1. Modern Automotive Technology PowerPoint for by Russell Krick
Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois

2. Chapter 72
Brake System
Diagnosis and Repair

3. Contents Brake system problem diagnosis Brake system inspection
Vacuum booster service
Hydraulic booster service
Master cylinder service
Brake system bleeding
(Continued)

4. Contents Brake line and hose service Disc brake service
Brake disc (rotor) service
Drum brake service
Parking brake adjustment

5. Brake System Problem Diagnosis
Gather information from the customer or service writer about any symptoms:
smells, abnormal brake pedal movements, or improper braking action
Road test the vehicle if necessary
Perform a brake inspection
Decide what adjustments or repairs are needed

6. On-Board Diagnostics
Self-diagnostics may be available on vehicles, especially those equipped with anti-lock brake systems
Connect a scan tool to the diagnostic connector
Read any stored diagnostic trouble codes
Check the scan data for anti-lock brake operating values

7. Brake Vibration
Shows up as a chatter, pulsation, or shake in the brake pedal or steering wheel
Occurs only when the brakes are applied
Front brake problems may be felt mostly in the steering wheel
Pulsation in the brake pedal may be caused by brake problems at any wheel

8. Brake Vibration Possible causes: warped disc out-of-round brake drum
hard spots on the disc or drum

9. Grabbing Brakes
Brakes apply too quickly, even with light brake pedal application
Possible causes:
malfunctioning brake booster
brake fluid or grease on the linings
worn brake linings
faulty metering valve
mechanical problem in the wheel brake assembly

10. Excessive Pedal Effort
Noticeable increase in the amount of foot pressure needed to apply the brakes
Possible causes:
seized wheel cylinder or caliper piston
collapsed brake hose or crimped line
faulty master cylinder
contaminated linings
disconnected brake booster vacuum line or defective booster

11. Pulling Brakes
The vehicle veers to the right or left when the brakes are applied
Possible causes:
seized caliper or wheel cylinder piston
grease- or fluid-coated lining
leaking cylinder
faulty automatic adjuster
brake lining dust in a drum brake assembly

12. Spongy Brake Pedal
The brakes will apply, but the pedal does not feel solid
Possible causes:
air in the brake system
faulty residual check valve in the master cylinder
maladjusted brake shoes

13. Dropping Brake Pedal
The pedal slowly moves all the way to the floor when steady pressure is applied to it
Pumping usually restores pedal height momentarily
Possible causes:
internal leak in the master cylinder
external fluid leak in any component

14. Low Brake Pedal
The pedal travels too far toward the floor before braking
Possible causes:
inoperative brake adjusters
maladjusted master cylinder push rod
mechanical problem in the wheel brake assemblies

15. Dragging Brakes
The brakes remain partially applied when the brake pedal is released
To detect dragging brakes, carefully feel each brake assembly
dragging brakes will be abnormally hot

16. Dragging Brakes Possible causes:
seized wheel cylinder pistons or parking brake cables
overadjusted parking brake or master cylinder push rod
weak return springs
brake fluid contamination
master cylinder problems

17. No Brake Pedal
Very dangerous condition in which the brake pedal moves to the floor with no braking action
Possible causes:
hydraulic system leak that causes the loss of the brake fluid
faulty master cylinder
A complete loss of braking is unlikely on a system with a dual master cylinder

18. Brake Warning Light On
Indicates either an internal leak (master cylinder) or an external leak
Unequal pressure in the dual master cylinder system has caused the warning light switch to shift to one side

19. Braking Noise Noises include grinding sounds, squeaks, or rattles
Metal-on-metal grinding sound when braking
caused by worn brake linings

20. Braking Noise Squeak when braking Rattles
caused by glazed, or hardened, brake linings; a dry brake drum backing plate; or a wear indicator rubbing on the rotor
Rattles
caused by a missing anti-rattle clip or loose parts

21. Brake System Inspection
Most manufacturers recommend a periodic inspection of the brake system
When inspecting the brake system, check the brake pedal action; fluid level; and the condition of the brake lines, hoses, and wheel brake assemblies

22. Brake System Problems

23. Checking Brake Pedal Action
Apply the brake pedal and compare the movement to specifications
Brake pedal application specs:
pedal height
pedal free play
pedal reserve distance

24. Brake Pedal Measurements

25. Brake Pedal Measurements
Using a yardstick to measure the distance from the steering wheel to the brake pedal

26. Checking Brake Fluid
Remove the master cylinder cover or view the level through the side of the plastic reservoir on some models
Typically, the brake fluid level should be 1/4" (6 mm) from the top of the reservoir

27. Checking Brake Fluid

28. Checking for Leaks
Inspect for leaks whenever the fluid level in the master cylinder is low
Check brake lines, hoses, calipers, and wheel cylinders
Check below the master cylinder mounting point at the cowl or booster
Leaks show up as darkened, damp areas

29. Checking the Parking Brake
Apply the parking brake
The pedal or lever should not move more than 2/3 of full travel
The parking brake should keep the vehicle from moving with the engine idling and the transmission in drive
Inspect the cables for fraying and high friction

30. Checking Wheel Brake Assemblies
Raise the car on a lift or jack stands
Remove one front wheel and one rear wheel
Inspect the disc brake assemblies
Inspect the drum brake assemblies

31. Inspect the brake pad linings (minimum thickness 1/8" or 3 mm)
Disc Brake Inspection
Inspect the brake pad linings (minimum thickness 1/8" or 3 mm)

32. Inspect the rotors for scoring or heat damage
Disc Brake Inspection
Inspect the rotors for scoring or heat damage

33. Disc Brake Inspection

34. Drum Brake Inspection Remove the brake drums
The brake shoe linings should be at least 1/16" (1.5 mm) thick
Check the linings for glazing or contamination from brake fluid or differential oil

35. Drum Brake Inspection Check the drum for cracks or heat damage
A badly scored drum must be machined
Check for leaks, wear, and damaged parts

36. Vacuum Booster Service
Inspect the brake booster and the vacuum hose
hoses may collapse or harden
To test the booster, pump the brake pedal to remove any vacuum
Apply the brake and start the engine
the pedal should drop slightly as engine manifold vacuum develops

37. Removing the Booster

38. Vacuum Brake Booster

39. Rebuilding the Booster
Following the service manual procedures, replace the diaphragm, the valves, and other plastic or rubber parts
Most boosters are rebuilt by specialty shops

40. Hydraulic Booster Service
Check all the hydraulic lines for signs of leakage
If the booster is inoperative, check the power steering fluid level
Most boosters are not serviceable without special equipment and procedures

41. Master Cylinder Service
A faulty master cylinder may leak fluid past the rear piston or leak internally
Inspect for external leakage where the master cylinder mounts to the booster or cowl
Internal leakage will cause the pedal to slowly sink to the floor when pressure is applied

42. Master Cylinder Removal
Disconnect the brake lines using a line wrench
Unbolt the master cylinder from the booster or cowl
On a vehicle without a power-assist booster, disconnect the push rod from the brake pedal assembly

43. Master Cylinder Rebuild
Following the service manual procedures, drain the fluid and disassemble the unit
Honing may be used to remove minor corrosion or pits from the cylinder
surface must be in perfect condition
Measure piston-to-cylinder clearance
Inspect each component and replace all cups and seals

44. Master Cylinder Rebuild
Clean and lubricate the components with brake fluid and reassemble the unit

45. Removes air from inside the master cylinder
Bench Bleeding
Removes air from inside the master cylinder

46. Installing a Master Cylinder
Bolt the master cylinder to the firewall or booster
Check the adjustment of the push rod if specified
Install the brake lines with the fittings lightly tightened

47. Installing a Master Cylinder
Bleed the air from the fittings
Tighten the fittings
Fill the reservoir with fluid
Check brake pedal feel and road test the vehicle

48. Brake System Bleeding
Air in the brake system will compress, causing a spongy brake pedal
Bleeding involves the use of fluid pressure to force air out of the brake system bleeder screws
Two methods are used:
manual bleeding
pressure bleeding

49. Manual Bleeding
Attach one end of a hose to a bleeder screw and place the other end in a jar containing brake fluid
Have another technician apply light foot pressure on the brake pedal
Open the bleeder screw while watching for air bubbles flowing from the hose

50. Manual Bleeding Close the bleeder screw
Have your helper release the brake pedal
Repeat the steps until the flow from the hose is clear and free of bubbles
Perform the operation on all the brake assemblies, starting farthest from the master cylinder

51. Manual Bleeding

52. Pressure Bleeding
Uses a pressure bleeder tank, which contains brake fluid under pressure

53. Pressure Bleeding Fill the tank with fluid
Charge the tank with 10–15 psi (69–103 kPa) of air pressure
Fill the master cylinder with fluid
Install the adapter and hose on the master cylinder
Open the valve in the hose

54. Pressure Bleeding
Attach one end of a hose to a bleeder screw and place the other end in a jar containing brake fluid
Open the screw until the fluid entering the jar is clear of bubbles

55. Repeat the steps on the other wheel brake assemblies
Pressure Bleeding
Repeat the steps on the other wheel brake assemblies

56. Flushing a Brake System
Extends the life of the brake system components
Done by pressure bleeding all the old fluid out of the system
Removes contamination, such as dirt, rust, corrosion, oil, or moisture
Bleed each wheel brake assembly until clean fluid flows from the bleeder screw

57. Brake Line and Hose Service Lines are subject to corrosion or damage
Hoses may deteriorate over time
When replacing brake lines, use approved double-wall steel tubing

58. Tools and Procedures

59. Disc Brake Service Main steps in disc brake service:
replacing worn brake pads
rebuilding or replacing caliper assemblies
turning (machining) the brake discs
bleeding the system

60. Replacing Brake Pads Loosen the wheel lug nuts
Raise the vehicle on a lift or jack stands
Remove the wheels

61. Use a large C-clamp to push each piston back into its cylinder
Replacing Brake Pads
Use a large C-clamp to push each piston back into its cylinder

62. Unbolt the calipers and slide them off the discs
Replacing Brake Pads
Unbolt the calipers and slide them off the discs

63. Replacing Brake Pads
Support the calipers to prevent hose damage, and then remove the old pads

64. Replacing Brake Pads
Install the anti-rattle clips on the new pads and fit them into the calipers

65. Replacing Brake Pads Slide the caliper assemblies over the discs
Assemble the mounting hardware
Make sure all bolts are torqued to specs
Install the wheel and tighten the lug nuts to specs

66. To remove the piston, apply low air pressure
Rebuilding a Caliper
To remove the piston, apply low air pressure

67. Pry the old dust boot out of the caliper
Rebuilding a Caliper
Pry the old dust boot out of the caliper

68. Remove the old seal from the caliper
Rebuilding a Caliper
Remove the old seal from the caliper

69. Keep the parts organized
Rebuilding a Caliper
Keep the parts organized

70. Rebuilding a Caliper Honing can remove minor imperfections
Lubricate the hone with brake fluid

71. Rebuilding a Caliper Inspect the piston for wear or damage
Clean all parts in an approved cleaner
Coat the parts in brake fluid

72. Work the new seal into the bore groove
Rebuilding a Caliper
Work the new seal into the bore groove

73. Rebuilding a Caliper
Install the new boot in its groove and slide the piston squarely into the caliper

74. Brake Disc (Rotor) Service
It is important to check the condition of the disc
Manufacturers provide specifications for maximum disc runout and minimum disc thickness

75. Measuring Disc Runout
Runout is the amount of side-to-side movement measured near the outer edge of the friction surface
Typical maximum runout:
0.004" (0.10 mm)
If runout is beyond specs, turn the disc on a brake lathe to true its friction surfaces

76. Using a dial indicator, rotate the disc while watching needle movement
Measuring Disc Runout
Using a dial indicator, rotate the disc while watching needle movement

77. Measuring Disc Thickness
The thickness will decrease as the disc wears
The minimum thickness may be printed on the side of the disc
If the disc thickness is under specifications, replace the disc

78. Measuring Disc Thickness
Using an outside micrometer, measure at several points around the disc

79. Resurfacing a Disc
Involves machining a disc’s friction surfaces on a brake lathe to correct runout, thickness variation, or scoring
Mount the disc on the brake lathe according to the lathe manufacturer’s recommendations
With the machine feeds and controls set properly, machine smooth surfaces on the disc

80. Always read the operating manual before using a brake lathe
Resurfacing a Disc
Always read the operating manual before using a brake lathe

81. Typical rotor mounting on a brake lathe
Resurfacing a Disc
Typical rotor mounting on a brake lathe

82. Install a damper to prevent vibration while machining the rotor
Resurfacing a Disc
Install a damper to prevent vibration while machining the rotor

83. Brake Lathe
This lathe has a large cover to protect operators and others in the shop from flying debris

84. On-Car Brake Lathe
Useful on vehicles where the brake disc is hard to remove or where the manufacturer specifies on-car rotor machining
Mounts on the vehicle’s steering knuckle
An electric motor turns the disc during the machining process

85. A stand-mounted electric motor rotates the disc
On-Car Brake Lathe
A stand-mounted electric motor rotates the disc

86. On-Car Brake Lathe
The lathe assembly has controls for feeding cutters into the disc surface

87. Disc Brake Reassembly
After installing the rotor, fit the caliper assembly into place
High-temperature silicone is used on the backs of the pads to help prevent brake rattle and squeal
Apply a small amount of silicone grease to the caliper mounting bolt threads

88. Disc Brake Reassembly
Disc brake components

89. Disc Brake Reassembly

90. The rotor and lining surfaces should be perfectly clean after repairs
Disc Brake Reassembly
The rotor and lining surfaces should be perfectly clean after repairs

91. Drum Brake Service
Service is needed anytime your diagnosis finds faulty drum brake components
Common drum brake faults:
leaking wheel cylinder
worn or contaminated linings
scored drum
seized parking brake components

92. Spring removal and adjustment tools
Tools and Procedures
Spring removal and adjustment tools

93. Tools and Procedures
A brake vacuum is being used to prevent inhalation of brake lining dust

94. Drum Brake Disassembly
Drum brake components

95. Drum Brake Disassembly
Remove the wheels and brake drums and, if necessary, back off the adjuster to ease the removal of a worn drum

96. Drum Brake Disassembly
Use a brake spring retracting tool to remove the upper shoe retracting springs
Use a hold-down spring tool to remove the hold-down springs

97. Drum Brake Disassembly
Lift the brake shoes off the backing plate
Remove the automatic adjuster mechanism
Clean the backing plate

98. Servicing Wheel Cylinders
A cylinder must be replaced or rebuilt if it shows signs of leakage or sticking
Many shops service the wheel cylinders anytime the linings are replaced
Wheel cylinder rebuilding involves honing the cylinder and replacing the rubber cups and boots

99. Note the wheel cylinder components
Drum Brake Assembly
Note the wheel cylinder components

100. Brake Drum Resurfacing
Needed when the drum is scored, out-of-round, or worn unevenly
Mount the drum on the lathe
Wrap a silencing band around the drum
Feed the cutting tool against the inner surface of the drum
Adjust the depth of the cut to lathe specs and activate the automatic feed

101. Brake Drum Resurfacing
Use the correct collars and hubs to secure the drum to the lathe shaft

102. Brake Drum Resurfacing
This brake lathe has a shoe grinder, which will arc shoes to fit the drum

103. Measuring Brake Drum Diameter
Typically, a drum
should not be machined more than 0.060" (1.5 mm) oversize
The drum diameter is often stamped on the drum
Use a drum micrometer to measure the diameter

104. Drum Brake Reassembly Clean the wheel bearings
Inspect the bearings for wear or damage
Pack the bearings with grease and install new grease seals

105. Drum Brake Reassembly
Wipe high-temperature grease on the raised pads on the backing plate and on the star wheel threads

106. Install the new shoes and the adjuster mechanism on the backing plate
Drum Brake Reassembly
Install the new shoes and the adjuster mechanism on the backing plate

107. Preadjusting Drum Brakes
Ensures proper initial brake system operation
Fit a brake adjusting gauge into the brake drum
Set the gauge for the inside diameter of the drum
Fit the gauge over the brake shoes
Adjust the brake until the linings touch the gauge

108. Preadjusting Drum Brakes
Fitting the gauge into the brake drum
Adjusting the shoes

109. Preadjusting Drum Brakes
Another method of preadjusting the brakes:
use a brake spoon to turn the star wheel
turn the wheel until the brake drum drags slightly when rotated by hand

110. Parking Brake Adjustment
To adjust the parking brake, tighten an adjustment nut on the cable mechanism
Shorten the cable until the brakes apply firmly within the first 2/3 of the pedal or lever travel
Do not overtighten the brake
brakes should not drag when released

111. Parking Brake Cables