58S01T0 hydraulic brakes operation and diagnosis 2004

1 - 1LESSON 1: HYDRAULIC BRAKES THEORY AND OPERATION Hydraulic Brakes Operation and Diagnosis February, 2004 CONTENTS OBJECTIVES LESSON 1: HYDRAULIC BRAKES THEORY AND OPERATION Introduc

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Ford Customer Service Division Technical Training

MEDIUM DUTY TRUCK HYDRAULIC BRAKES

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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 accomplishing service 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 the individual doing the work This manual cannot possibly anticipate all such variations and provide advice or cautions as to each 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 a specific purpose NOTES give you added information that will help you to complete a particular procedure CAUTIONS are given to prevent you from making an error that could damage the vehicle WARNINGS remind you to be especially careful

in those areas where carelessness can cause personal injury The following list contains some general WARNINGS that you should follow when you work on a vehicle.

• Always wear safety glasses for eye protection.

• Use safety stands whenever a procedure requires you to

be under the vehicle.

• Be sure that the ignition switch is always in the OFF

position, unless otherwise required by the procedure.

• Set the parking brake when working on the vehicle If you

have an automatic transmission, set it in PARK unless

instructed otherwise for a specific service operation If

you have a manual transmission it should be in

RE-VERSE (engine OFF) or NEUTRAL (engine ON) unless

instructed otherwise for a specific service operation.

• Operate the engine only in a well-ventilated area to avoid

the danger of carbon monoxide.

• Keep yourself and your clothing away from moving parts

when the engine is running, especially the fan and belts.

• To prevent serious burns, avoid contact with hot metal parts 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, loose hanging jewelry, and loose clothing before beginning to work on a vehicle Tie long hair securely behind your head.

• Keep hands and other objects clear of the radiator fan blades Electric cooling fans can start to operate at any time by an increase in underhood temperatures, even though the ignition is in the OFF position Therefore, care should be taken to ensure that the electric cooling fan is completely disconnected when working under the hood.

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

The descriptions, testing procedures, and specifications in this handbook were in effect at the time the handbook was approved 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 manual

is intended merely as an example of the types of tools, lubricants, materials, etc recommended for use Equivalents, if available, 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 Breathing

the 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 health when 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 fibers Dust and dirt should be disposed of in a manner that prevents dust exposure, such as sealed bags The bag must be labeled per OSHA 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, technicians should 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 technicians concerned with performing brake or clutch service should be present in the area.

Technical Support Operations Ford Customer Service Division February, 2004

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Mission Statement:

All dealership personnel will treat every customer as a potential lifetime purchaser, communicating a professional image which embraces honesty and concern for customer wants and needs.

4 Vehicles serviced right on the first visit.

5. Service status provided within one minute

of inquiry.

6. Vehicle ready at agreed upon time.

7. Thorough explanation of work done, coverages and changes.

1. Appointment available within one day of

the customer’s requested service day.

2. Write-up begins within four minutes of

arrival.

3. Service needs courteously identified,

accurately recorded on Repair Order,

and verified with customer.

These seven service standards provide a process and product value that are compelling reasons for owners to purchase and repurchase Ford or Lincoln-Mercury products These standards also help to attract 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 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.”

Technician’s Role

Acquire the skills and knowledge for competency in your specialty via

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Contents INTRODUCTION AND PREREQUISITE REVIEW

FORD BRAKES SERVICE TECHNICIAN SPECIALITY TRAINING (STST) CURRICULUM Intro - 2Curriculum Goals Intro - 3Air Brake System Operation and Diagnosis Instructor-Led Course Description Intro - 3Course Objective Intro - 3Lesson Objectives Intro - 3Audience Intro - 3Course Prerequisites Intro - 3Evaluation Intro - 4Student Guide Intro - 4Service Standards Intro - 5PREREQUISITE REVIEW Intro - 6

LESSON 1: HYDRAULIC BRAKES THEORY AND OPERATION

Introduction To Hydraulic Brake Systems 1 - 2Hydraulic Description 1 - 3Hydraulic Operation 1 - 4Brake System Overview 1 - 5Master Cylinder 1 - 6Hydro-Max Description 1 - 8Hydro-Max Operation 1 - 9ABS Description 1 - 16ABS Operation 1 - 17Parking Brake System 1 - 18Auxiliary Brake System Description and Operation 1 - 19

LESSON 2: COMPONENTS

Hydraulic Brake System Components 2 - 2Disc Brake System Components 2 - 3Hydro-Max System Components 2 - 13ABS System Components 2 - 19Parking Brake System Components 2 - 26

LESSON 3: DIAGNOSIS

Diagnosis and Testing 3 - 2Preliminary Brake System Checks 3 - 3Diagnostic Test 3 - 4Common Customer Concerns 3 - 12Brake Pedal Conditions 3 - 15Hydro-Max Booster Diagnostics 3 - 24ABS Diagnostics 3 - 28Meritor-WABCO Toolbox Software Functions 3 - 29Standard ABS Testing 3 - 31Standard ABS Component Testing 3 - 31

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GLOSSARY Glossary - 1

TOOL LIST Tool - 1

ROTUNDA ORDER FORM Rotunda - 1

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Intro - 1February, 2004

Hydraulic Brakes Operation and Diagnosis

INTRODUCTION AND PREREQUISITE REVIEW

OBJECTIVES

Review the Ford Medium Duty Truck Brakes

Service Technician Speciality Training (STST)

Prerequisite Review

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The Ford Medium Duty Truck Brakes Service Technician Speciality Training (STST) Curriculum consists of fivecourses related to brake system operation and diagnosis Each course in the curriculum is a “building block” forthe next course in the curriculum.

This curriculum is designed for technicians who want to learn the methods and techniques to properly diagnoseand service brake systems and components

Courses of The Ford Medium Duty Truck Brakes Service Technician Speciality Training (STST) Curriculum

MD TRUCK BRAKES CURRICULUM MAP

Electrical/Electronic Curriculum

MD Truck Hydraulic Brakes Theory and Operation Web Based Training - Course Code 58S03W0

MD Truck Air Brakes Theory and Operation Web Based

Training - Course Code 58S01W0

MD Truck Air Brakes Service and Diagnosis Web Based

Training - Course Code 58S02W0

MD Truck Hydraulic Brakes Operation and Diagnosis Instructor-Led

Training - Course Code 58S01T0

MD Truck Air Brakes Service and Diagnosis InstructorLed Training

-Course Code 58S02T0 FORD MEDIUM DUTY (MD) TRUCK BRAKES SERVICE TECHNICIAN SPECIALITY

TRAINING (STST) CURRICULUM

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INTRODUCTION AND PREREQUISITE REVIEWCurriculum Goals

The goals of this curriculum are to provide:

The necessary training to enable the technician to identify, diagnose and perform timely “Fix It Right TheFirst Time On Time” repairs

Increased customer satisfaction

Increased technician productivity

Fewer repeat repairs

Medium Duty Truck Hydraulic Brakes Operation and Diagnosis Instructor-Led Course

Description

This is the first instructor-led course in the Medium Duty Truck Brakes Curriculum It is a two-day course tated by an instructor This course is designed to provide hands-on opportunities for technicians to learn andimprove their skills using tools and equipment; and to apply knowledge learned in previous curriculum courses

facili-Course Objective

Given the information presented in the Ford Medium Duty Hydraulic Brake System Operation and DiagnosisCourse, the necessary service information and tools, technicians will be able to perform accurate, timely, cost-effective diagnosis and repair of ABS, Hydro-Max, and basic hydraulic brake systems on Ford Motor CompanyMedium Duty Trucks

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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 second day The hands-on evaluation is a pass/fail type

Hands-on evaluations will be conducted with exercises in:

– ABS diagnosis

– Written evaluation

– Special tool usage

In order to pass the course, you must demonstrate acceptable skills at the evaluated hands-on exercises and youmust answer at least 80% of the written post test questions correctly

Student Guide

The Student Guide contains the worksheets used at the workstations for each of the two days You must completeeach worksheet

IMPORTANT: Actively participate in exercise reviews This is your opportunity to ask questions and clear up any

areas that you may not fully understand

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INTRODUCTION AND PREREQUISITE REVIEW SERVICE STANDARDS

Mission Statement

All dealership personnel will treat every customer as a potential lifetime purchaser, communicating a professionalimage that embraces honesty and concern for customer wants and needs

Dealer-to-Customer Service Standards

Appointment available within one day of the customer’s requested service day

Write-up begins within four minutes of arrival

Service needs courteously identified, accurately recorded on Repair Order, and verified with customer

Standard 4

Vehicles Serviced Right on the First Visit:

Service status provided within one minute of inquiry

Vehicle ready at agreed upon time

Thorough explanation of work done, coverages and charges

The technician is the most important player 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

FORDSTAR Network (new model and curriculum)

New Model (self-study and instructor-led)

Repeat vehicle sales

Increased service department utilization

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

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PREREQUISITE REVIEW

INTRODUCTION

This course begins with a review of the content covered in the prerequisite web-based courses The review isdesigned to help you recall the key points and basic concepts of these courses Comprehension of these key pointsand concepts is essential to being successful in this course

Directions: Select the best answer for the questions listed on the following pages.

1 Friction is:

A Applied fluid pressure

B Resistance of movement between two surfaces in contact

C The amount of movement of a hydraulic component

D Energy of motion

2 Heat energy is:

A Created by friction

B Able to be compressed

C Used to multiply force

D None of the above

3 Friction occurs between:

A Kinetic energy and motion

B The brake backing plate and the axle

C The brake pad and the spinning rotor

D All of the above

4 Which of the following statements are true about levers?

A Levers are used to multiply force

B Levers are used to overcome resistance

C Levers are supported at a point called a fulcrum

D All of the above

5 Which of the following are hydraulic principles?

A Liquid in a confined space will not compress

B When pressure is applied to liquid in a confined space, the pressure will be transferred equally in alldirections

C A hydraulic system can be used to increase or decrease force or motion

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6 Ford medium duty trucks utilize a hydraulic booster called?

C Reservoir diaphragm gasket

D None of the above

9 The receives signals from the wheel speed sensors and processes the information todetermine if ABS operation is necessary

A Brake on/off switch

B Hydraulic Control Unit

C ABS control module

D ABS indicator lamp

10 It is necessary to purge the air from the master cylinder whenever it is replaced This action is called:

A Bench bleed

B Gravity bleed

C Full bleed

D Manual bleed

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NOTES

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1 - 1

Hydraulic Brakes Operation and Diagnosis February, 2004

CONTENTS OBJECTIVES

Introduction to hydraulic brake systems Hydraulic description and operationHydraulic brake system overview Master cylinder description and operationHydro-Max description and operationABS description and operationParking brake description and operationAuxiliary brake system description and operation

Upon completion of this lesson the student will

Hydro-Max system operation

hydraulic brake system

brake system

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INTRODUCTION TO HYDRAULIC BRAKE SYSTEMS

As you have learned while taking the web-based training in this curriculum, the purpose of the MD truck lic brake system is to provide a safe method of stopping for a heavier vehicle

hydrau-The components of a medium duty truck hydraulic brake system are:

– Brake pedal assembly

– Brake booster

– Master cylinder

– Brake lines

– Wheel brake assemblies

This lesson will review the operation of these subsystems in order to help you perform diagnosis and service

The components of a hydraulic brake system can differ, however, all systems operate in a similar manner.The hydraulic brake system must provide balanced braking at all wheels

– This will provide maximum brake system performance

– Brake system balance can be affected by worn, damaged or faulty components

NOTE: For a more detailed explanation of the theory and operation of a hydraulic system refer to the web-based

training course

Hydraulic Brake System

MDH-001

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1 - 3

Hydraulic theory operates on a few important principles These principles include:

– Liquid in a confined space will not compress

– When pressure is applied to liquid in a confined space, the pressure will be transferred equally in alldirections

– A hydraulic system can be used to increase or decrease force or motion

12 lbs (4.5 kg) of Force

48 lbs (18 kg) Lift

Liquid Connecting Tube

MDH-002

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Hydraulic Operation with Equal Size Pistons

Suppose two cylinders of equal diameter are placed side by side with a tube connecting them The system isfilled with liquid Each cylinder contains a piston If you push down on one of the pistons, the other pistonwill move an equal distance and with equal force

Since the liquid will not compress and the cylinders are the same diameter, the same amount of liquid, andmotion is transferred from one cylinder to the other

When pistons of different sizes are used, motion and force can be increased or decreased Suppose a smallpiston acts on a large piston The larger piston will move with more force However, it will move a shorterdistance

When a large diameter piston acts on a smaller piston, the opposite is true The smaller piston slides farther inits cylinder than the large piston, but it moves with less force

HYDRAULIC OPERATION

1 Piston Sroke 5 cm (2 inch) 2 Pressure Applied 15 kPa (2 psi)

MDH-003

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1 - 5

2

4

5 6

7

Hydraulic Brake System

Description and Operation

The standard hydraulic brake system featured on the Ford medium duty trucks consist of the following:

Ford MD trucks use a front/rear split hydraulic brake system The primary brake system controls the frontdisc brakes and the secondary system controls the rear disc brakes

It is very important to note that the hydraulic brake system uses two total separate fluids The power steeringpump, which provides brake boost uses automatic transmission fluid The master cylinder uses DOT 3 brakefluid

BRAKE SYSTEM OVERVIEW

5 6 7 8

Master Cylinder

Hydro-Max Booster

Rear Disc Rotor

Wheel Speed Sensor Power Steering Gear Power Steering Pump Front Disc Rotor

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1 2 3

4 5

6 MINI MASTER CYLINDER

1

2

3

4 5 6

Low Pressure

High Pressure

Brake Pedal Push Rod

Electric Motor (not operating) Primary Piston

Secondary Piston Mini Master Cylinder Operation

MDH-005

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1 - 7

Further movement of the primary piston creates a pressure in the primary pressure chamber causing thesecondary piston and actuator to move As the secondary piston and actuator move, the secondary compensat-ing valve closes, shutting off the passage between the secondary pressure chamber and the reservoir sectionserving the secondary chamber Additional movement of the primary piston causes both chambers to buildpressure

When the load on primary piston is removed, fluid pressure in each chamber, combined with return springforce, causes the primary and secondary piston to return to their initial released position Each actuator opensits respective compensating valve, reopening the passage between the individual reservoir sections and itsassociated pressure chamber

Should the rate of release be great enough to cause a partial vacuum in a chamber, the compensating valve willopen to allow replenishment of fluid in the cylinder bore

Any excess fluid remaining at the end of the stroke due to “pumping” and/or volume change due to ture fluctuation is released as the compensating valve ports open

tempera-MINI MASTER CYLINDER (continued)

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HYDRO-MAX DESCRIPTION

The hydro-max brake system has an electrically powered reserve hydraulic pump that operates if there is a

malfunction of the hydraulic pump system or when the engine is OFF It also has a mechanical push throughcapability if both of the other systems malfunction The push through provides a greatly reduced braking power,and the vehicle should not be operated in this mode except for emergency removal of the vehicle from the road.The system uses two totally separate fluids for operation

– Power steering fluid (ATF) in the pump, steering gear and power brake booster unit The system fill isaccomplished at the power steering pump reservoir and air is automatically removed from the systemwhile the pump is operating

– Hydraulic brake fluid is used in only the master cylinder Adding fluid and bleeding air from the systemare accomplished in the same manner as with manual or vacuum boosted brakes

The Hydro-Max booster works with a mini-master cylinder to supply the stopping power to the split lic brake system

hydrau-The mini-master cylinder actuating system for each set of brakes is mechanically separated into two dent hydraulic systems Hydraulic failure in one system does not affect function of the other system

Hydro-Max Booster and Master Cylinder

1

2

MDH-006

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1 - 9

8

1

4 5

6 7

Power Piston

HYDRO-MAX OPERATION

The primary function of the booster is to receive hydraulic fluid pressure through the inlet pressure port anduse this pressure against the power piston to drive the output push rod against the primary piston and actuatorsub-assembly in the mini-master cylinder

Under normal conditions, depressing the brake pedal will force the input pedal rod against the valve rod andthe reaction piston The reaction piston moves forward to close the pressure poppet (pressure valve) Closingthe pressure valve reduces the fluid flow into the area in front of the power piston (low pressure chamber).This action increases the forward pressure acting on the large diameter power piston, which in turn forces theoutput push rod into the master cylinder This action causes the Mini-Master cylinder to operate as previouslydescribed

The area between the hydro-max push rod forward o-ring and the primary piston rear o-ring of the mastercylinder is vented to the atmosphere This venting prevents mixture of the brake fluid with the power steeringfluid in the event one or both of these o-rings begin leaking

Integral Flow Switch (closed)

Inlet Pressure Port

Input Pedal Rod

Output Push Rod Primary Piston Secondary Return Spring Integral Flow Switch (open) Hydro-Max Operation

MDH-007

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Hydro-Max Operation (continued)

Engine Running - No Brake Application

When the total system is functioning properly and the hydraulic pump is supplying the Hydro-Max unit, theflow through the unit includes the following:

– Flow pressure from the power steering pump holds the hydro-max booster inlet check valve open

– Before the brake pedal is applied, fluid passes freely through the pressure valve and into the low pressurechamber

– Fluid passing out of the unit holds the flow switch open, preventing operation of the electric motor pump.– No pressure is applied to the power piston and the master cylinder push rod is at rest

– No action takes place in the master cylinder and no brake application is experienced

Flow Switch

Inlet Check Valve

Pressure Valve (open)

Brake Pedal Push Rod (at rest)

Low Pressure Chamber Master Cylinder Push Rod (at rest) Flow Switch (open)

Fluid Return Engine Running - No Brake Application

MDH-008

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1 - 11

Engine Running - Light Brake Application

When the brake pedal has been depressed slightly, the power assist action of the Hydro-Max unit begins Theflow through the unit includes the following:

– Flow pressure from the power steering pump holds the hydro-max booster inlet check valve open

– The brake pedal push rod begins to close the pressure valve As the flow is restricted, pressure builds-up inthe high pressure chamber The power piston is pushed by the build-up of pressure and results in powerboosted movement to the master cylinder through the master cylinder push rod

– Fluid passing out of the unit holds the flow switch open, preventing operation of the electric motor pump.– The forward movement of the master cylinder push rod forces the primary piston and actuator away fromits compensating valve

– Hydraulic pressure builds in the primary braking system and both the primary (front) and secondary (rear)brakes are applied

Engine Running - Light Brake Application

5 6 7

Brake Pedal Push Rod (partly applied)

Reaction Piston

High Pressure Chamber

Master Cylinder Push Rod Begins To Move Primary Piston (moves)

Flow Switch (open)

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6 7 8

1

2 3

4 5

Engine Running - Normal Brake Application

In a normal braking application (firm pedal, but not panic) the flow through the system includes the ing:

follow-– Flow pressure from the power steering pump holds the hydro-max booster inlet check valve open

– Brake pedal push rod moves inward and the pressure valve partially closes

– Pressure to the power piston is high

– The master cylinder push rod moves further into the master cylinder

– Fluid passing out of the unit holds the flow switch open at the electric pump

– Both the primary and secondary actuator pistons are moved past the respective compensating valve andboth the secondary and primary systems are pressurized

Master Cylinder Push Rod

Primary Piston

Secondary Piston Secondary Compensation Valve (seated) Primary Compensation Valve (seated) Flow Switch (open)

Engine Running - Normal Brake Application

MDH-010

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1 - 13

8

1 2 3

4 5

6 7

Engine Running - Maximum Brake Application

In a maximum braking application (emergency stop) the flow through the system includes the following:– Flow pressure holds the inlet check valve open

– The brake pedal push rod moves inward, virtually closing off fluid flow through the pressure valve Thisresults in maximum rated pressure on the power piston, which is transferred to the master cylinder throughthe master cylinder push rod

– The pressure regulator spring compresses and allows the pressure valve to open slightly and bypass fluidthrough the pressure valve orifice when maximum preset pressure is exceeded

– Fluid passing out of the unit holds the flow switch open, preventing operation of the electric motor pump.– Both the primary and secondary actuator pistons are moved to the maximum braking position

Inlet Check Ball (open)

Pressure Valve (almost totally closed)

Pressure Regulator Assembly

Brake Pedal Push Rod (fully applied)

Master Cylinder Push Rod (max output) Primary Piston

Secondary Piston Flow Switch (open) Engine Running - Maximum Brake Application

MDH-011

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NOTE: Operation of the master cylinder and wheel brakes is the same as described for normal

operation The electrical backup system should not be used for extended braking but only to get the vehicle to a service facility.

WARNING: THE VEHICLE SHOULD BE DRIVEN WITH EXTREME CAUTION AND

IMMEDIATE SERVICE IS NEEDED.

Hydraulic Boost Malfunction - Reserve Operation

5 6 7

Flow Switch (closed)

Inlet Check Valve (closed)

Increased Pedal Effort at Push Rod

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1 - 15

6

8 7

1 2

3 4

5Hydro-Max Operation (continued)

Complete Boost Malfunction - Manual Brake Application

In the event that complete loss of all power assist occurs during vehicle operation, it is still possible

to bring the vehicle to a controlled stop by push-through manual application of the master cylinder Brake pedal effort and travel will be greatly increase and vehicle stopping distance will be signifi- cantly longer.

– Operation of the master cylinder is as described previously for normal operation.

WARNING: DO NOT ATTEMPT TO DRIVE THE VEHICLE EXCEPT FOR EMERGENCY REMOVAL FROM THE ROADWAY.

Inlet Port (no flow)

Check valve opens (to relieve pressure)

Electric Motor Pump (not operating)

Master Cylinder Push Rod Direct Mechanical Force From Brake Pedal Flow Switch (closed)

Return Port (no flow) Complete Boost Malfunction - Manual Brake Application

MDH-013

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Vehicles equipped with hydraulic brakes are also equipped with a 4-channel, 4-wheel anti-lock brake system(4WABS), manufactured by Meritor-WABCO An anti-lock control system is intended to prevent wheel lockupduring panic stops and in situations where road conditions (wet or icy) may lessen traction By preventing lockup,the driver can maintain steering control Anti-lock brake systems (ABS), however, are federally mandated forvehicles weighing 19,500 pounds or more.

Under normal braking, fluid from the master cylinder enters the hydraulic control unit (HCU) and exitswithout pressure control

ABS System

ANTI-LOCK BRAKE SYSTEM (ABS) DESCRIPTION

1

2

3

4 5

ABS Warning Light

Wheel Speed Sensor

Hydraulic Control Unit (HCU)

Brake ON/OFF Switch (BOO) Dual Piston Caliper

MDH-014

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1 - 17

ANTI-LOCK BRAKE SYSTEM (ABS) OPERATION

An anti-lock control system is intended to prevent wheel lockup during panic stops and in situations whereroad conditions (wet or icy) may lessen traction By preventing lockup, the ABS system allows the driver tomaintain steering control The anti-lock control system prevents wheel lockup by controlling brake fluidpressure

The anti-lock brake system (ABS) control module controls fluid pressure by opening and closing four pairs ofsolenoid operated valves — a dump and isolation valve for each wheel Under normal braking, fluid from themaster cylinder enters the hydraulic control unit (HCU) and exits without pressure control

If a difference in wheel speed, as measured by the wheel speed sensor, signals an approaching lockup tion, the anti-lock control module will first close off pressure from the master cylinder to the affected wheel.The isolation valve is used for this purpose If this action does not bring the wheel back from the edge oflockup, the anti-lock control module will open the dump valve, relieving all pressure to the affected wheel.The anti-lock control module will then alternate between the isolation and dump valve to maintain a pressurebelow lockup Depending on conditions, the anti-lock control module may pulse the valves up to 18 times persecond

condi-Fluid released from the system by the dump valves accumulates in the reservoirs — one for the front chamber

of the master cylinder and one for the rear chamber This fluid is returned to the master cylinder by the pump.The pump shuts off when wheel speeds return to normal

1

2

3

4 5 6

Master Cylinder

Pump Element

Isolation Valve

Dump Valve Low Pressure Accumulator Brake Disc

ABS Operation

MDH-015

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2

PARKING BRAKE SYSTEM

Manual Parking Brake

The current model year medium duty trucks with hydraulic brakes use a driveline mounted parking brake

Previous models were mounted on the transmission output

The driveline mounted parking brake is a simple drum brake assembly with stationary-mounted, internalexpanding shoes and a drum that rotates with the driveshaft

The park brake is applied by pulling on the park brake lever

This applies tension to the cable, which activates the parking brake shoes

Manual Parking Brake System

MDH-016

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1 - 19

MDH-017

Exhaust Brake System

AUXILIARY BRAKE SYSTEM DESCRIPTION AND OPERATION

Exhaust Brake Description

An exhaust brake is an auxiliary braking system that attaches to the engine exhaust system The exhaust brakefunctions by partial closing off the exhaust pipe, creating an increase in exhaust pressure

During vehicle deceleration, the engine must turn against the back pressure creating a braking effect of thedrive wheels The effect of the exhaust brake is to make the engine act as a compressor The exhaust brake isused to aid the service brakes in slowing the vehicle down, reducing service brake wear The maximum

allowable exhaust back pressure is 241 kPa (35 psi) at 2,860 rpm

Exhaust Brake Operation

The exhaust brake consists of an air actuated cylinder attached to a butterfly type valve The air cylinder iscontrolled by a pneumatic valve mounted on the frame rail The pneumatic valve is controlled by the enginecontrol module (ECM) through the exhaust brake relay

With the exhaust brake ON/OFF switch in the ON position, the accelerator pedal released and the clutch pedal

in the up (clutch engaged) position, the exhaust brake will be activated When the accelerator pedal or clutchpedal is depressed, or when the anti-lock brake system (ABS) is activated, the exhaust brake will deactivate

5 6 7

1

2

3

4

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NOTES

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2 - 1

February, 2004Hydraulic Brakes Operation and Diagnosis

CONTENTS OBJECTIVES

LESSON 2: HYDRAULIC BRAKE SYSTEM COMPONENTS

Hydraulic brake system components overviewDisc brake system components

Hydro-Max system components Anti-Lock Brake System componentsParking brake system components

Upon completion of this lesson the student will

be able to:

system

booster brake system

hydraulic brake system

system

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HYDRAULIC BRAKE SYSTEM COMPONENTS

Current model year Ford medium duty trucks are equipped with a standard 4-wheel ABS hydraulic brake system,manufactured by Meritor-WABCO

The hydraulic braking system uses dual-piston caliper disc brakes in both front and rear

Both front and rear brakes use a vented disc rotor

The medium duty trucks are equipped with a brake pedal-actuated dual brake system It is split front and rear,with the front wheel brakes comprising one hydraulic circuit and the rear wheel brakes the other circuit The system consists of the following:

– Hydro-Maxbrake booster

– Brake master cylinder

– Front disc brake calipers

– Rear disc brake calipers

– Brake tubes and hoses

– Anti-lock brake system

Hydraulic Rear Disc Brake

MDH-018

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2 - 3

Disc Brake Pad

COMPONENT FUNCTION:

Brake pads press against the sides of the rotor, slowing or stopping the rotor’s rotation

COMPONENT LOCATION:

One pad is located on each side of the rotor

DESCRIPTION AND OPERATION:

Disc brake pads are constructed of friction material riveted or bonded to a steel backing plate

Brake pad friction materials are constructed of the following:

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2.Visually inspect the pad lining by checking each visible end and inspecting through openings of caliper Iflining thickness at the thinnest point appears to be 4.76 mm (3/16 inch) or less, the pads must be replaced.

3 It is recommended that all disc brake pads be replaced at the same time since this will maintain balanced

braking of the vehicle If complete replacement is not desirable or necessary, be sure that all disc brake pads onone axle (both sides) are replaced at the same time

NOTE: When replacing disc brake pads, be sure to use the same lining material type on both axles Mixing lining

types can result in unbalanced braking and pad wear

4 Disc brake pads should not be replaced because of moderate erosion or pitting This is a normal characteristic ofsemi-metallic pad lining material Should erosion reduce the polished contact area to less then 80% of totalsurface area, replace pads

5 Disc brake pads with lining material that shows excessive erosion at the edges or from the contact area withrotor must be replaced

6 Pads must be replaced if an examination of disc brake pads reveals excessive chipping or flaking and 80% orless contact area with rotor

NOTE: The polished contact area is represented in the illustration by the white area on the pad surface.

7 Disc brake pads must be replaced if contaminated by oil, grease or other foreign material which cannot be easilyremoved with a clean rag

Disc Brake Pads (continued)

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Disc Brake Caliper

DESCRIPTION AND OPERATION:

The current model year medium duty trucks use a dual-piston, floating or sliding caliper

Previous model years used a quad piston, fixed caliper

A disc brake caliper consists of the following components:

– Piston(s)

– Piston seal(s)

– Piston dust boot(s)

The caliper pistons push against the inboard disc brake pad which forces the lining of both inboard and

outboard disc brake pads against the rotor during brake pedal application

Disc Brake Calipers

MDH-020

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2 Remove caliper pistons from caliper using pliers designed for disc brake caliper piston removal If pliers are notavailable or pliers cannot remove pistons, remove pistons using compressed air Refer to previous illustration.

NOTE: If using compressed air to remove the pistons and piston boots, use air lines that are completely free of oil

and moisture

3 If using compressed air, place a block of wood between the caliper and caliper pistons Leave approximately 1

to 1-1/2 inch clearance between caliper pistons and block of wood

WARNING: USE JUST ENOUGH AIR PRESSURE TO EASE PISTONS FROM CALIPER BORE KEEP HANDS OUT OF AREA BETWEEN PISTON AND CALIPER IF HIGH PRESSURES ARE APPLIED, THE PISTON MAY POP OUT WITH CONSIDERABLE FORCE FAILURE TO

FOLLOW THESE INSTRUCTIONS MAY RESULT IN PERSONAL INJURY.

4 Remove plug from hydraulic line inlet port of caliper

5 Using an air blow nozzle, insert the nozzle into hydraulic line inlet port of caliper and inject air into caliperpushing caliper pistons out of caliper piston bores Refer to previous illustration

6 Remove block of wood and remove pistons from caliper using caliper piston pliers, if necessary

7 If pliers are not available, place a thin piece of cardboard over caliper piston opening Hold cardboard firmlyonto caliper and apply compressed air into caliper inlet port again The caliper pistons should pop out of caliperand the cover will contain the pistons keeping them from flying out and causing personal injury

8 If the caliper pistons are seized or cocked and do not come out, release air pressure and use a soft (brass)

hammer to rap sharply on and around the end of the pistons Then reapply air pressure to remove pistons If notdamaged, save for reinstallation

9 Remove piston boot from the caliper piston bore by prying them out with a small blunt screw driver Be carefulnot to damage the caliper piston bore in the caliper or piston boot If not damaged, save for reinstallation

10 Remove piston seal from inside piston bore of the caliper Do NOT reuse piston seal

11 Repeat Steps 9 and 10 above to remove the other piston boot and seal Refer to previous illustration

12 Visually inspect caliper for damage or defects to piston bores or piston seal and piston boot grooves If

damage or defects are found, repair or replace as required

Disc Brake Calipers (continued)

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