was there any air (hissing) noise as the pedal was applied?  

h

5. Is the vacuum booster operating properly? If not, go to step 6. The student may make a diagnostic decision on the vacuum at steps 7, 8, or 9.  

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6. Turn off the engine.

Task Completed h

7. Disconnect the hose or valve directly from the vacuum booster body. Did a hissing sound occur as the hose or valve was disconnected? If yes, what repairs are indicated? If not, go to step 8.  

h

8. Connect a vacuum gauge to the outlet side (booster end) of the valve and start the engine. Record the gauge reading, if any. Is a full-engine vacuum (15 in. Hg to 20 in. Hg) available at this connection? If yes, what repairs are indicated? If not, go to step 9.  

h

9. Remove the booster hose from the engine intake nipple and connect the vacuum gauge in its place. Is a full-engine vacuum (15 in. Hg to 20 in. Hg) available at this connection? Does this vehicle use a vacuum pump in addition to manifold vacuum? If yes, what repairs are indicated?  

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10. Based on your observations in steps 7, 8, and 9, what is the condition of the booster system? Are repairs indicated? What are they?  

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Problems Encountered    Instructor’s Response   

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Date _________________

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REPLACE A VACUUM BOOSTER Upon completion and review of this job sheet, you should be able to replace a vacuum brake booster. ASE Education Foundation Correlation This job sheet addresses the following MLR/AST/MAST task: E.1. Check brake pedal travel with and without engine running to verify proper power booster operation. (P-2) E.2. Identify components of the brake power assist system (vacuum and hydraulic); check vacuum supply (manifold or auxiliary pump) to vacuum-type power booster. (P-1) This job sheet addresses the following AST/MAST task: E.3. Inspect vacuum-type power booster unit for leaks; inspect the check-valve for proper operation; determine needed action. (P-1) E.5.

Measure and adjust master cylinder pushrod length. (P-3)

Tools and Materials Service manual Hand tools Measuring device as specified by service manual Describe the vehicle being worked on: Year _____________________ Make _____________________ Model _____________________ VIN ________ Engine type and size ________ ABS yes or now ________ If yes, type _______ Procedure

Task Completed

1. Pushrod adjustment? ________________ Explain procedures _______________________  Booster fastener(s) torque  Master cylinder fastener(s) torque 

h

WARNING  Disable the supplemental inflatable restraint system (SIRS) or air bag system when working on or near the system wiring. Accidental discharge of the air bag could cause injury. 2. Disarm SIRS (air bag) if equipped.

h

3. Disconnect stoplight switch.

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4. Disconnect brake pedal pushrod from pedal.

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5. Remove booster fasteners from under the dash if necessary.

h

6. Disconnect vacuum hose and electrical connections, as needed, from booster.

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7. Remove the master cylinder from the booster fasteners.

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8. Move the master cylinder away from the booster.

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9. Remove booster fasteners as needed.

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10. Remove the booster from the vehicle.

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11. Install the new booster and torque fasteners.

Task Completed h

12. Reinstall the master cylinder and torque fasteners.

h

13. Connect electrical connections and the vacuum hose.

h

14. Connect the pushrod to the brake pedal.

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15. Measure and adjust the pushrod to manufacturer’s specifications. Explain the procedure.  

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16. Connect the stoplight switch.

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17. Start engine and test brake booster. Explain the results.  

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18. Stop the engine and pump the brake pedal to exhaust the booster.

h

19. Hold the brake pedal down and start the engine. The pedal should fall away but retain firmness without being spongy. Results: ________________________________  20. Test the stoplights. Results:   NOTE:  A test drive may be necessary to test the operation of the brake switch on vehicles equipped with antilock brakes or cruise control. If necessary, do so with caution. WARNING  Before moving the vehicle after a brake repair, pump the pedal several times to test the brake. Failure to do so may cause an accident with damage to vehicles or the facility, or personal injury. WARNING  Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to this precaution could lead to serious personal injury and vehicle damage.

Caution Before working on the brakes of a vehicle with an ABS, consult the service manual for precautions and procedures. Failure to follow procedures to protect ABS components during routine brake work could damage the components and cause expensive repairs.

Caution Always clean around any lines or covers before removing or loosening them. Dirt or other contaminants will void the warranty and may damage the system components.

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21. Arm the air bag system as needed.

Task Completed h

22. When the repair is complete, clean the area, store the tools, and complete the repair order.

h

Problems Encountered    Instructor’s Response   

Caution Do not twist or bend the hydraulic lines leading to the master cylinder. Most master cylinder lines can flex enough for the master cylinder to clear the booster without disconnecting the lines. Violent jerking motions could kink or twist a brake line and prevent full brake application.

Caution Do not remove protective shipping seals, covers, or plugs before installing the device. Dirt and other contaminants may enter and damage the system components or void warranty.

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Chapter 7

Disc Brake Service

Upon completion and review of this chapter, you should be able to: ■■

■■ ■■ ■■

Diagnose disc brake problems, including poor stopping, pulling, or dragging caused by problems in the caliper, the caliper installation, the hydraulic system, or the rotor. Remove, inspect, and replace brake pads. Remove and replace a caliper. Overhaul a caliper, including disassembly, inspection, adjustment, replacement, and reassembly of all parts.

■■

■■ ■■ ■■ ■■

Clean a disc brake installation using vacuum or aqueous cleaning equipment. Remove and replace brake rotors. Inspect and measure rotors for wear.

Basic Tools Basic technician’s tool set Rotor micrometer Dial indicator

Machine a rotor to correct dimensions and finish on a brake lathe. Reinstall wheels, torque lug nuts, and make final brake system checks and adjustments.

Terms To Know Aqueous Bearing end play Bedding in Burnishing

Discard dimension Heat checking Loaded caliper Nondirectional finish

Cross-feed

Parallelism

Rotor lateral runout Rust jacking Vernier caliper

SERVICE PRECAUTIONS Specific CAUTIONS and WARNINGS are given throughout this chapter where needed to emphasize safety. The following general precautions apply to many different disc brake service operations and are presented at the beginning of this chapter to highlight their overall importance. ■■ When servicing disc brakes, never use an air hose or a dry brush to clean the brake assemblies. Use OSHA-approved cleaning equipment to avoid breathing brake dust. See Chapter 1 in this Shop Manual for details on working safely around airborne asbestos fibers and brake dust. ■■ Do not spill brake fluid on the vehicle; it may damage the paint. If brake fluid does contact the paint, wash it off immediately. To keep fluid from spraying or running out of lines and hoses, wrap the fittings with shop cloths when disconnecting them. ■■ Always use the DOT type of brake fluid specified by the vehicle manufacturer. Do not mix different brands of brake fluid. ■■ During servicing, keep grease, oil, brake fluid, or any other foreign material off the brake linings, calipers, surfaces of the rotors, and external surfaces of the hubs. 285

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Handle brake rotors and calipers carefully to avoid damaging the rotors or nicking or scratching brake linings.

Classroom Manual page 149

DIAGNOSING DISC BRAKE PROBLEMS Diagnosing has always been a key to good first-time automotive repair, but it has become an increasingly important function as the vehicle systems become more interlocking and electronically controlled or actuated. Poorly performing disc brakes usually result from worn brake pads or other parts, poorly fitted or incorrectly assembled parts, or rotor problems, such as grooving, distortion, or grease and dirt on the rotor surface. Worn pads increase the braking effort needed to stop the vehicle, but the same problem can be caused by a sticking or sluggish caliper piston. Installing the wrong type of brake pad can result in brake fade. A lot of technical effort, knowledge, and skill are covered by the single word inspect a vehicle maintenance schedule as it relates to the brake system. Inspect means different things to different people; but in any case, it means more than a quick glance at the calipers, hoses, lines, and master cylinder fluid level. If problems are suspected in the disc brakes, road test the vehicle. Instructions for a safe, complete road test are given in Chapter 7 of this manual. Even driving across the driveway and into the service bay can reveal a lot about brake system condition. As the pedal is applied, check for excessive travel and sponginess. Listen for noises: not just the obvious sounds of grinding pads or pad linings, but mechanical clanks, clunks, and rattles. A vehicle that pulls to one side when the brakes are applied may have a bad caliper or loose caliper at one wheel. Grease or brake fluid may have contaminated the pads and rotor, or the pad and lining may be bent or damaged. Grabbing brakes also may be caused by grease or brake fluid contamination or by a malfunctioning or loose caliper. Worn rotors or pads also may cause roughness or pedal pulsation when the brakes are applied. For a complete inspection, the wheels must be removed for a clear view of the brake pads and caliper mounting hardware. Some manufacturers, such as Ford, say to lubricate the caliper slides. Now is a good time to do it; and on any vehicle, it is a good idea to verify smooth operation of the calipers and lubricate if necessary.

SERVICE TIP  A customer may complain of a clicking noise that occurs every time the brakes are applied or released. Sometimes it happens in forward braking or in reverse braking, but it is noticeable only at slow speeds. This noise can occur when the pad hardware is either missing or damaged and the pads are moving back and forth in the caliper. Check the history of the vehicle for recent brake repairs and then check the brake caliper for the correct hardware.

Inspect the wheel and brake assembly for obvious damage that could affect brake system performance. Check the following:

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1. Tires for excessive or unusual wear or improper inflation 2. Wheels for bent or warped rims 3. Wheel bearings for looseness or wear 4. Suspension system for worn or broken components 5. Improper mounting of caliper and rotor 6. Brake fluid level in the master cylinder 7. Signs of leakage at the master cylinder, in brake lines or hoses, at all connections, and at each wheel

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SERVICE TIP  Most brake squeals occurs under light (not hard) braking at low to moderate (not high) speeds. Sometimes brakes will squeal when stopping in reverse but not when going forward. When troubleshooting brake noise complaints, check brake operation carefully under all moderate driving conditions.

If the vehicle is driven in an area where salt is used on the road during the winter, it is very important to check brake assemblies frequently. Salt water and rust damage caliper slides and pad-mounting hardware. Cars with rear disc brakes often have complicated parking brake mechanisms, so inspect them closely; lubricate where necessary.

INSPECTING BRAKE PADS Disc brake pad linings should be inspected regularly at the time or mileage intervals recommended by the carmaker. Manufacturers’ recommendations vary from as often as every 7, 500 miles to as seldom as every 30,000 miles. Most pad inspection recommendations, however, seem to be at 12,000-, 15, 000-, or 30,000-mile intervals or every 12 months to 24 months. A convenient time to check pad wear is when the wheels are removed for rotation, which is typically every 5,000 miles to 7,000 miles. Because of the wide range of carmakers’ inspection recommendations, always check the preventive maintenance schedule for the vehicle being serviced. Follow these basic steps for any disc brake pad inspection: 1. Raise the vehicle on a hoist or safety stands. Be sure it is properly centered and secured on the stands or hoist. 2. Mark the relationship of the wheel to the hub to ensure proper wheel balance on reassembly. An easy way to do this is to make a chalk mark on one wheel stud and on the wheel next to that stud. If the rotor and the hub are a two-piece floating assembly, chalk mark the rotor and the hub after removing the wheel. The chalk marks ensure that all rotating parts are indexed to each other and help to avoid wheel balance problems. 3. Remove the wheel and tire from the brake rotor. Be careful not to hit the brake caliper, the rotor splash shield, and the steering knuckle or suspension parts. 4. If the rotor and hub are a two-piece assembly, reinstall two wheel nuts to hold the rotor on the hub. 5. On most disc brakes, the pads can be inspected without removing the calipers. Check both ends of the outboard pad by looking in at each end of the caliper. As shown in Figure 7-1, these are the areas where the highest rate of pad wear occurs. Also check the lining thickness on the inboard pad to be certain it has not worn prematurely. If the caliper has an opening in the top, look through it to view the inboard pad and lining (Figure 7-2). Some calipers do not have such openings, and the center areas of the pads cannot be inspected without removing the caliper.

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Special Tools Lift or jacks with stands Impact tools Chalk

Caution Some imported linings, discs, and drums may still contain asbestos fibers. The fibers may cause serious eye and breathing injuries.

SERVICE TIP  When you are troubleshooting a brake-pull problem with disc brakes, remember to check the caliper slides (ways) or pins for burrs, gouges, rust, or any other problem that could keep the caliper from moving properly. If damaged or defective caliper mountings delay or interfere with caliper movement, the vehicle will pull to the opposite side as that brake applies first. Loose mounting bolts on a caliper support can cause similar brake-pull problems.

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Chapter 7 Caliper

Brake pads

Rotor and hub

Outboard lining

Figure 7-1  Inspect both ends of the outboard pad by looking in at each end of the caliper. If the caliper has an opening at the top, check the inboard and outboard pads.

Figure 7-2  Most calipers have an opening in the top of the casting that provides a good view of both pads.

As the disc brakes are inspected, observe the bushings and linkages of the steering and suspension mechanism. Worn steering or suspension may cause a noise or pull as the brakes are applied or released.

6. On vehicles with floating or sliding calipers, check for uneven wear on the inboard and outboard linings. If the inboard pad shows more wear than the outboard pad, the caliper should be overhauled or replaced. If the outboard pad shows more wear, the sliding components of the assembly may be sticking, bent, or damaged. In any case, uneven brake wear is a sign the pads or calipers need service. 7. To inspect the lining surfaces, remove the pads from the calipers. This is not usually necessary as part of routine brake inspection, but if the customer complains of poor brake performance, inspect the lining surfaces regardless of thickness. Replace the pads if the linings are glazed (shiny and smooth), heat damaged, cracked, or contaminated with dirt or brake fluid. A glazed brake pad lining can result in a hard brake pedal feel and less effective stopping.

A glazed brake pad lining can cause a hard brake pedal and poor stopping ability.

If the customer complains that the brakes are making a high-pitched squeal, immediately suspect an audible brake pad wear indicator, signaling that the system needs service (Figure 7-3). Instrument panel warning lamps also are indicators that the pads have worn past specifications.

SERVICE TIP  When the pads wear to the point that the sensor contacts the rotor, the brake-warning lamp on the instrument panel lights (Figure 7-4). After the pads are replaced, the lamp may stay lit until the car has been driven about a quarter mile. The electronic control unit simply has to “learn” that the worn pads have been replaced before it will turn off the lamp.

SERVICE TIP  Many pads have a vertical groove about midway the length of the pad (see Figure 7-5). When checking the pads through the caliper opening, the groove is visible. If pad wear is down to or near the bottom of the groove, then it is time for new pads.

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Pad

Rotor

Rotor

Wear indicator

New Pad

289

Wear indicator

Worn Pad

Figure 7-3  As the pad linings wear, the wear indicator eventually hits the rotor and makes noise to warn the driver that new pads are needed.

Shoe

Lining New Pad and Lining

Ready for Replacement

Figure 7-5  Any lining worn to the thickness of the metal backing pad needs replacement. Note the depth difference between the grooves of the two pads.

Figure 7-4  This lamp indicates that the brake pads should be checked for wear and replaced as needed.

Service information specifies a minimum lining thickness, but it can be measured accurately only if the pads are removed from the calipers. Most carmakers specify a minimum lining thickness of 1/32 inch. Ford, however, wants you to change brake pads when the lining is 1/8 inch thick or less. By any measure, 1/32 inch may be the minimum thickness to prevent rotor scoring, but braking efficiency is dramatically reduced with worn linings. Worn linings cannot dissipate heat adequately, and the last 1/32 inch of lining will wear and peel off much faster than the first 1/32 inch of fresh linings. When visually evaluating pad lining wear, consider that any lining worn to the thickness of the metal backing pad needs replacement (Figure 7-5).

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Caution Use extreme care when repairing brakes equipped with electronic wear indicators. Use only the specified tools and procedures to prevent damage to the components.

If you are unsure how to reinstall the brake caliper assembly, disassemble only one side at a time to give you an example for reference.

DISC BRAKE SERVICE OPERATIONS Disc brake service consists of these three general operations: 1. Pad replacement 2. Caliper overhaul or replacement 3. Rotor resurfacing when necessary Pad replacement is the most frequent disc brake service because pads are intended to wear as they operate. Calipers may require overhaul to replace worn parts or fix leaks and corrosion. Calipers need not be overhauled at every pad replacement, however, if they are in good shape. Years ago, rotors were routinely resurfaced at every brake job. Lighter rotors on late-model vehicles do not have the mass of iron found in rotors of the 1960s and 1970s. General practice today is to resurface rotors if they are grooved, scored, pulsating, or otherwise badly worn or if runout and parallelism measurements are out of limits. Rotors cannot be resurfaced beyond minimum thickness specifications, which are discussed later in this chapter.

Vehicle Preparation For pad, caliper, or rotor service, raise the vehicle on a hoist or safety stands, remove the wheels, and disassemble the brakes to the extent necessary for the planned service. Follow these four general preparation steps for all disc brake service: 1. Use a brake fluid siphon, or syringe, to remove approximately two-thirds of the brake fluid from the front or disc brake reservoir on a front-rear split system (Figure 7-6). On a diagonally split system, remove about half the fluid from both master cylinder reservoirs. 2. Raise the vehicle on a hoist or safety stands and support it safely. 3. Remove the wheels from the brakes to be serviced. Brakes are always serviced in axle sets, so remove both front wheels, both rear wheels, or all four. 4. Vacuum or wet-clean the brake assembly to remove all dirt, dust, and fibers.

Figure 7-6  Remove some brake fluid from the master cylinder reservoir. This reduces the chance of an overflow if fluid is forced back into the reservoir when the piston is forced back into its bore.

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Removing brake fluid from the master cylinder is an important preliminary step for all disc brake service. If fluid is not removed, it may overflow into the reservoir and spill as the caliper pistons are moved back into the caliper bores for caliper or pad removal. After siphoning fluid from the reservoir, replace the reservoir cover and safely discard the removed brake fluid. SERVICE TIP  If a customer complains about noisy disc brakes, compare the pads installed on the car to the original equipment manufacturer (OEM) pads. The grooves and chamfers on OEM pads are often there to reduce squeaks and squeals. “Economical” aftermarket pads often do not include these features. OEM pads may cost a bit more, but they can be the cure for a customer complaint.

291

Special Tools Lift or jack with stands Syringe Impact tools Brake service cleaning equipment Tubing with catch basin

Loaded Calipers Loaded calipers are rebuilt calipers that come with brake pads and mounting hardware fully installed (Figure 7-7). They eliminate the need to overhaul calipers and prevent many of the errors commonly committed when performing caliper service. These mistakes include forgetting to bend brake pad locating tabs that reduce vibration and noise, leaving off antirattle clips and pad insulators, or reusing worn or corroded mounting hardware that limits caliper movement and reduces pad life. Loaded calipers provide an attractive alternative to pad replacement and caliper overhaul for disc brake service on many vehicles. Use of loaded calipers reduces labor time and ensures that all components that should be replaced are replaced. However, be sure the loaded calipers have quality pad materials. Calipers should also be matched side to side with the same type of friction materials. When one caliper is bad, both should be replaced with the same type of loaded caliper. Whether or not to use loaded calipers for a particular brake job is as much a business decision as a technical decision. If a shop’s labor rate is high, loaded calipers may actually be more economical for the customer than the labor costs of overhauling the original calipers. In addition, loaded calipers usually have a manufacturer’s warranty for all materials and labor that went into the rebuilding.

Classroom Manual page 167

Figure 7-7  A loaded caliper is a rebuilt caliper with new hardware, seals, and pads.

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However, not all calipers for all vehicles are available as rebuilt, loaded assemblies. The job of a skilled brake technician still includes the ability to overhaul a caliper thoroughly and properly. Many shop owners also prefer to overhaul all calipers for complete brake jobs so that they know the condition of all calipers and the quality of the parts and materials used in their service. If loaded calipers are used for brake service on a particular vehicle, do not overlook the necessary inspection, cleaning, and lubrication of the caliper supports on the vehicle suspension. Also do not overlook brake rotor inspection and service. Rotors may require resurfacing if grooved or warped, or replacement if worn past their discard dimensions. Even the best loaded calipers cannot operate properly if installed on damaged or rusted mounting hardware or if they are forced to operate with defective rotors. SERVICE TIP  The best method to prevent reservoir overflow is to open the caliper bleeder screw and run a bleeder hose into a container to catch the fluid expelled when the piston is forced back into its bore. Opening the bleeder screw also makes it easier to move the piston. This is the recommended way to push pistons back on any brake system but is especially important on ABS to prevent damaging the hydraulic valve body. It is still good practice, however, to remove some fluid from the reservoir even when the bleeder screw is opened at the caliper.

BRAKE PAD REPLACEMENT FOR FLOATING OR SLIDING CALIPERS Replace pads and linings in axle sets only. An axle set contains four pads: the inner and outer pads for the caliper at each wheel. Do not try to interchange pads between right and left calipers to equalize wear. Even if only one pad in a set of four is badly worn, replace all four pads after fixing the problem that caused the uneven wear. To replace brake pads, raise the vehicle on a hoist or safety stands and prepare it as explained previously in this chapter. The details of pad replacement vary with the design of a particular caliper, but some general steps are common to all calipers. Photo Sequence 12 shows a typical replacement procedure for floating caliper disc brake pads. Figure 7-8 is an exploded view of a typical floating caliper disc brake, showing the pad installation. If unfamiliar with a particular caliper design, work on one side of the car at a time. The assembled caliper on the opposite side will be a guide for correct installation of pads and other parts. Bleeder valve

Piston boot

Inboard pad Outboard pad

Figure 7-8  Exploded view of a typical floating caliper and pads.

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Photo Sequence 12

Typical Procedure for Replacing Brake Pads

P12-1  Begin front brake pad replacement by removing brake fluid from the master cylinder reservoir, or reservoirs, for the disc brakes. Use a siphon to remove about one-half of the fluid.

P12-2  Raise the vehicle on the hoist, making certain it is positioned correctly. Mark and remove the wheels.

P12-3  Inspect the brake assembly, including the caliper, brake lines and hoses, and rotors. Look for fluid leaks, broken or cracked lines or hoses, and a damaged brake rotor. Fix any problems found before replacing the pads.

P12-4  Loosen and remove the caliper mounting pins or bolts.

P12-5  Lift and rotate the caliper assembly up and off of the rotor. Note that a one-piece rotor is shown.

P12-6  Remove the old pads from the caliper.

P12-7  To avoid damaging the caliper, suspend it from the underbody with a strong piece of wire.

P12-8  Check the condition of the caliper mounting pin insulators and sleeves. Clean and lubricate with brake lubricant.

P12-9  Install a hose from the bleeder screw to the container. Open the bleeder screw.

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Photo Sequence 12 (continued)

P12-10  Use a C-clamp and wood (or the old inboard pad) to force the piston back into its bore. Just before the piston bottoms, close the bleeder screw.

P12-11  Close the bleeder screw just before the piston bottoms in the bore. Remove the C-clamp and check the piston boot. Install the new pads. If needed, install new mounting pins and sleeves.

P12-12  Set the caliper with its new pads onto the rotor and install the mounting pins. Check the assembly for proper position. Torque the pins to specifications.

P12-13  Install the tire and wheel and torque to specifications. Then press slowly on the brake pedal several times to set the brakes.

SERVICE TIP  Incorrectly installed clips, springs, and other hardware used to hold a disc brake pad to the caliper or the piston often cause a low brake pedal and the inability to bleed the hydraulic system properly. If the hardware is installed incorrectly, the pads may appear to fit and may stay in place but be out of position. Out-of-position pads often cause the caliper and piston to travel farther than normal to apply the brakes. This requires a greater-than-normal fluid volume in the caliper and more pedal travel to supply the extra fluid. All the air may be removed from the system by normal bleeding, but no amount of bleeding will cure the low pedal until the pads are installed correctly.

Pad Removal On most calipers, it is necessary (or at least convenient) to push the piston into the caliper bore to provide clearance between the linings and the rotor and to ease caliper removal. Before retracting the caliper piston, install a hose on the caliper bleeder screw and place the other end into a container partially filled with clean brake fluid. Then loosen the

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bleeder screw to relieve hydraulic pressure and prevent the return of dirty fluid back to the master cylinder during piston retraction. Verify that some brake fluid has been removed from the master cylinder to make room for any fluid that may be forced back from the retracting piston. If fluid has not been removed, do so now. WARNING  Brake fluid may be irritating to the skin and eyes. In case of contact, wash skin with soap and water, or rinse eyes thoroughly with water. WARNING  Wear safety glasses or face protection when using brake fluid. Injuries to the face and/or eyes could occur from spilled or splashed brake fluid.

Several methods may be used to retract caliper pistons. One method is to install a large C-clamp over the top of the caliper and against the back of the outboard pad (Figure 7-9). Slowly tighten the clamp to push the piston into the caliper bore far enough so that the caliper can be lifted off the rotor easily.

SERVICE TIP  The following three suggested methods for retracting the piston(s) should only be used to gain clearance for the old pads and caliper to slip off the rotor. Once the caliper is dismounted and the pads removed, the piston(s) should be fully retracted into the bore using a C-clamp as discussed earlier.

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If one pad is worn much more than its mate, suspect a sticking piston or slide mechanism on the caliper.

Special Tools Lift or jack with stands Hand tools C-clamp or small prybar

On some calipers, the piston can be forced back in its bore with a prybar placed between the inboard pad lining and the rotor prior to removal (Figure 7-10). On other calipers, large slip-joint pliers placed over the inboard side of the caliper and a tab on the inboard pad can be used to squeeze the piston into its bore (Figure 7-11). Care must be taken to prevent cocking the piston. On older, fixed-caliper brakes, prying the pistons back into their bores is the usual way to provide clearance for pad removal. Then the pads can be removed without demounting the caliper from the caliper support (Figure 7-12).

End of screw against outboard pad End of clamp against caliper

Figure 7-9  Use a C-clamp to retract the piston into the caliper bore.

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Chapter 7

Prybar

Caliper

Caliper support (anchor plate) Caliper Pad

Caliper-to-anchor mounting pin

Rotor Slip-joint pliers

Figure 7-10  Caliper pistons can be retracted with a prybar. Figure 7-11  Caliper pistons can also be retracted by squeezing them with large slip-joint pliers. Rotor

Pad

Caliper

Figure 7-12  Pads in the fixed caliper on some older vehicles can be removed with the caliper in place over the rotor. The large arrow is pointing to clips that hold the retracted piston(s) in place.

SERVICE TIP  Disc brake rotor and pad diagnoses complement each other. The pads cannot be evaluated separately from the rotor condition and vice versa. For example, if used pads are worn pretty thin and seem to be harder than most, check the rotors carefully for hot spots and checking. Hard, thin pads can act like cutting tools on the rotors.

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Figure 7-13  Some calipers can be rotated up on the upper mounting pin to replace the pads.

Some calipers can be rotated off the rotor on one guide pin, usually the top one (Figure 7-13). Remove the bottom pin and rotate the lower end of the caliper up. The pads can then be removed without completely removing the caliper from the vehicle. It is best, however, to either remove the upper pin or slide the caliper from the upper pin so the pin can be cleaned and lubricated.

Rear Caliper Retraction Rear brakes that utilize the drum-in-hat design can be pushed back with the same methods as the front brake calipers. Do not use a C-clamp, slip-joint pliers, or a prybar to retract the piston of a rear caliper with a parking brake mechanism that moves the piston to apply the parking brakes. Trying to force this kind of piston back into its bore against the parking brake mechanism usually damages the parking brake. Ford rear disc brakes of this type, for example, require a special tool to rotate the piston back into its bore on the automatic adjuster screw of the brake mechanism (Figure 7-14). If unfamiliar with a rear caliper parking brake, refer to the vehicle service information before trying to retract the caliper piston. There are several other tools available for retracting rear caliper piston. Some are easier to use than others. Some of the same tools can be used on front brake caliper for piston retraction. Remove the caliper bolts and sleeves from a floating caliper or the support keys from a sliding caliper. Then remove the caliper from the caliper support. It is not necessary to disconnect the brake hose from the caliper if the caliper is not going to be removed from the vehicle. Suspend the caliper from the vehicle underbody or suspension with a heavy length of wire or rope. Do not let the caliper hang from the brake hose. If the outboard pad is clipped to the caliper, pry it off with a prybar (see Figure 7-15) or tap it off with a small hammer. Inspect the pad hardware before removing the pads. The hardware must fit in a certain way and can be broken if forced. Also note the amount and type of hardware used. Many times the hardware consists of small pieces that can easily get lost if care is not exercised. Then remove the inner pad from the piston and the inner part of the caliper housing. Note the position of all springs, clips, shims, and other hardware used to attach the pads and to prevent noise. Inspect the mounting bolts and sleeves and other miscellaneous hardware for corrosion and damage. Inspect all rubber or plastic bushings for cuts and nicks. If any part is damaged, install new parts when the caliper is reinstalled. Do not try to polish away corrosion.

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Caution Prevent brake fluid from coming in contact with the vehicle’s finish. Brake fluid damages paint and finish immediately on contact. If fluid contacts the finish, wash area thoroughly with running water, using soap if possible.

Caution Do not depress the brake pedal when the pads are being removed, installed, or have been removed from the caliper. Without the pads positioned properly, the piston could be forced from the bore when the pedal is depressed.

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Chapter 7 Rotate clockwise until piston seats

3 8

in. rachet and extension

Caliper Drive nibs (2 or 4 per side)

Drive hole

Piston

Piston turning tool

Figure 7-14  One type of piston retracting tool. Clip

Caliper

Outboard pad

Figure 7-15  Some outboard pads can be pried off with a prybar.

SERVICE TIP  Tapered pad wear up to 1/8 inch is normal for some floating caliper disc brakes. Before installing new pads, compare wear on all four pads in an axle set.

Pad Installation A complete set of springs, clips, shims, and other miscellaneous pieces may be available as a pad hardware kit for popular brake assemblies. Installing such a kit is often a practical and economical choice when replacing pads or doing other caliper service. Some pad kits come with new hardware. If the pads appear serviceable, use a vernier caliper precision scale, outside micrometer, or other precision measuring instrument to measure the thickness of each brake pad lining (Figure 7-16). Compare the pad thickness against service manual specifications. For example, the standard brake pad thickness may be 0.50 inch (12.5 mm). The service

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Figure 7-16  If necessary, measure the pad to determine if it is serviceable or to compare wear between different pads on the same axle.

limit may be 0.060 inch (1.6 mm). This measurement does not include the pad backing plate thickness. If the lining thickness is close to or less than the service limit, replace all pads on both calipers as a set. From a practical standpoint, if the old pads are removed, it is unlikely that they will be reinstalled unless they are almost brand-new and undamaged. If the pads are serviceable, however, they can be reinstalled in their original positions only. Switching pad positions may reduce braking power. The pads must also be free of grease or brake fluid if they are to be reused. Replace contaminated brake pads and wipe any excess grease off the parts. Measuring pad thickness precisely as shown in Figure 7-16 can sometimes be helpful when troubleshooting brake pulling problems or abnormal pad wear. Before installing the new pads, wipe the outside of the piston dust boot with denatured alcohol. Use a C-clamp to bottom the piston in the caliper bore with the bleeder screw open, taking care not to damage the piston or the dust boot. Do not rush the piston. Apply slow, steady force and the piston(s) will slide in easily without cocking or building excessive pressure. Excessive pressure will blow brake fluid out of the reservoir or capture container and onto the finish. When the piston is bottomed in the bore, lift the inner edge of the boot next to the piston and press out any trapped air. The boot must lie flat. When specified in the vehicle service manual, apply any recommended noise suppression compound or shims to the backs of pads during reassembly to minimize noise (Figure 7-17). Some technicians prefer to use shims or compound on all pad installations. Others use shims or compound only when recommended by the pad manufacturer or carmaker. In all cases, shims and compound are antinoise devices and do not affect pad attachment to the caliper. Do not use both noise suppression compound and a shim on the same pad, unless directed by the manufacturer’s service manual or bulletin. It is also important to check for rust jacking. Rust developing between the metal backing pad and the brake lining causes rust jacking. The rust actually pushes the pad material away from the pad and can cause cracks in the pad material. If the replacement pads have audible wear sensors, the pad must be installed so that the sensor is at the leading edge of the pad in relation to wheel rotation. This does not mean at the top or front of the caliper. The rotor must contact the edge of the pad that holds the sensor first as the rotor rotates forward through the caliper; this is the pad

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Special Tool Vernier caliper or precision scale Always replace brake pads as a set. If the brake pads are wearing unevenly, check the calipers and mounting hardware for binding. Catch a leak early by looking under the dust boot mounted on the piston. Use a plastic pick to carefully pull the edge of the boot out just enough to check for moisture. Some vehicle manufacturers require that the hardware be replaced each time the pads are changed. It is usually best to replace the hardware unless the vehicle has low mileage and is on its first or second brake repair.

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Chapter 7 Noise suppression compound

Shim

Typical disc pads with a shim

Typical disc pads with noise suppressant applied

Figure 7-17  You can use noise suppression compound or a soft shim on the back of a brake pad to help reduce noise, but do not use both on the same pad.

There are several brands of brake lubricant on the market. Use a well-known brand and make certain that it is labeled as disc brake grease.

leading edge. If the vehicle has electronic lining wear sensors that light a warning lamp on the instrument panel, install the pads and sensors according to the manufacturer’s service manual procedures. Install the inboard pad and lining by snapping the pad retaining spring into the piston’s inside opening (Figure 7-18). The pad retainer spring is usually staked to the inboard pad. The pad must lie flat against the piston. After the pad is installed, verify that the boot is not touching the pad. If it is, remove the pad and reposition the boot. Install the outboard pad in the caliper and secure any locking tabs as necessary. The exact methods and parts used for pad installation vary with brake design (Figures 7-19 and 7-20). You may have to bend the retaining flanges or tabs of some pads to ensure secure attachment to the caliper. If you do not bend the retaining flanges, a rattle during may occur when the brakes are not applied. The pads can be snapped into place using a method shown in Figure 7-21, or with a large pair of channel locks. If you service one side of the car at a time, the opposite caliper is available as a guide for pad installation. On floating calipers, liberally coat the inside diameter of the bushings with brake lubricant before installing the mounting bolts and sleeves (Figure 7-22). For sliding Piston

Clip mounted to pad

Caliper

Move clip from old to new pad

Pad support spring

Variations of pad clips and spring

Figure 7-18  Many inboard pads have retainer springs that snap into the inner opening of the piston.

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Retainer flange

Outboard pad

Tab

Anvil

Figure 7-19  Many outboard pads have retaining flanges or tabs that snap around the outboard part of the caliper.

Figure 7-20  Bend the outboard pad retaining flange when required for secure attachment.

Used outer pad

Used inner pad

Caliper housing Bushing

New outer pad

Figure 7-21  Some outboard pads can be snapped into place with a C-clamp and a couple of old pads or pieces of wood.

Flexible seal boot

Lube exterior of bushing and bolt with brake lubricant

Figure 7-22  Lubricate the inside of the caliper bushing as highlighted here.

calipers, lubricate the caliper ways on the caliper support and the mating parts of the caliper housing with the recommended lubricant (Figure 7-23). Caliper ways may be known as caliper slides. This is where a sliding caliper slides on its support. After the new pads are installed and the calipers remounted on the caliper supports, add fresh brake fluid to the master cylinder reservoir to bring it to the correct level. Then start the engine without moving the vehicle and apply the brake pedal. The pedal probably will go to the floor as the caliper pistons move out to take up the clearance between the new pads and the rotors. Do not pump the pedal fast when seating the pads. Slow, smooth pumps fill the caliper bores without agitation and tend to extend the piston more smoothly. Recheck the brake fluid level and add more fluid as needed. Apply the pedal several more times until it becomes firm, and verify that the fluid is at the correct level. A four-wheel brake repair is an ideal time to flush the system. It is best to check for air anyway, and a few minutes more will replace all of the old fluid.

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Mounting bolt

Caution Before trying to move the vehicle, press the brake pedal several times to make sure the brakes work and seat the pads against the rotor. Bleed the brakes as necessary and then road test the vehicle.

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Chapter 7 Caliper support (anchor plate)

Caliper ways

Caliper housing

Caliper support spring

Retaining screw Caliper support

Figure 7-23  For a sliding caliper, lubricate the caliper ways, support spring, and the mating areas of the caliper housing, as highlighted here.

Theoretically, if the brake lines were not disconnected and the pistons were not removed from the calipers, air will not have entered the system and bleeding should not be necessary. It is good practice, however, to bleed the brakes to ensure that the hydraulic system is free of air and at least some of the contaminates that may be present in the fluid. If the pedal seems at all spongy or low after pad replacement, brake bleeding is required. If brake bleeding does not restore proper pedal action and brake performance, inspect the system thoroughly for leaks. The calipers may need to be removed and disassembled to check for corroded caliper bores and leaking seals that let air into the system. After proper pedal action is restored, recheck fluid level, turn on the ignition, and release the parking brake. Verify that the brake warning lamp on the instrument panel is not lit. On vehicles with rear brake rotors, make certain the parking brake releases properly; if it does not, the pads can become severely overheated. SERVICE TIP  Avoid the temptation to improve pad cooling by cutting a groove in new pad linings that were made without a groove. The manufacturer knows best. It did not groove the pad lining for a reason. Cutting a groove in the field can weaken the lining material and actually cause overheating because of the reduced contact area.

Road Test and Pad Burnishing Whenever new brake pads are installed, they need a short period of controlled operation that is called a burnishing or bedding in period. Burnishing polishes the pads and mates them to the rotor finish. Road testing the vehicle performs this burnishing procedure and verifies that the brakes work properly. WARNING  Road test a vehicle under safe conditions and obey all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to this precaution could lead to serious personal injury.

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New pads require burnishing to establish full contact with the rotor and to heat and cure any resin left uncured in the friction material. Whether the rotors were refinished or not, new pads do not initially make full contact with the rotor surfaces but require a period of light wear to establish this contact. Also, when brake linings are manufactured, some of the resin materials may remain uncured until the pads are put into service. If fresh pads are subjected to hard braking, the resins can boil to the surface of the pads and cause glazing when they cool. The pads then may never operate properly. Burnish the brake pads during the initial road test by driving at 30 mph to 35 mph (50 kph to 60 kph) and firmly but moderately applying the brakes to fully stop the car. Do this five or six times with 20 seconds to 30 seconds of driving time between brake applications to let the pads cool. Then drive at highway speeds of 55 mph to 60 mph (85 kph to 90 kph) and apply the brakes another five or six times to slow the car to 20 mph (30 kph). Again, allow about 30 seconds of driving time between brake applications to let the brake pads cool. Finally, advise the customer to avoid hard braking for the first 100 miles of city driving or the first 300 miles of highway driving.

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Burnishing or bedding in is the process of applying friction materials to each other to create a desired wear pattern.

DISC BRAKE CLEANING Disc brakes stay much cleaner than drum brakes. A disc brake is partly shrouded by the wheel, but it is largely exposed to circulating air. Dust and dirt created by pad wear and accumulated through normal driving are thrown off by the centrifugal force of the spinning rotor. Some brake dust accumulates inside the wheel and partially on the caliper. Proper and safe cleaning of brake assemblies and components is as important for disc brakes as it is for drum brakes.

Classroom Manual pages 160

SERVICE TIP  Excessive brake temperatures are usually associated with brake fade problems, but overheated brakes also can cause pulling or grabbing problems. For example, an overheated caliper piston can stick in its bore and cause the brake at one wheel to grab. Similarly, cheap brake linings of uncertain frictional coefficient can grab and pull when they get hot.

WARNING  Do not blow dust and dirt off brake assemblies with compressed air outside of a brake-cleaning enclosure. Airborne dust and possible asbestos fibers are an extreme respiratory hazard.

Vacuum enclosures and aqueous or water-based cleaning equipment are among the most popular for brake service and should always be used to clean brake assemblies and components. General-purpose parts washers also can be used to clean brake parts after they are removed from the car. Chapter 2 of this Shop Manual describes various kinds of brake-cleaning equipment and tools. Always ensure that cleaning equipment is in proper working condition and follow the manufacturer’s instructions for the specific equipment in your shop. Asbestos waste and other brake debris (dust) must be collected, recycled, and disposed of in sealed impermeable bags or other closed, impermeable containers. Any spills or release of asbestos-containing waste material from inside of the enclosure or vacuum hose or vacuum filter should be immediately cleaned up using vacuuming or wet-cleaning methods. Review the asbestos safety instructions in Chapter 1 of this Shop Manual. The following paragraphs contain general information about brake-cleaning equipment that

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can be used to clean the caliper and rotor while they are installed on the vehicle. A generalpurpose parts washer can be used to clean parts removed from the vehicle.

Cleaning with Vacuum-Enclosure Cleaning Systems

Special Tool Brake-cleaning tools/ equipment One of the simplest brake-cleaning tools is a hand-operated spray bottle filled with soapy water. Place a catch basin under the brake assembly and spray liberally. The waste water can be poured into a hazardous waste container for later disposal.

Special Tool Vacuum brake cleaner

Vacuum-enclosure cleaning and containment systems consist of a tightly sealed protective enclosure that covers and contains the brake assembly (Figure 7-24). The enclosure has built-in, impermeable sleeves and gloves that allow inspecting and cleaning of the brake parts while preventing the release of dust and potential asbestos fibers into the air. Examine the condition of the enclosure and its sleeves before beginning work. Inspect the enclosure for leaks and a tight seal. See Photo Sequence 2 in Chapter 2 for details. A high-efficiency particulate air (HEPA) filter vacuum is used to keep the enclosure under negative pressure as work is done. Because particles cannot escape the enclosure, compressed air can be used to remove dust and dirt from brake parts. Once the dirt is loose, draw it out of the enclosure with the vacuum port. The dust is then trapped in the vacuum cleaner filter. When the vacuum cleaner filter is full, spray it with a fine mist of water, then remove it and immediately place it in an impermeable container. Label the container as follows: WARNING  Brake material contains asbestos fibers. Avoid creating dust. Dust can create a cancer and lung disease hazard.

Cleaning with Wet-Cleaning Systems Low-pressure wet-cleaning systems wash dirt from the brake assembly and catch the cleaning solution in a basin (Figure 7-25). The cleaner reservoir contains water with a nonpetroleum solvent or wetting agent. To prevent any asbestos-containing brake dust from becoming airborne, control the flow of liquid so that the brake assembly is gently flooded. The solvent also is effective for removing brake fluid and oil or grease from brake parts. Some wet-cleaning equipment uses a filter. When the filter is full, first spray it with a fine mist of water, then remove the filter and place it in an impermeable container. Label and dispose of the container as described earlier.

Glovebag collection system

HEPA vacuum cleaner

Figure 7-24  This full-enclosure asbestos vacuum system traps brake dust and helps keep the shop’s air free of dust.

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Figure 7-25  Typical low-pressure, wet-cleaning equipment.

Cleaning with Vacuum-Cleaning Equipment Several types of vacuum-cleaning systems are available to control brake dust in the shop. The vacuum system must have a HEPA filter to handle asbestos dust (Figure 7-26). A generalpurpose shop vacuum is not an acceptable substitute for a special brake vacuum cleaner with a HEPA filter. After vacuum cleaning, wipe any remaining dust from components with a damp cloth. Because they contain asbestos fibers, the vacuum cleaner bags and any cloth used in asbestos cleanup are classified as hazardous material. Such hazardous material must be disposed of in accordance with OSHA regulations. Always wear your respirator when removing vacuum cleaner bags or handling asbestos-contaminated waste. Seal the cleaner bags and cloths in heavy plastic bags. Label and dispose of the container as described previously.

Special Tool Parts washer

Cleaning with Parts Washers Almost all shops have a parts washer that is used to clean miscellaneous small and medium-size parts that are removed from vehicles (Figure 7-27). The equipment reservoir holds solvent that is recirculated by an electric pump. A nozzle is used to apply solvent to parts, and heavy dirt can be loosened with a cleaning brush. Filters in the reservoir trap dirt and grease. Traditionally, parts washers have used petroleum solvent, but most current models use water-based solvents and detergents. Do not use petroleum-based solvents on rotors and drums. Cast iron is porous and will absorb the solvent. Solvent comes out during braking and will ruin new pads and shoes. A parts washer that uses only water-based solvents and detergents is usually safe for brake cleaning with no extra steps.

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Figure 7-26  A HEPA-equipped vacuum cleaner is a good tool for cleaning brake ­components.

Figure 7-27  Use a parts washer to clean the outside of calipers and similar dirty parts.

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BRAKE CALIPER SERVICE

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In the 1960s when disc brakes started to become standard equipment, brake calipers were overhauled routinely whenever pads were replaced. This is no longer a universal practice. When changing brake pads, however, the calipers should be inspected for damage, leakage, and general wear. Remember that a set of brake pads usually lasts at least 30,000 miles (48,000 km). If the technician does not overhaul or replace the calipers, he or she must be confident that the calipers will operate properly and safely until the next pad replacement. Generally, calipers are more likely to need overhaul or replacement if the car is 5 years old or older or has more than 50,000 miles (80,000 km) and the calipers have never been serviced. If the vehicle is driven hard or operated in very hot or cold temperatures, the calipers will need service sooner than calipers on a car used conservatively in a moderate climate. The details of caliper overhaul vary with caliper design, but all overhaul procedures share common principles. Photo Sequence 13 shows the major overhaul steps for a typical floating caliper. The following sections explain general guidelines and common steps that apply to most calipers.

Lift or jack with stands Impact tools C-clamp or small prybar Cloths Catch basin Syringe Classroom Manual page 171

Caliper Removal Much of the caliper can be inspected while it is mounted on the car, but it must be removed to closely examine the dust boot, the pistons and seals, and the mounting hardware, including bushings and sleeves. Removal procedures are different for different calipers, but the following are general guidelines. A brake hose can be attached to a caliper with a banjo fitting, a swivel fitting, or a rigid (non-swivel) fitting. If the hose is attached to the caliper with a banjo fitting or a swivel fitting, disconnect it from the caliper and be careful not to twist the hose as you loosen the fitting. Plug or cap the open end of the hose to keep dirt out of the brake lines. If the brake hose is attached to the caliper with a rigid fitting, disconnect the brake tubing from the hose at the hose mounting bracket and cap the end of the pipe to keep out dirt (Figure 7-28).

Do not forget to remove some of the brake fluid from the reservoir as needed.

Fitting

Retainer clip

Cap to prevent fluid loss, dirt entry

Brake hose

Figure 7-28  Cap or plug disconnected brake lines on the vehicles to keep out dirt.

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Photo Sequence 13

Typical Procedure for Rebuilding a Disc Brake Caliper

P13-1  Disconnect the brake hose from the caliper. Remove the caliper bolts, then remove the caliper completely from the vehicle and move to the workbench. Use a C-clamp to retract the piston fully. Aim the brake hose port toward a capture container.

P13-2  Inspect the bushings for cuts and nicks. Replace them if damage is found.

P13-3  Place a wooden block or shop rag in the caliper opposite the piston, then carefully remove the piston from the caliper by applying air pressure through the brake line hole.

P13-4  Remove the piston boot and seal, taking care not to damage the cylinder bore. Use a small wooden or plastic tool to remove the seal.

P13-5  Inspect for wear, nicks, corrosion, or damage.

P13-6  Use crocus cloth to polish out light corrosion. Replace the caliper if light polishing does not remove corrosion from around the seal groove.

P13-7  Clean the piston, caliper bore, and all parts with clean, denatured alcohol.

P13-8  Dry all parts with unlubricated compressed air. Blow out all passages in the caliper and the bleeder valve.

P13-9  Screw the bleeder valve and bleeder valve cap into the caliper housing. Tighten to specifications.

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Photo Sequence 13 (CONTINUED)

P13-10  Apply brake fluid to a new piston seal, and then install the piston seal in the cylinder groove. Make sure the seal is not twisted.

P13-11  Apply brake lubricant or brake fluid to a new piston boot, and then install the boot onto the piston.

P13-12  Lubricate the caliper bore and piston with brake fluid. Install the piston into the caliper bore and push it to the bottom of the bore.

P13-13  Seal the boot in the caliper housing counter bore using the proper seating tool.

P13-14  Lubricate the beveled end of the bushings with brake lubricant. Pinch the bushing and install it bevel end first into the caliper housing. Push the bushing through the housing bore.

P13-15  If desired, the caliper can be bench bled by using a hand-operated pressure bleeder. Pump new brake fluid through the hose opening until the fluid flows from the bleeder opening. Install the bleeder screw.

P13-16  Install new pads as shown in Photo Sequence 12. Then reinstall the caliper on the vehicle. Fill the master cylinder reservoir, seat the pads against the rotor, and bleed the system.

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WARNING  Do not place your fingers in front of the piston. Do not use high air pressure; use an OSHA-approved 30-psi nozzle instead. Cover the caliper with a shop towel to catch fluid spray. AUTHOR’S NOTE  Sometimes the right size plug may not be readily available. Try using the cap from a ballpoint pen. “Screw” the cap onto the flared or threaded fitting. The plastic cap will not damage the flare or threads and will work sufficiently as a plug.

Special Tool C-clamp or other tool to compress piston Note that any damage to the boot or any part of the caliper requires a rebuild at minimum.

Depending on the caliper design, clearance around the caliper installation, and the amount of pad wear, it may be easier to remove the pads before removing the caliper or to leave them installed and remove the complete assembly. If the pads are removed first, inspect the mounting hardware and set it aside for reinstallation or for closer examination and replacement. Remove clips and keys from sliding calipers and slide each caliper off its ways on the caliper support (Figure 7-29). Remove mounting pins or bolts from floating calipers and similarly slide each caliper off its caliper support (Figure 7-30). Inspect the mounting hardware for excessive wear, corrosion, and other damage. Remove all bolts holding a fixed (stationary) caliper to its support. Lift the caliper off the rotor and take it to a bench for further service. If this particular caliper design is new to the technician then she/he should work on the caliper for one side of the car at a time and use the caliper for the other side for assembly and installation reference.

Caliper Key

Locating screw

Mounting pin

Caliper support (anchor plate)

Caliper support

Caliper housing

Mounting pin

Mounting sleeve

Figure 7-29  On this sliding caliper, remove the locating screw and then drive the key out with a drift punch.

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Figure 7-30  Remove the mounting pins or bolts from a floating caliper.

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Caliper Inspection When replacing brake pads as explained previously in this chapter, inspect the calipers closely. Routine, preventive maintenance brake inspection is another important time to check the calipers. Inspection can be more thorough and complete if the calipers are off the car and the pads removed. Look at the following five areas and check for these conditions during complete caliper inspection: 1. Inspect the entire outside of the caliper body for cracks and other major damage. Replace any damaged caliper. 2. Inspect the piston dust boot closely for holes and tears. Be sure it is correctly installed in the piston and caliper and that no openings exist that could let dirt or water into the caliper bore. If the dust boot is damaged or defective in any way, replace or overhaul the caliper. 3. If the dust boot is okay, inspect the caliper closely for leakage. Any sign of leakage means that a piston seal is leaking and the caliper must be replaced or overhauled. WARNING  Wear safety glasses and take appropriate measures to keep brake from spraying or draining from calipers when retracting caliper pistons.

4. With the caliper off the car, use a C-clamp (Figure 7-31), large slip-joint pliers, or a hammer handle to slowly force the piston to the bottom of its bore. Be careful not to damage the dust boot or seal. Note how the piston feels as it moves. If it sticks or moves unevenly, remove the piston to check for rust and scoring. Refer to specific service manual procedures to retract the pistons on rear calipers with parking brake linkage attached to the pistons. 5. Inspect all caliper mounting parts for rust and damage. If a caliper passes these general checks and the vehicle is relatively new or has low mileage, it is reasonable to replace the pads without overhauling or replacing the calipers. If a caliper shows any signs of damage, excessive wear, or age, it should be replaced or overhauled. Just as pads are replaced in axle sets, calipers must always be serviced in pairs for each end of the vehicle.

Bleeder Screw Removal Before starting to overhaul any caliper, try to loosen the bleeder screw (Figure 7-32) with a bleeder screw wrench or a six-point socket. Bleeder screws often get stuck or frozen into Caliper

Screw of C-clamp inside of piston

Figure 7-31  Compress the piston into its bore while checking piston movement and the condition of the dust boot.

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Figure 7-32  Be sure the bleeder screw can be removed before proceeding further with caliper overhaul.

Special Tools Torch Penetrating oil Bleeder screw removal tool

Caution Do not apply heat to a caliper made of aluminum or other lightweight material. The caliper will be weakened at a minimum and destroyed in most cases.

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the caliper, particularly in aluminum caliper bodies or on cars driven on salted roads in the winter. A frozen bleeder screw is often a sign of extreme wear or age that immediately makes the caliper a candidate for replacement. If replacement calipers are not readily available, however, the frozen screw must be replaced to restore the caliper to proper operation. If the bleeder screw does not loosen easily with a wrench, do not continue to force it until it breaks. Many frozen screws can be loosened by applying penetrating oil to the outer threads and letting it work its way into the screw hole. Wait 10 minutes after applying penetrating oil and then place a short piece of pipe over the screw so that the pipe does not contact the screw but rests on the caliper body. Hit the pipe several times with a hammer to break the surface tension between the screw and the hole and to help the oil work into the threads. Repeat the penetrating oil and hammer steps several times and try to loosen the screw. There are special tools available to make this task much easier. WARNING  Do not apply heat to a sealed or semisealed hydraulic system. If heat must be applied to a caliper, remove the piston and fluid first. The port for the hydraulic line could act like a jet, spurting hot brake fluid out. Heat could cause a rupture and cause injury.

If the bleeder screw still will not turn, heat may help to loosen it. These steps should be completed with the caliper removed from the car and clamped in a bench vise. Remove the piston, fluid, and seals/boots. Heat the area of the caliper body around the screw with a torch and apply penetrating oil to the outer screw threads. Repeat this several times and try to turn the screw with a wrench. For a particularly stubborn bleeder screw, it may help to invert the caliper in the vise so that the screw is at the lowest point of the caliper. Ensure that some brake fluid is in the caliper bore and covers the inner end of the bleeder screw. Add an ounce or two through the hose connection port if necessary. Make sure the hose connection port is opened during heating. This will allow the pressure to escape. Once again, heat the caliper body. Brake fluid can work its way past the tip of the hot bleeder and into the inner threads to help loosen the screw. If the bleeder screw breaks or cannot be loosened by these methods, replace the caliper. If a replacement is not available, the broken screw can be drilled out and the caliper rethreaded. Because bleeder screws are made of hard steel and because of the awkwardness of the caliper, drilling and retaping should be done by a machine shop to ensure hole and new threads are “squared” to the caliper body.

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Caliper Piston Removal Caliper pistons fit in their bores with only a few thousandths of an inch of clearance so even a small amount of rust, corrosion, or dirt can make them hard to remove. Caliper pistons are rarely loose enough in their bores to remove them by hand, so three common methods are used for removal: compressed air, mechanical, and hydraulic. The following sections explain piston removal for single-piston calipers. WARNING  Wear safety glasses whenever removing caliper pistons. Keep your hands away from the piston when using compressed air or hydraulic pressure for removal. Cover the open hydraulic ports and the perimeter of the piston bore with clean shop cloths and take other necessary precautions to avoid spraying brake fluid. Clean up any spilled fluid immediately. Use a block or other device to prevent the piston from being explosively expelled from the bore.

Compressed Air Piston Removal.  Using compressed air to remove a caliper piston is probably the oldest and most common method. It requires several precautions, however. Compressed air removal works best on pistons that are somewhat free or only moderately stuck in their bores. Compressed air contains a lot of energy that is released suddenly when the piston pops free, and it is hard to control the amount of air pressure applied to the piston. If the piston is not restrained when it is loosened, component damage or personal injury can occur. Observe all precautions in the preceding and following warnings when using compressed air to remove a piston.

Special Tools Air pressure regulator OSHA-approved blowgun

WARNING  Never use full shop air to remove a piston from a caliper unless that is the only option available. A regulator should be used to apply air gradually. Do not exceed about 30 psi of air pressure without taking additional precautions for containing the piston. Serious injuries could occur as the piston exits the bore.

Follow these seven steps for compressed air piston removal: 1. Remove the caliper from the car, and clamp it securely in a bench vise by one of its mounting points. 2. Place a wooden block wrapped in shop cloths in the outer pad area. The block should be thin enough to let the piston move outward in its bore but thick enough to keep the piston from leaving the bore completely. 3. Cover the caliper with cloths as necessary to keep brake fluid from spraying during removal. Old brake pads could be used to contain the piston’s travel, but check to see if they are thick enough. 4. If an OSHA-approved safety nozzle that limits nozzle air pressure to 30 psi is available, use it as first choice to remove the piston. 5. If an OSHA-approved nozzle is not available but the air pressure can be regulated, start with about 30 psi and gradually increase line pressure. Use the lowest possible air pressure to loosen the piston. If regulated line pressure is not possible, apply air in short increments. Do not exceed normal maximum shop pressure of 90 psi to 100 psi. 6. Insert an air nozzle with a rubber tip into the brake hose port, and gradually apply air pressure (Figure 7-33). Keep your fingers away from the piston. 7. When the piston pops free, remove the air nozzle and the wooden block, and extract the piston the rest of the way by hand.

Special Tool Piston removal tool

Mechanical Piston Removal.  Mechanical piston removal is a method that uses a special tool to grip the inner bore or opening of the piston and then provides leverage to twist the piston out of the caliper. This method works best with pistons that are only mildly stuck

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Shop cloths

Caliper

Figure 7-33  Carefully pop the piston out of the caliper bore with compressed air. Cushion the piston with shop cloths and use the lowest air pressure possible.

in their bores. It is often the fastest way to remove multiple pistons from a caliper because when one of two pistons in one side of a caliper is removed, the fluid passages to that piston must be blocked to apply air pressure to the other piston. Follow these four steps for mechanical piston removal: Using a tool to remove the piston is the safest and should be tried first.

1. Remove the caliper from the car and clamp it securely in a bench vise by one of its mounting points. 2. Insert the removal tool into the piston opening and grip the inner surface of the piston securely (Figure 7-34). With a pliers-type tool, squeeze the handles tightly. With an expanding tool, turn the locking bolt until the tool grips the piston tightly.

Caliper

Brake piston pliers Piston

Figure 7-34  Use piston removal pliers to remove multiple pistons from a caliper.

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3. Rotate the piston while working it back and forth in its bore until it loosens and slides out of the caliper. 4. If the piston cannot be removed manually, use compressed air or hydraulic pressure. Hydraulic Piston Removal.  The most common way to use hydraulic pressure to remove caliper pistons is to use the vehicle brake system while the calipers are still connected to the brake lines. The vehicle hydraulic system can apply much more pressure than can shop compressed air, and it is easier to control that pressure through brake pedal application. Hydraulic removal requires no special tools and is relatively fast. It is a two-person operation, however. Vehicle hydraulic pressure cannot be used for piston removal if air is present in the lines or if the master cylinder is bypassing internally.

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Special Tools Cloths Coworker Blocking Catch basin

WARNING  Because hydraulic piston removal uses the vehicle brake system, you must take extra precautions to keep brake fluid from spraying or draining onto the vehicle finish or onto yourself. If a piston pops out of its bore with several hundred pounds of hydraulic pressure behind it, almost a pint of fluid will spray from the caliper and lines.

SERVICE TIP  If the piston is stuck so badly that other methods did not work, replace the caliper. Do not use hydraulics to completely remove a near-frozen piston. The danger is not worth any money that may be saved.

Follow these nine steps for hydraulic piston removal: 1. Check the fluid level in the master cylinder and add fluid if necessary. Ensure that reserve vacuum is available in the vacuum booster. 2. Raise the vehicle on a hoist or safety stands, and support it securely. 3. Remove both front or both rear calipers from the caliper supports, and hang them from the chassis or suspension with heavy wire. 4. Place a wooden block in the caliper opening that is thick enough to keep the piston from being ejected from its bore while still allowing piston movement. 5. Place large pans under the calipers to catch any fluid that may drain from the calipers. 6. Have an assistant gradually apply the brake pedal to force the pistons from their bores. If several pedal applications are needed to loosen the pistons, it may be necessary to add fluid to the master cylinder. 7. When the pistons are loosened from their bores and pressed against the wooden blocks, disconnect and cap the brake hoses, and remove the calipers from the vehicle. 8. Take the calipers to a work bench, and drain the brake fluid into a suitable container. 9. Remove the pistons from their bores by hand. If hydraulic pressure cannot loosen a severely stuck caliper piston, it is probably so badly rusted or corroded that the caliper assembly should be replaced. Special hydraulic service equipment is available to remove pistons with the caliper off the vehicle. Such equipment makes piston removal a one-person operation, independent of the vehicle hydraulic system.

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Mechanical removal tools can be used effectively on multiple-piston calipers, but they may not provide enough force to remove a badly stuck piston. If a set of fixed calipers must be overhauled, remember these tricks for piston removal:

SERVICE TIP  Use the hydraulic method to remove a piston with the caliper on the vehicle only if the piston seems to be free.

■■

■■

■■

■■

If the caliper can be separated into two halves, the pistons may be removed more easily from each side with air or hydraulic pressure or mechanical removal tools. Install a C-clamp onto each piston, or install blocks so that the pistons can move about half their lengths. This will allow the loosest piston to move and then stop so the other piston can be moved. Once all pistons have reached the blocks (C-clamps), install thinner blocks or loosen C-clamps and reapply pressure. This time when the pistons are stopped, remove the blocks (C-clamps). The pistons should now come out the remaining distance with hand force. If the pads can be removed while the calipers are installed on the car, more space will exist between the pistons and the rotor. Cover the rotor with shop cloths to protect its surface and use compressed air to pop the pistons out of the caliper. They will move far enough to loosen them, but the rotor will keep them from moving out of the bores completely so that they retain enough air pressure to loosen all pistons. With the caliper removed from the car, place a block of wood in the caliper that is thin enough to let the pistons loosen in their bores but thick enough to hold them in the bores. Then apply air pressure to loosen the pistons.

SERVICE TIP  Piston removal from fixed (stationary) calipers with two or four pistons requires some special techniques. If compressed air or hydraulic pressure is used, the loosest piston will come out first, and the caliper will no longer hold pressure.

Dust Boot and Seal Removal—Caliper Cleaning

Special Tools Catch basin Crocus cloth Denatured alcohol Brush

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After the piston is removed, remove the dust boot from the caliper. If the boot stays attached to the caliper, use a small prybar to remove it from its groove (Figure 7-35). If the dust boot is attached to the piston, remove and discard it. Use a wooden or plastic pick to remove the piston seal from the caliper bore (Figure 7-36). To avoid scratching the caliper bore, do not use a screwdriver or metal pick. Before discarding the old piston seal, examine its shape. If it is anything but a squarecut seal, remember the direction in which it was installed so that the new seal can be installed correctly. Sketch the seal shape if it helps to remember the correct installation direction. After the caliper is disassembled, clean it with brake-cleaning solvent or alcohol and a soft-bristled brush. Use a plastic Scotchbrite scouring pad to remove dirt and varnish from caliper bores. Do not use a wire brush on the caliper bore, the piston, or dust boot attaching points. A wire brush will scratch and nick caliper bore and piston surfaces, which will cause leaks after reassembly.

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Piston dust boot

Figure 7-35  Remove the piston dust boot from its groove in the caliper.

Piston seal

Figure 7-36  Use a wooden or plastic (not metal) pick to remove the piston seal from its groove.

Use crocus cloth lubricated with brake fluid to remove light rust, dirt, corrosion, or scratches from the caliper bore and the piston. Wash any areas cleaned with crocus cloth using brake-cleaning solvent or alcohol to remove all abrasive materials. If light corrosion cannot be removed from the caliper bore with crocus cloth, the bore can be honed, as explained later in this chapter. Heavy corrosion or rust or severe pitting and scratching on the piston or its bore indicate that the complete caliper should be replaced.

SERVICE TIP  Standard-use calipers are almost never honed. If honing is required, the best repair is caliper replacement. Hone only those calipers that cannot be replaced or are very expensive. Generally, the labor and warranty cost of honing are not worth the trouble to the shop or the customer.

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Caliper Internal Inspection

Special Tools Denatured alcohol Hone Vise

If the caliper appears serviceable after it is disassembled and cleaned, inspect the piston and the caliper bore closely. If there is any doubt about the serviceability of the caliper or piston, replace with a new caliper. Scratched or rusted calipers may be honed if necessary, but excessive honing may create too much clearance between the piston and the bore. In such a case, the caliper must be replaced. Inspect metal pistons for corrosion and scratching. Remember that the outside surface of the piston provides the sealing surface, so even minor scratches can create leakage. If the piston is chrome plated, make sure that the plating is not scuffed or flaked away. Similarly, the outer anodized surface of an aluminum piston must not be worn away. Replace any piston with a damaged surface finish. Inspect phenolic plastic pistons for cracks and chips. Phenolic is a thermosetting resin normally used to mold or cast plastics. This type of piston had problems during its first years of use. It has since been refined and works well in most instances. Generally speaking, a phenolic piston will not damage the caliper bore. Small surface chips or cracks away from sealing surfaces are acceptable, but the best choice is to replace any piston that has surface damage.

Caliper Honing and Piston Clearance Older fixed calipers that had pistons with stroking seals were routinely honed to provide a fresh, uniform sealing surface on the caliper bore. Single-piston, floating, or sliding calipers are not routinely honed because the caliper bore is not the sealing surface. After cleaning as explained above, a caliper bore can operate satisfactorily with light scratches or pits. Heavier corrosion, scratches, or pits often can be removed with a hone as follows:

Caution Do not use machining oil as a lubricant for honing. This oil promotes metal removal, and the caliper bore may become oversized quickly. Use only brake fluid as the honing lubricant.

1. Remove the caliper from the car and clamp it securely in a bench vise by one of its mounting points. 2. Install the proper size hone with fine-grit stones in a variable-speed electric drill. 3. Lubricate the bore and the hone with clean brake fluid. 4. Insert the hone in the bore, and operate the drill at about 500 rpm. 5. Move the hone at moderate speed back and forth in the bore but do not let the hone come completely out of the bore while the drill is running. 6. After about 10 seconds, stop the drill and remove the hone. 7. Wipe the bore with a clean cloth, and inspect it to see if it has been cleaned satisfactorily. 8. Repeat the honing operation until corrosion, scratches, and pits are satisfactorily removed. 9. After honing the bore, clean it thoroughly with brake-cleaning solvent, alcohol, or fresh brake fluid. If alcohol or brake-cleaning solvent is used, make a final cleaning pass with brake fluid. Be sure to remove all abrasive materials from the seal groove and fluid passages. Honing the bore of a floating or sliding caliper is a cleaning procedure, not a machining procedure for a sealing or bearing surface. Hone the bore only enough to remove the worst corrosion and surface wear. Piston clearance is more important than the final surface finish of the bore. Generally, the maximum piston-to-bore clearance is 0.002 inch to 0.005 inch (0.06 mm to 0.13 mm) for metal pistons and 0.005 inch to 0.010 inch (0.13 mm to 0.26 mm) for phenolic pistons. Refer to the specific vehicle service manual for exact specifications. After cleaning the honed bore, lubricate the bore and piston with fresh brake fluid. Then insert a feeler gauge with a thickness of the maximum allowable clearance into the bore. Try to insert the piston into the bore next to the feeler gauge. If the piston slides into

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the bore, the clearance is too great. Double-check the fit with a new piston, or measure the piston and bore diameters with micrometers to be sure. If clearance exceeds specifications, replace the entire caliper assembly.

Caliper Assembly After cleaning and inspecting the caliper and ensuring that it is suitable for overhaul, obtain any replacement parts that are needed, along with new seals, dust boots, and miscellaneous small parts. Assemble the caliper on a clean workbench, and be sure that your hands and tools are clean and free of grease and oil. Follow these six steps to assemble most floating or sliding calipers: 1. Lubricate the piston seal and the seal groove in the caliper bore with fresh brake fluid. If the seal is any shape other than square cut, be sure it is installed in the proper direction. Square-cut seals can be installed with either side facing in either direction. 2. Insert one edge of the seal in its groove and guide it into place by hand (Figure 7-37). Be careful not to twist, roll, or nick the seal. 3. Lubricate the piston and the caliper groove for the dust boot with fresh brake fluid (Figure 7-38). Ensure that the piston enters the caliper bore smoothly. Keep the piston square in the bore as it is being inserted into the bore. 4. If the dust boot attaches to the piston, install the boot as shown in Figure 7-39 and Figure 7-40. 5. Attach the dust boot to the caliper by one of the following three general methods, depending on dust boot design: A. If the dust boot is a press fit into the caliper, slide the piston into the dust boot and caliper bore until the boot snaps into its groove in the piston (Figure 7-41). Then drive the boot into place with the proper driver (Figure 7-42). B. If the dust boot is held in the caliper by a retaining ring, slide the piston into the dust boot and caliper bore until the boot snaps into its groove in the piston. Then push the outer edge of the boot into its groove in the caliper body. Ensure that the boot is seated correctly, and install the metal lock ring to hold it in the groove.

Caliper Press seal into place with finger

Piston Apply light coat of silicone grease to these areas before installing dust boot

Figure 7-37  Lubricate a new piston seal and install it by hand in the caliper.

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Piston seal

Figure 7-38  Lubricate the dust boot groove in the caliper.

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Caliper piston Slide dust boot downward over piston

Fold dust boot upward until it “snaps” into place Caliper piston

Figure 7-40  Then fold the boot back upward until it is in this position. Figure 7-39  Install a new dust boot on the piston and pull it downward, inside out.

Boot installer tool

Dust boot

Caliper piston

Figure 7-41  Slide the piston and boot into the caliper bore.

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Dust boot

Figure 7-42  Using the proper size driver, tap the dust boot into its retaining groove in the caliper.

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C. If the dust boot is retained by a lip that fits in a groove in the caliper bore, obtain special installation rings to make the job easier. Slide the boot over the correctly sized ring. Install the lip of the boot in the caliper groove; then slide the piston through the ring and boot into its bore. Remove the ring from the piston so that the inner lip of the dust boot snaps into the piston groove. 6. After the piston and dust boot are installed, finish assembling the caliper by following the steps for pad installation given earlier in this chapter.

SERVICE TIP  Some caliper rebuilding kits contain silicone lubricant for the seals and dust boots. If supplied, use this to lubricate the seal and boot during installation. The silicone lubricant improves corrosion protection in these areas.

Caliper Installation Refer to the caliper removal guidelines earlier in this chapter before installing a new or overhauled caliper. Installation is basically the opposite of removal, but vehicle service is never quite that simple. A few different steps always exist. Installation procedures are different for different calipers, but technicians should follow these general guidelines. Depending on the caliper design and clearance around the caliper installation, it may be easier to install the pads before or after caliper installation. If installing the pads first, be sure that all antirattle springs and clips are in place and that any necessary antinoise compound is applied. One of the most important points of caliper installation is lubrication of all moving parts on sliding or floating calipers. Apply the carmaker’s recommended brake lubricant to contact points on caliper surfaces and on the caliper ways. Lubricate sleeves and bushings of floating calipers according to the manufacturer’s directions. On all caliper installations, be sure to keep lubricant off rotor and pad surfaces. Install clips and keys on sliding calipers and slide each caliper onto its ways on the caliper support. Install mounting pins or bolts for floating calipers, and tighten all bolts to the specified torque with a torque wrench. Do not guess about brake fastener tightness. Install all bolts holding a fixed (stationary) caliper to its support. When installing a banjo fitting, check it for sealing washers. If equipped with washers, replace them with new washers. Connect the brake hose to the caliper, being careful not to twist the hose as you tighten the fitting.

SERVICE TIP  Some manufacturers and some technicians recommend bench bleeding the rebuilt or new caliper before installation. A hand-operated pressure bleeder can be used for this task. Remove the bleeder screw and hold the caliper over a capture container with the bleeder opening on top. Pump brake fluid through the hose fitting until it comes out of the bleeder opening. Plug the hose fitting and then install the bleeder screw. This does not remove the requirement to bleed the system on-vehicle, but it reduces overall time. On some calipers, it will save a lot of time because of the close area around the mounted caliper.

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ROTOR SERVICE Brake rotors are not routinely resurfaced as part of every brake job, as they were many years ago. Rotor service is still an important part of disc brake service, however, because maximum braking performance cannot be obtained with a rotor that is damaged or defective. Rotor service consists of these general operations: ■■ Rotor inspection ■■ Rotor measurement ■■ Rotor resurfacing or turning ■■ Rotor finishing

Rotor Inspection Inspect disc brake rotors (Figure 7-43) when the pads or calipers are serviced or when the wheels are rotated or removed for other work. Many rotor problems may not be apparent on casual inspection. Rotor thickness, parallelism, runout, flatness, and depth of scoring can be measured only with precision gauges and micrometers. Other rotor conditions should be checked with equal precision and thoroughness. After removal of the caliper, inspect a rotor using the following procedure: 1. If the rotor is dirty enough to interfere with inspection, clean it with a shop cloth dampened in brake-cleaning solvent or alcohol. If the friction surface is rusted, remove the rust with medium-grit sandpaper or emery cloth, and then clean with brake cleaner or alcohol. 2. Turn the rotor through a full revolution to view the inboard surface at an accessible point, usually in the area where the caliper was mounted. 3. Inspect both rotor surfaces for scoring and grooving. Scoring or small grooves up to 0.010 inch (0.25 mm) deep are usually acceptable for proper braking performance (Figure 7-44). To determine the depth of grooves and whether or not the rotor can be resurfaced within its thickness limits, use a brake (rotor) micrometer with a pointed anvil and spindle designed for this use. Rotor measurements are described in the next section. 4. Inspect the rotor thoroughly for cracks or broken edges. Replace any rotor that is cracked or chipped, but do not mistake small surface checks in the rotor for structural cracks. Surface checks will normally disappear when a rotor is surfaced just a

A

Figure 7-43  Rotor inspection begins before removing the rotor from the vehicle.

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B

C

Figure 7-44  The small grooves on rotor A are less than 0.010 inch (0.25 mm) and acceptable for continued use. Rotor B has deeper scoring and requires refinishing if the thickness allows. Rotor C has extreme taper and probably will not stand refinishing.

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Figure 7-45  Some typical rotor defects to check for.

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Figure 7-46  The groove in this rotor surface is machined to aid in cooling and noise reduction. Heat checking appears as small cracks in the surface of the rotor.

few thousandths of an inch. Structural cracks, however, can become more visible when surrounded by a freshly turned rotor surface. 5. Inspect the rotor surfaces for heat checking, which appears as many small interlaced cracks on the surface (Figure 7-45). Heat checking lowers the heat dissipation ability and friction coefficient of the rotor surface. Heat checking is more noticeable than minor surface checking and does not disappear with resurfacing. 6. Also inspect the surfaces for hard spots, which appear as round, shiny, bluish areas on the friction surface as shown in Figure 7-45. It may be possible to machine hard spots out of a rotor if the rotor has not been turned previously and has enough thickness for extended machining. Hard spots are difficult to machine, however, and may require special cutting bits for the brake lathe. Because of the difficulty and uncertainty involved in machining a rotor with hard spots, most carmakers recommend replacing a rotor with this kind of damage. 7. Inspect the fin areas of vented rotors for cracks and rust. Rust in cracks near the fins can cause the rotor to expand and lead to rotor parallelism, or thickness, variations and excessive runout, or even exploding the rotor. Machining the rotor may remove runout and thickness variations, but rotor expansion due to rust may cause these problems to reappear soon. Replacing rotors with rust damage of this kind can avoid service comeback problems. Some older rotors designs have a single deep groove manufactured into each surface (Figure 7-46). This groove helps to keep the pads from moving radially outward and reduces operating noise. If a brake rotor passes this preliminary inspection, proceed to measure it as explained in the following sections. A rotor cannot be returned to service or resurfaced if it does not meet all thickness specifications.

Rotor Measurement Various micrometers and dial indicators are needed to measure a rotor. A micrometer is used to measure rotor thickness and parallelism, as well as taper. Parallelism is achieved when both sides of the rotor are exactly parallel to each other. Loss of parallelism happens during normal wear and tear. A dial indicator is used to measure rotor runout. Some rotors require an additional surface depth measurement.

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Caution Ensure the fitting is not cross-threaded when reconnecting. Cross-threading could damage the fitting or the component, or both.

Caution Use the correct fastener torque and tightening sequence when installing components. Incorrect torque or sequencing could damage the fastener(s) or components.

Caution Do not use paint, lubricants, or corrosion inhibitors on fastener(s) unless specified by the manufacturer. Add-on coating of any type may affect torquing, clamping, or may damage the fastener(s). Parallelism means that the surfaces of the rotor are parallel to each other. Thickness variations or taper in the rotor cause a loss of parallelism.

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SERVICE TIP  If the brake hose was disconnected from the vehicle’s brake line, it is easiest to connect the hose to the line before connecting it to the caliper. This allows the hose to be “wiggled” so the fitting threads are more easily aligned. The typical brake fitting can be easily damaged by not aligning the matching threads properly and attempting to tighten the fitting with a wrench. This method does not apply to a hose with a male fitting that screws into the caliper opening. There are two methods that can be used in that case. The first is to connect the hose to the line as noted above and then rotate the caliper like a nut so it screws onto the hose. This may not properly position the hose without some twisting once the caliper is installed on the vehicle, however. The best method with a malefitted hose is to screw it into the caliper opening and torque the hose to specification. Then use care in aligning and connecting the hose to the line on the vehicle.

When the discard dimension of a rotor is reached, it must be removed from service. The resurfacing dimension must be .015 to .030 wider than the discard dimension to allow for wear.

If unsure about the resurfacing limits or replacement requirements for any rotor, check the vehicle service information.

Rotor Thickness and Parallelism.  All brake rotors should have a discard-thickness dimension cast into them (Figure 7-47). If a discard dimension cannot be found on a rotor or if it is hard to read, check a service information for thickness specifications. The discard dimension seems like a simple specification, but you must understand its complete meaning and how to apply it to rotor service. A third measurement or specification that is of more importance to the technician than the discard dimension is the maximum refinishing limit. If the rotor measures less than the refinishing limit, then the rotor is discarded. On newer vehicles, this limit is not very much smaller than the standard thickness. See Table 7-1, which was quoted from the 2012 Buick Enclave service information for rear disc rotors. Most vehicle manufacturers are listing rotor refinishing limits in their service information. Rotor discard-thickness dimensions or refinishing limits are given in two or three decimal points (hundredths, thousandths, or ten-thousandths of an inch or hundredths of a millimeter), such as 1.25 inch, 1.375 inch, 0.750 inch, or 24.75 mm. When measuring rotor thickness, subtract 0.015 inch to 0.030 inch (0.40 mm to 0.75 mm) to allow for wear after the rotor is returned to service. If resurfacing the rotor, it must similarly be 0.015inch to 0.030-inch thicker than the discard dimension after surfacing to allow for wear. A rotor should not be returned to service, with or without resurfacing, if its thickness is at or near the refinishing limit.

Figure 7-47  The discard dimension, or minimum thickness specification, is cast or stamped into all disc brake rotors.

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Table 7-1  ROTOR SPECIFICATION

Brake disc thickness: Standard: New rotor thickness 29.0 mm (1.14 inches) Maximum refinishing limit: 27.7 mm (1.09 inches) Maximum scoring depth 1.5 mm (0.959 inches)

Rotor parallelism refers to thickness variations in the rotor from one measurement point to another around the rotor surface. Thickness variations and excessive rotor runout are the major causes of brake pedal pulsation. Thickness variation, or parallelism, is measured at the same time as basic rotor thickness. Use a micrometer graduated in ten-thousandths of an inch or hundredths of a millimeter to measure rotor thickness as follows: SERVICE TIP  Give your customers a short course in brake noise that is easy to understand and that will make them more responsible car owners. Explain that a low-pitched grinding or rumble during braking is often the metal-to-metal sound of worn pads or shoes grinding away the rotors or drums. A shrill screech that sounds like fingers being dragged across a chalkboard is usually a pad wear indicator telling the driver that it is time for brake service. Some motorists have the idea that light squeaks and squeals are normal. If squeaky brakes develop suddenly where no noise had been present before, however, it can mean that the pads are wearing down toward the replacement point. A thick new pad may not vibrate at an audible frequency, but the vibration frequency can change and produce noise when the pad wears.

1. Raise the vehicle on a hoist or safety stands and remove the wheels. If the rotor is removable from the hub (a floating, two-piece rotor), place flat washers on all wheel studs and reinstall the wheel nuts. Torque the nuts to specifications in the specified tightening pattern to minimize any possible runout (Figure 7-48). 2. If the caliper must be removed to measure the rotor, hang it from the underbody or suspension with heavy wire so it will not drop. Do not let the caliper hang from the brake hose. 3. Place an outside micrometer or a brake micrometer about 1/₈ inch (10 mm) in from the outer edge of the rotor and measure the thickness (Figure 7-49). Compare the measurement to specifications. 4. Also check the vehicle service manual for an allowable thickness variation. Many carmakers hold tolerances on thickness variations as close as 0.0005 inch (0.013 mm). 5. Repeat the measurement at about eight points, equidistant (45 degrees) around the surface of the rotor, and compare each measurement to specifications (Figure 7-50). Take all measurements at the same distance from each edge so that rotor taper does not affect measurement comparisons. If the rotor is thinner than the minimum thickness at any point or if thickness variations exceed limits, the rotor must be replaced. 6. If the rotor is deeply grooved, it must be thick enough to allow the grooves to be completely removed without turning the rotor to less than its minimum thickness. To measure the depth of the grooves on both sides of the rotor, obtain a micrometer with a pointed anvil and spindle. Measure rotor thickness to the bottom of the deepest grooves in about eight places. If rotor thickness at the bottom of the deepest grooves is at or near the discard dimension, replace the rotor.

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Figure 7-48  Reinstall the wheel nuts in the specified pattern to hold a hubless rotor on the hub or axle flange for measurement. Attach dial indicator clamp to steering knuckle Dial indicator Measure 8–12 points Micrometer

X

X X

X

Figure 7-49  The rotor and hub runout is measured with a dial indicator mounted to some fixed point on the vehicle (left). The rotor thickness and parallelism can be measured with a standard outside micrometer, as shown on the right, but is more easily done with an electronic brake micrometer.

Micrometer

Figure 7-50  Check for thickness variations by measuring at 8 to 12 points around the rotor.

Rotor Lateral Runout.  Excessive rotor lateral runout causes the rotor to wobble from side to side as it rotates (Figure 7-51). This wobble knocks the pads farther back than normal, which causes the pedal to pulse or vibrate as it is applied. There may be an increase in brake pedal travel because the pistons must move a greater distance to contact the rotor surface. For best brake performance, lateral runout should be less than 0.003 inch

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Pad Caliper

Piston Rotor

Figure 7-51  Excessive lateral runout of the rotor knocks the piston back into its bore and causes pedal pulsation and increased pedal travel.

(0.08 mm) for most vehicles. Some manufacturers, however, specify runout limits as small as 0.002 inch (0.05 mm) or as great as 0.008 inch (0.20 mm). Runout measurements are taken only on the outboard surface of the rotor. Using a dial indicator and suitable mounting adapters, measure runout as follows: SERVICE TIP  There is a special tool available to check parallelism at the rotor. The tool is U-shaped with a dial indicator plunger forming one side of the U. Placing the tool on the rotor and rotating the rotor through the tool causes the dial indicator needle to deflect back and forth from zero. The amount of deflection is the amount of warpage.

1. Raise the vehicle on a hoist or safety stands and remove the wheels. If the rotor is removable from the hub (a floating, two-piece rotor), place flat washers on all wheel studs and reinstall the wheel nuts. Torque the nuts to specifications to remove looseness from runout measurements. 2. If the caliper must be removed to measure runout, hang it from the underbody or suspension with heavy wire so it will not drop. 3. If the caliper is not removed but the rotor drags heavily on the pads as it is rotated, remove fluid from the master cylinder, and push the pistons back in the calipers as explained previously in this chapter. 4. If the rotor is mounted on adjustable wheel bearings, readjust the bearings to remove bearing end play from the runout measurements. Do not overtighten the bearings. Bearing end play is the amount of preload applied to the bearing. Preload is the bearing with the right amount of tension to prevent side-to-side movement and wobble but allows the bearing and its supported device to spin free. Bearing adjustment instructions are in Chapter 3 in this Shop Manual. On rotors bolted solidly to the axles of front-wheel drive (FWD) cars, bearing end play is not a factor in rotor runout measurement. If excessive bearing end play is noted, the hub assembly

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Special Tools Outside micrometer or vernier caliper Service manual Parallelism is the thickness uniformity of a disc brake rotor; both rotor surfaces must be parallel with each other within 0.001 inch or less. Discard dimension is the minimum thickness of a brake rotor or the maximum diameter of a drum.

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Figure 7-52  The dial indicator can be mounted in several ways as long as the face remains stable.



Special Tools Dial indicator Lift or jack with stands Impact tools Service manual



or the bearings must be replaced. Bearing end play is best checked with a dial indicator set up to measure wheel wobble. 5. Clamp the dial indicator support to the steering knuckle or other suspension part that will hold it securely as you turn the rotor (Figure 7-52). 6. Be sure the rotor surface is free of dirt and rust in the area where you will place the dial indicator tip. 7. Position the dial indicator so that its tip contacts the rotor at 90 degrees. Place the indicator tip on the friction surface about midway between the inner and outer edges of the friction area of the rotor. Do not place the dial indicator in a grooved or scored area. 8. Turn the rotor until the lowest reading appears on the dial indicator; then set the indicator to zero. 9. Turn the rotor through one complete revolution and compare the lowest to the highest reading on the indicator. This is the maximum runout of the rotor. If the dial indicator reading exceeds specifications, resurface or replace the rotor.

SERVICE TIP  You can use a dime to make a simple check. Place the dime into the groove with Roosevelt’s head toward the scored groove. If the dime goes into the groove far enough that the top of his head disappears, the groove exceeds 0.060 inch and may need to be resurfaced or replaced.

Special Tools Depth micrometer Ford’s special rotor gauge Service information

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If the rotor is a floating type, try repositioning it on the hub one or two bolt positions from its original location and repeat the runout measurement. If repositioning a floating rotor fixes an excessive runout condition, make index marks on the rotor and hub so that the rotor will be installed in the correct position. If the rotor is mounted on nonadjustable wheel bearings that have any amount of end play, this end play must be accounted for in rotor runout measurements. To make this measurement, press in on the rotor and turn it to the point of the lowest dial indicator reading. Set the indicator to zero, and pull outward on the rotor. Read the indicator, which now shows the amount of bearing end play. Then turn the rotor to the point of the highest reading and pull outward. Subtract the end play reading from the reading at this point to determine runout of the rotor alone.

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0

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0 1 2 3 4 5

15.1 mm (0.597 in.)

5

Disc Brake Service

Rotor surface gauge and ball

Rotor

54.0 mm dia. (2.125 in.)

Figure 7-53  A special gauging with a depth micrometer and a gauge ball is needed to ensure the inner surface depth of a rotor.

Rotor Friction Surface Depth Measurement.  Ford Motor Company and others call for an additional rotor measurement after the rotor has been removed for resurfacing. This measurement indicates how much metal can be safely removed from the inboard surface of the rotor. It requires a depth micrometer and a special gauge. One-piece rotor and hub assemblies use a ball-type gauge (Figure 7-53); removable (floating) rotors use a pyramid-shaped template. With the rotor off the vehicle, remove the grease seal and inner bearing from a onepiece rotor. Place the gauge ball or template inside the rotor. Ensure that the inboard friction surface is clean and place the depth micrometer on the surface with the spindle centered over the gauge. Set the micrometer to the initial setting given in the vehicle service manual. Then turn the micrometer until the spindle contacts the gauge. The difference between the initial reading and the reading with the micrometer touching the gauge is the maximum amount of metal that can be removed during resurfacing. If the micrometer contacts the gauge at the initial setting or if you must retract the micrometer to place both legs flat on the friction surface, the rotor cannot be safely resurfaced according to Ford. SERVICE TIP  Manufacturers try to hold rotor thickness variation to less than 0.002 inch. A rotor machined to this tolerance will wear evenly with little or no thickness variation during its service life. When initial thickness variation exceeds 0.008 inch, rotor wear will be rapid and uneven.

Removing a Rotor To remove a rotor from the vehicle, raise the vehicle on a hoist or safety stands and remove the wheel and tire. Remove the caliper from the rotor and suspend it from the vehicle underbody as explained earlier in this chapter.

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Caliper with pads

Knuckle

Figure 7-54  Remove a floating (two-piece) rotor from the mounting flange.

Before removing a rotor, mark it “L” or “R” for left or right so that it gets reinstalled on the same side of the vehicle from which it was removed. It is advisable to place alignment marks on the rotor and hub also. If the rotor is a two-piece floating rotor, index the rotor and hub, then remove it from the hub by pulling it off the lug studs (Figure 7-54). If it cannot be pulled off by hand, apply penetrating oil on the front and rear rotor-to-hub mating surfaces. Strike the rotor between the studs with a rubber or plastic hammer. If this does not free the rotor, attach a three-jaw puller to the rotor and pull it off. When separating a floating rotor from its mounting flange, clean any rust or dirt from the mating surfaces of the hub and rotor. Neglecting to clean rust and dirt from the rotor and hub mounting surfaces before installing the rotor will result in increased rotor lateral runout, leading to premature brake pulsation and other problems. If the rotor and hub are a one-piece assembly, remove the outer wheel bearing and lift the rotor and hub off the spindle. Be careful not to hit the inner bearing on the spindle when removing the hub. SERVICE TIP  Sometimes a ball-peen hammer works better in loosening a rotor than a plastic or rubber one. However, before swinging that hammer, install the wheel nuts onto the studs so the threaded ends of the studs are protected. A misaimed strike with the hammer will ruin a stud with additional cost in time and parts. This would be a time when the shop and technician picks up the tab.

Installing a Rotor WARNING  Always check ventilated rotors prior to installing them on the vehicle. Installed on the wrong side of the vehicle, they will cause rapid heat buildup during braking and will damage or destroy the rotor.

New rotors come with a protective coating on the friction surfaces. To remove this coating, use carburetor cleaner, brake cleaner, or solvent recommended by the carmaker. Whether the original or refinished rotor or a new rotor is being reinstalled, sand the rotor surfaces with 80-grit to 150-grit aluminum oxide sandpaper, as recommended by the carmaker. After sanding the rotor, wash it with denatured alcohol; then do not touch the surface with your hands.

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Six-nut wheel

Figure 7-55  Tighten wheel nuts in the specified sequence to the specific torque value.

Sanding a rotor establishes a nondirectional finish on the surface that will not start a premature wear pattern on the pads. The nondirectional sanded surface also helps pad break in and reduces brake noise. If the rotor is a two-piece floating rotor, make sure all mounting surfaces are clean. Apply a small amount of silicone dielectric compound to the pilot diameter of the disc brake rotor before installing the rotor on the hub. Reinstall the caliper as explained in the caliper rebuilding procedures. Install the wheel and tire on the rotor and torque the wheel nuts to specifications, following the recommended tightening pattern (Figure 7-55). Failure to tighten in the correct pattern may result in increased lateral runout, brake roughness, or pulsation. If the rotor is a fixed, one-piece assembly with the hub that contains the wheel bearings, clean and repack the bearings and install the rotor as explained in Chapter 3 of this Shop Manual. After lowering the vehicle to the ground, pump the brake pedal several times before moving the vehicle. This positions the brake linings against the rotor. If so equipped, turn the air suspension service switch back on before starting the engine. SERVICE TIP  Hub and rotor mating areas can be cleaned with an electric drill and a special wire brush tool. See Figure 7-62 and Chapter 2 of this Shop Manual for the details of this tool.

SERVICE TIP  Rotor runout and thickness variation, or lack of parallelism, work together to cause pedal pulsation and premature rotor wear. Runout causes the high spot on the rotor to hit the pads harder than the other rotor areas, which causes rotor thickness to wear unevenly.

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Preventing Runout and Thickness Problems Runout and thickness, or parallelism, problems can compound each other. For example, excessive runout causes the high spot of the rotor to hit the pad harder each time it rotates with the brakes off, which, in turn, causes the high spot to wear faster, gets much hotter, and leads to a parallelism problem. To avoid—or at least reduce—runout and parallelism problems, observe these guidelines during various steps of rotor service: ■■ Measure rotor runout before removing the rotor from the vehicle, and measure it again after mounting the rotor on a bench lathe. Runout should be the same on the vehicle and on a bench lathe. If it is not, machining may actually add runout to the rotor. ■■ Check the runout of a bench lathe arbor frequently. As little as 0.002 inch of runout in a lathe arbor can add runout to a rotor during machining. ■■ Do not overtighten the rotor mounting on a bench lathe arbor. Overtightening the mounting can add runout during machining; tighten by hand. ■■ If bearing races are to be replaced in a hub-type (one-piece) rotor, replace them before machining the rotor, not after. ■■ Re-indexing a hub-less or floating rotor on a wheel hub may reduce runout. ■■ A lightweight hub used with a hub-less or floating rotor can actually warp and acquire runout. If such a problem is suspected, remove the rotor and measure runout of the hub mounting surface while the hub is on the vehicle.

REFINISHING BRAKE ROTORS Brake rotors should be refinished only under the following conditions: ■■ If the rotor fails lateral runout or thickness variation checks ■■ If there is noticeable brake pulsation ■■ If there are heat spots or excessive scoring that can be removed by resurfacing ■■ If the rotor exceeds refreshing limits It is not necessary to refinish rotors as a matter of habit during brake service. WARNING  Wear safety glasses or face protection when using machining equipment. Injuries to the face or eyes could occur from flying chips of metal.

The minimum thickness specification for all brake rotors is the discard dimension. Do not use a brake rotor that does not meet these specifications. A refinished rotor must be thicker than its discard dimension. Refer to the service manual for exact specifications. A rotor that has been refinished too thin will not have proper heat transfer capabilities and should be replaced. WARNING  Do not attempt to use a brake lathe without training. The minimum training is studying the lathe’s operator manual. Serious injury or damage could occur if the lathe is improperly set up.

When refinishing a rotor, remove the least amount of metal possible to achieve the proper finish and parallelism, which helps to ensure the longest service life from the rotor. Never turn the rotor on one side of the vehicle without turning the rotor on the other side. Left- and right-side rotors should be the same thickness, generally within 0.002 inch to 0.003 inch. Similarly, equal amounts of metal should be cut off both surfaces of a rotor. This is particularly critical on rotors used with stationary, fixed calipers. If the rotor is not surfaced equally on both sides, it will not be centered in the caliper opening when installed (Figure 7-56).

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Dimension C

Dimension D

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Dimension C

Dimension D

Figure 7-56  A fixed caliper must be centered and parallel with the rotor. In a few cases, you can shim the caliper mounting for proper alignment but not always.

WARNING  Do not use rotors that are below or near minimum thickness. A too-thin rotor could shatter during braking, possibly causing an accident or serious injury. Legal action could be taken against the shop and technician.

Ideally, a rotor used with a floating or sliding caliper should be turned equally on both sides. Heat transfer capabilities may be reduced on a ventilated rotor if unequal amounts of metal are removed from the surfaces. From a practical standpoint, one side of a rotor used with a movable caliper can be turned a few thousandths of an inch more than the other as long as total thickness is within limits. Ford rotors described in the section on friction surface depth measurement have limits on the amount of metal that can be removed from the inboard surface.

SERVICE TIP  Never assume that new rotors are parallel. Always check them before installing. If they are more than 0.002 inch out of parallel, swap them with the parts vendor.

Turning New Rotors Most carmakers and parts manufacturers recommend against refinishing new rotors unless measured runout exceeds specifications, which does not happen often. New rotors have the correct surface finish, which may be disturbed by turning on a lathe. Making a light cut on a new rotor may produce excessive lateral runout and result in brake shudder after only a few thousand miles. Clean any oil film off the rotor with brake-cleaning solvent or alcohol and let the rotor air dry before installing it on the vehicle. Lacquer thinner cleans the shipping compound from a rotor quicker. However, the thinner must be used in an open, ventilated area and must be stored in a tightly capped, labeled container.

Brake Lathes Both bench-type, off-vehicle lathes (Figure 7-57) and on-vehicle lathes (Figure 7-58) are used to refinish rotors. Regardless of the type of lathe used, the equipment should be

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Figure 7-57  AAMCO brake lathes like the one shown are found in most brake repair shops and are preferred by many older technicians.

(a)

(b)

Figure 7-58  A typical on-the-car (on-vehicle) brake lathe.

serviced regularly according to the manufacturer’s maintenance procedures to maintain correct operation. If this is the first time this lathe is being used, it may be advisable to use a dial indicator to check the trueness of the lathe shaft, stationary, and rotating. On a bench lathe, the rotor is mounted on the lathe arbor and turned at a controlled speed while cutting bits pass across the rotor surfaces to remove a few thousandths of an inch of metal. The lathe turns the rotor perpendicularly to the cutting bits so that the entire rotor surface is refinished. Most lathes can operate at slow, medium, and fast speeds through a series of drive belts. Different cutting assemblies are used for rotors and for drums. Most rotor cutting assemblies have two cutting bits. The rotor mounts between the bits and is pinched between them. As the cut is made, the same amount of surface material is cut from both sides of the rotor. Some lathes use only one bit for rotor refinishing and separate cuts of equal amounts must be taken from each side. When using a lathe with only one cutting bit, do not take the rotor off the lathe until both sides are cut. Always cut both sides of the rotor without removing it from the arbor. This ensures that both sides of the rotor will be parallel after refinishing. Check the accuracy of the cuts with a dial indicator and an outside micrometer. Even a 0.001-inch to 0.002-inch variation in positioning the rotor on the lathe can add runout to a rotor. This will cause pedal pulsation and reduce braking efficiency.

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The attaching adapters, tool holders, vibration dampers, and cutting bits must be in good condition. Make sure mounting adapters are clean and free of nicks. Always use sharp cutting tools or bits and use only replacement cutting bits recommended by the equipment manufacturer. Dull or worn bits leave a poor surface finish, which will affect braking performance. The tip of the cutting bit should be slightly rounded, not razor sharp. This rounded tip is more important for turning a drum where a pointed-tip bit can cut a spiral groove into the drum. Even when turning a rotor, however, a pointed bit can leave small grooves that work against the nondirectional finish needed on a rotor.

Mounting a Rotor on a Bench Lathe The mounting procedure for a rotor depends on whether the rotor has wheel bearings mounted in its hub. A one-piece rotor with bearing races in the hub mounts to the lathe arbor with tapered or spherical cones (Figure 7-59). A two-piece rotor removed from its hub is centered on the lathe arbor with a spring-loaded cone and clamped in place by one or two large cup-shaped adapters (Figure 7-60).

335

Caution Do not overtighten the rotor cones and adapter onto the lathe spindle. Damage to the rotor or the lathe may occur.

Rotor

Cushion collar Inner adapter cone

Arbor nut

Outer adapter cone

Figure 7-59  Rotors with hubs mount on a bench lathe by using adapter cones in the bearing races.

Rotor

Hubless adapter

Spring

Outer adapter Cushion collar

Inner adapter

Arbor nut

Figure 7-60  Hub-less rotors mount on a bench lathe by using hub-less adapters that sandwich the rotor between them.

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For one-piece rotors and hubs with bearings installed, remove the outer bearing and the inner bearing and grease seal before mounting the rotor on the lathe arbor. When mounting a one-piece rotor and hub, check the inner bearing races (cones) to be sure they are secure in the hub. If either race is loose, replace all bearings and races. Refer to Chapter 3 in this Shop Manual for bearing removal and installation instructions. Remove all grease and dirt from the bearing races before mounting the rotor. It is sometimes necessary to steam clean the grease out of the hub. Index the rotor on the wheel-bearing races to ensure that the machining is accurately indexed to the axis of the rotor. Use the appropriate cones and spacers to lock the rotor firmly to the arbor shaft (Figure 7-61). For hub-less rotors, clean all rust and corrosion from the hub area with coarse sandpaper or a wire brush (Figure 7-62). As with bearing-type rotors, use the proper cones and spacers to mount the rotor to the arbor shaft. When the rotor is on the lathe, install a rubber, spring-type, or puck-type vibration damper on the outer circumference of the rotor (Figure 7-63) to prevent the cutting bits from chattering during refinishing. Use of the vibration damper results in a smoother finished surface. The damper also helps reduce unwanted noise. Photo Sequence 14 shows the general procedures for mounting a floating rotor on a brake lathe. For a onepiece disc/hub, refer to Photo Sequence 20 for general mounting procedures.

Figure 7-61  On the left is a floating rotor clamped and centered on the lathe’s arbor. The right shows a one-piece hub and rotor assembly. Note the different centering and clamping devices and types of vibration dampers.

Figure 7-62  Clean the dirt and rust from the hub-mounting area of the hub-less rotor.

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Figure 7-63  A close-up of a spring-type vibration damper installed around the edge of the rotor. This damper is growing in use.

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337

14 Mounting a Floating Rotor (Drum) on a Brake Lathe Photo Sequence

P14-1  Clean the inside and outside of the rotor where the lathe’s centering cone and clamps will be in contact with the rotor. Select a centering cone that fits into the rotor’s center hole without protruding too much in either direction.

P14-2  Slide the inner clamp onto the arbor followed by the centering cone tension spring.

P14-3  Slide the cone onto the arbor followed by the rotor. The rotor is mounted in the same way as on the vehicle.

P14-4  Push on the rotor to compress the spring, and then hold the rotor in place as the outer clamp is fitted onto the arbor. The two clamps, inner and outer, must be the same size.

P14-5  Keep the pressure on the installed parts as the spacers and bushing are installed on the rotor.

P14-6  Hold all parts in place as the arbor nut is installed and tightened to lathe manufacturer specifications.

P14-7  Install the vibration damper. The damper may be a flexible strap or spring that fits the outer circumference of the rotor, or two padlike devices that are forced against each side of the rotors similar to installed disc brake pads.

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P14-8  The rotor is now properly mounted and ready for the final check before machining.

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Machining a Rotor on a Bench Lathe Before removing any metal from the rotor, verify that it is centered on the lathe arbor and that extra runout has not been created by the lathe mounting. If the rotor is not centered and square with the arbor, machining can actually add runout. To check rotor mounting, make a small scratch on one surface of the rotor, as follows:

SERVICE TIP  A disc brake rotor should have a smooth, nondirectional finish for optimum braking and pad life, but how smooth is smooth? Actually, a “smooth” rotor surface is pretty well polished to a 30-, 40-, or 50-microinch finish. A quick way to judge the surface finish is to draw a line with a common ballpoint pen along the radius of the rotor at any point. If the line looks like a solid smooth line and not a series of dots or dashes, the surface is close to the desired finish.

WARNING  Wear safety glasses or face protection when using machining equipment. Injuries to the face or eyes could occur from flying chips of metal.

1. Begin by backing the cutting assembly away from the rotor and turning the rotor through one complete revolution to be sure there is no interference with rotation. 2. Start the lathe and advance the cutting bit until it just touches the rotor surface near midpoint. WARNING  A brake lathe can produce a lot of torque. Do not wear loose clothing or unrolled long-sleeved shirts while machining or setting up the lathe.

3. Let the cutting bit lightly scratch the rotor, approximately 0.001 inch (0.025 mm) deep. 4. Move the cutting bit away from the rotor and stop the lathe. If the scratch is all the way around the rotor, the rotor is centered and you can proceed with resurfacing. WARNING  Do not attempt to make adjustments or perform other actions in or near the cutting head. Allow the rotor to come to a complete halt before loosening the nut. The lathe produces sufficient torque to break bones or cause other injuries.

Special Tools Bench-mounted brake lathe Sufficient and correct rotor adapters Service manual

5. If the scratch appears as a crescent (Figure 7-64), either the rotor has a lot of runout or it is not centered on the arbor. In this case, loosen the arbor nut and rotate the rotor 180 degrees on the arbor; then retighten the nut. 6. Repeat step 2 through step 4 to make another scratch about ¼ inch away from the first. 7. If the second scratch appears at the same location on the surface as the first, the rotor has significant runout, but it is properly centered on the lathe and you can proceed with machining. 8. If the second scratch appears opposite the first on the rotor surface, remove the rotor from the lathe arbor and recheck the mounting. WARNING  Do not allow the lathe to operate without close monitoring. Do not allow other persons to work near the lathe until it stops running. Inattention or lack of monitoring could cause a serious accident.

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Scratch cut

ta Ro

te 180°

Loosen arbor nut

Figure 7-64  Check rotor runout by making a light scratch cut (top). Then rotate the rotor 180 degrees on the lathe arbor (bottom) and make the second cut. The position of the second cut helps to indicate the cause of any runout present.

In extreme cases, the lathe arbor shaft may be bent. If the second test scratch appears as a crescent in a different area from the first scratch, the rotor is wobbling on the arbor 0.003 inch (0.076 mm) to 0.004 inch (0.010 mm) or more. Do not resurface the rotor because additional runout could be machined into the rotor, causing a pedal pulsation. One of three conditions is the likely cause of the wobble: a bent lathe arbor, distorted mounting adapters, or excessive rotor runout. The last is the most common. To determine if the arbor is bent, mount a dial indicator on the lathe and disconnect lathe power. Release the pulley belt tension by moving the controlling lever; then rotate the arbor slowly by turning the drive pulleys. Observe the dial indicator needle. Movement of the needle more than one division (0.001 inch or 0.025 mm) indicates a bent arbor. Contact the lathe manufacturer for lathe service information. A distorted mounting adapter sometimes can be corrected by installing it on a precision metal-working lathe and machining it. It is usually more practical to replace a defective adapter, however. Rotors with excessive runout can be resurfaced if the amount and position of runout is marked when the rotor is on the vehicle and these same conditions can be reproduced on the bench lathe. Extreme runout correction is explained in a later section of this chapter. Determining Machining Limits.  To determine the approximate amount of metal to be removed, turn on the lathe and bring the cutting bit up against the rotating disc until a slight scratch is visible as you did to verify rotor centering. Turn off the lathe, and reset the depth-of-cut dial indicator to zero (Figure 7-65). Find the deepest groove on the face of the rotor, and move the cutting bit to that point without changing its depth-of-cut setting. Now use the depth-of-cut dial to bottom the tip of the cutter in the deepest groove. The reading on the dial now equals or is slightly less than the amount of metal to be removed to eliminate all grooves in the rotor. For example, if the deepest groove is 0.019 inch (0.483 mm) deep, the total amount to be removed may be 0.020 inch (0.508 mm).

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Figure 7-65  The depth-of-cut dial has two graduated scales: thousands of an inch, and millimeters. The dial is used to set the cutting depth.

Using a disc rotor micrometer is sometimes quicker to determine the amount of material to be removed from a rotor.

For best results with cuts that have a total depth greater than 0.015 inch (0.381 mm) take two or more shallow cuts rather than one deep cut. Adjusting Lathe Settings.  Before starting to machine the rotor, consider and adjust three lathe settings: lathe speed (rpm), cross-feed, and depth of cut. The lathe speed usually stays constant throughout the machining operations, but most lathes have at least two or three speed settings. Select the best speed for the rotor you are machining according to the lathe manufacturer’s instructions. Most rotors can be refinished and sanded satisfactorily at 150 rpm to 200 rpm. The cross-feed is the distance the cutting bit moves across the friction surface during each lathe revolution. The cross-feed and the depth of cut work together for a correct finish. A cross-feed that is too fast and a deep depth of cut will cause the rotor to vibrate and leave gouges in the material. The rotor will have to be replaced in this instance. A cross-feed of 0.006 inch (0.152 mm) to 0.010 inch (0.15 mm to 0.25 mm) per revolution is good for rough cuts on most rotors. Make the finish cut at a slower cross-feed of about 0.002 inch (0.05 mm) per revolution. The depth of cut is the amount of metal removed by the cutting tool in each pass across the rotor. Limit the depth of cut to 0.006 inch or 0.007 inch (about 0.15 mm) for each pass. Make the finish cut at the same depth for organic pads, but semi-metallic linings work best with a finish cut on the rotor made at a depth of 0.002 inch (0.05 mm). Machining the Rotor.  To make the series of refinishing cuts, proceed as follows: 1. Reset the cutter position so the cutting bits again just touch the un-grooved surface of the inside of the rotor. 2. Zero the depth-of-cut indicators on the lathe. 3. Turn on the lathe, and let the arbor reach full running speed. 4. Turn the depth-of-cut dials for both bits to set the first pass cut. Turning these dials moves the bits inward. The dial is calibrated in thousandths-of-an-inch or millimeter increments. The first cut should only be a portion of the total anticipated depth of cut. 5. When the cutting depth is set for the first cut, activate the lathe to move the cutting bits across the surface of the rotor. After the first cut is completed, turn off the lathe and examine the rotor surface. Areas that have not yet been touched by the bits will be darker than those that have been touched (Figure 7-66).

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Figure 7-66  The first cut should remove most of the worn area of the rotor.

6. If there are large patches of unfinished surface, make another cut of the same depth. When most of the surface has been refinished, make a shallow finishing cut at lower arbor speed. Repeat the slow finishing cut until the entire rotor surface has been refinished. 7. Do not remove any more metal than necessary for a uniform surface finish, free of grooves. Make sure the refinished rotor thickness is above or beyond its service limit. To ensure this, remeasure the refinished rotor with a micrometer to determine its minimum thickness and compare this measurement to the manufacturer’s minimum refinished thickness specification. It is very important that the rotor surface be made nondirectional after machining. (Figure 7-67). This is important to help the new pads seat to the rotor. Breaking the direction finish can also prevent the pads from being pulled and making a clicking sound on light braking on some applications. Dress the rotor surfaces with a sanding disc power tool with 120-grit to 150-grit aluminum oxide sandpaper. Sand each rotor surface with moderate pressure for at least 60 seconds. You can also do the job with a sanding block with 150-grit aluminum oxide sandpaper. With the rotor turning at approximately 150 rpm, sand each rotor surface for at least 60 seconds with moderate pressure (Figure 7-68). After the rotor has been sanded, clean each surface with hot water and detergent, which will float out the smallest particles of iron and abrasive materials. Then dry the rotors thoroughly with clean paper towels. If working in an area of high humidity or if the rotors will not be reinstalled immediately, wipe the friction surfaces with denatured alcohol and a clean cloth to be sure that all moisture is removed.

Special Tools Bench-mounted brake lathe Sufficient and correct rotor adapters Micrometer Power or hand sanding disc Hot soapy water with basin Service manual

Machining to Remove Excessive Rotor Runout.  Rotors with excessive runout may have been machined incorrectly previously, or the rotor may have become distorted by overtightening the wheel nuts. Such a rotor can be resurfaced if the amount and position of runout is marked when the rotor is mounted on the vehicle and these same conditions can be reproduced on the bench lathe. Proceed as follows: 1. Check the rotor lateral runout with the rotor on the vehicle as explained earlier in this chapter. The maximum clockwise rotation of the dial indicator needle indicates the place where the rotor has its maximum outward deflection. Mark this spot on the rotor hub with a plus (1) mark. 2. After marking the rotor, remove it from the vehicle and mount it on the lathe with the proper mounting adapters.

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Final finish should be a nondirectional crosshatch pattern

Figure 7-67  A nondirectional finish on the surface of a rotor is a crosshatched pattern that does not follow the arc of rotor rotation. The surface helps pad break-in and reduces brake noise.

Figure 7-68  Use a sander to apply a nondirectional finish.

3. Install the dial indicator on the lathe and adjust the indicator pointer to the outside rotor surface. 4. Slowly turn the rotor clockwise and observe whether the runout amount and location are the same as they were on the car. If the readings are not the same as they were on the car, loosen the arbor nut and reposition the rotor and the adapters on the rotor. Repeat this procedure until the rotor runout matches the runout measured on the car as previously described.

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5. When the conditions on the vehicle have been re-created on the lathe, machine off an amount of material equal to the maximum lateral runout. If the rotor runout on the lathe cannot be made to match the runout found on the car, the rotor should be replaced. To determine the runout of the rotor hub of a two-piece floating rotor, mount the dial indicator point against the hub flange. Rotate the axle and observe the movement of the dial indicator needle.

On-Vehicle Lathes Excellent refinishing results can be achieved with an on-vehicle brake lathe (Photo Sequence 15 and Figure 7-69). One advantage of an on-vehicle lathe is that the rotor does not have to be removed from the spindle or the hub. On-vehicle lathes also are ideal for rotors with excessive runout problems. The time and trouble needed to reproduce the exact runout condition on a bench lathe arbor is eliminated or reduced when you refinish the rotor on the vehicle. To install the lathe, remove the wheel and then remove the caliper from its support and hang it out of the way with heavy wire. To hold a two-piece floating rotor to its hub, reinstall the wheel nuts with flat washers or adapters provided by the lathe manufacturer against the rotor. Torque the wheel nuts to specifications in the prescribed sequence to keep from introducing any runout into the rotor. Attach the lathe to the rotor using the hardware that comes with the lathe. Follow the manufacturer’s mounting and operating instructions precisely. As with the bench lathe, the cutting bits of the on-vehicle lathe straddle the rotor and depth-of-cut settings are made using adjustment knobs. The dial marks determine the depth of cut each tool is taking from the rotor surface. The wheel bearings and spindle or axle serve as the lathe arbor, so they must be in good condition. Excessive bearing end play may prevent the use of an on-vehicle lathe or require bearing replacement before an on-vehicle lathe can be used. If any end play is present in an adjustable tapered roller bearing, carefully tighten the adjusting nut by hand just enough to remove all end play before installing the lathe. After turning the rotor, readjust the bearing to specification as explained in Chapter 3 of this Shop Manual. Some on-vehicle lathes mount on the caliper support, on the hub, or on a separate stand. Depending on lathe design, the rotor may be rotated by vehicle engine power or by the lathe’s electric motor during refinishing. The newer units do not use vehicle engine power.

Figure 7-69  This on-car lathe has its own drive motor.

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WARNING  Using the engine to turn the rotor puts a lot of torque into the assembly even at idle speeds. Ensure that the caliper, hoses, and any wiring harness are tied back from the rotor and lathe. Injuries could occur from cut hoses or loose components.

If the engine is used to turn the rotor, the lathe can be used only on drive wheels. However, a problem exists because the differential gearing in the transaxle transmits the power to the opposite wheel, not to the rotor to be resurfaced. To prevent that opposite wheel from turning, that wheel can be lowered to the floor. This may reduce floor-to-lathe clearance to the point where it is difficult to run the lathe, however. Another way to transfer drive power to the rotor is to lock the brakes at the opposite wheel. Ensure that the caliper on the side being machined is secured by a wire and clear of the lathe mechanism. Use a small C-clamp to slightly or completely push the piston into that caliper body. Leave the C-clamp in place until the rotor is machined. In this manner, the brakes can be applied using the brake depression tool from the alignment area. Otherwise, keep a second person in the driver’s seat. Start the engine, shift the transmission into first gear or reverse (depending on location of the lathe), and idle the engine as slowly as possible. The rotor should rotate as slowly as possible to provide a smooth surface. Spinning the rotor too fast will cause the tool bits to overheat and wear out faster. Excessive rotor speed during machining can damage the rotor. During machining, the rotor must turn into the cutting edges of the bits. Depending on the design of the lathe, rotor rotation may change from one side of the car to the other. Therefore, the engine can drive the rotor in first gear or reverse to get the proper rotation. Cross-feed of an on-vehicle lathe may be automatic or manually controlled. If operated manually, advance the cutting bits slowly and steadily across the rotor. Set an automatic cross-feed to 0.003 inch (0.08 mm) per revolution. Depth of cut should be shallower than on a bench lathe. Make successive cuts at a depth or 0.004 inch to 0.002 inch (0.10 mm to 0.05 mm) until the desired finish is achieved. Self-powered lathes that drive the rotor with a motor mounted in the lathe have become more popular than lathes that use the engine to drive the rotor. Not only can a self-powered lathe be used on nondriving wheels, rotor speed can be controlled more exactly, and avoids dealing with engine exhaust inside the shop. Self-powered, on-vehicle lathes produce almost as much torque as the engine at idle. Use extreme caution with this type of lathe.

15 Typical Procedure for On-Vehicle Brake Lathe Photo Sequence

P15-1  The vehicle is placed safely on the hoist and raised to a comfortable level.

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P15-2  Check the wheel bearings for looseness before beginning to machine the rotors. Any looseness can cause runout in the rotor as it is machined. If the bearings are of the adjustable tapered type, it may be necessary to temporarily tighten the bearing by hand and then readjust when finished.

P15-3  The wheels are removed.

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Photo Sequence 15 (CONTINUED)

P15-4  Remove the brake caliper and suspend it to avoid damaging the rubber brake hose.

P15-5  Install the adaptor that will be used to power the wheel with the lathe motor. The adaptor is installed and torqued to the proper tightness according to the lathe manufacturer.

P15-6a  The cutting head is installed according to the manufacturer’s specifications. Make sure to follow the manufacturer’s instructions exactly.

P15-6b  A special spring is placed on the rotor to prevent vibrations that may cause chatter marks on the finished rotor.

P15-7  Some lathes will have a runout adjustment that must be performed to prevent movement of the lathe while powering the wheel. Follow the manufacturer’s instructions on this step.

P15-8  The technician brings the lathe bits into contact with the rotor in preparation for the first cut. A scratch cut is made by turning the depth of cut adjustment into the rotor on both sides. Then manually feed the bits inward until they are past the inner pad contact line. Next set the lathe stop for the inward feed, or in-feed.

P15-9  Set an automatic cross-feed to 0.003 inch (0.08 mm) per revolution. Depth of cut should be 0.004 inch to 0.002 inch (0.10 mm to 0.05 mm) until the desired finish is achieved, unless otherwise instructed by the lathe or vehicle manufacturer.

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P15-10  Shift the lathe to automatic operation at the fast-feed rate. Switch the lathe to feed outward for the first rough cut. After the lathe completes the first cut, turn off the lathe motor and check the uniformity of the cut. Make additional cuts if necessary, with the final cut at a depth of 0.002 inch (0.05 mm).

P15-11  The finished rotor will have a nondirectional finish is applied with a sanding block with 150-grit aluminum oxide sandpaper. With the rotor turning at approximately 150 rpm, sand each rotor surface for at least 60 seconds with moderate pressure. The technician will need to clean and metal shavings from the area before reassembling the caliper and wheel. If taper roller bearings were tightened for the rotor finish, readjust them to the proper setting.

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Photo Sequence 15 (CONTINUED)

P15-12  The technician torques the wheel lugs to prevent distortion of the rotor.

P15-13  The technician test drives the vehicle to check the repair.

As mentioned earlier, an on-car lathe may be mounted on the brake caliper support or on its own stand and indexed to the hub and the wheel studs. Each lathe has its own operating instructions, which you must follow carefully. All lathe operating procedures include most of the following steps: 1. Check for wheel bearing end play. If end play on an adjustable bearing is noted, adjust the bearing to remove all end play. If end play exceeds the carmaker’s specifications on a nonadjustable bearing, replace the bearing. 2. Check the fluid level in the master cylinder, and be sure it is not overly full. Remove fluid if necessary by connecting a flexible hose to the bleeder screw and running it to a catch container. This helps prevent corrosion and dirty fluid from reentering the master cylinder. The reservoir should be about half full when the caliper pistons are pushed back to demount the caliper in case fluid does not flow freely from the screw. 3. Place the transmission in neutral, release the parking brake, and raise the vehicle on a hoist to an appropriate working height. 4. Remove the wheel from the first rotor to be serviced. Remove any rust or corrosion from the axle or hub flange rotor mounting area, the rotor’s matching surface to the flange, and around the wheel studs. This will help solve many runout problems. 5. Install spacers on the studs if required for the rotor drive adapter and reinstall the wheel nuts. Torque the nuts to specifications in the prescribed sequence. Even if the rotor is a one-piece rotor and if the vehicle engine is used to drive it for machining, it is a good idea to reinstall and properly torque the wheel nuts, ensuring that any runout created by wheel nut torque is removed during machining. 6. Remove the caliper from its support (push the piston back in its bore if necessary) and hang the caliper out of the way from the chassis or suspension, using a suitable support. Do not hang the caliper from the brake hose. 7. If the lathe is to be mounted on the caliper support, be sure that the area on the support around the mounting holes is free of dirt, rust, and gouges. Select the proper lathe-mounting adapters and mount the lathe on the caliper support. Tighten all fasteners securely. 8. If the lathe is self-powered, attach the wheel drive adapters to the wheel studs and align the drive motor stand with the hub axis. Lock the stand wheels and plug in the power cord.

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9. Turn on the motor before moving the cutting bits close to the rotor to be sure the motor is turning in the right direction. 10. With the rotor turning in the right direction, operate the hand wheel to move the cutting bits until they are ½ inch in from the outer edge of the rotor. Then turn the depth-of-cut micrometer until the bits just lightly touch both rotor surfaces. 11. Perform a scratch test before machining the rotor. 12. Turn the hand wheel to move the bits outward and remove rust and dirt from the outer edge of the rotor. 13. Manually feed the bits inward until they are past the inner pad contact line. Then set the lathe stop for the inward feed, or in-feed. 14. Rotate both micrometer knobs clockwise for an initial cut of no more than 0.004 inch (0.10 mm). 15. Shift the lathe to automatic operation at the fast-feed rate. Switch the lathe to feed outward for the first rough cut. 16. After the lathe completes the first cut, turn off the lathe motor and check the uniformity of the cut. Make additional cuts if necessary, with the final cut at a depth of 0.002 inch (0.05 mm).

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Special Tools Service manual Vehicle specific rear disc tools Lift or jack with stands

SERVICE TIP  Do not overlook the rear brakes when servicing a car with four-wheel disc brakes. Although the rear brakes do only 20 percent to 25 percent of the braking, they can run hotter than the front brakes on some cars because of the way the rear wheels are shrouded. Also, if the rear brakes are not up to full capacity, the front brakes will be overworked and wear out more quickly.

REAR DISC BRAKE INSPECTION AND REPLACEMENT Rear disc brakes are used on many vehicles. In most cases, the rear brakes are identical to the front disc brakes except for some type of parking brake mechanism. Figure 7-70 is an exploded view of a Honda rear disc brake that is typical of one with a parking brake mechanism. Photo Sequence 16 illustrates and explains pad

Classroom Manual Page 177

Cam boot

O-ring Adjusting bolt

Washer

Circlip Spring

Cam Lever

Nut Spring

Cone Piston Piston seal

Caliper support

Boot

Figure 7-70  Service of this rear disc brake is explained in Photo Sequence 16.

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replacement and caliper overhaul of this typical rear disc brake. All illustrations are provided by Honda Motor Co., Inc. To complete this rear caliper service, install the caliper on the caliper bracket, and tighten the caliper bolts to torque specifications. Reconnect the brake hose to the caliper with new sealing washers and tighten the banjo bolt to specifications. Then reconnect the parking brake cable to the arm on the caliper. Finally, reinstall the caliper shield. Top off the master cylinder reservoir and bleed the brake system. Depress the brake pedal several times, and then adjust the brake pedal. Before making adjustments, be sure that the parking brake arm on the caliper touches the pin.

Photo Sequence 16

Typical Procedure for Overhauling a Rear Brake Caliper Parking brake cable

Clip

Caliper bolts

Lock pin

P16-2  Disconnect the parking brake cable from the lever on the caliper by pulling out the lock pin.

Caliper shield

P16-1  Raise the vehicle on the lift and remove the rear wheels. The rear caliper may be protected by a plastic shield. Remove this shield and the bolts securing the caliper.

Caliper body

Pad retainer

Brake hose Washers

P16-3  Disconnect the brake hose from the caliper, remove the caliper mounting bolts, and lift the caliper off its support. To keep dirt from entering the caliper body, clean the outside of the caliper before disassembly.

Pads

Shim

P16-4  Remove any pad shims and retainers and lift the pad spring out of the caliper. Then pull the pads off the caliper.

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Photo Sequence 16 (CONTINUED)

Caliper bracket bolt

Flat washer

Wheel nut

P16-5  Check the condition of the rotor as instructed earlier in this chapter. Thoroughly clean the rotor surface and inspect it for defects and damage. Measure rotor thickness and runout.

Caliper bracket

P16-6  Remove the bolts securing the caliper bracket and lift off the bracket. Thoroughly clean the caliper bracket.

Piston boot Lock nut wrench

Screws Piston

Rotor Threaded hole

P16-7  This is a two-piece rotor that must be removed from the hub. Remove the screws and pull the rotor off the hub.

Extension bar

P16-8  To remove the caliper piston from the bore, use a proper size locknut wrench and extension bar. Turn counterclockwise to back the piston out of the bore. When the piston is free, remove the piston boot.

Piston

P16-9  Carefully inspect the piston for wear. Replace the piston if it is worn or damaged in any way.

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Piston seal

P16-10  Remove the piston seal from the caliper with the tip of a wooden or plastic scraper. Do not scratch the bore.

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Photo Sequence 16 (CONTINUED) Caliper body

Brake hose

Brake spring compressor

Snapring pliers

Washers

P16-11  Removing the brake spring and its related parts from the caliper requires several special tools. Install a rear caliper guide in the cylinder so the cutout on the guide aligns with a tab on the brake spring cover. Rear caliper guide Adjusting spring

Specified distance from shop manual

Cup Bearing

Spacer Spring cover

Adjusting bolt

P16-13  After removing the circlip, remove the spring compressor from the caliper. Then remove the spring cover, adjusting spring, spacer, bearing, adjusting bolt, and cup.

Sleeve piston

Rod

P16-12  Install a brake spring compressor between the caliper and the caliper guide. Turn the shaft of the compressor to compress the spring. Use snapring pliers to remove the circlip that holds the spring. Return spring

Parking lever and cam assembly

Cam boot

O-ring

P16-14  Next remove the sleeve piston and O-ring. Then remove the rod from the can.

P16-15  Remove the return spring, the parking lever and cam, and the cam boot from the caliper body. Do not loosen the parking nut on the parking lever and cam with the cam installed in the caliper. If the lever and shaft must be separated, secure the level in a vise before loosening the parking nut.

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351

Photo Sequence 16 (CONTINUED)

Return spring

Parking lever and cam assembly

Cam boot replace

P16-17  Install the rod in the cam, followed by a new O-ring, lubricated with fresh brake fluid, on the sleeve piston. Then install the sleeve piston so the hole in the bottom of the piston is aligned with the rod in the cam and the two pins on the piston are aligned with the holes in the caliper. Clip

Parking brake cable

Lock pin

P16-16  Begin caliper reassembly by packing all cavities of the needle bearing with the specified lubricant. Coat the new cam boot with brake lubricant and install it in the caliper. Apply brake lubricant to the area on the pin that contacts the cam. Install the cam and lever into the caliper body. Then install the return spring. If the cam and lever were separated, reassemble them before installing the cam in the caliper.

P16-18  Install a new cup with its groove facing the bearing side of the adjusting bolt. Fit the bearing, spacer, adjusting spring, and spring cover on the adjusting bolt; then install it in the caliper bore.

Caliper body

Brake hose Washers

P16-19  Install the special caliper guide tool in the caliper bore, aligning the cutout on the tool with the tab on the spring cover. Adjust the special tool as shown in P16-18.

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P16-20  Install the brake spring compressor and compress the spring until the tool bottoms out.

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Photo Sequence 16 (CONTINUED) Piston seal— apply silicone grease

Piston seal— apply silicone grease

P16-21  Make sure that the flared end of the spring cover is below the circlip groove. Then install the circlip and remove the spring compressor. Ensure that the circlip is properly seated in the groove.

P16-22  Coat the new piston seal with fresh brake fluid and the piston boot with silicone lubricant and installed them in the caliper.

Piston boot Lock nut wrench

Outer pad shim Apply Molykote® M 77 or equivalent to pad side of shim.

Inner pad shim Apply Molykote® M 77 or equivalent to pad side of shim.

Piston Extension bar

P16-23  Coat the outside of the piston with brake fluid and install it on the adjusting bolt while rotating it clockwise with the locknut wrench.

Brake pads

Retainers

Caliper bracket

P16-24  Install the new or refinished rotor and the clean caliper bracket. Install the new brake pads, pad shims, retainers, and springs onto the caliper bracket. Wear indicator

Piston Brake pad

Tab

Cutout

P16-25  Install the new or refinished rotor and the clean caliper bracket. Install the new brake pads, pad shims, retainers, and springs onto the caliper bracket.

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353

CASE STUDY It is usually not a good idea to buy into problems caused by someone else. Here is an example of why. The owner of a truck wanted to save a couple bucks, so he changed his front brake pads himself. Shortly afterward, the truck started intermittently pulling to the right during braking. The owner took the truck to a shop and asked for help. The brake techs at the shop found that the rotors had excessive runout and that the calipers were in pretty sad shape, with some visible leakage. The techs surfaced the rotors and replaced the calipers. They also replaced the idler arm, which had excessive play. The brakes now worked fine on a test drive, so the truck was delivered to its owner. A week later, it was back. This time, the truck randomly pulled both left and right. Again, the rotors got checked carefully, and the new calipers were exchanged on warranty. During the second service, one caliper mounting bolt was found to be loose and was tightened properly when the second set of calipers were installed. Again, the brakes were fine on a road test, and again the truck was returned to its owner. Two weeks later, after a long trip, the truck was back at the shop with brake pull occurring again. This time the brake tech went through all the system lines and hoses. Pressure gauges installed on the calipers revealed erratic pressure at the front brakes. Apparently during the ­do-it-yourself brake bleeding after the first set of pads, dirt got into the system and partly clogged the hoses. If a qualified shop had done the job to begin with, the problem probably never would have developed.

ASE-STYLE REVIEW QUESTIONS 1. While servicing the front disc brakes on a FWD vehicle, Technician A determines the right wheel brake pad is worn and replaces both the right and left wheel pads. Technician B determines the brake pads are not worn but rotates their position to ensure even pad wear. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 2. After servicing the disc brakes on a vehicle, Technician A reinstalls the wheel lug nuts using an impact wrench to ensure a tight fit. Technician B refills the master cylinder reservoirs to the proper level. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 3. Technician A says that loaded calipers are replacement calipers that come with pads and hardware already installed. Technician B says that loaded calipers should be installed in axle sets. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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4. Technician A says that it is very important that the rotor surface be made nondirectional during refinishing. Technician B says that rotors should always be refinished as part of routine disc brake service. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. When performing disc brake work, Technician A works on one wheel at a time to allow the other caliper to be used as a guide. Technician B hangs the calipers from the brake hoses as a convenience to speed up the job. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 6. When measuring rotor runout, Technician A uses a micrometer, Technician B uses a dial indicator. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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7. Technician A says that a one piece hub uses the bearing races and special cones to mount the rotor on the lathe arbor. Technician B says that hub-less rotors cannot be mounted on a bench lathe. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

9. When refinishing a rotor on a lathe, the rotor wobbles excessively, Technician A says that the lathe arbor may be bent. Technician B says that the mounting adapters of the lathe may be distorted. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

8. Technician A says that the minimum wear thickness of a rotor is the discard thickness of the rotor. Technician B says that the refinishing dimension is cast into a rotor. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

10. After servicing front disc brakes, Technician A reinstalls the wheel and tire and tightens the nuts in the recommended tightening pattern. Technician B pumps the brake pedal several times to position the new pads before test driving the vehicle. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

ASE CHALLENGE QUESTIONS 1. Rear disc brakes are being discussed. Technician A says that a stuck right rear caliper could cause a pull to the right when the brakes are applied. Technician B says that an overheated rear rotor could be caused by misadjusted parking brake cable. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 2. The results of a road test are being discussed; the vehicle stops true but has a small vibration. Technician A says that the vehicle probably has the wrong brake pads. Technician B says that there is a problem with parallelism or runout. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

4. Technician A says that new brake pads require burnishing after replacement. Technician B says that the proper burnishing requires several panic stops from 40 mph. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. Four-wheel disc parking brakes are being discussed. Technician A says that some parking brakes could completely fail but not affect the service brakes. Technician B says that a parking brake that was left on could destroy the pads and rotors. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

3. A vehicle has a hard pedal but little braking effect. Technician A says that the pads are glazed. Technician B says that the piston seal is not allowing the brakes to self-adjust. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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Name ______________________________________

Date _________________

DIAGNOSING DISC BRAKE PROBLEMS Upon completion of this job sheet, you will be able to diagnose poor stopping, noise, pulling, grabbing, dragging, or pedal pulsation problems.

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JOB SHEET

30

ASE Education Foundation Correlation This job sheet addresses the following AST/MAST task: D.1. Diagnose poor stopping, noise, vibration, pulling, grabbing, dragging, or pulsation concerns; determine necessary action. (P-1) Tools and Materials Basic hand tools Protective Clothing Goggles or safety glasses with side shields Describe the vehicle being worked on: Year _______________ Make ______________ Model ______________ VIN _______________ Engine type and size _______________ Procedure 1. Begin the inspection of the disc brake system by checking the tires for excessive or unusual wear or improper inflation. What did you find? _________________________________________________________________________ 2. Wheels for bent or warped wheels. What did you find? _________________________________________________________________________ 3. Wheel bearings for looseness or wear. What did you find? _________________________________________________________________________ 4. Suspension system for worn or broken components. What did you find? _________________________________________________________________________ 5. Brake fluid level in the master cylinder. What did you find? _________________________________________________________________________ 6. Signs of leakage at the master cylinder, in brake lines or hoses, at all connections, and at each wheel. What did you find? _________________________________________________________________________ 7. Road test the vehicle. As you apply the brake pedal, check for excessive travel and sponginess. What did you find? _________________________________________________________________________ 8. Listen for noises, not just the obvious sounds of grinding pads or pad linings, but mechanical clanks, clunks, and rattles. What did you find? _________________________________________________________________________ 9. If the vehicle pulls to one side when the brakes are applied, check for a bad caliper or loose caliper at one wheel. Also check for signs of grease or brake fluid that may have contaminated the pads and rotor. Check for distorted or damaged brake pads.

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Grabbing brakes also may be caused by grease or brake fluid contamination or by a malfunctioning or loose caliper. What did you find? _________________________________________________________________________ 10. Remove the wheels and make a careful inspection of the brake pads and caliper mounting hardware. If the brakes are equipped with caliper slides, check them as well. What did you find? _________________________________________________________________________ 11. Check for worn rotors or pads. These may also cause roughness or pedal pulsation when the brakes are applied. What did you find? _________________________________________________________________________ Problems Encountered ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ Instructor’s Comments ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________

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Name ______________________________________

Date _________________

REPLACE BRAKE PADS Upon completion and review of this job sheet, you should be able to replace the brake pads on a front wheel disc brake and inspect the disc brake components.

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31

ASE Education Foundation Correlation This job sheet addresses the following MLR tasks: D.1. Remove and clean caliper assembly; inspect for leaks and damage/wear; determine necessary action. (P-1) D.2. Inspect caliper mounting and slides/pins for proper operation, wear, and damage; determine necessary action. (P-1) D.3. Remove, inspect, and/or replace brake pads and retaining hardware; determine necessary action. (P-1) D.4. Lubricate and reinstall caliper, brake pads, and related hardware; seat brake pads and inspect for leaks. (P-1) D.5. Clean and inspect rotor and mounting surface; measure rotor thickness, thickness variation, and lateral runout; determine necessary action. (P-1) D.9.

Retract and re-adjust caliper piston on an integral parking brake system. (P-2)

D.10.

Check brake pad wear indicator; determine necessary action. (P-1)

This job sheet addresses the following AST/MAST tasks: D.2. Remove and clean caliper assembly; inspect for leaks, damage and wear; determine needed action. (P-1) D.3. Inspect caliper mounting and slides/ pins for proper operation, wear, and damage; determine needed action. (P-1) D.4. Remove, inspect, and/or replace brake pads and retaining hardware; determine needed action. (P-1) D.5. Lubricate and reinstall caliper, brake pads, and related hardware; seat brake pads; inspect for leaks. (P-1) D.6. Clean and inspect rotor and mounting surface, measure rotor thickness, thickness variation, and lateral runout; determine needed action. (P-1) D.10.

Retract and readjust caliper piston on an integrated parking brake system. (P-2)

D.11.

Check brake pad wear indicator; determine needed action. (P-1)

Tools and Materials Lift or jack and jack stands Impact tools C-clamp Disc brake silencer Mechanic wire Torque wrench Describe the vehicle being worked on: Year _____________________ Make _____________________ Model _____________________ VIN ____________________________ Engine type and size _____________________________ ABS ______________ yes ______________ no ______________ If yes, type ________________

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Caution Before working on the brakes of a vehicle with an ABS, consult the service manual for precautions and procedures. Failure to follow procedures to protect ABS components during routine brake work could damage the components and cause expensive repairs.

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Procedure

Task Completed

1. Does the vehicle have ABS? Yes______________________ No______________________ If yes, highlight the precautions required by the manufacturer concerning ABS and routine brake repairs. _________________________________________________________________________ Caliper/adapter torque _____________________________________ Wheel nut torque 2. Inspect the fluid level in the master cylinder. Adjust so the reservoir is about half full.

h

3. Lift the vehicle and remove the wheel assembly.

h

WARNING  Wear safety glasses or face protection when using brake fluid. Injuries to the face or eyes could occur from spilled or splashed brake fluid. 4. Inspect the brake caliper mounting area for ABS components, caliper and adapter, and general condition of the steering, suspension, and brake components on each side of the vehicle. Check the brake pad wear indicator. Identify the type of rotor and caliper. Results: _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ 5. Position a catch basin and clean braking components. Dispose of the waste as required by law and shop policy.

h

6. Select the correct wrench and remove the caliper or adapter mounting fasteners.

h

7. Slide the caliper/adapter from the rotor. Use a prybar, if necessary, to pry the pads far enough to clear any ridge on the rotor on the front wheels. a. If you are replacing the pads on the rear of the vehicle, describe the process of retracting the caliper pistons if the parking brake mechanism is incorporated into the calipers. _________________________________________________________________________

h

8. Use mechanic wire to hang the caliper/adapter from a vehicle component.

h

9. Remove the pads and anti-rattle (hardware) clips from the caliper.

h

10. Inspect the rotor for damage. Measure the thickness of the rotor, compare to specification, and determine serviceability. See Job Sheet 30/31 for rotor machining. Results: _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ 11. Inspect the caliper piston boot, slide pins, and/or slide areas on the adapter and caliper. Results: _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________

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12. Use a C-clamp or similar tool to press the piston completely into the bore.

Task Completed h

13. Clean the slide pins or areas and lube with disc brake lubricant only.

h

14. Coat the metal portion of each of the new pads with disc brake silencer if silencer shims are absent. Allow to dry set (about 5 minutes).

h

NOTE:  The next two steps may have to be adjusted depending on how the hardware and pads fit into the caliper and caliper support. 15. Install the inner pad and anti-rattle springs (hardware), if required, into the caliper. Ensure that the pad mates properly with the piston and the anti-rattle springs are installed properly.

h

16. If necessary, install the slide pins onto the caliper and caliper adapter.

h

17. Slide the caliper/adapter with pads installed over the rotor and align the fastener holes.

h

18. Install and torque the caliper/adapter fasteners.

h

19. Install the wheel assembly and torque the lug nuts.

h

20. Repeat step 2 through step 20 for the opposite wheel.

h

21. Lower the vehicle when both wheel assemblies have been installed.

h

22. Press the brake pedal several times to seat the pads to the rotor.

h

23. Check the brake fluid level and top off as needed.

h

WARNING  Before moving the vehicle after a brake repair, pump the pedal several times to test the brake. Failure to do so may cause an accident with damage to vehicles, facility, or personal injury. 24. Perform a brake test to ensure the brakes will stop and hold the vehicle. Do this test before moving the vehicle from the bay.

h

25. When the repair is complete, clean the area, store the tools, and complete the work order.

h

Caution Always clean around any lines or covers before removing or loosening them. Dirt and other contaminants will void the warranty and may damage the system components.

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Caution Do not depress the brake pedal when the pads are being removed, installed, or have been removed from the caliper. Without the pads positioned properly, the piston could be forced from the bore when the pedal is depressed.

Caution Make certain the friction material, not the metal, faces the rotor. Serious damage to the rotor could occur if the pad is installed backwards.

Caution Use the correct fastener in the correct manner. Replacement fasteners must meet the specifications for that application.

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Caution Make certain that the fitting is not crossthreaded when reconnecting. This could damage the fitting or the component, or both.

Caution If possible, never use brake fluid from a previously opened container. Once opened, even tightly capped containers can draw moisture from the air.

Caution Use the correct fastener torque and tightening sequence when installing components. Incorrect torque or sequencing could damage the fastener(s) or components). Do not use an impact wrench alone to tighten wheel lugs.

Caution Before adding brake fluid, consult the vehicle service information. Many manufacturers require a specific classification of brake fluid to be used.

Caution Prevent brake fluid from coming in contact with the vehicle’s finish. Brake fluid damages paint and finish immediately on contact. If fluid contacts the finish, wash area thoroughly with running water using soap if possible.

Caution Do not reuse brake fluid. Discard old brake fluid according to EPA and local regulations.

Problems Encountered    Instructor’s Response   

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Name ______________________________________ Date _________________

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JOB SHEET

32

MEASURING ROTOR RUNOUT Upon completion and review of this job sheet, you should be able to measure a brake rotor for runout. ASE Education Foundation Correlation This job sheet addresses the following MLR tasks: D.5. Clean and inspect rotor and mounting surface, measure rotor thickness, thickness variation, and lateral runout; determine needed action. (P-1) D.6.

Remove and reinstall/replace rotor. (P-1)

This job sheet addresses the following AST/MAST tasks: D.6. Clean and inspect rotor and mounting surface, measure rotor thickness, thickness variation, and lateral runout; determine needed action. (P-1) D.7.

Remove and reinstall/replace rotor. (P-1)

Tools and Materials Dial indicator with clamping mount or magnetic mount Brake rotor micrometer or outside micrometer Service information Describe the vehicle being worked on: Year _____________________ Make _____________________ Model _____________________ VIN _____________________________ Engine type and size _____________________________ ABS _______________ yes ______________ no _______________ If yes, type _______________ Procedure

Task Completed

NOTE: See Job Sheet 30 for gaining access to the rotor. 1. Rotor discard dimension:  Rotor refinishing dimension:  Type of rotor:  Any special precautions to be followed for this rotor?    2. Gain access to the rotor using Job Sheet 30. In most cases, it is not necessary to remove pads from the caliper for this job sheet.

h h

3. Use the brake or outside micrometer to check the thickness of the rotor. Measure at four places. Give measurements in SAE and metric. 1 _________________ 2 _________________ 3 _________________ 4 _________________ Based on the measurements, is the rotor serviceable? _______________ If not, what should be the next action?     NOTE TO INSTRUCTORS: The above step is not needed for this job sheet, but it is included to show students there is no reason to measure runout if the rotor is unserviceable. Such measurement would be a waste of labor.

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4. Install the lug nuts to hold the rotor firmly against the hub if required.

Task Completed h

5. Check the wheel bearing for excessive end play. Correct as needed.

h

6. Install the dial indicator mount onto a suspension member.

h

7. Extend the mount’s linkage over the rotor and install the dial indicator.

h

8. Move the dial indicator so the plunger will contact the machined surface of the rotor about one-third of the way out from the center.

h

9. Adjust the dial indicator until the plunger is against the rotor and retracted about halfway into the indicator.

h

10. Set the dial face to zero.

h

11. Rotate the rotor slowly while observing the needle on the dial indicator. Results:    Recommended action:   

h

12. Move the dial indicator so the plunger will contact the machined surface of the rotor about two-thirds of the way out from the center.

h

13. Repeat step 9 through step 11 and record the results and recommendation.

h

14. Complete any actions necessary to replace, machine, and install the rotor onto the vehicle.

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15. When the repair is complete, clean the area, store the tools, and complete the repair order.

h

Problems Encountered    Instructor’s Response   

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Name ______________________________________

Date _______________

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JOB SHEET

33

MACHINING BRAKE ROTORS OFF-VEHICLE Upon completion and review of this job sheet, you should be able to measure and machine a brake rotor. ASE Education Foundation Correlation This job sheet addresses the following MLR tasks: D.5. Clean and inspect rotor and mounting surface, measure rotor thickness, thickness variation, and lateral runout; determine needed action. (P-1) D.6. Remove and reinstall/replace rotor. (P-1) D.8. Refinish rotor off vehicle; measure final rotor thickness and compare with specification. (P-1) Tools and Materials Bench-mounted brake lathe Service manual Brake disc (rotor) micrometer or outside micrometer Describe the vehicle being worked on: Year _____________________ Make _____________________ Model ______________________ VIN _____________________________ Engine type and size _____________________________ ABS _______________ yes _______________ no _______________ If yes, type ______________ Procedure

Task Completed

NOTE: See Job Sheet 30 for gaining access to the rotor. 1. Rotor discard dimension:  Rotor refinishing dimension:  Type of rotor:   Any special precautions to be followed for this rotor? ____________________________  

h

2. Remove the wheel assembly, caliper, and caliper support as necessary to gain access to the rotor (see Job Sheet 27). Remove the rotor.

h

3. Inspect the rotor. Does its condition make it inadvisable to machine? _______________ If yes, explain. 

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4. Measure the thickness of the rotor (at least 12 points equally spaced around the rotor). Give measurements in SAE and metric sizes. 1 __________ 2 ____________ 3 __________ 4 ___________ 5 ___________ 6 __________ 7 __________ 8 ___________ 9 __________ 10 __________ 11 __________ 12  5. Measure the deepest groove, if any. Is it deep enough to affect machining? If yes, explain and make a recommendation.  

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NOTE TO INSTRUCTORS: The following steps are based generally on a bench brake lathe by AMMCO with one spindle and a floating rotor. Other lathes and/or rotors may require additional instruction for the student.

Task Completed

6. Select a centering cone that fits about halfway through the center hole on the rotor. 7. Select two identical clamps that fit the rotor without interfering with the machined surfaces of the rotor. 8. Slide one clamp onto the lathe shaft, open end out. 9. Slide on a spring, followed by the centering cone. 10. Slide on the rotor and outer clamp followed by the bushing, spacer (if needed), and the nut. Tighten; do not overtighten the nut. 11. Install the damping strap or pad as required. 12. Adjust the assembly inward toward the lathe body until it stops. Back out two turns. 13. Adjust the cutting head so the rotor fits about center between the cutting tips. 14. Move the cutting tips until they meet the rotor and reverse out about half a turn. 15. Adjust the cutting tips until they meet the rotor and reverse out about half a turn. 16. Ensure that the area around the lathe is clear and the lathe’s drive mechanism is in neutral. Switch on the motor. 17. Adjust each cutting bit slowly until it comes in contact with the turning rotor. Hold in place and set the sliding scale to zero. 18. Reverse the bits away from the rotor and switch off the motor. Observe the scratch around the rotor. Is it even all the way around on each side of the rotor? If not, does the missed area on one side correspond with a scratch on the other side? Does the scratch indicate that the rotor is warped, or is there a problem with the setup or machine? Record your observations and make a recommendation on the next step.   19. Assuming that the rotor may be machined and the setup is correct, ensure that the cutting bits are away from the rotor. Switch on the motor and move the cutting bit toward the inside (rear) edge of the rotor’s friction surface. 20. Adjust the cutting head until the cutting tips seem to be aligned with the rear (inward toward hub) of the machines surfaces.

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21. Adjust the cutting tips until they contact the rotor. 22. Continue adjusting the tips until the scale is between 0.002 inch (0.5 mm) and 0.007 inch (0.6 mm). Both tips should cut into the surfaces. A 0.002-inch cut is the minimum, whereas a 0.007-inch cut is the maximum for a single cut. 23. Engage fast speed on the lathe. 24. Observe the rotor as it is being machined. Are there dark (uncut) areas?  Explain the next step to be taken.   25. If the answer to step 24 is no, go to step 30. If the answer is yes, go to step 26.

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26. When the cutting tips clear the rotor, disengage the drive and move the cutting tips back to the starting point.

Task Completed h

27. Adjust the cutting tips to 0.002 inch (0.5 mm) deeper and engage fast cut.

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28. Repeat step 19 through step 25.

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29. When the cutting tip clears the rotor, disengage the drive.

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30. Move the cutting tips to the starting point and set to cut 0.002 inch deeper, for semimetallic pads or 0.002 inch to 0.006 inch for organic pads.

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31. Engage the drive mechanism in slow speed.

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32. When the cutting bits clear the rotor, disengage the drive and stop the motor.

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33. When the rotor stops turning, remove it from the lathe.

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34. Wash the rotor in running hot, soapy water using a brush if possible. If a basin is required, use hot, soapy water and a brush to clean the machined surfaces.

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35. Rinse with clear water and blow dry with an OSHA-approved blowgun.

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36. Install the rotor onto the vehicle.

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37. Use Job Sheet 30 to install the caliper and other components.

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38. When repair is complete, clean the area and lathe, store the tools, and complete the repair order.

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Problems Encountered    Instructor’s Response   

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Name ______________________________________ 

Date _________________

367

JOB SHEET

34

MACHINING BRAKE ROTORS ON-VEHICLE Upon completion of this job sheet, you should be able to machine a rotor mounted on the vehicle. ASE Education Foundation Correlation This job sheet addresses the following MLR tasks: D.5. Clean and inspect rotor and mounting surface, measure rotor thickness, thickness variation, and lateral runout; determine necessary action. (P-1) D.7. Refinish rotor on vehicle; measure final rotor thickness and compare with specification. (P-1) This job sheet addresses the following AST/MAST tasks: D.6. Clean and inspect rotor and mounting surface, measure rotor thickness, thickness variation, and lateral runout; determine necessary action. (P-1) D.8. Refinish rotor on vehicle; measure final rotor thickness and compare with specification. (P-1) Tools and Materials Basic hand tools On-vehicle brake lathe Describe the vehicle being worked on: Year _____________________ Make _____________________ Model _____________________ VIN _____________________________ Engine type and size ____________________________ ABS ______________ yes _______________ no _______________ If yes, type _______________ Procedure

Task Completed

1. Any special precautions to be taken with machining rotors on-vehicle equipped with ABS? Yes _______________ No _______________ Rotor discard dimension (Do not remove the rotor if the dimensions are not readily visible.) ______________________________ SAE ___________________________ mm Rotor refinishing dimension ____________________ SAE _____________________ mm Type of rotor ________________________________ Any special precautions to be followed for this rotor? ____________________________ 

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2. Lift the vehicle to about waist level and remove the tire and wheel assembly. 3. Remove the caliper, caliper adapter (mount), pads, and hardware. Use a wire to suspend the caliper from a suspension or body component, ensuring it is clear of the rotor and lathe during machining.

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4. Use an outside (brake) micrometer to measure rotor thickness and parallelism. Note any wheel bearing movement and correct as necessary. Record your rotor measurements. Minimum thickness by measurement _______________ inch or _______________ mm Does the rotor meet the refinishing dimension? Can the rotor be machined and still meet the discard specification? Does any parallelism measurement exceed 0.002 inch (0.05 mm)?

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Will machining the rotor to parallelism cause it not to meet minimum thickness specification?  Based on your inspection and measurement, is the rotor serviceable as is, does it need machining, or must it be replaced?   NOTE TO INSTRUCTORS: The following instructions are generally based on a ProCut on-vehicle brake lathe. Other lathes may use slightly different procedures and connections. Consult the lathe’s operator manual before proceeding. 5. Remove the rotor’s retaining clips if present and clean the mating surfaces of the hub, rotor, and lathe adapter.

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6. Select and mount the adapter over the lug nut studs. Install and torque lug nuts to no more than 25–30-foot pounds in correct sequence.

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7. Connect the lathe to the adapter ensuring there is no space between the faces of the adapter and lathe flange.

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8. Mount and center the cutting head over the rotor. There are two methods of doing this based on the model of lathe.

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9. Ensure the area around the rotor and adapter is clear of obstacles.

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10. Press the START button and allow the lathe to check and adjust for lateral runout. If the green light on the lathe does not illuminate within 90 seconds, stop the machine and recheck the setup.

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11. Center the cutting head with the tool arms far enough apart to provide clearance to clear the rotor. Move the cutting head to about halfway over the friction surface.

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12. Use the rear cutting bit to scratch the friction surface, and then do the same to the front surface. In case of gouges in the rotor surface, bottom the cutting bit into the deepest one. This becomes the base reference because the Pro-Cut operates as singlepass lathe.

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13. Zero the two adjusting knobs. Back each knob out about two marks (0.005 in.).

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14. Move the cutting head to the inner edge of the friction surface. Ensure the cutting head is not pushed against the rotor center boss or any stationary vehicle components.

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15. Set the two adjusting knobs to ZERO plus the amount of depth needed. Each graduated line is 0.0025 inch.

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16. Switch on the lathe and allow it to complete the total machining before stopping it.

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17. Inspect the rotor on both sides. Does it need additional machining?  If yes, return to step 14, except add another 0.002 inch (0.05 mm) to each adjustment knob’s current reading and perform step 16. If no, proceed to step 18.

SERVICE TIP  It is best to leave the steering wheel unlocked. Depending on the front fender well opening, it may be necessary to steer the front wheels full left or right to properly install the cutting head over the rotor.

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Caution Read and ensure you understand the operation of the lathe before proceeding. On-vehicle brake lathes generate a lot of rotational torque during operation. It can easily break a bone or cause other injury or property damage if operated improperly.

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18. Disconnect the power supply from the lathe and remove the lathe from the rotor.

369

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19. Measure the rotor’s thickness. Is the rotor still serviceable based on current thickness?  20. Install the caliper and the wheel assembly. Lower the vehicle and press the brake pedal several times to seat the pads. 21. Conduct a test drive. SERVICE TIP  When using the Pro-Cut lathe, it may be necessary to perform additional tasks to ensure proper machining. The following tasks should not add more than 15 minutes to the overall task:

A. Trucks with speed-sensitive axles may lock during machining. Try rotating the wheel by hand and if it seems that the rotation resistance is increased, disconnect the drive shaft at the rear U-joint. B.  Switch off the electric locking differential on All-Wheel-Drive (AWD) vehicles. C. AWD without electric locking differential and at temperatures below freezing may require a warm-up drive to heat the oil in the viscous coupling. D.  Vehicles with locking, floating rear axle should have the axle removed.

Problems Encountered    Instructor’s Response  

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Caution The vehicle transmission must be in neutral. The parking brake must be released if this is a rear rotor. Damage to the refinishing lathe or the vehicle may occur if the lathe cannot drive the rotor freely.

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Caution Regardless of the lathe being used, always read the complete instructions found the lathe’s operator manual. Injury or damage could occur when procedures are not followed.



Caution SERVICE TIP  Pro-Cut recommends using soap and warm water in a spray bottle. Use lots. Once washed down, use a clean cloth (not shop rags) or white paper towels to dry the friction surface. Brake cleaner is not recommended because it will not remove the machining grit from the very narrow grooves on the friction surface.

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If the lathe appears to bind or does bind, immediately switch off the motor. Do not try to make any adjustment or clear any obstacles with the lathe in operation. Serious injury could result, or damage to the lathe or vehicle could occur.

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Disc Brake Service

Name ______________________________________ 

Date _________________

PROPERLY BURNISHING BRAKE PADS AFTER REPLACEMENT Upon completion of this job sheet, you will be able to correctly burnish brake pads after replacement.

371

JOB SHEET

35

ASE Education Foundation Correlation This job sheet addresses the following MLR task: D.11. Describe importance of operating vehicle to burnish/break-in replacement brake pads according to manufacturer’s recommendation. (P-1) This job sheet addresses the following AST/MAST task: D.12. Describe importance of operating vehicle to burnish/break-in replacement brake pads according to manufacturer’s recommendation. (P-1) Tools and Materials Service information Vehicle for test drive Protective Clothing Goggles or safety glasses with side shields Describe the vehicle being worked on: Year _____________________ Make _____________________ Model _____________________ VIN _____________________________ Engine type and size ____________________________ Procedure Road Test and Pad Burnishing Whenever new brake pads are installed, they need a short period of controlled operation that is called a burnishing or bedding in period. Burnishing polishes the pads and mates them to the rotor finish. Road testing the vehicle performs this burnishing procedure and verifies that the brakes work properly. WARNING  Road test a vehicle under safe conditions and obey all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to this precaution could lead to serious personal injury. New pads require burnishing to establish full contact with the rotor and to heat and cure any resin left uncured in the friction material. Whether the rotors were refinished or not, new pads do not initially make full contact with the rotor surfaces but require a period of light wear to establish this contact. Also, when brake linings are manufactured, some of the resin materials may remain uncured until the pads are put into service. If fresh pads are subjected to hard braking, the resins can boil to the surface of the pads and cause glazing when they cool. The pads then may never operate properly. 1. Burnish the brake pads during the initial road test by driving at 30 mph to 35 mph (50 kph to 60 kph) and firmly but moderately applying the brakes to fully stop the car. Do this five or six times with 20 seconds to 30 seconds of driving time between brake applications to let the pads cool. Describe the change in the brake pedal feel as the vehicle was driven.    

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2. Now, drive at highway speeds of 55 mph to 60 mph (85 kph to 90 kph) and apply the brakes another five or six times to slow the car to 20 mph (30 kph). Again allow about 30 seconds of driving time between brake applications to let the brake pads cool. 3. Finally, advise the customer to avoid hard braking for the first 100 miles of city driving or the first 300 miles of highway driving.

Task Completed h h

4. Describe the importance of burnishing the brake pads after replacing the brake pads.    Problems Encountered    Instructor’s Response   

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Chapter 8

Drum Brake Service

Upon completion and review of this chapter, you should be able to: ■■

■■ ■■

■■

■■

Diagnose drum brake problems, including poor stopping, pulling, grabbing, and dragging. Determine and perform needed repairs. Remove, clean, inspect, and service brake drums. Remove, clean, and inspect brake shoes and linings and related hardware, including all springs, pins, clips, levers, and adjusters. Determine and perform needed repairs. Clean and remove loose dirt, rust, and scale from the brake backing plates. Inspect and determine if backing plate replacement is needed. Disassemble, clean, inspect, and ­overhaul a wheel cylinder. Replace

■■

■■

■■

■■ ■■ ■■

all cups, boots, and damaged hardware. Properly lubricate brake shoe support pads on backing plates, adjusters, and other drum brake hardware.

Basic Tools Basic technician’s tool set Hydraulic floor jack

Identify brake lining friction material from the edge code, and select correct brake linings for a given vehicle. Identify primary and secondary shoes of a duo-servo brake and leading and trailing shoes of a leading-trailing brake and install them correctly. Refinish brake drums on a brake lathe. Adjust brake shoes and reinstall brake drums or wheel bearings. Reinstall wheels, torque wheel nuts, and make final adjustments.

Terms To Know Discard diameter Drum web Floating drum Hard spots

Heat checks Hold-down springs Piston stop Push (speed) nut

Return spring Threading

SERVICE PRECAUTIONS Specific CAUTIONS and WARNINGS are given throughout this chapter where needed to emphasize safety. The following general precautions apply to many different drum brake service operations and are presented at the beginning of this chapter to highlight their overall importance. ■■ When servicing drum brakes, never use an air hose or a dry brush to clean the brakes. Use OSHA-approved cleaning equipment to avoid breathing brake dust. See Chapter 1 in this Shop Manual for details on working safely around airborne asbestos fibers and brake dust. ■■ Do not spill brake fluid on the vehicle; it may damage the paint. If brake fluid does contact the paint, wash it off immediately. To keep fluid from spraying or running out of lines and hoses, cover the fittings with shop cloths when disconnecting them. 373

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■■

Always use the DOT type of brake fluid specified by the vehicle manufacturer. Whenever possible, do not mix different brands of brake fluid. During servicing, keep grease, oil, brake fluid, or any other foreign material off the brake linings and drums. Handle brake shoes and drums carefully to avoid scratching the drums or nicking or scratching brake linings.

DIAGNOSING DRUM BRAKE PROBLEMS

Classroom Manual page 186

Many of the diagnostic procedures for drum brakes are similar to those listed in Chapter 7 on disc brakes. If problems are suspected in the drum brakes, road test the vehicle. Instructions for a safe, complete road test are given in Chapter 2 of this Shop Manual. Even driving across the driveway and into the service bay can reveal a lot about brake system condition. WARNING  Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to this precaution could lead to serious personal injury and ­vehicle damage.

Check for excessive travel and sponginess as the pedal is applied (Figure 8-1). Listen for noises: not just the obvious sounds of linings grinding on the drums, but mechanical clanks, clunks, and rattles. For a complete inspection, the wheels must be removed for a clear view of the brake shoes, attaching hardware, and drum (Figure 8-2). Inspect the wheel and brake assembly for obvious damage that could affect brake system performance. Check the following: 1. Tires for excessive or unusual wear or improper inflation 2. Wheels for bent or warped rims

Figure 8-1  Apply the brake pedal and check for excessive travel and sponginess.

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Drum Brake Service Backing plate

375

Brake assembly Drum web

Drum

Figure 8-2  The first step of drum brake service is to inspect all the parts in the complete assembly.



3. Wheel bearings for looseness or wear 4. Suspension system for worn or broken components 5. Brake fluid level in the master cylinder 6. Signs of leakage at the master cylinder, in brake lines or hoses, at all connections, and at each wheel cylinder 7. Damaged or improperly adjusted brake shoe 8. Loose, glazed, or worn lining 9. Weak or bad return springs and hold-down springs. Return springs pull the shoes to the released position after the pedal is released. Hold-down springs hold the shoes to the backing but allow the shoes to move as needed during braking 10. Loose backing plate 11. Self-adjusters not operating 12. Oil, grease, or brake fluid on lining 13. Damaged or improperly machined drums A damaged or improperly adjusted brake shoe may cause brake drag or grab, pulling to one side, wheel lockup, hard pedal, excessive pedal travel, or noisy operation. A loose lining may cause pull to one side or persistent brake chatter. Glazed or worn linings are the most common cause of drum brake problems. Such problems include hard pedal, pulling to one side, wheel locking, brake chatter, excessive pedal travel, noisy brakes, grabbing brakes, or little or no braking power. A broken or weakened return spring (Figure 8-3) will cause the brake to drag or the vehicle to pull to one side. A loose backing plate can cause brake drag, brake chatter, or a locked wheel. If the self-adjuster operates incorrectly, the brake shoes will be improperly adjusted. The car may then pull to one side, have excessive pedal travel, or have a clicking sound in the shoes. Oil, grease, or brake fluid on the linings can cause hard pedal, brake pull, wheel lock, brake chatter, uneven braking, noisy brakes, grabbing brakes, or loss of braking power. Grease or oil that is flung around the inside of the fender well is a sign of complete axle seal failure. The brakes must be replaced along with the seal. Damaged or distorted brake drums also adversely affect braking. Excessive pedal travel may be a sign of a cracked drum. But as discussed in Chapter 4 of this Shop Manual, excessive pedal travel also may be caused by trouble in the hydraulic system. An

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Chapter 8 Spread or collapsed coils

Damaged shank

Hook Spread

Discoloration

Bent or twisted shank

Figure 8-3  Inspect the shoe return springs for the damage noted. Also perform a bounce test. Drop the spring on a floor or steel table: if you hear a ring, it is a good spring; if you do not, the spring is defective.

out-of-round drum can cause the brake to drag and chatter, and the vehicle also may pull to one side. A scored drum can cause uneven braking with noisy or grabbing brake action. Drums that have become bell mouthed or distorted allow only partial lining contact and a twisting of the brake shoe that results in excessive pedal travel and hard pedal pressure. Threaded drums result when a dull or poorly shaped cutting bit is used to resurface the drums. These threads cause the brake shoes to move toward or away from the backing plate according to the direction of the thread spiral. This action creates a snapping or clicking action, which is especially noticeable on light brake applications at low speeds. A faulty wheel cylinder also may be the cause of brake drag, wheel lock, side pull, or a noisy and grabbing brake. If any of these conditions are found during the test drive, remove the drums and inspect the brakes. Any wear in the shoes, shoe hold-down and retracting hardware, drums, or wheel cylinder will make a complete brake system overhaul necessary. Disc brakes allow for a quick inspection every time the wheel is removed, but drum brake components remain covered by the drum when the wheel is removed. Fortunately, drum brakes wear about half as quickly as disc brakes, and the recommended inspection interval for many vehicles is now 30,000 miles or every 2 years. Many state vehicle inspection laws specify that drums must be pulled at regular intervals and the system inspected. Always remove the drums for inspection whenever the customer has a brake-related complaint or concern or whenever a problem is suspected. Always service drum brakes and linings in axle sets. If the car has antilock brakes and one wheel stays locked momentarily, the difference in wheel speed may light the ABS warning lamp. If this is a persistent problem, replacing semi-metallic linings with organic linings is often a cure.

SERVICE TIP  In very cold weather, rear brake shoes can freeze to the drum surface. It takes the right (or wrong) combination of circumstances to cause this. It is most common when the parking brake is applied in damp weather or after driving through water and left applied when temperature drops below freezing. High metallic content in the brake linings further aggravates the problem.

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DRUM BRAKE SERVICE OPERATIONS Drum brake service consists of the following general operations: ■■ Drum removal ■■ Brake cleaning and inspection ■■ Wheel cylinder service ■■ Shoe replacement and hardware installation ■■ Drum refinishing and reinstallation ■■ Brake adjustment

Vehicle Preparation For most drum brake service, the vehicle must be raised on a hoist or safety stands, wheels removed, and brakes disassembled to the extent necessary for the planned service. Follow these general preparation steps: Disconnect the battery ground (negative) cable. If the vehicle has electronically controlled suspension, turn the suspension service switch off. Raise the vehicle on a hoist or safety stands and support it safely. Remove the wheels from the brakes to be serviced. Brakes are always serviced in axle sets, so you may remove both front wheels, both rear wheels, or all four. Vacuum or wet-clean the brake assembly to remove all dirt, dust, and fibers.

Classroom Manual page 190

Special Tools Lift or jacks with stands Impact tools Chalk

BRAKE DRUM REMOVAL The brake drum must be removed for all brake service except bleeding the wheel cylinder and lines or a basic manual adjustment. Removal procedures are different for fixed and floating drums. In some cases, the parking brake may have to be adjusted to add some slack (Figure 8-4). Self-adjusters (Figure 8-5) may have to be adjusted to gain shoe-todrum clearance for drum removal. Wear on the drum friction surface creates a ridge at the unworn rim of the drum. As the self-adjusters move the shoes outward to take up clearance, the shoe diameter becomes larger than the ridge diameter. If adjustment is not retracted, the drum ridge may jam on the shoes and prevent drum removal (Figure 8-6). Trying to force the drum over the shoes may damage brake parts.

Parking brake equalizer

Figure 8-4  Loosen the parking cables if necessary to ensure enough shoe clearance for drum removal.

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Periodic inspection of the drum brakes can prevent excessive wear and problems from a lack of maintenance, such as ridge formation on the drums.

Caution Do not step on the brake pedal while a brake drum is off, or the wheel cylinder will pop apart.

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378

Chapter 8 Backing plate

Adjusting tool

Drum

Worn drum Ridge

Self-adjuster lever

Star wheel Brake shoe

Welding rod

Figure 8-5  Use a heavy piece of wire, such as a piece of welding rod, to move the adjusting lever away from the star wheel. Then rotate the star wheel to release brake adjustment for drum removal.

Figure 8-6  These shoes have adjusted to fit a badly worn drum, and the drum will jam on the lining if you try to remove it without backing off the brake adjustment.

AUTHOR’S NOTE  A good friend of mine applied for a job at a governmental agency as a technician. He had to pass the civil service exam, be ASE certified, and pass a “shop” exam. He had to perform several repairs and tests within a certain length of time. One part of the exam was removing a brake drum from the rear of the vehicle. Of course, the drum would not come off, and he had a choice of tools. A large prybar and hammer was in the tool cart, as well as a drum brake-adjusting tool (spoon) and a welding rod. My friend used the welding rod to hold the selfadjuster mechanism out of the way and retracted the shoes with the brake spoon. He then removed the drum without damaging the brake hardware, drum, or wheel cylinder. The instructor said that only about one in 50 “technicians” who applied for the job passed this part of the test and that he usually had to keep brake hardware in stock to repair their shop test guinea pig. My friend started the next day.

Before removing a drum, mark it “L” or “R” for left or right so that it gets reinstalled on the same side of the vehicle from which it was removed.

Special Tools Dust cap pliers Cotter pin puller Brake adjusting tool (spoon)

Fixed (One-Piece) Drum Removal Brake drums that are made as a one-piece unit with the wheel hub were common several years ago as rear drums on a FWD vehicle. A technician may still occasionally run into one-piece units, so they are included in this text. The hub contains the wheel bearings and is held onto the spindle by a single large nut (Figure 8-7). This nut also is used to adjust bearing end play. Remove a fixed drum mounted on tapered roller bearings as follows: Release the parking brake if removing a rear drum. Use a pair of dust cap pliers or large slip-joint pliers to remove the dust cap from the hub. Remove the cotter pin from the castellated nut or nut lock on the spindle. Then remove the nut lock, if used. Remove the drum retaining nut and thrust washer. Pull outward on the drum to slide it off the spindle (Figure 8-8). If the drum drags or catches on the brake shoes, slide it back onto the spindle and temporarily

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Drum Brake Service

Brake drum

Cotter pin

Thrust washer

Outer bearing cone

Brake drum retainer nut

379

Nut lock

Grease cap

Figure 8-7  To remove a one-piece drum and hub, remove the single large retaining nut and slide the drum and hub off the spindle along with the bearings.

Figure 8-8  The drum brake assembly is covered by the drum.

reinstall the spindle nut. Then retract the parking brake and the brake shoe adjustment. Brake adjustment is explained at the end of this chapter; parking brake adjustments are covered in Chapter 9 of this Shop Manual. When removing the drum, be careful not to drop the outer wheel bearing on the floor and do not drag the inner bearing across the spindle, particularly the threads at the end of the spindle.

Shops typically repack the wheel bearings and install new seals as a part of a brake repair.

Special Tool SERVICE TIP  Diagonal wire cutters work very well in removing push nuts. An impact screwdriver is a very useful tool for loosening drum retaining screws.

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Brake adjusting tool (spoon)

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Chapter 8

Occasionally the inner bearing race of a drum sticks on a spindle and prevents easy drum removal. In such a case, use a puller to remove the drum. After the drum is removed, use another puller or pair of small prybars to remove the bearing race from the spindle. After any drum is removed, inspect the grease in the hub and on the bearings. If the grease is dirty or dried out and hard, it is a clue to possible bearing damage. Set the drum and all bearing parts aside for cleaning and close inspection. If the grease seems to be in good condition, place the drum on a bench with the open side down. Cover the outer bearing opening with a shop cloth to keep dirt out. SERVICE TIP  The drums on some import vehicles have countersunk screws holding them to the hub or axle flange. An impact screwdriver may be required to loosen the screws. Other import drums may have two small (6 mm-8 mm) threaded holes through which bolts can be screwed to break the drum loose from the hub/ axle flange. Both drum types will have the screws or holes between the wheel studs.

₅ SERVICE TIP  Do not use SAE /₁₆ threads in these holes. The SAE bolt will seem to fit; however, as soon as torque is applied the internal threads in the holes will rip.

Floating (Two-Piece) Drum Removal

A floating drum is a brake drum that is separate from the wheel hub or axle. Floating drums are the most common type used with RWD vehicles.

Caution Do not attempt to hit directly on the drum between the studs. It is probable that the hammer will hit and damage at least one stud. Use the drift pin to deliver the hammer’s force to the drum. If a drift pin is not available and a hammer is used, partially reinstall the wheel nuts to protect the end of the stud.

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Floating drums are separate from the wheel hub or axle. On a RWD vehicle, the drums are held in place on studs in the axle flange by the wheel and wheel nuts. Some FWD cars have rear hubs that contain sealed bearings and are mounted to the chassis on a spindle. These installations use a floating drum that is mounted on studs on the hub flange and held in place by the wheel and wheel nuts. On many floating drums, push (speed) or Timmerman nuts may be holding the drum onto two or three studs (Figure 8-9). Push nuts are made from thin stamped steel. They will not accept much torque. These push nuts are used to hold the drum and hub or axle together during vehicle assembly, before the wheels are installed. On most vehicles, the push nuts or speed nuts do not need to be reinstalled during service. Some Ford vehicles, however, have wheel studs with high shoulders that can catch the drum and hold it at an angle if you are not careful when installing the wheel. Install new push nuts on these vehicles to hold the drum squarely against the axle or hub flange before installing the wheel. Remove a fixed drum mounted on a hub or an axle flange as follows: 1. Release the parking brake. 2. Remove the push nuts, if installed, by grabbing each one with a pair of pliers and twisting it off the stud. 3. Use a scribe or paint to make index marks on the drum and the hub so that the drum can be reinstalled in its original location. Others may have two internally threaded holes 180 degrees apart. Bolts (typically 8 mm by 1.25 threads) are screwed into these holes and the drum is pushed off the axle/hub flange. 4. If the drum is not rusted or stuck to its flange, lift it off and move it to a bench. If the drum drags or catches on the brake shoes, slide it back onto the flange or hub and retract the parking brake and the brake shoe adjustment. Brake adjustment is explained at the end of this chapter; parking brake adjustments are covered in Chapter 9 of this Shop Manual.

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381

Drum web center section

Apply penetrating oil; strike with drift and hammer

Axle or hub

Figure 8-9  Speed nuts are used to hold the brake drums in place during vehicle assembly. They can be cut off and discarded when the drums are pulled off the vehicle for the first time.

Figure 8-10  The center hole of a floating drum may catch on the axle flange or hub as you try to remove it.

5. Penetrating oil may assist in loosening a stuck drum. If the drum is stuck to its flange or hub (Figure 8-10), use a large scribe or center punch to scribe around the joint at the drum and flange and break the surface tension. If the drum is still stuck, strike the edge of it with a dead-blow hammer at a 45-degree angle to loosen it. If a dead-blow hammer is not available, place a block of hard wood against the drum and strike it with a large ball-peen hammer. If the drum remains stuck, use a puller to separate it from the flange. Photo Sequence 17 shows most of the steps for typical brake drum removal from a rear axle.

17 Typical Procedure for Removing a Brake Drum from a Rear Axle Photo Sequence

P17-1  Release the parking brake and raise the car on a hoist. Mark the position of the wheel to the axle flange so the wheel can be reinstalled in the same position on the flange. This ensures proper wheel balance.

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P17-2  Remove the wheel nuts holding the wheel to the hub and pull off the tire and wheel.

P17-3  Mark the position of the brake drum to the axle flange so the drum can be reinstalled in the same position on the flange.

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Photo Sequence 17 (CONTINUED)

P17-4  If necessary, remove tension from the parking brake cables by loosening the adjusting nut at the equalizer.

P17-7  While holding the pawl away from the star wheel, use a screwdriver or brake adjuster to back off the star wheel about two dozen clicks or until the drum is loose on the wheel studs.

P17-10  Inspect the brake assembly for broken springs, heat damage, leaking wheel cylinders, and other wear.

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P17-5  Remove the plastic or metal plug from the backing plate slot to expose the adjuster. Some adjusters are accessed by removing a metal plug on the drum.

P17-8  Remove the drum from the studs and the axle flange. Some drums may be secured to the flange by two small screws. Remove them to remove the drum.

P17-6  Insert a small wire hook through the slot and push the adjusting lever away from star wheel about 1/16 inch.

P17-9  If the drum is stuck to the flange, tap it lightly with a soft-faced mallet. If it is really stuck, free it as explained in the previous section of this chapter.

P17-11  Inspect the drum for scoring or other damage.

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DRUM BRAKE CLEANING Thorough cleaning of the brake assembly is a bigger job on drum brakes than on disc brakes. Dirt and dust created by drum brake lining wear stays inside the enclosure formed by the drum and backing plate. Fine metallic particles caused by drum wear combine with lining dust to create a unique brake grime, most of which accumulates on the backing plate, the shoes, the springs, and other parts of the brake assembly. SERVICE TIP  The use of a puller to remove a brake drum must be done with care. Tap the drum as the puller applies pulling force. The puller could crack, bend, or otherwise damage the drum.

WARNING  Do not blow dust and dirt off brake assemblies with compressed air outside of a brake cleaning enclosure. Airborne dust and possible asbestos fibers are an extreme respiratory hazard.

Special cleaning equipment is available for brake service and is discussed in Chapter 7 of this Shop Manual. Always ensure that cleaning equipment is in proper working condition and follow the manufacturer’s instructions for the specific equipment in your shop. Thoroughly clean the backing plates, struts, levers, and other metal parts to be reused. Examine the rear wheels for evidence of oil or grease leakage past the wheel bearing seals. Such leakage could cause brake failure and indicates the need for additional service work. Brake dust waste must be collected, recycled, and disposed of in sealed, impermeable bags or other closed, impermeable containers. Any spills or release of brake waste material from inside of the enclosure or vacuum hose or vacuum filter should be immediately cleaned up using vacuuming or wet-cleaning methods. Review the asbestos safety instructions in Chapter 1 of this Shop Manual.

Cleaning with Vacuum-Enclosure Cleaning Systems Vacuum-enclosure cleaning systems consist of a tightly sealed protective enclosure that covers and contains the brake assembly (Figure 8-11). The enclosure has built-in, ­impermeable sleeves and gloves that let you inspect and clean the brake parts while preventing the release of dust and potential asbestos fibers into the air. Examine the condition of the enclosure and its sleeves before beginning work. Inspect the enclosure for leaks and a tight seal.

Special Tool Vacuum brake cleaner

Cleaning with Wet-Cleaning Systems Low-pressure wet-cleaning systems wash dirt from the brake assembly and catch the cleaning solution in a basin (Figure 8-12). The cleaner reservoir contains water with an organic, nonpetroleum solvent or wetting agent. To prevent any asbestos-containing brake dust from becoming airborne, control the flow of liquid so that the brake assembly is gently flooded. Wash the backing plate, the shoes, and other brake parts used to attach the shoes before removing the old shoes. The cleaning solution must be treated as hazardous waste when changed. The filter on most cleaners with a filtration system is also treated as hazardous waste.

Cleaning with Vacuum Cleaning Equipment Several types of vacuum cleaning systems are available to control brake dust in the shop. The vacuum system must have a HEPA filter to handle asbestos dust (Figure 8-13).

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Glovebag collection system

HEPA vacuum cleaner

Figure 8-11  This full-enclosure asbestos system traps brake dust and helps keep the shop’s air free of dust.

Figure 8-12  Typical wet-cleaning equipment with a catch basin.

Figure 8-13  A HEPA-equipped vacuum cleaner is a good tool for cleaning brake components.

A general-purpose shop vacuum is not an acceptable substitute for a special brake vacuum cleaner with a HEPA filter. After vacuum cleaning, wipe any remaining dust from components with a damp cloth.

Special Tool Brake cleaning tools/ equipment

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Cleaning with Parts Washers Almost all shops have a parts washer that is used to clean miscellaneous small and medium-size parts that are removed from vehicles. Traditionally, parts washers have used

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petroleum solvent, but many current models use water-based solvents and detergents. Do not use petroleum-based products to clean rotors and drums. Cast iron is porous and will hold the solvent and damage newly installed shoes. A parts washer that uses water-based solvents and detergents as the only solvent is safe. When the cleaning agent is changed, the old liquid is treated as hazardous waste.

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Special Tool Parts washer

DRUM BRAKE ASSEMBLY INSPECTION Rear drum brakes wear much more slowly than front disc brakes because only 20 percent to 40 percent of the braking effort is provided by the rear brakes. On older four-wheel drum brake systems, front-to-rear wear is more equal, but front brakes still tend to wear more than rear brakes. Most drum brakes today are used on the rear wheels with disc brakes on the front, but it is still important not to overlook rear brake inspection during any brake service. After the drum is removed, set it aside for inspection and measurement as explained later in this chapter. Then inspect the shoes and linings, the wheel cylinders, the springs, and other parts as explained below. Inspect each brake assembly before disassembly to help identify causes of problems. For example, if there is contamination on a brake lining, it could be brake fluid or gear oil. In either case, it indicates that the wheel cylinder and the axle oil seal should be checked very closely. Similarly, unusual wear on springs, struts, or levers can be a clue to incorrectly installed parts or abnormal operation. Such problems can be more easily identified while inspecting the complete assembly.

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Special Tool Vernier caliper or precision scales

Lining and Shoe Inspection Inspect three general conditions of the lining: thickness, wear pattern, and damage. Use a precision scale or a depth micrometer to measure lining thickness precisely. A tire depth gauge is also an excellent tool to measure lining thickness (Figure 8-14). Lining thickness is the first thing—but not the only thing—that determines the need for replacement. Most carmakers specify a minimum lining thickness of 1/32 inch (0.030 in. or 0.75 mm) above the shoe table or above the closest rivet head.

Figure 8-14  Use a depth micrometer to measure lining thickness precisely.

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This thickness recommendation does not mean that a lining worn to �/₃₂ inch should continue in service; it means that �/₃₂ inch is the absolute minimum safe thickness at which the brake lining can perform to its minimum requirements. Worn linings cannot dissipate heat adequately, and the last �/₃₂ inch of lining will wear much faster than the first �/₃₂ inch of fresh linings. From a practical and safe standpoint, relined shoes should be installed before the lining has worn to the thickness of the shoe table at its thinnest point above the table or the closest rivet. This is approximately �/₃₆ inch. Use a depth gauge or scale graduated in �/₃₂-inch or �/₆₄-inch increments to measure lining thickness at several points. Also inspect the lining for cracks, missing rivets, and looseness. Check for contamination from grease, oil, or brake fluid. A leaking wheel cylinder can deposit brake fluid on the linings. A leaking oil seal on a rear drive axle can let gear oil from the differential get onto the brakes. A less frequent, but possible, cause of lining contamination is a leaking grease seal for the wheel bearings in a hub. If linings are damaged or contaminated in any way, they must be replaced. Remember also that brake linings are serviced in axle sets so all linings for both wheels must be replaced if any are damaged. Check the linings for unequal wear on any shoe of an axle set (Figure 8-15). Also look for uneven lining wear on any one shoe. If one lining on a duo-servo brake is worn more than the other, be sure the primary and secondary shoes are installed in the right locations. The primary shoe with the shorter lining should be the forward shoe. If the linings on one wheel are worn more than the other, that drum may be scored or rough. Uneven wear from side to side on any one set of shoes can be caused by a tapered drum. Check for parking brake cables to see that they are not sticking. If brake shoes and linings have a slight blue coloring, it indicates overheating. In this case, the brake adjuster springs and hold-down springs should be replaced. Overheated springs lose their tension and could allow a new lining to drag and wear prematurely if not replaced. If the lining of one shoe on one wheel is worn more than the other, check the less worn shoe for binding and incomplete application. A problem such as this is more likely to occur on a leading-trailing brake than on a duo-servo brake. If the lining is worn more in the center than the ends or vice versa, the lining may not have been arced properly to the drum diameter. If so, check the lining-to-drum fit closely when installing new shoes with a resurfaced drum. If the linings are worn more at the end where the parking brake applies the shoes, the parking brake may be adjusted too tightly. Linings worn badly at the toe or heel also may indicate an out-of-round drum.

SERVICE TIP  If a customer complains that the rear brakes lock easily or that the ABS activates at the rear during light to moderate braking, check the basics before condemning the expensive ABS hardware. Grabbing rear drum brakes are often caused by contaminated or cracked linings, fatigued return springs, or grossly uneven brake adjustment from one side to the other.

Wheel Cylinder and Axle Inspection If left undetected and unrepaired, a leaking wheel cylinder can drain most of the fluid from half of the brake system, and the leaking fluid will contaminate and ruin the brake lining. Brake operation and safety are seriously compromised by a defective wheel cylinder. Brake fluid contamination can cause the brakes to grab upon application. Inspect the outside of the wheel cylinder for leakage. Then pull back the dust boots and look for fluid at the ends of the cylinder (Figure 8-16). Minor dampness or seepage and some staining are acceptable, but any noticeable liquid fluid means that the cylinder

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Figure 8-15  Inspect the linings for unequal wear, as well as for thickness, cracks, fluid or grease contamination, and other damage. Unequal wear is most common at the indicated points.

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Figure 8-16  Pull the boot slightly away from the cylinder and check for liquid or fluid within the boot.

should be overhauled or replaced. Also, be sure that the pushrods engage the shoes properly. Check the cylinder mounting on the backing plate for looseness and missing fasteners. Most cylinders are held to the backing plate by small cap screws, but some are secured with clips. Brake spring tension and tight clearances in the mounting hole can make a clip-mounted cylinder seem secure even when the clip is missing. Inspect this type of cylinder mounting closely. Inspect the brakes on a rear drive axle for contamination by gear oil leaking from the axle seal. Use a flashlight to inspect thoroughly behind the axle flange. If a leaking seal is found in the early stages, replace it before gear oil gets to the brake linings. Similarly, inspect the backing plate for grease leaking past the inner wheel bearing seal of a nondriving hub. Some vehicle manufacturers require that the hardware be replaced each time the shoes are changed. This is also recommended if the vehicle has high mileage or aged hardware.

Backing Plate, Spring, and Hardware Inspection Backing plates are rarely replaced unless they are damaged in an accident. Close inspection of the backing plate can solve problems with other brake parts, however. Inspect for a broken or bent plate or other obvious damage. Also look for uneven wear or scarring on the shoe support pads (Figure 8-17), which could indicate a bent shoe or incorrectly installed parts. Place a straightedge across two of the shoe support pads as far from each other as possible to check the straightness of the backing plate. If the straightedge does not contact both pads evenly and squarely, remove the backing plate for closer inspection and measurement. Check to see that deep grooves (scarring) have not been worn into the backing plates, which could cause the shoes to hang. Inspect the return and hold-down springs for damage and unusual wear (Figure 8-18). Pry the brake shoes slightly away from the backing plate and release them. The holddowns should pull the shoes sharply back to the plate. Inspect self-adjuster levers, pawls, and springs for wear and replace any defective parts (Figure 8-19). Pawls are the levers that actuate the self-adjuster (star wheels). Many shops

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Figure 8-17  The shoe support pads must be cleaned and lubricated with brake lubricant before installing the shoes.

Spread or collapsed coils

Damaged shank

Cable plate

Hook Spread Adjuster spring

Discoloration

Bent or twisted shank

Figure 8-18  Inspect the springs for heat damage (discoloration), damaged or spread coils, and spread connecting hooks.

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Adjuster cable Adjusting pawl

Adjusting screw assembly

Figure 8-19  Inspect all of these self-adjuster parts for wear and damage.

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389

Return spring

Parking brake strut

Parking brake lever

Conduit

Parking brake cable

Figure 8-20  Inspect the parking brake linkage for wear and damage.

make it standard practice to replace self-adjuster cables at each brake job, but at least inspect them for broken strands and obvious wear and stretching. Some new self-adjuster kits may not include all levers. Check the parking brake linkage for damage and rust. Be sure that all parking brake levers and links are properly lubricated and free to move easily (Figure 8-20). A can of pressurized chain and cable lubricant can be used to lubricate a parking brake cable. Pull the cable out as far as possible and spray the visible cable into the end of the conduit. Work the cable back and forth several times and then clean any excess lubricant from the cable and conduit end. See Chapter 9 of the Shop Manual for further details on parking brake service.

Classroom Manual pages 202

SERVICE TIP  If one piece of the brake hardware is damaged and needs replacing, replace all of the hardware on both sides. Hardware for drum brakes usually comes in kits that will include enough parts for both sides. Most brake hardware kits do not include hardware for the self-adjuster. It is not unusual to replace the brake hardware and not the self-adjuster or vice versa.

DRUM BRAKE DISASSEMBLY Duo-servo brakes and leading-trailing brakes all have a pair of shoes, return springs, holddowns, and self-adjusters, but a lot of variety exists in the individual parts of drum brake assemblies. Figure 8-21 shows the components of a typical leading-trailing drum brake. Figure 8-22 shows a duo-servo drum brake. Refer to these figures and Photo Sequence 18 for general guidance during disassembly and reassembly.

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Cup

Boot

Holddown spring and cap

Spring Cylinder

Piston

Spring

Adjusting screw socket

Parking brake pin, washer, and clip

Adjusting pivot nut

Washer Adjusting screw

Parking brake lever

Retracting spring

Secondary shoe

Holddown spring and cap

Primary shoe

Figure 8-21  Exploded view of a typical leading–trailing drum brake assembly.

Return spring Holddown spring and cap

Return spring

Strut spring

Boot

Cup Piston

Primary shoe

Holddown spring and cap

Parking brake strut

Spring

Cable plate

cylinder

Adjuster spring

Pivot nut

Adjuster

Adjuster cable

Secondary shoe

Socket Adjusting screw

washer

Figure 8-22  Exploded view of a typical duo-servo drum brake assembly.

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18 Typical Procedure for Disassembling a Drum Brake Photo Sequence

P18-1  Remove the top return spring from the anchor and shoe. Remember which shoe return spring is on top. It must be reassembled in the same position.

P18-2  Remove the retaining spring from the secondary shoe. Do not remove the primary shoe retaining spring at this time.

P18-4  Remove the parking brake strut and spring from the primary shoe. Withdraw it to the front. Remember which end holds the spring and which end faces forward.

P18-5  Remove the retaining spring on the primary shoe. Do not allow the shoe and selfadjuster mechanism to drop.

P18-7  Clean and lubricate the shoe support pads now. This is a common area that may be forgotten.

P18-8  Laying out the brake components in roughly the same position as they were on the vehicle will help in repositioning them correctly during assembly.

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P18-3  Rotate the secondary shoe forward and down. Catch the self-adjuster as the shoe releases the tension.

P18-6  There are two means to disconnect the parking brake from the primary shoe. One way is to remove the clip from the parking brake lever pin where it passes through the shoe. Do not lose the waved washer behind the shoe. The other way is to disconnect the cable from the lever as shown. The lever can be removed from the shoe later.

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Special Tools Lift or jack with stands Impact tools Return spring pliers Hold-down spring removal tool Service manual

Caution Do not depress the brake pedal when the shoes are being removed, installed, or have been removed from the backing plate. Without the shoes positioned properly, the pistons could be forced from the wheel cylinder when the pedal is depressed.

Caution Prevent dropping the self-adjusting screw assembly during disassembly and assembly. There is a small wave washer between the adjusting screw and the nearest end. This washer can be lost easily. Without it, the self-adjusting screw may bind and not adjust correctly. Normally, the entire screw assembly must be purchased to replace this washer.

SERVICE TIP  Brake shoe return springs can be weakened by excessive heat and hard use but they may still look good. One traditional way to identify workhardened and weak springs is to drop them on a concrete floor. If the springs land with a dull plop, they are good. If they land with a sharp ping and bounce off the floor, they have been overheated or work hardened and should be replaced.

AUTHOR’S NOTE  You will note some differences between the text and Photo Sequence 18. The text generally follows manufacturer-recommended sequence, whereas the photo sequence is my way of doing it. Both will work, and you may even find a better method of doing it.

If not thoroughly familiar with the brake design being serviced, obtain the vehicle service manual and refer to the procedures and illustrations. Remember that the brakes are mounted the same on both sides of most vehicles. After observing one side and moving to the opposite side, remember that what was at the right hand is now at the left hand. It also may help to service the brake on one side of the vehicle at a time and use the brake on the opposite side as an assembly reference. Remember that left-hand and right-hand parts of many drum brakes look the same but are not. If parts, such as self-adjusters, are interchanged from one side to the other they will not work properly. Raise the vehicle on a hoist or safety stands, remove the drum, and clean the brake assembly as explained earlier in this chapter. Then follow the general guidelines in the following sections, along with specific vehicle service procedures, to service drum brakes. WARNING  Wear safety glasses or face protection when using brake fluid. Injuries to the face or eyes could occur from spilled or splashed brake f luid. Brake fluid is irritating to the skin and eyes. In case of contact, wash skin with soap and water or rinse eyes thoroughly with water and seek medical attention for the eyes.

The shoe return springs are usually the first parts to be removed because their tension holds most of the other parts in place, but before removing the springs study their installation (see Figure 8-19). Keep fingers away from the return springs during removal and installation. If a spring slips off a tool or mounting point, its strong tension can cause injury or damage. Note how the springs are hooked over anchor posts and to which holes in the shoe webs they are attached. Special brake spring pliers and other tools are available for spring removal and installation (Figure 8-23). The rear brakes on some GM cars have a large horseshoe-shaped spring that serves as both a return spring and a hold-down spring (Figure 8-24). Special lever-type pliers are used to remove and install it (Figure 8-25). SERVICE TIP  There is a mistaken notion in some shops that the pads on drum brake backing plates on which the shoes ride should be ground and sanded with a power sander to get them as smooth as possible. Do not do it. Yes, you should remove any big gouges or ridges with a file and lightly sand the pads by hand to clean them, but that is it. Grinding or power sanding can cut the pads down to different heights and cause the brake shoes to cock and bind and may also weaken the backing plate. Finish off any cleaning or light sanding with a light coat of brake lubricant, and that part of the brake job is completed.

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393

Brake spring tool

Figure 8-23  Use a brake spring tool to disengage the return springs from the anchor.

Unispring

Figure 8-24  The rear brakes on some GM cars have a large horseshoeshaped spring (Unispring) that serves as both a return spring and a holddown spring. Use prybar end of pliers Use scissor end of pliers

Install

Remove

Adjust

Figure 8-25  Use these special pliers to remove a GM Unispring. The pliers are also used to operate the self-adjusting ratchet mechanism prior to installing the brake drum.

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Caution Prevent brake fluid from coming in contact with the vehicle’s finish. Brake fluid damages paint and finish immediately on contact. If fluid contacts the finish, wash the area thoroughly with running water and soap if possible.

Caution Always clean around the lines or covers before removing or loosening them. Dirt and other contaminants will void the warranty and may damage system components.

After removing the return springs, remove the lighter hold-down springs and clips. Again, special tools are available to make the job easier and to avoid damage to parts. At this point, the shoes are loosened from the backing plate, and shoe-to-shoe springs and self-adjuster parts can be removed easily. Carefully note the positions in which the parts are installed so that you can reinstall them correctly. Disconnect the parking brake cables and linkage from rear brakes with parking brake levers and struts (Figures 8-26 and 8-27). It is often easiest to disconnect the parking brake linkage after the shoes are loosened from the backing plate to release tension on the cables. On some brakes, sections of the shoe webs fit into the ends of the wheel cylinder pistons. On other brakes, short pushrods, or shoe links are installed between the cylinder pistons and the shoes. If the brakes being serviced have wheel cylinder pushrods, remove them for cleaning and reinstallation later. If the wheel cylinders are not removed, install cylinder clamps (Figure 8-28) to keep the pistons from popping out of the cylinders. On some brake assemblies, wheel cylinder clamps can make disassembly and reassembly easier by holding the cylinder pistons in place while removing and reinstalling the shoes.

Parking brake lever

Cable

Figure 8-26   Pull the parking brake lever forward and disconnect the cable from the end of the lever. Brake shoe

Wave washer

Parking brake lever U-clip

Wheel cylinder clamp

Figure 8-27  Then remove the clip and washer to separate the parking brake lever from the secondary or trailing brake shoe.

Figure 8-28  Install wheel cylinder clamps to keep the pistons from popping out of the cylinders when you disassemble the brakes.

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Wheel cylinder retainer Bolts

Wheel cylinder

Wheel cylinder Backing plate

Backing plate A

B

Figure 8-29  Two common ways to mount wheel cylinders to backing plates are with small bolts or cap screws (A) or with a spring-type retainer ring (B).

Although a wheel cylinder can be overhauled while installed on the backing plate, it really should be done with the cylinder removed. Dirt and abrasive particles from cleaning and honing can be removed from the cylinder more easily and kept out of the hydraulic lines and fittings. Remove the cylinder by disconnecting the brake line and removing its mounting screws or clip (Figure 8-29). Cap the brake line after the wheel cylinder is removed to keep dirt out of the hydraulic system. After all parts are disassembled, inspect them again for damage that may have been hidden when they were installed. Clean individual parts in a parts washer and remove any remaining dirt from backing plates, parking brake linkage, and other parts still attached to the vehicle with brake cleaning equipment described previously. The next major section of this chapter explains the options for wheel cylinder service or replacement. These paragraphs are then followed by procedures for drum brake reassembly.

WHEEL CYLINDER SERVICE

Special Tools Denatured alcohol Hone Vise

SERVICE TIP  On passenger cars and light trucks, it is more economical to the shop and customer to just replace the wheel cylinder instead of rebuilding. Always inspect the old wheel cylinder closely, however. The inspection may provide clues to the age and contamination of the brake fluid and the general condition of other hydraulic brake components.

If external inspection reveals anything more than the slightest seepage or staining around a wheel cylinder, the cylinder should be disassembled for internal inspection, which can be done with the cylinder mounted on the backing plate. It is possible to overhaul some cylinders while they are installed. If the cylinder is recessed into the backing plate or if

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access is blocked by piston stops, parking brake linkage, or an axle flange, the cylinder must be removed for service. It is often faster to remove a wheel cylinder for overhaul than to struggle for clearance around other parts mounted on or near the backing plate. Moreover, dirt and abrasive particles from cleaning and honing can be removed from the cylinder more easily and completely on the bench than on the car. Wheel cylinders are often overlooked during brake service. If the cylinder is not inspected closely and overhauled or replaced, its continued service life may well be shorter than the service life of new linings. Therefore, the next brake service may be needed sooner than necessary to fix damage from a leaking cylinder. The brake shoe return springs hold the wheel cylinder pistons retracted in the cylinder bore. The pistons do not continually move outward as the linings wear as do disc brake caliper pistons. Nevertheless, over the life of drum brake linings, wheel cylinder pistons shift slightly in their bores. Corrosion and sludge can accumulate behind the piston seals (Figure 8-30), which can accelerate seal wear as the seals are pushed backward in the bore when new shoes are installed. This potential problem can be magnified if brake fluid is not changed regularly. The difference in piston seal position may be only several thousandths of an inch, but the possible problem can be compounded by long intervals between brake service due to very slow and gradual lining wear. For all of these reasons, many shops make it standard practice to overhaul or replace wheel cylinders whenever new shoes are installed. Some wheel cylinders cannot be rebuilt but must be replaced if there is leakage or damage.

SERVICE TIP  On some cylinders the return spring is strong enough to push one or both pistons out. If you loosen the bleeder screw and push in on both ­pistons, some fluid is removed from the cylinder. Hold the pistons in place as the bleeder screw is tightened; this forms a low-pressure area that keeps the pistons in place. If the pistons are pushed outward by the return spring, they will draw fluid from the brake line and possibly allow air to enter the cylinder and line. If they do not move, air usually will not enter the bore. In either case, bleeding the brakes is shortened by a minute or two. Also, if you have done this much work to the brakes, there is no reason not to completely flush the system clear of all old brake fluid.

Cup Piston

Deposits and corrosion

Figure 8-30  Corrosion and dirt can accumulate in wheel cylinders, which is another reason to service them every time the drum brakes are serviced.

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397

DRUM BRAKE REASSEMBLY Although drum brake reassembly is usually the opposite of disassembly, a few special steps are important to do the job correctly. Generally, do not use lubricated compressed air on brake parts because damage to rubber parts may result. Remember also that if any hydraulic part is removed or disconnected, it is necessary to bleed all or part of the brake system. Begin by installing new or overhauled wheel cylinders if the old ones were removed. Remove the caps from the brake line fittings and install the fittings into the cylinders, using a flare-nut wrench. It is very important to verify the locations of all components in a brake assembly. Compare the new brake shoes to the old ones to be sure that holes for springs and clips are in the same locations and that the new linings are positioned in the same locations on the shoes. This comparison of new and old brake shoes is particularly important for the primary shoes of duo-servo brakes. If a hardware kit is obtained, be sure it includes everything needed. Also verify that right-hand and left-hand shoes are identified for installation on the correct wheel. Some shoes have pins for adjuster levers that will only fit correctly if installed on the specified right or left wheel (Figure 8-31). Some shoes have welded reinforcements to help support the web and table. The welds may interfere with mounting and brake operation if the shoes are installed on the wrong sides. A few brands mark the shoes “L” or “R” to designate the side of installation. Return springs, hold-down parts, and even parking brake levers may allow the wrong shoe to be installed on the wrong side of the car. Some part of the assembly will not fit, however, if the shoes are installed on the wrong sides. Photo Sequence 19 shows the general installation of a duo-servo brake assembly.

A four-wheel brake repair is an ideal time to flush the system. It is best to check for air anyway and a few minutes more will replace all of the old fluid.

Table

Anchor end

Lining

Web Weld

Adjusting end Pin

Pin

Pin

Figure 8-31  Verify that right-hand and left-hand shoes are identified for installation on the correct wheel.

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19 Typical Procedure for Installing a Drum Brake Assembly Photo Sequence

P19-1  Compare the new parts with the old to ensure that the correct ones are available.

P19-2  Depending on how the parking brake was disconnected, there are two means to connect it: Slide the lever pin with the washer installed through the primary shoe and install a new retaining clip, or connect the cable to the lever as shown.

P19-3  Hold the self-adjuster mechanism in place of the primary shoe as the retaining spring is attached.

P19-4  Pull the top of the secondary shoe forward and fit the parking brake strut between the two shoes. The large slot in the strut goes to the rear and the spring to the front.

P19-5  Fit the holed end of the cable over the anchor and move the running end to the side. Install the shoes’ return springs.

P19-6  Route the cable behind the primary return spring and down to the self-adjuster pawl position.

P19-7  Install the pawl and its spring(s).

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P19-8  Pull the lower ends of the shoes apart and fit the self-adjuster between the two shoes. After releasing the shoes, check to make sure that the self-adjuster is correctly linked to the shoes and that the star wheel is to the rear.

P19-9  Hook the cable to the pawl and push up on the pawl. Route the cable over the cam. After releasing the pawl, ensure that the cable stayed in place on the cam.

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Photo Sequence 19 (CONTINUED)

P19-10  Check each component of the assembled drum brake for proper positioning and anchoring.

WARNING  When replacing the return springs with new ones or reinstalling the old ones, ensure that the correct spring is placed on the correct shoe. Sometimes the return springs for the front and rear shoes are different in shape, strength, and color.

Classroom Manual page 196

SERVICE TIP  Trying to align the threads between the tubing fitting and the wheel cylinder can be difficult because the steel tubing cannot be flexed to allow alignment. Try this. Before installing the cylinder mounting fasteners, connect the tubing to the wheel cylinder. This allows you to wiggle the wheel cylinder around to more easily align the threads. Once the fitting is screwed partially into the cylinder’s inlet port, then position and install the cylinder’s fasteners. Finally tighten the fitting. This will save you some aggravation and possible damage to the threads.

After determining the correct shoe locations, transfer any parking brake linkage parts from the old shoes to the new shoes. Any U-clips and wave washers that are bent for installation or that receive constant wear during operation should be replaced. Remove nicks and rough spots from the raised shoe pads on the backing plate with emery cloth and then clean the area. Lightly coat the shoe pads with brake lubricant. Make sure that the backing plate bolts and bolted-on anchor pins are torqued to specifications. Ensure that riveted anchor pins are secure. Install hold-down parts using the appropriate tools to mount the shoes on the backing plate. Connect parking brake linkage at the appropriate point during reassembly. This will vary for different brake designs. Lightly coat the surface of the parking brake pin with brake lubricant. Disc brake lubricant works well with drum brakes also. Install the lever on the pin with a new washer and clip (Figure 8-32). Attach the parking brake cables and be sure their movement is not restricted.

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Some return springs are color coded. When installing replacement springs, be sure they are a matching color.

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Chapter 8 Threaded components will be marked L - Left side R - Right side

Brake shoe

Wave washer Button

Socket

Screw threads

Washer A

U-clip

Web

Parking brake lever

Identification lines

Pivot nut

Socket Adjusting screw

Washer

B

Figure 8-32  Installing the parking brake lever to the brake shoe.

Figure 8-33  Look for left and right identification on adjuster assemblies. If an adjuster is installed on the wrong side of the car, it will not work. Typical Daimler Chrysler (A) and Ford (B) adjusters are shown here.

If the brakes being serviced have wheel cylinder pushrods or links, install them between the wheel cylinder pistons and the shoes. If pushrods are not used, ensure that the shoe webs fit into the ends of the wheel cylinder pistons correctly. Once again, ensure that left-hand and right-hand parts have not been interchanged from one side of the car to the other. This is particularly important for duo-servo star wheel adjusters, which have left- and right-hand threads (Figure 8-33). The self-adjuster linkage for leading-trailing brakes also has definite left-hand and right-hand parts (Figure 8-34).

L

Leading shoe Brake shoe adjusting lever

Figure 8-34  This adjuster strut for a leading–trailing brake has specific right-hand and left-hand installation positions.

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Disassemble the adjuster and clean the parts in denatured alcohol. Clean the threads with a fine wire brush. Make sure that the adjusting screw threads into the threaded sleeve over its complete length without sticking or binding. Ensure that none of the star wheel teeth are damaged. Lubricate the screw threads with brake lubricant, being careful not to get any on the star wheel teeth. Also apply brake lubricant to the inside of the socket and the socket face. Finally, apply a continuous bead of lubricant to the open ends of the threaded sleeve and socket (end cap) when the threads are fully engaged. When you install self-adjusters, set them close to their fully retracted positions. For example, screw a star wheel adjuster into the threaded sleeve until it bottoms and then turn it outward one or two turns. Setting the adjusters in a retracted position makes it easier to install the shoes and their return springs. After the shoes are installed, check the adjusters again and adjust them outward just enough to take up any slack between the adjusters and the shoes. Before installing any of the adjuster cables, links, levers, guides, and other parts, inspect each carefully for the kinds of wear and damage shown in Figure 8-35. Many technicians and shop owners choose to replace all of the self-adjuster parts whenever drum brakes are serviced to ensure proper operation. After the self-adjusters are installed, check their operation by prying the shoe to which the linkage is attached lightly away from its anchor or by pulling the cable or link to make sure the adjuster advances easily, one notch at a time. Adjuster cables tend to stretch, and star wheels and pawls can become blunted after a long period of use. Leave the adjusters close to a fully retracted position and the shoes at a minimum diameter. After brake assembly is complete, make the preliminary brake adjustment as explained in the following section.

401

There are several brands of brake lubricant on the market. Use a well-known brand and ensure that it is labeled as brake grease.

Special Tools Lift or jack with stands Impact tools Return spring pliers Hold-down spring removal tool Service information

Stretched, frayed cable

Bent, rusty cable guide Stretched adjuster spring Worn, bent or cracked adjuster lever

Adjuster assembly

Washer Rusty, tight threads

Stripped star wheel

Figure 8-35  Check all self-adjuster parts closely for damage and wear.

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SERVICE TIP  If a brake shoe web has several holes close to each other, mark the one into which the end of a return spring is installed. Then match it to the corresponding hole in the replacement shoe. This saves time and hassle when installing new shoes, and it helps to verify that replacement shoes and return springs are the correct match for the vehicle.

WARNING  Wear safety glasses and keep your fingers away from the return springs during removal and installation. If a spring slips off a tool or mounting point, its strong tension can cause injury and damage.

Installing the return springs is usually the last step—or close to the last step—of brake reassembly. Use brake spring pliers and other special tools as required for spring installation (Figure 8-36). Be sure to install each spring in the proper direction and in the proper holes in the shoe webs. Many return springs have longer straight sections at one end than at the other. If a spring is installed in the wrong hole on the shoe web, its operating tension will not be correct. Some vehicles require that a certain return spring be placed on top of the other. For instance, the return spring for the front shoe may have to be installed on the anchor first. This setup ensures the tip of the curve of the spring hook does not hang on parking brake components or other brake components. If a spring is stretched too far to install it in a wrong hole, damage to parts or personal injury can result. If the shoes seem not to fit at the upper anchor, recheck the parking brake and self-adjuster for proper installation.

Brake spring tool

Figure 8-36  Use special tools and be very careful when installing brake shoe return springs.

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Drum Installation At this point, it is time to do the initial brake adjustment and install the drum. The next sections of this chapter cover initial brake adjustments and manual service adjustments of self-adjusters for duo-servo and leading-trailing brakes. Because brake drum inspection, measurement, and refinishing are separate operations that can be done independently of servicing the brake assembly, drum service is covered in the last sections of this chapter. If the brake drum is a floating type that is installed over the wheel studs on an axle flange or hub, it can be installed after the initial brake adjustment. Speed nuts or push nuts that may have been installed on the drum when the vehicle was assembled can be reinstalled to help hold the drum in place while the wheel is installed. Their use is not essential, however. If the drum is a one-piece assembly of drum and wheel hub, refer to Chapter 3 in this manual for instructions on cleaning, packing, installing, and adjusting wheel bearings.

BRAKE ADJUSTMENT Unlike disc brakes in which self-adjustment is a basic design feature, drum brakes require manual adjustment when assembled. Furthermore, almost all drum brakes have selfadjuster mechanisms, which are parts that specifically readjust the brakes as the linings wear. With or without self-adjusters, drum brakes may require periodic manual adjustment to ensure proper lining-to-drum clearance. Correct brake adjustment ensures the proper brake pedal position and operation for safe braking.

Classroom Manual Page 197

Initial Adjustment When installing the brake shoes and finish assembling all the brake components, the self-adjusters are retracted so that the shoes are at the minimum diameter. Before installing the drum, you should readjust the shoes to take up most of the clearance with the drum. This will make the final adjustment after the drum is installed faster and more accurate. Before making the initial adjustment of rear drum brakes, check the parking brake cable adjustment. The parking brake may have been adjusted to remove slack with the old brake shoes installed. New shoes with fresh linings can reduce the lining-to-drum clearance allowed by the parking brake, even when the brake is released. If necessary, back off the parking brake adjustment before the initial manual adjustment of the brake shoes. The parking brake must operate freely with the brake shoes and linings centered on the backing plate. Check the parking brake and readjust it if necessary as a final step after manual adjustment of the service brakes. Refer to Chapter 9 of this Shop Manual for parking brake adjustment procedures. Initial adjustment requires a brake shoe caliper (Figure 8-37), which is a measuring tool that gauges the inside diameter of the drum and the outside diameter of the installed shoes. Place the caliper into the drum as shown in Figure 8-37 and slide it back and forth to open the jaws to their widest point. Then tighten the lock screw to hold the caliper jaws in position. Depending on the type of caliper used, the jaw opening on its opposite side is now set to equal the drum diameter or to a specific smaller diameter. The installed diameter of the brake shoes should be adjusted to approximately 0.020 inch to 0.040 inch (0.50 mm to 1.00 mm) smaller than the drum diameter. Check vehicle service information for exact specifications. If the caliper opening used to gauge the brake shoes equals the drum diameter, readjust it undersized by the specified amount and then place it over the widest point of the brake

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Special Tools Brake tool adjuster (spoon) Brake shoe caliper

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Figure 8-37  Measure the inside diameter of the drum with the brake drum micrometer and tighten the locknut.

Figure 8-38  Flip the caliper over and place it over the widest point of the brake shoes. Adjust the brake shoes until they touch the caliper pads.

shoes. As an alternative, leave the caliper set to the drum diameter and use a feeler gauge between the caliper and one shoe to adjust the shoes. If the caliper has built-in compensation for the drum and shoe diameters, simply place it over the widest point of the shoes. With the caliper in place over the shoes (Figure 8-38), rotate the star wheel adjuster to expand the shoes until the caliper just slides over them without binding. Hold the selfadjuster pawl away from the star wheel with a screwdriver or a heavy wire hook while adjusting the star wheel. Some leading-trailing brakes have a separate star wheel or other adjuster for each shoe. For this type of brake assembly, adjust each shoe an equal amount. After the initial adjustment, install the brake drum and apply the brakes several times to verify that the pedal is fairly high and firm. This will also center the shoes within the drum. Bleed the brakes, if necessary, to ensure that the lines are free of air. Then make a final, manual adjustment of the brakes as explained in the following paragraphs.

Manual Adjustment Precautions

Special Tool Brake tool adjuster (spoon)

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Even with self-adjusters, drum brakes may need manual adjustment to compensate for incomplete self-adjustment at some time in their service life. Manual adjustment also may be required to verify that self-adjusters are working equally on each wheel of an axle set and to correct the adjustment if they are not. Some technicians rely on the self-adjusters to make the final adjustment automatically after new shoes are installed. This is not the best practice, however, because initial adjustment is only a rough adjustment and may not be equal on both wheels of an axle set. As a result, self-adjustment then may remain unequal, particularly on lightly used rear drum brakes of an FWD car. A final manual adjustment verifies an equal and complete adjustment on both wheels. Perform manual brake adjustments with the vehicle supported on a hoist or stands and off the ground so that the wheels can rotate during adjustment. Exact adjustment procedures are different for different brake designs but all are based on the principle of expanding the shoes until they contact the drum and then backing off the adjustment a specified amount. With the brakes adjusted and the drum installed, pump the pedal once or twice to center the shoes. Recheck the brake adjustment. The pedal application will center the two shoes and provide a better adjustment. Generally, duo-servo brake adjustments are backed off more than leading-trailing brake adjustments because duo-servo brakes need more clearance for the servo action to develop proper leverage.

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On some vehicles, it may be necessary to tighten the adjuster quite a bit after the linings first contact the drum. Then when the adjustment is backed off, it may feel as if excessive retraction of the shoes is needed to get free wheel rotation. In addition, the pedal may feel springy or spongy when it is applied. All these symptoms are signs that the shoes are not properly arced to the drum. Excessive adjuster travel in either direction indicates that the shoes are bending due to incomplete lining contact with the drum. The only satisfactory long-term solution to this problem is to measure the shoe arc, remove the shoes, and either replace them with properly arced shoes or have the shoes arced to match the drum diameter and brake installation. Figure 8-39 shows

Lining

Shoe Drum radius 5.000 inch Lining thinner at ends

Uniform lining thickness over all Lining radius 4.980 inch Shoe Drum

Lining Undersize lining

Cam-ground lining

Lining thinner at this end Drum Anchor

Lining has constant radius

Shoe is off-center in drum

Lining Lining thicker at this end

Fixed-anchor offset lining

Figure 8-39  Three common profiles for the lining arc of new brake shoes.

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three common kinds of lining arcing profiles. The arc profile must match the original design of the brake assembly. Before performing any of the following brake adjustments, be sure that the parking brake is fully released. If the parking brake is holding the brake shoes off their anchors or is improperly adjusted in any way, back off the parking brake adjustment. Some noticeable slack should be present in the cables, and the linkage should not bind. Readjust the parking brake as explained in Chapter 9 of this Shop Manual after adjusting the service brakes. Parking brakes are ALWAYS adjusted after the service brakes.

Duo-Servo Star Wheel Adjustment Duo-servo brakes use a single star wheel adjuster in the link that connects the bottoms of the brake shoes. Rotating the star wheel moves both shoes at the same time and adjusts the clearance with the drum as an assembly. Most duo-servo brakes are adjusted manually through a hold in the backing plate (Figure 8-40), but some cars have an adjustment hole in the outboard web of the drum (Figure 8-41). This latter style requires wheel and tire removal for brake adjustment. The adjusting hole, in either the backing plate or the drum, is usually closed with a rubber, plastic, or metal plug that can be removed easily with a punch. After adjustment a rubber plug should be reinstalled to keep dirt and water out of the brakes. Some brakes are built without the hole in the backing plate or drum, but the location for the hole is scored or lanced. At the time of the first brake adjustment, the scored area (or knock out) must be removed with a drill or by knocking it out with a small chisel or punch. After the brakes are adjusted, the hole should be closed with a plug as described above. To adjust duo-servo brakes, insert a brake adjusting tool or a flat-blade screwdriver through the adjusting hole to engage the notches of the star wheel. With the other hand, use another small screwdriver or a wire hook to push or pull the self-adjuster pawl away from the star wheel. The method of disengaging the self-adjuster is different depending on brake design and on whether the adjuster is reached through the backing plate or through the drum. It is possible to force the star wheel against the self-adjuster without disengaging it. However, if this is done, it will quickly wear down the teeth of the star wheel and the edge of the pawl. The self-adjuster will not operate properly then and may never adjust the brakes during their service life. Always disengage the self-adjuster before manually turning the star wheel.

Backing plate

Adjusting tool

Backing plate Drum

Drum

Self-adjuster lever

Self-adjuster lever

Wire

Star wheel

Screwdriver

Adjusting tool Star wheel

Figure 8-40  If the adjustment opening is in the backing plate, use a screwdriver to push the self-adjuster lever away from the star wheel during manual adjustment.

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Figure 8-41  If the adjustment opening is in the drum, use a wire hook or bent piece of welding rod to pull the self-adjuster lever away from the star wheel during manual adjustment.

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To expand the adjuster link and decrease lining-to-drum clearance, the handle of the adjusting tool is usually moved upward to turn the star wheel. To retract the adjuster link and increase lining-to-drum clearance, move the tool handle downward. This general rule SERVICE TIP  A thin piece of plain brazing rod can be used to hold off the self-adjuster pawl during brake adjusting. The rod is strong enough to do the job and is small enough not to interfere with the adjusting tool.

can vary for different brake designs, however, and even from one side of the car to the other. Check the vehicle service information for instructions. Rotate the vehicle wheel by hand as the brakes are adjusted. For duo-servo brakes, rotate the wheel in the direction of forward rotation while expanding the shoes. The selfenergizing operation and servo action of the shoes will help to center the shoes in the drum during adjustment. Exact adjustment instructions vary from one carmaker and one brake design to another. Some instructions say to adjust the brakes outward until a light drag is felt on the drum as the wheel is turned. Other instructions call for a heavy drag or locking the wheel. The instructions then direct that the shoes be backed off or retracted a specific number of notches or clicks of the star wheel. Generally, retract the shoes more on a duo-servo brake than on a leading-trailing brake. It is very important to follow exactly service manual instructions for a given brake design. It is equally important that the adjustment be equal on both sides of the vehicle to avoid brake pull and to ensure equal lining wear.

Leading-Trailing Star Wheel Adjustment Most leading-trailing brakes have a single star wheel adjuster similar to the adjuster for duo-servo brakes. The adjuster linkage is mounted higher on the shoe webs (Figure 8-42) than the adjuster link used for duo-servo brakes, because leading shoes and trailing shoes are rigidly anchored to the bottom of the backing plate. Rotating the star wheel expands and retracts the shoes, just as it does for duo-servo brakes, and the self-adjuster mechanism usually must be retracted or released for manual adjustment. Just as for duo-servo brakes, the adjusters for leading-trailing brakes have definite left-hand and right-hand parts (Figure 8-43). Verify that the adjusters are installed correctly before trying to adjust the brakes.

Wheel cylinder

Star wheel adjuster Adjustment hole (rubber plug removed)

Figure 8-42  This star wheel for a leading-trailing brake is mounted higher on the brake assembly than the adjuster for a duo-servo brake.

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Chapter 8 This chamfer indicates right-hand thread

This boss indicates left-hand thread

Arrows indicate direction of forward rotation

Figure 8-43  Note the identification of the left-hand and right-hand adjuster parts on this leading–trailing brake.

Special Tool Brake tool adjuster (spoon)

Some leading-trailing brakes have a separate star wheel or other adjuster for each shoe. For this kind of brake assembly, adjust each shoe an equal amount. Leading-trailing brakes with quadrant adjusters are not adjusted by turning a star wheel but by manually moving the toothed quadrant. Refer to the vehicle service manual for special procedures and tool requirements. Like duo-servo brakes, rotate the vehicle wheel by hand while adjusting leading-trailing brakes. Rotation methods are a bit different, however. If the brake has a single star wheel, start by rotating the wheel forward until specified drum contact is made. Then rotate the wheel in reverse to verify adjustment. If the brake has separate star wheels for each shoe, rotate the wheel forward while adjusting the forward shoe; then rotate the wheel in reverse as the rear shoe is adjusted. Again, exact adjustment instructions vary from one carmaker and one brake design to another. Generally, retract the shoes less on a leading-trailing brake than on a duo-servo brake. Follow service manual instructions exactly for a given brake design to obtain equal adjustment on both sides of the vehicle. After adjustment, install the plug in the adjustment access hole to keep dirt and water out of the brakes.

CUSTOMER CARE  If you have a customer who is a very cautious and careful driver and always avoids panic stops or any kind of hard braking, recommend a brake inspection and adjustment check at every oil change. This kind of driver may never apply the brakes hard enough to activate the self-adjusters. Also remind those drivers whose vehicle brakes are adjusted by parking brake action to always apply the parking brake before exiting the vehicle.

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BRAKE DRUM SERVICE Brake drums are resurfaced more often than disc brake rotors. In fact, most shops make drum refinishing a standard part of complete drum brake service. The drums must be removed from the brakes anyway for any kind of service except simple adjustment, and many drum problems cannot be identified completely until the drum is mounted on a lathe. Maximum braking performance cannot be obtained with a drum that is damaged or defective. Complete drum service consists of these general operations: ■■ ■■ ■■

Drum inspection Drum measurement Drum resurfacing or turning

Drum Inspection WARNING  Never use a drum that exceeds or is near its discard limits. Thin drums can overheat or shatter. This may cause a vehicle accident. The shop and technician may be held liable.

Classroom Manual page 187

Brake drums work like a heat sink. Their job is to absorb heat and dissipate it to the air. As drums wear from normal use or are thinned by refinishing, the amount of metal available to absorb and release heat is reduced. As a result, the drums operate at increasingly higher temperatures. The drum structural strength also is weakened by the loss of metal. Braking forces can distort the drum’s shape or lead to cracking or other problems. Drum inspection is the process of identifying these problems and deciding which can be serviced by refinishing and which require drum replacement. An earlier section of this chapter explained the importance of inspecting the brake shoes and linings for indications of drum problems. For example, if the linings on one wheel are worn more than the other, that drum may be scored or rough. Uneven wear from side to side on any one set of shoes can be caused by a tapered drum. Linings worn badly at the toe or heel may indicate an out-of-round drum. If brake shoes and linings have a slight blue coloring, that indicates overheating, which is a clue to check the drum for the same condition. If the lining is worn more in the center than at the ends or vice versa, the lining may not have been arced properly to the drum diameter. If so, check the lining-to-drum fit closely when installing new shoes with a resurfaced drum. To see what a bell-mouthed drum looks like, take a small cone paper cup, cut off the closed end, and open the cup. The cup is now bell-mouthed. The smaller end represents the closed end of the brake drum. Continue by inspecting the drum itself for the following conditions: ■■

■■

■■

Scored Drum Surface. Inspect the drum braking surface for scoring by running your fingernail across the surface (Figure 8-44). Any large score marks mean that the drum must be resurfaced or replaced. The most common cause of drum scoring (Figure 8-45A) is when road grit or brake dust becomes trapped between the brake lining and drum. Glazed brake linings that have been hardened by high temperature, or inferior linings that are very hard, also can groove the drum surface. Excessive lining wear that exposes the rivet heads or shoe steel will score the drum surface. If the scoring is not too deep, the drum can be refinished. Bell-Mouthed Drum. Bell mouthing is shape distortion caused by extreme heat and braking pressure (Figure 8-45B). It is most common on wide drums that are weakly supported at the outside of the drum. Bell mouthing makes full drum-to-lining contact impossible, so braking power is reduced. Drums must be refinished or replaced. Concave Drum. A concave wear pattern (Figure 8-45C) is caused by a distorted shoe that concentrates braking pressure on the center of the drum.

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Figure 8-44  To evaluate the amount of scoring in a drum, inspect it and run your fingernail across the drum surface.

Hard spots are circular blue-gold glazed areas on drum or rotor surfaces where extreme heat has changed the molecular structure of the metal. Heat checks are small cracks on drum or rotor surfaces that usually can be machined away. Drums that have severe heat checks must be replaced unless there is an economic or availability problem. The drum web is the closed side of a brake drum.

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A

B

C

D

Scored drum

Bell-mouthed drum

Concave drum

Convex drum

Figure 8-45  Typical brake drum wear patterns and defects.

■■

■■

■■

■■

■■

Convex Drum. A convex wear pattern (Figure 8-45D) is caused by excessive heat or an oversized drum, which allows the open end of the drum to distort. Hard Spots. Hard spots, or chilled spots, in the cast-iron surface result from a change in metallurgy caused by heat. They appear as small raised areas (Figure 8-46A). Brake chatter, pulling, rapid wear, hard pedal, and noise may occur. Hard spots can be ground out of the drum, but since only the raised surfaces are removed, they can reappear when heat is reapplied. Drums with hard spots should be replaced. Threading. An extremely sharp or chipped tool bit or a lathe that turns too fast can literally cut a thread into the drum surface. During brake application, the shoes ride outward on the thread, then snap back with a loud crack. Threading can also cause faster lining wear and interfere with shoe alignment during braking. To avoid threading the drum surface, use a properly shaped bit and a moderate-to-slow lathe speed. Heat Checks. Unlike hard spots, heat checks are visible on the drum surface (Figure 8-46B). They are caused by high temperatures. Heat-checked drums may have a bluish-gold tint, which is another sign of high operating temperatures. Hardened carbide lathe bits or special grinding attachments are available to service these conditions. Cracked Drum. Cracks in the drum are caused by excessive stress. They may appear anywhere, but they are most common near the bolt circle or at the outside of the drum web (Figure 8-46C). Cracks also may appear at the open edge of the braking surface. Fine cracks often are hard to see and often do not appear until after machining. Any crack, no matter how small, means the drum must be replaced.

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Out-of-Round Drums. Slightly out-of-round drums usually appear good to the eye, but the problem causes pulling, grabbing, and pedal vibration or pulsation. An out-of-round or egg-shaped condition (Figure 8-47) is often caused by heating and cooling during normal brake operation. An out-of-round drum can also be caused by setting the parking brake while the drums are hot. A severely out-of-round drum will cause pedal pulsation and/or vibration during braking. To test for an out-of-round drum before the drum is removed, adjust the brake to a light drag and feel the rotation of the drum by hand. Any areas of heavy drag or no drag may indicate a problem. Remove the drum and measure it at several points to determine the amount of distortion. A brake drum that is out of round enough to cause vehicle vibration or roughness when braking should be refinished. Remove only enough stock to return the brake drum to roundness.

A Hard or chill spots

B Heat checks

11-inch

11.3-inch

C Cracked drum web

Figure 8-46  Hard spots, heat checks, and cracks are common drum problems.

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Figure 8-47  An out-of-round drum will have unequal diameter measurements.

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Hard spots can cause chattering during drum machining, leaving a very rough finish.

■■

Grease or Oil Contamination. If the drums have been exposed to leaking oil or grease, thoroughly clean them with a nonpetroleum solvent such as denatured alcohol or brake cleaner. Locate the source of the oil or grease leak and fix the problem before reinstalling new or refinished drums. SERVICE TIP  Tapping the drum lightly with a hammer will give an indication if it is cracked. Set the drum, open side up, and tap the outside with a hammer. A good drum will produce a bell-like or ringing sound, whereas a cracked drum will have a flat, dull sound without any ring.

Drum Measurements During brake service, every drum must be measured with a drum micrometer or gauge to make sure that it is within the safe size limits. An old rule of thumb for drum refinishing was that a drum could be turned to 0.060 inch beyond its original diameter and should be replaced if its diameter was 0.090 inch or more beyond its original size. Thus, a 10-inch drum could be turned to 10.060 inches and should be discarded at 10.090 inches or more. The first step of drum measurement is to check the discard diameter, or maximum inside diameter, that is cast or stamped on the outside of the drum (Figure 8-48). The discard diameter is the allowable wear dimension, not the allowable machining dimension. There must be 0.030 inch (0.75 mm) left for wear after machining. That is, the refinished drum diameter must be at least 0.030 inch (0.75 mm) less than the discard diameter. If this dimension is exceeded, the drum will wear beyond its maximum allowable diameter during normal operation. SERVICE TIP  Not many manufacturers are supplying a refinishing limit dimension for brake drums at the time of this printing. However, never assume anything with regard to automotive specifications. When working with the newest drum brake systems, check the service manual for the latest information.

Special Tools Brake drum micrometer Service manual Inside micrometer

Ford Motor Company specifically says that a drum must be replaced if its diameter exceeds the discard dimension at any point. If unsure about any drum dimensions for refinishing or replacement, refer to the vehicle service manual for specifications. MIN

.

Discard diameter

MAX. DIA ..

XX X.

X

Figure 8-48  The discard diameter is cast or stamped into every brake drum made since the early 1970s.

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11.375 in.

Figure 8-49  Begin drum measurement by setting the micrometer to the nominal drum diameter.

Begin measuring a drum by setting the drum micrometer to the nominal drum diameter such as 11.375 inches or 276 mm (Figure 8-49). Refer to service information if unsure about the original diameter. Then insert the micrometer into the drum. Insert the end with the movable plunger first and hold it against the drum as you insert the fixed end of the micrometer. Hold the anvil steady against the drum surface, and move the dial end of the micrometer back and forth until the highest reading on the dial indicator is obtained (Figure 8-50).

Dial indicator

Figure 8-50  Insert the micrometer in the drum, hold the fixed anvil firmly against the inside surface, and carefully rock the dial indicator end until the highest reading is achieved. Take four measurements, 45 degrees apart.

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Chapter 8 11.375 in. 40 30

50

60 70 80

90 100 110

20

120

10

130

0

11.375 in. + 0.015 in. = 11.390 in.

Figure 8-51   Add the dial indicator reading to the original micrometer setting to get the drum diameter.

Add the dial indicator reading to the nominal drum diameter on the micrometer. For example, if the micrometer was set to 11.375 inches and the dial indicator reads 0.015 inch, the diameter is 11.375 plus 0.015, which equals 11.390 inches (Figure 8-51). Compare this reading to the drum discard dimension and remember that it must be 0.030 inch (0.75 mm) or more under the discard dimension to allow for refinishing. Take at least four measurements, 45 degrees apart around the drum opening. Measuring the drum at four locations around its opening checks for an out-of-round condition as well as measuring the overall diameter. If the highest and lowest diameter measurements vary by 0.006 inch (0.15 mm) or more, machine the drum to correct the out-of-round condition. This guideline applies even if the drum is otherwise in good condition and within the maximum diameter limits. An out-of-round drum can cause brake chatter, grabbing, and pedal pulsation if not corrected. The basic drum micrometer measurement indicates the drum diameter and whether it can be refinished. If the drum is deeply scored, however, the diameter must be measured at the bottom of the deepest groove. To do this, a drum micrometer adapter with pointed anvils or a machinist’s inside micrometer with a long extension to span the drum diameter is needed. Again, the diameter measured at the deepest groove must be 0.030 inch (0.75 mm) or more under the discard dimension. Severe bell-mouth, concave, or convex wear may be visible to your eye or indicated by abnormal lining wear, but an inside micrometer should be used to measure precisely for these conditions. To check for any kind of wear or distortion across the drum surface, take several measurements in a straight line from the inside to the outside of the drum. Then repeat the measurements at about four positions, 45 degrees apart around the drum opening. If the highest and lowest measurements taken at any straight-line position across the drum vary by 0.006 inch (0.15 mm) or more, machine the drum to correct the problem. If the drums are smooth and true and within safe limits, any slight scores can be removed by polishing with fine emery cloth. If scoring or light grooves cannot be removed by hand, the drum must be refinished or replaced. Even slightly rough surfaces should be turned to ensure a true drum surface and to remove any possible contamination on the surface from previous brake linings and road dust. Many shops now use a newer version of the drum micrometer (Figure 8-52). The measurements are done in the same manner as with an older drum micrometer, but it is easier and faster with the new tool. Snap-on Tools and others have an electronic brake drum micrometer (Figure 8-53). This tool is even easier and faster than the tool mentioned above, primarily because the measurements can be converted from inches to metric with a push of a button. The tools shown in Figures 8-52 and 8-53 can measure all light vehicle drums up to about 14 inches or 365 mm.

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Figure 8-52  This drum caliper eliminates the need to set up the caliper and then adjust the reading according to the drum diameter. The diameter can be measured directly from this caliper in both metric and SAE.

Figure 8-53  An electronic drum caliper is quick, easy to read, and can convert between measuring systems.

REFINISHING BRAKE DRUMS Brake drums with moderate to severe scoring or other defects can be refinished by either turning (cutting) or grinding on a brake lathe (Figure 8-54). Only enough metal should be removed to obtain a true, smooth friction surface. If too much metal is removed from a drum, the following unsafe conditions can result:

Figure 8-54  A typical bench brake lathe for machining (turning) drums and rotors.

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Brake fade caused by the thin drum being unable to absorb heat during braking Poor and erratic braking due to distortion of the drum ■■ Noise caused by a thin drum vibrating during operation ■■ Drums cracking or breaking during a very hard brake application If one drum must be machined, the other drum on the same axle also must be machined to the same diameter so that braking will be equal at both wheels. Drum diameters must be within 0.005 inch of one another. ■■

Classroom Manual pages 187

Special Tools Bench brake lathe Catch basin Hot soapy water

■■

Brake Lathes Brake drums are refinished on bench lathes made specifically for drum machining. Many models of drum lathes exist, but regardless of the lathe used, it should be serviced regularly according to the manufacturer’s maintenance procedures. Different cutting assemblies are used for rotors and for drums. The attaching adapters, tool holders, vibration dampers, and cutting bits must be in good condition. Make sure mounting adapters are clean and free of nicks. Always use sharp cutting tools or bits and use only replacement cutting bits recommended by the equipment manufacturer. Dull or worn bits leave a poor surface finish, which will affect braking performance. The tip of the cutting bit should be slightly rounded, not razor sharp. This is even more important for turning a drum than for a rotor. A sharply pointed bit can cut a spiral groove into the drum that will cause noisy and erratic brake operation. SERVICE TIP  It is not always necessary to refinish a drum to remove minor score marks. You can remove them with sandpaper or emery cloth.

Mounting a Drum on a Lathe The mounting procedure for a drum depends on whether the drum has wheel bearings mounted in its hub. For one-piece drums and hubs with bearings installed, remove the inner bearing and grease seal before mounting the drum on the lathe arbor. Refer to Chapter 3 in the Shop Manual for bearing removal and installation instructions. A one-piece drum with bearing races in the hub mounts to the lathe arbor with tapered or spherical cones. A two-piece drum removed from its hub is centered on the lathe arbor with a spring-loaded cone and clamped in place by two large cup-shaped adapters. Remove all grease and dirt from the bearing races before mounting the drum. It may be necessary to steam clean the grease out of the hub. Index the drum on the wheel bearing races to ensure that the machining is accurately indexed to the drum axis. Use the appropriate cones and spacers to lock the drum firmly to the arbor shaft. For floating drums without bearings, clean all rust and corrosion from the hub area with emery cloth or 120-grit sandpaper and use the proper cones and spacers to mount the drum to the arbor shaft. When mounting a one-piece drum and hub, check the inner bearing races (cones) to be sure they are secure in the hub. If either race is loose, replace the drum and all bearings. When the drum is on the lathe, install a rubber or spring-type vibration damper on the outer diameter of the drum (Figure 8-55) to prevent the cutting bits from chattering during refinishing. Use of the vibration damper results in a smoother finished surface. The damper also helps reduce unwanted noise. Photo Sequence 20 shows the general procedures for mounting a one-piece drum/hub on a brake lathe. For a floating drum, refer to Photo Sequence 14 for general mounting procedures.

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Figure 8-55  Install a vibration damper to keep the drum from chattering while being refinished.

Photo Sequence 20

Mounting a One-Piece Disc/Hub (Drum/Hub) on a Brake Lathe

P20-1  Ensure that the hub cavity is completely clean and that the bearing races are firmly secure within the hub.

P20-2  Select a tapered cone that fits into each bearing race. Normally the outer bearing race requires a slightly smaller cone than the inner race.

P20-4  Hold the drum/hub onto the inner cone as the outer tapered cone is fitted onto the bore and into the outer bearing race.

P20-5  Hold everything in place on the arbor as the necessary spacer and/or bushing is installed onto the arbor.

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P20-3  After sliding the inner tapered cone onto the arbor, fit the hub onto the cone.

P20-6  Screw on the arbor nut. It is a reverse (left-hand) thread. The interior of one end of the nut is not threaded. This end of the nut is facing the spacer/ bushing when installed on the arbor.

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Photo Sequence 20 (continued)

P20-7  Install the vibration damper around the outer circumference of the drum.

Caution Do not attempt to use a brake lathe without training. The minimum training is studying the lathe’s operator manual. Serious injury or damage could occur if the lathe is improperly set up.

P20-8  The drum/hub is now properly mounted and ready for the final checks before machining.

Machining a Drum on a Lathe WARNING  Many bench brake lathes are designed to machine both rotors and drums. Read the operating instructions. In Figure 8-57 is an item called the ­cross-feed lever that will move the cutting bit away from the lathe’s arbor. It is used to machine rotors. If engaged during drum machining, the cutting bit will cut a deep gouge in the drum and will eventually lock the machine down. Ensure the cross-feed lever is in its neutral position before mounting the drum to the lathe arbor.

Before removing any metal from the drum, verify that it is centered on the lathe arbor and that extra runout has not been created by the lathe mounting. If the drum is not centered and square with the arbor, machining can actually add runout. To check drum mounting, make a small scratch on one surface of the drum as follows: 1. Begin by backing the cutting assembly away from the drum and turning the drum through one complete revolution to be sure there is no interference with rotation. 2. Start the lathe and advance the cutting bit until it just touches the drum surface near midpoint of the drum’s friction area. WARNING  A brake lathe can produce a lot of torque. Do not wear loose clothing or unrolled long-sleeved shirts while machining or setting up the lathe. WARNING  Do not attempt to make adjustments or perform other actions in or near the cutting head. Allow the drum to come to a complete stop before loosening the nut. The lathe produces sufficient torque to break a bone or cause other injuries. WARNING  Do not allow the lathe to operate without close supervision. Do not allow other persons near the lathe until it stops. Do not leave the lathe until it stops running. Inattention or lack of monitoring could cause an accident.

3. Let the cutting bit lightly scratch the drum, approximately 0.001 inch (0.025 mm) deep (Figure 8-56).

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Second scratch cut

First scratch cut

Figure 8-56  A pair of scratch cuts will help you check for an out-of-round condition, as well as for the drum mounting on the lathe.

4. Move the cutting bit away from the drum and stop the lathe. If the scratch is all the way around the drum, the drum is centered and you can proceed with resurfacing. 5. If the scratch appears intermittently, either the drum is out of round or it is not centered on the arbor. In this case, loosen the arbor nut and rotate the drum 180 degrees on the arbor; then retighten the nut. 6. Repeat step 2 through step 4 to make another scratch about ¼ inch away from the first (Figure 8-57). 7. If the second scratch appears intermittently, but at or near the first scratch test, the drum is significantly out of round, but it is properly centered on the lathe and you can proceed with machining. 8. If the second scratch appears opposite the first on the drum surface, remove the drum from the lathe arbor and recheck the mounting. In extreme cases, the lathe arbor shaft may be bent. To determine if the arbor is bent, mount a dial indicator on the lathe and disconnect lathe power. Release the pulley belt tension by moving the controlling lever; then rotate the arbor slowly by turning the drive pulleys. Observe the dial indicator needle. Movement of the needle more than one division (0.001 in.) indicates a bent arbor. Contact the lathe manufacturer for lathe service information. A distorted mounting adapter sometimes can be corrected by installing it on a precision metal-working lathe and machining it. It is usually more practical to replace a defective adapter, however. Adjusting Lathe Settings.  Before starting to machine the drum, consider and adjust three lathe settings: lathe speed (rpm); cross-feed (depth of cut), and spindle feed (speed of travel across the drum surface). The lathe speed usually stays constant throughout the machining operations, but most lathes have at least two or three speed settings. Select the best speed for the drum being machined according to the lathe manufacturer’s instructions. Most drums can be refinished and sanded satisfactorily at 150 rpm.

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Cross-feed lever in neutral

Spindle-feed hand wheel: When turned clockwise, the spindle retracts in toward the lathe

In In

Cross-feed hand wheel: When turned clockwise, the tool moves in toward the lathe Clockwise rotation

Cross-feed lever in neutral

Automatic spindle-feed control

Spindle-feed hand wheel: When turned counterclockwise, the spindle moves out from the lathe

Out Out Cross-feed hand wheel: When turned counterclockwise, the tool moves away from the lathe Counterclockwise rotation

Figure 8-57  On most lathes, the spindle-feed hand wheel controls the movement of the cutter in and out of the drum, and the cross-feed hand wheel controls the depth of cut. Note that the wheels can be operated in either clockwise or counterclockwise rotation.

The spindle feed is the distance the cutting bit moves across the friction surface during each lathe revolution. A spindle feed of 0.010 inch to 0.020 inch (0.25 mm to 0.50 mm) per revolution is good for rough cuts on most drums. Make the finish cut at a slower spindle feed of about 0.002 inch to 0.005 inch (0.05 mm to 0.15 mm) per revolution. Most lathes have SAE and metric measurements. The cross-feed, or depth of cut, is the amount of metal removed by the cutting tool in each pass across the drum. A setting of up to 0.015 inch (about 0.40 mm) can be used for a rough cut but only about 0.005 inch (0.15 mm) for the finish cut. Figure 8-57 shows the cross-feed and spindle-feed controls for a typical drum lathe. Note that the lathe can be operated clockwise or counterclockwise, depending on the desired spindle-feed direction. The cross-feed scale has metric and SAE graduations. Machining the Drum.  When certain that the drum is securely mounted and properly centered, turn on the lathe and adjust it to the desired speed. Then advance the cutting bit to the open edge of the drum and remove the ridge of rust and metal that has formed there. Use several light cuts of 0.010 (0.254 mm) inch to 0.020 (0.508 mm) inch rather than one heavy cut.

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Next, move the cutting bit to the closed (inner) edge of the drum and remove the ridge that also is present there. As the ridges are removed, note the point of the smallest drum diameter. Position the cutting bit at this point and adjust the hand wheel that controls the depth of cut to zero. This is the starting point for further depth-of-cut adjustments. Reposition the cutting bit to the closed (inner) edge of the drum and adjust it for a rough cut as specified previously. The hand wheel micrometer is graduated to indicate the amount of metal removed from the complete diameter. For example, if the hand wheel indicates 0.010 inch (0.254 mm) the lathe has made a cut 0.005 inch (0.127 mm) deep in the drum surface. Adjust the cross-feed for a rough cut and engage the cross-feed mechanism. The lathe will automatically move the cutting bit from the inner to the outer edge of the drum. Make as many rough cuts as necessary to remove defects but stay within the dimension limits of the drum. If the cutting bit chatters as it passes over hard spots in the drum surface, grind the surface or discard the drum. Complete the turning operation with a finish cut as specified previously. After turning, keep the drum mounted on the lathe, and deburr it with 80-grit sandpaper (do not use emery cloth) to remove all minute rough and jagged surfaces. If the drum does not clean up when turned to its maximum machining diameter, it must be replaced. Some replacement brake drums are semifinished. A semifinished drum may require additional machining to obtain the proper dimensional specifications and surface finish. Fully finished drums do not require additional machining unless it is needed to match the diameter of an old drum on the same axle set or has been stored incorrectly. A quick, light scratch test on a new drum may prevent a comeback. New drums are also protected with a rustproofing coating that must be thoroughly cleaned off the friction surfaces. Use a non-petroleum solvent such as brake cleaner or lacquer thinner to remove the coating. Cleaning a Refinished Drum.  The surface of a freshly refinished drum contains millions of tiny particles. If these metal particles are not cleaned away, they will become embedded in the brake lining. When the brake lining becomes contaminated with metal shavings, it becomes a fine grinding stone and soon scores the drum. The metal particles can be removed from the drum by washing thoroughly with hot, soapy water and wiping with a lint-free rag. Use compressed air to thoroughly dry the clean drum. After washing, wipe the inside of the drum (especially the newly finished surface) with a lint-free white cloth dipped in denatured alcohol or brake cleaning solvent. Use a cleaner that does not leave a residue. This operation should be repeated until dirt is no longer visible on the wiping cloth (Figure 8-58). Allow the drum to dry before reinstalling it on the vehicle.

Figure 8-58  Cleaning a drum after refinishing.

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Torque stick Figure 8-59  You should not install wheel nuts directly with an ­impact wrench, but using a torque stick of the correct specification is ­acceptable.

Drum Installation If the drum is a two-piece floating drum, make sure all mounting surfaces are clean. Apply a small amount of silicone dielectric compound to the pilot diameter of the drum before installing the drum on the hub or axle flange. If the drum has an alignment tang or a hole for a locating screw, make sure it is lined up with the hole in the hub or axle flange. If push nuts or speed nuts were used to hold the drum in position, they may be reinstalled. Their use is not mandatory, however. Install the wheel and tire on the drum and torque the wheel nuts to specifications, following the recommended tightening pattern (Figure 8-59). Failure to tighten in the correct pattern may result in increased lateral runout, brake roughness, or pulsation. If the drum is a fixed, one-piece assembly with the hub that contains the wheel bearings, clean and repack the bearings and install the drum as explained in Chapter 3 of this Shop Manual. After lowering the vehicle to the ground, pump the brake pedal several times before moving the vehicle. This positions the brake linings against the drum and verifies that pedal operation is correct. If the vehicle is so equipped, turn the air suspension service switch back on. CUSTOMER CARE  Advise your customers to avoid unnecessary hard braking during the first 500 miles after brakes are relined. This is a critical break-in period for linings. A little early care can dramatically increase the life of the linings.

CASE STUDY The brake job was almost finished on the Hyundai Excel, but the new rear wheel cylinders would not hold their pushrods out against the shoes. When the brake pedal was released, the pistons retracted fully into the wheel cylinder bores. Consequently, the first time the pedal was pressed, it would go to the floor. The new aftermarket wheel cylinders did not have internal springs, but the tech working on the job thought that might be the problem. He checked with a dealer service department and found that the original Hyundai wheel cylinders did have springs. A set of OEM cylinders solved the problem. The moral of the story is to always make certain that aftermarket parts truly are equivalent to original equipment parts.

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ASE-STYLE REVIEW QUESTIONS 1. Before trying to remove a brake drum for service, Technician A backs off the brake shoe adjuster. Technician B takes up all slack in the parking brake cable. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 2. When inspecting a wheel cylinder, Technician A finds liquid brake fluid behind the piston boot and rebuilds the wheel cylinder based on this fact. Technician B does not rebuild the wheel cylinder if only dampness is found in the boot. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 3. When adjusting the brake shoes on a car with self-adjusting brakes, Technician A moves the self-adjusting lever away from the star wheel. Technician B says it is best policy to just force the star wheel against the self-adjuster without disengaging it. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 4. Drum linings are badly worn at the toe and heel areas of the linings. Technician A says that the problem is an out-of-round drum. Technician B says that the problem is a tapered drum. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. Technician A says that the drum discard dimension is the maximum diameter to which the drums can be refinished. Technician B says that the drum discard diameter is the maximum allowable wear dimension and not the allowable machining diameter. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

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6. When machining a drum on a brake lathe, Technician A uses a spindle speed of approximately 150 rpm. Technician B makes a series of shallow cuts to obtain the final drum diameter. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 7. Technician A says that if the drum-to-lining adjustment is correct, the diameters of the two drums on an axle set do not matter as long as they do not exceed the discard dimension. Technician B says that the drum diameters on given axles must be exactly the same. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 8. Technician A says that new drums must be cleaned to remove the rustproofing compound from the drum surface. Technician B says that refinished drums must be cleaned to remove all metal particles from the drum surface. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 9. Technician A says that brakes with linings with more wear at the wheel cylinder end indicate a normal wear condition. Technician B says that if one lining on a duo-servo brake is worn more than the other, the shoes may be installed incorrectly. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 10. Technician A says that weak or broken return springs can cause brake drag or pulling to one side. Technician B says that the same problems can be caused by a loose backing plate or an inoperative self-adjuster. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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ASE CHALLENGE QUESTIONS 1. While discussing mounting a drum on a lathe, Technician A says a two-piece drum mounts to the lathe arbor with tapered or spherical cones. Technician B says a one-piece drum is centered on the lathe arbor with a spring-loaded cone and clamped in place by two large cup-shaped adapters. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 2. Brake drums are being discussed. Technician A says that hard spots in the drums may cause brake chattering. Technician B says that chattering is usually caused by fluid-soaked brake pads. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

4. Technician A says a tire depth gauge can be used to measure lining thickness. Technician B says most carmakers specify a minimum lining thickness of 1/32 inch (0.030 in. or 0.75 mm) above the shoe table or above the closest rivet head. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 5. Wheel cylinders are being discussed. Technician A says that a leaking wheel cylinder may cause the wheel to grab or lock. Technician B says that dampness or seepage found inside the wheel cylinder dust boot is not considered a cause for replacing the wheel cylinder. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

3. While discussing brake lathe cutting bits, Technician A says the tip of the cutting bit should be razor sharp. Technician B says a slightly rounded bit can cut a spiral groove into the drum that will cause noisy and erratic brake operation. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

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Name ______________________________________ 

Date _________________

DIAGNOSING DRUM BRAKE PROBLEMS Upon completion of this job sheet, you will be able to diagnose poor stopping, noise, pulling, grabbing, dragging or pedal pulsation problems.

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ASE Education Foundation Correlation This job sheet addresses the following MLR task: C.4. Inspect wheel cylinders for leaks and proper operation; remove and replace as needed. (P-2) This job sheet addresses the following AST/MAST tasks: C.1. Diagnose poor stopping, noise, vibration, pulling, grabbing, dragging or pedal pulsation concerns; determine necessary action. (P-1) C.5. Inspect wheel cylinders for leaks and proper operation; remove and replace as needed. (P-2) Tools and Materials • Basic hand tools Protective Clothing Goggles or safety glasses with side shields Describe the vehicle being worked on: Year ______________ Make ______________ Model ______________ VIN ______________ Engine type and size ____________________________________________________________ Procedure 1. Begin the inspection of the drum brake system by checking the tires for excessive or unusual wear or improper inflation. What did you find?   2. Wheels for bent or warped rims. What did you find?   3. Wheel bearings for looseness or wear. What did you find?   4. Suspension system for worn or broken components. What did you find?   5. Brake fluid level in the master cylinder. What did you find?   6. Signs of leakage at the master cylinder, in brake lines or hoses, at all connections, and at each wheel. What did you find?  

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7. Road test the vehicle. As you apply the brake pedal, check for excessive travel and sponginess. What did you find?   8. Listen for noises: not just the obvious sounds of grinding shoes or shoe linings, but mechanical clanks, clunks, and rattles. What did you find?   9. If the vehicle pulls to one side when the brakes are applied, check for glazed or worn linings, broken or weakened return spring, loose lining, inoperative self-adjuster, an out-of-round drum, or a faulty wheel cylinder at one wheel. Also check for signs of grease or brake fluid that may have contaminated the shoes and drum. Check for distorted or damaged brake pads. Grabbing brakes also may be caused by grease or brake fluid contamination. What did you find?   10. Remove the drums and inspect the brakes. Any wear in the shoes, shoe hold-down and retracting hardware, drums, or wheel cylinder should be noted and corrected during a complete brake system overhaul. What did you find?   11. Check for worn shoes; glazed or worn linings; damaged or improperly adjusted brake shoes; a loose backing plate; oil, grease, or brake fluid on the linings; faulty wheel cylinders; loose linings; out-of-round drums; or broken or weakened return springs. What did you find?   Problems Encountered    Instructor’s Comments   

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Name ______________________________________ 

Date _________________

REPLACE BRAKE SHOES Upon completion and review of this job sheet, you should be able to replace the brake shoes on a rear-wheel drum brake and inspect the drum brake components.

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ASE Education Foundation Correlation This job sheet addresses the following MLR tasks: A.1. Research vehicle service information including fluid type, vehicle service history, service precautions, and technical service bulletins. (P-1) B.4. Select, handle, store, and fill brake fluids to proper level; use proper fluid type per manufacturer specification. (P-1) C.1. Remove, clean, and inspect brake drum; measure brake drum diameter; determine serviceability. (P-1) C.3. Remove, clean, inspect, and/or replace brake shoes, springs, pins, clips, levers, adjusters/self-adjusters, other related brake hardware, and backing support plates; lubricate and reassemble. (P-1) C.5.  Pre-adjust brake shoes and parking brake; install brake drums or drum/hub assemblies and wheel bearings; make final checks and adjustments. (P-1) This job sheet addresses the following AST/MAST tasks: A.2.  Research vehicle service information including fluid type, vehicle service history, service precautions, and technical service bulletins. (P-1) B.9. Select, handle, store, and fill brake fluids to proper level; use proper fluid type per manufacturer specification. (P-1) C.2. Remove, clean, and inspect brake drum; measure brake drum diameter; determine serviceability. (P-1) C.4. Remove, clean, inspect, and/or replace brake shoes, springs, pins, clips, levers, adjusters/self-adjusters, other related brake hardware, and backing support plates; lubricate and reassemble. (P-1) C.6. Pre-adjust brake shoes and parking brake; install brake drums or drum/hub assemblies and wheel bearings; perform final checks and adjustments. (P-1)

Caution Before working on the brakes of a ­vehicle with an ABS, consult the service manual for ­precautions and ­procedures. Failure to follow procedures to protect ABS ­components during routine brake work could damage the components and cause expensive repairs.

Tools and Materials • Lift or jack and jack stands • Impact tools • Return spring tool Describe the vehiclebeing worked on: Year ___________________ Make ___________________ Model___________________ VIN ___________________ Engine type and size___________________ ABS___________________ yes___________________ no___________________ If yes, type___________________ Procedure 1. Highlight the precautions required by the manufacturer concerning ABS and routine brake repairs.    Wheel nut torque __________________________________________________________

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2. Inspect the fluid level in the master cylinder. Adjust so the reservoir is about half full.

Task Completed

3. Lift the vehicle and remove the wheel assembly.

h

WARNING  Wear safety glasses or face protection when using brake fluid. Injuries to the face or eyes could occur from spilled or splashed brake fluid.

h

4. Inspect the brake drum mounting. Are there fasteners holding the drum, is the drum rusty, or are there any other item(s) that may affect drum removal? Explain and make a recommendation. __________________________________________________________________________ __________________________________________________________________________  5. Remove drum. 6. Inspect the drum for damage. Measure the diameter of the drum, compare to specification, and determine serviceability. See Job Sheet 35 for drum machining.

h

Results:__________________________________________________________________ __________________________________________________________________________ 7. Position a catch basin and clean braking components. Dispose of the waste as required by law and shop policy. NOTE TO INSTRUCTORS:  The following steps are based on a floating drum and a duoservo brake system with a cable-operated self-adjuster. Service on other type drums or brake systems may require additional training or guidance for the student. 8. Select the return-spring tool (pliers) and remove the top return spring from the anchor. Mark or lay out in order of removal. 9. Remove the second return spring and self-adjuster cable. Mark or lay out in order of removal. 10. Use the retainer-spring tool to remove the spring from front (secondary) shoe. Mark or lay out in order of removal. 11. Remove the shoe and detach it from the self-adjuster and self-adjuster spring. 12. Do not drop self-adjuster components. Mark or lay out in order of removal. 13. Use the retainer-spring tool to remove the spring from the rear (primary) shoe. Mark or lay out in order of removal.

h

Caution Do not depress the brake pedal when the shoes are being removed, installed, or have been removed from the system. Without the shoes installed properly, the wheel cylinder pistons could be forced from the bore when the pedal is depressed.

14. Remove the shoe and detach it from the self-adjuster mechanism and parking brake cable or lever. Mark or lay out in order of removal. 15. Remove parking brake lever from rear shoe if necessary. 16. Inspect the wheel cylinder dust boot. Check under edge of boot for brake fluid. Results and recommendation.________________________________________________ __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________

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h

Caution Compare the new shoes to the hold shoes. They should be exactly alike except the new shoes may have additional lining material. If in doubt, consult the instructor, service manual, or parts supplier to ensure the new shoes are correct. Installing incorrect shoes will affect braking.

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Drum Brake Service

17. Clean the slide areas on the backing plate and lube with brake lubricant only. Disc brake lubricant is sufficient.

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Task Completed h

NOTE: The next two steps may have to be adjusted depending on how the hardware and shoes fit onto the backing plate and self-adjuster components. 18. Install the parking brake lever onto the rear shoe if necessary.

h

19. Connect the parking brake lever to the parking brake cable as needed.

h

20. Install the rear shoe and self-adjuster actuator onto the backing plate.

h

21. Install the retainer spring.

h

22. Install the front shoe and retaining spring.

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23. Install the top end of the cable and then install the return springs in reverse order of removal.

h

24. Install the self-adjuster spring.

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25. Disassemble the self-adjuster, clean, lube, and reassemble if not done previously. Screw the self-adjuster to the minor position.

h

26. Install the self-adjuster by pulling the front shoe forward and inserting the selfadjuster between the two shoes.

h

27. Install the spring for the self-adjuster mechanism on the rear shoe.

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28. Use the brake gauge to set the initial adjustment of the brakes.

h

29. Install the drum and complete the brake adjustment as needed.

h

30. Install the wheel assembly and torque lug nuts.

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31. Lower the vehicle almost to the floor when both brakes are completed and the wheel assemblies have been installed.

h

32. Press the brake pedal several times to center the shoes.

h

33. Check brake adjustment and make changes as required. When completed, lower the vehicle to the floor.

h

34. Check the brake fluid level and top off as necessary.

h

Caution WARNING  Before moving the vehicle after a brake repair, pump the pedal several times to test the brake. Failure to do so may cause an accident with damage to vehicles or facility, or personal injury. 35. Perform a brake test to ensure that the brakes will stop and hold the vehicle. Do this test before moving the vehicle from the bay. 36. When the repair is complete, clean the area, store the tools, and complete the work order. Problems Encountered    Instructor’s Encountered 

Before adding brake fluid, consult the vehicle service information. Most manufacturers require a specific classification of brake fluid to be used.

h

Caution Never use brake fluid from a previously opened container. Once opened, even tightly capped containers will absorb moisture from the air.

 

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Drum Brake Service

Name ______________________________________ 

Date _________________

431

JOB SHEET

MACHINING BRAKE DRUMS

38

ASE Education Foundation Correlation Upon completion and review of this job sheet, you should be able to measure and machine a brake drum. This job sheet addresses the following MLR tasks: A.1. Research vehicle service information including fluid type, vehicle service history, service precautions, and technical service bulletins. (P-1) C.1. Remove, clean, and inspect brake drum; measure brake drum diameter; determine serviceability. (P-1) C.2. Refinish brake drum and measure final drum diameter; compare with specification. (P-1) This job sheet addresses the following AST/MAST tasks: A.2. Research vehicle service information including fluid type, vehicle service history, service precautions, and technical service bulletins. (P-1) C.2. Remove, clean, and inspect brake drum; measure brake drum diameter; determine serviceability. (P-1) C.3. Refinish brake drum and measure final drum diameter; compare with specification. (P-1) Tools and Materials • Bench-mounted brake lathe • Service information • Brake drum micrometer Describe the vehicle being worked on: Year ___________________ Make ___________________ Model ___________________ VIN ___________________ Engine type and size ___________________ ABS ___________________ yes ___________________ no ___________________ If yes, type ___________________ Procedure

Task Completed

1. Determine the drum discard diameter ________________________________________ Type of drum _____________________________________________________________ Any special precautions to be followed for this drum? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 2. Remove wheel assembly to gain access to the drum. Remove the drum.

h

3. Inspect the drum. Does its condition make it inadvisable to machine? ______________ ___________________ If yes, explain. _________________________________________________________________________

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4. Measure the internal diameter of the drum (at least two points equally spaced around the drum) 1 _____________________________ 2 _____________________________

Task Completed

5. Measure the deepest groove, if any. Is it enough to affect machining? If yes, explain and make recommendations. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ NOTE TO INSTRUCTORS: The following steps are based generally on a bench-brake lathe by Raybestos with one spindle and a floating brake drum. Other lathes or drums may require additional instruction for the student. 6. Select a centering cone that fits about halfway through the center hole of the drum.

h

7. Select two identical clamps that fit the drum without interfering with the cutting head of the lathe.

h

8. Slide one clamp onto the lathe shaft, open end out.

h

9. Slide on a spring followed by the centering cone.

h

10. Slide on the drum followed by the outer clamp, bushing, spacer (if needed), and the nut. Tighten, but do not overtighten, the nut.

h

11. Install the damping strap.

h

12. Adjust the assembly inward toward the lathe body until it stops. Reverse out two turns.

h

13. Adjust the cutting head so it will reach the inner edge of the machined surface of the drum.

h

14. Move the drum out (away from the lathe) until the cutting tip is about halfway through the machined surface.

h

15. Adjust the cutting tip until it meets the drum and reverse out about half a turn.

h

16. Ensure the area around is clear and the lathe’s drive mechanism is in neutral. Switch on the motor.

h

17. Adjust the cutting tip slowly until it comes in contact with the turning drum. Hold in place and set the sliding scale to zero. Move cutting bit away from drum.

h

18. Adjust the cutting head until the cutting tip is aligned with the rear edge of the machined surfaces.

h

19. Adjust the cutting tip until it contacts the drum.

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20. Continue adjusting the tip until the scale is set between 0.002 inch and 0.015 inch.

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21. Engage the fast speed on the lathe.

h

22. Observe the drum as it is being machined. Are there dark (uncut) areas? Explain the next step to be taken. ______________________________________________________ ________________________________________________________________________ ________________________________________________________________________

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23. If the answer to step 22 is no, go to step 27. If the answer to step 22 is yes, go to step 24.

Task Completed h

24. When the cutting tip clears the drum, disengage the drive and move the cutting tip back to the starting point.

h

25. Adjust the cutting tip to cut 0.002 inch deeper and engage fast cut.

h

26. Repeat step 18 through step 25 as needed.

h

27. When the cutting tip clears the drum, disengage the drive.

h

28. Move the cutting tip to the starting point and set to cut between 0.002 inch and 0.005 inch deeper.

h

29. Engage the drive mechanism in slow speed.

h

30. When the cutting bit clears the drum, disengage the drive and stop the motor.

h

31. When the drum stops turning, remove it from the lathe.

h

32. Wash the drum in running hot, soapy water and with a brush if possible. If a basin is required, use hot soapy water and a brush to clean the machined surfaces.

h

33. Rinse with clear water and blow dry with an OSHA-approved blowgun.

h

34. Install the drum on the vehicle.

h

35. Use Job Sheet 34 to install shoes and other components.

h

36. When the repair is complete, clean the area and lathe, store the tools and adapters, and complete the repair order.

h

Problems Encountered    Instructor’s Comments   

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Parking Brake Service

Upon completion and review of this chapter, you should be able to: ■■ ■■ ■■ ■■

Diagnose parking brake problems. Inspect the parking brake system for wear, rust, binding, and corrosion. Clean or replace all system parts as needed. Lubricate the parking brake system.

■■

Adjust calipers with integrated parking brakes.

■■

Adjust the parking brake and check system operation.

■■

Service electric parking brake systems.

Basic Tools Basic technician’s set Hydraulic lift or safety stands

PARKING BRAKE TESTS Parking brake service primarily consists of testing the system operation, adjusting the cables and linkage, and replacing components when necessary. In addition, auxiliary drum parking brakes used with some rear disc brakes may require adjustment or repair and warning lamp switches may require service. Checking the service brake pedal travel is the first step in diagnosing a potential parking brake problem on manually applied systems. The next step is to inspect and test the parking brake control and the linkage. Finally, a performance test will verify that the parking brake can hold the vehicle stationary as required by motor vehicle safety standards. Electrical and electronic systems have modules that monitor and control system operation and operate on the vehicle’s controller area network (CAN). These systems have their own unique trouble codes and system procedures.

Rear Drum Brake Pedal Travel Because the service brake shoes are the parking brakes for vehicles with rear drum brakes, service brake adjustment directly affects parking brake operation. If lining-to-drum clearance is excessive, the parking brake linkage may not have enough travel to apply the parking brakes completely. If the parking brake lever or pedal must be applied to the full limit of its travel to engage the parking brakes, excessive clearance or slack exists somewhere in the system. The technician cannot tell immediately, however, if that clearance or slack is in the cables and linkage or in the shoe adjustment. To isolate the looseness in the system, press the service brake pedal and note its travel. If brake pedal travel seems excessive, the rear drum service brakes may need adjustment. Always check and adjust the service brakes before adjusting the parking brake linkage.

Rear Disc Brake Pedal Travel Many current vehicles with rear disc brakes utilize auxiliary brake shoes inside a specialized rotor that is called drum-in-hat. These disc brakes have a small set of brake shoes that are only used to apply the parking brakes. This allows the disc brake caliper to only be used 435

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for the service brakes and eliminates many of the problems associated with rear integral caliper style parking brakes. To apply the older style rear integrated parking brake calipers, the rear disc brakes on GM and Ford cars have lever-operated mechanisms inside the caliper pistons. These mechanisms include self-adjusters that keep the caliper piston from retracting too far in its bore. If the self-adjusters do not work properly, both the service brake pedal and the parking brake control linkage may have excessive travel. Figure 9-1 shows a cross section of the parking brake mechanism in the GM rear caliper. Owners of GM cars with integral caliper rear disc brakes should be reminded to use the parking brake regularly and not rely on the transmission park position to hold the car stationary. Applying and releasing the parking brakes keeps the parking brakes adjusted and keeps the mechanism from seizing. The most practical remedy for defective selfadjusters is to replace the calipers. The self-adjusters can be rebuilt, however, if replacement calipers are not available. To check parking brake operation on some Ford vehicles with rear disc brakes (Figure 9-2), push the parking brake lever on the caliper forward by hand. If it moves more than 20 degrees, the self-adjuster needs readjustment. To do this, start the engine and apply the service brakes 40 to 50 times with moderate pressure. Wait about 1 second between pedal applications. Then stop the engine and apply the pedal another 30 times with heavy foot pressure. If the travel of both the service brake pedal and the parking brake pedal or lever does not decrease, the rear calipers must be rebuilt or replaced. Figure 9-3 shows an exploded view of a Honda rear caliper. It uses a cam-and-bolt mechanism to make the brake adjustment, and it uses the cam to turn the bolt, much like the self-adjusters on drum brakes. The cam is moved by application of the arm attached to the parking brake cables. If the parking brake is used properly, there is usually no requirement to adjust the parking brake for pad wear. When the parking brake is applied, the arm is moved to force the caliper piston outward. If the piston moves far enough, the arm moves the cam and cam lever, which, in turn, turn the bolt and prevent the piston from returning to its previous position within its bore. Piston seal Cone

Piston

Screw

Outboard brake pad

Rotor

Parking brake lever

Inboard brake pad Internal thread nut

Figure 9-1  A GM screw-and-nut parking brake mechanism for rear disc brakes.

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437

Caliper housing

Operating shaft

Balls

Operating lever

Automatic adjuster

Piston

Figure 9-2  A Ford ball-and-ramp parking brake mechanism for rear disc brakes.

Pins

Cam boot

O-ring Adjusting bolt

Washer

Circlip Spring

Cam Lever Pin boots

Cone

Nut Spring

Piston Piston seal Boot

Caliper bracket Shim

Shim

Brake pads

Figure 9-3  When the cable is pulled, the arm moves the cam and cam lever. The lever rotates the sleeve piston, which is attached to the adjusting bolt. If the movement is enough, the rod prevents the piston from fully returning to its previous position within the bore.

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Chapter 9 Left parking brake cable Right parking brake cable

Front rod

Adjusting nut Equalizer

Figure 9-4  It is best to clean and lubricate the adjusting nut and front rod threads before attempting to turn the adjusting nut. Hold the rod on the unthreaded portion with pliers during movement of adjusting nut.

Although a manual adjustment of this portion of the parking brake is not normally needed, there is an adjustment available at the cable equalizer (Figure 9-4). Normally this adjustment is used when new components of the braking system are installed, if the parking brake needs to be backed off during caliper rebuild or replacement, and sometimes when new pads are installed. The adjustment is simple: Remove the protective plate from the bottom of the vehicle body; use the appropriate wrench to turn the adjusting nut clockwise to tighten or counterclockwise to slacken the cables. Hold the front rod with pliers while turning the adjusting nut. This is the most common type of parking adjustment.

Linkage Inspection and Test Remind the customer that the parking brake is for holding the vehicle and not for stopping it. Many vehicles use the parking brakes to self-adjust the service brakes. If the service brake pedal is firm and has normal travel, the parking brakes should be fully applied when the lever or pedal moves one-third to two-thirds of its travel. Some carmakers say that the parking brakes should be applied completely when the ratchet mechanism moves a specified number of notches (Figure 9-5). If the parking brake lever or pedal travels more than specified, the linkage adjustment is too loose. In this case, the brakes may not be applied well enough to hold the vehicle Up

Lever-locked notches

Down Lever-locked notches: Cars with rear disc brakes: 7–11 Cars with rear drum brakes: 4–8

Figure 9-5  Some carmakers specify a certain amount of travel for the parking brake lever.

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stationary, especially on a hill. If the parking brake lever or pedal travels less than specified, the linkage adjustment is too tight, which can cause the brake linings to drag on the drum or rotor when the vehicle is moving and lead to brake fade and premature lining wear. Overly tight parking brake linkage for rear drum brakes also can interfere with accurate service brake adjustment. If the lever or pedal travel is within the specified range, raise the vehicle on a hoist with the parking brakes released. Rotate the rear wheels by hand and check for brake drag. Have an assistant operate the parking brake control while you check the movement of the cables and linkage. The pedal or lever should apply smoothly and return to its released position. The parking brake cables should move smoothly without any binding or slack. Protective conduit should be in good shape. Also inspect the cables (Figure 9-6) for broken strands, corrosion, and kinks or bends. If the brakes drag or the linkage binds in any way, the parking brakes must be adjusted or repaired as necessary. Clean and lubricate the parking brake and noncoated metal cables with a brake lubricant. See Photo Sequence 21 for a typical inspection and adjustment procedure. Damaged cables and linkage must be replaced. The parking brake cables on some vehicles are coated with a plastic material. This plastic coating helps the cables slide smoothly against the nylon seals inside the conduit end fittings. It also protects the cable against corrosion damage. Plastic-coated cables do not need periodic lubrication, but these cables should be handled carefully during service. Avoid contact with sharp-edged tools or sharp surfaces on the vehicle underbody. Damage to the plastic coating will impair the smooth operation of the system and can also lead to corrosion.

439

Swollen plastic coatings are a sign of underlying damage to the cable.

SERVICE TIP  Failure to use the parking brakes regularly is a leading cause of complaints about a low brake pedal. This is particularly true on some leading-trailing drum brakes that use the parking brake linkage to adjust the service brakes, and it is also a common problem with rear disc brakes. Advise your customers to use the parking brakes and do not overlook failure to use the parking brakes as the cause of a low-pedal problem.

Rear cables Rear cable

Equalizer

Front cable

Parking brake mechanism

Front cable

Figure 9-6  Inspect the cables for damage.

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30-percent grade

Figure 9-7  The parking brake must hold the vehicle on a 30-percent grade for 5 minutes in both the forward and the reverse directions.

A small amount of brake drag is normal for rear disc brakes, but heavy drag usually indicates an over-adjusted parking brake mechanism. To determine if the mis-adjustment is in the linkage or in the caliper self-adjusters, disconnect the cables at a convenient point so that all tension is removed from the caliper levers. If brake drag is reduced, inspect the external linkage and lubricate, adjust, or repair it as necessary. If brake drag is still excessive with the parking brake linkage disconnected, check the caliper levers to be sure that they are returning fully against their stops. If the caliper levers are operating correctly and brake drag remains excessive, the calipers must be repaired or replaced.

Performance Test FMVSS 135 requires that the parking brakes hold the vehicle stationary for 5 minutes on a 30 percent grade in both the forward and reverse directions (Figure 9-7). This standard can be the basis of a performance test for the parking brakes. Stop the vehicle on a grade of approximately 30 percent, put the transmission in neutral, apply the parking brakes with moderate force, and release the service brakes. It is not necessary to wait a full 5 minutes, but the vehicle should remain stationary for a reasonable amount of time. Perform this test with the vehicle facing in both directions on the grade.

CABLE AND LINKAGE ADJUSTMENT Classroom Manual page 215

Parking brake cable and linkage adjustment should be checked in accordance with the specific vehicle maintenance schedule. Most carmakers call for parking brake inspection at 7,500-mile or 15,000-mile intervals (12,000 km to 24,000 km). Parking brake adjustment also should be checked as part of every brake service job. Parking brake linkage often requires adjustment after rear shoes or pads have been replaced and adjusted. Adjustment locations vary from one linkage design to another. Most pedal-operated parking brakes have the adjustment at a point under the center of the vehicle (Figure 9-8). Rear cables

Front cable

Adjuster nut Equalizer

Figure 9-8  Typical undercar adjustment for pedal-operated parking brakes.

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Cables to wheels

Adjusting nut Parking brake lever

Equalizer

Front cable Warning lamp switch (may be mounted under or to side of lever)

Figure 9-9  Adjustment points for lever-operated parking brakes usually are accessible from inside the car.

Lever-operated brakes may have the adjustment under the vehicle, but it is more often located at the point where the cable or cables attach to the lever, and it is accessible from inside the car (Figure 9-9). Part of the center console or floor trim may have to be removed for adjustment access. The service brakes must always be adjusted correctly before adjusting the parking brake linkage. If drum brake shoe adjustment is too loose, trying to adjust the parking brake may pull the shoes off their anchors or away from the wheel cylinder. The parking brakes may appear to be adjusted correctly when actually they are not. Service brake operation and further adjustment also may be adversely affected. If service brake adjustment is unequal from side to side and one pair of shoes is looser than the other, the parking brake linkage may engage one wheel brake more tightly than the other. Only one wheel will provide stationary holding power, and parking brake effectiveness will be reduced. The problem of unequal service brake adjustment is most critical on lever-operated parking brakes that may have a separate cable for each wheel. The lever moves each cable equally, but if one wheel brake adjustment is loose, full cable travel will not fully apply that wheel brake. A typical cable adjuster has a threaded rod at the end of a cable and two jam nuts on the rod where it passes through an equalizer or a cable anchor. If the nuts are rusted or corroded, soak them with penetrating oil before trying to adjust the linkage. To prevent damage to the threaded adjusting rod, clean the grease and dirt from the threads on either side of the adjusting nut before trying to turn the nut. Forcing the nut over dirty threads may damage the threads on the nut or the rod. Also lubricate the threads of the adjusting rod before turning the nut. To make the adjustment, hold the adjuster nut with one wrench while loosening the locknut with another wrench. Then turn the adjuster nut to lengthen or shorten the cable as required. If the cable tries to twist as the adjuster nut is turned, grip an unthreaded section of the rod with locking pliers and hold the cable while turning the adjuster nut. Finally, hold the adjuster nut in place with one wrench, and retighten the locknut with another. On linkage with a separate adjustment for each cable, adjust each cable equally.

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Special Tools Service information Brake adjusting tool (spoon) Lift or jack with stands

Special Tools Service information Lift or jack with stands

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Drum Brake Cable Adjustment If the service information is available for the vehicle, follow the adjustment instructions in the manual. Photo Sequence 21 shows a typical parking brake linkage adjustment for rear drum brakes. Most adjustment procedures include these eight basic steps: 1. Block the wheels, place the transmission in neutral, and release the parking brakes. 2. If the vehicle is equipped with automatic ride control, turn it off. Raise the vehicle on a hoist so that the wheels are off the ground.

Photo Sequence 21

Typical Procedure for Inspecting and Adjusting Rear Drum Parking Brakes

P21-1  Proper adjustment of the parking brake begins with setting the parking brake to a near fully applied position.

P21-2  Raise the car on the hoist and make sure it is secure. Position the vehicle so you can rotate the rear wheels freely. (If the parking brake is applied and adjusted properly, you should be unable to rotate the wheels.)

P21-3  Carefully inspect the entire length of the parking brake cable. Look for fraying, breakage, and deterioration.

P21-4  Spray all exposed metal areas of the cable assembly with penetrating oil. This ensures a free-moving system.

P21-5  Inspect the adjustment mechanism. Clean the threaded areas and make sure the adjusting nuts are not damaged.

P21-6  If the parking brake needs adjustment when checked in P21-2, complete the following adjustment procedures: Loosen the adjustment locknut, then adjust the parking brake by tightening the adjusting nut.

P21-7  When you can no longer turn the wheels by hand, stop tightening the adjusting nut.

P21-8  Lower the vehicle and release the parking brake.

P21-9  Raise the vehicle and rotate the wheels. If the wheels turn with only slight drag, the parking brake is properly adjusted.

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443

Photo Sequence 21 (CONTINUED)

P21-10  After the proper adjustment is made, tighten the adjusting locknut. Apply a coat of brake grease to all contacting surfaces of the adjustment assembly.

3. If required, adjust the service brakes according to the carmaker’s instructions before adjusting the parking brakes. 4. Verify that the parking brake linkage is clean, properly lubricated, and operating freely. 5. Tighten the linkage until the brakes drag as the wheel is rotated by hand. 6. Then loosen the adjustment until the wheel just turns freely. 7. Apply the parking brakes until the wheel locks, and check the pedal or lever travel. The parking brakes should be fully applied when the pedal or lever moves one-third to two-thirds of its full travel or as specified by the manufacturer. 8. Apply and release the parking brakes several times, and verify that the wheels turn freely when the brakes are released and are locked when the brakes are applied. Some carmakers specify that parking brakes should be partially applied during adjustment. This is intended to apply a specific amount of slack in the linkage when the brakes are released. Instructions usually require the parking brake lever or pedal be applied a specific number of notches on the ratchet mechanism. Then adjust the brakes following the steps above.

Special Tool Service information

Disc Brake Cable Adjustment The parking brake cables for the rear disc brakes on most vehicles are adjusted similarly to the drum brake cables described previously. The caliper levers that apply the caliper pistons are an added adjustment point, however. After servicing a rear brake caliper, operate the service brakes to position the brake pads before adjusting the parking brake. Begin by loosening the parking brake adjusting nut. Then start the engine and press the brake pedal several times to position the pads for normal operation. Before tightening the cables in any way, leave them loose and be sure that they exert no tension on the caliper levers. Move the caliper levers by hand to verify that they move freely and that they return fully to their unapplied positions. If the calipers have stop lugs, be sure that the levers return completely to these stops. Tighten the cable adjustment to remove all slack and until the levers just start to move. Then back off the adjustment until the levers are just released, but the cables are not slack. Apply and release the parking brakes several times to be sure that the levers return to the fully released positions each time.

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If the parking brakes do not release, check for binding of the parking brake cable.

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Pin

Lever

Figure 9-10  The rear disc parking brake for a midsize Honda.

Special Tools Service information Brake adjusting tool (spoon)

As another example, Figure 9-10 shows the rear disc parking brakes for a midsize Honda. On this design, the lever of the rear brake caliper must contact the brake caliper pin. To make the adjustment, pull the parking brake hand lever up one notch and then tighten the adjusting nut (see Figure 9-9) until the rear wheels drag slightly when turned. Next, release the parking brake lever and verify that the rear wheels do not drag when turned. Make any readjustments necessary. If the equalizer is properly adjusted, the rear brakes should be fully applied when the parking brake lever is pulled up five to ten notches. If the parking brake pedal or lever does not engage the brakes completely at one-third to two-thirds of its travel, the self-adjusters in the calipers are not working properly. Try to adjust the self-adjusters by operating them as explained previously under the pedal travel test instructions. It is more likely, however, that the caliper will require repair or replacement.

Auxiliary Drum Brake Shoe Adjustment and Replacement The auxiliary drum parking brakes used with many disc brakes require two separate adjustments. The cable and linkage adjustment is based on the same principles explained previously for drum brake cable adjustment. However, the parking brake shoes must be adjusted separately, before any adjustments are made to the cables and linkage. Most auxiliary drum parking brakes have manual star wheel adjusters similar to the adjusters on drum service brakes (Figure 9-11). The adjuster is usually accessible through a hole in the outer surface in the drum portion of the rotor (Figure 9-12). On some cars, the adjuster is accessible through the hole for one of the wheel bolts. If the adjuster is accessible through a hole in the rotor, remove the wheel and then reinstall two or three wheel nuts to hold the rotor on the hub. If the adjuster is accessible through a wheel bolt hole, remove one wheel bolt, leaving the wheel installed. Some adjusters are accessible through an opening in the inboard side of the backing plate (Figure 9-13). The star wheel adjuster on the parking brake is a simple device that can be operated with a screwdriver. Tighten the star wheel until the brakes lock, and then back off the adjustment the specified number of notches or clicks.

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Shoe

445

Shoe

Cable

Adjuster Star wheel

Figure 9-11  Auxiliary drum parking brake adjustment location.

Expand shoes

Retract shoes

Figure 9-12  The adjusters for some auxiliary drum parking brakes are accessible through the outboard drum surface.

The shoes and linings of auxiliary drum parking brakes usually outlive the vehicle on which they are installed. If they require replacement, the procedure is similar to the procedures for drum service brakes. The drum portion of the brake rotor cannot be resurfaced, but resurfacing should never be necessary because the parking brakes are applied and released only when the vehicle is stationary. Rotating friction should never be applied to the drum area of the parking brake rotor. Some newer vehicles use a similar method to adjust the drum-in-hat parking brakes but with some cautions that may save the technician time. When adjusting the parking brakes on a Chrysler 300 Series, the star wheel is accessed through the backing plate just like many other vehicles (Figure 9-14). The manufacturer directs that the parking brakes be adjusted until the wheel locks. The adjuster is then backed off six detents or teeth. At this point the wheel should be free to turn. If not, back off the adjuster one detent or tooth at a time. Chrysler states that the star adjuster should not be backed off more than 17 detents, however, because the adjuster screw will screw out of its shell and separate. Then the entire disc brake assembly will have to be removed along with at least some portion

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Adjuster protective plug Backing plate

Access window

Adjuster Caliper

Adjusting star wheel

Figure 9-13  Some auxiliary drum parking brakes are adjusted through the backing plate. NOTE: Access window is enlarged to show detail.

Figure 9-14  Remove the protective plug to gain access to the parking brake adjuster.

of the parking brakes to reconnect the star wheel assembly. A 10- to 15-minute job could become a 1-hour job and additional labor costs for which the customer should not be held responsible. This particular vehicle series does not require any adjustments on the parking brake cable(s). Instead all adjustments are done at the shoes in a manner very similar to standard drum brakes. It is not an uncommon procedure, however. Study the service manual if not experienced with the type of vehicle and parking brake system being serviced.

CABLE AND LINKAGE REPAIR AND REPLACEMENT Classroom Manual page 215

Special Tools Penetrating oil Cleaning solvent Catch basin Wire brush Propane torch

Parking brake cables and linkage can easily last the life of a vehicle if they are inspected, lubricated, and adjusted according to specifications. In areas of the country that experience cold, wet weather, high humidity, and where the roads are salted in winter, corrosion and rust may damage the cables and prevent proper operation. A cable—especially a plastic-coated cable—that is routed too close to the exhaust may be damaged due to heat. The cable may stick or seize in the conduit, or individual strands may fray and rust. A sticking or seized cable can be loosened, lubricated, and adjusted. Because of the labor required, however, it is often more practical to replace the cable. Parking brake linkage installations may have one to four cables, and their locations depend on vehicle and brake system designs. The details of cable replacement are always slightly different from one vehicle to another, but the following sections outline the principles of removing and installing parking brake cables.

Freeing Seized Cables Do not apply lubricant or heat to a plastic-coated parking brake cable.

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If a cable is only moderately corroded or sticking slightly, or if a replacement is unavailable, you can free the cable by working penetrating oil into the ends of the conduit. Let the oil soak in for a few minutes and then try to move the cable in and out of the conduit. Several applications of oil may be needed. A good alternative to penetrating oil is a chain and cable lubricant. This type of lubricant works its way into the cable or chain and provides longterm protection on parking brake cables.

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Most corrosion and damage is confined to the first few inches of cable inside the conduit or to the cable sections outside of the conduit. The problem is that when the cable is applied, this corrosion is drawn into the conduit where it may bind. It may be necessary to disconnect one or both ends of the cable for access to corroded sections, however. When the cable starts to move in the conduit, slide it in and out as far as it will go and continue to apply penetrating oil. Remove corrosion with solvent and emery cloth, steel wool, or a wire brush. You may need to apply heat to a seized cable to free it completely. In this case, disconnect and lower the cable away from the vehicle, or remove it completely, if possible. When the cable moves freely and dirt and corrosion have been removed, lightly lubricate the exposed sections of the cable with brake grease to avoid future problems.

Front (Control) Cable Replacement WARNING  Disable the supplemental inflatable restraint system (SIRS) or air bag system when working on or near the system wiring. Accidental discharge of the air bag could occur, causing injury or damage.

If the parking brakes are operated by a lever, the control cable attachment is usually accessible from inside the car. A few lever-operated cables are accessible from under the car, however. If the parking brakes are operated by a pedal, the control cable attachment is usually under the instrument panel. Because of the awkward access to most such installations, it is a good idea to disconnect the battery ground cable to avoid damaging any electrical system components before working under the instrument panel. Also review the precautions in Chapter 1 of this Shop Manual about working around air bag installations. To start replacing the control cable, release the parking brakes and raise the vehicle on a hoist. Disconnect the lower end of the cable from the equalizer before trying to disconnect the upper end. The lower end is more accessible, and disconnecting it first provides slack to help disconnect the upper end and any mounting clips or grommets. Disconnect the upper end of the cable from the control pedal or lever (Figure 9-15) but do not pull it out of the vehicle yet. First, fasten a length of cord or flexible wire to the brake cable inside the car. Then pull the cable through the floor or fire wall from under the vehicle. Disconnect the cable from the cord or wire, and leave the cord or wire in place through the cable opening. Fasten the cord or wire to the replacement cable and use the cord or wire to help draw the cable through the opening in the floor or fire wall. Connect the upper end of the new cable to the pedal or lever, and reinstall all mounting clips, brackets, and grommets. If any attaching hardware is damaged, install new parts. Then connect the lower end of the cable to the equalizer or to an in-line connector on the rear cable. Adjust the parking brakes as explained previously. SERVICE TIP  The following sections cover some simple cable replacement procedures. Some newer vehicles require that the front seat, portions of the dash and steering column cover, and the door sill be removed to gain access to the complete cable system. Still others require that rubber sealing grommets through the floor and/or bulkhead be replaced when new cable(s) are installed. Some cable replacement jobs can take several hours compared to older vehicles in which most parking brake cables could be replaced in an hour. Check the service information and labor guide before providing an estimate to the customer.

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Caution Do not apply heat to plastic-lined conduit. If uncertain, err on the cautious side and do not heat. Damage to the conduit may result.

Special Tools Service information Lift or jack with stands

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Disconnect here

Horseshoe clip Front cable

Figure 9-15  Disconnect the upper end of the cable from the control pedal or lever.

Rear Cable Replacement Almost all vehicles have two rear parking brake cables that are connected to the equalizer or adjuster. With the vehicle on a hoist, remove the cable adjusting nuts. Then disconnect the front end of the rear cable from the equalizer or from the front brake cable. To remove the cable from a drum brake, first remove the wheel and brake drum. Disconnect the end of the rear cable from the rear parking brake lever on the rear shoe (Figure 9-16). Use the proper size offset box end wrench or screwdriver to Backing plate

Rear cable conduit

Cable retainer

Disconnect cable from parking lever

Figure 9-16  Disconnect the end of the cable from the brake shoe.

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depress the conduit retaining prongs and slide the pronged fitting out through the hole in the backing plate (Figure 9-17). On a typical rear disc brake, the cable conduit is secured at the rear disc brake by a clip or pin that connects the end of the cable to the parking brake lever on the caliper (Figure 9-18). Remove the clip and pin to free the cable. It may be necessary to remove grommets and pronged retainers before the rear cable can be freed. The routing of lefthand and right-hand rear parking brake cables may be different. Refer to the vehicle service manual for details and specific instructions. Attach the new rear cable to the equalizer or adjuster. Install all grommets and clips used to secure the cable. Follow the original routing pattern.

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Disconnect cable from parking lever

Cable retainer

Figure 9-17  Use a box wrench to retract the conduit retaining prongs. A 13-mm box wrench is the common size used for this task.

Caliper

Lever

Parking brake rear cable and conduit

Retaining clip

Figure 9-18  Disconnect the end of the cable from the parking brake lever on rear disc brakes.

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Braking systems have self-adjusting brakes, but it is still a good idea to inspect the system whenever doing brake system service.

On drum brakes, insert the cable and conduit into the hole in the backing plate. Ensure that the retaining prongs lock the conduit in place where it passes through the backing plate. Hold the brake shoes in place on the backing plate and engage the brake cable into the parking brake lever. Install the brake drum and the wheel. Install the brake cable adjusting nut. Adjust the parking brakes as explained previously. On disc brakes, insert the parking brake rear cable and conduit end into the rear disc brake caliper and install the retaining clip or pin that secures the cable to the lever. Adjust the parking brakes as explained previously. WARNING  Cars and light trucks have supplemental inflatable restraint systems, known as air bags. To avoid accidental deployment of the air bag and possible injury or vehicle damage, always disconnect the battery ground (negative) cable. And wait 10 minutes before working near any of the impact sensors, steering column, or instrument panel. Do not use any electrical test equipment on any of the air bag system wires or tamper with them in any way unless specifically directed by your instructor.

PARKING BRAKE LAMP SWITCH TEST Classroom Manual page 214

With the ignition on and the parking brakes applied, the switch should close to light the BRAKE warning lamp on the instrument panel and remind the driver that the parking brakes are applied.

SERVICE TIP  The typical ohmmeter display should read zero or near zero ohms when the switch is closed. An open switch will cause a reading of “OL” or the number “1,” both of which mean an open circuit.

To test a typical parking brake switch, first gain access to the switch, which is often the hardest part of the job. For lever-operated parking brakes, it may be necessary to remove all or part of the center console. For pedal-operated parking brakes, locate the switch on the pedal bracket under the instrument panel.

Up

Down

Body ground Positive terminal

Figure 9-19  Testing the parking brake switch on a lever-operated installation.

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After locating the switch, disconnect the electrical harness connector and apply the brake pedal or lever. Then use an ohmmeter or continuity tester to check the switch. The switch should be closed and continuity should exist with the pedal or lever applied. The switch should be open, with no continuity, with the pedal or lever released. With the brake lever pulled up, use a continuity checker to ensure continuity exists between the positive terminal and a good ground (Figure 9-19). Continuity should be broken when the brake lever is in the down position.

ELECTRIC PARKING BRAKE SERVICE Electric parking brakes may have electrical, mechanical, or hydraulic problems. The mechanical and hydraulic portions involve the rear service brakes, and problems may also be apparent in the operation of the service brakes. This section assumes that the mechanical and hydraulic components are good and only the electrical side is discussed.

Control Systems The electric parking brake is controlled by the driver and the electronic brake control module (Figure 9-20). The control switch (usually located on the console) is used to activate the parking brake system. Many systems use a switch that mimics the parking brake lever. The switch is pulled up to apply the parking brake and pushed down to release the parking brake. Additionally, if the driver puts the vehicle into gear and applies the accelerator pedal, then the brake is turned off. Electronic parking brake systems can also be used to hold the vehicle on a hill. Some systems can use the vehicle’s stability control to hold the vehicle with the hydraulic brakes whereas some systems use the electrical actuator to apply the parking brakes. BMW, Honda, and VW use an autohold feature that can be used to hold the vehicle in place after coming to a complete stop. The system is released when the accelerator is applied. This is useful for stop-and-go traffic with an automatic transmission as well as a hill-hold feature for manual transmission–equipped vehicles. In the past, if the parking brake was used to try and stop the vehicle in an emergency, the rear wheels would generally lock up and driver control was compromised. The electrically actuated brakes can provide a more balanced braking response without locking the rear brakes because the ABS sensor information is available to the parking brake module. Using the parking brake to stop the vehicle (in an emergency situation) can be done by pulling up on the brake switch and holding it until the vehicle comes to a stop. Still, this

Figure 9-20  Electrically operated parking brake (from rear disc).

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would not be recommended unless it is a true emergency. On the Cadillac CTS, the electronic brake control module keeps track of the number of dynamic applies and sets a code to replace the pads when a number of applies has been reached. Remember that the hydraulic system still has two separate hydraulic systems in case one should fail, so the event that the parking brake would be used to stop the vehicle would be extremely rare.

System Modules The electric parking brake system has a module that is part of the vehicle network (Figure 9-21). The Cadillac system will activate the red “BRAKE” warning lamp if a problem affecting vehicle safety is detected. The parking brake symbol on the dash will illuminate if a problem exists with the parking brake, but the vehicle can be driven to obtain service.

Electrical Actuator Used with Cables These units have an electronic control module and motor that (Figure 9-22) applies tension to the brake cables similar to the standard manual parking brake control. This unit could have mechanical or electrical problems. The cable(s) are adjusted similarly to Driver switch

Stability control module

Park brake control module

B+ Electrical actuator

Figure 9-21  A simplified drawing of the relationship between the Park Brake Control Module and the vehicle’s computer network. Serial data is shared throughout the network.

Figure 9-22  An electronic parking brake control module that includes the cable tension motor.

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standard cables. If the parking brakes partially apply, check the service brakes, the parking brake cable(s), and parking brakes adjustment first. If they do not apply at all, check the fuse for the motor. If the fuse is good, locate and gain access to the motor’s connection harness. Test the harness and then the motor according to service procedures. If sufficient voltage is present and the motor meets the manufacturer’s specifications, then the motor will probably have to be replaced. This is a self-contained unit, and internal repairs should not be attempted.

Electrical Direct Apply This, too, is an electric motor. In fact, there are two, one at each rear wheel integral with the caliper (Figure 9-23). Whereas the cable system could be used with drum brakes and some rear disc brakes, this system is used with rear disc brakes using the caliper to apply the parking brake force. Generally, the motors work like the screw-and-nut or the balland-ramp rear disc parking brakes. This system could function electrically and still not apply the parking brakes directly, however. Vehicles with the electric parking brake have a switch in the center console or on the dashboard, which takes the place of the manual parking brake system, the foot pedal and release handle. In case of insufficient electrical power, the electric parking brake cannot be applied or released.

GM’s Electrically Operated Integrated Caliper (Direct Apply) The parking brake operation is controlled by the Electronic Brake Control Module. When the park brake switch is pulled up, the Electronic Brake Control Module applies 12 volts and ground to the apply circuits, which causes the left and right park brake actuators to activate. This causes the park brakes to engage. When the park brake switch is pressed down, the Electronic Brake Control Module supplies 12 volts to the release control circuits.

Electric Parking Brake Apply/Release The driver can activate the parking brake on some GM vehicle stopped or moving by lifting up on the parking brake switch. If the parking brake is applied with the vehicle in motion, a warning chime will sound and the warning message, "Release Park Brake Switch," will appear on the dash. If applied while the vehicle is stationary, the red park

Figure 9-23  A caliper with integral electric motor to apply the parking brake instead of cables.

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The GM Park brake may apply by itself at times to perform a self-check on the parking brake system, which is normal.

brake light will flash while the actuators are applying the brakes. The red park brake light will then stay on. If a message of “Service Park Brake” is displayed on the dash, there is a problem with the electric parking brake, and it is partially applied or released. The red “Park Brake” lamp will also flash. To release the electric parking brake, turn the ignition to “ON” or “RUN” position, and, while holding the service brake pedal, push down on the parking brake switch on the console. The red “Park” brake lamp should turn off. Check and repair the electrical side of the system in the same manner as the two previous systems. If the electrical system checks out, make sure the motor is mounted to the caliper correctly before condemning it. If the motor is loose on the caliper or its driver is not positioned on the caliper correctly, the motor will function correctly but still not be able to properly apply the caliper enough to hold the vehicle in place. A good point to remember about all three systems is that if installed correctly the first time, none of the electrical components noted will move out of position; they will function almost perfectly during the life of the vehicle. Service is usually needed only if some portion of the electrical system or a component fails, and that is seldom.

Rear Brake Service If the rear brakes are to be replaced on a system with integral parking brakes, the calipers have to be “opened” with a scan tool. A general procedure for a VW vehicle would follow this basic procedure:

1. Scan tool with appropriate software installed onto vehicle. 2. Select “chassis systems.” 3. Select “parking brake.” Go to “basic settings.” 4. Select “open parking brake.”

After opening the rear calipers, the rear brakes can be serviced. After servicing the rear brakes, the caliper is reinstalled. The technician can go back to basic settings, and then select “close parking brake” to have the system reset the brakes to the proper position.

Diagnosis of Electrical Parking Brake Systems Parking brake systems are integrated into the vehicle’s communication network, just as the other major systems on the vehicle. The parking brake assembly has its own unique trouble codes that are utilized to assist in diagnosis. Figure 9-24 shows a partial list of trouble codes for the electric parking brake system on a 2012 Cadillac CTS. Code

Problem

DTC C028A

C028A 01 park brake C028A 02 park brake C028A 04 park brake C028A 08 park brake C028A 28 park brake

DTC C028B

C028B 08 park brake motor position sensor signal performance-signal invalid C028B 26 park brake motor position sensor signal low frequeny C028B 29 park brake moror position sensor signal too few pulses C028B 2A park brake motor position sensor signal too many pulses

DTC C028D

DTC C028D Replace park brake pad malfunction

DTC C056F

DTC C056F Electronic control unit software not programmed

motor motor motor motor motor

circuit circuit circuit circuit circuit

short to battery short to ground open performance-signal invalid performance-signal invalid

Figure 9-24  A partial list of codes for the Cadillac electric parking brake system.

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CUSTOMER CARE  Parking brakes are not designed for use in place of the service brakes and should be applied only after the vehicle is brought to a complete stop, except in an emergency. If you suspect a customer is using the parking brakes for other than their intended job, remind him or her of the dangers of this practice and stress the importance of keeping the service brakes in good working order.

CASE STUDY A vehicle had the pads for its rear disc brakes replaced as part of a routine brake job. Soon afterward, the owner complained that the rear brakes seemed to be dragging. The tech who worked on the car originally got the comeback. He inspected and lubed the rear caliper slides to ensure that the calipers would move freely. Of most importance, he carefully adjusted the parking brake cables and double-checked to be sure that the pistons and pads retracted completely. That was the cure for the problem. When you service rear brakes—discs or drums—always check and adjust the parking brakes to be sure that the rear brakes do not drag.

ASE-STYLE REVIEW QUESTIONS 1. Technician A says that auxiliary drum parking brakes on a car with rear disc brakes are adjusted with a star wheel adjuster. Technician B says that mechanically actuated rear disc parking brakes (as part of the caliper) have self-adjusters. Who is correct?. A. A only C. Both A and B B. B only D. Neither A nor B 2. Technician A says the parking brake cable ­conduit retainer can be released using a box end wrench once the cable has been released from the parking brake lever. Technician B says the parking brake cable can be removed from a drum brake system with the drum in place. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 3. While lubricating the parking brake system, Technician A applies graphite to the contact areas of plastic-coated cables. Technician B applies a quality grease to metal cables. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

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4. During parking brake adjustment, Technician A checks and adjusts the drum-to-lining clearance before adjusting the parking brakes. Technician B says if the service brake pedal is firm and has normal travel, the parking brakes should be fully applied when the lever or pedal moves one-third to two-thirds of its travel. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. Technician A says the electric parking brake is controlled by the driver and the electronic brake control module. Technician B says many systems use a switch that is pulled up to apply the parking brake and pushed down to release the parking brake, or it will release when the vehicle is put into gear. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 6. Technician A says that the shoes and linings of auxiliary (drum-in-hat) drum parking brakes usually outlive the vehicle on which they are installed. Technician B says that the small drum for the auxiliary parking brakes can be machined just like a regular brake drum. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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7. When adjusting the parking brake linkage, Technician A cleans and lubricates the threads of the adjusting mechanism bolt to avoid damaging it. Technician B makes certain the rear wheels do not drag when the parking brake is fully released. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 8. While discussing electrical direct apply parking brakes, Technician A says the parking brake system must be reset with a scan tool after the brake pads have been replaced. Technician B says the scan tool must be used to retract the caliper piston. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

9. Adjustment to rear disc brake parking brakes is being discussed. Technician A says that on some systems, a rear disc parking brake hand lever is pulled up one notch and the adjusting nut is tightened until the rear wheels drag slightly when turned. Technician B says after servicing a rear brake caliper, operate the service brakes to position the brake pads before adjusting the parking brake. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 10. Technician A says an ohmmeter or continuity tester should be used to check the brake warning lamp switch. The switch should be open, with no continuity, with the pedal or lever released. Technician B says the parking brake warning lamp switch should be closed and continuity should exist with the pedal or lever applied. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

ASE CHALLENGE QUESTIONS 1. While discussing electrically actuated parking brakes, Technician A says that even though it is not recommended, the electrically operated parking brake can be used to stop the vehicle in a true emergency. Technician B says the reason for this is electrically actuated brakes can provide a more balanced braking response without locking the rear brakes because the ABS sensor information is available to the parking brake module. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 2. The parking brake control mechanism is being discussed. Technician A says that corrosion on the exposed portion of the cable should not cause the brakes to hang. Technician B says that a cable guide that is too close to the exhaust system could cause the parking brakes not to release due to heat damage. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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3. Technician A says that the auxiliary (drumin-hat) drum parking brakes used with many disc brakes require two separate adjustments. Technician B says the parking brake shoes must be adjusted separately before any adjustments are made to the cables and linkage. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 4. Drum parking brakes are being discussed. Technician A says to start replacing the control cable, release the parking brakes and raise the vehicle on a hoist. Technician B says the upper end of the cable is more accessible, and disconnecting it first provides slack to help disconnect the upper end and any mounting clips or grommets. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. Technician A says the driver can activate the parking brake on some GM vehicles while stopped or moving by lifting up on the parking brake switch. Technician B says that if the parking brake is applied with the vehicle in motion, a warning chime will sound, and the warning message, "Release Park Brake Switch," will appear on the dash. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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Name ______________________________________ 

Date _________________

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39

ADJUSTING PARKING BRAKE CABLES Upon completion and review of this job sheet, you should be able to adjust the parking brake cable. ASE Education Foundation Correlation This job sheet addresses the following MLR task: F.2.  Check parking brake system components for wear, binding, and corrosion; clean, lubricate, adjust and/or replace as needed. (P-2) This job sheet addresses the following AST/MAST task: F.3.  Check parking brake system components for wear, binding, and corrosion; clean, lubricate, adjust and/or replace as needed. (P-1) Tools and Materials • Lift or jack and stands • Service information • Impact tools • Brake adjusting tool Describe the vehicle being worked on: Year _____________________ Make _____________________ Model _____________________ VIN _____________________________ Engine type and size _____________________________ ABS ______________________ yes _____________________ no _____________________. If yes, type  Procedure

Task Completed

1. Wheel nut torque:  Method of measuring and adjusting parking brake:     2. Operate the parking brakes and test holding ability. Measure, if necessary, following instructions in the service manual.

h

3. Make certain that the parking brakes are released.

h

4. Lift the vehicle and remove the wheel assembly.

h

5. Check service brake adjustment. Correct as necessary. NOTE TO INSTRUCTORS: This job sheet is set up based on a duo-servo brake system using a foot-operated lever and cables with the parking adjustment at the equalizer under the vehicle.

h

6. Loosen the locknut.

h

7. Turn the adjusting nut or bolt to remove excessive slack from the brake cable or to set cable to manufacturer’s specifications.

h

8. Operate the parking brakes and check against the manufacturer’s test data.

h

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9. If the parking brake meets manufacturer’s specifications, install any components removed and ensure that the wheels rotate smoothly with the parking brake off.

Task Completed h

10. Lower the vehicle to the floor.

h

11. Test the parking brake.

h

12. When the repair is complete, clean the area, store the tools, and complete the repair order.

h

Problems Encountered    Instructor’s Response   

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Name ______________________________________ 

Date _________________

TESTING PARKING BRAKE WARNING LIGHT CIRCUIT Upon completion and review of this job sheet, you should be able to inspect and test the parking brake warning light circuit.

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ASE Education Foundation Correlation This job sheet addresses the following MLR task: F.3.  Check parking brake operation and parking brake indicator light system operation; determine necessary action. (P-1) This job sheet addresses the following AST/MAST task: F.3.  Check parking brake operation and parking brake indicator light system operation; determine necessary action. (P-1) Tools and Materials • Service information • Wiring diagram • Component locator • Digital multimeter • Jumper wire Describe the vehicle being worked on: Year _____________________ Make _____________________ Model _____________________ VIN _____________________________ Engine type and size _____________________________ ABS ______________________ yes _____________________ no _____________________. ­ If yes, type  Procedure 1. From service information, obtain a copy of the brake warning lamp circuit to help answer the following questions. A. Location of the parking brake warning light switch:   B.  Special procedures from service information. Is the parking brake lamp operated from a conventional switch, or is it turned on by the instrument panel cluster on a signal from another module on the vehicle network?   NOTE: KOEO is key on, engine off. 1. Perform an operational check on the warning light. A. KOEO, parking brakes on. Is the light lit? If the answer is yes, test is complete and system is functional. If the answer is no, go to step 2. Results  B.  KOEO, parking brakes off. Is the light off? If the answer is yes, test is complete and system is functional. If the answer is no, go to step 3. Results 

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2. KOEO, light is off, parking brakes are on.

Task Completed

A .  Turn key off.

h

B.  Locate parking brake warning light switch and disconnect the harness.

h

C .  Connect a jumper wire from the wire to good ground.

h

D.  KOEO. Is the light on? If the answer is no, go to step E. If the answer is yes, check adjustment of switch and/or replace switch. Results  E. Key off. Connect the multimeter between the wire and ground, black lead to ground.

h

F.  KOEO. Is battery voltage showing? If the answer is yes, replace warning lamp. If the answer is no, replace the warning lamp. If the light is now lit, the circuit is good. If the lamp still is not lit, then the circuit between the ignition switch, warning lamp, and the ground circuit must be checked. Consult the instructor and service manual for diagnostic routine. Results  3. KOEO, parking brakes are off, warning light is on. A. Check master cylinder reservoir for low-level warning light. If equipped, top off brake fluid. Did the light go out? If the answer is yes, test is complete and system is functional; reconnect harness and perform operational test again. If the answer is no, go to step B. Results  B.  Locate parking brake warning light switch. Disconnect.

h

C. KOEO, parking brakes off, did the light go out? If the answer is no, the circuit between the ignition switch, warning lamp, and the ground circuit must be checked. Consult the instructor and service manual for diagnostic routine. If the answer is yes, go to step D. Results  D.  Adjust or replace switch. Perform operational test again.

h

Problems Encountered    Instructor’s Response   

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Electrical Braking Systems Service

Upon completion and review of this chapter, you should be able to: ■■

Inspect and test the brake system to determine if a complaint is related to the base brakes system or the antilock system.

■■

Relieve high pressure from an ABS hydraulic accumulator.

■■

■■

Bleed an ABS.

■■

■■

Explain the purposes and major ­features of diagnostic trouble codes.

■■

Explain the differences between current and history trouble codes.

■■

■■ ■■

Use a computer pin voltage, or pin out, chart to perform voltage and resistance tests on computer control circuits.

■■

■■

■■

Perform resistance and voltage ­waveform tests on a speed sensor and its circuit. Set up and test a wheel speed sensor with an oscilloscope. Interpret AC and DC signal waveforms. Remove and replace a wheel speed sensor. Remove and replace an ABS computer (control module). Test and replace Delphi DBS-7 system components. Test and replace Bosch ABS 9.0 components.

Basic Tools Basic technician’s tool set Appropriate service information DMM

Terms To Know Automated bled procedure Current code Diagnostic trouble code (DTC)

Electromotive force (EMF) Electrostatic discharge (ESD) History code

Oscilloscope Reference voltage

INTRODUCTION The basic concept of antilock braking (ABSs) dates back to the 1950s, but digital electronic control was not available until the 1980s. ABSs were installed on slightly more than 3 percent of domestic vehicles produced in 1987, on more than 50 percent by 1995, and all new passenger cars built after 2012 have ABS because stability control was mandated in 2012. Stability control has its basis in ABS braking. (More on stability control is ­discussed in the next chapter.) As ABS has grown, the variations in designs have increased. For this reason, the manufacturer’s specifications, service instructions, and electrical ­circuit diagrams for the system being serviced must be available and utilized. ABSs are more likely to suffer from basic brake system problems than from problems in the ABS control circuitry or components, which means the technician should be familiar with the normal braking system and how to diagnose its problems. Worn tires can cause frequent ABS cycling especially on wet roadways. A scan tool to read trouble codes and perform some system tests will be necessary. This chapter contains basic ABS troubleshooting information, as well as general test and repair guidelines that apply to most systems and three specific systems.

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Classroom Manual page 241

Traction control systems are also discussed in this chapter because they basically use the same components as the ABS. Traction control applies the brakes to prevent a wheel from spinning on a low-traction surface. Traction control is almost the opposite of ABS. ABS stops a wheel from locking up, and traction control prevents a wheel from spinning. The addition of traction control came early in the development of electronic braking systems because only the addition of two valves and a pump and software changes made it operational on an existing ABS system.

BRAKE SYSTEM TROUBLESHOOTING An ABS is an electrically controlled hydraulic system. The ABS function will not work if the base brakes do not work properly in their non-antilock mode. Some ABS problems will be electrical, but many will result from a hydraulic system malfunction. When such problems are detected by the ABS control module, it will disable the antilock function and light the antilock indicator lamp on the instrument panel. The cause can be as simple as a low hydraulic fluid level or a leaking hose, line, or connection.

Special Tool Coworker All the instrument panel warning indicators will light at some point during the “bulb check” generally right after the engine starts on late-model vehicles. They may light at key-on in older vehicles. They remain on for a few seconds and then go out, if there is no problem detected by the system, and of course if the parking brake is not applied.

Brake System Check Use the following quick and simple brake system check to help determine if the base brake system is working properly and whether the problem is electrical or hydraulic. Several of these tests were discussed earlier in this manual as checks for the base brake system. To check the base brake system: 1. Shut the engine off and check the master cylinder fluid level. On most late-model cars, this can be done by cleaning the translucent reservoir, and visually noting the fluid level in relation to the embossed line or mark on the reservoir (Figure 10-1). To evaluate fluid condition, remove the reservoir cap or cover. 2. Start the engine and note the brake and ABS indicator lamps. When the ignition is switched on, the BRAKE lamp and ABS indicator lamp should light for a few seconds, and then go out (Figure 10-2). (Older vehicles had a bulb check when the ignition was on or while starting. See service information for a particular vehicle as necessary.) 3. Apply and release the parking brake. The BRAKE lamp should light when the parking brake is applied and go out when it is released. The ABS indicator lamp should light when the engine starts, remain on for a few seconds after the engine starts, and then go out.

Fluid reservoir

Figure 10-1  On many vehicles, you can check the brake fluid level through the translucent master cylinder reservoir.

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Figure 10-2  Typical bulb check. Note ABS and brake lamps.

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4. Check the operation of the stop lamps by pressing the brake pedal while a coworker watches both fender-mounted lamps and the CHMSL to make sure they light when the pedal is applied and go off when the pedal is released. If the vehicle uses an electronic lighting module, the key may have to be on for the brake lamps to operate. 5. With the engine running, pump the brake pedal rapidly several times. The pedal height should remain about the same. If it increases during pumping, or if a very spongy feeling during pedal application is noted, air may be trapped in the hydraulic lines. It is common for the brake pedal on a car with antilock brakes to feel slightly softer than a car without them. On many systems the pedal can be forced to the floor with firm pressure. The important thing to check for is the uniformity or repeatability of the brake pedal operation. Pedal height and feel should remain ­constant as the pedal is applied and released. If they change with repeated pedal applications, air may be trapped in the brake lines. 6. If the car has vacuum-assisted power brakes, start the engine and run it at medium speed for a short time, and then shut it off. Wait about 90 seconds and then apply the brake pedal moderately several times. The brake pedal should feel firmer with each stroke. When the vacuum reserve is exhausted, depress the brake pedal firmly and restart the engine. The pedal should drop slightly and then hold as vacuum is applied to the booster. 7. Check the condition of the vacuum hose between the power booster and intake manifold. Start the engine and listen for a hissing noise from the hose or hose connection. Such a noise indicates a vacuum leak. Replace the hose if it is deteriorated; replace the hose clamps if the hose connections are not tight. 8. Inspect all brake hoses, lines, and fittings for damage, deterioration, leakage, or chassis interference. This inspection requires that the vehicle be raised on a hoist. Fix any defects found. WARNING  Use caution and obey all highway laws during the road test. Inattention to traffic while attempting to read a scan tool could result in an ­accident and serious injury.

9. Finally, test drive the vehicle to evaluate brake system performance. Accelerate to about 20 mph and use normal braking to stop the car. If it stops smoothly within 25 feet without swerving, the brakes are probably in good working order. Under current braking, beginning from 25 mph or 30 mph, the brake pedal may pulsate and the ABS light may come on for a moment if an ABS event occurs.

Troubleshooting with the Brake Pedal The brake pedal is a helpful diagnostic tool that is easily used by a trained technician. The technician can determine the probable cause of a wide variety of brake system problems by identifying apparent symptoms as the pedal is applied. Figure 10-3 lists symptoms and probable causes that can be determined in this way.

CUSTOMER CARE  Advise your customers that pumping the brake pedal on a vehicle with antilock brakes actually defeats the operation of the antilock system. In fact, rapidly pumping the brake pedal may set a DTC and turn the ABS warning lamp on.

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Probable cause

Pedal surging, brake chatter, vehicle surge during braking

Front discs out of round; excessive disc thickness variation; bearings out of adjustment; rear drums out of round; hard spots caused by overheating

Brakes grab

Hard spots on front discs or rear drums; cracked pads or shoe linings

Car pulls to one side

Misaligned front end; drum brake components malfunctioning; frozen caliper pistons or contaminated front brake pads; pinched lines or leaking seals

Excessive pedal effort

Insufficient engine vacuum; defective booster; vacuum leak; frozen piston; contaminated or glazed linings

Rear brakes drag

Misadjusted parking brake; rear brakes out of adjustment; weak shoe return springs; frozen wheel cylinder pistons

All brakes drag

Frozen brake pistons; misadjusted stop lamp switch; restricted pedal return; defective master cylinder; contaminated brake fluid

Low-speed disc brake squeak

Worn pad lining

Scraping noise when brakes are applied

Brake linings completely worn out

Intermittent chirp when drum brakes are applied or released

Insufficient backing plate pad lubricant

Intermittent clunk when drum brakes are applied

Threaded drums

Rear-wheel lockup

Contaminated linings; front calipers frozen; defective combination valve

Pedal low and spongy with excessive pedal travel

Insufficient fluid in system; air in hydraulic system

Pedal low and firm with excessive pedal travel

Brakes out of adjustment

Brakes release slowly and pedal does not fully return

Frozen caliper or wheel cylinder pistons; defective drum brake return springs; binding pedal linkage; backing plate grooved

Brakes drag and pedal does not fully return

Contaminated brake fluid; defective master cylinder; defective vacuum booster or vacuum check valve; binding pedal linkage or lack of lubrication

Figure 10-3  An experienced technician can tell a great deal about the condition of a brake system just by the pedal feel.

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ABS HYDRAULIC SYSTEM SERVICE AUTHOR’S NOTE  Certain precautions must be taken when servicing the base brakes of some older ABS installations. The technician must understand the system components and their operation before trying to bleed the brakes or perform other service(s) that requires opening the hydraulic system. Always consult service information before servicing a system, especially for the first time.

Classroom Manual pages 246

An integrated ABS installation using a pressurized accumulator is similar to the hydroboost power brake system in that both use hydraulic pressure for brake boost. In both designs, the hydraulic fluid is under very high pressure. For example, some ABS accumulators have 2,600 psi of hydraulic pressure in the system whenever the ignition switch is on. Removing a component from this system without first discharging the pressure can result in a messy and potentially dangerous situation. WARNING  Before opening the hydraulic system of an ABS installation, review the manufacturer’s service instructions, with particular attention to safety precautions that relate to hydraulic pressure. Do not loosen any fittings or otherwise open hydraulic lines where pressure may be present. Failure to comply may result in vehicle damage or injury.

Depressurizing the System (Relieving Accumulator Pressure) The technician must refer to the carmaker’s service procedures if it is necessary to check brake fluid level, bleed the brakes, or open a hydraulic line to replace a component. These service procedures determine if it is necessary to depressurize the hydraulic accumulator first. For example, some systems must be depressurized to bleed the brakes, but the other systems require that the accumulator be fully pressurized when bleeding the rear brakes. When the automaker’s procedure requires that the system be depressurized, the ignition switch should be off. Pump the brake pedal at least 25 times with about 50 pounds of pedal force. As the accumulator pressure discharges, a change in pedal feel will be noticed. When an increase in pedal effort is felt, pump the pedal a few more times. This will remove all hydraulic pressure from the system. Some systems may require up to 50 pedal applications to relieve accumulator pressure completely. It is always better to proceed on the side of caution, so apply the pedal a few more times after the pressure seems to have been relieved.

Special Tool Service information

Fluid Level Check and Refill Some older integrated antilock systems require different procedures to check and refill the fluid reservoir. There are various ways to check the fluid level in most ABS systems; the best way to make sure you are following the correct procedure is to follow the service information.

Special Tool Service information

Checking the Fluid Level Brake fluid levels can generally be checked on modern ABS units without de-pressurizing the ABS system, but many older ABS systems did require that the system be depressurized to check the fluid level. Make certain to pay attention to the under-hood labels and service information before adding fluid to an ABS system.

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The automated bleed procedure uses a scan tool to actuate the solenoids in the hydraulic modulator while doing a brake bleeding procedure. If this were not used, air could be trapped in the modulator that would not be released until the vehicle had an ABS event.

Bleeding the System Bleeding an ABS is fundamentally the same as bleeding a non-ABS hydraulic system. Some variety exists in extra steps that may be required for different systems. On one hand, some nonintegral ABS installations can be bled in the same way as a non-ABS hydraulic system, with no extra steps, especially if the BPMV was not replaced or if the fluid level was allowed to become very low. If air enters the BPMV, then a scan tool will probably be necessary to remove all the air from the system. The details of bleeding procedures can change from one model year to the next, so reviewing the carmaker’s instructions is always a good idea.

Automated Brake System Bleeding TRW 440 V ABS Special Tools Service information Tubing with transparent container Scan tool Coworker

Caution Brake fluid is corrosive to body finish and the paint on the vehicle lifts. Brake fluid is also irritating to the skin and the eyes. Always use a capture container when bleeding brakes to reduce human and equipment exposure.

Sometimes an antilock brake system can be difficult to bleed. This is particularly true in the case of brake BPMV replacement, because there can be air trapped in the valve body of the modulator. On the 2011 Lucerne with the TRW 440 V ABS system (Figure 10-4), the brakes should be bled manually or with a pressure bleeder first, and then if the pedal still feels spongy, then the system can be bled with the help of a scan tool performing what is called the automated bled procedure. The automated bled procedure will actuate the valves in the BPMV during the bleeding process to release any air that could be trapped inside the unit. On most ABSs a coworker can speed up the bleeding process, especially if the vehicle is raised. A general procedure to start the automated bleed process goes as follows:

1. Scan tool is installed in the vehicle. 2. Select “diagnostics.” 3. Select “chassis.” 4. Select “EBCM.” 5. Select “Special Functions.” 6. Select “automated bleed.” Follow the instructions from the scan tool exactly. The individual calipers should be bled in the following order: LF, RF, RR, and LR. When the procedure is completed, check the fluid levels and test drive the vehicle.

WARNING  If a system requires that a high-pressure accumulator be charged to bleed the brakes, follow the manufacturer’s instructions and precautions exactly when working with high-pressure hydraulic components.

Figure 10-4  A TRW 440 V ABS hydraulic modulator.

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Some manufacturers state that either pressure bleeding or manual bleeding is acceptable for their various ABS installations. Others specify either one method or the other. Use only the DOT 3, DOT 4, or synthetic brake fluid specified by the vehicle manufacturer. When bleeding an ABS hydraulic system, it is good practice to flush the system completely to ensure that all old fluid and possible contamination are removed. The following paragraphs summarize the special instructions for bleeding some of the most popular systems. These sections do not cover all possible ABS installations, however, and should not be substituted for manufacturers’ specific procedures. They do provide general guidelines and examples of ABS bleeding methods. Before bleeding any antilock system, repair any conditions that would set diagnostic trouble codes and clear all codes from computer memory.

Bleeding Bosch ABS 9.0 The following procedure is recommended for Bosch ABS 9.0 vehicles. 1. Pressure bleed the base brake system according to the bleeding equipment manufacturer’s instructions. 2. If the brake pedal travel and feel is okay, then it is not necessary to do the automated bleed procedure. Circumstances that call for the automated bleed procedure are as follows: ■■ Pedal height is too low or feels spongy. ■■ Air is suspected in the BPMV from a large loss of fluid or replacement of the modulator itself. 3. The automated bleed procedure is utilized to make sure that the modulator is free of air. Air can be trapped behind some of the solenoids in the modulator that might escape conventional bleeding.

Automated Bleed Procedure Bosch ABS 9.0 The bleeding procedure for the ABS 9.0 is very similar to that of the Lucerne, detailed earlier. 1. Before starting the automated brake bleed procedure, make sure the battery condition is good and it is fully charged. If it is not, the automated bleed may abort before it is complete. 2. Remove the wheels and inspect the brake system. Repair any problems noted before continuing. 3. Install the scan tool, and establish communication with the vehicle. 4. Follow the on-screen directions from the scan tool. 5. Reinstall wheels and top off the brake fluid reservoir, if needed. 6. Check for proper pedal height and test drive for proper operation.

Brake Pressure Sensor Calibration Bosch ABS 9.0 and Others The brake pressure sensor is an integral part of the BPMV. The pressure sensor is used by the EBCM to see how much force the driver is calling for during braking. Bosch ABS 9.0 has a brake assist feature, as do many others. The brake pressure sensor reading is used by the EBCM to increase braking pressure to the wheels in the event of a panic stop. If the BPMV or the EBCM is replaced on a vehicle with Bosch ABS 9.0 and many other systems, the brake pressure sensor must be recalibrated using a scan tool. The scan tool will give instructions on the procedure once communication is established.

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SERVICE TIP  Some vehicles require the manufacturer’s scan tool to properly bleed their ABSs. Many aftermarket scanners cannot perform this task correctly.

Caution Do not use DOT 5 ­silicone brake fluid in an ABS. ABS operation will be degraded. A scan be used to command some vehicle actuators to perform certain tasks. There are several different levels of scan tools available. Of course, the most capable scan tool is the manufacturer’s scan tool.

The DBC-7 can be bled using routine pressure, suction, or manual bleeding provided no air has entered the system. Like all brake systems, anytime components other than the pads or shoes are replaced, assume that air has entered the system. To bleed an air-­ contaminated DBC-7 system a pressure bleeder and scan tool must be used following the guidelines described next. Connect the pressure bleeder to the reservoir of the master cylinder and the scan tool to the OBD-II 16-pin connector under the dash. Turn the ignition switch to RUN with the bleeder screws closed. Use the pressure bleeder to pressurize the system to 35 psi. Set the scan tool to “automatic bleed procedure.” The valves and solenoid in the BPMV will cycle on/off for 1 minute. The scan tool will now indicate that each wheel be bled. The pump will operate during the bleeding process. The valves for the wheel to be bled will cycle for 1 minute. This procedure will repeat for each wheel. After the last wheel is bled, the scan tool will cycle the solenoids for 20 seconds to purge the system of any remaining air. Depressurize the pressure bleeder and disconnect it from the master cylinder. The final step is to apply the pedal several times to check for height and feel. If the pedal is still low or spongy, repeat the entire process.

SERVICE TIP  If a brake-pull problem develops after bleeding an ABS, completely flush and bleed the system again. If sludge or dirt of any kind gets trapped in antilock brake solenoids or valves, it can unbalance hydraulic pressure at the wheels—even for non-ABS braking. Flushing the dirt out of the system often solves an antilock brake pulling problem.

SERVICE TIP  Before forcing a caliper piston back into its bore to remove the caliper or change the pad, attach a bleeder hose to the caliper bleeder screw, put the other end in a container of clean brake fluid, and open the bleeder.

Never pinch a brake line to prevent fluid from flowing back to the reservoir; damage to the line may result.

That is only half the preparation, however. Next you have to keep old fluid from flowing back up the brake lines when you push the piston back in its bore. The best method to prevent contaminated brake fluid from returning to the master cylinder is to lightly pressurize the system. To do this use the alignment’s brake depressor to apply the brake pedal about a half inch. This will block the ports in the master cylinder and hold moderate pressure in the lines. Then, push the piston slowly and steadily back in its bore. Any sediment in the caliper bore will be forced out through the bleeder, not back into the brake system where it can damage expensive ABS components.

Bleeding a 2010 Ford Flex ABS The Ford Flex bleeding procedure says that the preferred method of bleeding the brakes is with a pressure bleeder. First top of the master cylinder fluid level. Be sure to recheck the fluid level in the master cylinder before starting to bleed each caliper. Place the vehicle on the lift so that the bleeder screws are accessible. The rear brakes are bled first, starting at the

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left rear. Have a helper apply steady foot pressure on the brake pedal while the bleeder is open for each wheel. When clear fluid flows from the LR caliper, close off the bleeder screw. Apply the parking brake about five times, and then bleed the LR brake again until clear fluid flows out of the caliper. Repeat the same for the RH side, and again apply the parking brake five times after bleeding the first time. If the BPMV was replaced the service bleed procedure will have to be performed with the scan tool, and then manually pressure bleed the system again. Consult the Ford service information for the most correct information.

GENERAL ABS TROUBLESHOOTING The following sections outline the troubleshooting principles for ABS control systems and for individual components. These guidelines apply to all antilock systems. The most benefit gained from any diagnostic guideline is when it is used as part of organized, systematic troubleshooting. The six major steps for accurate troubleshooting are as follows:

1. Understanding and verification of the customer’s complaint 2. Basic vehicle check-out and visual inspection 3. Check for technical service bulletins 4. Control system diagnosis 5. Operating symptom diagnosis 6. Intermittent problem diagnosis

469

Caution Never pinch off a flexible brake hose with any clamping tool. Damage to the hose’s internal lining, which could result, is a dangerous braking condition.

Sometimes the best source of information about a vehicle is ignored: the owner/ driver.

The details of these steps are nothing new or revolutionary. These steps are simply up-to-date applications of proven test principles. The following sections explain how to use these principles effectively.

Verify the Customer’s Complaint Get the customer to describe the problem in as much detail as possible. Ask questions such as the following: ■■ Does the problem exist all the time or some of the time? Does it occur regularly or at random? ■■ Does the problem occur at certain times or temperatures? ■■ What are all the symptoms: noises, vibrations, smells, vehicle performance, or any combination the above? ■■ Has the problem occurred before? If so, what was done to fix it? ■■ When was the vehicle last serviced, and what was done to it? Listen to the customer’s complaint carefully, and get as much information as possible. Avoid asking closed-end questions such as: “Does it happen when the engine is hot?” Ask open-ended questions such as: “What temperature is the car when this happens?” Finally, check the vehicle to verify that the problem exists as described. Try to re-create the conditions that the customer describes. It may not always be possible to duplicate the conditions exactly, but try to come as close as possible. A road test of the vehicle or leaving the vehicle standing overnight to re-create a cold-operating problem may be necessary. If the problem caused a history code, try to get the code to recur during testing.

Basic Inspection and Vehicle Checkout The system computer does not monitor or control all parts of the ABS. The mechanical components, vacuum and hydraulic lines, wiring, and mechanical parts, should be inspected first. The technician also should check for body damage, mechanical damage or tampering, and newly installed accessories. The following steps will make the inspection and checkout easier. Remember that most ABS problems originate with the base brakes.

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Before getting all wrapped up in all the possibilities, check the brake fluid level. Some ABSs will switch on both warning lights if the fluid is low. The simple things sometimes cause the greatest diagnostic problems. SERVICE TIP  Most vehicles with ABS utilize some sort of initialization ­ rocedure—sometimes when the key is first turned on, sometimes at a prescribed p speed threshold. Sometimes a customer may comment on a noise, such as a clicking sound. Make sure you know which sounds are normal and which are not.

Inspect and Check Out the Vehicle.  Look for obvious faults and try to eliminate simple problems first. Look for loose or broken wires, connectors, and hydraulic lines or hoses. Check for leaks. Check for mechanical and electrical tampering and collision damage. After completing the basic inspection and checkout of a system, begin the control system diagnosis. If the ABS or brake light is on, check for codes. Check for Technical Service Bulletins.  Now that you have verified the repair and understand the problem, do a bulletin search before doing a lot of diagnostic work. A bulletin may save you time in your diagnosis.

Test the Control System Special Tools Service information Scan tool

Test from the general to the specific. If an immediate look at the computer system for the cause of a problem is done, other possible causes may be overlooked. The basic inspections and tests described in other sections of this Shop Manual begin with general checks or area tests. Testing the computer control system also should begin with general area tests before moving on to pinpoint tests. SERVICE TIP  Dirty or damaged wheel speed sensors and damaged sensor wiring harnesses are a leading trigger to turn on ABS warning lamps. Do not rush to condemn the ABS computer or BPMV before checking the speed sensors and their signals carefully.

DIAGNOSTIC STRATEGY If the warning lamp lights steadily with the engine running, it indicates that a system problem exists. The following section on trouble codes explains the differences between current and history codes and permanent and intermittent faults. See if the scan tool can communicate with the various modules on the vehicles network. If the scan tool cannot communicate with the individual modules on the vehicle network, then a networking problem may exist. There are a vast number of different network configurations. The network configuration for a 2016 Chevrolet Cruze is shown in Figure 10-5. Check the service information for the particular vehicle you are working with for specific information. Self-test programs and diagnostic modes operate differently on different vehicles, but all provide the same basic kind of information. The same DLC used for engine diagnostics is also used for ABS diagnostics. The following paragraphs outline the common features and principles of trouble code diagnosis. SERVICE TIP  A poor ground connection for the ABS controller will generally lead to the storage of multiple, nonrelated codes.

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BCM

14

6 DLC

Human– machine interface module

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ECM

Control solenoid valve assembly

Telematics interface control module

Frontview camera module EBCM Power steering control module

Figure 10-5  An ABS/stability network configuration for a 2016 Chevrolet Cruze.

Troubleshooting Trouble Codes.  Automotive computers can test their own operation and the operation of input and output circuits. Most computers have one or more of the following self-test capabilities: They can recognize the absence of an input or output signal or a signal that is continuously high or low when it should not be. They can recognize a signal that is unusual or out of limits for a period of time or a signal from one sensor that is abnormal when compared to the signal from another sensor. They can send a test voltage signal to a sensor or actuator to check a circuit, or they can operate an actuator and check the response of a sensor. If the computer recognizes a condition that is not correct, it records a diagnostic trouble code (DTC). A DTC can indicate a problem in a particular circuit or subsystem, but it does not always pinpoint the exact cause of the problem. Checking DTCs is an overall or area test of the system. Most manufacturers put trouble codes for the ABS system as “C” codes for Chassis. The codes are not standardized among manufacturers like the “generic” engine performance codes. The term diagnostic trouble code has been widely applied to codes for all automotive control systems. Two general terms used for all codes are current codes and history codes. A partial list of codes and a short description of their meanings is shown in Figure 10-6. SERVICE TIP  None of the vehicle’s computer can register or set a code for a faulty mechanical condition. The computer’s self-test consists of sending an electronic signal through its system and then reading the signal return. Although a mechanical fault cannot be detected directly, the fault may affect some electronic component thus causing the ABS warning lamp to light. Low brake fluid level may cause the ABS control module to set a code for the BPMV.

Current Codes.  A current code indicates a failure that is present at the time of testing and permanent until it is fixed. If the ignition is turned off and the codes cleared, a current

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A current code is ­indicating the fault is present at the time of testing.

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CODE

Component

Description

DTC C012A

Brake Master Cylinder Pressure Sensor

Improper signal from the brake pressure sensor inside the hydraulic modulator

DTC C0035-C0051

Wheel Speed Sensors and Circuits

Wheel speed sensors and circuit performance

DTC C0110

Hydraulic pump motor malfunction

Low voltage or open at the pump motor circuit

C0115

Hydraulic pump motor stuck

Pump motor is commanded on, but no motor voltage is returned

C0116

Pump motor relay failure

Internal failure of the pump motor relay, which is an integral part of the hydraulic modulator

DTC C0121

Valve relay circuit malfunction

The valve relay is engaged during normal system operation and provides voltage to the solenoid valves.The EBCM determines the health of the relay based on output voltage from the relay

C0161

Brake switch circuit

The EBCM compares the signal of the brake pedal pressure sensor with the brake pedal position as reported by the BCM. When these two do not agree, this code is set.

DTC C0245 Wheel Speed Sensor Frequency Malfunction

Wheel Speed Sensor Frequency Malfunction

This code sets with a short to voltage on any of the wheel speed sensors, or electrical interference on any of the circuits for the wheel speed sensors.

Figure 10-6  Partial list of ABS codes for Bosch ABS 9.0 from a 2016 Chevrolet Cruze.

Special Tools Service information Scan tool Digital multimeter

A history code is a code that set in the past, but now the ­problem that caused the code to set is not ­present. This adversely affects diagnosis. Sometimes called a soft code.

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code will reappear immediately or within a few minutes because the problem still exists until corrected. Hard codes indicate full-time problems that are not too difficult to diagnose. Ford refers to current codes as on-demand codes because they are detected by the computer immediately on demand when it runs a self-test. A current code enables the technician to go right to a certain area or areas and begin pinpoint testing. Carmakers’ diagnostic charts or pinpoint test procedures are designed to troubleshoot current codes. The procedures assume that the problem is present at the time of testing. History Codes.  A history code indicates an intermittent problem: one that comes and goes. Soft codes are the computer’s way of remembering a problem that occurred sometime in the past before testing but that is not present now. The problem may not reappear if the codes are cleared, and a retest of the system is done. It may have happened at a certain speed or temperature or under some other conditions that cannot be re-created in the shop. Ford refers to history codes as continuous memory codes because they are stored continuously in the computer’s memory until cleared. Some GM divisions call history codes on late-model vehicles history codes and identify them as such on the computer’s data stream. Because history codes indicate intermittent problems, diagnostic charts and pinpoint tests usually do not isolate the problem immediately. The special intermittent test procedures later in this section will help troubleshoot history codes accurately. To find the problems that cause history codes, electrical connectors should not be opened or disconnected until they have been checked in normal operation or by doing a wiggle test. Disconnecting and reconnecting a connector may temporarily solve a problem without revealing the root cause.

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SERVICE TIP  The input of the customer requesting service was discussed earlier. This is particularly true when the customer complains of a service light that switches on and off without any noticeable change in braking performance. In order to properly diagnose this problem, it is necessary to learn exactly when, how, and what caused the lamp to light.

Without background information, the technician may not be able to duplicate the condition causing the problem. The vehicle is returned to the customer with a “could not duplicate” statement. This statement is unsatisfactory to the customer, the technician, and the business. Always question the customer in detail when dealing with a history code complaint. Determine Whether Codes Are Current or History.  After checking trouble codes, write down any codes that may be present. Remember that if the codes are cleared, history codes will not reappear right away. For such systems, each code must be repaired and cleared in sequence and then the system must be retested until no more codes appear. If a code is a current code, the technician can go to the manufacturer’s test or troubleshooting chart for that code number. If it is determined that a code is a history code, use the intermittent diagnostic procedures outlined later in the chapter to help pinpoint the problem. All carmakers advise that trouble codes should be diagnosed and serviced in a basic order: current codes first followed by history codes. If a code cannot be duplicated, do not start replacing parts unless the manufacturers service information suggests otherwise.

Symptom Byte (Code Sub-Types) Some codes have a subtype or symptom byte addition that helps the technician actually help pinpoint the cause of the problem. A few of the GM system symptom bytes are found in Figure 10-7. Ford also uses a similar method of a five-digit code followed by a two-digit failure byte. Ford uses the failure byte designations on their continuous memory codes to help diagnose intermittent problems on history codes. To see an example of this on a GM vehicle, refer back to Figure 10-6 and code C0110, hydraulic pump motor malfunction. The code can actually be listed as C0110 with a sub-byte following, such as C0110 03, for low voltage detected on the motor circuit, or C0110 07, for a high voltage on the ground circuit. This is just a small sample of what is available from the scan tool for the ABS 9.0 system.

A symptom byte is an addition to a trouble code helps the technician pinpoint problems more accurately in GM vehicles. Ford has a similar system called a failure byte..

Operating Range Tests The signal from an analog sensor can drift out of range as the sensor ages or wears. Some sensors can develop an erratic signal, or dropout, at one point in the signal range. A loose or corroded ground connection for a sensor also can force the signal out of limits. If you have symptom byte indicators from a late-model vehicle, you may be able to identify these types of problems with the scan tool. Use a DVOM, an oscilloscope, or other appropriate instrument to test the sensor signal at the sensor connector and, if necessary, at the main connector to the computer to help pinpoint the problem further. Back probing many sensor connectors or installing jumper wires will provide connection points for the meter. A breakout box or harness may be needed to check sensor signals at the main computer connector. If possible, operate the sensor through its full range and check the signal at several points.

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An oscilloscope can also be helpful in some instances when inspecting the quality of an electrical signal, for example a quick glitch that may not appear on a DVOM.

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Chapter 10 The following Symptom Bytes are for general electrical failures

Symptom Byte

Symptom Byte Description

Symptom Byte Definition

00

—

Faults that do not fit a category.

01

Short to Battery

Battery voltage is measured on an input that should not be that high.

02

Short to Ground

Ground is shown on an input for too long.

03

Low Voltage

Control module sees voltage as too low.

04

Open

This sub type is used for failures where the Electronic Control Unit determines an open circuit via lack of bias voltage, low current flow, no change in state of an input in response to an output, etc.

05

High Voltage/Open

This sub type is used for failures where the condition detected by the Electronic Control Unit is the same for either indicated failure mode.

06

Low Voltage/Open

This sub type is used for failures where the condition detected by the Electronic Control Unit is the same for either indicated failure mode.

07

High Voltage

This sub type is used for failures where the Electronic Control Unit measures a voltage above a specified range but not necessarily a short to battery.

08

Performance–Signal Invalid

This sub type is used for failures where the value of the signal is not plausible given the operating conditions.

09

Too Fast Transitions

Signal changes faster than reasonably allowed.

0A

Too Slow Transitions

Signal changes slower than allowed.

0B

High Current

Control Module measures current that is too high.

0C

Low Current

Control Module measures current that is too low.

0D

High Resistance

Control Module reads too much resistance in monitored circuit.

0E

Low Resistance

Circuit resistance is too low.

0F

Signal Erratic

Signal is momentarily erratic.

Pulse width and frequency modulated signal problems detected by symptom byte (sub-type) 21

Incorrect Period

Length of time for one cycle is incorrect.

22

Too Short Low-Time

Low part of the signal is too short.

23

Too Long Low-Time

Low part of pulse is too long.

24

Too Short High-Time

High part of pulse is too short.

25

Too Long High-Time

High part of pulse is too long.

26

Low Frequency

Control module detects frequency of signal is too low.

Figure 10-7  Symptom Byte List for GM vehicles using Bosch ABS 9.0. 

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Use Computer Pin Voltage Charts.  A computer pin voltage or pin out chart identifies all the connector terminals at the main computer connector by number, circuit name, and function. The voltage or resistance levels that should be present under various conditions also are sometimes listed. Some circuits have different voltage specifications with the key on and the engine off, during cranking, and when the engine is running. Use the pin voltage charts to check input and output signals at the computer. Figure 10-8 is an example 25

26

37

38

14

24

1

2

12

Pin

13

Function

1

B+

4

RF Wheel Speed Sensor

7

Brake Fluid Level Sensor

8

LF Wheel Speed Sensor

13

Ground

14

High Speed GMLAN Serial Data (-) 1

15

High Speed GMLAN Serial Data (-) 1

16

RF Wheel Speed Sensor

17

Wheel Speed Sensor Control Signal

18

Wheel Speed Sensor Signal Left Rear

19

Wheel Speed Sensor Control Left Front

20

High Speed GMLAN Serial Data (-) 2

25

Battery Positive Voltage

26

High Speed GMLAN Serial Data (+) 1

27

High Speed GMLAN Serial Data (+) 1

28

Serial Data Communication Enable

29

RR Wheel Speed Sensor signal

31

LR Wheel Speed Control 2

33

High Speed GMLAN Serial Data (+) 2

38

Ground

Figure 10-8   BOSCH 9.0 ABS pinout of EBCM connector.

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Chapter 10

Backprobe at connector DIGITAL MULTIMETER RECORD

MAX MIN

0.100 V 0 1 2 3 4 5 6 7 8

%

9 0

HZ

MIN MAX

HZ

mV mA A

V

A

V

A

Redundant grounds

mA A

COM

V

Battery

Figure 10-9  With any circuit closed and current flowing, voltage drop across any ground connection and the battery negative (–) terminal must be no more than 0.1 volt (100 millivolts).

of part of a pin out chart for the main connector at an ABS control module. Checking signals at the computer is closely related to sensor operating range tests.

Special Tools Service information Wiring diagram Electronic component locator

Check Ground Continuity.  With the key on, circuit energized, and current flowing, use a digital voltmeter to check the voltage drop across the main computer ground connection and across the ground connection of any sensor that you think may be causing a problem (Figure 10-9). Low-resistance ground connections are critical for electronic control circuits. With the ignition on, voltage drop across the ground connection for any on-off electronic circuit should be 0.1 volt or less. The voltage drop across a high-resistance ground connection in series with a sensor circuit reduces the signal voltage of the sensor. This ground resistance can offset the signal voltage enough to cause serious problems. For example, a 0.5-volt drop across the ground connection on a sensor that operates on a 5-volt reference equals a 10 percent measurement error.

Troubleshooting Intermittent Problems Intermittent problems can be the hardest to diagnose and fix. If the technician is lucky, the intermittent problem will set a history code in the computer memory. This gives a clue, at least, about the general area in which to start testing. Remember, however, that if the codes are cleared, the problem may not recur right away. The conditions that caused the problem may have to be simulated or the vehicle road tested to catch the intermittent fault. The following paragraphs outline some basic points that can help the technician troubleshoot intermittent problems. Use Wiggle Tests and Actuator or Sensor Special Tests.  Most control systems have long-term memory that will record history codes for intermittent problems. Ford recommends wiggle tests in which the car computer and a scan tool are put in communication so that the scan tool will indicate when a history code is set. Then tap or wiggle wiring and connectors to try to get the problem to occur. If the problem does occur, remember

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what was done when the code set. Use the scan tool to read the codes from the car again to verify the fault. Many vehicles have special tests that let the technician command the computer to switch actuators on and off for testing. Most scan tools, for example, can command the solenoids of the BPMV on and off while the vehicle is on the rack. With an assistant operating the scan tool, the technician can see if the brakes respond to commands form the scan tool. For instance, if the brakes are applied and the LF wheel is commanded into pressure release, then the wheel should turn on the rack by hand even with the brakes applied. Check Connectors for Damage.  Many intermittent problems are caused by damaged connectors and terminals. Unplug the connectors in the problem circuit and inspect them carefully for: Bent or broken terminals Corrosion Terminals that have been forced back in the connector shell, causing an intermittent connection Loose, frayed, or broken wires in the connector shell NOTE: Do not use spray electrical contact cleaner on a harness connector unless the wiring harness has been disconnected from the ABS controller. Electrostatic discharge (ESD) may damage the ABS controller. Many harnesses for the ABS brakes are damaged by the continual flexing of the suspension and steering. Road Test and Record Data.  Drive the vehicle and try to duplicate the problem. Use the snapshot or data recording function of a scan tool to record the computer data when the problem occurs. Then analyze the data in the shop to try to locate the cause. Usually ABS codes have very detailed information included on the scan tool, such as how fast the vehicle was traveling, whether or not the brakes were applied, and how many miles have been traveled since the code set.

SWITCH TESTING ABS control systems receive relatively simple input signals compared to powertrain control systems. Input signals for an ABS computer or control module come principally from switches and speed sensors. The following sections outline common troubleshooting guidelines for these common devices. The brake switch, the cruise control switch, and the brake fluid warning switch are examples of ABS input signals that come from simple switches. When used as a control system sensor, a switch provides a digital, on-off, high-low voltage signal. Such a signal indicates either one or the other of two operating conditions such as “brakes released” or “brakes applied.” To provide this kind of input signal, the switch may be installed between the battery and the computer or between the computer and ground. If the switch is installed between the computer and ground, a reference voltage is applied to the switch circuit inside the computer, across a fixed resistor (Figure 10-10). A pull up resistor creates the on-off condition that can be recognized as a digital signal. The fixed resistor is often called a pull up resistor because it pulls the reference voltage up to the opencircuit level when the switch is open and drops the voltage when the switch is closed. The computer takes its input signal internally at a point between the resistor and the switch. The reference voltage for the switch circuit is most often the 5-volt reference used for other computer circuits. For some circuits, it may be full system voltage (approximately

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Caution Do not reroute cables or use wheel sensors from other model vehicles during repairs. The speed signals could be wrong for the repaired vehicle or be distorted by electromotive force (EMF) from other magnetic/ electrical fields.

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Chapter 10 Pull up resistor B+

Signal high

Controller Switch open = high voltage signal

Pull up resistor B+

Signal low

Controller Switch closed = low voltage signal

Figure 10-10  The basic switch circuit used to provide an on–off input signal to a computer.

Electromotive force (EMF) is the proper terminology for voltage. EMF always creates a magnetic field around a conductor. This may interfere with EMF (or the voltage signal) in an adjacent conductor.

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12 volts) or some other voltage level. The important thing to remember is that the voltage signal to the computer is either high or low, depending on the switch position, and indicates one of two operating states. Testing a switch circuit is the basic process of placing the switch in a known operating position (open or closed) and using a voltmeter to check the voltage signal received by the computer. One common way to do this is to back probe the switch circuit wire terminal at the computer harness connector with the positive (1) lead of the voltmeter. ­Figure 10-11 shows this test method with the switch both open and closed. Many circuits can be checked with the scan tool as well, depending on the model year and type of vehicle involved. With the switch open, no current flows in the circuit so no voltage can be dropped across the fixed resistor. The input signal is open-circuit reference voltage, and that is what the test voltmeter should read. With the switch closed, current flows through the circuit, and the fixed resistor drops all of the reference voltage. The input signal is near zero volts, and that is what the test voltmeter should read. If the switch is easily accessible, you also can remove or disconnect it from the circuit and check continuity with an ohmmeter or self-powered test lamp (Figure 10-12).

Wheel Speed Sensor Testing Analog (Magnetic Reluctance) Sensor Resistance Testing.  All pickup coil sensors have resistance specifications. One basic test for any speed sensor is to disconnect it from its circuit and measure its resistance by connecting an ohmmeter across the two terminals of the sensor wiring harness (Figure 10-13). If resistance is out of limits, either high or low, replace the sensor.

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DIGITAL MULTIMETER MAX MIN

RECORD

V

0 1 2 3 4 5 6 7 8

Back probe at connector

%

9 0

479

HZ

MIN MAX

HZ

mV mA A

V

A

V

A

V

COM

mA A

Figure 10-11  Back probe the switch circuit at the computer harness connector and operate the switch to test the input voltage signal.

DIGITAL MULTIMETER RECORD

MAX MIN

OL

0 1 2 3 4 5 6 7 8

%

9 0

HZ

MIN MAX

HZ

mV mA A

V

A

V

A

mA A

COM

V

Figure 10-12  Use an ohmmeter or self-powered test lamp to check continuity with the switch disconnected from the circuit.

A resistance test for a speed sensor is only a starting point, however. Sensor resistance often can be within limits, but the sensor can produce a faulty signal. Damage to the sensor trigger wheel (tone ring), for example, can produce an uneven signal even when the pickup coil is electrically in good condition.

Digital (Magnetoresistive Sensor) Testing

Reference voltage is a fixed voltage supplied to the sensor by a voltage regulator inside the computer or control module.

Many but not all of the modern digital wheel speed sensors use an encoded magnetic ring with alternating north and south magnetic poles to determine wheel speed down to very low speeds, as discussed earlier in this textbook. The encoder ring for

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Chapter 10

Figure 10-13  An ohmmeter can be used to check the resistance of a magnetic reluctance sensor.

Figure 10-14  A magneto-resistive sensor shown with its magnetic encoder.

Different manufacturers may refer to reference voltage as VREF or REFV.

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most magnetoresistive sensors looks very different from the encoder ring for a magnetic reluctance sensor. The encoder ring can be seen on a disconnected spindle in Figure 10-14. Testing a WSS with an Oscilloscope.  The best way to test a wheel speed sensor is with an oscilloscope. An oscilloscope is a test instrument that can display voltage or amperage over a period of time with a graph display. The primary difference between oscilloscopes is the labeling of the controls and which control to activate to achieve a satisfactory graph. Photo Sequence 22 shows a typical sequence for setting up an oscilloscope.

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+2 1.5 1 Voltage

.5 0 .5 1 1.5 –2 0

10

20

30 40

50

60

70

80

90

Time (ms) Good Wheel Speed Sensor

Figure 10-15  A good analog or sine waveform will form a positive voltage value to an equal negative voltage value in smooth, even slopes. A typical PM WSS will produce less than 2 volts.

+2

+2

1.5

1.5

1

1

.5

.5 Voltage

Voltage

A good PM wheel sensor will create a waveform similar to the one shown in Figure 10-15. Note that the highest voltage is between 1.5 volts and 2 volts. This signal is typical of a wheel sensor signal when the wheel is rotated by hand at about 20 to 30 revolutions per minute. Also note that the slope of ascending and descending voltage is mostly smooth and uniform. Figures 10-16 and 10-17 show a too high voltage reading and a too low voltage, respectively, at the same wheel speed. The voltage slopes are ragged and uneven. Even if the voltage signal value were close to correct, this ­“wobbly” graph would point to a problem with the sensor or possibly the wheel and/or axle assembly.

0

.5

1

1

1.5

1.5 0

10

20

30 40

50

60

70

80

90

–2

0

10

20

30 40

50

60

70

80

Time (ms)

Time (ms)

High-voltage Wheel Speed Sensor

Low-voltage Wheel Speed Sensor

Figure 10-16  This PM WSS is generating over 2 volts, which is considered too high a voltage output.

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Oscilloscope or scan tool with PC graphing or graphing multimeter Service information Wiring diagram Electronic component locator

0

.5

–2

Special Tools

90

Figure 10-17  This PM WSS is hardly generating any voltage. The controller will probably not be able to read a voltage this low.

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Chapter 10

Photo Sequence 22

Setting an Oscilloscope for Use

P22-1  Switch on the oscilloscope’s power. Some oscilloscope instructions recommend that the instrument be connected to the vehicle’s power supply.

P22-2  Some oscilloscopes allow you to pick a sensor from a list. This picks the correct time and voltage measurement to start.

P22-3  Once the display screen shows the graphing chart, set the voltage to 0.5 volt. This means each horizontal grid line is valued at one-half volt.

P22-4  Set the time scale to 20 ms. Each vertical line now represents 20 ms of time.

P22-5  Select either AC or DC voltage from the menu. AC should be used for PM speed sensors and DC for a magnetoresistive type.

P22-6  A. Unplug the harness electrical connector. For a magnetic reluctance (analog) sensor connect the oscilloscope in this manner. B. For a magnetoresistive sensor use a wiring diagram and determine which wire is the sensor return and back probe that wire with the positive lead and ground the black lead to a good chassis ground.

A magnetoresistive sensor will produce a positive voltage signal similar to the one shown in Figure 10-18, but the digital signal may be positive or negative polarity. The depicted signal would be commonly referred to as a square wave. Figures 10-19 and 10-20 show a typical signal for a slow wheel and a fast wheel, respectively. The voltage is the same but the frequency of the signals is different. Some oscilloscopes have sample “perfect” waveform patterns for each type of sensor they are capable of testing. They can also store patterns for later use. While a signal is present on the display, press the FREEZE button on the oscilloscope. The pattern will be frozen and can be saved. Follow the oscilloscope’s instructions to save this waveform. Once saved, locate the example or test pattern and compare it to the one just saved. Although there will be some minor differences between the two, they should be reasonably similar. The use of the oscilloscope on specific ABS/TCS brands is discussed later. Checking Speed Sensor Bias Voltage.  A speed sensor with a pickup coil can generate a signal voltage through the electromagnetic action of the rotating trigger wheel and the magnetic field surrounding the coil winding. It does not need a reference voltage provided by the computer, as a magnetoresistive sensor does.

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+2

+2 1.65 V

1.5 1

1

0.9 V

0.9 V

.5 Voltage

Voltage

1.65 V

1.5

.5 0

0

.5

.5

1

1

1.5

1.5

–2

483

0

10

20

30 40

50

60

70

80

–2

90

0

10

20

30 40

50

60

70

Time (ms)

Time (ms)

Digital Waveform

Magnetoresistive Wheel Speed Sensor for Slow Wheel

Figure 10-18  A typical digital (DC) waveform generated by a wheel speed sensor like the magnetoresistive type. This is commonly called a square waveform and may be either positive or negative in polarity.

80

90

Figure 10-19  Compare this typical DC waveform for a slow turning wheel to the one depicted in Figure 10-20.

+2 1.65 V

1.5 1

0.9 V

Voltage

.5 0 .5 1 1.5 –2

0

10

20

30 40

50

60

70

80

90

Time (ms) Magnetoresistive Wheel Speed Sensor for Fast Wheel

Figure 10-20  This DC waveform is typical of a fast turning wheel. Compare it to Figure 10-18.

However, most ABS speed sensors receive a bias voltage from the system computer for two reasons: ■■ The bias voltage lets the system computer detect an open or a short circuit for the sensor before the wheel turns. ■■ The bias voltage elevates the sensor signal off the common ground plane of the vehicle electrical system to reduce signal interference. Figure 10-21 shows a simple speed sensor bias voltage circuit that uses a pull up resistor inside the computer. The bias voltage varies from manufacturer to manufacturer. It may be the 5 volts used for other computer circuits, or it may be a different value such as 1.5 volts or 1.8 volts. Check the carmaker’s test procedures and system specifications to determine the required bias voltage when troubleshooting a speed sensor circuit.

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Chapter 10

Speed sensor (magnetic pickup)

Bias voltage

B+

IC

Signal monitor

Figure 10-21  Simplified speed sensor circuit showing bias voltage and the signal monitor point.

The computer monitors the sensor signal at a point between the fixed pull up resistor and the pickup coil (see Figure 10-21). When power is applied to the circuit, current flows through the pull up resistor and through the pickup coil to ground. The voltage drop at the signal monitor point is a predetermined portion of the reference voltage and a known value that is part of the computer program. If an open circuit exists, no current flows through the circuit, and no voltage is dropped across the pull up resistor. The signal monitor voltage will be high: equal to opencircuit bias voltage (Figure 10-22). In this case, the computer will immediately set a trouble code for an open circuit fault. If a shorted or grounded circuit exists, all—or almost all—of the bias voltage is dropped across the pull up resistor. The signal monitor voltage will be lower than the programmed signal monitor voltage (Figure 10-23). In this case, the computer will immediately set a trouble code for a grounded or shorted circuit. Bias voltage +

Bias voltage + Pull up resistor Pull up resistor

Signal monitor low

Signal monitor high

Open circuit

Pickup coil resistance

Grounded or shorted circuit

Pickup coil resistance

Open circuit

Signal monitor HIGH

Figure 10-22  If the sensor circuit is open, signal monitor voltage will be high.

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Grounded or shorted circuit

Signal monitor LOW

Figure 10-23  If the sensor circuit is grounded or shorted, signal monitor voltage will be low.

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5V

0V

0V

–5 V 20 ms

+ slope

Figure 10-24  Waveform of a defective analog wheel speed sensor.

485

–5 V 20 ms

+ slope

Figure 10-25  Good analog sensor waveform.

The simple voltage divider circuit shown in Figures 10-22 and 10-23 lets the computer detect an electrical fault as soon as the ignition is turned on. The wheel does not need to turn even one revolution. A technician can verify an open- or short-circuit fault by connecting a voltmeter between the high-voltage side of the pickup coil circuit and ground. Depending on the circuit fault, the meter should read close to full bias voltage or close to zero volts with the ignition on. Some speed sensors receive a bias voltage to raise the signal above the common ground plane of the vehicle electrical system, as well as to detect open- and short-circuit problems. Ford Motor Company particularly favors this type of signal biasing. Figures 10-24 and 10-25 are signal waveforms from an analog (PM style WSS) speed sensor. Note that the waveforms in both figures are evenly shaped sine waves. High resistance in the circuit of Figure 10-24 created a trouble code by offsetting the signal voltage too high above the zero-voltage point (shown by the small rectangle at the right side of the waveform) and reducing the signal amplitude. The programs for many Ford control systems require that a biased ac signal voltage still must cross a certain amount below the zero point of the voltage scale. The signal in Figure 10-24 barely drops below zero volts. The signal in Figure 10-25, however, clearly drops below zero volts to the negative side of the scale and has a greater amplitude than the signal in Figure 10-24. The circuit conditions shown in these two illustrations can be seen only when bias voltage is applied to the circuit and the sensor is operating. An oscilloscope or a graphing multimeter is an important tool for troubleshooting these kinds of problems in any ABS speed sensor circuit.

Testing a Magnetoresistive WSS The return signal will be approximately 0.9 volt or 1.65 volts at 7 mA and 14 mA, respectively. A digital multimeter (DMM) and an oscilloscope are needed to properly test the magnetoresistive sensor. Before testing the sensor ensure that the remaining sensor circuit is good and that there are 12 volts from the controller to the sensor as measured with a DMM. If the circuitry is correct, connect the oscilloscope to the sensor by back probing into the sensor/harness connection. Set the oscilloscope to voltage and adjust the scale to the 0.5 volt reading and 20 milliseconds (ms). Refer back to Photo Sequence 22 for general steps to set up the oscilloscope. The initial voltage reading will be approximately 1.6 volts or 0.9 volt depending on the location of a tooth to the sensor head. Rotate the wheel slowly by hand while observing the oscilloscope display. The signal voltage should form a square wave digital pattern (Figure 10-26). The repeating waveform should be consistent with a high voltage of about 1.6 volts and a low voltage of 0.9 volt.

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Special Tools Service information Wiring diagram Electronic component locator Lift or jack with stands

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Chapter 10

+2 1.65 V

1.5 1

0.9 V

Voltage

.5 0 .5 1 1.5 –2

0

10

20

30 40

50

60

70

80

90

Time (ms) Digital Waveform

Figure 10-26  This positive square waveform has a low of about 0.9 volt and a high of about 1.6 volts.

ABS COMPONENT REPLACEMENT

Classroom Manual page 242

Troubleshooting and diagnosis are larger factors in ABS service than is component replacement. Preceding sections of this chapter provide general guidelines for the most common troubleshooting requirements. Vehicle manufacturers also provide specific test procedures for specific components in their service manuals. Look for this information in carmakers’ service manuals or aftermarket information sources. When a component does require replacement, the methods are generally straightforward mechanical procedures. Some special tools may be needed to service some ABS components. You can find this information, along with replacement procedures, in manufacturers’ and aftermarket service manuals. WARNING  ABS service may require opening the hydraulic system. ABS hydraulic systems may operate with pressures of 2,000 psi or higher. The system must be completely depressurized before opening any hydraulic connection. In most cases, the system can be depressurized by applying and releasing the brake pedal at least 25 times. Follow the vehicle manufacturer’s instructions for complete information on hydraulic system service and safety.

SERVICE TIP  When doing any kind of service work on an ABS, let the system be the guide. Many ABS components have decals (usually yellow) with important service directions. For example, many ABS accumulators have decals with instructions on how to depressurize the system before opening the hydraulic lines or checking fluid level. The decals are there for the technician’s benefit. Pay attention to them.

Photo Sequence 23 shows the key steps of a typical ABS pump and motor removal. This sequence outlines basic pump service for a GM Teves system. These or similar steps are examples of common component replacement methods.

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Photo Sequence 23

Pump and Motor Removal

P23-1  You will need fender covers, a combination wrench set, a flare-nut wrench set, a syringe, and fresh brake fluid.

P23-2  Place the fender covers on the vehicle and disconnect the battery ground (negative) cable.

P23-3  Press and release the brake pedal 30–40 times to depressurize the accumulator. The pedal should become firmer and travel less when the accumulator is depressurized.

P23-4  Disconnect the electrical connectors from the pressure switch and the motor.

P23-5  Use a clean syringe to remove about half of the brake fluid from the reservoir.

P23-6  Unscrew the accumulator from the hydraulic module. Then remove the O-ring from the accumulator.

P23-7  Disconnect the high-pressure hose from the pump.

P23-8  Disconnect the wire retaining clip. Then pull the return hose out of the pump body.

P23-9  Remove the bolt that attaches the pump and motor to the hydraulic module.

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Photo Sequence 23 (continued)

P23-10  Remove the pump and motor assembly by sliding it off the locating pin.

Wheel Speed Sensor Replacement A problem in a wheel speed sensor may require replacement of the sensor pickup coil and its harness or the tone ring or both. Some wheel sensors have an adjustable air gap between the sensor head and the teeth on the tone ring. An equal number of sensors are nonadjustable. If a sensor is adjustable, follow the carmaker’s adjustment procedure exactly. Some nonadjustable sensors use a lightweight plastic or paper spacer on the mounting surface (Figures 10-27 and 10-28). The spacer sets the air gap correctly. A new spacer of the correct thickness should be used whenever a sensor is reused. Manufacturers differ in their requirements for servicing the wiring harnesses on speed sensors. The short, two-wire harness that is part of the sensor assembly on GM vehicles is made with very fine wire strands to provide maximum flexibility with minimum circuit resistance. GM specifies that the sensor harness should not be repaired by any method. If it is damaged, the complete sensor assembly must be replaced. Chrysler says that the harnesses on most of its wheel speed sensors can be repaired by soldering and reinsulating with heat-shrink tubing. Because of the importance of signal accuracy from a wheel speed sensor, it is generally preferable to replace a sensor assembly, including the harness, instead of trying to repair the harness. Consult the manufacturer’s specifications before deciding how to service these components. Many sensors have a short jumper harness that can be replaced at a relatively low cost. Sensor tone rings that are pressed on the inside of the rotor or on the axle shaft often can be replaced. If the sensor ring is an integral part of the wheel bearing assembly, hub assembly, or the outer constant velocity joint on the axle, the entire component must be replaced if the sensor ring is damaged. Observe these additional guidelines when servicing ABS wheel speed sensors: ■■ Unplug sensor electrical leads when replacing suspension components. ■■ If a sensor tone ring (trigger wheel) is replaceable, fit the new one in place by hand. Do not hammer or tap the sensor in place. ■■ If a wheel sensor ring or tone wheel is replaceable and is pressed into place, do not remove the old ring or install a new one by hammering or prying. Use a hydraulic press with the proper special tools. ■■ Remove the vehicle wheel when replacing a wheel sensor. ■■ Some wheel sensors require an anticorrosion coating before installation to prevent galvanic corrosion. Never substitute grease unless the carmaker specifies its use. Sensor assemblies that are a permanent part of the wheel bearing and hub assembly are used on many late-model GM cars. They need no adjustment and plug directly into the vehicle wiring harness.

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Wheel sensor

Paper air gap adjusting disc Wheel sensor

Polyethylene strip

Figure 10-27  Some wheel speed sensors use a plastic spacer to set the air gap correctly.

Figure 10-28  Other wheel speed sensors use a paper spacer. In either case, the spacer should not be removed during sensor installation.

Computer (Control Module) Replacement Vehicle computers do fail but not with great frequency or regularity. Too many computers have been replaced because someone “thought it might be the problem,” or “didn’t know what else to do.” Too often, computer replacement does not cure the problem. The shop has spent several hundred dollars and still has a car to fix. Before deciding to replace a computer, always check the manufacturer’s technical service bulletins (TSBs) for specific information on revised computer part numbers and the problems they were designed to correct. Also check with dealership parts departments for the latest part number information. Computers and other electronic parts usually are special-order items. All electronic parts are absolutely, positively nonreturnable. Once purchased, they are the shop’s. To avoid costly, unnecessary computer replacement, check these items: 1. Battery voltage supply to the computer and the main system ground. Be sure the battery is fully charged and provides at least 9.6 volts to 10 volts during cranking. Be sure the charging system is maintaining correct battery charge. Most computers receive battery voltage through a fuse or fusible link. Be sure that battery voltage is available at the specified terminals of the computer’s main connector. Most computers are grounded remotely through several wires in the harness. Trace and check the ground connections to ensure good continuity. 2. Operation of a system power relay. Some computers receive power through a system power relay. If the vehicle is so equipped, check the relay operation. This relay may be remote mounted or underneath the electrohydraulic plastic cover. SERVICE TIP  Beware of electrostatic discharge (ESD) when handling e­ lectronic components. ESD is static electricity that can destroy the microscopic circuits of electronic integrated circuits. If some simple precautions are taken, however, ESD problems can be avoided.

3. Sensor reference voltage and ground circuits. Many sensors share a common reference voltage supply from the computer and a common ground. Incorrect or erratic reference voltage or a bad common ground can affect operation of several sensors simultaneously. The symptoms may appear as if the computer has a major system problem. Repairing a wiring connection may correct the problem.

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4. Resistance and current flow through all computer-controlled solenoids and relays. Every output device (solenoid or relay) controlled by a computer has a minimum resistance specification. The actuator resistance limits the current through the computer output control circuit. If the actuator is shorted, current can exceed the safe maximum and damage the computer. In most cases, current through a computercontrolled output device should not exceed 0.75 ampere (750 mA). Before replacing a computer, check all output circuits for shorts or low resistance that could damage the computer.   WARNING Be sure that the ignition is off when removing and installing a control module or other electronic component.

SERVICE TIP  The best method to prevent damage to electronic components from static is to always wear an antistatic strap during the repairs. The strap can be worn on the wrist or may be a waist belt. Some companies require their technicians to wear one as part of the uniform.

As a general rule, the system computer should be at the bottom of the list of things to replace. Again, computers can fail, but a sensor or actuator problem, bad wiring, or a mechanical fault is a more likely cause of a problem. ESD occurs when two dissimilar materials are rubbed together or quickly separated from each other. Electrical charges build up on the surfaces and then discharge when a circuit path is available. If a person slides across the front seat of a car and then touches a metal surface, he or she can build up and then discharge several thousand volts of static electricity. ESD of 8,000 volts to 10,000 volts is very common and the person will not even feel or see it. When ESD generates a small spark from the fingertip to a metal surface and the snap is felt, a charge of 40,000 volts to 50,000 volts of ESD is involved. High-voltage ESD does not hurt a person because it is moving only a few microamperes of current. That small amount of current, however, can destroy the microscopic interconnections of an integrated circuit. Those few microamps blow the circuit as does a low-current fuse. ESD problems can be avoided by observing a few simple precautions when handling electronic components: ■■ Do not remove an electronic part from its packing material until it is time for installation. ■■ Do not hold an electronic part by its connector pins. ■■ Before entering a vehicle to remove or replace an electronic part, touch an exposed metal part of the vehicle to discharge any static charge from your body. ■■ Avoid sliding across upholstery or carpeting when removing or installing an electronic part. If this is not possible, touch an exposed metal part of the vehicle with a free hand before installing a new component. ■■ When available, use an antistatic grounding strap attached to the wrist and clipped to a metal part of the vehicle body to prevent static charges from accumulating.

TESTING SPECIFIC MANUFACTURERS’ SYSTEMS Most ABS system testing is very similar to what is described in this text. The featured systems of the Bosch 9.0 and the Delphi DBC-7 have been the focus since the procedures

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for testing them are very similar to other brands except in some terminology and DTC numbering and definition. Each system discussed here uses a scan tool as the primary tester or individual testing of each suspected device one by one.

DELPHI DBC-7 A scan tool is the quickest way to provide initial diagnosing and some testing of the DBC-7 system. The scan tool can retrieve DTCs and data, and it can activate certain devices within the system and measure their response to commands. Photo Sequence 24 shows the general steps to program and connect a scan tool to the DBC-7 data link connector under the dash. But as with any malfunctioning system on a vehicle, a well-conducted test drive will tell the technician about the system’s performance. If the ABS amber warning light is on, retrieve the DTC(s). If none are significant enough to be a safety issue and the service brakes seem to be satisfactory, clear the codes and conduct a test drive. Figure 10-29 shows the list of the types of possible codes for GM antilock brake systems. All ABSs conduct a proof-out or test of their electronic circuits when the ignition switch is turned to RUN. The DBC-7 is no different. During key on, engine off, the dash warning lights will illuminate and the EBCM cycles the solenoid and pump on/off. It checks the system for proper operation and conducts an internal check as well. At speeds above 10 mph, the EBCM will conduct a dynamic test the first time the brakes are applied. The driver may feel some pedal movement and more slowing than anticipated. The WSSs are also monitored continuously while the vehicle is being operated. If a fault is detected, the ABS warning lamp will be illuminated and the ABS will be deactivated until a repair is accomplished. Should the dynamic rear proportioning be affected by the fault, then the red brake lamp will also be switched on. Because the fault codes were cleared prior to the test drive, check to see if one or more of the same codes were set during the test drive. This gives the technician the most probable starting point in the final diagnosis and repair. At times a code setting malfunction during the last drive cycle does not reappear during the next drive. Then that code is moved to the history file and the warning light will not be illuminated. After 100 drive cycles and no new codes set, all previously set codes will be cleared. A scan tool is required to clear all system DTCs if they remain set. It is also best to remember to clear the codes once all repairs are completed.

Red locking tab

Classroom Manual pages 242

Sliding connector

Figure 10-29  Unlock the red tab and slide the connector to open the EBCM housing.

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Photo Sequence 24

Typical Procedure for Using a Scan Tool on the Delphi Dbc-7

P24-1  Attach the communication cable to the scan tool.

P24-2  Connect the scan tool to the data link connector (DLC) with the ignition off.

P24-3  Turn on the scan tool by depressing the power button.

P24-4  Press enter to access the main menu.

P24-5  Select diagnostics.

P24-6  Select the correct year of the vehicle.

P24-7  Select the correct type of the vehicle.

P24-8  Turn on the ignition, but leave the engine off.

P24-9  Select the chassis, body style, and brake application. You may now choose data list mode to monitor system conditions such as wheel speed sensors and brake switch input. Trouble codes may be viewed, or, if required, the special functions mode will operate ABS components such as the pump and relays. The snapshot mode can be used to capture a fault as it occurs on a controlled test drive.

P24-10  After the problem has been isolated and repaired, clear all stored trouble codes, and test drive. Always turn the ignition off before disconnecting the scan tool from the DLC.

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A scan tool provides the technician with a means to retrieve DTCs and current operating data known as enhanced data. These data include the status of the brake switch, ABS activity, ETC/TCS activity, TCS switch, drive cycles since the DTC was set, the vehicle’s current speed, and much more. Some standard specifications for the DBS-7 are: The ground resistance for the EBCM is 5 ohms or less and the pump resistance is 2 ohms or less between the terminals. WSS on the DBS-7 should be at least 100 mV when the wheel is rotated at 1 revolution per second. One thing that is true for using DTCs as the diagnostic starting point is: Once the DTC is retrieved and defined, refer to the service information for the diagnostic charts and follow the steps in the charts exactly. Trying a shortcut may make the repair take much longer and could create additional costs to the shop and technician.

EBCM Replacement Replacement of parts is very similar to the procedures discussed under the component removal section. However, not all components are accessed easily. Read the service information carefully, paying particular attention to CAUTIONS and WARNINGS. To replace the EBCM, perform the following actions first:

1. Turn the ignition switch to off. 2. On a 3.8L engine, remove the fuel injector sight shield. 3. Remove the fender upper diagonal brace. 4. Disconnect the accelerator and cruise control cables at the bracket. 5. Disconnect and move the cruise control module from the strut tower. 6. Remove the air intake duct.

The EBCM is now accessible. Start with unlocking the red tab and then sliding the connector cover to open (Figure 10-30). Clear the area around the EBCM before unplugging the harness connector. There are four retainers holding the EBCM and the BPMV together. Remove the retainer and gently pull the two sections apart. The installation is the reverse of the removal procedures. Be careful mating the EBCM and BPMV together and tighten the four retainers to 44 in.-lb. (5 Nm). Once the EBCM is in place and all connections and removed components are reinstalled, turn the ignition to RUN but do not START the engine. Perform the diagnostic system check covered in the first paragraphs of this section.

BPMV Replacement Perform the first six steps in EBCM replacement. Disconnect, plug, and move the brake lines (pipes) from the BPMV body (Figure 10-31). Shift the lines to one side and then disconnect, plug, and shift the two master cylinder lines at the BPMV unit. Remove the two bolts and one nut holding the BPMV to the bracket and strut tower. Disconnect the ground strap at the BPMV end and remove the EBCM/BPMV assembly from the vehicle. If only the BPMV is being replaced, separate it from the EBCM as discussed above. The installation is the reverse of removal. Once the assembly has been reinstalled and all removed or disconnected components are in place, it is necessary to use the automated bleed process to clear the system of air.

Wheel Speed Sensor Replacement DBC-7 To replace any wheel speed sensor on the DBC-7, first lift the vehicle and remove the appropriate wheel and tire assembly. To remove a front-wheel speed sensor, first disconnect the jumper harness from the speed sensor (Figure 10-32). Remove the brake caliper and rotor, followed by the hub and bearing assembly (Figure 10-33). The hub and bearing assembly is separated from the steering knuckle by removing the three fasteners and using

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Hub and speed sensor assembly

BPMV

Vehicle harness

Wheel speed sensor connector

Figure 10-31  The jumper harness from the vehicle harness to the WSS connector lead. Figure 10-30  Remove and plug all the brake lines (tubes) at the BPMV end. Brake caliper supports Steering knuckle Steering knuckle

Puller

Drive axle nut Hub and bearing assembly

Hub and bearing assembly

Figure 10-33  The hub and bearing assembly is removed from the steering knuckle using a puller, like the one shown.

Figure 10-32  The DBC-7 WSS is integrated into the hub and wheel speed sensor. The entire assembly is replaced as a unit.

a puller (Figure 10-34). The installation of the front-wheel speed sensor is the reverse of removal. With all components in place and the vehicle resting on its wheels, perform the diagnostic system check. Note that this system uses a wheel speed sensor that is integral to the hub and bearing, so there is considerably more work involved to change the sensor. The removal of the rear sensor is similar to that of the front. After removing the tire and wheel assembly, disconnect the harness from the speed sensor (Figure 10-35).

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Speed sensor Retaining bolt

Wheel speed sensor Electrical connector

Figure 10-34  Unplug the rear harness from the rear-wheel sensor. Like its counterpart at the front, this sensor is incorporated into the hub and bearing assembly.

Figure 10-35  Removal of the wheel speed sensor.

Remove the hub and bearing assembly. The installation, like always, is the reverse of the removal. Always perform the diagnostic system check any time a DBC-7 component is replaced.

Switches and Warning Lights DBC-7 System The instrument cluster is generally a job for a specialist repair station. Usually the same people who repair radios and navigation units repair instrument clusters. Most of the time the instrument cluster cannot be repaired in the shop. If necessary to remove a cluster, the new technician must closely follow the step-by-step instructions and use the special tools outlined in the vehicle’s service information. Pulling or prying in the wrong place can result in damage to some expensive plastic. The cluster will probably have to be reinitialized (programmed) when it is installed as well.

BOSCH ABS 9.0 The Bosch ABS 9.0 mostly uses familiar testing and service procedures to most other ABS/ TCS/ESC systems in use. The Bosch ABS 9.0 uses magnetoresistive wheel speed sensors as do every other modern electronic braking system.

Classroom Manual page 246

Initial Diagnosis The ABS warning light will illuminate during the bulb check, it will usually stay illuminated immediately after engine start, and it will stay on for around 5 seconds. If there is a problem in the ABS system, the ABS amber lamp will stay on to indicate the problem. The red brake warning lamp will also illuminate on bulb test, again for a few seconds after the initial engine start or if a base brake problem is detected. It may also stay on with the amber light in case of ABS failure if the problem affects the stopping efficiency of the vehicle. The red brake warning lamp will also illuminate if the BCM is receiving an

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indication that the parking brake is applied. The BCM sends a message to the instrument cluster to turn on the lamp. The startup cycle occurs when the ignition switch is switched to RUN. The system will start performing self-tests on all its electrical components. At approximately 10 mph the EBCM commands the solenoids in the BPMV to be cycled and that their operation to be confirmed.

Test Drive Diagnosis It is important to note that most ABS systems will allow some wheel slip during braking to gain maximum stopping traction. This allowed slip may cause some tire chirping on some surfaces, but it is not a sign of total lockup. The system measures or allows wheel slippage based on the following slip values: 0 percent 5 free turning wheel 25 percent to 30 percent 5 allowable slippage 100 percent 5 total lockup This means the system will allow up to 25 percent to 30 percent of slippage. The wheel in question is turning at a speed 25 percent to 30 percent more slowly than the other wheels at a given speed. The tire may chirp on some road surfaces. The easiest way to determine if the ABS is functioning properly is a road test on dry pavement. Accelerate the vehicle to about 20 mph to 25 mph and lock the brakes down, forcing the system into an ABS active mode. Once the vehicle has stopped, check behind the vehicle for black marks on the pavement. If there are no black marks, the system is functioning properly.

Premature (Low-Speed) ABS Activation During the test drive the technician should be listening and feeling for premature ABS functioning. Premature ABS operation may occur at any speed, with any braking force, and on any type of road surface. Some symptoms of premature ABS are clicking sounds from the BPMV, pump operation, and/or pedal pulsations, which occur with normal braking that usually does not activate the ABS system. Neither brake warning light will illuminate nor will any fault codes be stored. The first items to check in the event of premature or low-speed ABS operation are tires and base brake problems. Contaminated or glazed linings can cause a wheel brake to grab, which activates the ABS system. Also consider the tires. Are the tires providing good traction? If not, the ABS will detect them sliding, especially on low-traction pavements. If these factors are not causing the premature ABS operation, it may be necessary to use a scan tool. Check the following components to isolate the root cause of the fault: damaged or incorrect tone wheels, damaged speed sensor mount, loose sensor fasteners, air gap too large between the sensor and tone wheel, or excessive tone wheel runout. Any of these faults could cause premature ABS functioning and should be examined closely during the diagnosis. SERVICE TIP  Premature ABS functioning is common on gravel road surfaces. The tire tends to slide more easily and the ABS will switch on.

Front-Wheel Speed Sensor Replacement Lift the vehicle and remove the tire and wheel assembly. Remove the sensor-retaining bolt, and pull the sensor from the steering knuckle. (Figure 10-35). Remove the inner fender liner to gain access to the cable retainers (Figure 10-36). Next, disconnect the sensor harness from the main harness in the engine compartment. To install, connect the harness to the main harness in the engine compartment, route and attach the harness cable to the

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Retaining clips

Figure 10-36  Remove the inner fender liner to gain access to the cableretaining clips.

body, reinstall the inner fender liner. Install the wheel speed sensor, and tighten the retaining bolt to 6 Newton Meters (53 lb in). Mount the tire and wheel assembly and road test the vehicle to ensure that the service brakes and the ABS are working properly.

Rear-Wheel Speed Sensor Replacement Rear-wheel speed sensor replacement is very much like replacing the front sensor. Remove the tire and wheel, and remove the sensor-retaining bolt (Figure 10-37). Then unclip the wheel speed sensor cable, and disconnect the harness connector. Retaining bolt

Wheel speed sensor

Figure 10-37  Removing the rear-wheel speed sensor.

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Brake Pressure Modulator Valve and EBCM Replacement The first step in this replacement procedure is to disconnect the battery. Clean all around the BPMV and the brake lines thoroughly (Figure 10-38). Using a crowfoot wrench, loosen and disconnect the master cylinder lines and brake tubes at the BPMV ends, and plug the disconnected brake lines (Figure 10-39). Disconnect the BPMV 24-pin electrical connector by moving the lock up as far as possible. This removes the lock and disconnects the plug (Figure 10-40). Remove the BPMV fasteners. Lift the BPMV out of the bracket and remove it. Remove the bracket from the BPMV. Once the BPMV is free from its bracket, separate the BPMV and the EBCM (Figure 10-41). If the EBCM is replaced, then the EBCM as well as the brake pressure sensor inside the EBCM will have to be reprogrammed. Bleed the service brakes; do an automated bleeding sequence, as described earlier in the chapter; and then road test.

Crowfoot wrench

EBCM

Figure 10-38  A typical BPMV configuration. The EBCM is attached to the BPMV.

Figure 10-39  Using a crowfoot wrench is the only way to properly loosen and torque the brake line (tube) fittings.

BPMV

EBCM

24-pin connector EBCM Lock

Figure 10-40  Once the lock is unsnapped and moved, the 24-pin connector can be removed from the EBCM.

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Figure 10-41  The BPMV and the EBCM can be separated from each other after their removal from the vehicle.

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Warning Lamps The instrument cluster on the majority of vehicles built within the last several years is not serviceable in the typical shop. The instrument panel has actually become another computer module on the automotive network. The gauges and lights are actually told to display based on serial data, not a direct reading from any sensor or switch. Most instrument clusters are sent out to specialty instrument panel repair shops. Many times a cluster that has already been rebuilt is exchanged, which helps reduce down time while a cluster is being repaired. Additionally, the instrument cluster will also need to be reprogrammed or reinitialized once it has been replaced. SERVICE TIP  Most of the latest systems in use share many common ­elements, but it is always necessary to verify that the right information is used. Always make sure to check service information for the specific repair for the ­vehicle concerned. As the newer systems begin to show up for repairs, consult the latest service information, recalls, and technical service bulletins for up-to-date diagnostic testing.

CASE STUDY A vehicle came into the shop with the owner complaining of the ABS activating at a very low speed. All the normal checks were made, brakes were inspected, everything appeared to be okay, except for the fact that the ABS activated with the vehicle on dry pavement and coming to a slow stop. The technician took an assistant out to drive while the technician read the scan tool and everything looked normal. The technician finally decided that the BPMV had to be the source of the problem. After replacing the expensive modulator, the vehicle still had the same problem. At this point he decided to go to the shop foreman for help. The foreman told the technician to replace the rear shoes and resurface the drums, even though they did not appear to be contaminated in any way or worn to the point of needing replacement. When the shoes were replaced and the drums were machined, the vehicle performed normally. There are two lessons here: Start with the basics, and do not be afraid to ask a more experienced technician when you need help.

ASE-STYLE REVIEW QUESTIONS 1. Brake bleeding an ABS is being discussed. Technician A says that the Delphi DBC-7 must have the service brakes bled three times in sequence. Technician B says that a scan tool might be required to bleed an ABS system, especially if there was a large amount of fluid lost or the BPMV was replaced. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 2. When multiple trouble codes are present in an ABS, look for: A. a weak connection at a common ground. B. an open circuit. C. low-voltage signals. D. high-voltage signals.

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3. While discussing a braking problem with a customer, Technician A says it is important to ask exactly when a problem occurs. Technician B saysit is important to ask what was done during the last service. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 4. Technician A says that the amber ABS warning lamp signals an ABS malfunction. Technician B says that the red BRAKE warning lamp also can signal an ABS problem. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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5. Technician A says that pumping the brake pedal on a vehicle with antilock brakes actually defeats the operation of the antilock system. Technician B says that rapidly pumping the brake pedal may set a DTC and turn the ABS warning lamp on. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

8. Technician A says it is important to note that most ABS systems will allow some wheel slip during braking to gain maximum stopping traction. Technician B says this allowed slip may cause some tire chirping on some surfaces, but it is not a sign of total lockup. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

6. Technician A says an ABS is an electrically controlled hydraulic system. Technician B says the ABS function will work if the base brakes do not work properly in their non-antilock mode. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

9. Technician A says that traction control adds several new components to a vehicle and requires testing through their own diagnostic connectors. Technician B says that traction control is an example of adding new features to a vehicle primarily through computer software. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

7. While discussing the Bosch ABS 9.0 system; Technician A says the ABS warning light will illuminate during the bulb check, it will usually stay illuminated immediately after engine start, and it will stay on for around 5 seconds. Technician B says if there is a problem in the ABS system, the ABS amber lamp will stay off, indicating an ABS problem. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

10. Servicing a Bosch ABS 9.0 system is being discussed. Technician A says the brake pressure sensor is an integral part of the BPMV. Technician B says the brake pressure sensor must be recalibrated using a scan tool if the EBCM or BPMV is replaced. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

ASE CHALLENGE QUESTIONS 1. While discussing bleeding the Ford Flex ABS system, Technician A says that the preferred method to bleed the brakes is gravity bleeding. Technician B says that the front brakes are bled first, starting at the left front brake. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 2. Technician A says ABS is more likely to suffer from basic brake system problems than from problems in the ABS control circuitry or components. Technician B says worn tires can cause frequent ABS cycling, especially on wet roadways. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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3. While checking the base braking system. Technician A says with the engine running, pump the brake pedal rapidly several times. The pedal height should remain about the same. Technician B says that if the brake pedal decreases during pumping, or if a very hard feeling during pedal application is noted, air may be trapped in the hydraulic lines. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

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4. Technician A says brake fluid levels can generally be checked on modern ABS units without depressurizing the ABS system. Technician B says many older ABS systems did require that the system be depressurized to check the fluid level. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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5. Technician A says that some speed sensors receive a bias voltage to raise the signal above the common ground plane of the vehicle electrical system. Technician B says that bias voltage can be used by the computer to detect open and short circuit problems. Who is correct? A. A only B. B only

C. Both A and B D. Neither A nor B

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Name ______________________________________ 

Date _________________

BRAKES/ABS/STABILITY CONTROL WARNING LAMPS CHECK Upon completion of this job sheet, you will have tested the ABS warning lamp circuit and its ability to detect a fault. You will also identify the various electronic braking components found on the vehicle you are using in the shop.

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ASE Education Foundation Correlation This job sheet addresses the following MLR tasks: B.5.

Identify components of hydraulic brake warning light system. (P-3)

G.1.

Identify traction control/vehicle stability control system components. (P-3)

This job sheet addresses the following AST/MAST tasks: B.10.

Inspect, test, and/or replace components of brake warning light system. (P-3)

B.11.

Identify components of hydraulic brake warning light system. (P-2)

Identify and inspect electronic brake control system components G.1.  (ABS, TCS, ESC); determine needed action. (P-1) Tools and Materials • Scan tool Describe the vehicle being worked on: Year ____________________ Make ____________________ Model _____________________ VIN ____________________ Engine type and size ___________________________________ ABS type _____________________________________________________________________ Procedure Electronic Braking Component Identification 1. Based on the make and model of the vehicle, there can be great variation in the systems you might see in the shop. 2. What type and model of system is used on your vehicle? Use service information to determine if this system is Teves, Kelsy Hayes, Bosch, or another. Name the manufacturer of the unit here.  3. Identify the locations of each of the following components of the electronic braking system: A. BPMV (Also known as hydraulic modulator) _______________________________ B. EBCM (Control Module) _______________________________________________ C. ABS Relay ____________________________________________________________ D. Fuses for the system are located: __________________________________________ E. Master cylinder ________________________________________________________ F. Brake Booster _________________________________________________________ Is the brake booster hydraulic or vacuum-assist type? 

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4. Set the parking brake. Turn the key to run. Did the red parking brake lamp come on, or did the driver information warning come on? If not, start the vehicle and see if the light comes on. Describe what you observed.   5. Describe the normal operation of the ABS lamp by using service information. When does the vehicle go through a bulb test?   6. Observe the operation of the traction control light. Is it operating as designed?  7. Turn the traction control system off. Does the system tell you that the system is turned off?  8. Does your vehicle use a brake fluid level sensor or a differential pressure sensor to warn of a brake fluid leak?  9. If your vehicle is equipped with stability control, can it be disabled? If so, is there a warning lamp to inform you that the system is turned off?   Problems Encountered    Instructor’s Response   

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Name ______________________________________ 

Date _________________

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USE SCAN TOOL TO SCAN ABS FOR CODES

42

Upon completion and review of this job sheet, you should be able to use a scan tool to retrieve ABS trouble codes. ASE Education Foundation Correlation This job sheet addresses the following MAST tasks: Diagnose electronic brake control system electronic control(s) and G.4.  components by retrieving diagnostic trouble codes, and/or using recommended test equipment; determine needed action. (P-2) Tools and Materials • Service information • Scan tool Describe the vehicle being worked on: Year ____________________ Make ____________________ Model  VIN ____________________ Engine type and size _____________________________________ ABS type  NOTE TO INSTRUCTORS: The following procedures are based on a MODIS from Snap-on Tools. The vehicle is an OBD-II-equipped vehicle. The use of other scan tools or vehicles may require additional instruction for the student. Procedure

Task Completed

1. Remember that some scan tools require that vehicle ID be entered before making a connection to the DLC. VIN _____________________________________________________________________ 2. Enter the vehicle identification into the scan tool by:

A. Selecting “Domestic” or “Import.”



B. Select the manufacturer. Manufacturer 



C. Select model and year.



D. The scan tool should state that the vehicle ID is stored and the button can be released. Is the vehicle identified correctly? 

3. Select and connect the scan tool OBD-II connector to the scan tool.

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4. Connect the scan tool to the vehicle’s OBD-II connector.

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5. The scan tool should switch on, identify itself, and show the identification for the vehicle entered in step 2. If correct, press the Y (yes) button. Results: __________________________________________________________________ 6. At the next screen, select “ABS.” (Some scan tools list ABS under Chassis)

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7. Switch ignition to KOEO.

Task Completed h

8. The scan tool should show a “C” code, or some electronic brake related codes can also be “B” codes. Various data should also be displayed. Record all codes or data displayed on this screen. Also note if the codes are history or current. Results: ________________________________ 9. If any other information is displayed, correct the data or consult the service information for the vehicle and scan tool to resolve conflicts. Example of an error message may be:

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NO COMMUNICATION. IS KEY ON? ENSURE THE CABLE IS PROPERLY CONNECTED, ETC (or words to that effect). 10. Once all trouble codes have been recorded, switch the ignition to off.

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11. Use service information and the scan tool to establish a preliminary diagnosis on a possible cause of the DTC.

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12. When the task is complete, store the tools and complete the repair order.

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Problems Encountered    Instructor’s Response   

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Name ______________________________________ 

Date _________________

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TESTING AN ABS WHEEL SPEED SENSOR

43

Upon completion and review of this job sheet, you should be able to inspect and test an ABS wheel speed sensor with an oscilloscope. ASE Education Foundation Correlation This job sheet addresses the following AST/MAST task: Identify and inspect electronic brake control system components (ABS, TCS, G.1.  ESC); determine needed action. (P-1) This job sheet addresses the following MAST tasks:

G.4.  Diagnose electronic brake control system electronic control(s) and components by retrieving diagnostic trouble codes, and/or using recommended test equipment; determine needed action. (P-2) Test, diagnose, and service electronic brake control system speed sensors G.7.  (digital and analog), toothed ring (tone wheel), and circuits using a graphing multimeter (GMM)/digital storage oscilloscope (DSO) (includes output signal, resistance, shorts to voltage/ground, and frequency data). (P-2) Tools and Materials • Service information • Wiring diagram • Component locator • Oscilloscope • Lift or jacks with stands Describe the vehicle being worked on: Year ____________________ Make ____________________ Model  VIN ____________________ Engine type and size  ABS ___________________ yes ___________________ no ___________________ If yes, type  Procedure for Analog Wheel Speed Sensor

Task Completed

1. If vehicle is FWD, set transaxle to neutral and ignition to accessory position.

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2. Lift the vehicle until one of the front wheel sensors is accessible.

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3. Turn wheels to left or right for better access to the sensor.

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4. Locate and disconnect the speed sensor.

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5. Measure the resistance of the analog or magnetic reluctance sensor and record here: ___________________Ohms. 6. Program the oscilloscope according to its operator’s manual to read an AC voltage waveform.

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7. Connect the oscilloscope leads to the terminals on the sensor.

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Procedure for a Magnetic Reluctance Sensor

Task Completed

NOTE: Do not measure the resistance of a magnetic reluctance sensor! It may destroy the sensor. 1. Using service information, determine which sensor lead is supply power and which sensor lead is signal.

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2. Sensor signal wire color and circuit number  3. Sensor voltage supply wire color and circuit number_____________________________ 4. Carefully back probe the signal wire to the sensor; ground the black lead to the oscilloscope according to the oscilloscope’s manufacturer ’s instructions.

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For Both Sensors, Follow the Steps Below. NOTE: If the oscilloscope has a printer or data storage capabilities, use either or both to print or save the graphs. 1. Rotate the wheel at a constant speed while observing the graph.

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2. Freeze and save/print the graph.

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3. Speed the wheel faster while observing the graph. General results: Include voltage levels and frequency readings    4. Freeze and save/print the graph.

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5. Stop the wheel(s).

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6. After the wheel(s) have stopped, disconnect the oscilloscope and reconnect the harness to the sensor.

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7. Lower the vehicle.

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8. Shift the transaxle to park, switch the ignition to off, and set the parking brakes.

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9. Compare the saved/printed graphs to the oscilloscope example file or the figures in the text.

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10. Record the operational action of this speed sensor and make any recommendation.     11. What would happen to the waveform if the signal were shorted to ground? How would you diagnose a shorted signal wire?  12. What would happen to the waveform if the signal were open? How would you diagnose an open signal wire? 

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Problems Encountered    Instructor’s Response    SERVICE TIP  If the oscilloscope operator can stay clear and keep the leads clear of the wheel, a coworker can rotate the wheel using the engine.

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Name ______________________________________ 

Date _________________

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JOB SHEET

REPLACE AN ABS WHEEL SPEED SENSOR

44

Upon completion and review of this job sheet, you should be able to replace an ABS wheel speed sensor. ASE Education Foundation Correlation This job sheet addresses the following AST/MAST task:

G.1.  Identify and inspect electronic brake control system components (ABS, TCS, ESC); determine needed action. (P-1) This job sheet addresses the following MAST task:

G.7.  Test, diagnose, and service electronic brake control system speed sensors (digital and analog), toothed ring (tone wheel), and circuits, using a graphing multimeter (GMM)/digital storage oscilloscope (DSO) (includes output signal, resistance, shorts to voltage/ground, and frequency data). (P-1) Tools and Materials • Service information • Lift or jack with stands • Impact tools Describe the Vehicle Being Worked On: Year ____________________ Make ____________________ Model ____________________ VIN ____________________ Engine type and size  ABS ____________________ yes____________________ no ____________________ If yes, type  Procedure

Task Completed

1. Determine: Wheel sensor fastener torque  Wheel lug nut torque  Special tools and procedures for setting air gap  2. Lift vehicle to a good working height.

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3. Remove the wheel assembly.

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4. Inspect the area around the speed sensor.

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5. Remove any component blocking access to the speed sensor and/or fasteners. Items removed, if any.

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 6. Remove the speed sensor.

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7. Inspect the tone ring as much as possible. Results:



 8. Remove the new speed sensor from its shipping carton.

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9. Install the speed sensor into its mounting.

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10. Secure the special tools and set the air gap to specifications.

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11. Install and torque the speed sensor fastener.

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12. Install the wheel assembly and torque the lug nuts to specifications.

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13. Lower the vehicle.

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14. Clear any ABS codes and road test.

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15. When the repair is complete, clean the area, store the tools, and complete the repair order.

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Problems Encountered    Instructor’s Response   

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Name ______________________________________ 

Date _________________

DIAGNOSING ABNORMAL PEDAL FEEL IN AN ELECTRONICALLY CONTROLLED BRAKE SYSTEM

513

JOB SHEET

45

Upon completion and review of this job sheet, you should be able to diagnose abnormal pedal feel in an ABS braking system. You should be able to bleed the braking system of an ABS/TCS-equipped vehicle using the service manual procedure. ASE Education Foundation Correlation This job sheet addresses the following MAST tasks: Diagnose poor stopping, wheel lock-up, abnormal pedal feel, unwanted G.3.  application, and noise concerns associated with the electronic brake control system; determine needed action. (P-2) G.5.  Depressurize high-pressure components of an electronic brake control system. (P-3) G.6.

Bleed the electronic brake control system hydraulic circuits. (P-1)

Tools and Materials • Service information • Lift or jack with stands • Impact tools • Scan tool • Brake fluid • Hand tools • Safety glasses and gloves Describe the vehicle being worked on: Year ____________________ Make ____________________ Model ____________________ VIN ____________________ Engine type and size 

Caution If this ABS vehicle is equipped with an accumulator, it is under high pressure. Always check with the service manual for proper procedures before starting work on a system with an accumulator.

Type of ABS system on vehicle  Procedure 1. Identify the location of the following components. A. BPMV:  B. High Pressure pump (if equipped):  C. Accumulator (if equipped):  D. EBCM:  2. Describe the brake pedal feel on the vehicle. Are there any unusual noises associated with the braking system?   3. Using the service information for the vehicle, what preliminary diagnosis would you make for this vehicle? 

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4. If this vehicle is equipped with an accumulator, what is the proper procedure for bleeding the pressure off the system before servicing the system?

Task Completed

  5. What is the proper procedure for bleeding a single caliper on this vehicle?   6. What bleeding procedure does the manufacturer recommend if the system has ingested air throughout the system, such as the replacement of the BPMV assembly?   7. Does the manufacturer recommend a pressure or manual bleed procedure? Or is there no preference?  8. Is there an automated bleed procedure (with a scan tool) involved in servicing this vehicle? If so, describe the procedure below.   9. Describe the order in which the wheels should be bled.   10. Place the vehicle on the rack.

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11. Remove the wheels.

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12. Bleed the brakes as described in the service manual.

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13. Reinstall and torque the lug nuts.

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14. Clear any codes that might have been set from servicing the vehicle.

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15. Test drive the vehicle and make sure it is safe to drive. Start in a clear area in the parking lot. Do the brakes feel normal? ________________________________ Problems Encountered    Instructor’s Response   

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A current code is ­indicating the fault is present at the time of testing.

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Advanced Braking Systems

Upon completion and review of this chapter, you should be able to: ■■ ■■ ■■

Describe the service and diagnosis of ABS/TCS systems. Describe the diagnostic procedures for stability control system. Explain the service of the stability ­control sensors.

■■ ■■

Explain the diagnosis of active braking. Explain the general diagnosis of a regenerative braking system on a hybrid vehicle.

Terms To Know Throttle actuator control (TAC)

Tire pressure monitor System (TPMS)

Regenerative braking

As we saw in Chapter 11 of the Classroom Manual, vehicles have become more focused on safety and drivability as automotive development has expanded from concentrating on emission control and fuel mileage. At the same time, the role of the technician has grown to the point that the vehicles produced today must be serviced by a trained technician. The time has come that has been predicted for the past several years; the days of the shade-tree mechanic are gone. Those who accept the challenge of developing the necessary skills to be relevant in the industry are in very high demand. The repair of these systems is going to separate the “parts changers” and the true technician. Those who embrace these new technologies are rewarded not only with the pride of accomplishment, but also with the knowledge that they possess a truly marketable skill.

STABILITY CONTROL SYSTEMS Antilock/Traction Control and Stability Control Systems As you recall from previous chapters, stability control is actually an offshoot of ABS braking/traction control. The ABS system used with stability control will be a four-channel system to control all four wheels independently. Stability control uses the ABS concepts of controlling wheel lock-up and traction control, with the added inputs of a steering wheel position sensor, yaw sensor, and/or lateral accelerometer. Since stability control systems are working to prevent wheel lock-up in real time, the job of the proportioning and metering valves have been replaced by electronically controlled systems such as dynamic rear proportioning DRP and electronic brake distribution (EBD). The development of the high-speed computer network in the vehicle allows the computer modules available to share and act on information in virtually real time. There are many names for stability control systems; sometimes a single manufacturer has used several at the same time. A few of the more common names are shown in Figure 11-1.

Some manufacturers refer to dynamic rear proportioning as electronic brake distribution, or EBD.

Classroom Manual page 250 515

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Chapter 11 Manufacturer

Name for Stability Control System

Chrysler

Electronic Stability Program (ESP)

BMW

Dynamic Stability Control (DSC)

General Motors

Stabilitrak

Honda

Vehicle Stability Assist (VSA)

Ford

Vehicle Dynamic System (VDS)

Volkswagen

Electronic Stability Program (ESP)

Figure 11-1  Some common names for stability control systems in use.

Diagnostic System Check Most manufacturers recommend a basic system check before starting diagnosis of a computer system. These checks are essential to prevent a technician from going down a long diagnostic path, only to find out that a failing battery was the cause of a “computer” problem. Always follow the recommended diagnosis. Sometimes a “shortcut” will actually waste valuable time and money.

Performing Preliminary Checks Understand What the Customer Is Describing.  The customer is the best source of information; make sure that the problem is understood before trying to fix the complaint. Many times, it may be necessary to test-drive the vehicle with the customer. Technicians may be hesitant to do this, but you can prevent information from being lost in translation from the service advisor to the technician. In addition, if the problem is tough to duplicate, you are showing the customer that you are doing all you can to solve the problem. Verify the Complaint.  Make certain you understand and can duplicate the concern before diving into a “problem” that could be a normal condition. If you cannot duplicate the problem, ask for more information from the service advisor. If necessary, ask them to call the customer for clarification. Check for Any Bulletins That May Be Pertinent to the Problem.  Other technicians may have already done the legwork with a field service technician. Sometimes the e­ ngineers have developed a new part that might take care of the problem. Always check for a bulletin; with the electronic search engines available, they can save many headaches. Check for Any Trouble Codes.  Check for any trouble codes that might be present in the vehicle. Also, check for any communication network “U” codes that might indicate a problem with the vehicle network. Remember that the network is an integral part of the stability control system. The ECM, EBCM, TCM, and IPC all have to communicate with each other. Make sure all the modules are communicating as part of the network and reporting as present on the scan tool. See the specific manufacturer’s service information on how to check for integrity of the network. AUTHOR’S NOTE  Nothing agitates a customer like making arrangements to drop off a vehicle, leaving it with the shop all day, and then picking it up that afternoon with a note that says, “no problem found” on the repair order. To the customer, the problem does exist. It might be a normal condition, it may not be “acting up” when the technician drove the car, or the service advisor did not get enough information. In any event, you may wind up losing a customer. The service business is very competitive. If you do not take the time to satisfy your customers, someone else will.

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STABILITY CONTROL AND THE VEHICLE NETWORK The stability control network of modules, depending on the manufacturer, may include the engine control module (ECM) or power train control module (PCM), electronic brake control module (EBCM), instrument panel control module (IPC), and transmission control module (TCM). Some vehicles may use a separate vehicle stability control (VSC) module. A typical network is shown in Figure 11-2. The driver can turn off some stability control systems with a switch on the dash. A light will illuminate on the dash to remind the driver that the system is deactivated. In many cases, the system will reactivate on the next key cycle. Many systems tell the driver when the stability control is active, so that the driver is aware when the vehicle is helping itself to get through the situation. Hopefully the driver will realize that they are pushing the boundaries of the vehicle’s performance!

Classroom Manual page 256

System Self-Check The stability system will do a start-up initialization to make sure the system is ready and ensure its safe operation. Part or all of the start-up initialization may occur at key-on and/ or at a certain speed while driving. Some systems perform initialization test at 3 mph, 7 mph, and still others at 14 mph. Customers may often comment that they can hear a noise at a certain speed every morning while driving, so it is important that you are familiar with these normal sounds of the initialization of the system. Some normal characteristics may be interpreted as a problem by the driver. If the stability control system becomes active during a vehicle maneuver, a pulsation may be felt in the brake pedal, like what the driver experiences during an ABS stop. If any of the components or inputs to the stability control system has problems, then the system may be deactivated. A diagnostic trouble code (DTC) will be set for the appropriate system as needed. It is also important to note that a sensor vital to the stability control system, such as the throttle position (TP) sensor trouble code, even though this sensor is generally associated with engine performance, may also cause the stability control system to shut down. The stability control system is monitored continually over the vehicle’s controller area network (CAN) communication network.

Vehicle Stability Control System

EBCM

ECM

TCM

IPC

Figure 11-2  Stability control relies on the vehicle network to gather large amounts of information and share it in virtually real time.

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AUTHOR’S NOTE  When I was working as a technician, we had a customer complaining of a “thumping sound in the trunk when backing up.” The vehicle was driven over several situations forward and backward. The customer could not duplicate the problem for us either. A bulletin was found for an intermittent rear suspension loose lumber sound. The parts were ordered and installed. Customer returned a few days later and still had the problem. This time the customer said that the problem happened only after the vehicle sat for a few hours. Eventually, we discovered that the noise was ABS initialization. Even though I had driven many of the same vehicles, I had not noticed this sound before, but I always noticed it after that experience!

SYSTEM COMPONENT SERVICE Classroom Manual page 258

Many of the troubleshooting procedures are the same as they are for ABS and traction control systems, so those components will not be detailed here. Some of the more general procedures are included here. Of course, always look for the specific repair information from the manufacturer for the vehicle concerned for an actual repair.

Electrohydraulic Control Unit System Control Valves.  The electrohydraulic control unit (BPMV) (Figure 11-3) usually contains the brake pressure modulator valve (BPMV, Figure 11-4) that houses the necessary valves to control the application of the antilock brakes, traction control, and stability control systems. Most BPMVs also contain the EBCM, as well as the brake pedal pressure sensor and the ABS pump motor incorporated. The EBCM is an important part of the vehicle network, and stability control incorporates the ECM, TCM, and EBCM. Some systems also use a stability control computer as well as the EBCM. Many tests can be performed with the scan tool to determine the functionality of the spool valves by controlling the output of the EBCM with the scan tool on command, similar to that which is performed during ABS service.

Brake modulator Pump motor EBCM

Figure 11-3  This electrohydraulic control unit has the brake fluid pump, EBCM, and hydraulic modulator in one unit.

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Figure 11-4  A brake modulator valve body and brake fluid pump. The EBCM has been removed.

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Brake Pressure Sensor.  The brake pressure sensor measures the brake pressure applied by the driver to the master cylinder. The sensor is built into the BPMV and is not serviceable separately. This input gives the EBCM a measure of the driver’s intentions, whether it is a panic stop or just normal braking. The stability control system can then calculate the amount of brake pressure necessary given the angle of turn, vehicle speed, and lateral acceleration, or yaw. On a KIA the pressure sensor DTC is C1235. Diagnosis is straightforward but requires a scan tool. ■■ First the scan tool is used to clear the DTC. ■■ The brake pressure parameter is pulled up on the scan tool. ■■ The brake pressure is read with the key on engine off, brakes not applied. The ­pressure should be 0 bar. ■■ The brakes are then applied and the pressure should rise according to pedal pressure. If the reading is erratic, then a known good BPMV is substituted. If the problem is fixed, then the steering angle sensor must be relearned by the BPMV. ■■ If the problem cannot be duplicated at this time, then the connections and wiring connectors should be inspected for damage. Remember that parts should not be replaced if the problem cannot be verified. Yaw Sensor/Lateral Accelerometer.  The trouble codes for the yaw/lateral acceleration sensor on a 2011 Corvette are as follows: DTC C0186 00 Lateral Accelerometer Circuit DTC C0186 5A Lateral Accelerometer Signal Not Plausible DTC C0196 00 Yaw Rate Circuit DTC C0196 5A Yaw Rate Signal Not Plausible As you can see, the yaw sensor/lateral accelerometer is combined on this vehicle, and both sensors can perform their own independent self-test. The yaw sensor communicates on the CAN with the EBCM. If there are no codes stored for a yaw communication circuit or network codes, the power and ground circuits to the sensor are checked; if these are good, then the yaw sensor is replaced (Figure 11-5).

Steering Angle Sensor.  The steering angle sensor (Figure 11-6) is one of the most important sensors in the stability control system. The steering angle (sometimes called steering wheel position sensor) does require some attention during some routine service procedures.

519

A “C” code is a Chassis system code. A bar is a measure of pressure and equals 14.5 psi.

The lateral acceleration sensor can also be called the “G” sensor.

Some vehicles have a longitudinal acceleration sensor as well as a yaw and lateral acceleration sensors.

Steering Angle Sensor Centering.  The steering angle sensor will have to be re-centered (or relearned) following service such as: ■■ A front wheel alignment or outer tie rod replacement ■■ Steering angle sensor replacement

Figure 11-5  A yaw sensor.

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Figure 11-6  A steering angle sensor.

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Accident damage Intermediate shaft replacement ■■ Steering column or steering gear replacement ■■ (EBCM, BPMV) replacement The centering procedure must be performed with the steering wheels straight ahead, transmission in Park, key on, and engine off. The scan tool is installed and any trouble codes that have set are cleared. The special functions screen of the scan tool is used to calibrate the steering angle sensor. The instructions on the scan tool are followed to recalibrate the sensor. After the sensor is calibrated, turn the key off and wait for one minute. Then turn the key on and clear any stored trouble codes in the system. ■■ ■■

BRAKE WARNING INDICATORS There are as many indicators of problems to the driver as there are systems to monitor. The customer might report one or more of these indications to you when they see these indications.

Red Brake-Warning Indicator The red brake-warning lamp is usually an indication of a base brake (not antilock- or stability-control-related) system failure, such as low brake fluid. It can also indicate that the parking brake is applied. On a late-model vehicle, the red brake-warning lamp is turned on by the IPC module, as requested by the BCM. The EBCM can also request the red brake-warning lamp if the dynamic rear proportioning system (DRP) system has a problem. Earlier-model vehicles activated an incandescent lamp by providing a ground for the bulb if the brake fluid level was low, the differential brake-warning switch was activated, or the emergency brake was applied. All systems will illuminate the red “brake” warning lamp as a bulb test on start-up.

ABS Indicator The ABS indicator illuminates when there is a problem with the ABS system and has traditionally been an amber color. If the ABS indicator is the only indicator on, the base braking system is still fully functional. The EBCM sends a serial data message to the instrument panel cluster requesting the ABS lamp illumination. The IPC also does a bulb check during startup. The lamp will also be illuminated if the EBCM is not responding to the vehicle network. Of course, if the red brake lamp is on for a base brake problem, then the ABS lamp will also be on because if the base brakes are compromised, so will the ABS function.

“Traction Control Off” Indicator The IPC will turn the “traction off ” indicator when the driver has disengaged the system or if a problem exists that has been detected by the EBCM. Remember that the traction off indication may also come on if a problem in the base brake or ABS system is detected because many of the components are interrelated.

“Stability Control Off” Message A “stability control off ” message can be displayed when a base brake, ABS, or traction control problem, such as the following, exists: ■■ The sensor self-test takes too long to complete. ■■ A failure in a monitored component. ■■ Failure of a module or network wiring.

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■■

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The control solenoids are overheating owing to continuous use; the EBCM will shut the system down long enough for the unit too cool down. The ECM is not able to comply with requests from the EBCM.

Computer-Controlled Electric Steering Like the other components used in the stability control system, the power steering control system is part of the vehicle network (Figure 11-7). Any problem with the vehicle network can cause a problem with the power steering system, so always check for any “U” codes. Electric power steering systems have been coming into their own over the past few years, so a look at diagnostics for an electric steering with a column mounted DC motor will be used in this example. GM used an electric steering column on some GM products. The electrical power steering control module and power steering motors can be replaced on some models, and on others the entire steering column must be replaced. The scan tool can display the torque applied to the steering column in Newton-meters, the rotation of the steering column in degrees, and the vehicle speed as obtained form the ECM. The scan tool is also used to recalibrate the steering position sensor whenever an alignment, accident damage, or module replacement is necessary.

Classroom Manual page 253

DTC C0460 00.  Steering motor rotational sensor- The power steering control module (PSCM) detects open, short to ground, or short between any of the motor rotational sensor circuits. The scan tool should be used to check for the proper reading as the wheel is turned 90 degrees from center in both directions. 1. Disconnect and back probe Terminals 1 and 3 of connector X-2; the reading should be 10-200 ohms (Figure 11-8). If this reading is not obtained, check the wiring to the sensor; if it is OK, then the motor should be replaced. 2. Back probe Terminals 3 and 6 of X-2; the reading should be 3K–10K Ohms (Figure 11-9). If this reading is not obtained, check the wiring to the sensor; if it is okay, then the motor should be replaced. 3. Back probe Terminals 5 and 3 of X-2; the reading should be 6K–20K ohms (Figure 11-10). If this reading is not obtained, check the wiring to the sensor; if it is okay, then the motor should be replaced. 4. Test for greater than 1 megohm of resistance between Terminal 3 and the motor flange (Figure 11-11). This makes sure the wiring is not shorted to ground. 5. If all the circuits test normal, test or replace the power steering control module.

Throttle Actuator Control An important part of stability control is the throttle actuator control (TAC). One of the first things that stability control will do is ask the ECM to back off the throttle and/or reduce the ignition timing before it takes any action at the brakes. The TAC system has a few unique features because it is a “throttle-by-wire” system. The accelerator pedal position (APP) sensor sends the input from the driver to the ECM, the ECM sends the signal

Throttle actuator ­control is an integral part of the stability control system because the throttle application can be controlled by the computer, allowing it to back off the throttle during dangerous situations.

Figure 11-7  An electric power steering rack.

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Chapter 11 10--200 ohms DIGITAL MULTIMETER RECORD

MAX MIN

%

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9 0

HZ

Connector end X-2

MIN MAX

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mV mA A

V

A

V

A

mA A

COM

6

4

3

1

V

Figure 11-8  Checking for resistance across Terminals 1 and 3 of the power steering motor.

3K--10K ohms DIGITAL MULTIMETER RECORD

MAX MIN

%

0 1 2 3 4 5 6 7 8

9 0

HZ

MIN MAX

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Connector end X-2

mV mA A

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A

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mA A

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4

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Figure 11-9  Checking the resistance between Terminals 3 and 6.

to the throttle body module, and the throttle plate is moved according to the driver’s input. Of course, since the throttle is a very important input, if the ECM sees any variation from normal in the throttle position or pedal position sensor signal, the vehicle power and speed are limited to around 25 mph or totally eliminated. The driver may see a “reduced power,” “service stability system,” or similar message along with an illuminated malfunction indicator lamp (MIL). Figure 11-12 shows the approximate readings for the dual TP sensors. There are two sensors made into the same housing. TP sensor 1 starts out at 0 volts and increases with increasing throttle angle. TP sensor 2 starts out at 5 volts and goes to 0 volts at full throttle. Figure 11-13 shows a basic schematic diagram for the system. If the TP sensor, TAC module, or ECM is replaced, then the TP sensor adaptation will have to be relearned.

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6K--20K ohms DIGITAL MULTIMETER RECORD

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9 0

HZ

MIN MAX

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mV V

A

V

A

Connector end X-2

mA A

COM

mA A

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6

4

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1

Figure 11-10  Checking for a grounded internal wiring in the motor case. There should be more than one million ohms resistance.

>1 M ohms DIGITAL MULTIMETER RECORD

MAX MIN

%

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9 0

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MIN MAX

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mV mA A

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A

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6 A

mA A

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Motor case 3

1

Figure 11-11  Checking for a grounded internal wiring in the motor case. There should be more than one million ohms resistance.

Tire Pressure Monitoring Systems If the system is operating normally, and the “check tire pressure” indication is received on the instrument panel, then the tire pressure needs to be checked. If the “service tire monitor” message is displayed, then the system has set a code and needs to be serviced. There are two common problems experienced so far with the TPMS systems. First is the temperature changes that occur during fall and spring can cause the “check tire pressure lamp” to come on. Since temperature and pressure are directly related, lower temperatures mean lower pressures. Secondly, some systems have to be “relearned” when the tires are rotated.

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There is a special tool required on some vehicles to initiate a retraining of the sensors.

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4.17 V 4.02 V 4V TP sensor 2

Voltage

3V

2V TP sensor 1

1V .93 V

.86 V

0%

Throttle opening

100 %

Figure 11-12  Dual TP sensor voltage ranges. (NOTE: There are several types of sensors; always use the chart for your specific vehicle.)

Some systems can relearn their own positions depending on model year and make. Some scan tools can read the condition of the key fob battery as well as the condition of the batteries in the individual tire pressure monitors.

The remote-control door lock receiver is the tire pressure monitoring system (TPMS) module on GM vehicles.

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If the wheel positions are not relearned when the tires are rotated, then many times the owner winds up putting air in the wrong tire if the pressures go low. The tire pressure monitors are located in the wheels and have their own power supply that is expected to last about 10 years. Chrysler tire pressure sensors have three modes of operation: sleep, park, and drive. Sleep mode is used when the sensors are new, and park mode is used when the tires are in stationary and drive modes. Some of the Chrysler tire sensors can learn their own positions with a transponder built into the wheel well near the tire. The transponder can send a signal to the sensor near the wheel; when the sensor responds, the TPMS module can identify the corresponding wheel. The GM tire pressure monitors have two modes of operation: stationary and rolling. In the stationary mode if the pressure does not change, the sensors do not send a signal to the remote-control door lock receiver (RCDLR). When the tires begin to roll, centrifugal force causes the wheel sensors to send a signal to the RCDLR every 30 seconds and a pressure change message to the RCDLR when there is a change in pressure. If a substantial change in pressure is noted, then the warning on the dash is illuminated. On most systems, if the tire pressure is corrected, the warning light will go out after driving the vehicle. With the GM system, trouble codes are set if the sensors do not transmit a signal for 18 minutes, or do not go into “rolling mode” from “stationary mode” when the other wheels have changed from “stationary” to “rolling.” When the wheels are rotated or a sensor replaced, a special tool is available to retrain the sensors to the TPMS module. The TPMS module is placed into the training mode, and the special tool is placed near the valve stem in the special sequence. On some systems,

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TPS 1 Electronic throttle control system M

Throttle body

PCM

Accelerator pedal position (APP) sensor

TPS 2

Figure 11-13  The PCM monitors several signals simultaneously.

when the wheel is learned, the horn will chirp in confirmation. Even on systems that will do their own retrain, it is a good idea not to return a vehicle to the customer with warning lights on.

ACTIVE CRUISE CONTROL Active cruise control systems allow the driver to set the following distance of the vehicle ahead. The brakes can be applied and the throttle reduced anytime a slower vehicle is detected ahead by the system’s radar. Once the path is clear, the cruise control takes the vehicle back to the original set speed. Of course, any malfunction of the communication network or involved system modules of trouble codes will disable the active cruise control (ACC). The cruise control module interprets the data on slower vehicles and asks the ECM and EBCM to control the brake and throttle to maintain a safe distance. The cruise control module even asks for the brake lights to be illuminated when braking is requested (since the driver is not actually hitting the brake pedal). The BCM is the gateway module and interprets the following distance and cruise control switch activation requested by the driver. The BCM also requests that the IPC illuminates a warning lamp on the dash to tell the driver that the active cruise control system is applying the brakes. The system is disabled if the driver applies the throttle or brakes. The EBCM can also shut the system down if it calculates that the brakes are getting too hot from the automatic braking. The transmission control module can help keep the brakes cool by downshifting to slow the vehicle down when requested to do so. DTC C1002 will set for the active cruise control for a Cadillac model. This is a radar misalignment code, and the system has to be aimed mechanically in a method similar to headlamp aiming with a pattern drawn on a wall. If the active cruise control module is replaced, the operation of the system will have to be relearned by driving the vehicle.

The tires are the most important part of vehicle stability control. If the tires are underinflated or severely worn, vehicle safety is compromised.

Cadillac calls their active cruise control distance sensing cruise control (DSCC).

REGENERATIVE BRAKING SYSTEMS Most, if not all, hybrid vehicles use a feature called regenerative braking, which is described in the Classroom Manual Chapter 11 as well. Most drivers are not accustomed to the way regenerative braking feels on application in comparison to the way hydraulic brakes feel. Some drivers may comment that the vehicle tends to slow at different rates, even though the pedal is applied at a steady level. This is due to the action of the various controllers blending the brake operation between regenerative and hydraulic braking. If

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Caution Make certain that all safety precautions are followed whenever working on or around a hybrid vehicle. Always remove the service plug and keep it in your pocket so another technician cannot reinstall the plug. Wear highvoltage gloves and shoes as prescribed by the manufacturer.

a hydraulic pump is employed for assist, the driver may hear and feel the pump running as well. Pressure to the rear brakes can be reduced during regenerative braking through the dynamic rear proportioning feature. Since regenerative braking occurs on the front wheels, this allows the greatest benefit of energy recapture. A regenerative braking sensor gives the EBCM feedback to help provide appropriate blend of regenerative as well as hydraulic braking. Although several codes are available for the regenerative braking system sensor, a closer examination of the two will give a general idea of the basic diagnostic concepts. AUTHOR’S NOTE  If a stability control indicator comes on with no codes stored, turn the key off and then start the vehicle drive until it does its initialization ­self-test. The lamps should be commanded off if there are no problems. Do not replace any components until the self-test is re-run.

DTC C012A 00 Regenerative Axle Pressure Sensor Performance (Chevrolet Volt) The regenerative brake pressure sensor is a pressure transducer that is integral to the brake pressure modulator (Figure 11-14). The diagnostic procedure is very short in this case. This code is one of several for the regenerative pressure transducer; for this code, the signal from the sensor is erratic. When a code for the regenerative sensor sets, the ABS, traction control (TCS), and stability program are turned off for the duration of the key cycle. If the code clears, the code is stored in memory and the red “brake” and “ABS/Stability Control” lights come on, and the driver information center tells the driver that the stability control has been disabled as well. The code will stay in the system for 40 drive cycles, even if the condition that set the code no longer exists. Diagnosis for the code is very straightforward. 1. The vehicle is placed in service mode. 2. The EBCM learn procedure is performed with a scan tool. 3. Next, the system is checked for codes that include the regenerative pressure transducer. 4. If the codes for the transducer reset, replace the brake pressure modulator. 5. If the code resets after the replacement of the brake pressure modulator, the EBCM is replaced and configured for the vehicle.

Hydraulic modulator

EBCM

Figure 11-14  The hydraulic modulator and the EBCM are mounted together and can be serviced separately.

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The procedure seems odd to most of us in that a part is replaced, and if the code resets, then another part must be replaced. Usually, testing is done to make sure that only one part is replaced for a repair. This situation is different; in that the EBCM and the BPMV are connected together, so there are no external connections to check; the scan tool is communicating with the EBCM over the vehicle network, and the EBCM is measuring the performance of the sensor. This means that if the EBCM is giving false indications of the brake pressure transducer, the technician will have no way to tell which part is actually defective because the brake pressure transducer cannot be checked or serviced separately (at least at this time).

C1259/58 HV System Regeneration Malfunction (Toyota Prius) The Toyota Prius uses two motor generators, MG1 and MG2. MG1 is driven by the ­gasoline engine and generates the power to charge the main storage battery. MG2 is generally used as an electric motor drive but will act as a generator when the drive wheels are turning the generator. The Toyota Prius uses regenerative braking that begins as soon as the accelerator pedal is released. The stability control module communicates with the EBCM. If a C1259/58 code sets in the system, the brake and stability control lights come on, but if the problem goes away, the code is not stored in the system. The power management ECU communicates with the stability control module; it sets the code when the module runs its internal check. If the code is current in the system, the procedure to diagnose the code is as follows: 1. Clear the codes from the system. 2. If the code resets, then replace the power management ECU. 3. If the code does not reset, then the system checks are run again to try to duplicate the problem.

ASE-STYLE REVIEW QUESTIONS Multiple Choice 1. Technician A says some manufacturers refer to dynamic rear proportioning as electronic brake distribution, or EBD. Technician B says that some manufacturers refer to dynamic rear proportioning as dynamic rear braking (DRB). Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 2. Technician A says that stability control uses the ABS concepts of controlling wheel lock-up and traction control. Technician B says there are added inputs of a steering wheel position sensor, yaw sensor, and/or lateral accelerometer. Who is correct? A. A only B. B only

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C. Both A and B D. Neither A nor B

3. Technician A says that a diagnostic system check is only important if the complaint cannot be duplicated. Technician B says that the circuit check should be performed anytime a computer system problem is suspected. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 4. The stability control network of modules, depending on the manufacturer, may include all the following modules but one: A. engine control module (ECM) B. power train control module (PCM) C. electronic brake control module (EBCM) D. electronic pedal actuator (EPA) 5. Technician A says any problem with the vehicle network can cause a problem with the electronic power steering system. Technician B says always check for any “S” codes. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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6. Technician A says the yaw sensor/lateral accelerometer sensors can be combined into one sensor. Technician B says only the lateral acceleration sensor can perform a self-test. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 7. Technician A says that the red brake-warning lamp is generally an indication of a base brake failure. Technician B says that the EBCM can turn on the red brake-warning lamp by signaling the IPC. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 8. Technician A says the throttle actuator control can reduce the throttle during an ABS event. Technician B says the accelerator pedal position sensor sends the input from the driver to the ECM, and the ECM sends the signal to the throttle body. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

9. Technician A says that the Prius MG1 motor is driven by the gasoline engine and generates the power to charge the main storage battery. Technician B says MG2 is used only as an electric motor. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 10. Technician A says some of the Chrysler tire ­pressure sensors can learn their own positions with a transponder built into the wheel well near the tire. Technician B says that a special tool can also retrain the tire pressure sensors when the tires are rotated or a sensor is replaced. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

ASE CHALLENGE QUESTIONS 1. Technician A says a tire pressure sensor has at least two modes of operation. Technician B says the tire pressure sensors only transmit signals when the vehicle is sitting still. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

4. Technician A says part or all of the start-up ­initialization may occur at key-on and/or at a ­certain speed while driving. Technician B says some systems perform initialization test during a stability control event. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

2. Technician A says that hybrid vehicles can ­capture some of the energy lost in braking as ­electrical power. Technician B says that the regeneration pressure sensor is built into the hydraulic modulator on the Chevrolet Volt. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

5. Technician A says on the Chevrolet Volt, the EBCM and the brake pressure modulator are connected together, so there are no external connections to check when a code for the regeneration pressure sensor is being checked out. Technician B says the scan tool is communicating with the EBCM over the vehicle network. Who is correct?

3. Technician A says the Toyota Prius uses regenerative braking that begins as soon as the accelerator pedal is applied. Technician B says the Prius stability control module communicates with the LLQW. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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A. A only B. B only

C. Both A and B D. Neither A nor B

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ELECTRONIC BRAKE CONTROL DIAGNOSIS Upon completion of this job sheet, you will be able to inspect and test electronic brake system components. You will also be able to diagnose poor stopping, wheel lock-up, abnormal pedal feel or pulsation, and noise concerns caused by the electronic brake system. ASE Education Foundation Correlation This job sheet addresses the following AST/MAST tasks: G.1. Identify and inspect electronic brake control system components (ABS, TCS, ESC); determine needed action. (P-1) This job sheet addresses the following MAST task: G.3. Diagnose poor stopping, wheel lock-up, abnormal pedal feel, unwanted application, and noise concerns associated with the electronic brake control system; determine needed action (P-2) Tools and Materials Basic hand tools Service manual Protective Clothing Goggles or safety glasses with side shields Describe the vehicle being worked on: Year ______________ Make _______________ Model _______________ VIN _______________ Engine type and size  Procedure

Task Completed

NOTE: Always follow the vehicle manufacturer’s procedures when diagnosing antilock brake systems. In general, ABS diagnostics require three to five different types of testing that must be performed in the specified order listed in the service manual. The types of testing may include the following: pre-diagnostic inspections and test drive, warning light symptom troubleshooting, on-board ABS control module testing (trouble code reading), and individual trouble code or component troubleshooting. Procedures for conducting the system’s self-test and component testing are included in another job sheet. 1. Place the ignition switch in the START position while observing both the red brakewarning light and the amber ABS indicator lights. Both lights should turn on. Start the vehicle. Describe what happened to the lamps, and if the system is functioning normally.   2. With the ignition switch in the RUN position, the antilock brake control module will perform a preliminary self-check on the antilock electrical system. Using the service information as your guide, describe the self-test. Does the vehicle have to be driven to complete the self-test? If it has to be driven, at what speed is the self-test completed?  

h

3. Use the following as guidelines for determining what the brake warning lights are telling you. After comparing your test results with these guidelines, explain what was indicated by the light display you observed.  

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If the EBCM detects a problem with the system, the amber ABS indicator lamp will light to alert the driver to the problem. No antilock braking will be available. Normal, non-antilock brake performance will remain. The red BRAKE warning lamp will be illuminated when the brake fluid level is low, the parking brake switch is closed, the bulb test switch section of the ignition switch is closed, or when certain ABS trouble codes are set.

Task Completed

4. Using a scan tool, check the codes from the system and record them here along with a brief description of the problem area.    5. Conduct a thorough visual inspection of all ABS and brake components. Also check for worn or damaged wheel bearings, and check the condition of the tires and wheels. Look for signs that the vehicle may have poor wheel alignment. Describe what you found and what needs to be done before further diagnosis of the ABS. Remember that faulty base brake system components may cause the ABS system to shut down. Do not condemn the ABS system too quickly.   6. After the visual inspection is completed, and the brakes are stopping the vehicle safely, test drive the vehicle to evaluate the performance of the entire brake system. Begin the test drive with a feel of the brake pedal while the vehicle is sitting still.

h

7. Then accelerate to a speed of about 20 mph. Bring the vehicle to a stop using normal braking procedures. Look for any signs of swerving or improper operation. Describe what happened.   8. Next, accelerate the vehicle to about 25 mph in a safe place away from traffic, and apply the brakes with firm and constant pressure. You should feel the pedal pulsate if the antilock brake system is working properly. Describe what happened.   9. During the test drive, both brake warning lights should remain off. If either of the lights turns on, take note of the condition that may have caused it. After you have stopped the vehicle, place the gear selector into PARK or NEUTRAL and observe the warning lights. They should both be off. Describe what happened.   10. Summarize the condition of the ABS on this vehicle.    

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Problems Encountered    Instructor’s Response   

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PERFORM STABILITY SYSTEM TESTS WITH A SCAN TOOL Upon completion of this job sheet, you will be able to diagnose brake system electronic controls and components using self-diagnosis and/or recommended test equipment.

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ASE Education Foundation Correlation This job sheet addresses the following MAST task: G.4. Diagnose electronic brake control system electronic control(s) and components by retrieving diagnostic trouble codes and/or using recommended test equipment; determine needed action. (P-2) Tools and Materials Scan tool Service information Protective Clothing Goggles or safety glasses with side shields Describe the vehicle being worked on: Year ____________________ Make ____________________ Model____________________ VIN ____________________ Engine type and size  Describe the type of stability system found on the vehicle: Procedure 1. Connect a scan tool and record any trouble codes that might affect the vehicle stability system.   2. Perform a bulletin search for your assigned vehicle, and describe what you found for the ABS or stability control systems. Does your vehicle have any bulletins that apply?  3. Conduct a visual inspection: A. Check the master cylinder fluid level. Record your findings:   B. Inspect all brake hoses, lines, and fittings for signs of damage, deterioration, and leakage. Inspect the hydraulic modulator unit for any leaks or wiring damage. Record your findings:   C. Inspect the brake components at all four wheels. Make sure that no brake drag exists and that all brakes react normally when they are applied. Record your findings:   



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D. Inspect all electrical connections for signs of corrosion, damage, fraying, and disconnection. Record your findings:    E. Describe the process of re-centering (relearning) the steering wheel angle sensor.   F. Describe the type and number of yaw and accelerometers that the vehicle has. Where are these sensors located?   G. If the vehicle is equipped with an active suspension system, describe its operation.  



Problems Encountered    Instructor’s Response   

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DESCRIBE A REGENERATIVE BRAKING SYSTEM Upon completion of this job sheet, you will be able to describe a regenerative braking system on a hybrid vehicle.

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ASE Education Foundation Correlation This job sheet addresses the following MLR/AST/MAST task: G.2.

Describe the operation of a regenerative braking system. (P-3)

Tools and Materials Service information Scan tool Protective Clothing Goggles or safety glasses with side shields Describe the vehicle being worked on: Year ____________________ Make ____________________ Model ____________________ VIN ____________________ Engine type and size  Procedure 1. Write a brief description of how regenerative braking works on the vehicle you have in the shop.    2. Are there any technical bulletins associated with the regenerative braking for this vehicle?    INSTALL A SCAN TOOL CAPABLE OF COMMUNICATING WITH THE STABILITY CONTROL SYSTEM. 3. Are there any codes stored for the regenerative braking system on the vehicle? If so, list them here.    4. How many PIDS are associated with the regenerative braking system. List them here.   

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5. When does the system perform its self-test?    6. Describe how this system behaves differently than a normal braking system. Describe how the system might generate a customer complaint.    7. Describe the problems you may have had while performing this lab.    Problems Encountered    Instructor’s Response   

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Diagnose Vehicle Braking Concerns Caused by Vehicle Modifications

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Upon completion of this job sheet, you will be able to diagnose vehicle braking concerns caused by vehicle modifications. ASE Education Foundation Correlation This job sheet addresses the following MAST tasks: G.8. Diagnose electronic brake control system braking concerns caused by vehicle modifications (tire size, curb height, final drive ratio, etc.). (P-1) Tools and Materials Service information Scan tool

Protective Clothing Goggles or safety glasses with side shields Describe the vehicle being worked on: Year ____________________ Make ____________________ Model ____________________ VIN ____________________ Engine type and size  Procedure 1. Describe the nature of the customer concern.    2. Could this problem be caused by vehicle modifications, such as improper tire size, improper ride height, or wrong final drive ratio?    3. If the customer installs tires of different sizes, describe how this would affect ABS, TCS, and VSC.    4. If the customer installs tires that are bigger than those specified for the vehicle or changes the final drive (differential) ratio, how would this affect wheel speed sensor readings?   

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5. How would a VSC be affected by a change in ride height, specifically a yaw or G-sensor?    6. Does service information for the vehicle being worked on include details about how to reprogram the ECM/PCM for tire size or pinion changes? If so, what are they?   

Problems Encountered    Instructor’s Response   

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Appendix Ase Practice Examination

1. Technician A says that if the master cylinder pushrod is adjusted too long, the brakes might not be able to fully apply. Technician B says that if the master cylinder pushrod is adjusted too short, the brakes might drag. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

6. A vehicle drifts to the right while driving. Technician A says that a crimped line to the left wheel could be the cause. Technician B says that the interior of the right brake hose could be damaged. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

2. While discussing master cylinders, Technician A says normal brake lining wear causes a slight drop in fluid level. Technician B says a sure sign of brake fluid contamination with mineral oil is the swelling of the master cylinder cover diaphragm. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

7. Technician A says service information circuit diagrams or schematics make it easy to identify common circuit problems. Technician B says if several circuits fail at the same time, check for a common power or ground connection. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

3. Technician A says that master cylinder leaks can be internal or external. Technician B says that a leaking master cylinder will remove paint from the area below the master cylinder. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 4. While discussing brake lines, Technician A says that copper tubing can be used for brake lines. Technician B says that brake lines can use doubleflare or an ISO flare fittings. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 5. Technician A says to replace a double-flare fitting with an ISO-type fitting as new brake lines are required. Technician B says that flexible brake hoses allow movement of components. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

8. Technician A says that there is a vacuum check valve in line between manifold vacuum source and the booster. Technician B says this check valve is to allow air pressure into the booster during wide-open throttle operation of the engine. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 9. Drum brakes are being discussed. Technician A says that a grabbing brake could be traced to a leaking axle seal. Technician B says that a leaking wheel cylinder can also cause drum brake grabbing. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 10. Before trying to remove a brake drum for service, Technician A uses the self-adjuster to back off the brake shoes. Technician B adjusts the parking brake cable to remove the slack. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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11. While discussing brake lining damage, Technician A says that uneven wear from side to side on any one set of shoes can be caused by a tapered drum. Technician B says linings ­contaminated with brake fluid must be replaced. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 12. While discussing a “threaded” brake drum, Technician A says an extremely dull tool bit or a lathe that turns too slowly can cut a thread into the drum surface. Technician B says that during brake application, the shoes ride outward on the thread, then snap back with a loud crack. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 13. While discussing drum refinishing, Technician A says that the drum machining debris should be cleaned with brake cleaner. Technician B says that hot, soapy water should be used. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 14. Technician A says that the drum discard dimension is the maximum diameter to which the drums can be refinished. Technician B says that the drum discard diameter is the maximum allowable wear dimension. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 15. The rear brakes are being serviced. Technician A says that the small drum-within-disc for the parking brake should be machined in the same manner and as frequently as a regular drum. Technician B says that the parking brake may be applied by an electric motor attached directly to the front brake caliper. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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16. Technician A says some parking brakes use three cables, a front cable, and two rear cables. Technician B says that some parking brakes use an electrically operated motor to apply the parking brakes. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 17. Technician A says the parking brake lever is hinged at the top of the web of the secondary or trailing shoe. Technician B says the parking brake strut transfers movement from the parking brake lever to both shoes. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 18. Technician A says that tapered wheel bearings retainer nut should be torqued to 60 foot-pounds after repacking. Technician B says that tapered roller bearings should be cleaned in gasoline and repacked. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 19. Disc brake calipers are being discussed. Technician A says that a single caliper may have one, two, or more pistons. Technician B says that the piston seal is known as an O-ring seal. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 20. When discussing disc brake pads, Technician A says that organic linings are a composite material made from bonding nonmetallic fibers. Technician B says that asbestos brake pads are still being imported into the United States. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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541

21. Two technicians are discussing a disc brake ­caliper. Technician A says that calipers use springs to retract the seals after a brake ­application. Technician B says that fixed calipers typically use one piston. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

27. Technician A says the amount of braking power from a vacuum booster is directly related to the area of the diaphragm. Technician B says a booster with a small diaphragm would provide more power assist. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

22. Technician A says after a rotor has been machined, a nondirectional finish must be applied. Technician B says after a rotor has been machined, it should be cleaned in hot soapy water. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

28. Technician A says that vacuum is retained by the check valve from the booster when the engine is turned off. Technician B says that vacuum is on one side of the booster diaphragm when the engine is turned off. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

23. A vehicle with disc brakes has uneven brake pad wear. Technician A says to check for binding slide pins. Technician B states this could be caused by a sticking caliper piston. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

29. Technician A says that a hydro-boost unit utilizes hydraulic pressure from the power steering pump to provide boost. Technician B says that the hydroboost unit uses an accumulator that can provide power assist in case the engine dies. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

24. A vehicle has a pulsation when coming to a stop and applying the brakes. What is a possible cause? A. Excessive wheel runout B. Excessive rotor runout C. A leaking grease seal D. A frozen caliper 25. While discussing audible brake wear sensors, Technician A says if the replacement pads have audible wear sensors, the pad must be installed so that the sensor is at the leading edge of the pad in relation to wheel rotation. Technician B says this does not mean at the top or front of the caliper. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 26. Vacuum power brake boosters are being discussed. Technician A says a soft brake pedal could be caused by a defective brake booster diaphragm. Technician B says a soft pedal could also be caused by a vacuum leak. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

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30. Technician A says that a too-low current draw may mean that an actuator or sensor is not functioning properly. Technician B says that an actuator can monitor module and sensor operation electronically. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 31. While discussing ABS and traction control ­s ystems, Technician A says most of the same components are used in both systems. Technician B says the TCS also interfaces with the engine (PCM) and transmission (TCM) control modules to prevent wheel slip. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 32. Technician A says that the speed of a wheel is calculated by the ABS module from the signal generated by a wheel sensor. Technician B says that a wheel speed sensor can be analog or digital. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B

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Appendix

33. Technician A says that antilock brakes regulate the brake pressure to all the wheels at the same time. Technician B says that antilock brakes all require DOT 5 brake fluid. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 34. Technician A says that tires in poor condition can affect ABS operation. Technician B says that ABS can compensate for base brake problems. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 35. Technician A says that a wheel speed sensor can be affected by a missing tooth on the tone ring. Technician B says that the tone ring and the wheel speed sensor have to be replaced as a set. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 36. Technician A says ABS brakes require a hydraulic booster. Technician B says that ABS can use a vacuum or hydraulic booster. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 37. While discussing rotor machining, Technician A says that a scratch cut can reveal mounting problems before machining begins. Technician B says a measurement of rotor thickness is necessary after machining is finished. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B 38. While discussing brake pedal position sensors, Technician A says the BCM monitors the position of the brake pedal position sensor and sends this information to the EBCM. Technician B says that brake pedal position sensor signal is a critical input to the vehicle stability control system. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

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39. Technician A says that brake fluid should be stored with the container cap on tightly to prevent evaporation. Technician B says brake fluid must be stored in an air-tight container to prevent the absorption of water. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 40. While discussing brake fluid, Technician A says DOT 3 brake fluid is used by most vehicles today. Technician B says that DOT 5 can be ­substituted for DOT 3 with no problems. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 41. Technician A says that a leaking brake line can be spliced with a compression fitting. Technician B says that a brake line has to be replaced, not repaired. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 42. Technician A says that it is acceptable to clean a brake assembly off with an air hose or dry brush. Technician B says if brake fluid contacts a painted surface, wash it off immediately. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 43. While discussing ABS brakes, Technician A says ABS is excellent in improving stopping distance. Technician B says ABS is excellent in directional control. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 44. Technician A says that a solenoid converts mechanical action to electric energy. Technician B says that an actuator uses electric current to perform a mechanical action. Who is correct? A. A only C. Both A and B B. B only ­D. Neither A nor B

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Ase Practice Examination

45. Technician A says the ABS is monitoring the speeds of all four wheels. Technician B says the first step in ABS action is the isolation of the wheel that is slowing down the fastest when ­braking. Who is correct? A. A only B. B only

C. Both A and B D. Neither A nor B

46. Technician A says that a hydraulic system can transmit power and force. Technician B says that a hydraulic system can multiply force. Who is correct? A. A only B. B only

C. Both A and B D. Neither A nor B

47. Technician A says that the master cylinder has two separate hydraulic systems in case one fails. Technician B says that the force from the master cylinder is reduced by the larger area of the caliper piston. Who is correct? A. A only B. B only

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C. Both A and B D. Neither A nor B

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48. Technician A says that the output frequency of the wheel speed sensor decreases with speed. Technician B says that a permanent magnet wheel speed sensor produces a DC voltage signal. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 49. Technician A says brake systems use hydraulics to increase force for brake application. Technician B says this is called mechanical ­advantage. Who is correct? A. A only C. Both A and B B. B only D. Neither A nor B 50. Technician A says dynamic rear proportioning (DRP) uses active control and the existing ABS to regulate brake pressure to the rear wheels. Technician B says dynamic rear proportioning (DRP) works to prevent rear wheel lock-up during hard braking. Who is correct? C. Both A and B A. A only B. B only D. Neither A nor B

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GLOSSARY GLOSARIO

Note: Terms are highlighted in bold, followed by Spanish translation in color. 1,1,1-Trichloroethane  1,1,1-Trichloroethane is a chlorinated cleaning solvent often used in aerosol brake cleaners. 1,1,1-Tricloroetano  1,1,1-El Tricloroetano es un solvente ­clorinado para limpieza a menudo utilizado en limpiadores de frenos en aerosol. accumulator  A container that stores hydraulic fluid under pressure. It can be used as a fluid shock absorber or as an alternate pressure source. A spring or compressed gas behind a sealed diaphragm provides the accumulator pressure. Acumulador  Un recipiente que almacena líquido hidráulico bajo presión. Este puede ser utilizado como líquido amortiguador o como una fuente de presión alterna. Un resorte o gas comprimido detrás de un diafragma sellado proporciona presión al acumulador. Active braking system  A braking system that uses radar to detect hazards in front of the vehicle. Many have the ability to apply the brakes if the driver does not respond to warnings to stop. Sistema de frenado activo  Un sistema de frenado que utiliza radar para detectar peligros frente al vehículo. Muchos tienen la capacidad de aplicar los frenos si el conductor no responde a advertencias de detenerse. American Wire Gauge (AWG)  A system for specifying wire size (conductor cross-sectional area) by a series of gauge numbers. The lower the number, the larger the wire cross section. Calibre de Cable Americano (AWG) Un sistema  Para especificar el tamaño del cable (área de la sección transversal del conductor) por medio de calíbres numéricos. Entre menor sea el número, mayor será la sección transversal del cable. Amplitude  Signal strength or the maximum measured value of a signal. Amplitud  Intensidad de la señal, o el máximo valor medido de una señal. Analog  A signal that varies proportionally with the information that it measures. In a computer, an analog signal is voltage that fluctuates over a range from high to low. Análogo  Una señal que varía proporcionalmente con la información que mide. En una computadora, una señal análoga es voltaje que fluctúa sobre un rango de alto a bajo. Aqueous  Water based. Acuoso  Con agua como base. Asbestos  The generic name for a silicate compound that is very resistant to heat and corrosion. Its excellent heat dissipation abilities and coefficient of friction make it ideal for automotive friction materials, such as clutch and brake linings. Asbestos fibers are a serious health hazard if inhaled, however. Asbesto  El nombre genérico de un compuesto de silicato que es muy resistente al calentamiento ycorrosión. Sus excelentes capacidades de disipación de calor y coeficiente de fricción lo hacen ideal para materiales de fricción para automoción, como el embrague y revestimientos de frenos. Sin embargo, las fibras de amianto constituyen un serio peligro para la salud si se inhalan, sin embargo.

Asbestosis   A progressive and disabling lung disease caused by inhaling asbestos fibers over a long period of time. Asbestosis  Una enfermedad pulmonar progresiva e incapacitante causada por inhalar fibras de asbesto durante un largo periodo de tiempo. Aspect ratio  The ratio of the cross-sectional height to the crosssectional width of a tire expressed as a percentage. Relación de aspecto La  Relación entre la altura de la sección transversal y el ancho de la sección transversal de un neumático expresada como un porcentaje. Automated bleed procedure  A special mode that allows removal of trapped air in an ABS system requiring a scan tool to initiate. Procedimiento de sangrado automatizado  Un modo particular que permite la eliminación de aire atrapado en un sistema ABS; necesitando una herramienta de escaneo para iniciar. autoranging  A feature of an electrical test meter that lets it shift automatically from one measurement range to another for a given value such as voltage or resistance. Autorango Una  Característica de un medidor de prueba eléctrico que permite cambiar automáticamente de una escala de medida a otra para un valor determinado, como tensión o resistencia. Backing plate  The mounting surface for all other parts of a drum brake assembly except the drum. Placa de refuerzo  La superficie de montaje para todas las otras partes de un ensamblaje de frenos de tambor, excepto el tambor. Banjo fitting  A round, banjo-shaped tubing connector with a hollow bolt through its center that enables a brake line to be connected to a hydraulic component at a right angle. Ajuste del cárter  Conector redondo, en forma de banjo, atravesado en el centro por un perno ahuecado, que permite conectar una línea de frenos a un componente hidráulico en el ángulo correcto. Bearing driver  A special tool used to press a bearing race into a rotor. Llave para balinera  Una herramienta especial que es utilizada para presionar una balinera un rotor. Bearing end play  The designed looseness in a bearing assembly. Holgura de la balinera La  Flojedad diseñada para el ensamblaje de la balinera. Bearing packer  Special tool used to pack grease into a bearing. Embalador de balinera  Herramienta especial que es utlizada para embalar grasa en una balinera. bedding-in  See burnishing. Lustre  Véase satinado. Bench bleeding  The process of filling a master cylinder with brake fluid, clamping it in a vise, and bleeding air from it before installing it on a vehicle. Sangrado de banco  Proceso de relleno de un cilindro maestro con líquido de frenos sujetándolo con un tornillo y sangradodel aire antes de instalarlo en un vehículo.

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Glossary Bleeder screw  A screw that opens and closes a bleeding port in a caliper or a wheel cylinder. Tornillo de sangrado  Tornillo que tapa y destapa el puerto de sangrado en un émbulo o en un cilindro de la rueda. Brake bleeding  A procedure that pumps fresh brake fluid into the brake hydraulic system and forces out air bubbles and the old aerated fluid through bleeding ports in calipers and wheel cylinders. Sangrado de frenos  Procedimiento que inyecta líquido de frenos nuevo al sistema de frenos y obliga a salir a las burbujas de aire y al líquido viejo en forma de gas por los puertos de sangrado y émbulos de las ruedas ruedas. Brinelling  Damage to a bearing caused by an impact. Hendiduras  Daño en una balinera provocado por un golpe. Brush hone  A cylinder hone made of abrasive modules attached to flexible nylon cords that are attached to the hone shaft. A brush hone removes peaks or high spots on the surface of a cylinder bore and produces a flattened or plateaued finish. Also called a flex hone. Cepillo pulimentador  Cilindro hecho de módulos abrasivos unidos a cuerdas de nylon flexible que estan unidas al eje del pulimentador. El cepillo de pulimentar elimina picos o partes altas en la superficie del hueco de un cilindro y realiza un acabado plano o liso. También llamado pulimentador flexible. Burnishing  The process of applying friction materials to each other to create a desired wear pattern. Satinado El  Proceso de aplicación de manera recíproca de materiales de fricción para crear un patrón de desgaste deseado. Camber  The inward or outward tilt of the wheel measured from top to bottom and viewed from the front of the car. Combadura  La combadura hacia adentro o hacia afuera de la rueda medida desde arriba hacia abajo y vista desde la parte de enfrente del vehículo. Canadian Center for Occupational Health and Safety (CCOHS)  A Canadian federal agency similar to the U.S. OSHA with a similar mandate, responsibility, and authority. Centro de Salud y Seguridad Ocupacional Canadiense (CCOHS)  Una agencia federal canadiense parecida a la OSHA de EE.UU. con un mando, responsabilidad y autoridad similar. Carbon monoxide  A poisonous gas that is a by-product of incomplete combustion; also an air pollutant. Monóxido de carbono Un  gas venenoso que es derivado de una combustión incompleta; también es un contaminante atmósferico. caster  The backward or forward angle of the steering axis viewed from the side of the car. Inclinación del eje  El ángulo trasero o delantero del eje de dirección visto desde el costado del auto. Center high-mounted stoplamp (CHMSL)  A third stoplamp on vehicles built since 1986, located on the vehicle centerline no lower than 3 inches below the rear window (6 inches on convertibles). Luz trasera alta de frenado (CHMSL)  Una tercera luz de frenado en vehículos construida desde 1986, situada en el centro del vehículo no más de 3 pulgadas por debajo del vidrio trasero (6 pulgadas en los convertibles). Chlorinated hydrocarbon solvents  Solvents used because of the ability to dissolve oils, greases, and other materials. Disolventes de hidrocarburos clorados  Solventes que son utilizados debido a su capacidad para disolver aceites, grasas y otros materiales.

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cold inflation pressure  The tire inflation pressure after a tire has been standing for 3 hours or driven less than 1 mile after standing for 3 hours. Presión de inflado en frío  La presión de inflado del neumático después que ésta ha estado en reposo por tres horas o haber recorrido menos de 1 milla después de haber estado en reposo por 3 horas. Cross-feed  The distance the cutting bit of a brake lathe moves across the friction surface during each lathe revolution. Alimentación transversal  La distancia que recorre la punta de corte de un torno de freno a lo largo de la superficie de fricción durante cada revolución del torno. Crosshatch  A crisscross pattern formed by a cylinder hone. Cruceta  Un patrón entrecruzado formado por un pulimentador de cilindros. cup expander  A metal disc that bears against the inner sides of wheel cylinder seals to hold the seal lips against the cylinder bore when the brakes are released. This keeps air from entering the cylinder past the retracting pistons and seals. Expansor de copa  Un disco metálico que se sostiene de los lados internos de los empaques del cilindro de la rueda para sujetar los bordes de los empaques al accionar los frenos. Esto impide que el aire entre al cilindro más allá de los pistones y los sellos. cup seal  A circular rubber seal with a depressed center section surrounded by a raised sealing lip to form a cup. Cup seals are often used on the front ends of hydraulic cylinder pistons because they seal high pressure in the forward direction of travel but not in the reverse. Sello de copa  Junta de goma circular con una sección central hundida rodeada por un borde de junta saliente que forma una copa. Los sellos de copa a menudo se usan en los extremos frontales de los pistones de los cilindros hidráulicos porque impiden el paso de alta presión hacia delante pero no en el ­sentido contrario. current code  A current code is indicating that the fault is ­present at the time of testing. código actual  Un código actual indica que la falla está presente en el momento de la prueba. cylinder hone  An abrasive tool used to remove dirt, light corrosion, and machining irregularities from a cylinder bore. pulimentador de cilindros  Herramienta abrasiva usada para eliminar la suciedad, la corrosión leve y las irregularidades de la superficie interior de un cilindro. Department of Transportation (DOT)  The U.S. government executive department that establishes and enforces safety regulations for motor vehicles and for federal highway safety. Departamento de Transportes (DOT)  El departamento ejecutivo del Gobierno de los EE.UU. que establece y hace cumplir las normas de seguridad para vehículos a motor y para la seguridad vial federal. diagnostic energy reserve module (DERM)  Used to test the air bag system, store codes if a fault is detected, and supply the system with a prime voltage. módulo de diagnóstico de reserva de energía (DERM) Se usa para probar el sistema de air bag, almacenar códigos si se detecta un fallo, y proporcionar tensión principal al sistema. diagnostic trouble code (DTC)  A numerical code generated by an electronic control system that has self-diagnostic capabilities as the result of a system self-test or monitoring to indicate a problem in a circuit or subsystem or to indicate a general condition that is out of limits; also called trouble codes, service codes, or fault codes by various carmakers.

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Glossary

código de problema de diagnóstico (DTC)  Código numérico generado por un sistema electrónico de control que posee capacidades de autodiagnóstico como resultado de una prueba o control propio del sistema para indicar un problema en un circuito o subsistema, o para indicar una condición general que se sale de los límites; los diversos fabricantes de automóviles también los denominan códigos de problemas, códigos de servicio o códigos de fallos. diaphragm  A flexible membrane, usually made of rubber, that isolates two substances or areas from each other. A rubber diaphragm isolates brake fluid in the master cylinder reservoir from the air. A diaphragm separates the two chambers of a power brake vacuum booster. diafragma  Membrana flexible, por lo común de goma, que aisla una sustancia o una zona de otra. Un diafragma de goma aísla del aire el líquido de frenos en el depósito del cilindro maestro. Un diafragma separa las dos cámaras de un reforzador de vacío en frenos de potencia. digital  A signal that is either on or off and that is translated into the binary digits 0 and 1. In a computer, a digital signal is voltage that is low or high or current flow that is on or off. digital  Señal que está activada o desactivada y que se traduce por los dígitos binarios cero y uno. En un computador, una señal digital es una tensión alta o baja, o flujo de corriente que está abierto o cerrado. digital multimeter (DMM)  A volt, ohm, milliamp meter— also called a volt-ohm-milliamp (VOM) meter or a digital volt-ohmmeter (DVOM)—that tests voltage, resistance, and current. multímetro digital (DMM)  Medidor de voltios, ohmios, miliamperios—también llamado medidor VOM o medidor digital de voltios-ohmios (DVOM)—que prueba la tensión, la resistencia y la corriente. digital storage oscilloscope (DSO)  Oscilloscope that stores digital images of voltages over time. osciloscopio de almacenamiento digital (DSO) Osciloscopio que almacena imágenes digitales de voltajes a través del tiempo. discard diameter  The maximum inside diameter that is cast or stamped on a brake drum. The discard diameter is the allowable wear dimension, not the allowable machining dimension. diámetro de descarte  El diámetro interior máximo que se funde o estampa en un tambor de frenos. El diámetro de descarte es la dimensión de desgaste tolerable, no la dimensión de moldeo permisible. discard dimension  The minimum thickness of a brake rotor or the maximum diameter of a drum. If disc or drum wear exceeds the discard dimensions, the disc or drum must be replaced. A disc or drum should never be machined to the discard dimension. dimensión de descarte  Grosor mínimo de un rotor de frenos o diámetro máximo de un tambor. Si el desgaste del disco o el tambor excede las dimensiones de descarte, el disco o el tambor deben reemplazarse. Nunca se debe disponer un disco o tambor hasta la dimensión de descarte. DOT 3, DOT 4, and DOT 5  U.S. Department of Transportation specification numbers for hydraulic brake fluids. DOT 3, DOT 4 y DOT 5  Números de especificación del Departamento de Transportes de los EE.UU. para los líquidos de frenos hidráulicos. double flare  A type of tubing flare connection in which the end of the tubing is flared out and then is formed back on to itself. doble ensanche  Tipo de conexión de tubos en la que el extremo del tubo se acampana y luego se vuelve a doblar.

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drum web  The closed side of a brake drum. membrana del tambor  Lado cerrado de un tambor de freno. duo-servo brake  A drum brake that develops self-energizing action on the primary shoe, which in turn applies servo action to the secondary shoe to increase its application force. Brake application force is interrelated for the primary and the secondary shoes. Also called a dual-servo or a full-servo brake. freno servoduo  Freno de tambor que desarrolla acción autónoma sobre la zapata primaria, que a su vez aplica servoacción a la zapata secundaria para aumentar su fuerza de aplicación. La fuerza de aplicación de freno es interrelacionada para las zapatas primarias y las secundarias. También se conoce como freno servo dual o totalmente asistido. electromotive force (EMF)  The proper terminology for voltage. EMF always creates a magnetic field around a conductor. This may interfere with EMF (or the voltage signal) in an adjacent conductor. fuerza electromotriz (EMF)  La terminología apropiada para el voltaje. EMF crea siempre un campo magnético alrededor de un conductor. Esto puede interferir con EMF (o la señal del voltaje) en un conductor adyacente. electrostatic discharge (ESD)  Dischage of static electricity from a non-conductive surface to a conductive surface. descarga electrostática (ESD)  Descarga de electricidad estática de una superficie no conductora a una superficie conductora. Environmental Canada  The Canadian version of the U.S. EPA with requirements that relate to Canada’s more northern environment and citizens. Environmental Canada  La versión canadiense de la EPA de EE.UU. con requisitos que se relacionan a los medioambientes y ciudadanosdel norte de Canadá. Environmental Protection Agency (EPA)  The U.S. government executive department that establishes and enforces regulations to protect and preserve the physical environment, best known for regulations relating to air quality. Agencia Protectora del Medio Ambiente (EPA)  Departamento gubernamental de EE.UU. que establece y hace cumplir las normas que protegen y preservan el entorno f ísico, más conocido por las normas que regulan la calidad del aire. equalizer  Part of the parking brake linkage that balances application force and applies it equally to each wheel. The equalizer often contains the linkage adjustment point. compensador  Parte del acoplamiento del freno de estacionamiento que equilibra la fuerza ejercida y la aplica por igual en ambas ruedas. Con frecuencia, el compensador incluye el punto de ajuste del acoplamiento. etching  Damage to a bearing surface by corrosive substances. decapado  Daño a la superficie de un cojinete provocado por sustancias corrosivas. Extraction Procedures (EP)  Materials that leach one or more heavy metals in concentrations greater than 100 times primary drinking water standard concentrations are considered toxic. Procedimientos de extracción (EP)  Los materiales que dejan filtrar uno o varios metales pesados en concentraciones que superan cien veces las normas básicas para el agua potable se consideran tóxicos. Federal Motor Vehicle Safety Standards (FMVSS)  The U.S. government regulations that prescribe safety requirements for various vehicles, including passenger cars and light trucks. The FMVSS regulations are administered by the U.S. Department of Transportation (DOT).

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Glossary Estándares Federales de Seguridad para Vehiculos Automotor (FMVSS)  Las regulaciones del gobierno de los Estados Unidos que establecen requisitos de seguridad para varios vehículos, incluyendo automóviles de pasajeros y camiones de carga. Las regulaciones de los FMVSS son administradas por Departamento de Transporte de Estados Unidos. fixed caliper brake  A brake caliper that is bolted to its support and does not move when the brakes are applied. A fixed caliper must have pistons on both the inboard and the outboard sides. Calibrador fijo de freno  Un calibrador de freno que está empernado a su soporte y que no se mueve al accionar los frenos. Un calibrador fijo debe tener pistones tanto en el lado exterior como en el interior. Floating caliper  A caliper that is mounted to its support on two locating pins or guide pins. The caliper slides on the pin in a sleeve or bushing. Because of its flexibility, this kind of caliper is said to float on its guide pins. Calibrador flotante  Un calibrador que esta montado a su soporte sobre dos patas o pernos. El calibrador corre sobre el perno en una camisa o bushin. Debido a su flexibilidad, se dice que éste tipo de calibrador flota sobre sus pernos. Floating drum  A brake drum that is separate from the wheel hub or axle. A floating drum usually is held in place on studs in the axle flange or hub by the wheel and wheel nuts. Tambor flotante  Un tambor de freno que está separado del cubo o eje de la rueda. Un tambor flotante está usualmente sujetado en su lugar con espárragos en la brida del eje cerca de la rueda y tuercas de la rueda. Floating rotor  A rotor and hub assembly made of two separate parts. Rotor flotante  Un rotor y un ensamblaje de eje hecho de dos partes separadas. Force  Power working against resistance to cause motion. Fuerza  Energía que opera en contra de la resistencia para producir movimiento. friction  The force that resists motion between the surfaces of two objects or forms of matter. Fricción  La fuerza que opone resistencia al la frición entre las superficies de dos objetos o formas de material. fusible link  A wire of smaller gauge that is connected into a circuit to act as a fuse. A fusible link will melt when exposed to excessive current to protect other circuit components. Enlace de fusible  Un alambre de menor calibre que es conectado a un circuito para actuar como un fusible. Los enlaces de fusibles se derriten cuando son expuestos a una excesiva corriente para proteger otros componentes del circuito. galling  Smearing of metal on a bearing surface due to a lack of lubrication. corrosión  Difuminado de metal en la superficie de un cojinete debido a la falta de lubricación. graphing meters  Electronic diagnostic instruments that come in different sizes and capabilities and that can graph the flow of electrical values; commonly known as scopes or oscilloscopes. Medidores gráficos  Herramientas de diagnóstico electrónico que son de diferentes tamaños y capacidades, y que pueden graficar el flujo de los valores eléctricos; se les conoce comúnmente como ámbitos u osciloscopios. gravity bleeding  The process of letting old brake fluid and air drain from the brake hydraulic system through a wheel bleeder screw.

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extracción de vapor de la gravedad  Proceso que permite drenar el líquido de frenos sucio y el aire del sistema hidráulico de frenos a través de un tornillo extractor de vapor de la rueda. hard code  A diagnostic trouble code from a vehicle computer that indicates a problem that is present at the time of testing; may or may not keep the system from operating. May also be called a current code. Código dif ícil  Un código de diagnóstico de problemas de la computadora de un vehiculo el cual indica un problema que está presente al momento de prueba; pudiése o no impedir que el sistema opere. hard spots  Circular blue-gold glazed areas on drum or rotor ­surfaces where extreme heat has changed the molecular ­structure of the metal. puntos duros  Zonas circulares vidriadas de color oro azulado en las superficies del tambor o del rotor, que aparecen donde el calor excesivo ha cambiado la estructura molecular del metal. heat checks (heat checking)  Small cracks on drum or rotor ­surfaces that usually can be machined away. grietas térmicas  Pequeñas fisuras en las superficies del tambor o del rotor que normalmente se pueden hacer desaparecer con una máquina. heat-shrink tubing  Plastic tubing that shrinks in diameter when exposed to heat; used to insulate electrical wiring and repairs. tuberías que se contraen con calor  Cañerías de plástico que encogen al ser expuestas al calor; se usan para aislar cables eléctricos y en reparaciones. height-sensing proportioning valve  A proportioning valve in which hydraulic pressure is adjusted automatically according to the vertical movement of the chassis in relation to the rear axle during braking; sometimes also called a weight-sensing proportioning valve. válvula dosificadora de detección de altura  Válvula dosificadora en la que la presión hidráulica se ajusta automáticamente según el movimiento vertical del chasis en relación con el eje trasero durante el frenado; a veces también se la denomina válvula dosificadora de detección de peso. high-efficiency particulate air (HEPA) filter  A filter that removes the smallest particulates from air. filtro de macropartículas de aire de gran eficiencia (HEPA)  Filtro de aire que retiene las partículas más pequeñas. high impedance  High input resistance provided by a digital meter. alta impedancia  Gran resistencia de entrada proporcionada por un medidor digital. History code  A history code is a code that set in the past, but now the problem that caused the code to set is not present. This adversely affects diagnosis. Sometimes called a soft code. Código de historia  Un código de historia es un código que se estableció en el pasado, pero el problema que causó que el código se estableciera ya no está presente. Esto afecta negativamente el diagnóstico. A veces llamado código suave. hold-down springs  Small springs that hold drum brake shoes in position against the backing plate while providing flexibility for shoe application and release. resortes de sujeción  Pequeños resortes que mantienen las zapatas de frenos de tambor en posición contra la placa de refuerzo, a la vez que dan flexibilidad para aplicar y soltar la zapata. hydro-boost  A hydraulic power brake system that uses the power steering hydraulic system to provide boost for the brake system.

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reforzador hidráulico  Sistema hidráulico de frenos de potencia que utiliza el sistema hidráulico de dirección de potencia para reforzar el sistema de frenado. hydroplane  The action of a tire rolling on a layer of water on the road surface instead of staying in contact with the pavement. Hydroplaning occurs when water cannot be displaced from between the tread and the road. aquaplaning  Acción de un neumático que rueda sobre una capa de agua sobre la superficie vial en lugar de mantenerse en contacto con el pavimento. El “aquaplaning” se produce cuando no se puede desplazar el agua entre los dibujos del neumático y la calle. hygroscopic  The chemical property or characteristic of attracting and absorbing water, particularly out of the air. Polyglycol brake fluids are hygroscopic. higroscópico  Que posee la propiedad química o característica de atraer y absorber agua, en especial del aire. Los líqui-dos de frenos con poliglicol son higroscópicos. integral ABS  ABS unit that incorporates the master cylinder, hydraulic modulator, and in some cases the electronic brake control module. sistema de ABS integral  Unidad de ABS que incorpora el cilindro maestro, el modulador hidráulico y, en algunos casos, el módulo de control de freno electrónico. International System of Units or metric system International System of Units or metric system is the modern international metric system used by the automotive industry and other industries. Sistema Internacional de Unidades o Sistema Métrico  El Sistema Internacional de Unidades o Sistema Métrico es el moderno sistema metrico internacional usado por la industria automotriz y otras industrias. ISO flare  A type of tubing flare connection in which a bubbleshaped end is formed on the tubing; also called a bubble flare. ensanche ISO  Tipo de conexión con ensanche del tubo en el cual un extremo toma forma de burbuja; también se le llama ensanche de burbuja. lateral runout  A side-to-side variation or wobble as the tire and wheel are rotated. desviación lateral  Variación u oscilación de un lado a otro cuando se hacen girar el neumático y la rueda. leading shoe  The first shoe in the direction of drum rotation in a leading-trailing brake. When the vehicle is going forward, the forward shoe is the leading shoe, but the leading shoe can be the front or the rear shoe depending on whether the drum is rotating forward or in reverse and whether the wheel cylinder is at the top or the bottom of the backing plate. The leading shoe is self-energizing. zapata tractora  Primera zapata en la dirección de giro del tambor en un freno de tracción-remolque. Cuando el vehículo avanza, la zapata delantera es la tractora, pero la zapata tractorapuede ser la delantera o la trasera dependiendo de si el tambor está girando hacia delante o hacia atrás y de si el cilindro de la rueda está en la parte superior de la placa de refuerzo o en la inferior. La zapata tractora es autónoma en cuanto a energía. leading-trailing brake  A drum brake that develops self-energizing action only on the leading shoe. Brake application force is separate for the leading and the trailing shoes. Also called a partial-servo or a nonservo brake. freno tracción-remolque  Freno de tambor que desarrolla una acción autónoma sólo sobre la zapata tractora. La fuerza de aplicación de freno es independiente para las zapatas tractoras y para las de remolque. También se conoce como freno parcialmente asistido o freno no asistido.

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linear  In a straight line. lineal  En línea recta. loaded calipers  Pairs of calipers sold as service replacements that have been overhauled and are loaded with new pads. The complete caliper assembly is ready to install when purchased. calibres cargados  Pares de calibres vendidos como repuestos revisados y a los que se han colocado nuevas pastillas. Al comprarlo, el conjunto está listo para ser instalado. manual bleeding  The process of using the brake pedal and master cylinder as a hydraulic pump to expel air and brake fluid from the system. Manual bleeding is a two-person operation. extracción de vapor manual  Uso del pedal del freno y el cilindro maestro como bomba hidráulica como procedimiento para expulsar el aire y el líquido de frenos del sistema. La extracción de vapor manual es una operación para realizar entre dos. material safety data sheets (MSDS)  Information sheets issued by the manufacturers of hazardous materials. An MSDS provides detailed information on dangerous ingredients, corrosiveness, reactivity, toxicity, fire and explosion data, health hazards, spill and leak procedures, and special precautions. Federal law requires that an MSDS be available for each hazardous material in your workplace. hojas de datos de seguridad de materiales (MSDS)  Hojas de información proporcionadas por los fabricantes de materiales peligrosos. Una MSDS ofrece información detallada sobre ingredientes peligrosos, corrosión, capacidad de reacción, toxicidad, datos sobre incendios y explosiones, peligros para la salud, procedimientos en caso de derrame o goteo de estos materiales, y precauciones especiales a tomar. La ley federal exige que haya una MSDS para cada material peligroso en el lugar de trabajo. maximum refinishing limit  A brake rotor measurement that determines the point at which a rotor should not be refinished even if the minimum thickness is correct. Límite máximo de re-acabado  Medida del rotor del freno que determina el punto en el que al rotor no debe de dársele un reacabado aun si está correcto el grosor mínimo. metering valve  A hydraulic control valve used primarily with front disc brakes on RWD vehicles. The metering valve delays pressure application to the front brakes until the rear drum brakes have started to operate. válvula de dosificación  Válvula de control hidráulica que se usa principalmente con frenos delanteros de disco en vehículos RWD. La válvula de dosificación demora la aplicación de presión a los frenos delanteros hasta que hayan comenzado a funcionar los frenos traseros de tambor. multiple  A metric measurement unit that is larger than the stem unit through multiplying by a power of ten. múltiplo  Unidad del sistema métrico mayor que la unidad base, que resulta de multiplicar por una potencia de diez. nondirectional finish  A finish on the surface of a rotor that will not start a premature wear pattern on the pads. The nondirectional sanded surface also helps pad break in and reduces brake noise. pulido adireccional  Pulido de la superficie de un rotor que no muestra un patrón de desgaste prematuro en las pastillas. Una superficie lijada adireccional también favorece la aplicación de la pastilla y reduce el ruido de la frenada. non-integral ABS  ABS unit that has a traditional vacuum booster and master cylinder, and a separate hydraulic modulator. ABS no integral  Unidad de ABS que tiene un reforzador de vacío y cilindro maestro tradicionales, además de un modulador hidráulico separado.

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Glossary Occupational Safety and Health Administration (OSHA)  A division of the U.S. Department of Labor that establishes and enforces workplace safety regulations. Administración de Seguridad y Salud en el Trabajo (OSHA)  División del Departamento de Trabajo de EE.UU. que establece y hace cumplir las normas de seguridad en el lugar de trabajo. Ohms  (Ω) The unit used to measure the amount of electrical resistance in a circuit or an electrical device. One ohm is the amount of resistance present when one volt forces one ampere of current through a circuit or a device. Ohm is abbreviated with the Greek letter omega (Ω). ohmio  Unidad usada para medir la cantidad de resistencia eléctrica de un circuito o de un aparato eléctrico. Un ohmio es la cantidad de resistencia presente cuando un voltio hace pasar un amperio de corriente a través de un circuito o de un aparato. El ohmio se abrevia con la letra griega omega (Ω). O-ring  A circular rubber seal shaped like the letter “O.” toroide  Junta de goma circular con la forma de la letra “O.” oscilloscope  An electronic test instrument that can display ­voltage or amperage over a period of time as a graph display. osciloscopio  Instrumento de prueba electrónica que puede mostrar el voltaje o el amperaje por un período de tiempo en forma de gráfica. parallel circuit  An electrical circuit in which all the loads are connected to form more than one current path with the power source. circuito paralelo  Circuito eléctrico en el que todas las cargas se conectan de manera que formen más de una ruta con la fuente de alimentación. parallelism  Thickness uniformity of a disc brake rotor. Both surfaces of a rotor must be parallel with each other within 0.001 inch or less. paralelismo  Uniformidad de grosor de un rotor de freno de disco. Ambas superficies de un rotor deben ser paralelas entre sí con una tolerancia de 0,001 pulgada o menos. Pascal  A metric measure of pressure, named for a scientist who did extensive work in hydraulics. Pascal  Una medida métrica de presión que lleva el nombre de un científico que realizó un extenso trabajo en hidráulica. pedal free play  The clearance between the brake pedal or booster pushrod and the primary piston in the master cylinder. holgura de pedal  Holgura entre el pedal del freno o la varilla de refuerzo y el pistón primario en el cilindro maestro. permanent magnet (PM) generator  A reluctance sensor that generates a voltage signal by moving a conductor through a permanent magnetic field. generador de magneto permanente (PM)  Sensor de reluctancia que genera una señal de tensión al mover un conductor a través de un campo magnético permanente. piston stop  A metal part on a brake backing plate that keeps the wheel cylinder pistons from moving completely out of the cylinder bore. tope de pistón  Parte metálica de la placa de refuerzo del freno que impide que los pistones del cilindro de la rueda se salgan del hueco del cilindro. phosgene  A powerful poisonous gas that can be formed by burning some solvents. fosgeno  Un poderoso gas venenoso que puede formarse al ­quemar ciertos solventes.

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pressure bleeding  The process of using a tank filled with brake fluid and pressurized with compressed air to expel air and brake fluid from the system. Pressure bleeding is a one-person operation. extracción de vapor a presión  Proceso en el que se utiliza un tanque lleno de líquido de frenos y se ejerce presión con aire comprimido para expulsar el aire y el líquido de frenos del sistema. La extracción de vapor a presión es una operación para realizar una sola persona. pressure differential  The difference between two pressures on two surfaces or in two separate areas. The pressures can be either pneumatic (air) or hydraulic. diferencial de presión  Diferencia entre dos presiones en dos superficies o áreas distintas. La presión puede ser neumática (aire) o hidráulica. pressure differential valve  A hydraulic valve that reacts to a difference in pressure between the halves of a split brake system. When a pressure differential exists, the valve moves a plunger to close the brake warning lamp switch. válvula de diferencial de presión  Válvula hidráulica que reacciona ante una diferencia de presión entre las dos partes de un sistema de frenos dividido. Cuando hay una diferencia de presión, la válvula mueveunpistón que cierra el conmutador de la luz indicadora de freno. primary shoe  The leading shoe in a duo-servo brake. The primary shoe is self-energizing and applies servo action to the secondary shoe to increase its application force. Primary shoes have shorter linings than secondary shoes. zapata primaria  Zapata guía en un servofreno dual. La zapata primaria es autónoma y aplica una servoacción a la zapata secundaria para aumentar su fuerza de aplicación. Las zapatas primarias tienen forros más pequeños que las secundarias. proportioning valve  A hydraulic control valve that controls the pressure applied to rear drum brakes. A proportioning valve decreases the rate of pressure application above its split point as the brake pedal is applied harder. válvula de dosificación  Válvula de control hidráulico que controla la presión aplicada a los frenos de tambor traseros. Una válvula de dosificación disminuye la proporción de aplicación de presión por encima de su punto de separación cuando se presiona más fuerte el pedal del freno. push (speed) nut  A lightweight, stamped steel retainer that pushes onto a stud to hold two parts together temporarily. tuerca de empuje (velocidad)  Dispositivo de retención ligero, de acero estampado, que presiona contra un borne para juntar dos piezas temporalmente. quick take-up master cylinder  A dual master cylinder that supplies a large volume of fluid to the front disc brakes on initial brake application, which takes up the clearance of low-drag calipers. cilindro maestro de tensor rápido  Cilindro maestro doble que proporciona una gran cantidad de líquido a los frenos de disco delanteros en la primera frenada, compensando la holgura de los calibres de baja resistencia. radial ply tire  Tire construction in which the cords in the body plies of the carcass run at an angle of 90 degrees to the steel beads in the inner rim of the carcass. Each cord is parallel to the radius of the tire circle. neumático de capas radiales  Fabricación de neumáticos en los que los cordones de las capas del cuerpo de la carcasa se fijan con un ángulo de 90 grados a las nervaduras de acero en el borde interior de la carcasa. Cada cordón es paralelo a los radios del círculo del neumático.

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radial runout  An out-of-round condition in which the radius of the wheel or tire is not consistent from the wheel center to any point on the rim or the tread. desgaste radial  Pérdida de redondez en la que el radio de la rueda o neumático no es consistente desde el centro de la rueda a cualquier punto de la llanta o de la rodadura. reaction disc (or plate and levers)  The components in a vacuum power booster that provide pedal feel or feedback to the driver. disco de reacción (o placa y palancas)  Componentes de un reforzador de vacío que proporcionan sensaciones en el pedal o respuesta al conductor. reamer  A tool that is used to smooth the interior of a pipe or tube where the cutter broke through the metal wall. escariador  Herramienta que se usa para alisar el interior de un conducto o tubo donde la herramienta de cortar perforó la pared metálica. reference voltage  A fixed voltage supplied to the sensor by a voltage regulator inside the computer or control module; as the sensor changes, the return voltage is altered and sent back to the computer for use. Most computer control systems operate with a 5-volt reference voltage. tensión de referencia  Tensión fija suministrada al sensor por un regulador de tensión del interior del computador o módulo de control; al cambiar el sensor, la tensión de vuelta se altera y se envía de vuelta al computador para su uso. La mayoría de los sistemas de control por computador funcionan con una tensión de referencia de 5 voltios. refractometer  A test instrument that measures the deflection, or bending, of a beam of light. refractómetro  Instrumento de prueba que mide la deformación, o desviación, de un rayo de luz. regenerative braking  Recapture of electrical power by using a generator to slow the vehicle instead of wasting it through heat. frenado regenerativo  Recaptura de energía eléctrica mediante el uso de un generador para reducir la velocidad del vehículo en vez de desperdiciarla por medio de calor. reluctance sensor  A magnetic pulse generator or pickup coil that sends a voltage signal in response to varying reluctance of a magnetic field. sensor de reluctancia  Generador de impulsos magnéticos o bobina captadora que envía una señal de tensión como respuesta a una variación en la reluctancia de un campo magnético. replenishing port  The rearward port in the master cylinder bore; also called by other names. puerto de abastecimiento  Puerto situado más atrás en el hueco del cilindro maestro; también tiene otros nombres. return spring  A strong spring that retracts a drum brake shoe when hydraulic pressure is released. resorte de vuelta  Resorte fuerte que retrae una zapata de freno de tambor cuando se libera la presión hidráulica. road force balancers  A special type of wheel balancer that can take into account the force of the road and make a very accurate balance. balanceadores de fuerza de carga  Un tipo especial de balanceador de rueda que puede tomar en cuenta la fuerza de la carretera y realizar un balanceo muy preciso. rosin flux solder  Solder used for electrical repairs that does not contain acid flux or other corrosive materials. soldadura de flujo de resina de trementina  Aleación para soldar usada en reparaciones eléctricas, que no contiene fundente ácido ni otros materiales corrosivos.

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rotor  The rotating part of a disc brake that is mounted on the wheel hub and contacted by the pads to develop friction to stop the car. Also called a disc. rotor  Parte giratoria de un freno de disco que va montada en el buje de la rueda y entra en contacto con las pastillas para causar el rozamiento que detiene el vehículo. También llamado disco. rotor lateral runout  Rotor wobble from side to side as it rotates. desviación lateral del rotor  Oscilación del rotor de un lado a otro mientras gira. rust jacking  Rust that can form under the brake pad material and push the pad material off of the backing plate. levantamiento por óxido  Óxido que puede formarse debajo del material de la pastilla de freno y empujarlo hacia fuera de la placa de fijación. scan tool  A test computer that plugs into a diagnostic connector on a vehicle and reads trouble codes and other operating information from a vehicle onboard computer. herramienta scan  Computador de prueba que se enchufa a un conector de diagnóstico en un vehículo y lee los códigos de problema y otras información de funcionamiento en un computador de a bordo del vehículo. secondary shoe  The trailing shoe in a duo-servo brake. The secondary shoe receives servo action from the primary shoe to increase its application force. Secondary shoes provide the greater braking force in a duo-servo brake and have longer linings than primary shoes. zapata secundaria  Zapata de remolque en un servofreno dual. La zapata secundaria recibe acción asistida de la primaria para aumentar su fuerza de aplicación. Las zapatas secundarias proporcionan mayor potencia de frenado en un servofreno dual y tienen forros más grandes que las primarias. self-adjuster  A cable, lever, screw, strut, or other linkage part that provides automatic shoe adjustment and proper liningto-drum clearance as a drum brake lining wears. autoregulador  Cable, palanca, tornillo, puntal u otro mecanismo de unión que proporciona un ajuste automático a la zapata y la holgura adecuada entre forro y tambor cuando se desgasta el forro de un freno de tambor. semimetallic lining  Brake friction materials made from a mixture of organic or synthetic fibers and certain metals; these linings do not contain asbestos. forro semimetálico  Materiales de fricción del freno hechos con una mezcla de fibras orgánicas o sintéticas y ciertos metales; estos forros no contienen amianto. series circuit  An electrical circuit in which all the loads are connected in series with each other to form a single current path. circuito en serie  Circuito eléctrico en el cual todas las cargas están conectadas en serie entre sí formando una sola ruta para el flujo de corriente. series-parallel circuit  An electrical circuit in which some loads are in parallel with each other and one or more loads are in series with the power source and with the parallel branches. circuito paralelo en serie  Circuito eléctrico en el cual algunas cargas están conectadas en paralelo entre sí, y una o más cargas están en serie con la fuente de alimentación y con las ramas paralelas. servo action  The operation of a drum brake that uses the selfenergizing operation of one shoe to apply mechanical force to the other shoe to assist its application. Broadly, servo action is any mechanical multiplication of force.

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Glossary servoacción  Acción de un freno de tambor en el que una zapata actúa de forma autónoma al aplicar una fuerza mecánica a la otra zapata y ayudarla en su funcionamiento. Más ampliamente, una servoacción es cualquier multiplicación mecánica de una fuerza. setback  A difference in wheelbase from one side of a vehicle to the other. retroceso  Diferencia en la distancia entre ejes en un lado y otro del vehículo. sliding caliper  A caliper that is mounted to its support on two fixed sliding surfaces, or ways. The caliper slides on the rigid ways and does not have the flexibility of a floating caliper. calibre de desplazamiento  Calibre que se monta al soporte sobre dos superficies o vías fijas de deslizamiento. El calibre se desliza por vías rígidas y no tiene la flexibilidad de un calibre flotante. slope  The numerical ratio, or proportion, of rear drum brake pressure to full system pressure that is applied through a proportioning valve. If half of the system pressure is applied to the rear brakes, the slope is 1:2, or 50 percent. atenuación diferencial  Razón numérica o proporción entre la presión del freno de tambor trasero y la presión total del sistema que se aplica a través de una válvula de dosificación. Si la mitad de la presión del sistema se aplica a los frenos traseros, la atenuación diferencial es 1:2 ó del 50 por ciento. sodium azide  The explosive compound used to inflate an air bag. azida de sodio  Compuesto explosivo que se emplea para inflar un air bag. soft code  A diagnostic trouble code from a vehicle computer that indicates a problem not present at the time of testing, indicating an intermittent problem that occurred sometime before testing; stored in long-term computer memory and usually erased after fifty to one hundred ignition cycles if the problem does not occur. May also be called a history code. código blando  Código de problema de diagnóstico originado en el computador del vehículo que indica un problema no existente en el momento de la prueba, señalando un problema intermitente que ocurrió antes de la prueba; queda almacenado en la memoria a largo plazo del computador y se suele borrar después de entre cincuenta y cien ciclos de encendido si la falla no vuelve a presentarse. solderless connector  A wiring repair connector that is joined to two wires by physical crimping. conector sin soldadura  Conector para reparar el cableado que se une a dos cables ajustándolo f ísicamente. specific gravity  The weight of a volume of any liquid divided by the weight of an equal volume of water at equal temperature and pressure. The ratio of the weight of any liquid to the weight of water, which has a specific gravity of 1.000. gravedad específica  Peso de un volumen de cualquier líquido dividido por el peso de un volumen igual de agua a la misma presión y temperatura. La relación entre el peso de cualquier líquido y el del agua, que tiene una gravedad específica de 1,000. splice clip  A special, noninsulated connector used with solder to connect two wires. grapas de empalme  Conector especial, sin aislamiento, que se utiliza con soldadura para conectar dos cables. split point  The pressure at which a proportioning valve closes during brake application and reduces the rate at which further pressure is applied to rear drum brakes.

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punto de separación  Presión a la que la válvula de dosificación se cierra durante la aplicación de los frenos y se reduce la relación con la que se aplica más presión a los frenos de tambor traseros. spool valve  A cylindrical sliding valve that uses lands and valleys around its circumference to control the flow of hydraulic fluid through the valve body. válvula de carrete  Válvula cilíndrica de deslizamiento que usa partes planas y hundimientos en su circunferencia para controlar el flujo del líquido hidráulico a través del cuerpo de la válvula. square-cut seal  A fixed seal for a caliper piston that has a square cross section. junta cuadrada de pistón  Junta fija para un pistón de calibre con sección transversal cuadrada. squib coil  A tungsten wire used to ignite the solid fuel of the inflator module. bobina detonadora  Alambre de tungsteno usado para la ignición del combustible sólido del módulo inflador. star wheel  A small wheel that is part of a drum brake adjusting link. Turning the star wheel lengthens or shortens the adjuster link to position the shoes for proper lining-to-drum clearance. rueda en estrella  Rueda pequeña que forma parte de un acoplamiento de ajuste de un freno de tambor. Al hacer girar la estrella se alarga o acorta el acoplamiento para poner en posición las zapatas y conseguir una tolerancia conveniente entre forro y tambor. steering knuckle  The outboard part of the front suspension that pivots on the ball joints and lets the wheels turn for steering control. charnela de dirección  Parte exterior de la suspensión delantera que pivota en las juntas de bola y permite que las ruedas giren para controlar la dirección. stem unit  Any metric unit to which a prefix can be added to indicate larger or smaller measurements to some power of ten. For example, kilometer is formed by adding the prefix “kilo” to the stem unit “meter.” unidad base  Cualquier unidad métrica a la que se puede añadir un prefijo para indicar medidas mayores o menores en potencias de diez. Por ejemplo, kilómetro se forma añadiendo el prefijo “kilo” a la unidad base “metro.” submultiple  A metric measurement unit that is smaller than the stem unit through dividing by a power of ten. submúltiplo  Unidad del sistema métrico menor que la unidad base que resulta de dividir por una potencia de diez. supplemental inflatable restraint system (SIRS)  The driver or driver/passenger side protection used during a forward direction collision. sistema supletorio inflable de retención (SIRS)  Protección de lado del conductor o del conductor/pasajero utilizada durante una colisión frontal. surge bleeding  A supplementary bleeding method in which one person rapidly pumps the brake pedal to dislodge air pockets while another person opens the bleeder screw. Surge bleeding is a two-person operation but should not be used as the only bleeding procedure for a brake system. extracción de vapor por impulsos  Método suplementario de extracción de vapor en el cual una persona bombea rápidamente el pedal del freno para desalojar las bolsas de aire mientras otra abre el tornillo extractor. La extracción de varpor por impulsos se hace entre dos personas, pero no se debe emplear comoúnico procedimiento de extracción de vapor para un sistema de frenos.

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552

Glossary

symptom byte  A symptom byte is an addition to a trouble code, which helps the technician pinpoint problems more accurately in GM vehicles. Ford has a similar system called a failure byte. octeto de síntomas  Un octeto de síntomas es una adición a un código de problemas que ayuda al técnico a localizar problemas con más veracidad en vehículos GM. Ford tiene un sistema similar que se llama octeto de fallas. tandem booster  A power brake vacuum booster with two small diaphragms in tandem to provide additive vacuum force. reforzador en serir  Reforzador de vacío para frenos con dos pequeños diafragmas en tándem que proporcionan más fuerza vacío. tapered roller bearing  A specific kind of bearing that is based on tapered steel rollers held together in a cage. cojinete de bolillas cónicas  Clase específica de cojinete que se basa en bolillas cónicas de acero encerradas en una jaula. Technical Service Bulletins (TSB)  A vehicle manufacturer bulletin that outlines the details for the diagnosis and repair of a specific fault in a specific range of vehicles; is not considered a warranty or recall issue. Boletines de Servicio Técnico (TSB)  Boletín del fabricante del vehículo que resalta los detalles para el diagnóstico y reparación de una falla específica en un tipo de vehículo. No se considera como garantía o asunto de retiro. tetrachloroethylene  A colorless solvent used in dry cleaning and degreasing and has been found to be a carcinogen. tetracloroetileno  Un solvente incoloro que se utiliza en el lavado en seco y el desengrasado, y que se considera carcinógeno. threading  A brake drum that has been machined incorrectly, resulting in a finish that causes the brake shoes to move outward on the drum during braking. roscado  Un tambor de freno que se rectificó incorrectamente, provocando un acabado que hace que las zapatas de los frenos se muevan hacia fuera en el tambor durante el frenado. Throttle Actuator Control (TAC)  Motorized throttle plate that replaces the conventional throttle cable by computer control. Control del actuador del acelerador (TAC)  Placa de aceleración motorizada que reemplaza el cable convencional del acelerador por el control de computadora. Tire Pressure Monitor System (TPMS)  Electronic tire pressure reporting system that warns of improperly inflated tire. Sistema de monitoreo de presión de neumáticos (TPMS)  Sistema electrónico de reporte de presión de neumáticos que advierte si hay un neumático inflado en forma incorrecta. toe angle  The difference in the distance between the centerlines of the tires on either axle (front or rear) measured at the front and rear of the tires and at spindle height. ángulo de separación  Diferencia de la distancia entre las líneas centrales de los neumáticos en cada eje (delantero o trasero) medida en las partes delantera y trasera de los neumáticos y a la altura del husillo. torque stick  An extension for an impact wrench that includes the correct size socket for a wheel nut and that acts as a torsion bar to limit the torque applied by the impact wrench when installing a wheel. varilla de momento de torsión  Extensión para llave de impacto que incluye la boca de tamaño correcto para una tuerca de la rueda, que actúa como barra de torsión para limitar el momento de torsión aplicado por la llave cuando se instala una rueda.

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trailing shoe  The second shoe in the direction of drum rotation in a leading-trailing brake. When the vehicle is going forward, the rear shoe is the trailing shoe, but the trailing shoe can be the front or the rear shoe depending on whether the drum is rotating forward or in reverse and whether the wheel cylinder is at the top or the bottom of the backing plate. The trailing shoe is non-self-energizing, and drum rotation works against shoe application. zapata de remolque  Segunda zapata en la dirección de giro del tambor en un freno de tracción-remolque. Cuando el vehículo avanza, la zapata trasera es la remolcada, pero la zapata de remolque puede ser la delantera o la trasera dependiendo de si el tambor está girando hacia delante o hacia atrás y de si el cilindro de la rueda está en la parte superior de la placa de refuerzo o en la inferior. La zapata de remolque no es autónoma, y el giro del tambor funciona contra la aplicación de la zapata. tread wear indicator  A continuous bar that appears across a tire tread when the tread wears down to the last 2/32 (1/16) inch. When a tread wear indicator appears across two or more adjacent grooves, the tire should be replaced. indicador de desgaste de la rodadura  Barra continua que aparece transversalmente en la rodadura del neumático cuando ésta se desgasta más de 2/32 (1/16)  pulgadas. Cuando aparece el indicador de desgaste de rodadura cruzando dos o más hendiduras adyacentes, se debe cambiar el neumático. trichloroethane  Solvent used in degreasing. Being phased out due to ozone depletion properties. tricloroetano  Solvente utilizado para el desengrasado. Se va a eliminar debido a sus propiedades de agotar el ozono. trichloroethylene  Solvent used in degreasing that can cause heart problems, and is also known as a carcinogen. tricloroetileno  Solvente utilizado en el desengrasado, que puede provocar problemas cardíacos y también se considera carcinógeno. tubing bender  A collection of interchangeable curved sections used to bend a tube or pipe to the correct radii without crimping. acodador  Colección de secciones curvas intercambiables que se emplean para doblar un tubo o conducto hasta obtener el radio correcto sin estrecharlo. tubing cutter  A cutter used to cut a pipe or tube at a flat angle. cortatubos  Herramienta cortante empleada para cortar un conducto o tubo en ángulo recto. vacuum  In automotive service, vacuum is generally considered to be air pressure lower than atmospheric pressure. A true vacuum is a complete absence of air. vacío  En relación con los automóviles, el vacío se suele considerar como una presión de aire menor que la atmosférica. Un vacío verdadero es la completa ausencia de aire. vacuum bleeding  The process of using a vacuum pump filled with brake fluid and attached to a wheel bleeder screw to draw old brake fluid and air from the system. Vacuum bleeding is a one-person operation. extracción de vapor por vacío  Proceso en el que se usa una bomba de vacío llena de líquido de frenos y unida a un tornillo extractor de rueda para extraer del sistema el aire y el líquido de frenos viejo. La extracción de vapor por vacío es una operación para realizar una sola persona. vacuum suspended  A term that describes a power brake vacuum booster in which vacuum is present on both sides of the diaphragm when the brakes are released. The most common kind of vacuum booster.

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Glossary de suspensión de vacío  Término que describe un reforzador de vacío para frenos en el que existe vacío a ambos lados del diafragma cuando se sueltan los frenos. El tipo más común de reforzador de vacío. vent port  The forward port in the master cylinder bore; válvula de ventilación  Válvula delantera de la parte interior del cilindro principal; también recibe otros nombres. ventilated rotor  A rotor that has cooling fins cast between the braking surfaces to increase the cooling area of the rotor. rotor ventilado  Rotor que tiene álabes refrigerantes entre las superficies de frenado para aumentar la superficie refrigerante del rotor. vernier caliper  A measuring caliper with a vernier scale for very fine measurements. The scale may be graduated in U.S. customary or metric units. calibre vernier  Calibre de medir con una escala vernier para mediciones afinadas. La escala puede estar graduada en unidades métricas o en las tradicionales americanas. vernier scale  A fine auxiliary scale that indicates fractional parts of a larger scale. escala vernier  Escala auxiliar afinada que indica fracciones de una escala mayor.

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volt  The unit of electrical force or pressure. voltio  Unidad de fuerza o presión eléctrica. wear-indicating ball joint  A ball joint with a visual indicator to show the amount of wear on the joint. juntas de bola de indicación de desgaste  Junta de bola con un indicador visual que muestra la cantidad de desgaste de la rótula. wheel cylinder  The hydraulic slave cylinder mounted on the backing plate of a drum brake assembly. The wheel cylinders convert hydraulic pressure from the master cylinder to mechanical force that applies the brake shoes. cilindro de la rueda  Cilindro hidráulico auxiliar montado en la placa de refuerzo de un conjunto de frenos de tambor. Los cilindros de la rueda convierten la presión hidráulica del cilindro maestro en la fuerza mecánica que se aplica a las zapatas de freno. Workplace Hazardous Materials Information Sheet A Canadian form used to list the health hazards of hazardous material. Similar to the EPA’s material safety data sheet. Hoja informativa de Materiales Peligrosos en el Lugar de Trabajo  Formulario canadiense que se usa para hacer una lista de los daños a la salud causados por material peligroso. Similar a la hoja de datos de material de seguridad de la EPA.

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Index

Note: Page numbers in bold print reference non-text material

A ABS. See Antilock brake systems (ABS) ABS indicator, 520 Accidents, 1 Accumulator, 465, 466, 544 Active braking system, 544 Active cruise control (ACC) systems, 525 Actuator tests, 476 Additional respiratory safety, 14 Air bag safety, 22–23 job sheet, 31–32 Air bag systems. See Supplemental inflatable restraint ­systems (SIRS) Air ratchet, 69, 69 Amber ABS lamp, bulb test, 134 American Wire Gauge (AWG) system, 223, 544 Ampere (A), 84 Amplitude, 485, 544 Analog, 544 Anodized finish, 318 Antilock brake systems (ABS) base brake system troubleshooting, 462, 462–463 using brake pedal, 464 with brake pedal, 463, 464 bulb check, 462 checking fluid levels, 148 component replacement, 486–490 computer (control module) replacement, 489–490 pump and motor removal, photo sequence, 487–488 wheel speed sensor replacement, 488–489, 489 diagnostic strategy check connectors for damage, 477 check ground continuity, 476 computer pin voltage charts, 475–476 current code, 471–472 determination, 473 diagnostic trouble code, 471 DLC, 470 history code, 472–473 network configuration, 2016 Chevrolet Cruze, 470, 471 operating range tests, 473–474 self-test programs, 470 symptom byte (code sub-types), 473 troubleshooting intermittent problems, 476–477 troubleshooting trouble codes, 471 warning lamp lights, 470 hydraulic pressure safety, 22, 22

hydraulic system service, 465–469 automated bleed procedure Bosch ABS 9.0, 467 bleeding Bosch ABS 9.0, 467 bleeding the system, 466–469 brake pressure sensor calibration Bosch ABS 9.0, 467–468 depressurizing the system, 465 fluid level check and refill, 465 manufacturers’ systems testing, 490 Delphi DBC-7, 491–495, 491–494 service skills, 461 speed sensor testing, 478–486, 479–486 switch testing, 477–486, 478–486 system check, 462, 462–463 traction control system, 462 troubleshooting, 469–477 basic inspection and vehicle checkout, 469–470 check for technical service bulletins, 470 inspect and check out, vehicle, 470 intermittent problems, 476–477 operating range tests, 473–474, 474 testing computer control systems, 470–473 trouble codes, 471 Antilock/traction control, 515–516, 516 Aqueous, 78, 303, 544 Aqueous cleaning equipment, 303 Asbestos, 11, 544 cleaning, 77 health issues, 11–14, 13 precautions, 11–14, 13 avoiding asbestos dust, 11–12 breathing hazards, 11–14, 13 housekeeping and brake dust, 4 Asbestosis, 12, 544 ASE certification, 25, 25 Aspect ratio, 544 Assembly fluid, 81 Automated bleed procedure, 466–467, 544 Automated bleed procedure Bosch ABS 9.0, 467 Automated brake system bleeding TRW 440 V ABS, 466–467 automated bleed procedure, 466 Bosch ABS 9.0, 467 Automatic bleed procedure, 468 Autoranging, 544 Auto ranging test meter, 84 Auxiliary brake shoes, 435

554

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Index Auxiliary drum brake shoe adjustment and replacement, 444–446, 445–446 AWG. See American Wire Gauge (AWG) system Axle inspection, 386–387

B Backing plate, 387–389, 394–396, 395, 399, 406, 406, 544 inspection, 387–389, 389 Ball joints, 120–121 wear-indicating, 120, 121 Banjo fitting, 203, 203, 205, 544 BCM. See Body control module (BCM) Bearing driver, 115, 544 Bearing end play, 327, 544 Bearing packer, 114, 544 Bearing race, removal and installation photo sequence, 111 Bedding in period, 302, 544 Bell-mouthed drum, 409 Bench bleeding, 157–161, 157, 158, 544 Bench bleeding master cylinders, 157–161, 157, 158 job sheet, 189–190 photo sequence, 159–160 using syringe, 158–161 Bench lathes, 335–337, 335–343, 339–342 machining rotor, 338–343, 339–342 adjusting settings, 340 deterring limits, 339, 340 job sheet, 363–365, 367–369 removing excessive rotor runout, 341–343 steps, 340–341, 341–343 mounting rotor, 335–337, 335–338 photo sequence, 337 Bendix pushrod gauge check, 262, 262 Bleeder screw, 163, 164, 545 freeing frozen screw, 166–167 removal, 311–312, 312 Bleeder valve wrench, 61–62, 62 Bleeding ABS systems, 466–469 bench, 157–161, 157, 158 Bosch ABS 9.0, 467 gravity, 176, 178 hydro-boost, 269–270 manual, 168–172, 170, 172 pressure, 172–175, 173–174 sequences, 165–166 surge, 178 vacuum, 167, 175, 175–176, 177 on the vehicle, 162–163, 163 wheel brake sequences, 167–168, 168 Body control module (BCM), 222 Boiling point, brake fluid, 147 Booster components, identifying/inspecting job sheet, 277–278 Boot drivers, rings, and pliers, 63–64, 64

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Bosch ABS 9.0, 495 automated bleed procedure, 467 bleeding, 467 BPMV and EBCM replacement, 498 brake pressure sensor calibration, 467–468 front-wheel speed sensor replacement, 496–497, 495, 497 initial diagnosis, 495–496 magnetoresistive wheel speed sensors, 495 pinout of EBCM connector, 475 premature (low-speed) ABS activation, 496 rear-wheel speed sensor replacement, 497, 497 symptom byte, 474 test drive diagnosis, 496 warning lamps, 499 Box wrench, 61, 61 Brake actuation unit, 273 Brake adjustment, 403–408, 404–408 duo-servo star wheel adjustment, 406, 406–407 initial adjustment, 403–404, 404 leading-trailing star wheel adjustment, 407–408, 407–408 manual adjustment precautions, 404–406, 405 Brake bleeding, 163, 165–168, 545 Brake caliper service, 307–321 assembly, 319–321, 319–320 bleeder screw removal, 311, 311–312 cleaning, 316–317, 317 dust boot and seal removal, 316–317, 317 honing and piston clearance, 317–318 inspection, 310, 311 installation, 321 internal inspection, 318 piston removal, 313–316, 314 rebuilding, photo sequence, 308–309 removal, 307, 310, 310 Brake cleaning solvents, 14 Brake cylinder hones, 65, 65 Brake drum service, 409–415, 410–415 drum inspection, 409–412, 410–411 measurements, 412–415, 412–415 See also Drum Brake electrical and electronic component service, 216–227 troubleshooting procedure, 217 Brake fluid contamination, 144, 146, 386 DOT rating, 142, 142 DOT 5 silicone fluid, 142, 143, 146 job sheet, 185–186 precautions, 141–143, 142 replacement, 180–181 service, 143–147, 144, 146 Brake fluid level switch test, 223 Brake grease, 81–82 Brake hoses inspection, 202–203, 202 installation, 204, 204–205

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556

Index

Brake hoses (continued) job sheet inspecting and diagnosing, 237–239 replacing, 243–244 removal, 203, 203–204, 204–205 Brake lamps, 463 Brake lathes, 70–71, 70–71, 333–335, 334, 415, 416 adjusting settings, 419–420, 420 bench lathe, 335–337, 335–343, 340–343 on-vehicle, 343–347, 344–345 Brake line inspection, 201–203 and diagnosis, job sheet, 237–239 Brake pads burnishing, job sheet, 371–372 inspecting, 287–289, 288–289 job sheet, 357–360, 371–372 pad installation, 298–302, 299–301 pad removal, 294–298, 295–298 photo sequence, 293–294 replacement, for floating or sliding calipers, 292–302, 292–302 road test and pad burnishing, 302–303 Brake pedal free play inspection and adjustment, 136–141, 137, 139, 253–254, 254 height adjustment, 138, 138–139, 139, 254–255, 254–255 job sheet, 513–514 mechanical check, 135, 135 position switch, 140–141 travel and force test, 135–136, 136 troubleshooting with, 463, 464 Brake pedal effort gauge, 66, 66 Brake pedal position (BPP) sensor, 141 procedure for calibrating, 141 procedure to recalibrate, 255 Brake performance, 10 Brake pressure modulator valve (BPMV), 273, 463, 466, 467 replacement, 493, 494, 498 Brake pressure sensor, 519 calibration Bosch ABS 9.0, 467–468 recalibration, 273 Brake problems and concerns, job sheet, 231–233 Brake-pull problem, 468 Brake service laws and regulations, 10–11 Brake shoe auxiliary, 435 contamination, 215 inspection, 385–386 job sheet, 427–429 Brake shoe adjusting gauge (calipers), 57–58, 58 Brake stoplamp system, job sheet, 245–246 Brake systems isolating problems, 97–98 road test, 133–134, 134 safety regulations, 9–11, 10 safety requirements, 9

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warning with IPC on vehicle network, 220, 221 warnings and cautions, 11, 11 table Brake warning indicators, 520–525 ABS indicator, 520 computer-controlled electric steering, 521, 521–523 red brake warning indicator, 520 stability control off message, 520–521 throttle actuator control (TAC), 521–523, 524, 525 tire pressure monitoring systems, 523–525 traction control off indicator, 520 Brinelling, 113, 545 Brush hone/honing, 65, 66, 545 Bubble flare. See ISO or bubble flare Bulb check, 462 Bulletins, technical service, 470 Burnishing, 302–303, 545

C Caliper piston removal tools, 64, 65 Caliper support, 178, 287, 291–292, 292, 295–296, 316–321, 319–320 Caliper ways, 300, 301 Camber, 121, 134, 545 Camber angles, 120, 121 Canadian Center for Occupational Health and Safety (CCOHS), 17, 545 Carbon monoxide, 3–4, 4, 545 Carrying safety, 8–9 Case studies ABS activation, 499 dirt, caliper body, 353 master cylinder replacement, 181 original equipment parts, 422 parking brake adjustment, 455 power brake service, 273 tire size variation, 122 wiring harness check, 228 Caster, 120–121, 545 CCOHS. See Canadian Center for Occupational Health and Safety (CCOHS) Center high-mounted stoplamp (CHMSL), 218, 545 Certifications for technicians, 25 Check valve bleeder hose, 172 Chemical poisoning, 15–16 Chemical safety, 14–16, 15–16 Chevrolet Cruze 2016, network configuration, 470, 471 Chlorinated hydrocarbon solvents, 15, 545 CHMSL. See Center high-mounted stoplamp (CHMSL) Chrysler booster replacement, 270 Chrysler 2010 300 Series switch service, 139, 140 Circuit testers, 83, 83 Circuit troubleshooting, 220, 222 Cleaning equipment, 76–79, 77–79 photo sequence, 80 safety, 21–22, 21, 79, 81

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Index Cold inflation, 545 Combination valves, 216, 216 Compressed air caliper piston removal, 313, 314 Compressed air safety, 4, 14, 22, 68–69, 68 Computer-controlled electric steering, 521, 521–523 Computer (control module) replacement, 489–490 Conduit, 439 Connector repair, 225, 227 hard-shell connectors, 225, 227 molded connectors, 225, 227 Containment systems, 76–79, 77–79 Corrosion, 447 Corrosivity, 20 Crimping, 223–225, 224 Crocus cloth, 308, 317 Cross-feed, 340, 545 Crosshatch, 342, 545 Cup expander, 545 Cup seal, 151, 181, 545 Current codes, 471–472, 473, 545 Cylinder hones, 65, 65, 545

D DBC-7 system, 467, 468 switches and warning lights, 495 wheel speed sensor replacement, 493–495 Delco-Moraine pushrod gauge check, 262–263, 263 Delphi DBC-7 switches and warning lights, 495 wheel speed sensor replacement, 493–495 Delphi Chassis ABS-VI, 260, 262 Delphi DBC-7, 468, 491–495, 491–492, 494–495 BPMV replacement, 493, 494 EBCM replacement, 491, 493 scan tool usage, photo sequence, 492 switches and warning lights, 491 wheel speed sensor replacement, 494, 494–495 Department of Transportation (DOT), 9, 545 Depressurizing ABS, 465 Depth gauges, 53, 53 Diagnostic energy reserve module (DERM), 545 Diagnostic strategy, 470–477 Diagnostic trouble code (DTC), 471, 545 current code, 471–472 history code, 472 Dial indicators, 55–56, 56 Diaphragm, 74, 248, 251, 261, 546 Digital (magnetoresistive sensor) testing, 479–480 Digital multimeter (DMM), 84, 84, 546 Digital signal, 477, 482, 546 Digital storage oscilloscope (DSO), 85, 86, 546 Discard diameter, 412, 412, 546 Discard dimension, 324, 324, 546 Disc brake, 435–438 job sheet, 355–356 rear, 435 Disc brake service

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557

brake caliper service, 307–321, 308–311, 314, 317, 319–320, 435–436 brake pad replacement for floating or sliding calipers, 292–302, 292–302 cable adjustment, 443–444, 444 cleaning, 303–304 diagnosing problems, 286–287 inspecting brake pads, 287–289, 288–289 rear disc brake inspection and replacement, 347, 348–352 refinishing brake rotors, 332–347, 333–346 rotor service, 322–331, 322–331 service operations, 290–292 loaded calipers, 291, 291–292 vehicle preparations, 290, 290–291 service precautions, 373 DMM. See Digital multimeter (DMM) DOT. See Department of Transportation (DOT) DOT 3, DOT 4, and DOT 5, 141–142, 546 DOT 5 silicone fluid, 142, 143, 146 Double flare, 211, 211–212, 546 Drum inspection, 409–412, 410–411 installation, 403, 422, 422 measurements, 412–415, 412–415 refinishing, 415–421, 415, 417–418, 420–422 cleaning, 421, 421 Drum brake, 108, 165, 215 Drum brake adjusting tools, 63, 64 Drum brake cable adjustment, 442–443 brake drum service, 442 Drum brake service brake adjustment, 403–408, 404–408 brake drum removal, 377–382, 377–382 fixed (one-piece) drum, 377–379, 378–380 floating (two-piece) drum, 380–381, 381 from rear axle, photo sequence, 381–382 brake drum service, 409–415, 409–415 cleaning, 383–385, 384 diagnosing problems, 374–376, 374–375 disassembly, 389–395, 390–395 disassembly, photo sequence, 391 inspection, 385–389, 385, 387–389 installation, photo sequence, 398–399 job sheet, 425–426, 431–433 operations, 377 vehicle preparation, 366 reassembly, 397–403, 399–402 refinishing brake drums, 415–421, 415, 417, 419–421 service precautions, 373 wheel cylinder service, 395–396, 396 Drum-in-hat, 435 Drum micrometer, 53–54, 54 Drum web, 410, 546 DSO. See Digital storage oscilloscope (DSO) DTC. See Diagnostic trouble code (DTC) Duo-servo brake, 406–407, 546

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558

Index

Duo-servo star wheel adjustment, 406, 406–407 Dust boot and seal removal, 316–317, 317

E EBCM replacement, 491, 493 Electrically operated integrated caliper (direct apply), 453 Electrical principles, 85–87, 87 Electric parking brake service, 451–454, 451–454 apply/release, 453–454 control systems, 451–452, 451 diagnosis of, 454, 454 electrical actuator used with cables, 452, 452 electrical direct apply, 453, 453–454 GM’s electrically operated integrated caliper, 453 rear brake service, 454 system modules, 452, 452 Electrohydraulic control unit, 518–519, 518–520 brake pressure sensor, 519 steering angle sensor, 519, 519–520 system control valves, 518, 518 yaw sensor/lateral accelerometer, 519, 519 Electrohydraulic power booster system servicing, 271–272, 272 servicing, brake actuation unit, 273 Electromotive force (EMF), 477, 478, 546 Electronic brake control diagnosis, job sheet, 529–531 Electronic brake control module (EBCM), 273, 453 housing, unlock, 491 replacement, BPMV and, 498 Electronic control module, 452 Electronic lighting module, 463 Electronic test equipment, 82–85, 83–86 Electrostatic discharge (ESD), 477, 489, 546 Enclosure equipment, 76, 77 Environmental agencies, 16–17 Environmental Canada, 17, 546 Environmental Protection Agency (EPA), 12, 16–17, 546 EP. See Extraction procedures (EP) Equalizer, 438, 438, 441, 447, 448, 546 Equipment cleaning safety, 21–22 ESD. See Electrostatic discharge (ESD) Etching, 113, 546 Extraction procedures (EP), 20, 546 Eye protection, 5–7, 5–6 photo sequence, 7

F Face protection, 5–7, 6 Failure byte, 473 Fasteners, 45, 46 Federal Motor Vehicle Safety Standards (FMVSS), 9, 546 Feeler gauges, 57, 57 Fire control, 24–25, 24 Fire extinguisher care and use, job sheet, 39 First aid, 6, 6, 7

64540_em_indx_hr_554-570.indd 558

Fixed caliper brake, 295, 547 Fixed (one-piece) drum removal, 378–380, 379 Flare fittings, 210–213, 211–213 Flare-nut wrench, 61, 62 Floating caliper, 292, 292, 547 Floating drum, 380, 547 Floating (two-piece) drum removal, 380–381, 381 Floating rotor, 328, 329, 330, 547 Fluid bypass test, 151–152 Fluid level check and refill (ABS), 465 Fluid loss test, 253 FMVSS. See Federal Motor Vehicle Safety Standards (FMVSS) Force, 49, 547 Ford, 472 checking ABS fluid level, 148 Ford Flex bleeding, 468 Freeing seized cables, 446–447 Friction, 70, 547 Friction surface depth measurement, 329, 329 Front (control) cable replacement, 447, 448 Fusible link, 489, 547

G Galling, 110, 547 General Motors checking ABS fluid level, 148 Graphing meters, 85, 86, 547 Gravity bleeding, 176, 178, 547 Grease, 81 Ground continuity test, 476 Grounded circuit, 221

H Hand protection, 7–8 Hand tools, 61–63, 61–63 Hard code, 472, 547 Hard-shell connectors, 225, 227 Hard spots, 410, 547 Hardware inspection, 387–389, 390 Hazardous communications, 17–20, 18–19 Hazardous waste handling of, 20–22, 20–21 Health issues, asbestos, 11–14, 13 Heat checking, 323 Heat checks, 410, 547 Heat-shrink tubing, 223, 547 Height-sensing proportioning valve, 547 High-efficiency particulate air (HEPA) filter vacuum, 77, 304, 383–384, 384, 547 High impedance, 85, 547 History codes, 472–473, 547 Hold-down springs, 375, 547 tool, 63 Honda adjusting the booster pushrod, 263, 264–265 servicing vacuum boosters on, 270–271, 271–272

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Index Honing master cylinder, 65 brush honing, 65 wheel cylinder, 394, 395–396 Housekeeping, 2–3, 2 and brake dust, 4–5 Hybrid vehicle electrical hazards, 23 job sheet, 35–36 Hydraulic brake system bleeding, 163–180, 164, 168, 169–175, 177, 179–180 electrical and electronic component service, 216–217 flushing and refilling, 180–181 line, fitting, and hose service, 201–213, 202–213 recentering pressure differential valve, 200, 200 stoplamp testing and switch adjustment, 217–228, 221, 224–227 valve servicing, 214–216, 214–216 Hydraulic caliper piston removal, 315–316 Hydraulic floor jack, 71 Hydraulic lift, 73–74 Hydraulic power brakes, 249, 250 Hydraulic pressure, relieving, 22, 22 Hydraulic system booster components, identifying/inspecting job sheet, 277–278 inspection, 148–149, 149 testing for trapped air, 149–150, 150 Hydro-boost, 249, 547 Hydro-boost power brake systems accumulator test, 268–269 air bleeding, 269–270 basic operational test, 268 booster fluid leakage, 268, 268 booster removal, 269 inspection, 265–267, 267 noise troubleshooting, 269 and power steering operation, 267 servicing, 269 Hydroplane, 100, 548 Hygroscopic, 147, 548

I Ignitability, 20 Impact wrenches, 69, 69 Instrument clusters, vehicle network, 222 Integral ABS systems, 152–154, 548 Internal leak test, 151 International System of Units or metric system, 46, 548 ISO or bubble flare, 212–213, 212–213, 548 job sheet, 241–242

J Jacks, 71, 72

K Kelsey-Hayes EBC 440 ABS system, 148

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559

L Lateral run out, 102–105, 104, 326–329, 326–328, 548 Leading shoe, 402, 548 Leading-trailing brake, 407–408, 407–408, 548 Leading-trailing star wheel adjustment, 407–408, 407–408 Leaks and proper operation check job sheet, 187–188 LED test light, 83, 83 Lifting safety, 8, 8–9 Lifting tools, 71, 72 Linear, 548 Linear measurement, 47, 48, 47–48 job sheet, 93–94 Lining inspection, 385–386, 385, 387 Linkage inspection and test, 438–440, 439 Loaded calipers, 291, 291–292, 548 Low-pressure wet-cleaning systems, 77–78, 78 Lubricants, brake, 81–82 assembly fluids, 81 grease, 82–83 for rubber parts, 82 wheel bearing grease, 82

M Magnetoresistive wheel speed sensor testing, 485–486, 486 Manual bleeding, 168–172, 170, 172, 548 with check valve bleeder hose, 172 disc brake caliper, photo sequence, 170–171 job sheet, 191–192 Master cylinder bench bleeding, 157–161, 157, 158 bleeding on the vehicle, 162–163, 163 brake fluid precautions, 141–143, 142 brake pedal mechanical check, 135, 136 brake system road test, 133–134, 134 checking fluid level, 143–147, 144 DOT 5 silicone fluid, 142, 143, 146 filling reservoir, photo sequence, 145 fluid level and condition, checking, 149, 151, 151 fluid service, 143–147, 144, 146 installing (non-ABS), 161, 161 pedal free play inspection and adjustment, 136–141, 137, 139 pedal travel and force test, 135–136, 136 pressure gauge set, 58, 59 pushrod adjustment, 162 rebuilding, 156–157, 157 removing (non-ABS), 153–154, 154 reservoir removal/replacement, 154–157, 155 scan tool to OBD-II 16-pin connector, 468 test and inspection, 148–152, 149–151 Material safety data sheets (MSDS), 15, 17, 18, 21, 548 usage, job sheet, 37–38 Maximum refinishing limit, 324, 548

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560

Index

Measuring systems, 46–49 metric system, 47–49, 48 U.S. customary system, 47 Measuring tools, 49–59, 50–59 Mechanical caliper piston removal, 313–315, 314 Metering valve, 167, 169, 173, 214–215, 214–215, 548 pressure bleeding vehicles with, 174–175 pressure test, 214–215 Metric system, 47–49, 47 table, 48 linear measurement, 47–48, 48 pressure measurement, 49 temperature measurement, 49 torque measurement, 49 volume measurement, 48, 48 weight measurement, 49 Micrometers, 50–53, 50–52 Molded connectors, 225, 227 MSDS. See Material safety data sheets (MSDS) Multimeters, 83–85, 84 Multiple, metric measurement, 47, 548

N Negative-pressure enclosure, 76, 77 Non-ABS master cylinder installing, 161, 161 job sheet, 189–190 removing, 153–154, 155 Nondirectional finish, 331, 548 Non-integral ABS syste ms, 152–154, 548

O Occupational Safety and Health Administration (OSHA), 12, 17, 549 Ohms (Ω), 84, 549 On-vehicle bleeding without bleeder screws, 162–163, 163 On-vehicle lathes, 343–347, 343, 344–346 photo sequence, 344–346 Open circuit, 218, 223 Open-end wrench, 61, 61 Open vent ports test, 152 Operating range tests, 473–476, 475 O-ring, 268, 549 Oscilloscope, 480–482, 481–482, 549 OSHA. See Occupational Safety and Health Administration (OSHA)

P Pad hardware, 297 Pad hardware kit, 298 Pad wear indicator, 287, 288, 326 Parallel circuit, 87, 87, 549 Parallelism, 323, 549 Parking brake, 386, 388–391, 389, 394, 394, 435–436, 451 Parking brake control, 451–452, 452 Parking brake lamp switch test, 450–451, 450

64540_em_indx_hr_554-570.indd 560

Parking brake service cable and linkage adjustment, 440–446, 441 auxiliary drum brake shoe adjustment and replacement, 444–446, 445–446 disc brake cable, 443–444, 444 drum brake cable, 442–443 job sheet, 457–458 cable and linkage repair and replacement, 446–450 freeing seized cables, 446–447 front (control) cable replacement, 447, 448 rear cable replacement, 448, 448–449 electric parking brake service, 451–454, 451–453 parking brake lamp switch test, 450–451, 450 tests, 435–440 job sheet, 459–460 linkage, 438–440, 439 performance, 440, 440 rear disc brake pedal travel, 435–436, 436–438 rear drum brake pedal travel, 435 Parking brake switch test, 222 Parts washer, 305, 306, 384 Pascal (Pa), 49, 549 Pawls, 387, 388, 398 Pedal. See Brake pedal Pedal free play, 136–137, 549 adjustment, 138–139, 139 Permanent magnet (PM) generator, 549 Personal safety eye protection, 5–7, 5 face protection, 5–7, 6 hand protection, 7–8 lifting and carrying, 8, 8 Phenolic plastic, 318 Phoenix injector, 178, 179, 180 Phosgene, 15, 549 Pickup coil speed sensor, 478, 482 Pin out chart, 475, 475 Pin voltage chart, 475, 475 Piston stop, 396, 549 Plastic-coated cable, 446 Polyglycol, 143 Power brakes adjusting booster pushrod on a Honda, 263, 264 brake pedal checks, 138–139, 139–140, 253–254, 254–255 electrohydraulic power booster system, 271–272, 272 hydraulically assisted, 249, 250, 251 hydro-boost, 264–268, 264–270 accumulator test, 268–269 air bleeding, 269–270 basic operational test, 268 booster fluid leakage, 268, 268 booster removal, 269 inspection, 265–266, 267 noise troubleshooting, 269 and power steering operation, 267 servicing, 269

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Index types of, 247–249, 248–250 vacuum-boost, 248–249, 249 booster installation, 256, 257–258, 259–260 booster overhaul, 260, 261 booster removal, 256–258, 257–259 photo sequence, 252–253, 257–258 pushrod length check, 260–263, 262 testing and diagnosis, 249–253, 252–253 Power tools, 66–70, 67–70 air ratchet, 69, 70 compressed air safety, 68–69, 68 impact wrenches, 69, 69 safety guidelines, 67–68, 67 Premature (low-speed) ABS activation, 496 Pressure bleeders, 74–76, 75–76 Pressure bleeding, 74–76, 172–175, 173–174, 178, 179, 549 job sheet, 193–194 vehicles with metering valve, 174–175 Pressure differential, 248, 549 Pressure differential valve, 200, 200, 549 two-piston valve, 200, 200 Pressure hazards, job sheet, 35–36 Pressure measurement, 49 Pressure problems job sheet, 235–236 Pressure tools, 58, 59 Primary shoe, 386, 390, 391, 398, 549 Probe light, 83, 83 Proportioning valves, 215–216, 216, 549 Pull up resistor, 477, 484 Push (speed) nut, 380, 381, 549 Pushrod adjusting on a Honda, 263, 264 adjustment, 162 length check, 260–263, 262 Pyrometer, 58

Q Quick take-up master cylinder, 152, 549 Quick take-up valve test, 152

R Radial ply tires, 98, 549 Radial runout, 102–105, 104, 550 Reaction disc (or plate and levers), 550 Reactivity, 20 Reamer, 66, 550 Rear cable replacement, 448, 448–449 Rear caliper retraction, 297 Rear disc brake pedal travel, 435–438, 436–438 Rear disc brake service, 345 overhauling caliper, photo sequence, 348–352 Rear drum brake pedal travel, 435 Rear drum parking brakes inspection and adjustment, photo sequence, 442–443 Red brake lamp, bulb test, 134

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561

Red brake warning indicator, 520 Red “Park Brake” lamp, 454 Reference voltage, 477, 550 Refinishing brake drums, 415–422, 415, 417–418, 419–422 brake lathe, 415, 416 machining drum on lathe, 418–422, 418–421 mounting drum on lathe, 416, 417 photo sequence, 417–418 Refractometer, 148, 550 Regenerative braking systems, 525–527, 550 C1259/58 HV system regeneration malfunction (Toyota Prius), 527 DTC C012A 00 regenerative axle pressure sensor performance (Chevrolet Volt), 526, 526–527 Release Park Brake Switch, 453 Reluctance sensor, 550 Repair, electric parking brake, 454 Repair order, 88–89, 89 Replenishing port, 151, 166, 550 Return springs, 375, 375, 550 installing, 402, 402 tool, 63, 64 Road force balancers, 105, 550 Road test, 133–134, 134, 477 Rosin flux solder, 223, 550 Rotor, 322, 550 Rotor lateral run out, 326–328, 326–328, 550 Rotor runout, job sheet, 361–362 Rotor service inspection, 322–323, 322–323 installing rotor, 330–332, 331 measurement, 323–329 friction surface depth, 329, 329 lateral run out, 326–328, 326–328 thickness and parallelism, 324–326, 324, 325 table, 326–327 preventing run out and thickness problems, 332 refinishing, 332–347, 332–346 removing rotor, 329–330, 330 turning, 333 Rubber lubricants, 82 Rust jacking, 299, 550

S Safety agencies, 16–17 air bag, 22–23 antilock brake hydraulic pressure, 22 asbestos precautions, 11–14, 13 brake systems, 9–11 chemical, 14–16, 15–16 cleaning equipment, 21–22, 21, 79, 81 compressed air, 68–69, 69 eye protection, 5–6, 5 face protection, 5–6, 6 fire control, 24–25, 24 first aid, 6–7, 6

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562

Index

Safety (continued) hand protection, 7–8 hoist, 71–74 lifting and carrying, 8–9, 8 power tools, 66–68, 67 supplemental inflatable restraint systems (air bags), 23 survey, job sheet, 27–28 vehicle operation, 3, 4 work area, 1 Safety stands, 71 Scan tools, 85, 85, 550 job sheet, 505–506 testing, 492 Secondary shoe, 385–386, 390, 391, 398–399, 550 Self-adjuster, 387–389, 388, 391, 392, 550 installing, 400, 401 Self-energizing operation, 407 Self-powered test light, 83 Self-test programs, 470 Semi-metallic lining, 14, 550 Sensor resistance testing, 478–479, 480 Sensors, 216, 222 Sensor special tests, 476 Series circuit, 87, 87, 550 Series-parallel circuit, 87, 87, 550 Service information, 87–89 Service manuals, 99, 99, 101 Service park brake, 454 Servo action, 406–407, 550 Setback, 122, 551 Shoe inspection, 385–386, 385, 387 Short circuit, 218, 223 SIRS. See Supplemental inflatable restraint systems (SIRS) Sliding caliper, 297, 551 Slope, 481, 551 Sodium azide, 551 Soft code, 472, 551 Soldering, 225, 227 Solder-less connector, 223–224, 224, 551 Solvents brake cleaning, 14–15, 15, 16 Specific gravity, 147, 148, 551 Speed sensor bias voltage, 482–485, 484–485 Speed sensor testing, 478–486, 479–486 photo sequence, 482 Splice clip, 225, 227, 551 Split point, 551 Spool valve, 265, 268, 551 Spring inspection, 387–389, 388–389 Square-cut seal, 316, 319, 551 Squib coil, 551 Stability control off message, 520–521 Stability control systems, 515–516 antilock/traction control, 515–516, 516 diagnostic system check, 516 performing preliminary checks, 516 system self-check, 517

64540_em_indx_hr_554-570.indd 562

vehicle network, 517 Stability system tests, job sheet, 533–534 Star wheel, 406, 406–408, 407, 551 adjustment, 406–408, 406–408 Steel ruler, 50 Steering angle sensor, 519, 519–520 Steering knuckle, 287, 551 Steering problems, 118, 120 Stem unit, 47, 551 Stoplamp switch adjusting, 139–140, 140 Stoplamp testing and switch adjustment, 217–228, 221, 223–227 brake fluid level switch test, 223 brake warning lamp circuit troubleshooting, 220–222, 221 computer controlled turn and stoplamps, 219–220, 220 electrical connector repair, 225, 227 electrical wiring repair, 223–225, 224, 227 parking brake switch test, 222–223 replacing bulbs, 220, 220 Stroking seal, 318 Submultiple, 47, 551 Supplemental inflatable restraint systems (SIRS), 23, 551 disabling air bag system, 22 sensors, 22 Surge bleeding, 178, 551 Suspension inspection, 118, 120–121 Switch testing, 477–486, 478–486 brake fluid level, 223 digital (magnetoresistive sensor), 479–480 parking brake, 222–223 wheel speed sensor testing, 478–486, 479–486 See also Stoplamp testing and switch adjustment Symptom byte, 473, 474, 552 System component service, 518–520 electrohydraulic control unit, 518–519, 518–520 System control valves, 518, 518

T Table, of brake shoe, 385–386 Tandem booster, 248, 552 Tape measure, 50 Tapered roller bearing service, 105–118, 106, 552 adjustment, photo sequence, 119 cleaning and inspection, 112–113, 113 guidelines, 108 installation and adjustment, 115–118, 115–118 lubrication, 113–114, 114 removal, 108–110, 108–110 troubleshooting, 106–108, 107 Technical service bulletins (TSB), 88, 552 Technicians training and certification, 25, 25 Temperature measurement, 49–50 Test drive diagnosis, 496

2/1/18 7:20 PM

Index Tetrachloroethylene, 15, 15, 552 Teves ABS fluid level, 148 Threading, 410, 552 Throttle actuator control (TAC), 521–523, 524, 525, 552 Tire pressure monitoring systems (TPMS), 523–525, 552 Tire service checking run out, 102–105, 102, 104 inflation, 98, 99 inspection, 98–101 installation, 101–102, 101–102 mismatched tires, 99–101, 100 rotation, 99, 99 tire wear, 99–101, 100 tread wear, 99, 100 Toe angles, 120, 121, 552 Tools, 45–89 brake lathes, 70–71, 71–72 cleaning equipment and containment systems, 76–79, 77–79 cleaning equipment safety, 79, 81 electronic test equipment, 82–85, 83–85 fasteners, 45, 46 hand, 61–63, 61–63 hoists, 71–74, 72 lifting, 71, 72 measuring, 49–59, 50–59 power, 66–69, 67–70 pressure bleeders, 74–76, 75–76 selection, storage, and care, 59–60 special, for brakes, 63–66, 63–66 wrenches, 61, 61 Torque measurement, 49 Torque stick, 101, 101, 552 Torque wrench, 62, 62–63 Traction control off indicator, 520 Traction control system, 462 Trailing shoe, 407, 552 Training for technicians, 25 Tread, 98–99 wear indicators, 99, 100, 552 1,1,1-trichloroethane, 15, 552 Trichloroethylene, 15, 552 1,1,1-Tricloroetano, 544 TSB. See Technical service bulletins (TSB) Tubing bending, 209–210, 209–210 cutting, 209, 209 fabricating, 206–210, 206–210 flare fittings, 210–213, 211–213 inspection, 201–202, 202 photo sequence, 207–208 removal and replacement, 206 tools, 66, 67 bender, 66 cutter, 66 reamer, 66 Tubing bender, 66, 552 Tubing cutter, 66, 552

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563

U U.S. customary systems, 47

V Vacuum, 75, 552 Vacuum bleeding, 167, 175, 175–176, 177, 552 job sheet, 195–196 Vacuum-boost systems, 248–249, 249 booster components, identifying/inspecting job sheet, 277–278 booster installation, 256, 257–258, 259–260 booster overhaul, 260, 261 booster removal, 256–258, 257–259 job sheet, 279–280, 281–283 pushrod length check, 260–263, 262–263 servicing on vehicles with EHB or VSA, 270–271, 271 testing and diagnosis, 249–253, 252–253 fluid loss test, 253 operational test, 251 vacuum supply tests, 251–253 Vacuum cleaning equipment, 79, 79, 305, 306, 383–384, 384 Vacuum-enclosure cleaning systems, 304, 304–305, 383, 384 Vacuum supply tests, 251–253 Vacuum-suspended vacuum booster, 248, 552 Valve servicing, 214–216, 214–216 combination, 216, 216 metering valves, 214–215, 214–215 proportioning valves, 215–216, 216 Vehicle for service preparation, job sheet, 41–43 Vehicle, inspect and check out, 470 Vehicle network, instrument clusters, 222 Vehicle operation, and safety, 2, 3 Vehicle preparations, 290–291, 290 Vehicle service data job sheet, 95–96 Vehicle stability control (VSC), 270 servicing vacuum boosters on, 270–271, 271–272 Ventilated rotor, 330, 333, 553 Vent port, 137, 553 Vernier calipers, 54–55, 55, 298, 553 Vernier scale, 54, 55, 553 Volt (V), 84, 553 Voltage, 84 Volume measurement, 48, 48 VSC. See Vehicle stability control (VSC)

W Warning lamp, 499 checking, 470, 471 circuit troubleshooting, 220–222, 221 job sheet, 503–504 low brake pad, 222 replacing, 495 switch, 200, 200 Water content, brake fluid, 147

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564

Index

Ways, caliper slides, 287 Wear-indicating ball joints, 120, 121, 553 Web, of brake shoe, 394, 397, 400 Weight measurement, 49 Wet-cleaning systems, 304–305, 305, 383, 384 Wet-cleaning tools and equipment, 78–79, 80 Wheel alignment, 118, 120–121 inspection, 121 Wheel assembly remove and install job sheet, 125–126 Wheel bearing remove, repack, and install job sheet, 127–128 Wheel bearing grease, 82 Wheel brake bleeding sequences, 167–168, 168 Wheel cylinder, 553 honing, 395, 396 inspection, 386–387, 387 removal, 394, 394 service, 395–396, 396 Wheel service bearing service, 105–118 checking run out, 102–105, 102, 104 inspection, 98–101 installation, 101–102, 101–102 Wheel speed sensor front-wheel replacement, 496–497, 497

64540_em_indx_hr_554-570.indd 564

job sheet, 507–509, 511–512 rear-wheel replacement, 497, 497 replacement, 488–489, 489, 493, 494–495 replacement DBC-7, 493–495 testing, 478–479, 479–486 magnetoresistive, 485–486, 486 oscilloscope, 480–481, 481–482 speed sensor bias voltage, 482–485, 484–485 Wheel studs inspecting and replacing job sheet, 129–131 Wiggle tests, 476 Wiring repair, 223–225, 224, 227 crimping, 223–224, 224 photo sequence, 225–227 soldering, 225, 227 Work area safety, 1–9, 2 accidents, 1 housekeeping, 2–3 job sheet, 29–30 vehicle operation, 3, 4 Workplace Hazardous Materials Information Sheet, 18, 553

Y Yaw sensor/lateral accelerometer, 519, 519

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