Agr1St4E

1A1-A9 refers to ASE section. Use Ctrl+f to find what you need. Also use ctrl+f to search for specific things (e.g. limited slip differentials) if they are not specified in the table of contents.
2 
3Table of Contents
4 
5A1: Engine Repair
6A. General Engine Diagnosis
7 B. Cylinder Head and Valve Train Diagnosis and Repair
8   C. Engine Block Diagnosis and Repair
9     D.Lubrication and Cooling Systems Diagnosis and Repair
10       E.Fuel, Electrical, Ignition, and Exhaust Systems Inspection and Service 
11 
12A2: Automatic Transmission
13A. General Transmission/Transaxle Diagnosis
14 B. In-Vehicle Transmission/Transaxle Maintenance and Repair
15  C. Off-Vehicle Transmission/Transaxle Repair
16 
17A3: Manual Trans & Axles
18A. Clutch Diagnosis and Repair
19 B. Transmission Diagnosis and Repair
20  C. Transaxle Diagnosis and Repair
21   D. Drive Shaft/Half-Shaft and Universal Joint/Constant Velocity (CV) Joint Diagnosis and Repair (Front and Rear Wheel Drive)
22    E. Rear Wheel Drive Axle Diagnosis and Repair
23     F. Four-Wheel Drive/All-Wheel Drive Component Diagnosis and Repair
24 
25A4: Suspension and Steering
26A. Steering Systems Diagnosis and Repair
27 B. Suspension Systems Diagnosis and Repair
28  C. Wheel Alignment Diagnosis, Adjustment, and Repair
29   D. Wheel and Tire Diagnosis and Service
30 
31A5: Brakes
32A. Hydraulic System Diagnosis and Repair
33 B. Drum Brake Diagnosis and Repair
34  C. Disc Brake Diagnosis and Repair
35   D. Power Assist Units Diagnosis and Repair
36    E. Miscellaneous Systems (Pedal Linkage, Wheel Bearings, Parking Brakes, Electrical, etc.) Diagnosis and Repair
37     F. Electronic Brake Control Systems: Antilock Brake System (ABS), Traction Control System (TCS), and Electronic Stability Control System (ESC) Diagnosis and Repair 
38 
39A6: Electrical
40A. General Electrical/Electronic System Diagnosis
41 B. Battery Diagnosis and Service
42  C. Starting System Diagnosis and Repair
43   D. Lighting Systems Diagnosis and Repair
44    E.Instrument Cluster and Driver Information Systems Diagnosis and Repair
45     F. Body 
46 
47A7: HVAC
48A. Heating, Ventilation, A/C (HVAC) and Engine Cooling System Service, Diagnosis, and Repair
49  B. Refrigeration System Component Diagnosis and Repair
50   C. Operating Systems and Related Controls Diagnosis and Repair
51 
52A8: Engine Performance
53A. General Diagnosis
54 B. Ignition System Diagnosis and Repair
55  C. Fuel, Air Induction and Exhaust Systems Diagnosis and Repair
56    D. Emissions Control Systems Diagnosis and Repair (Including OBD II)
57     E. Computerized Engine Controls Diagnosis and Repair (Including OBD II)
58 
59A9: Light Vehicle Diesel Engines
60A. General Diagnosis
61 B. Cylinder Head and Valve Train Diagnosis and Repair
62  C. Engine Block Diagnosis and Repair
63   D. Lubrication and Cooling Systems Diagnosis and Repair
64    E. Air Induction and Exhaust Systems Diagnosis and Repair
65     F. Fuel System Diagnosis and Repair
66 
67X1: Exhaust
68A. Exhaust System Inspection and Repair
69 B. Emissions Systems Diagnosis
70  C. Exhaust System Fabrication
71   D. Exhaust System Installation
72    E. Exhaust System Repair Regulations
73 
74End Table of Contents
75
76
77  Brakes (A5)
78A. Hydraulic System Diagnosis and Repair (12 Questions)
791. 
80Master Cylinder
81
821. Diagnose poor stopping, dragging, high or low pedal, hard or spongy pedal caused by the master cylinder; determine needed repairs.
83Modern brake systems consist of front disc brakes, rear drum brakes, master cylinder, lines, valves, power assist booster, brake pedal, and flexible hoses. Many vehicles today are equipped with front disc and rear disc brakes. For safe and effective brake operation, all components in the brake system must be in proper working order.
84
85The heart of the brake system is the master cylinder. The master cylinder is a hydraulic pump that is operated by a pushrod connected to the brake pedal or assisted by a brake booster. The purpose of the master cylinder is to convert the driver's mechanical force to hydraulic pressure. Master cylinders are divided into two separate hydraulic systems. On most vehicles, one system controls the rear brakes and the other system controls the front brakes. If a hydraulic failure occurs in one system of a dual system master cylinder, the other system remains operational. This provides a greater protection against a total hydraulic brake failure.
86
87Some master cylinders are split diagonally. In this system, one half of the master controls one front wheel on one side and one rear wheel on the other side. The diagonal split system is most often found on front-wheel drive vehicles. Master cylinders are manufactured of aluminum and have a separate plastic reservoir. Aluminum master cylinders are anodized, which is intended to extend the life of the master cylinder by reducing corrosion.
88
89Some common symptoms of master cylinder related problems are an improperly adjusted brake light switch or cruise control switch, causing brake drag by keeping the brake pedal partially depressed. This causes the master cylinder to maintain pressure on the brake system. Also, a binding brake pedal caused by worn pivot bushings can cause brake drag.
90
91Air in the hydraulic system will cause a low, spongy pedal. An internal leak in the master cylinder cups may also cause a low, sinking pedal. Always consider the level and condition of the brake fluid when diagnosing master cylinder problems. Refer to A Tasks 1. Diagnose poor stopping, pulling, dragging, or incorrect pedal travel caused by problems in the brake fluid; determined needed repairs and 4. Select, handle, store, and install proper brake fluids (including silicone fluids) in 4. – Bleeding, Flushing, and Leak Testing (A.4.1 and A.4.4) for more on brake fluid. A worn or corroded internal master cylinder bore may cause excessive pedal effort and brake drag. Another cause for brake drag is a blocked master cylinder compensation port or vent port.
92
93Brake drag will cause overheated brake linings. It is important to inspect the entire brake system after determining a master cylinder problem.
94
95
96  2. Diagnose problems in the stepbore/quick take-up master cylinder and internal valves (e.g. volume control devices, quick take-up valve, fast-fill valve, pressure regulating valve); determine needed repairs.
97
98The stepbore, or quick take-up, master cylinder incorporates two different size bore diameters. The stepbore master cylinder improves brake effectiveness in low drag disc brake calipers, which improves fuel economy. In a stepbore master cylinder, the forward bore is slightly smaller than the rear bore. This design allows the small bore of the cylinder to supply high-pressure with low volume. The large bore supplies high volume at low-pressure. The large bore system initially supplies a large volume of fluid to move the caliper piston and apply the brake pads. Once the pads are in contact with the brake rotors, the small bore applies higher hydraulic pressure.
99
100The aluminum bore of a stepbore master cylinder is anodized and cannot be honed. Honing would remove the hard bore coating. If the bore is pitted or damaged, the master cylinder must be replaced.
101
102Stepbore master cylinders must be bench bled due to severe mounting angle, the quick take-up valve, and the four-port step bore design. It is nearly impossible to bleed all the air from the master cylinder once it is installed.
103Diagnosing problems with a stepbore master cylinder requires attention to details that are not common to other types of master cylinders. Never overfill a stepbore master cylinder. Overfilling can cause the front brakes to drag or cause excessive brake pedal effort. Another cause for excessive pedal effort or a hard pedal on a stepbore master cylinder is a clogged or plugged quick take-up valve. On the other hand, if a quick take-up valve opens too early, this can cause a low pedal condition.
104
105A defective quick take-up valve could cause a front caliper to drag and result in premature, uneven pad wear.
106
107
108  3. Measure and adjust master cylinder pushrod length.
109Brake pedal height and pushrod adjustment are often overlooked when diagnosing a brake problem. Correct pushrod adjustment is very important for proper braking. The pushrod must have a very slight gap between the tip of the pushrod and its mating surface in the master cylinder. Most manufacturers' pushrod length can be adjusted by unlocking and rotating an adjustment nut that is on the tip of the pushrod. A pushrod that is too long may cause the master cylinder piston to over-travel. This may damage the pistons seals and lead to a master cylinder failure. A pushrod that is too long may also cause the piston seals to block off the compensating (vent) port, which may cause brake drag or lock-up. If a vehicle has had repeated master-cylinder failures, verify that the pushrod is not over-extended. A pushrod that is too short may limit the amount of brake pressure developed and reduce the overall braking ability of the vehicle.
110
111Always check the brake light switch after making any adjustments.
112
113
114  4. Check master cylinder for failures by depressing brake pedal; determine needed repairs.
115Three common complaints that can be caused by a faulty master cylinder are brake fade, spongy pedal, and excessive pedal effort. Before you condemn the master cylinder, a complete brake inspection of all components must be performed.
116
117If the brake pedal slowly sinks to the floor when applied and the vehicle is stopped with the engine running, there may be a leak in master cylinder cups. This is known as "bypassing." Air leaking past the master cylinder piston cups will cause air to enter the fluid and cause a spongy pedal.
118
119Swollen master cylinder cups may cause excessive pedal effort or can be the result of a corroded master cylinder bore. If the master cylinder reservoir cover seal is badly swollen, suspect brake fluid contamination from oil, transmission fluid, power steering fluid, etc. If fluid contamination is discovered, a complete inspection of the brake system must be performed. 
120Contaminated fluid will damage all rubber components and seals in the brake calipers, wheel cylinders, and other brake parts. You must flush all the contaminated fluid from the brake system and replace all seals and cups in the master cylinder, calipers, and wheel cylinders. In addition, any time the lines are disconnected from the master cylinder or any other component, the brake system must be bled to remove trapped air from the lines and master cylinder.
121
122
123  5. Diagnose the cause of master cylinder external fluid leakage.
124External leaks from the master cylinder are usually easy to diagnose. Thoroughly clean the master cylinder first and check the fluid level. Check the condition of the reservoir seal and make sure the cover snaps tightly into place. If the fluid level is low, it may be normal due to brake pad wear or it may be an indication of a leak.
125
126A complete visual inspection of the entire brake system must be performed to accurately determine any problems. If there is excessive fluid at the rear of the master cylinder, or if the paint on the booster is blistered, check for leaking brake fluid at the rear of the master cylinder. If a leak is present where the booster bolts up to the master cylinder, there will probably be brake fluid in the booster. The booster must be inspected and cleaned thoroughly or will have to be replaced.
127
128Some master cylinders have a brake fluid reservoir, which is fitted into the main body of the cylinder. The seals of the reservoir and the cap must be inspected for possible leaks.
129
130
131  6. Remove and replace master cylinder; bench bleed and test operation and install master cylinder; verify master cylinder function.
132Replacing the master cylinder is usually straightforward. Start by cleaning the exterior of the master cylinder and the area around the master cylinder. Remove the brake lines and plug the ports on the master cylinder and the brake lines. Disconnect any electrical wiring to the master cylinder. Remove the attaching nuts at the brake booster. If the vehicle has manual brakes, disconnect the pushrod from the brake pedal. Carefully lift the old master cylinder away from the vehicle to avoid spilling brake fluid on the vehicle's exterior. Use fender covers to avoid brake fluid damage to the paint. If brake fluid comes in contact with paint, wash immediately with water.
133
134Before the replacement master cylinder is installed, it must be bench bled. Firmly secure the master cylinder in a vise and fill the reservoir with clean brake fluid. Make sure the master cylinder is level. Usually the new or rebuilt master cylinder will come with a pair of plastic fittings and hoses. Screw the fittings into the master cylinder ports. Attach one end of the hose to each port and place the other end of the hose in the reservoir. Make sure that both hoses remain submerged in the brake fluid of the reservoir. Using a drift or dowel, slowly press the master cylinder piston in and out until the air is dispelled from the cylinder.
135
136Stepbore master cylinders require 75 to 100 psi (517.1 to 689.5 kPa) to open the quick take-up valve. An option is to use a bleeder syringe to suck the air from the rear step bore of the master.
137
138Mount the master cylinder back in the vehicle. Check pedal height and brake pedal freeplay. The entire brake system must be bled after the master is installed to insure all the air is purged from the lines. Road test the vehicle and verify proper master cylinder and brake operation.
139
140
141  2. Lines and Hoses 
1421. Diagnose poor stopping, pulling, or dragging caused by problems in the lines and hoses; determine needed repairs.
143
144The master cylinder is connected to the wheel cylinders and calipers by a network of brake lines and hoses. Brake hoses create a flexible link between the steel line at the frame or body and the brake calipers or wheel cylinders.
145
146The pressure and flow throughout the entire brake system must be within specification. Even a partial blockage in the lines or hoses can restrict the flow of fluid and cause problems. The applying brake pressure may be enough to force fluid through a restriction, but the affected brake may not release or will release slowly. This can cause brake drag. When the restriction affects one wheel, this can cause a pull to one side during braking.
147
148
149  2. Inspect brake lines and fittings for leaks, dents, kinks, rust, cracks, or wear; inspect for loose fittings and supports; determine needed repairs.
150A comprehensive brake inspection of the brake lines and brake hoses should be part of any brake system diagnosis.
151
152Kinks or dents in the brake lines may affect hydraulic pressure. Also inspect all fittings for leaks and secure connections. Check all attaching supports at the frame, undercarriage, rear suspension, and struts. Attaching brackets and supports may loosen up or corrode over time. This may cause a shift in a brake line or hose and may cause damage to a line. A major concern for older vehicles, and in areas where salt is used during winter months, is corrosion and rust. Rusted brake lines can actually become porous and eventually leak brake fluid. Should this occur, a new line will need to be installed, or the damaged section replaced. When you repair sections of brake line, the parts of the old line that were cut will need to be double flared and connected to the new section of line using unions. Never use compression fittings to connect two pieces of brake line.
153
154
155  3. Inspect flexible brake hoses for leaks, kinks, cracks, bulging, wear, or corrosion; inspect for loose fittings and supports; determine needed repairs.
156Because flexible brake hoses move with the natural movement of the steering and suspension, they must be inspected for wear. Front flexible brake hoses are especially susceptible to cracking and wear over time, as the wheels are turned left and right. Brake hoses should be inspected for bulging and wear marks caused by abrasion.
157
158Check for the improper installation of brake hoses. Twisted brake hoses to calipers or loose brake hoses at the attaching supports are problems you may encounter. Whenever a brake hose is replaced, make sure a new sealing washer is used.
159
160
161  4. Replace brake lines, hoses, fittings, and supports; fabricate brake lines using proper material and flaring procedures (double flare and ISO types).
162The ends of brake lines are either double flared design or have ISO (International Organization for Standardization) type flared fittings. Copper tubing should never be used in a brake system. Copper is subject to fatigue and corrosion over time and can result in a hydraulic failure.
163
164Factory replacement brake lines are often available. These lines are an exact fit with the proper end fittings. When brake lines are not available, it will be necessary to fabricate a new line. Replacement lines come in various lengths and diameters. Carefully choose the correct size brake line with the correct end fittings. Remove the old line and use it as template to fabricate the new line. A bending tool will be needed to bend tight angles. Although brake lines bend easy, be careful not to form any kinks in the process. Remember, always make sure of the end fittings: either double flared or ISO-type flare. Also, watch for use of metric and/or fractional fittings on double flare installations.
165
166When it becomes necessary to flare the ends of the brake line, one of two different tools will be needed: the double flaring tool and the ISO flare-forming tool. Never use compression fittings to join sections of brake line.
167Always use a flare nut wrench to loosen or tighten brake line fittings. An open-end wrench can damage the end by rounding the corners of the fitting nut. Make sure all supports are intact. Loose brake lines or hoses may result in damage or failure.
168
169The entire brake system must be bled after you install a new hose or line. Also, apply pressure to the brakes and inspect the repair for leaks. Road test the vehicle and confirm proper brake operation.
170
171
172  5. Inspect brake lines and hoses for proper routing and support.
173All brake lines and hoses must be routed correctly. Inspect all lines and hoses and make certain that they are routed away from components that may interfere or rub, which can cause damage. Also, make sure brake lines and hoses are not routed near any components that generate excessive heat, such as an exhaust manifold, exhaust pipe, or catalytic converter.
174
175Brake lines and hoses must be securely fastened to their supports. Unnecessary movement or vibration can lead to fatigue and eventual failure.
176When replacing a flexible brake hose, make sure that it meets OEM safety standards and that the hose is the exact size as the original. A hose that is too long may rub on a chassis or steering component. If the hose is too short, it may stretch and break when the moveable component reaches the end of its travel. Always replace the sealing washer every time a brake hose is serviced.
177
178
179  3. Valves and Switches (3 Questions) 
1801. Diagnose poor stopping, pulling, or dragging caused by problems in the hydraulic system valve(s); determine needed repairs.
181
182To provide evenly balanced braking and to warn of pending problems, many different valves are used in modern hydraulic brake systems. The most common valves are the metering valve, proportioning valve, and the pressure differential valve. These valves are sometimes housed in one assembly called the combination valve.
183
184Faulty valves can cause brake drag, rear wheel lock-up, or front wheel lock-up upon braking. An in-depth review of these valves will follow in the upcoming paragraphs.
185
186
187  2. Inspect, test, and replace metering, proportioning, pressure differential, and combination valves.
188The metering valve is used on vehicles with front disc and rear drum brake design. The metering valve delays the front disc brake operation until the rear drum brake shoes overcome the return spring tension. This will ensure simultaneous brake application of the front and rear brakes. Without this valve, the front disc brakes would apply too quickly.
189
190A faulty metering valve can cause nose-diving and front wheel lock-up when the brakes are applied. During this condition, too much initial brake pressure is being applied to the front disc brakes. Premature front disc pad wear will also result from a faulty meeting valve. Inspect the valve for leaks.
191
192The proportioning valve is also found on brake systems with front discs and rear drums. The proportioning valve controls and limits the pressure to the rear brakes. Under mild braking, the pressure to all wheels is about the same. As pedal effort increases, the possibility of rear wheel lock-up exists. The proportioning valve prevents rear wheel lock-up under heavy braking. Vehicles with split diagonal brake systems utilize dual proportioning valves.
193
194A malfunctioning proportioning valve may cause rear wheel lock-up under heavy braking, which may result in loss of vehicle control.
195
196The pressure differential valve is used to warn the driver of a hydraulic pressure failure. The valve also incorporates a switch that will close and illuminate the dash warning brake light. A small piston floats inside the pressure differential valve cylinder, which separates the two halves of the brake system. The piston is normally centered inside the valve. When one side of the brake system develops a serious leak, the piston will be forced to the low-pressure side.
197
198After the vehicle is repaired and brakes bled, the pressure differential valve should reset automatically. If the dash warning light does not go out, the valve may have to be re-centered. Check manufacturer's recommended procedure for centering the valve.
199
200A combination valve incorporates the metering valve, proportioning valve, and the pressure differential valve all in one assembly. If any function of the combination valve fails, the entire assembly must be replaced.
201
202
203  3. Inspect, test, replace, and adjust load or height sensing-type proportioning valve(s).
204The load-sensing proportioning valve is mounted on the chassis, and a linkage is connected from the valve to the rear axle. When the load is light, the linkage positions the internal valve so that brake pressure is reduced to the rear wheels during moderate brake applications. A heavy load on the rear suspension reduces rear chassis height. This action causes the linkage to move the valve in the height-sensing proportioning valve. Under this condition, the proportioning valve does not reduce pressure to the rear brakes during moderate brake application.
205
206One type of load-sensing proportioning valve uses a bracket attached to the axle. A spring connects the bracket to a lever on the end of the proportioning valve, which is mounted to the vehicle chassis.
207Weight transfer during hard braking will cause a change in chassis height. The increase in chassis height will decrease pressure to the rear wheels.
208Any modification that alters the ride height will affect how the height-sensing-type proportioning valve operates.
209
210
211  4. Inspect, test, and replace brake warning light, switch, sensor and circuit.
212When the pressure is equal in the primary and secondary sections of the master cylinder, the warning switch piston remains centered. In this position, the switch piston does not touch the switch pin. If the pressure is unequal between the primary and secondary master cylinder sections, the pressure difference moves the switch piston to one side. In this position, the switch piston pushes the spring-loaded switch pin upward and closes the warning light switch. This action illuminates the brake warning light.
213
214The brake warning lamp circuit may be tested by grounding the warning switch with the ignition switch on. Under this condition, the bulb should light. If the bulb is not lit, check the fuse, bulb, and connecting wires.
215
216
217  4. Bleeding, Flushing, and Leak Testing
2181. Diagnose poor stopping, pulling, dragging, or incorrect pedal travel caused by problems in the brake fluid; determine needed repairs.
219Brake fluid is the liquid that provides a means of transmitting hydraulic pressure from the master cylinder to the calipers and wheel cylinders. Brake fluid must meet federal requirements for viscosity, non-corrosive quality, water tolerance, high boiling point, and low freezing point.
220
221DOT 3 fluid and DOT 4 fluid are hygroscopic, which means they absorb moisture. Over time the quality of brake fluid diminishes and may lead to internal corrosion of brake components. Corrosion can lead to sticking or seized calipers and wheel cylinders, which may cause brake drag. Corrosion can also cause a wheel cylinder piston, master cylinder piston, or caliper piston to seize in its bore. The absorbed moisture can also lower the boiling point of the brake fluid, which will allow it to evaporate at high temperatures and create vapor in the lines. The vapor in the lines could lead to a soft and/or spongy pedal.
222
223Engine oil, transmission oil, or any fluid other than brake fluid will contaminate the brake system and may swell rubber components of the brake system and cause brake drag. If a brake system has been contaminated with a foreign substance, it will be necessary to flush all the contamination from the brake system. Also, a careful inspection of the entire brake system is necessary because of the increased probability of damaged brake components.
224
225
226  2. Bleed and/or flush hydraulic system using manual, pressure, vacuum, or surge gravity method(s).
227Brake systems function on the principle of hydraulics, which states that a liquid cannot be compressed. However, air is compressible, and if air is present in the brake system, the result will be a low and spongy pedal. Also, air contains moisture, which may lead to component corrosion.
228
229Air will enter the brake system when a hydraulic component is disconnected or if the level of master cylinder becomes too low. Bleeding the brakes is necessary to remove all the air in the brake system. Never reuse brake fluid.
230There are four common methods for bleeding brakes: manual bleeding, pressure bleeding, vacuum bleeding, and surge bleeding. Whatever method is chosen, some basic procedures are the same. Check the level of the fluid in the master cylinder and maintain that level throughout the bleeding process. On all vehicles, follow the manufacturer's bleeding sequence. Bleeder screws are provided at the master cylinder, wheel cylinders, and disc brake calipers, and sometimes on the combination valve. Air is purged from the system by opening these bleeder screws and forcing fluid through them.
231
232A pressure bleeder has an adapter connected to the top of the master cylinder reservoir. A hose is connected from this adapter to the pressure bleeder chamber in the top of the pressure bleeder. The pressure bleeder has an air chamber below the fluid chamber and a diaphragm that separates the air and fluid chambers. Shop air is used to pressurize the air chamber up to 15 to 20 psi (103 to 138 kPa). If the brake system has a metering valve, this valve may have to be held open with a special tool. The bleeder hose is connected from each bleeder screw to a container partially filled with brake fluid. Open the bleeder screw until a clear stream of brake fluid is discharged.
233
234During the vacuum bleeding procedure, a vacuum pump is connected to a sealed container. The pump can be either hand-held or powered by compressed shop air. With a hand-held pump, another hose is connected from the container to the bleeder screw. A one-way check valve is connected in the hose from the bleeder screw to the container. Operate the pump handle ten to fifteen times to create vacuum in the container. Open the bleeder screw until about 1 inch (25 mm) of brake fluid is pulled into the container. Repeat the procedure until the fluid coming into the container is free of air bubbles. With the air-powered vacuum bleeder, connect the hose from the device to the bleeder screw and open the bleeder. The vacuum created by the air-powered bleeder will draw the air and brake fluid into the container. Continue to draw the fluid from the bleeder until no air can be seen. Be sure to keep the master cylinder fluid reservoir full of fluid during the entire procedure.
235
236During a manual brake bleeding procedure, connect a bleeder hose from a bleeder screw to a container partially filled with brake fluid. Keep the end of this hose submerged below the level of the brake fluid in the container. Each wheel caliper or cylinder must be bled in the vehicle manufacturer's specified sequence in any bleeding procedure. Wheel calipers may be tapped with a soft hammer to help remove air bubbles. With the bleeder opened, have an assistant slowly press the brake pedal. Do not allow the master cylinder to bottom out, as dirt or corrosion that may exist in the end of the master cylinder may damage the piston seals. With the pedal pressed, close the bleeder screw. The pedal can then be released. Repeat this process until no air comes out of the bleeder.
237
238The surge method is a procedure that is sometimes used with manual brake bleeding. Surge bleeding is used in cases where it is difficult to remove trapped air from a wheel cylinder or brake caliper. In this method the pedal is first pumped several times. The bleeder screw is then opened and with a quick movement an assistant depresses the pedal. The pedal is then released slowly. Wait a few seconds and repeat. On the last down stroke of the pedal, close the bleeder quickly.
239
240Flushing the brake system involves continuing the bleeding process until all the fluid in the brake system is completely replaced. Flushing is recommended when brake fluid has been contaminated and also as a periodic brake service. Brake fluid absorbs moisture over time. Flushing removes the moisture and maintains the integrity of the brake components. If major brake components are replaced, flushing is highly recommended.
241
242
243 3. Pressure test brake hydraulic system.
244Using pressure gauges, the brake system can be checked for correct hydraulic pressure at different components. Following manufacturer's specification, it is possible to determine if the caliper, wheel cylinder, or part of the brake system is not receiving the correct pressure. Using pressure gauges can help in accurately diagnosing failed components.
245
246The proportioning valves connected to the rear wheels may be tested by connecting pressure gauges on the master cylinder side and wheel cylinder side of each proportioning valve. When the brake pedal is applied with light pressure and the master cylinder pressure is below the split point pressure, both gauges should indicate the same pressure. If the brake pedal pressure is increased and the master cylinder pressure exceeds the split point pressure, the master cylinder pressure should exceed the wheel cylinder pressure by the manufacturer's specified amount.
247
248After the brakes are bled, fill the master cylinder to the proper level. Following several firm applications of the pedal, the calipers should be checked for leaks at the piston seals and the hose attachment areas.
249
250
251  4. Select, handle, store, and install proper brake fluids (including silicone fluids).
252There are currently three types of brake fluid: DOT 3, DOT 4, and DOT 5. DOT 3 and DOT 4 are hygroscopic, which means they absorb moisture. All brake fluids must meet standards set by the Department of Transportation (DOT) and the Society of Automotive Engineers (SAE). The main difference between brake fluids is the point at which they begin to boil. DOT 3 is a glycol-based fluid that has a minimum boiling point of 401°F (205° C). DOT 4, which is also glycol-based, has a minimum boiling point of 446°F (230° C). DOT 5 brake fluid is silicone-based, is not hygroscopic, and has a minimum boiling point of 500°F (260° C).
253
254Due to their hygroscopic nature, DOT 3 and DOT 4 fluids have a limited shelf life. When a container of brake fluid is opened, the contents must be used as soon as possible. Always replace the cap on the container immediately. DOT 3 and DOT 4 will damage a painted surface, so care must be taken when handling brake fluid.
255
256The main advantages to DOT 5 silicone brake fluid are its high boiling point and the fact that it does not attract water. However, DOT 5 brake fluid is prone to aeration. Tiny air bubbles can form when the fluid is agitated. For this reason, DOT 5 fluid must never be used in a vehicle equipped with antilock brakes. DOT 5 fluid is also more difficult to bleed.
257
258When adding brake fluid, always use fresh fluid from a new container and always check for the correct fluid for that vehicle. Most vehicles use either DOT 3 or DOT 4 fluid. These fluids can be interchanged but really should not be mixed. DOT 5 fluid is not compatible with DOT 3 or DOT 4
259
260
261  B. Drum Brake Diagnosis and Repair
262
2631. Diagnose poor stopping, pulling, dragging, or incorrect pedal travel caused by drum brake hydraulic problems; determine needed repairs.
264A springy and spongy pedal is a condition where the brake pedal does not give firm resistance to foot pressure and feels elastic. It is normally caused by air in the hydraulic lines. Poor stopping ability may be caused by hydraulic problems such as contaminated fluid or air in the hydraulic system.
265
266Brake drag may be caused by hydraulic problems such as contaminated brake fluid, inferior rubber cups in the master cylinder or wheel cylinders, or plugged compensating (vent) ports in the master cylinder. An obstructed brake line or hose may also be the cause of brake drag. A restricted brake hose or line may also cause a pull to one side or reduce stopping ability.
267
268A seized wheel cylinder piston can cause brake drag if the piston is stuck in its bore. If the piston is stuck outward, it can cause brake drag and premature brake shoe wear. A leaking wheel cylinder can cause air to enter the system and loss of fluid. This will result in a low and spongy pedal. Poor-quality brake fluid or overheated brakes may lead to fluid boiling. At this point, the fluid can be compressed and a temporary loss of proper braking will occur.
269
270
271  2. Diagnose poor stopping, noise, pulling, grabbing, dragging, pedal pulsation, or incorrect pedal travel caused by drum brake mechanical problems; determine needed repairs.
272
273Brake squeal may be caused by bent backing plates, distorted drums, linings loose at shoe ends, improper lining position on the shoe, weak or broken hold-down springs, or loose wheel bearings. Brake chatter may be caused by improper brake adjustment; loose backing plates; contaminated linings; out-of-round, tapered, or barrel-shaped drums; cocked or distorted shoes; or loose wheel bearings.
274
275Pedal pulsation may be caused by out-of-round brake drums.
276Dragging or brake grabbing may be the result of contaminated brake shoes. Inspect the surface of the brake shoes for signs of brake fluid contamination or rear differential grease. Also, inspect wheel cylinders for seized pistons. If the wheel cylinder pistons do not retract when the brakes are not applied, this will result in brake drag. This drag will cause premature brake wear and overheated linings.
277
278Incorrect pedal travel caused by drum brakes can usually be blamed on shoes that are out of adjustment. The shoes must travel farther to contact the drums, which means that the driver must press the pedal farther for the shoes to make contact.
279
280
281  3. Remove, clean, inspect, and measure brake drums; follow manufacturers' recommendations in determining need to machine or replace.
282Brake drums should be inspected for cracks, heat checks, out-of-round, bell mouths, scoring, and hard spots. The inside drum diameter should be measured with a drum micrometer. If the drum diameter exceeds the maximum limit specified by the manufacturer, replace the drum. The drum diameter should be measured every 45 degrees around the drum. The maximum allowable out-of-round specified by some manufacturers is 0.0035 inch (0.09 mm). If the out-of-round exceeds specifications, the drum may be machined if the machining does not cause the drum to exceed the maximum allowable diameter.
283
284
285  4. Machine drums according to manufacturers' procedures and specifications.
286When you machine a brake drum, the drum must be installed securely and centered on the lathe. A dampening belt must be installed tightly around the outside of the drum to prevent the cutting tool from chattering on the drum. Many manufacturers recommend a rough cut tool of 0.005 to 0.010 inch (0.127 to 0.254 mm) and a finish cut tool depth of 0.005 inch (0.127 mm). After the machining procedure, the drum should be sanded to remove minor irregularities.
287
288The surface of a freshly refinished drum contains millions of tiny particles. These particles can remain free on the surface or can become lodged in open pores of the cast-iron drum. If these particles are not removed, they can become embedded in the linings. Once they are embedded in the linings, the linings become a fine grinding stone, which will score the brake drum.
289
290Start removing the particles by wet washing the lining with hot water, followed by wiping it with a lint-free cloth. Use compressed air to remove the remaining moisture. Finally, use a lint-free cloth moistened with denatured alcohol or brake cleaning solution. Repeat the final step until the cloth shows no signs of dirt.
291
292
293  5. Using proper safety procedures, remove, clean, and inspect brake shoes/linings, springs, pins, self-adjusters, levers, clips, brake backing (support) plates and other related brake hardware; determine needed repairs.
294Before removing brake shoes, be sure to clean the assembly with an approved cleaning method that will contain all brake dust and prevent it from becoming airborne. Remove the brake shoes using the proper tools to prevent any personal injury that may result from improper methods. All brake return springs should be inspected for distortion and stretching. Brake shoes should be inspected for broken welds, cracks, wear, and distortion. If the wear pattern on the brake shoes is uneven, the shoes are distorted. Check all clips and levers for wear and bending. Inspect the brake linings for contamination with oil, grease, or brake fluid. If contamination is found, locate the source and correct the failure prior to new shoe installation. Clean and lubricate adjusting and self-adjusting mechanisms.
295
296A bent backing plate will not align the brake shoes properly. The misaligned shoes will result in brake drag or grab. Loose backing plate anchor bolts may cause brake chatter because the brake shoes can become misaligned if the backing plate moves.
297
298If the brake shoes and linings have a slight blue coloring, this indicates overheating. In this case, the brake shoe adjusting screw springs and brake shoe hold-down springs should be replaced.
299
300Linings must be replaced when contaminated with grease, oil, or brake fluid. Operating a vehicle for any length of time with worn brake shoes and linings will quickly result in scored brake drums. Always replace parts that are near the end of their service life. Never replace linings on one brake assembly without replacing those on the opposite wheel.
301
302To check for leaks, pull back each wheel cylinder dust boot. Be careful, as some manufacturers do not recommend pulling back the wheel cylinder dust boots, because this may allow debris inside and damage the piston seals. Normally you will see a small amount of brake fluid present. This is not a cause for alarm, as it acts as a lubricant for the piston. However, large amounts of fluid behind the boot indicates the fluid is leaking past the piston cups and an overhaul or replacement is in order. Check the pads where the brake shoes rest on the backing plate. Look for any deep grooves in the brake shoe and lining contact pads that could resist brake shoe movement. Hand sand any grooves in the braking surface. If grooves are still present after sanding, the backing plate must be replaced. Any attempt to remove the grooves by grinding may result in improper brake shoe and lining to brake drum contact.
303
304With manual brake adjusters, the brakes must be periodically adjusted to limit pedal movement and the increased need for brake fluid. However, the wear is so gradual that the driver may not realize how much out of adjustment the brakes actually are.
305
306Automatic brake adjusters generally take the worry out of keeping the brakes properly adjusted. The automatic adjusters automatically adjust the clearance between the shoe linings and the drum.
307
308
309  6. Lubricate brake shoe support pads on backing (support) plate, self-adjuster mechanisms, and other brake hardware.
310
311Dry brake shoe ledges on the backing plate may cause a squeaking noise during brake applications. Lightly scored brake shoe ledges on the backing plate may be resurfaced and lubricated with high-temperature grease.
312Whenever the rear brake shoe and linings are removed, the parking brake rear cable and conduit tension should be checked.
313
314The ledges of the brake shoes that are positioned against the backing plates should be lubricated with the high-temperature grease recommended by the manufacturer.
315
316
317 7. Inspect wheel cylinder(s) for leakage, operation, and mounting; remove and replace wheel cylinder(s).
318During a wheel cylinder inspection, check for any leaks that are evident. A slight amount of moisture is acceptable, as a small amount of fluid provides for lubrication of the wheel cylinder. Any drops of brake fluid that are evident indicate a large leak and replacement of the wheel cylinder will be necessary. It is not advisable to remove the wheel cylinder dust boots during the inspection processes, as dirt and debris could get in the wheel cylinder bore and cause premature wear of the wheel cylinder bore and seals.
319
320Inspect the friction surface of the drum. If the surface does not show signs of wear (the surface is not shiny and worn), this could be evidence that the wheel cylinder is not operating. A pressure test may be made to determine the integrity of the hydraulic system to the wheel cylinder. If the hydraulic system is diagnosed as good, be sure to check the mounting of the wheel cylinder. A bent backing plate/wheel cylinder mount could cause reduced braking. A loosely mounted wheel cylinder could also cause the same condition. If all of the above checks turn out okay, suspect a faulty wheel cylinder.
321
322It is generally suggested that wheel cylinders be replaced in pairs. Dirt and corrosion often form in the bore of the wheel cylinder and lead to wheel cylinder failure. A leaking wheel cylinder will commonly contaminate the shoes and cause the need for shoe replacement as well. When a wheel cylinder is replaced, the hydraulic system will need to be bled. Follow the manufacturer's suggested bleeding sequence when bleeding the hydraulic system.
323
324
325  8. Install brake shoes and related hardware.
326When you install new brake shoes and hardware, the secondary shoe often has a longer lining than the primary shoe and goes on the side of backing plate pointing toward the rear of the vehicle. The primary shoe faces toward the front of the vehicle, and the primary and secondary shoe return springs are usually not interchangeable. The self-adjuster cable is usually routed on the secondary shoe.
327
328The adjuster must be installed in the proper direction so the star wheel is accessible through the backing plate opening or drum openings to allow for future removal of the shoes and to engage the self-adjuster lever. Be sure to lubricate the pads on the backing plates and any pivot points with appropriate lubricant before installing the shoes and hardware.
329
330
331  9. Pre-adjust brake shoes and parking brake before installing brake drums or drum/hub assemblies and wheel bearings. Before the brake drum is installed, position a brake adjusting gauge tool inside the brake drum and set the gauge for inside diameter. Next, position the gauge over the brake shoes and adjust the shoes to the gauge using the adjuster wheel. This procedure will pre-adjust the brake shoes and parking brake. This process is also simple and will save time.
332
333On front drum applications and some larger trucks, it will be necessary to adjust the wheel bearing after mounting the drum in place. Follow manufacturer's specifications for correct wheel bearing torque and procedure.
334
335
336  10. Reinstall wheel, torque lug nuts, and make final checks and adjustments.
337One area that is a common source of comebacks is improper wheel installation. Wheel studs are designed to retain some elasticity when the wheel is bolted to the vehicle. If the wheels are over-torqued, this elasticity along with the integrity of the wheel mounting surface are no longer consistent, which can result in brake noise, premature rotor warpage or lug nut and stud damage. Recheck brake fluid level, road test, and verify proper brake function. Apply the parking brake and ensure proper parking brake function
338
339
340C. Disc Brake Diagnosis and Repair
341
3421. Diagnose poor stopping, pulling, dragging, or incorrect pedal travel caused by disc brake hydraulic problems; determine needed repairs.
343Disc brake systems utilize a disc rotor, caliper assembly, and disc brake pads. The brake pads are positioned on both sides of the brake rotor and are squeezed against the disc rotor by hydraulic pressure acting on the caliper piston or pistons. It was once common to see vehicles built with disc brakes on the front wheels only; however, many cars and trucks today are equipped with four-wheel disc systems.
344
345A cause for dragging brakes could be faulty flex hoses. A restriction in the hose may allow-pressure to apply the caliper properly, but not permit the pressure to release. This will keep the piston partially applied and cause the brakes to drag.
346
347Faulty flex hoses can also swell and bulge and swell during brake application. This would cause the driver to feel a springy or soft pedal. Any swollen hoses should be replaced.
348
349Always inspect the disc rotor for signs of bluing or glazing, which is an indication of overheating. Carefully inspect caliper hardware, pins, and slides. Also, closely examine the wear on the disc brake pads for each caliper. Each pad should wear evenly if the same pressure is being applied to each pad. Uneven pad wear may be an indication of a caliper with a hydraulic problem.
350
351
352  2. Diagnose poor stopping, noise, pulling, grabbing, dragging, pedal pulsation or incorrect pedal travel caused by disc brake mechanical problems; determine needed repairs.
353There are two brake caliper designs: fixed and floating. Fixed caliper assemblies are rigidly bolted to the spindle or steering knuckle and do not move when the brakes are applied. Fixed caliper assemblies have pistons on both sides that apply hydraulic pressure against the brake rotor.
354
355Floating (or sliding) calipers usually have only one piston that is actuated by hydraulic pressure. The caliper moves or slides as pressure is applied to the caliper piston. This action causes movement or sliding of the caliper and as a result will cause both pads in the caliper assembly to apply pressure to both sides of the brake rotor. These calipers will either float on pins or slide on a machined surface or support bracket. A common problem with floating calipers is tapered brake pad wear. Seized, sticking caliper pins, worn hardware, or corrosion on the support surface can cause the caliper to not float during braking. If one caliper is sticking or seized, it may result in a pull to one side as the brakes are applied.
356
357If the caliper piston is seized, proper brake action will be affected. On vehicles with front disc brakes, a seized caliper piston on one side can cause a pull if the brake pads are not being actuated properly. If the right front caliper is working properly, but the left front caliper piston is seized in its bore, the vehicle will pull to the right when the brakes are applied. If the caliper piston is seized and does not retract when the brake pedal is released, dragging of the brakes will occur. This may cause a pull to one side without applying the brakes and will cause uneven brake wear. Inspect all caliper hardware, which includes anti-rattle clips, caliper pins, caliper slides, and shims. Worn or missing brake caliper hardware may cause noise, chattering, brake squeal, or brake pad rattling.
358
359A pulsation felt through the brake pedal could be the cause of excessive disc rotor runout or loose wheel bearings. Thickness variation (parallelism) will also cause brake pulsation. Sticking or seized calipers can cause brake drag and may damage the rotors due to overheating. This situation may also overheat the brake pads and cause premature, uneven wear.
360
361
362  3. Retract integral parking brake caliper piston(s) according to manufacturer's recommendations.
363Many vehicles with four-wheel disc brakes incorporate the parking brake mechanism within the rear brake caliper assembly. These calipers apply the piston hydraulically for normal braking and will apply the caliper piston mechanically when the parking brake is applied.
364The caliper piston will turn and extend outward when the parking brake cable acts on a lever connected to the rear of the brake caliper. As the caliper piston turns outward in its bore, the pads clamp the rotor and prevent the vehicle from rolling.
365
366To retract the caliper piston during rear pad replacement on this caliper design, you will need the aid of a special tool. Remove the caliper from its mounting position and remove the brake pads. Using the proper tool, rotate the caliper piston clockwise until it is seated back in its bore. The piston should rotate with some resistance but should retract under pressure applied from the tool. If the piston is seized, replace the caliper. Check parking brake function after reassembly. Adjust the parking brake cable as needed.
367
368
369  4. Remove caliper assembly from mountings; inspect for leaks and damage to caliper housing.
370After removing the caliper, carefully inspect all hardware, mounting contact points, caliper piston boot, and caliper housing. Thoroughly clean the caliper and mounting area. Inspect the dust boot for tears and for leaks from the piston. Also inspect the area where the brake hose connects to the caliper. Check the contact area where the caliper is positioned in the caliper anchor plate. Check for any physical damage to caliper housing or caliper. Any leaks from a caliper are unsafe, and the caliper must be replaced.
371
372
373  5. Clean, inspect, and measure caliper mountings and slides/pins for wear and damage.
374Inspect the caliper slide pins and sleeve assemblies for corrosion, and inspect all bushings for cuts and nicks. If damage to any of these parts is found, install new parts when the caliper is reinstalled. Do not attempt to polish away corrosion.
375
376The caliper must move freely on the slide or pins with no binding. Inspect the surface area where the caliper is positioned on the anchor plate. All hardware, springs, anti-rattle clips, and pins must be cleaned and inspected. Worn or corroded parts must be replaced.
377
378How the caliper mounts to the anchor or adapter is crucial for proper brake action. A loose caliper fit due to wear may cause brake noise or excessive caliper movement when the brakes are applied. The caliper may rock to one side rather than slide. This action is undesirable and must be corrected. Replacement of the caliper, slides, anchor plate, adapter, or caliper pins may be necessary if excessive wear is determined. All contact surfaces must be lubricated with appropriate brake caliper grease.
379
380
381  6. Remove, clean, and inspect pads and retaining hardware; determine needed repairs, adjustments, and replacements.
382A scraping or squeaking noise while braking may be caused by a pad wear sensor contacting the rotor. The scraping of the wear indicator indicates that the brake pads need replacement. If this problem is caught early, minimal damage will be done to the rotors. Remember that when you resurface or replace the rotors, the axle set must be either replaced together or have the same amount of machining done.
383
384Shop manuals all specify minimum pad thickness, but the pads can be measured only if the unit is disassembled. Inspect disc brake rotors whenever the pads or calipers are serviced, or when the wheels are rotated or removed for any other work.
385
386After removing the brake pads from the brake caliper, clean and inspect the brake pads, hardware, anti-rattle clips, and springs. Measure disc-pad lining and compare with manufacturer's specification. Check for tapered wear or cracked linings. Weak or broken springs or ant-rattle clips must be replaced. 
387Most caliper slide pins have a coating to protect against corrosion. If the pins pitted or corroded, do not attempt to clean or polish. The pins must be replaced. Use appropriate brake grease on pins, slides, and brake pad contacting points.
388
389
390  7. Clean caliper assembly; inspect external parts for wear, rust, scoring, and damage; replace any damaged or worn parts; determine the need to repair or replace caliper assembly.
391If a brake caliper is to be overhauled, it must be removed from the vehicle. Remove the brake hose and the attached caliper bolt. Carefully remove the caliper from its mounting. Discard the old copper washer used to seal the brake hose. A new sealing washer should always be used during caliper installation. Drain all brake fluid from the caliper and clean the exterior.
392
393Inspect any slide bores for excessive rust or wear that could allow the slide and caliper to move around. Check any mounting surfaces on the caliper that could prevent the caliper from sliding as it was designed. Any defects found should result in caliper replacement.
394
395Before disassembly, make sure the caliper bleeder screw opens. If the bleeder screw is seized and cannot be freed, the caliper will have to be replaced.
396The caliper piston can be removed either with air pressure or by using a piston removal tool. If using compressed air, clamp the caliper in a soft-faced vise and place a wooden block between the piston and the caliper body. Apply air pressure to the fluid inlet hole to force the piston from the caliper bore. A word of caution: the caliper piston will come out with extreme force—keep hands clear.
397
398After the piston is removed, carefully pry away the dust boot and the caliper seal. Thoroughly clean the caliper bore and inspect for corrosion and pitting. Minor imperfections on the bore surface can be removed by honing. The caliper will need to be replaced if there is severe corrosion or damage. If the caliper bore is honed, check the piston-to-bore clearance. If the clearance is beyond manufacturer's specification, the caliper must be replaced. Inspect the groove where the piston seal is installed in the caliper bore. Carefully inspect groove and bore for pitting and corrosion. Replace the caliper assembly if the seal groove or the caliper bore is damaged.
399
400Carefully examine the caliper piston for damage and wear. On chrome-plated pistons, make sure the chrome is not peeling. Also inspect the piston for scoring or pitting. On phenolic pistons, check for cracks, chips, or gouges. Always replace a piston that is damaged. A new dust boot and piston seal will be used for reassembly of the caliper.
401
402Before caliper reassembly, lubricate the caliper seal, piston, and bore with clean brake fluid. Install the seal in the caliper bore first. Then press the piston into the bore until it is fully seated. Using a suitable tool, install the dust boot. A C-clamp may be needed to help fully seat the piston.
403
404
405  8. Clean, inspect, and measure rotor with a dial indicator and a micrometer; follow manufacturers' recommendations in determining need to index, machine or replace the rotor.
406
407The rotor is measured for parallelism or thickness variation; this measurement should be made at eight locations (every 45 degrees) around the rotor. These measurements should be taken near the center of the friction surface. Replace the rotor if the thickness variations exceed the manufacturer's specifications.
408Remove the disc brake rotor, and clean and inspect for damage. Check for pitting, grooves, heat cracks, or damage on the friction surface of the brake rotor. Blue spots on the rotor face indicate excessive heat. Replace the rotor if there is cracking.
409
410Check all rotors for lateral runout (side-to-side wobble), parallelism (same thickness all the way around) and minimum thickness. Measurements can sometimes be made with the rotor still mounted on the vehicle with the caliper removed.
411
412Before checking lateral runout, if composite rotors are used, remove the rotor; clean the back of the rotor and hub surface. This will eliminate any rust or debris that could alter our readings. To check runout, mount a dial indicator to a solid surface. Place the indicator near the center of the friction surface and slowly rotate the rotor. See manufacturer's specifications. If runout is excessive, the rotor can sometimes be indexed on the hub to match high spots on the rotor with low spots on the hub. This may allow for runout to be within spec. Some aftermarket companies manufacture shim kits to correct lateral runout. Different thickness shims can be installed between the rotor and hub to correct lateral runout. A micrometer is used to check parallelism. Measure the disc rotor thickness in six or eight spots around the rotor and record the readings. See manufacturer's specifications. Excessive parallelism can cause brake pulsation, brake shudder, and chatter. Also, if the disc rotor thickness is below minimum specification, discard the rotor. Minimum thickness specification is usually stamped into the rotor or can be found in service manuals.
413
414If the disc rotor is not worn beyond specification, truing (or machining) can be performed. Machining the brake rotor involves the use of a brake lathe, which cuts both sides of the rotor in order to produce an even, smooth friction surface. Disc rotors must be machined in pairs to ensure smooth and even braking.
415
416
417  9. Remove and replace rotor.
418Disc brake rotors either slide off the axle flange or are mounted in place by the wheel bearing. First, remove the caliper. Do not let the caliper hang by the flex hose. If the rotor is mounted to the axle flange or wheel hub, clean the flange before installing the new rotor. If the rotor is mounted to a spindle and secured with wheel bearings, clean all the grease from the spindle and bearings. Repack the wheel bearings and apply a small amount of wheel bearing grease to the spindle shaft. Following the manufacturer's procedure, tighten and torque wheel bearings. Also, always replace the wheel bearing grease seal and use a new cotter pin. Check new rotors for runout, parallelism, and minimum thickness. Clean any oil film from the new rotor prior to installation.
419
420
421  10.Machine rotor, using on-car or off-car method, according to manufacturers' procedures and specifications.
422Machining the brake rotor involves the use of a brake lathe, which cuts both sides of the rotor in order to produce an even, smooth friction surface. Remove only enough metal stock to clean up the rotor surface. Never resurface one disc rotor. Disc rotors must be done in pairs to ensure smooth and even braking.
423
424Brake rotors can either be machined on the car or off the car, depending on vehicle design and factory recommendations. An advantage to an on-car brake lathe is that it compensates for any variation in the axle flange, hub, or spindle. When you machine rotors off the vehicle, a vibration damper must be positioned around the outside diameter of the rotor or on the rotor faces if the rotor is not vented. A fine grit (180) sanding pad should be used to sand the rotor surface after machining. This helps to knock the tops off of the sharp grooves left by the machining process. Equal amounts of metal must be removed from each side of the rotor.
425
426To determine the approximate amount of metal to be removed, turn on the lathe and bring the cutting bit up against the rotating disc until signs of a slight scratch are visible. Turn off the lathe and reset the depth-of-cut dial indicator to zero. Find the deepest groove on the face of the rotor and move the cutting bit to that point without changing its depth-of-cut position. Now use the depth-of-cut dial to bottom out the tip of the cutter in the deepest groove. The reading on the dial now equals or is slightly less than the amount of material needed to be removed to eliminate all of the grooves in the rotor surface. For the best results with cuts that have a total depth greater than 0.015 inch (0.38 mm), take two or more shallow cuts rather than one very deep cut.
427
428After machining the rotor, measure the rotor for minimum thickness. If the rotor was machined below minimum specification, discard the rotor. Also, give the rotor surface a non-directional finish using the proper lathe attachments. This will ensure proper brake pad to rotor surface contact. A sanding block using 180-grit sandpaper can also be used. Apply the sanding block for 30 seconds on each side of the rotor to achieve a smooth non-directional finish. Rotors must be washed thoroughly after machining. Soapy water works best. Simply submerge the rotor to remove leftover debris from machining. Brake clean and rags are not the preferred method because they usually leave behind metal debris that embeds in the new pads and can cause brake squeaks.
429
430
431  11.Install pads, calipers, and related attaching hardware; lubricate components following manufacturers' procedures and specifications; bleed system.
432Clean off all caliper supports and sliding surfaces before installing the caliper assembly and pads. Lubricate sliding surfaces or pins with approved lubricant. It will be necessary to push the caliper piston back in order to install the brake pads. Open up the caliper bleeder screw first and push the caliper piston back using the appropriate tool. It is not recommended to push the caliper piston back with the bleeder screw closed. The fluid, along with any dirt, can be pushed back through the lines and back-up to the master cylinder. Install the brake pads using new anti-rattle clips, shims, and other hardware to ensure the pads will sit properly and reduce the chance of squeal and noise. Tighten the caliper guide pins or bolts to the correct torque specification. Check the fluid level in the master cylinder and carefully pump the brake pedal until a firm pedal is felt. Bleed the system following the correct bleeding sequence and road test the vehicle to ensure proper brake performance.
433
434
435  12. Adjust calipers with integrated parking brakes according to manufacturers' recommendations.
436Some parking brakes on rear disc brake systems utilize a set of brake shoes located inside the hub of the brake rotor. Adjusting the internal parking shoes is performed by rotating the star wheel adjuster with a tool through a slotted opening found in the face of the rotor or an opening found on the splash shield. Rotate the star wheel until correct shoe-to-drum clearance is obtained. Next, apply the parking brake pedal or lever, and remove the slack from the cables, if necessary. There should be no drag at the rear wheels when the parking pedal or lever is released. Apply and release the parking mechanism several times to ensure proper parking brake operation.
437
438Rear disc brake systems that use the caliper piston to apply the parking function require only a cable adjustment.
439
440
441  13. Fill master cylinder to proper level with recommended fluid; inspect caliper for leaks.
442Upon completing any brake service, refill the master cylinder with the correct, clean fluid. The brake fluid level on most master cylinders should be 0.25 inch (6.35 mm) below the top. Many reservoirs are marked indicating full and refill levels. Check with the manufacturer for correct fluid type. Actuate the brake pedal to apply hydraulic pressure and inspect the calipers, lines, and hoses for leaks.
443
444
445  14. Reinstall wheel, torque lug nuts, and make final checks and adjustments.
446An impact wrench should not be used to tighten wheel lug nuts since the excessive torque from this procedure may distort drums and cause excessive rotor runout.
447
448All lug nuts must be tightened to correct torque specification. Over-tightening the lug nuts may damage the brake rotor hub and cause excessive rotor runout. Before road testing, apply the brake and parking brake to check for correct brake function. Road test the vehicle and ensure proper brake performance.
449
450
451  15. Road test vehicle and burnish/break-in pads according to manufacturer's recommendations.
452Road test the vehicle while checking for things like incorrect pedal height, pulling while braking, pulling after breaking, and any abnormal noises. If any of these are present, further diagnosis and repair will be necessary.
453
454Friction material needs to be seated to the matching rotor after pad replacement or machining the rotors. This break-in process is known as burnishing. Burnishing conforms the friction to the shape of the rotor, which allows for better stopping. The heat generated by this process will also cure the resins and other materials used to make up new pad lining. Failure to burnish newly replaced pads could result in a customer complaint of a hard brake pedal and/or reduced vehicle braking. To seat disc brake pads to the rotor; make approximately twenty complete stops from 30 mph(48 kph), or slow down from 50 mph (80 kph) to 20 mph (32 kph) the same number of times with light to medium pedal pressure. Allow at least a 30-second cool-down period between brake applications to prevent overheating. While performing this procedure, panic/hard stops, which would result in glazed pads, should be avoided. After a thorough burnishing procedure, it is normal to see smoke coming from new brake pads.
455
456
457D. Power Assist Units Diagnosis and Repair
458
4591. Test pedal free travel with and without engine running to check power booster operation.
460Power assist brakes contain a power booster connected to the master cylinder to reduce the required pedal travel and effort. With a relatively small amount of foot pressure, a great amount of hydraulic pressure can be produced. Most power brake boosters operate by engine vacuum and atmospheric pressure acting on a vacuum diaphragm. With the engine running, vacuum exists on both sides of the booster diaphragm. When the brake pedal is applied, a vacuum port is closed, which allows atmospheric pressure to enter one side of diaphragm chamber. This action moves the diaphragm assembly and applies the master cylinder.
461
462With the engine stopped, pump the brake pedal several times, and hold the pedal in the applied position. When the engine is started, the pedal should move slightly downward if the vacuum supply to the brake booster is normal. If the pedal does not move slightly downward, check the vacuum hose and the one-way check valve to the brake booster.
463
464To check the vacuum brake booster for air tightness, operate the engine for 2 minutes and then shut off the engine. Pump the brake pedal several times with normal braking pressure. If the brake booster is operating normally, the pedal should go down normally on the first brake application. The pedal should gradually become higher and harder to depress with each pedal application.
465
466
4672. Check vacuum supply (manifold or auxiliary pump) to vacuum-type power booster.
468Vacuum-assisted power brakes rely on a steady, adequate supply of manifold vacuum. Internal engine problems can affect power assist if manifold vacuum is lower than normal. Any vacuum leaks will also affect proper booster operation. A vacuum leak in the booster assembly can also occur. Low vacuum or a leaking booster will cause a hard brake pedal with little or no power assist. Engine vacuum should be 17 to 20 in.Hg (43 to 50 cm.Hg) at sea level at idle.
469
470To check for proper vacuum, disconnect the booster hose from the manifold and connect a vacuum gauge. On vehicles with auxiliary pumps, test for vacuum at the pump with the engine running. Vacuum should be 15 to 22 in.Hg (38 to 55 CM. Hg) at sea level. Compare that reading right at the booster to make sure the booster is being supplied with the same vacuum.
471
472
473  3. Inspect the vacuum-type power booster unit for vacuum leaks and proper operation; inspect the check valve for proper operation; repair, adjust, or replace parts as necessary.
474To check a one-way check valve in the brake booster vacuum hose, operate the engine at 2,000 rpm and then allow the engine to idle. Shut the engine off and wait 90 seconds. Pump the brake pedal five or six times. The first two pedal applications should be power assisted. If the first two brake applications are not power assisted, the one-way check valve is defective in the brake booster vacuum hose.
475
476Insufficient manifold vacuum, leaking or collapsed vacuum lines, punctured diaphragms, and leaky piston seals can all result in weak power unit operation. A steady hiss when the brake pedal is held down indicates a leak that can cause poor power unit operation. Hard brake pedal is usually the first signal that the unit is on the way to complete failure.
477
478Connect a vacuum gauge with a T-connection in the hose between the one-way check valve and the brake booster. With the engine idling, the vacuum should be 17 to 20 in.Hg at sea level (44 to 30.4 kPa absolute). If the vacuum is low, connect the vacuum gauge directly to the intake manifold and check this reading against the manufacturer's specifications.
479
480
481  4. Inspect and test hydro-boost system and accumulator for leaks and proper operation; repair or replace parts as necessary; refill system.
482The hydraulic power brake booster system (hydro-boost) is used on some cars and trucks. Hydro-boost systems use hydraulic pressure developed from the power steering pump to actuate the master cylinder. Some vehicles use belt-driven pumps; others use electric driven pumps. A hydro-boost system consists of a pump, booster assembly, master cylinder, and an accumulator.
483
484As the brake pedal is depressed, the booster pushrod and piston are moved forward. This action causes the spool valve to move and allow fluid flow behind the power piston. As hydraulic pressure builds, it actuates the master cylinder.
485
486The accumulator is used as a back-up should the hydraulic power source fail. Accumulators are either spring-loaded or contain gas under pressure. The accumulator is filled with hydraulic fluid and is pressurized when the brakes are applied. If the engine stalls or a failure occurs in the power steering pump, the accumulator will have an adequate amount of pressurized fluid to provide one to three power-assisted brake applications. To test the accumulator, run engine and then shut off. Wait 5 to 10 minutes and test brake assist. If the accumulator is working correctly, you will have two to three assisted applications.
487
488The inspection and testing of a hydro-boost system must include a complete inspection of the power steering pump, belt, lines, hose connections, and the hydro-boost unit. Any leaks in the power steering system will affect hydro-boost operation. Aerated power steering fluid will also cause the hydro-boost system to not function correctly. Low fluid level can cause a moan with a vibration in the pedal and steering column, usually experienced during parking or low-speed maneuvers. It's important to remember that the pressure needed to actuate the hydro-boost unit and master cylinder originates from the power steering pump assembly, which is usually operated by a belt, driven by the engine. A slipping belt or lower pump pressure will affect hydro-boost operation.
489
490Bleeding the power steering system will be necessary after repairs are made to the power steering system or to the hydro-boost assembly. To bleed the system, perform the following procedure:
491
4921.Start the engine and apply the brake pedal several times while turning the steering wheel from stop to stop. Turn the engine off and apply the brake pedal several more times to deplete accumulator pressure. Check fluid level and add if needed. If the fluid is foamy, let the vehicle stand for a few minutes and recheck fluid level. It may be necessary to repeat the process until all air is purged from the system.
493
4942. With the wheels off the ground and the engine stopped, turn the steering wheel from stop to stop. Check fluid level and add if needed. Lower the vehicle.
495
4963. Start the engine and apply the brake fluid several times while turning the steering wheel from stop to stop. Turn the engine off and apply the brake pedal several more times to deplete accumulator pressure. Check fluid level and add if needed. If the fluid is foamy, let the vehicle stand for a few minutes and recheck fluid level. It may be necessary to repeat the process until all air is purged from the system.
497
498
499E. Miscellaneous Systems (Pedal Linkage, Wheel Bearings, Parking Brakes, Electrical, etc.) Diagnosis and Repair
500
5011. Diagnose wheel bearing noises, wheel shimmy and vibration problems; determine needed repairs.
502The wheel bearings perform a major role in effective brake function and steering performance. There are two different types of wheel bearing designs used on modern automobiles: the adjustable tapered roller bearing and the non-adjustable sealed roller or ball bearing.
503
504Worn wheel bearings can cause a growling noise and vibration when the vehicle is driven. Checking for loose or worn wheel bearing should always be part of a complete brake inspection. A worn or improper wheel bearing adjustment can cause poor brake performance, poor steering, and rapid wheel bearing wear.
505
506Tapered wheel bearings can be disassembled, cleaned, re-greased, and adjusted. Sealed roller or ball bearing wheel bearings cannot be serviced and are replaced as a unit.
507
508
509  2. Remove, clean, inspect, repack wheel bearings, or replace wheel bearings and races; replace seals; replace hub and bearing assemblies; adjust wheel/hub bearings according to manufacturers' specifications.
510Tapered roller bearings are generally used on non-drive axles. The wheel bearings are mounted between a hub and a fixed spindle. To gain access to tapered wheel bearings, remove the wheel, brake rotor or drum, dust cap, cotter pin, and spindle nut. Next, remove the outer wheel bearing. Remove the hub/rotor or hub/drum assembly. Pry the wheel bearing seal and remove the inner wheel bearing. Thoroughly clean the wheel bearing, hub assembly, spindle shaft, and races. Carefully inspect the wheel bearings, spindle, and races for signs of wear. Discard bearings showing any signs of wear, chipping, bluing, or galling. Repack the wheel bearings with high-temperature grease. Never repack a wheel bearing without first removing all the old grease. Insert the inner bearing in the hub and lightly lubricate the new wheel seal with grease. Tap the seal in place using a seal driver. Carefully install the hub/rotor or hub/drum assembly on the spindle. Install the outer wheel bearing, washer, and spindle nut. Always reinstall a bearing in the same race.
511
512If the wheel bearings need replacing, it will be necessary to replace the bearing races also. Remove the bearing race from the hub using a brass drift or appropriate puller. Drive the new races into the hub until fully seated using a bearing race installer. If using a drift punch, tap the races a little at a time, moving the punch around the race to avoid cocking. Use a soft steel drift, never a hardened punch.
513
514It is very important to properly adjust tapered wheel bearings. Always check with the manufacturer's recommended procedure for the specific vehicle being serviced. There are two widely used methods for adjusting wheel bearings: the torque wrench method and the dial indicator method.
515
516In the torque wrench method, rotate the wheel in the direction of tightening while the spindled nut is tightened to the specified torque. This initial torque setting seats the bearings in the bearing race. The nut is then loosened until it can be rotated by hand. The nut is then torqued, this time to the lower specified value. Loosen the nut, if necessary, to install the cotter pin and lightly tap on the dust cap.
517
518To adjust the wheel bearings using the dial indicator method, start by tightening the spindle nut while spinning the wheel, to fully seat the bearings. Loosen the spindle nut until it can be rotated by hand. Mount a dial indicator so the indicator point makes contact to the machined outside face of the hub. Firmly grasp the sides of the rotor or tire, and pull in and out. Adjust the spindle nut until the end play is within manufacturer's specification. Typical end play range from 0.001 inch to 0.005 inch (0.03 to 0.13 mm). Install the cotter pin and dust cap.
519
520Sealed ball and roller bearings are not serviceable and must be replaced when they are defective or have damaged grease seals. Removing this type of bearing involves pressing the bearing from the bearing hub out of the spindle or knuckle assembly. Carefully inspect the bearing, hub, and spindle assembly for wear. Press the new bearing into the spindle/knuckle assembly and torque the axle nut following the manufacturer's procedure.
521
522
523  3. Check parking brake system; inspect cables and parts for wear, rust, and corrosion; clean or replace parts as necessary; lubricate assembly.
524The parking brake is a mechanical system integrated with the hydraulic brake system. It is intended to prevent the vehicle from rolling while it is parked. The rear wheels are held in place by a series of cables and linkages when either a parking brake pedal or hand lever is applied.
525
526The parking brake cables must move freely when applied. Inspect the cables and all parking brake components for wear, binding, rust, and corrosion buildup. Check for cable wear at points of contact. A frayed cable must be replaced. Inspect the parking brake or lever assembly for binding and malfunction. Make sure the parking brake ratchets into place and locks into position. Check all the attaching cable hardware inside the brake drum. For disc brakes, inspect the hardware and lever at the rear of the caliper for wear and malfunction. Lubricate the cables and pivot areas as needed. Some cables are coated and cannot be lubricated.
527
528
529  4. Adjust parking brake assembly; check operation.
530To check operation of the parking brake, raise the vehicle off the ground and apply the parking brake. The rear wheels should be locked in position. If the wheels can be rotated in the forward direction by hand with the parking brake applied, the parking brake may require adjustment. Before any adjustment is made, always check the condition of the brakes and drum brake adjustment. Worn rear brake shoes or brakes out of adjustment will affect the operation of the parking brake. If the parking brake is incorporated with the rear disc caliper, check the calipers for proper operation.
531
532To adjust the parking brake assembly, raise the vehicle off the ground and apply the parking brake two or three clicks. There should be no slack in the cables and a slight drag felt at the rear wheels. If necessary, adjust the equalizer nut until all the slack is removed from the cables and a slight drag felt at the rear wheel. Release the parking brake. The parking brake should release and the wheels should turn freely. Next, apply the parking brake about six clicks to see if the rear brakes lock. Make a final adjustment if needed. Check the service manual for specific procedure and number of required clicks to lock the rear wheel.
533
534
535  5. Test the parking brake indicator light, switch and wiring.
536Battery voltage is applied to the brake warning indicator light when the ignition is the run mode, bulb test mode, or start mode. The parking brake switch supplies the ground for the warning light. The ignition switch supplies an additional ground for the brake warning light in the start or bulb test mode to provide a means to check proper bulb function.
537
538A continually illuminated brake warning light may be caused by a grounded wire to the parking brake switch, a continually closed parking brake switch, or low fluid level in one section of the master cylinder reservoir. If an open circuit occurs in the wire to the parking brake switch, the brake warning light is not illuminated when the parking brake is applied.
539
540When the parking brake pedal is applied, it closes a switch that completes an electric circuit to the brake indicator light in the instrument panel. The parking brake applied indicator light will then light when the ignition is turned on. The light goes out when the parking brake is released or the ignition is turned off. In some vehicles, this same indicator light may be used to alert the driver to problems in the antilock brake system.
541
542
543  6. Test, adjust, repair or replace brake stop light switch, lamps, and related circuits.
544The brake light switch can be adjusted on some vehicles. The brake lights should operate when the brake pedal is depressed 0.25 inch (6.35 mm). Battery power is supplied to one side of the switch, which is normally open. When the brake pedal is depressed, the switch closes, supplying battery power to the brake light bulbs.
545
546If the brake lights do not operate, check for battery power to the brake light switch. If there is no battery power, check the fuse or check for an open wire to the brake light switch. If battery power is present at the switch, depress the brake pedal and check for battery power on the other side of the switch, which feeds battery power to the brake light bulbs. No power on the other side of the switch with the brake pedal depressed indicates a faulty switch.
547If the switch is operational and the brake lights do not operate, check for an open wire either on the battery feed side from the switch or ground side of the wiring harness at the brake light bulbs. Always consult the service manual for the specific wiring diagram when diagnosing the brake light circuit.
548
549Some brake light switches contain multiple contacts to control cruise control function and torque converter clutch operation. Also, the brake light circuit on many vehicles is integrated with the turn signal switch or combination switch in the steering column. A defective turn signal switch or combination switch may affect the brake light circuit. On vehicles equipped with antilock brakes, the brake switch is also an input to the brake control module.
550
551
552  7. Inspect and test brake pedal linkage for binding, looseness, and adjustment; determine needed repairs.
553Part of brake inspection includes checking the brake pedal and linkage for wear and proper function. Check for binding or worn bushings. Worn bushings or loose linkage may affect brake performance. If the vehicle was involved in an accident, check for a bent brake pedal.
554
555
556  F. Electronic Brake Control Systems: Antilock Brake System (ABS), Traction Control System (TCS), and Electronic Stability Control System (ESC) Diagnosis and Repair (7 Questions)
5571. 
558Follow manufacturers' service and safety precautions when inspecting, testing and servicing electronic brake control system, hydraulic, electrical, and mechanical components.
559Many vehicles today are equipped with antilock brake systems (ABS). Although, vehicle designs may differ, all antilock systems essentially function the same way. The ABS computer or control module monitors wheel speed, vehicle speed, and other vehicle functions. The wheel speed sensors send vital information to the ABS control module. When the control module senses that a wheel is about to lock up, it will regulate hydraulic pressure to the wheels in order to prevent lock-up. During a panic stop situation, the antilock brake system allows the driver to maintain directional control while providing maximum braking performance.
560
561Most of the services done to the brakes of an antilock brake system are identical to those in a conventional brake system. There are, however, some important differences. One of these is the bleeding of the brake system. Always refer to the appropriate procedures in the service manual before attempting to service the brakes on an ABS-equipped vehicle. Before servicing an antilock brake system, it is important that you understand the basics of electrical and electronic troubleshooting. Without this basic understanding, it will be difficult to follow the diagnostic procedures given in most service manuals.
562
563Servicing antilock brakes require following different safety precautions. Always refer to the service manual and review safety procedures for the specific vehicle being serviced.
564
565These common safety guidelines should be observed:
566
5671. Always wear safety glasses.
568
5692. Never open a bleeder valve or loosen a brake line on an integral antilock brake system when the accumulator is pressurized.
570
5713. Remove the pressure from the accumulator by pumping the brake pedal forty times with the ignition key in the off position.
572
5734. Never connect or disconnect any electrical connector or component with the key in the on position. This may damage the ABS controller.
574
5755. Never strike or tap on wheel speed sensor components. Striking these components may de-magnetize the wheel speed reluctor and will affect the signal strength of the sensor.
576
5776. Never mismatch tire sizes.
578
5797. DOT 5 fluid should never be used in antilock brake systems.
580
581
582  2. Diagnose poor stopping, wheel lock up, false activation, pedal feel and travel, pedal pulsation, and noise concerns associated with the electronic brake control system; determine needed repairs.
583The clicking noise during initial driving is a result of the ABS computer self-test mode in which the computer momentarily energizes the solenoid in the antilock brake system. On many systems, pedal pulsations are normal during ABS function; however, pedal pulsation during a normal stop when the ABS function is not operating may be caused by out-of-round drums or rotors with excessive runout.
584
585Vehicles equipped with antilock brakes will have different braking characteristics during extreme braking than vehicles without ABS. During normal braking conditions, the antilock portion of the brake system does not function. However, wheel speed sensors continuously send information to the ABS control module. When wheel lock-up begins to take place, the control module will modulate hydraulic pressure through a series of solenoids to prevent wheel lock-up and maintain steering ability. Correct tire size plays a critical role in antilock operation. Different size tires can affect ABS operation and may cause wheel lock-up. During the ABS function process, the driver can misinterpret normal ABS operation as a brake problem. A pulsation felt through the brake pedal during ABS operation is normal. Also, a whine or ratcheting noise can be heard as the solenoids are modulating hydraulic pressure to the wheels. Some systems use an antilock pump assembly, which will initiate from time to time to maintain pressure in the accumulator. The driver may hear an audible whine from the pump. If the pump runs continuously or is activated for longer periods of time, this may indicate a faulty accumulator.
586
587If no pulsation is felt under hard braking at speeds above 10 mph (16 kph), suspect an antilock malfunction. Below 10 mph, the antilock system is generally disabled.
588
589False activation of the electronic brake control system can sometimes be attributed to a sensor-to-toner wheel gap that is too large. Some sensors can be adjusted, while others may have other corrective actions. Damage to the sensor or other suspension components can lead to excessive gap. Sensors that bolt on to a sealed hub assembly can have rust buildup between the sensor and mounting surface. Cleaning the mounting surface should restore proper sensor-to-toner wheel clearance.
590
591
592  3. Observe electronic brake control system indicator light(s) at startup and during road test; determine if further diagnosis is needed.
593All antilock brake systems have some sort of self-test. This test is activated each time the ignition switch is turned on. You should begin all diagnostics with this simple test. To perform a typical ABS self-check sequence, place the ignition switch in the START position while observing both the red system light and the amber ABS indicator lights. Both lights should turn on. Start the vehicle. The red brake system light should turn off. With the ignition switch in the RUN position, the antilock brake control module performs a preliminary self-check on the ABS electrical system. During the self-check, the light remains on (3 to 6 seconds) and then should turn off. If a malfunction is detected during the test, the light will remain on and the system will shut down.
594
595
596  4. Diagnose electronic brake control system, electronic control(s), components, and circuits using on-board diagnosis and/or recommended test equipment; determine needed repairs.
597Most modern antilock systems have the ability to store an error message, called a fault code, should a malfunction occur. By using a scan tool, you can retrieve the fault code from the computer memory. The fault code will direct you to troubleshooting procedures and aid in diagnosing the malfunction. On some systems, achieving the fault code is accomplished by counting the number of times the ABS warning light flashes. Always consult the appropriate service manual for specific diagnostic procedures.
598
599Always begin your diagnosis with a complete visual inspection of the entire brake system and antilock system. Check fluid level, harness connectors, and wiring to components. If a fault code is stored in the ABS controller memory, follow the appropriate diagnostic procedure to diagnose the problem. Many systems allow the technician to view sensor and component data through a scan tool. Vital information, such as wheel speed sensor operation, can be viewed, compared, and analyzed. The use of a scan tool can greatly reduce the diagnostic time needed to solve tough ABS problems.
600
601
602  5. Bleed and/or flush the electronic brake control hydraulic system following manufacturers' procedures.
603Bleeding procedures for antilock brake systems will vary depending on the vehicle. Different antilock brake systems will require different bleeding methods. Some vehicles will require the use of a bi-directional scan tool to move solenoids or other components into a particular position. Many non-integral antilock brake systems can be bled using traditional methods. On most integral systems, a fully charged accumulator and special bleeding equipment are needed. Always refer to the service manual for specific recommended bleeding procedures.
604
605
606  6. Remove and install electronic brake control system components following manufacturers' procedures and specifications; observe proper placement of components and routing of wiring harness.
607
608Some antilock brake systems utilize a pump, motor, hydraulic actuator, and accumulator with the master cylinder in one single unit (called integral ABS). Other systems connect the ABS hydraulics to the master cylinder and other components by means of high-pressure hoses. Most ABS components, such as wheel speed sensors, control modules, and hydraulic actuators, are not serviceable and should be replaced if found defective.
609
610When connecting and disconnecting any ABS components, make sure that the ignition key is in the off position. Some manufacturers advise removing the battery cables. Always make sure the ignition key is off and brake system depressurized before starting any repairs. Pumping the brake pedal at least twenty-five to forty times will depressurize most antilock brake systems.
611
612All wiring to any ABS component must be routed in the exact same way as it was removed. Do not alter the position, routing, or mounting of the harness.
613
614
615  7. Test, diagnose and service electronic brake control system sensors (such as speed, yaw, steering angle, brake pedal position, etc.) and circuits following manufacturers' recommended procedures (includes output signal, resistance, shorts to voltage/ground, and frequency data).
616
617The wheel speed sensors continuously send signals to the ABS controller. The typical wheel speed sensor consists of a toothed ring (or tone wheel), made from ferrous metal, and a permanent magnet sensor. As the wheel turns, the wheel sensor produces a varying AC voltage based on the changing magnetic field. The strength of the signal is dependent upon the speed of wheel rotation. AC voltage will form a maximum positive voltage and a maximum negative voltage. This cycle is repeated many times and is known as a sine wave. By counting the number of cycles occurring each second, the ABS controller can determine the frequency of the wheel speed sensor. The controller can use this information and compare the frequency of one wheel speed sensor against another. A wheel speed sensor decelerating faster than another indicates an impending wheel lock-up.
618
619When testing a wheel speed sensor, start with a visual inspection of the sensor and wiring. Debris trapped around the sensor or ring can affect signal quality and strength. Also, if possible, check the air gap between the sensor and the toothed ring. A gap too wide may cause a weak signal or erratic readings. Inspect the toothed ring for debris, chips, or cracks. Some sensors are mounted in the differential with the tone ring located on the ring gear. Metal particles can accumulate around the sensor from bearing and gear wear.
620
621An ohmmeter can be used to check the resistance of the sensor. Compare the readings with the service manual. Probably the most accurate way to test a wheel speed sensor is with a digital storage scope. A scope can test the quality of the signal and spot any intermittent glitches in the sensor signal.
622
623The wheel speed sensor harness can also be a source of problems. The harness must be able to cleanly send information to the ABS controller. A misrouted sensor harness too close to a heat source or magnetic field can result in false information being sent to the controller. Corrosion in the harness or in a harness connecter can cause unwanted resistance in the wiring and a diminished wheel speed sensor signal. Always check the harness routing and check the continuity and quality of the harness wiring.
624
625
626  8. Diagnose electronic brake control system braking concerns caused by vehicle modifications (wheel/tire size, curb height, final drive ratio, etc.) and other vehicle mechanical and electrical/electronic modifications (communication, security, and radio, etc.).
627
628All ABS computers are specifically programmed for the particular vehicle they are controlling. All aspects of the vehicle are taken into account: vehicle weight, transmission type, tire size, differential, suspension characteristics, electronic devices, and more.
629
630Changing the tires and wheels to a size not recommended by the manufacturer can greatly affect ABS brake operation. The ABS controller is programmed to look for and expects to see specific information being sent by the wheel speed sensors. If the tire and wheel size are changed, the signal will be altered and may cause a malfunction. It should be noted that many late-model trucks have the ability to change their programming for optional tire sizes. As with all things relating to vehicles, every rule has an exception.
631
632Any modification to the vehicle may affect ABS operation. If an electronic device, such as radio or an alarm, is installed, make sure the wiring harness does not interfere with ABS harness. When replacing differentials and transmissions, always confirm the correct final drive ratio.
633
634
635  9. Repair wiring harness and connectors following manufacturers' procedures.
636Always handle the ABS harness with care when testing, repairing, or servicing components. Never probe through the harness insulation, and be very careful when back probing a connector. Follow all guidelines prescribed in the service manual for testing components, connectors, and wiring. If a harness connector is faulty, do not attempt to repair. If a replacement connector is not available, replace the harness. If a section of harness wiring is damaged, it is recommended to not repair the wire, but to replace the damaged harness.