air brake bendix

7/27/2019 Air Brake Bendix

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Ford Customer Service DivisionTechnical Training

Air Brake System

Operation an

Diagnosi

Student Guid

ORDER NUMBER: FCS-13990-R

COURSE CODE: 58S0

February, 2

3

3

1

42

FCS-13990-RFCS-13990-RFCS-13990-RFCS-13990-RFCS-13990-R


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IMPORTANT SAFETY NOTICE

Appropriate service methods and proper repair procedures are essential for the safe, reliable operation of all motor vehicles,as well as the personal safety of the individual doing the work. This manual provides general directions for accomplishingservice and repair work with tested, effective techniques. Following them will help assure reliability.

There are numerous variations in procedures, techniques, tools and parts for servicing vehicles, as well as in the skill of theindividual doing the work. This manual cannot possibly anticipate all such variations and provide advice or cautions as toeach. Accordingly, anyone who departs from instructions provided in this manual must first establish that he compromises

neither his personal safety nor the vehicle integrity by his choice of methods, tools or parts.

As you read through the procedures, you will come across NOTES, CAUTIONS, and WARNINGS. Each one is there for aspecific purpose. NOTES give you added information that will help you to complete a particular procedure. CAUTIONS aregiven to prevent you from making an error that could damage the vehicle. WARNINGS remind you to be especially carefulin those areas where carelessness can cause personal injury. The following list contains some general WARNINGS thatyou should follow when you work on a vehicle.

Always wear safety glasses for eye protection.

Use safety stands whenever a procedure requires you tobe under the vehicle.

Be sure that the ignition switch is always in the OFFposition, unless otherwise required by the procedure.

Set the parking brake when working on the vehicle. If youhave an automatic transmission, set it in PARK unlessinstructed otherwise for a specific service operation. Ifyou have a manual transmission it should be in RE-VERSE (engine OFF) or NEUTRAL (engine ON) unlessinstructed otherwise for a specific service operation.

Operate the engine only in a well-ventilated area to avoidthe danger of carbon monoxide.

Keep yourself and your clothing away from moving partswhen the engine is running, especially the fan and belts.

To prevent serious burns, avoid contact with hot metalparts such as the radiator, exhaust manifold, tail pipe,catalytic converter and muffler.

Do not smoke while working on the vehicle.

To avoid injury, always remove rings, watches, loosehanging jewelry, and loose clothing before beginning to

work on a vehicle. Tie long hair securely behind yourhead.

Keep hands and other objects clear of the radiator fanblades. Electric cooling fans can start to operate at anytime by an increase in underhood temperatures, eventhough the ignition is in the OFF position. Therefore, careshould be taken to ensure that the electric cooling fan iscompletely disconnected when working under the hood.

The recommendations and suggestions contained in this manual are made to assist the dealer in improving his dealership partsand/or service department operations. These recommendations and suggestions do not supersede or override the provisions othe Warranty and Policy Manual, and in any cases where there may be a conflict, the provisions of the Warranty and Policy Manuashall govern.

The descriptions, testing procedures, and specifications in this handbook were in effect at the time the handbook wasapproved for printing. Ford Motor Company reserves the right to discontinue models at any time, or change specifications,design, or testing procedures without notice and without incurring obligation. Any reference to brand names in this manualis intended merely as an example of the types of tools, lubricants, materials, etc. recommended for use. Equivalents, ifavailable, may be used. The right is reserved to make changes at any time without notice.

WARNING: Many brake linings contain asbestos fibers. When working on brake components, avoid breathing the dust. Breathingthe asbestos dust can cause asbestosis and cancer.

Breathing asbestos dust is harmful to your health.

Dust and dirt present on car wheel brake and clutch assemblies may contain asbestos fibers that are hazardous to your healthwhen made airborne by cleaning with compressed air or by dry brushing.

Wheel brake assemblies and clutch facings should be cleaned using a vacuum cleaner recommended for use with asbestos fibersDust and dirt should be disposed of in a manner that prevents dust exposure, such as sealed bags. The bag must be labeled peOSHA instructions and the trash hauler notified as to the contents of the bag.

If a vacuum bag suitable for asbestos is not available, cleaning should be done wet. If dust generation is still possible, techniciansshould wear government approved toxic dust purifying respirators.

OSHA requires areas where asbestos dust generation is possible to be isolated and posted with warning signs. Only techniciansconcerned with performing brake or clutch service should be present in the area.

Copyright 2004 Ford Motor Company Produced and Coordinated byTechnical Support OperationsFord Customer Service Division

February, 2004


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SERVICE STANDARDS

Mission Statement:

All dealership personnel will treat every customer as a potential lifetime

purchaser, communicating a professional image which embraces honesty andconcern for customer wants and needs.

4. Vehicles serviced right on thefirst visit.

5. Service status provided within one minute ofinquiry.

6. Vehicle ready at agreed upon time.7. Thorough explanation of work done, coverages

and changes.

1. Appointment available within one day of thecustomers requested service day.

2. Write-up begins within four minutes ofarrival.

3. Service needs courteously identified,accurately recorded on Repair Order, andverified with customer.

These seven service standards provide a process and product value that are compelling reasons forowners to purchase and repurchase Ford or Lincoln-Mercury products. These standards also help toattract new owners through favorable testimonials and improved owner satisfaction.

Standard 4

Fix It Right the First Time, on Time.

The technician is the most important player when it comes to Standard #4.

Why

Customers tell us Fixing It Right the First Time, on Time is one of the reasons they woulddecide to return to a dealer to buy a vehicle and get their vehicles serviced.

Technician Training

It is our goal to help the technician acquire all of the skills and knowledge necessary toFix it Right the First Time, on Time. We refer to this as competency.

Technicians Role

Acquire the skills and knowledge for competency in your specialty via

STST New Model

Web-Based Training FORDSTAR Ford Multimedia Training (FMT) Instructor-Led Instructor-Led

The Benefits

The successful implementation of standards means

Satisfied customers Repeat vehicle sales Repeat service sales Recognition that Ford and Lincoln/Mercury technicians are

the Best in the Business

Dealer-to-Customer Service Standards:


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Contents

IMPORTANT SAFETY NOTICE .............................................................................................................................. 1

INTRODUCTION AND PREREQUISITE REVIEW ...................................................................................... Intro - 1

Course Objectives ...................................................................................................................................... Intro - 2

Lesson Objectives ..................................................................................................................................... Intro - 2Course Prerequisites ................................................................................................................................. Intro - 2Evaluation ................................................................................................................................................... Intro - 3

WORKSHEET A .......................................................................................................................................... Intro - 5AIR BRAKE COMPONENT LOCATION AND FUNCTION ...................................................................... INTRO - 5

INTRODUCTION ................................................................................................................................................ 1 - 1INTRODUCTION TO AIR BRAKE SYSTEMS ................................................................................................... 1 - 2

Air Brake Components .................................................................................................................................... 1 - 3

OBJECTIVES....................................................................................................................................................... 1-1SYSTEM OPERATION - AIR SUPPLY SYSTEM................................................................................................. 1-2Air Compressor .................................................................................................................................................. 1-3

Governor ............................................................................................................................................................. 1-5Air Dryer .............................................................................................................................................................. 1-7

Air Dryer Service .............................................................................................................................................. 1-10Desiccant Replacement ................................................................................................................................... 1-11

Air Dryer Testing............................................................................................................................................... 1-12Single Check Valve ........................................................................................................................................... 1-13

Air Reservoir ..................................................................................................................................................... 1-14Air Reservoir Drainage System....................................................................................................................... 1-16Tank Valve ......................................................................................................................................................... 1-19

Safety Valve....................................................................................................................................................... 1-20Double Check Valve.......................................................................................................................................... 1-21

Air Pressure Gauge.......................................................................................................................................... 1-23

Low Pressure Indicator Switch ....................................................................................................................... 1-24Stoplight Switch ............................................................................................................................................... 1-25

OBJECTIVES....................................................................................................................................................... 2-1

SYSTEM OPERATION - AIR DELIVERY SYSTEM ............................................................................................. 2-2

Foot Control Valve .............................................................................................................................................. 2-3

Relay Valve .......................................................................................................................................................... 2-6

Quick Release Valve ........................................................................................................................................... 2-9

Air Brake Chambers ......................................................................................................................................... 2-10

OBJECTIVES....................................................................................................................................................... 3-1Cam Brakes ........................................................................................................................................................ 3-2

Automatic Slack Adjusters ................................................................................................................................ 3-4Free Stroke Measurement ................................................................................................................................. 3-7

Applied Stroke Measurement ............................................................................................................................ 3-8Brake Inspections .............................................................................................................................................. 3-9Brake Service ................................................................................................................................................... 3-10

Caging Procedure ............................................................................................................................................ 3-11Brake Relining .................................................................................................................................................. 3-12

Cam Brake Component Inspections............................................................................................................... 3-13

Cam Brake Reassembly................................................................................................................................... 3-14


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OBJECTIVES....................................................................................................................................................... 4-1

SYSTEM OPERATION - PARKING/EMERGENCY BRAKE SYSTEM ................................................................ 4-2

Parking Brake Control Valve .............................................................................................................................. 4-3Inverting Relay Valve .......................................................................................................................................... 4-5Spring Brake Chambers .................................................................................................................................. 4-12

OBJECTIVES....................................................................................................................................................... 5-1

INTRODUCTION TO AIR BRAKE SYSTEM DIAGNOSIS ................................................................................... 5-2SERVICE PRECAUTIONS ................................................................................................................................... 5-3

SYMPTOM-TO-SYSTEM-TO-COMPONENT-TO-CAUSE (SSCC) DIAGNOSTIC STRATEGY ........................... 5-4

AIR BRAKE SYSTEM TROUBLESHOOTING ..................................................................................................... 5-6

System Test 1 ...................................................................................................................................................... 5-7

System Test 2 ...................................................................................................................................................... 5-8System Test 3 ...................................................................................................................................................... 5-9System Test 4 .................................................................................................................................................... 5-10

System Test 5 .................................................................................................................................................... 5-11Brake Shoe and Component Inspection ........................................................................................................ 5-12

AIR BRAKE INSPECTION PROCEDURES ...................................................................................................... 5-13MAINTENANCE ................................................................................................................................................. 5-15

Contaminated Air ............................................................................................................................................. 5-16

Adjustments ..................................................................................................................................................... 5-17Air Compressor Diagnosis .............................................................................................................................. 5-18

AIR BRAKE CONCERNS .................................................................................................................................. 5-20BRAKE SHOE WEAR PATTERNS.................................................................................................................... 5-23

Brake Noise ...................................................................................................................................................... 5-24

OBJECTIVES....................................................................................................................................................... 6-1

ANTI-LOCK BRAKE (ABS) SYSTEM ................................................................................................................. 6-2AUTOMATIC TRACTION CONTROL (ATC) SYSTEM......................................................................................... 6-4

Anti-lock Control (ABS) Module ........................................................................................................................ 6-5Automatic Traction (ATC) Control ..................................................................................................................... 6-6ABS Relay Valve ................................................................................................................................................. 6-7

ABS and ATC Indicator Lights .......................................................................................................................... 6-8

ABS Modulator Valve ......................................................................................................................................... 6-9Wheel Speed Sensors and Wheel Speed Indicators ..................................................................................... 6-15ABS DIAGNOSIS............................................................................................................................................... 6-16

Performing Diagnosis ...................................................................................................................................... 6-17Diagnostic LEDs ............................................................................................................................................... 6-18CONTROL MODULE CONFIGURATION .......................................................................................................... 6-19

PARTIAL SHUTDOWN ...................................................................................................................................... 6-20

TOOL LIST....................................................................................................................................................Tool - 1


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NOTES


9/136Intro - 1February, 2004Air Brake Systems Operation and Diagnosis

INTRODUCTION AND PREREQUISITE REVIEW

OBJECTIVES

z Administer the prerequisite review

z Discuss the air brake system

CONTENTS

z Prerequisite Review

z Introduction to the air brake system



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Intro - 2 February, 2004 Air Brake Systems Operation and Diagnosis

Curriculum Goals

The goals of this curriculum are to provide:

z The necessary training to enable the technician to identify, diagnose and perform timely Fix It Right The

First Time On Time repairs

z Increased customer satisfaction.

z Increased technician productivity.

z Fewer repeat repairs.

Air Brake System Diagnosis and Service Instructor-Led Course Description

This course is a three-day course facilitated by an instructor. This course is designed to provide hands-on opportu-

nities for technicians to learn and improve their skills using tools and equipment; and to apply knowledge learned

in previous curriculum courses.

Course Objectives

Given the information presented in the Ford Air Brake System Diagnosis and Service Course, the necessaryservice information and tools, technicians will be able to perform accurate, timely, cost-effective diagnosis and

repair of the air brake system, the ABS, and the traction control braking systems on Ford Motor Company ve-

hicles.

z Describe air brake theory and operation.

z Explain air brake system operation.

z Identify Ford medium truck air brake system components.

z Explain air brake system diagnostics.

z Describe the components and operation of the ABS and ATC air brake systems.

z Explain ABS and ATC diagnostic procedures.

Lesson Objectives

Each lesson of this course starts with a list of objectives for the participants. The lesson objectives are designed to

support the course objective.

Audience

This course is designed for any Ford Medium Duty Truck service technicians. Additionally, this course is also

designed for training service technicians of Ford Designated Fleets.

Course Prerequisites

All students must have completed the first three courses in the curriculum prior to enrolling in this course. If you

have not completed all of the prerequisite courses please notify your instructor.

z Automotive Electrical 34S14T0

z Automotive Electronics 34S19T0

z Air Brake Theory and Operation Web Based Training - Course Code 58S01W0

z Air Brake Diagnosis Web Based Training - Course Code 58S02W0




Evaluation

Each technician attending this course will be required to pass a combination hands-on/written evaluation. This will

be administered on the afternoon of the third day. The hands-on evaluation is a pass/fail type.

z Hands-on evaluations will be conducted with exercises in:

Air brake system diagnosis

Air brake system service

ABS and traction control diagnosis

service publication CD-ROM/DVD navigation

special tool usage

In order to pass the course, you must demonstrate acceptable skills at the evaluated hands-on exercises AND you

must answer at least 80% of the written post test questions correctly.

Course Layout

z Introduction and Prerequisite Review

z Lesson 1: Air Supply System

z Lesson 2: Air Delivery System

z Lesson 3: Service Brake System

z Lesson 4: Parking Brake System

z Lesson 5: Air Brake Diagnosis

z Lesson 6: ABS and Traction Control


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SERVICE STANDARDS

Mission Statement

All dealership personnel will treat every customer as a potential lifetime purchaser, communicating a professional

image that embraces honesty and concern for customer wants and needs.

Dealer-to-Customer Service Standards

z Appointment available within one day of the customers requested service day.

z Write-up begins within four minutes of arrival.

z Service needs courteously identified, accurately recorded on repair order, and verified with customer.

Standard 4

Vehicles serviced right on the first visit:

z Service status provided within one minute of inquiry.

z Vehicle ready at agreed upon time.

z

Thorough explanation of work done, coverages and charges.The technician is the most important person when it comes to Standard 4.

Fix it Right the First Time, on Time

Why:

Customers tell us Fixing It Right the First Time, On Time is one of the top reasons they would decide to return

to a dealer to buy a vehicle and get their vehicles serviced.

Technician Training

It is our goal to help the technician acquire all of the skills and knowledge necessary to Fix It Right the First

Time, On Time. We refer to this as competency.

Technicians Role

The technicians role is to acquire the skills and knowledge for competency in your specialty via:

z FMT (self-study)

z FORDSTAR Network (new model and curriculum)

z New Model (self-study and instructor-led)

z STST (instructor-led)

z Web-Based Training (self-study)

Benefits

The successful implementation of standards means:

z Satisfied customers

z Repeat vehicle sales

z Increased service department utilization

z Recognition that Ford and Lincoln/Mercury technicians are the Best in the Business


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1. What is the most likely cause if there is a concern with cut-in pressure?

A. The compressor.

B. The relay valve.

C. The governor.

D. The quick release valve.

2. How often should reservoirs be drained?

A. Daily.

B. Weekly.

C. Monthly.

D. Yearly.

3. What pressure will the low air pressure warning light/buzzer activate?

A. 30 psi.

B. 50 psi.

C. 60 psi.

D. 90 psi.

4. The amount of slack adjuster movement required to bring the brake shoes and linings into contact with the

brake drum is ______________________.

A. Free Stroke

B. Down Stroke

C. Up Stroke

D. Applied Stroke

5. Which of the following diagnostic tools should be used when diagnosing the ABS system on medium duty

trucks?

A. The WDS.

B. The NGS.

C. Either A or B.D. None of the above.




6. Which of the following is measured when checking applied stroke?

A. The amount of movement that brings the brake shoes into contact with the drum.

B. The delivery pressure that comes from the foot control valve.

C. The amount of slack adjuster movement that occurs during a full brake application.

D. The rotational torque that applies the service brakes.

7. When testing the governor it should be checked ______________________.

A. at cut-in pressure.

B. at cutout pressure.

C. pressure with the vehicle off.

D. both cut-in and cutout pressures.

8. If there is excessive moisture in the system, which of the following is the likely cause?

A. The vehicles air filter is dirty.

B. The quick release valve is not operating correctly.

C. The air dryer is malfunctioning.

D. The reservoir is filled past capacity.

9. What is indicated if the VLT LED is green?

A. System is working properly.

B. There is a fault code stored.

C. Voltage is out of range.

D. The ECU is inoperative.

10. At what pressure must the stoplights illuminate?

A. Less than 2 psi.

B. Less than 5 psi.

C. Less than 7 psi.

D. Less than 10 psi.


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NOTES


17/136Overview - 1February, 2004

OVERVIEW

Air Brake Systems Operation and Diagnosis

CONTENTSOBJECTIVES

INTRODUCTION

z Overview of the course content.

z Air Brake System overview.

z Upon completion of this lesson the student will

be able to:

Describe the course objectives.

Identify the subsystems on an air brake

equipped vehicle.

Recognize that not all air brake vehicles are

equipped with the same components, but all

work in a similar manner.


18/136Overview - 2 February, 2004

OVERVIEW


INTRODUCTION TO AIR BRAKE SYSTEMS

As you have learned while taking the web-based training in this curriculum, the purpose of the air brake system is

to provide a safe method of stopping for a heavier vehicle.

z Air brake systems are divided into four subsystems. They are:

Air supply system.

Air delivery system.

Service brake system.

Parking/Emergency system.

The components of an air brake system can differ, however, all systems operate in a similar manner. The air

brake system must provide balanced braking at all wheels.

z This will provide maximum brake system performance.

z Brake system balance can be effected by worn, damaged or faulty components.

Note: For a more detailed explanation of the theory and operation of an air brake system refer to the web-based

training course.

2004 F-650/750

WARNING: BEFORE ATTEMPTING TO WORK ON THE AIR BRAKE SYSTEM, CERTAIN

PRECAUTIONS MUST BE OBSERVED. SINCE THE COMPRESSION AND STORAGE OF AIR

CAN BE COMPARED TO THE ENERGY IN A COILED SPRING, WHEN RELEASED, IT CAN

PRESENT A HAZARD IF NOT CORRECTLY RECOGNIZED. THE WHEELS OF THE

VEHICLE MUST ALWAYS BE CHOCKED SO THAT DEPLETION OF AIR WILL NOT

PERMIT THE VEHICLE TO ROLL.

AIR-001


19/136Overview - 3February, 2004

OVERVIEW


F-650/750

Air Brake Components

Using an air brake system to stop a medium-duty truck requires the proper operation of each of the subsystems.

For this to happen, each of the subsystems components must function correctly. Every component of each

subsystem has a task to perform that will allow the brake system to continue braking smoothly.

In this course we will look at each component, how the components operate, and the basic service procedures that

are important to insuring a correctly operating brake system.

AIR-002


20/136Overview - 4 February, 2004

OVERVIEW


NOTES


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LESSON 1: AIR SUPPLY SYSTEM

1 - 2 February, 2004 Air Brake Systems Operation and Diagnosis

z The compressor converts atmospheric air into compressed air.

z The compressor is driven by the vehicles engine and operates continuously while the engine is running.

z The compressor builds up the air pressure and feeds it to the air reservoirs of the supply system.

z The governor, which is located on the side of the compressor, maintains the required amount of air pressure in

the air reservoirs.

z The governor receives a signal pressure from the supply reservoir. When the signal pressure reaches the preset

cutout pressure the governor will prevent the compressor inlet valve from closing, thus preventing further air

from being compressed.

z The compressed air sent from the compressor through the discharge line may be sent through an air dryer prior

to reaching the air reservoirs.

z The air dryer collects and removes solid, liquid and vapor contaminants.

z The air reservoirs provide the compressed air for braking.

z There are at least three air reservoirs:

The supply reservoir, which cools the air, collects moisture and supplies air to the primary and secondary

air reservoir.

The primary reservoir, which is the air source for the rear brakes.

The secondary reservoir, which is the air source for the front brakes.

Both the primary and secondary tanks are equipped with one-way check valves to allow the air brakesystem to continue to operate in an emergency situation to bring the vehicle to a safe stop.

z A dual air pressure gauge has two needles, it reads pressures in the primary and secondary reservoirs.

SYSTEM OPERATION - AIR SUPPLY SYSTEM

Air Supply System

AIR-003

Item Description Item Description

Compressor

Governor

Air Dryer

Safety Valve

Low Pressure Indicators

Secondary Reservoir

Primary Reservoir

Supply Reservoir

1

2

3

4

6

7

8

9

5 Dual Air Gauge

1 2

3

4

56

7

89

10

10 One-way Check Valve


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Air Brake Systems Operation and Diagnosis February, 2004 1 - 3


Air Compressor

COMPONENT FUNCTION:

z The purpose of the air compressor is to build up and maintain the required amount of air pressure in the air

reservoirs of the supply system.

COMPONENT LOCATION:

z The air compressor is located inside the engine compartment.

DESCRIPTION AND OPERATION:

z There are two styles of compressors used depending on the vehicle engine design:

Belt driven.

Gear driven.

z Compressors are usually two cylinder, single stage, reciprocating piston design.

z Most compressors are composed of two major assemblies, the cylinder head and the crankcase.

Other major components include the compressor unloading mechanism and the governor.

z The cylinder head houses the intake and discharge valves and is installed on the upper portion of the crank-

case.

z The crankcase is a one piece casting combining the cylinder block and the crankcase.

The upper portion of the casting houses the cylinder bores and the unloader mechanism.

The lower portion contains the crankshaft and main bearings.

z The compressor is cooled by the engine coolant system and lubricated through the engine lubrication system.

Air Compressor


1 2Belt Driven Compressor Gear Driven Compressor

AIR-004

1

2


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Cutaway of an Air Compressor

Air Compressor (continued)


z The compressor is driven by the vehicles engine and operates continuously while the engine is running.

z The air system pressure developed during compressor operation is controlled by governor actuation of the

compressor unloader mechanism.

During the intake stroke, a slight vacuum is created above the piston in the cylinder bore causing the inletvalve to open and move from its seat.

Filtered atmospheric air then enters the cylinder until the piston reaches bottom dead center and begins to

reverse its travel.

As the piston begins its compression stroke, the inlet valve is closed, keeping the air from leaving the

cylinder through the inlet valve and the air is compressed.

As the air is compressed, it overcomes the spring force of the discharge valve and allows the compressed

air into the discharge line and to the reservoir.

As the piston moves downward, the discharge valve is closed and air is drawn into the cylinder by way of

the inlet valve, and the cycle begins again.

SERVICE:

In order to maintain a properly operating air brake system it is important that the compressor receives a clean

supply of air.

z Most vehicles rely on the vehicles air filter to maintain clean air, this makes vehicle maintenance a critical

factor for brake system efficiency.

z If a vehicle is equipped with a compressor mounted air strainer it must be properly installed and kept clean.


1

2

3

4

5

6

Inlet Valves

Discharge Valves

Rear End Cover

Rear Main Bearing Journal

Crankshaft

Piston

1

26

5

3

AIR-005

4


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Air Compressor Governor

Governor

COMPONENT FUNCTION:

z The purpose of the governor is to maintain brake system air pressure to a preset maximum and minimum

pressure level.

COMPONENT LOCATION:

z The governor is mounted to the side of the compressor and is typically connected to the supply reservoir and

the air dryer.


The governor controls the actual compression of air by actuating the compressor unloading mechanism.

z The governor receives a signal pressure from the supply reservoir and relays the signal to the air dryer.

z Depending on the signal pressure received, the governor opens or closes the path to the unloader mechanism.

Cutout pressure is the point that the governor opens the path, which allows air to reach the compressor

unloader piston and stops the compression cycle of the compressor.

Cut-in pressure is the point that the governor closes the path, which exhausts air from the compressor

unloader piston and starts the compression cycle of the compressor.

z When the signal pressure reaches the preset cutout pressure of approximately 897 kPa (130 psi), the governor

controls the unloader to prevent the compressor inlet valve from closing.

With the inlet valve unable to close, the compressor cannot compress the air drawn in and will exhaust itback through the inlet valve to the other cylinder (alternating the air back and forth between the cylinders)

z When the signal pressure from the reservoir drops to the cut-in pressure of approximately 724 kPa (105 psi),

the governor will control the unloader valve, which allows the inlet valve to close.

The air compressor will compress air and expel it through the discharge line to the supply reservoir or air

dryer.


1 2Compressor Governor

2

AIR-006

1


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Governor (continued)

SERVICE:

If during the diagnostic process you need to check the governors operation you should:

z Install a test gauge in the air lines, in the supply or service reservoir.

z Run the engine to build up air pressure.

z Check the cutout pressure, it should be 897 kPa (130 psi) maximum.

If the instrument panel air gauge is used, the pressure must range between approximately 724-897 kPa

(105-130 psi), allowing for gauge accuracy.

z With the engine running, slowly reduce the amount of air pressure in the system by applying and releasing the

brakes.

z Check the compressor cut-in pressure, it should be approximately 724 kPa (105 psi) minimum.

z If the governor does not correctly control compressor operation, it must be replaced. The governor is not

adjustable.

NOTE: Before installing a new governor, check the accuracy of the instrument panel air gauge with a test gauge.With the governor in its unloaded position and approximately 621-793 kPa (90-115 psi) reservoir pressure, check

for leaks at the base of the governor where it mounts to the compressor and repair as required.


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Air Dryer

AIR-007

Air Dryer

COMPONENT FUNCTION:

z The air dryer collects and removes solid, liquid and vapor contaminants from the air brake system.

COMPONENT LOCATION:

z Air dryers are located in the discharge line between the compressor and supply reservoir.


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Desiccant Cartridge Replacement

AIR-010

Air Dryer Service

Air dryers are very important to the delivery of clean, dry, oil-free air throughout the air brake system.

z If excessive oil is in the system it is a good indicator that the cartridge should be replaced.

A small amount of oil is normal in the system.

z The following considerations should be made prior to installing a new desiccant cartridge:

An outside air source has been used to charge the system. This air did not pass through the air dryer.

Air use is exceptionally high and not normal for a highway vehicle. This can be due to accessory air

demands or some unusual air requirement that does not allow the compressor to load and unload in the

usual way. Check for excessive air system leaks.

The air dryer has been installed in a system that has been previously used without an air dryer. This type

of system will be saturated with moisture and it can take several weeks of operation for the system to dry

out.

Location of the air dryer is too close to the air compressor. There must be a minimum of 1.8 m (6 ft) of

metal tubing between the compressor discharge port and air dryer supply port.

Vehicles operating in areas where more than a 17C (30F) range of temperature occurs in one day can

have small amounts of water accumulating in the air brake system. Under these conditions, small amounts

of water should not be considered an indication that the air dryer is not working.

WARNING: REMOVE ALL PRESSURE FROM THE AIR SYSTEM BEFORE DISCONNECTING

ANY COMPONENT, INCLUDING THE DESICCANT CARTRIDGE. PRESSURIZED AIR CAN

CAUSE INJURY.


1

2

3

4

5

Desiccant Cartridge Assembly

Desiccant Cartridge Sealing Rings

Cartridge Bolt O-Rings

Desiccant Cartridge Bolt

End Cover

1

2

34

5


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Desiccant Cartridge

AIR-011

Desiccant Replacement

If it is determined that the air dryer desiccant cartridge needs to be replaced, then the following procedure is a

general guideline. Always follow the appropriate service publication procedure.

Disassembly

To disassemble the air dryer:

z Use a wrench or socket, loosen the desiccant cartridge bolt.

z Then separate the desiccant cartridge from the end cover.

z Pull the desiccant cartridge bolt out of the end cover. Remove the desiccant cartridge.

z Remove and discard both o-rings from the desiccant cartridge bolt.

Cleaning and Inspection

z Using a clean rag, wipe the inside of the end cover clean. Pay particular attention to the cartridge bolt bore in

the end cover and the sealing surfaces for the large and small diameter desiccant cartridge sealing rings.

z Inspect for physical damage to the end cover.

z Inspect all air line fittings for corrosion and replace as necessary.

z Be sure to check the desiccant cartridge bolt paying particular attention to the threads and o-ring grooves. If

the bolt threads are damaged sufficiently to cause it to be difficult to hand thread it into the new desiccant

cartridge, replace the bolt.

Assembly

When reassembling the air dryer:

z Lubricate the o-rings, thoroughly wipe and clean the o-ring grooves, lubricate the end cover bore for the

desiccant bolt.

z Install both o-rings on the desiccant cartridge bolt, then using a twist motion insert the assembled desiccant

cartridge bolt in the end cover.

z Install the desiccant cartridge on the end cover making certain the cartridge is properly seated and flush on

the end cover.

It may be necessary to rotate the cartridge slightly until the anti-rotation lugs are properly aligned and

allow the cartridge to rest flush against the end cover.


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Air Dryer Testing

The following test should be performed prior to placing the vehicle back into service.

z Close all reservoir drain cocks. Build up system pressure to governor cutout and note that the air dryer

purges with an audible escape of air. Apply the service brakes several times until air pressure is reduced to

governor cut-in. Ensure that the system builds to full pressure and is followed by an air dryer purge.

z Check for excessive leakage around the head of the desiccant cartridge bolt and around the circumference ofthe desiccant cartridge where it is in contact with the end cover.

With the compressor loaded, apply a soap solution and observe that leakage does not exceed a 1 inch

bubble in 1 second.

If the leakage exceeds the maximum specified, remove and reinstall the desiccant cartridge. If leakage

persists replace the air dryer assembly.


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Air Reservoir

Air Tanks

COMPONENT FUNCTION:

z

Air reservoirs are tanks that provide storage of the compressed air used for braking.z They also cool the air and condense water vapor into a liquid.

COMPONENT LOCATION:

z Air reservoirs are usually mounted on the frame rail. The exact location may vary from vehicle to vehicle.


z There are at least three different reservoirs:

Supply

Primary

Secondary

z A supply reservoir is used to provide air to all other tanks used in the air brake system.

The supply reservoir may also be referred to as the wet tank.

The supply reservoir and the secondary reservoir may be in one divided tank.

z The primary reservoir is the air source for the rear brakes.

z The secondary reservoir is the air source for the front brakes.

AIR-013


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Air Reservoir (continued)

Dual Compartment Reservoir


z Some tanks have a separation inside, so that one storage tank is actually two different reservoirs.

For example, the supply reservoir may be located with the secondary reservoir in one tank, and although

they share the same shell, they actually perform two separate functions.

z Split-type tanks require an integral check valve, which may be internal or external.

The integral check valve provides a one-way passage of air from the supply reservoir in the tank to the

secondary reservoir. So if damage was to occur to the supply reservoir the secondary reservoir is pro-

tected against the loss of air.

z The operation of the integral check valve is as follows:

Under normal conditions the air pressure enters the supply reservoir and overcomes the check valve

spring, this moves the check valve off its seat and air pressure enters the secondary reservoir.

If air pressure is decreased or lost in the supply reservoir of the tank, the valve reseats and prevents air

flow from the secondary reservoir.

SERVICE:

z On an integral check valve you will have to remove the supply tank inlet line to check for a leaking check

valve.

AIR-014

1

2

3

4

5

6


4

5

6

Outlet Port

Integral Check Valve

Inlet Port

Supply Tank

Tank Divider

Secondary Reservoir

1

2

3


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AIR-015

Air Reservoir Drainage System

COMPONENT FUNCTION:

z Drain cocks or automatic moisture ejectors are used to drain condensation that accumulates in the reservoirs.

COMPONENT LOCATION:

z Drain cocks are installed at the bottom or end of each reservoir.

z Automatic moisture ejectors are usually mounted in the bottom or end of the reservoir.


z Drain cocks must be opened by hand.

CAUTION: Never strike the handle with a hammer or any other instrument, as the drain cock will be

damaged and leakage will develop.

z Automatic ejector valves operate as follows:

When there is no pressure in the system the inlet and exhaust valves are closed.

When the system is charged, a slight pressure opens the inlet valve, this permits air and contaminants to

collect in the sump cavity. This occurs until the governor cutout pressure is reached, then the inlet valve

closes.

When reservoir pressure drops, pressure in the sump cavity opens the exhaust valve and allows moisture

and contaminants to be exhausted until the sump cavity empties enough to close the exhaust valve.

1

2

3

Drain Cock


1

2

3Body

Handle

Spring


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Air Reservoir Drainage System (continued)

SERVICE:

Drain Cocks

z To check a manual drain cock for leakage:

Charge the air brake system, then test with a soap solution for leakage past the key and through the body

by coating the outside of the drain cock with a soap solution.

Leakage should not exceed 77mm (3 inch) soap bubbles in three seconds.

Automatic Moisture Ejector Valve

z If the automatic moisture ejector valve is functioning properly the following should occur:

With the system charged, apply the brake several times.

Check each time an application is made if an exhaust of air occurs at the exhaust port of the drain valve.

If no air comes out, push the wire stem. If air still doesnt come out, the filter or drain passage may be

plugged.

z To check the automatic moisture ejector valve for leakage:

With the system charged and pressure stabilized in the system, there should not be any leaks at the drain

valve exhaust.

A constant slight exhaust of air at the drain valve exhaust could be caused by excessive leakage in the air

brake system.

AIR-016

Automatic Moisture Ejector (Cutaway View)


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SERVICE:

Reservoir Draining

Moisture in the reservoirs can prevent the system from actuating smoothly and should be drained daily.

z

On vehicles equipped with drain cocks, open the drain cocks on all reservoirs until the pressure reaches 0 kPa(0 psi).

z If a vehicle is equipped with an automatic moisture ejector valve, but needs to be manually drained, use a tool

to press the stem on the bottom of the valve.

Drain Valves

WARNING: WHEN DRAINING THE SYSTEM, DO NOT LOOK INTO THE AIR JETS OR DI-

RECT THEM TOWARD A PERSON . THIS MAY CAUSE INJURY BECAUSE DIRT OR SLUDGE

PARTICLES CAN BE CARRIED IN THE AIR STREAM.

Air Reservoir Drainage System (continued)

Drain Cocks

1

AIR-017


1


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Tank Valve

AIR-018

Tank Valve

COMPONENT FUNCTION:

z Tank valves allow air pressure to build up in the brake system from an external air source.

COMPONENT LOCATION:

z Tank valves are located in one or more of the supply reservoirs.


z Tank valves may be quick connect or Schrader type valves.

SERVICE:

z Check tank valves for air leaks by performing the soap test.

There should be no leakage at the tank valve.

Tank Valve

1

1


1 2


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Double Check Valves (continued)

SERVICE:

z Double check valves can be bench tested or tested on the vehicle.

z To test a double check valve for proper operation two separately controlled air supplies must be connected to

the inlet ports:

Install a test gauge in the outlet port or in a line from the outlet port.

Apply and release air to one inlet port and ensure that the test gauge registers application and release.

Repeat this process in the other inlet port.

If a double check valve does not function properly it must be replaced.

z The leakage test on a double check valve should be performed at the inlet ports of the valve.

Disconnect the line from one inlet port.

Apply air to the other inlet port and coat opposite inlet port with soap solution.

Leaks should not exceed a 1-inch bubble in five seconds.


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NOTES


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LESSON 2: AIR DELIVERY SYSTEM

Brake Pedal

Foot Control Valve

COMPONENT FUNCTION:

The foot control valve controls the application of air pressure from the primary and secondary air reservoirs. The

air pressure delivery will vary in relation to the amount the brake pedal is pressed.

COMPONENT LOCATION:

z Standard brake pedal position.


Normal Operation - Primary Circuit:

z As the brake pedal is pressed, the plunger applies a force on the spring seat.

z The graduating spring compresses and in turn causes the primary piston to move.

z The primary piston, which incorporates the exhaust valve seat, closes the primary exhaust valve.

z As the primary exhaust valve closes, the primary inlet valve is moved off its seat, and air from the primary

service reservoir flows out the primary delivery port.

Normal Operation - Secondary Circuit:

z Once the primary inlet valve has moved off of its seat, air enters the relay piston cavity, which moves the relay

piston.

z The movement of the relay piston closes the secondary exhaust valve.

z As the secondary exhaust valve closes, the secondary inlet valve is moved off its seat allowing the secondary

air to flow out the secondary delivery port.

NOTE: The actions of the primary and secondary circuit valves occur at the same time.

AIR-025


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1

2

4

5

Brake Pedal Valve (cutaway)

Foot Control Valve (continued)

If a situation arises where air pressure is lost in one of the brake pedal circuits, the foot control valve is designed to

prevent complete brake failure.

Loss of Air Pressure - Primary Circuit:

z If air is lost in the primary circuit, while the brakes are being applied the secondary circuit will be activated.

As the brake pedal is pressed and no air pressure is present in the primary circuit supply and delivery

ports, the primary piston will mechanically push through and move the relay piston.

The movement of the relay piston closes the secondary exhaust valve and opens the secondary inlet valve.

This action allows air to flow out of the secondary delivery port.

z During loss of air pressure the brake pedal travel will be greater than normal to achieve push through to the

relay piston.

Loss of Air Pressure - Secondary Circuit:

z If air is lost in the secondary circuit, while the brakes are being applied, the primary circuit will continue to

function as normal.


1

2

3

5

6

7

Secondary Inlet and Exhaust Valve

Primary Piston

Rubber Spring Seat

Primary Inlet and Exhaust Valve

Relay Piston

Suspended-type Foot Control Valve

7

AIR-026

4 Rubber Spring


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Foot Control Valve (continued)

If the driver is concerned about a change in the vehicle braking characteristics such as, brakes apply too slowly, or

of a low pressure warning, you should check the primary and secondary brake circuits for proper operation or a

possible leak.

z To inspect the foot control valve for proper operation, check the delivery pressure. Perform the following

procedure using test gauges in the primary and secondary delivery system:

Apply the brake pedal, stop at various positions between the fully released and fully applied positions.

As the brake pedal is applied, view the test gauges and check for the pressures to vary equally and propor-

tionately with the movement of the pedal.

z After a full application is released, the reading on the test gauges should promptly drop to zero.

NOTE: The primary circuit delivery pressure will be approximately 14 kPa (2 psi) greater than the secondary

circuit delivery pressure with both supply reservoirs at the same pressure.

z To perform a leakage test the following procedure should be performed:

Apply the brake pedal as necessary to reach a pressure of 552 kPa (80 psi).

Coat the exhaust port and body of the brake valve with a soap solution.

Leakage should not exceed 25 mm (1 inch) bubbles in three seconds.

z If the brake valve does not operate properly or has excessive leakage the brake valve should be repaired or

replaced as necessary.


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Relay Valve


Applying

z As the brakes are applied air pressure is delivered to the control port and enters the cavity above the piston,

which forces the piston down.

z The exhaust seat moves down and seals off the exhaust passage.

z At the same time, the inlet valve moves off its seat, which allows supply air to flow from the primary reser-

voir, through the open inlet valve and into the brake chambers.

Balanced

z When the brake pedal is in the balanced position air pressure beneath the piston equals air pressure above the

piston.

z The inlet closes, the exhaust valve remains closed as line pressure balances delivery pressure.

z As delivered air pressure is changed the valve reacts instantly to the change, holding the brake application to

that level.

Releasing

z When air pressure is released from the control port, the exhaust seat is moved away from the exhaust valve,

opening the exhaust passage.

z The air pressure in the chambers is then exhausted through the exhaust port, releasing the brakes.

Relay Valve (cutaway)

1

4

2

3

5

6

7


5

6

7

Control Port

Inlet/Exhaust Valve

Spring

Delivery Port

Exhaust Cover Assembly

Supply Port

Piston

1

2

3

4

AIR-028


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Quick Release Valve

Quick Release Valve

COMPONENT FUNCTION:

z Quick release valves are used for rapid exhaust of air pressure from the front brake chambers (they may be

used on the rear brakes as well) so that the service brakes release quickly and the air doesnt have to travel

back to its source.

z In the parking brake system, when the parking brakes are applied, rapid exhaust of air occurs through the

quick release valve.

COMPONENT LOCATION:

z A quick release valve is mounted between the two front brake chambers and the two rear brake chambers on

some vehicles.


z Quick release valves operate as follows:

When air pressure passes through the quick release valve the quick release valves exhaust port is held

closed.

When air pressure decreases, the quick release valve exhaust port opens and releases the air pressure in the

service or spring brake chambers.

SERVICE:z To check the quick release valve for proper operation, apply and release the brakes, if the valve is functioning

properly then air pressure will be quickly exhausted through the exhaust port of the valve.

If there is a problem with the operation ensure that the exhaust port is not restricted.

z If you suspect the quick release valve of leaking, you should perform the following check:

Apply the brake.

Coat the exhaust port with a soap solution. Leakage should not exceed 25 mm (1 inch) bubbles in three

seconds.

Coat the body and cover with a soap solution. No leakage should occur.

AIR-030


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LESSON 3: SERVICE BRAKE SYSTEM

Cam Brake

Cam Brakes (continued)


5

6

7

1

2

3

4

7

1

3

4

5

6

Return Spring

Camshaft

Rollers

Brake Spider

Retaining Spring

Anchor Pins

2

AIR-034

Brake Shoe


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Automatic Slack Adjuster Components

Automatic Slack Adjusters

COMPONENT FUNCTION:

z The purpose of automatic slack adjusters is to change the forward motion created in the brake chamber into a

rotational torque that applies the service brakes, and to AUTOMATICALLY adjust to compensate for brake

shoe wear.

COMPONENT LOCATION:

z The arm of the slack adjuster is fastened to the push rod of the brake chamber with a yoke, and the slack

adjuster spline is installed on the brake cam shaft.

z Some automatic slack adjusters come in right and left hand configurations, as well as offset to fit clearance

requirements.


Automatic Slack Adjuster

z Automatic slack adjusters have an external manual adjustment in case a manual adjustment is needed.

z The key to a properly operating automatic slack adjuster is the ability to adjust during the early part of each

brake application.

Adjustment stops as brake torque builds up.

This prevents over-adjustment due to lining compensation or drum distortion.

Adjustment does not occur in specific increments, but makes very small adjustments as lining wear

occurs.


1

2

3

4

Link

Slack Adjuster

Grease Fitting

Hex Extension

1 2

4

AIR-035

3


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Automatic Slack Adjuster (On-Vehicle)

Automatic Slack Adjusters (continued)


z Automatic slack adjusters may be equipped with either of two yoke designs, both permit installation or

removal of the slack adjuster without disturbing the yoke body or its attached linkage.

The easy-on yoke assembly consists of an adapter that is threaded internally to match the push rod threads

and externally to match female threads in the yoke body.

The quick-connect yoke is designed for ease of installation in particularly close-coupled (short push rod)

installations. The adapter is threaded internally to match the push rod, but is designed to slide into the

yoke body and a corresponding groove in the adapter it is secured with a special flat washer and lock nut.Applied

z When the brakes are applied, the brake chamber push rod moves the yoke forward.

z As the push rod moves, the entire automatic slack adjuster rotates.

z As the slack adjuster rotates, the yoke pivots on the yoke pin.

z The adjusting linkage is pulled upward causing the adjusting crank to rotate clockwise.

z The adjusting mechanism is designed to have some freeplay, which ensures a set lining to drum clearance.

Released

z When the brakes are released, the push rod retracts into the brake chamber, returning the slack adjuster to thereleased position.

z As the slack adjuster rotates back towards the brake chamber, the yoke assembly pivots clockwise.

z The adjusting linkage moves, rotating the adjusting crank in the opposite direction it moved during applica-

tion.

z The initial rotation of the entire slack adjuster and the adjusting crank takes up the free play between the drive

sleeve and wormshaft.

AIR-036


1 2Brake Chamber Automatic Slack Adjuster

2

1


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550-620 kPa (80-90 psi) Pressure in Air Chamber Clamp-Type Air Chamber

less than 38.1 3.2 mm (1.5 0.125 inches)less than 38.1 3.2 mm (1.5 0.125 inches)

less than 38.1 3.2 mm (1.5 0.125 inches)


912

16

20

Adjust the stroke as short as possible without the brakes dragging. The vehicle may

be put out of service if the stroke is not:

Chamber Type

(Size)

24

Front Axle

24

Rear Axle

24 Long Stroke

30

36

38.1 3.2 mm

(1.5 0.125 inches)





DOT Adjusted Air Chamber Stroke Limits

When inspecting the slack adjusters check the air chamber applied stroke:

z Applied stroke is the amount of slack adjuster movement which occurs during a full brake application.

To check air chamber applied stroke, perform the following steps:

1. With the brakes released, measure and record the distance from the air chamber face to the center of the large

clevis pin.

2. Make a full brake application (85 psi).

3. Make the same measurement you performed in step 1 again.

4. Subtract the step 1 measurement from the step 3 measurement to obtain the applied stroke measurement.

The applied stroke must be within the specifications for the brake chamber size.

Applied Stroke Measurement


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Drum Brake Measurement

Brake Inspections

SERVICE:

Measurements

Prior to a brake relining you must perform a thorough inspection of the cam brakes. You must perform the appro-

priate measurements to check if the brake components are within specifications. A thorough inspection of the

system and taking the appropriate measurements are essential to making sure that all of the components will

function as they were intended.

When performing inspections and taking measurements the following components should be checked:

z Check brake drum diameter using a brake drum micrometer.

This is important because the diameter of the brake drum determines how much heat can be dissipated

during braking.

If any drum is larger than the other on an axle set, it can cause mild to severe braking problems.

z Inspect the brake shoes and take measurements using a brake shoe stretch gauge.

Brake shoes can become stretched, twisted, and worn out from excessive heat, so it is important to check

the brake shoes for wear or damage.

Before replacing the brake shoes, ensure you are replacing the shoes with friction material of proper

length and dimensions. The size of the anchor-end pinhole is also critical for proper alignment. If these

factors are good, then the life of the shoes will be increased.

z The brake spyder assembly keeps the brake components in alignment with the brake drum. Therefore, a brake

spyder gauge should be used to check the assembly for bends or distortions, as this will affect braking ability

and performance.

AIR-038


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Caging Process

Caging Procedure

SERVICE:

Brake Caging Procedure

If during brake service you must cage the spring brake follow the appropriate service publication procedures. A

general procedure is as follows:

1. Chock the wheels.

2. Pull the rubber plug from the hole on the spring brake end cap.

3. Remove the release bolt, nut and washer from the side of the brake air chamber.

4. Insert the release bolt into the spring brake chamber and into the internal T-slot. Turn the release bolt 90

degrees, until it locks and cannot be pulled out.

Caution: To avoid damage to the spring brake chamber, do not use air-driven tools to tighten the

release bolt nut. Do not exceed the torque specifications.

Charging the brake system with normal air pressure will ease the tightening process.

5. Install the washer and nut on the release bolt and tighten to the appropriate specification.

NOTE: Always follow workshop manual procedures.

AIR-040


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Cam Brake Component Inspections

SERVICE:

Component Inspection Tips

During the disassembly of the brakes check the following:

z Inspect all shoes for even wear.

If the shoes are not worn evenly, there will be failed or misadjusted components that will need to be

corrected prior to replacing the brake shoes.

z Inspect the lining surface for heat checking. If heat checking is present it may indicate any of the following:

One wheel is doing more work than it is designed to, thus causing excessive heat.

Improper friction material is used in the lining effort

Overloading, excessive heat or improper friction selection.

z Check the wear across each shoe.

An uneven pattern or excessive grooves can indicate the drums need replacing.

An uneven pattern can also indicate a bent spider or bell mouthed drum.

z Inspect lining surface for oil or grease.

Grease and oil on the friction material will cause the lining to glaze and prevent it from doing its share of

the braking.

WARNING: NEVER REUSE OR ATTEMPT TO CLEAN A GREASE OR OIL SOAKED BRAKE

LINING OR SHOE.

z Inspect drum surface for even wear.

Heat checks, cracks and blue spots are indications of excessive heat.

Never reuse a drum if diameter wear is not within specifications, or if heat checks are aligned across the

braking surface or if hard spots exist.

z Check S-cam for wear at the bushings, head and spline areas.

The wheel with a worn S-cam or worn S-cam bushings is more than likely not doing its share of the

braking.

z Inspect the wear difference between the brake shoes both front to rear and side to side.

If the wear is not equal, this may indicate an air-timing imbalance or different rated friction materials.

NOTE: Check for inconsistent use of elbows in air lines. One 90 degree elbow is equal to 7 inches of extra line.

z Inspect all brake air lines leading to chambers.

Replace air lines if you find they are cracked or damaged either externally or internally, especially if they

are contaminated with dirt, oil or water.


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LESSON 4: PARKING BRAKE SYSTEM

OBJECTIVES

z Upon successful completion of this lesson, techni-

cians will be able to:

Explain the operation of the parking brake

system.

Identify the purpose and function of compo-

nents used on the parking brake system.

Perform diagnosis and service of the parking

brake system.

CONTENTS

z Parking brake components and operation.

z Workstation 3A.

z Workstation 3B.

z Workstation 3C.

z Workstation 3D.


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Inverting Relay Valve

Inverting Relay Valve

COMPONENT FUNCTION:

z The inverting relay valve performs four functions:

Limits air pressure (hold-off pressure) from reaching the spring brake actuators (internal to the spring

brake chamber) to 655-722 kPa (95-105 psi).

Provides for quick release of air pressure from the spring cavity of the spring brake actuator. This allows

a fast application of the spring brake chambers.

Modulates spring brake actuator application (so that braking is proportional), should a failure occur in the

primary air brake system.

Prevents compounding of service and spring forces.

COMPONENT LOCATION:

z The inverting relay valve is located on the frame rail near the rear axle.


z The inverting relay valve may also be referred to as the brake inversion valve, relay inversion valve, or spring

brake modulator valve.

AIR-046


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Brake Application with Loss of Secondary Brake System

Inverting Relay Valve (continued)


Loss of Air in Secondary Circuit

z If a failure occurs in the secondary air system, and a brake application is necessary, reduced or no air pressure

would be delivered to the top of the control piston.

z However, the balance piston will not move, but rear braking is unaffectd because the primary circuit supplies

the rear brakes.

z The spring brake actuators will not be actuated.

AIR-049


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Parking



Parking

z When the knob of the parking brake control valve is pulled out (park position), the inverting relay valves

supply air pressure and the air pressure in the spring brake chamber is exhausted.

z The air on top of the balance piston is exhausted through the supply port to the atmosphere.

z When air pressure drops sufficiently, the balance piston opens the inlet valve, thus opening the larger passage

in the inverting relay valve.

z This will ensure rapid exhaust of the balance of air pressure in the spring brake chamber.

SERVICE:

Hold Off Pressure Check

z Proper operation of the inverting relay valve is critical to the operation of the air brake system. To test the

inverting relay valve for proper operation, chock the wheels and charge the air brake system to governor

cutout pressure. Then perform the following steps:

1. Begin by checking that the spring brakes apply quickly when the parking brake control valve is placed in thepark position.

2. Next, remove one line or plug from the delivery port of the valve and install a test gauge.

3. When the parking brake knob is pushed in, check to ensure that the spring brakes release fully.

4. Check the pressure gauge when the parking brake control valve is in the release position.

The spring brake hold-off pressure setting should be approximately 655-724 kPa (95-105 psi). If the

pressure reading is not within the proper specifications, the inverting relay valve should be replaced.

1

Park Control Valve

AIR-051


1 2


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One Way Check Valve Test

z Another check that should be performed when inspecting an inverting relay valve is of the single check valve

(which is within the inverting relay valve). To carry-out this test, perform the following procedure (still using

the pressure gauge):

1. Place the parking brake control valve in the park position.

The gauge reading should drop to zero promptly. If the pressure drop has a lag time of more than 1

second, it means the single check valve (within the inverting relay valve) is operating correctly.

Anti-Compounding Test

z For further testing, check for proper operation of the inverting relay valve with the parking control valve in the

park position and the released position.

z In the park position:

1. With a test gauge installed on the spring brake chamber apply the brake pedal several times, check that the

pressure reading increases each time the brakes are applied.

If there is no pressure, or the pressure does not increase the inverting relay valve is not functioning

correctly.

Loss of Primary Air Pressure Test

z In the released position:

1. Drain the primary reservoir completely.

2. Apply the service brake pedal several times, check that the pressure reading decreases each time the brakes

are applied.

After the foot control valve has been applied several times, pressure on the gauge should drop to the point

where release of the spring brakes will no longer occur.

Leak Check

z Another potential concern when inspecting inverting relay valve is leakage. To check the inverting relay valve

for leakage perform a soap test using the following steps:

1. Place the parking brake control valve in the release position. Use a soap solution to coat the modulator valve

exhaust and vent hole near the adjusting screw.

A small amount of bubble leakage is acceptable.


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LESSON 5: AIR BRAKE SYSTEM DIAGNOSIS

OBJECTIVES

z Upon successful completion of this lesson, techni-

cians will be able to:

CONTENTS

z Diagnosis of the air brake system.

Diagnose the air brake system.


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INTRODUCTION TO AIR BRAKE SYSTEM DIAGNOSIS

We all know "any job worth doing is worth doing right." Of the many systems on an automobile, no system

requires adherence to this philosophy more than the brake system. A complete brake failure is every driver's worst

nightmare. While complete brake failures are relatively rare on modern vehicles, they do happen. If a complete

brake failure occurs on a vehicle, "customer concern" will not nearly describe the feelings of the customer when

(and if) they arrive at the service department. This is why it is so important that brake service be performedcorrectly the first time, every time.

Once a technician diagnoses the cause of a brake concern, determining what service is required, and performing

that service is the final step in solving the brake problem.

This lesson will cover general service principles and procedures that are common to many air brake systems.

However, due to the number of vehicles marketed by Ford Motor Company, all service variations cannot be

covered in this book. Therefore, whenever performing brake service, always use the appropriate service publica-

tion for the vehicle you are working on.


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SERVICE PRECAUTIONS

WARNING: BEFORE ATTEMPTING TO WORK ON THE AIR BRAKE SYSTEM, CERTAIN

PRECAUTIONS MUST BE OBSERVED. SINCE THE COMPRESSION AND STORAGE OF AIR

CAN BE COMPARED TO THE ENERGY IN A COILED SPRING, WHEN RELEASED, IT CAN

PRESENT A HAZARD IF NOT CORRECTLY RECOGNIZED. THE WHEELS OF THE VE-

HICLE MUST ALWAYS BE CHOCKED SO THAT DEPLETION OF AIR WILL NOT PERMITTHE VEHICLE TO ROLL.

When performing brake service certain general precautions must be followed to help insure quality service. The

first rule is to know and adhere to all safety procedures as outlined in the vehicles workshop manual. Below is a

list of other general precautions to follow during air brake service, these include:

zzzzz Hoses will whip dangerously if disconnected under pressure.

zzzzz Follow the manufacturers recommended procedures when working on any air devices so as to avoid

injury or damage from parts which, when released, are subject to mechanical (spring) or pneumatic

propulsion.

zzzzz As system pressure is drained and the emergency brakes apply, hands must be away from the airchamber push rods and spring actuators which apply automatically with the loss of pressure. This also

applies when checking the service brake system.

zzzzz Reservoirs which are closest to the sources of compressed air (compressors or auxiliary sources) must

contain a safety valve in known working order and sufficient capacity to limit the reservoir pressure to

a safe maximum level.

zzzzz Install new air reservoirs only. Used air reservoirs must not be used as replacements.

zzzzz The safety valve must not be installed with a higher than specified value by the reservoir manufacturer,

vehicle manufacturer, or code to which the reservoir had been manufactured.

zzzzz Various actuators contain powerful internal springs that require special handling procedures. Note and

be guided by the warning tags on such units.


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LESSON 5: AIR B

air brake bendix

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