1. Chapter 32
Disc Brake System

2. Introduction (1 of 2)
Disc brakes use friction to create braking power.
Disc brakes create braking power by forcing flat friction pads against sides of rotating disc

3. Disc versus drum brakes.
Introduction (2 of 2)
Higher applied forces can be used in disc brakes than in drum brakes, because the design of the rotor is stronger than the design of the drum.
Disc versus drum brakes.

4. Disc Brake System (1 of 6)
Modern vehicles always equipped with disc brakes on at least the front two wheels.
Rotor
Caliper
Brake pads

5. Disc Brake System (2 of 6)
Pushrods transfer force through brake booster.
Master cylinder converts pedal force to hydraulic pressure.

6. The hub and hubless rotors.
Disc Brake System (3 of 6)
Hydraulic pressure transmitted via brake lines and hoses to piston(s) at each brake caliper.
Pistons operate on friction pads to provide clamping force
Rotors are free to rotate due to wheel bearings and hubs that contain them
Hub can be part of brake rotor or separate assembly that the rotor slips over and is bolted to by the lug nuts
The hub and hubless rotors.

7. Caliper mounting methods.
Disc Brake System (4 of 6)
The brake caliper assembly is normally bolted to the vehicle axle housing or suspension
Caliper mounting methods.

8. Disc Brake System (5 of 6) Advantages
Greater amounts of heat to atmosphere
Cooling more rapid
Rotors scrape off water more efficiently
Self-adjusting
Don’t need periodic maintenance
Easier to service

9. Disc Brake System (6 of 6) Disadvantages
Prone to noise (squeals and squeaks)
Rotors warp easier
Not self-energizing
Hard to use as parking brakes

10. Disc Brake Calipers (1 of 11)
Bolted to vehicle axle housing (steering knuckle)
Two types of calipers: fixed and sliding/floating

11. Disc Brake Calipers (2 of 11)
Fixed calipers with multiple pistons.
Fixed caliper being applied.

12. Disc Brake Calipers (3 of 11)
When the brakes are applied, hydraulic pressure forces the piston toward the rotor.
Takes up any clearance
Pushes pad into rotor
Once all clearance is taken up on outer brake pad, clamping force will increase equally on both brake pads, applying brakes.
Sliding/floating caliper application.

13. Disc Brake Calipers (4 of 11)
O-rings. A. Square cut O-ring and O-ring cut to show square section B. Square cut O-ring groove in caliper.

14. Disc Brake Calipers (5 of 11)
Square cut O-ring seals piston in disc brake calipers.
Compressed between piston and caliper housing
Keeps high-pressure brake fluid from leaking
Prevents air from being drawn into system

15. Disc Brake Calipers (6 of 11)
Square cut O-ring. A. Square cut O-ring during brake application B. Square cut O-ring during brake release.

16. Disc Brake Calipers (7 of 11)
Low-drag calipers designed to maintain larger brake pad-to-rotor clearance.

17. Disc Brake Calipers (8 of 11)
Although the phenolic pistons themselves do not corrode, the cast iron bore of the caliper does corrode and rust
can cause a phenolic piston to seize in the bore

18. Disc Brake Calipers (9 of 11)
Phenolic pistons transfer heat slower than steel pistons
Helps prevent boiling of the brake fluid
Heat transfer. A. Phenolic piston (slow heat transfer). B. Steel piston (fast heat transfer).

19. Disc Brake Calipers (10 of 11)
Bushings must be lubricated with high-temperature, waterproof disc brake caliper grease.
Floating calipers are mounted in place by guide pins and bushings

20. Disc Brake Calipers (11 of 11)
Sliding calipers slide in the caliper mount and are held in place by a spring steel clip.

21. Disc Brake Pads and Friction Materials (1 of 11)
Disc brake pads consist of friction material bonded or riveted onto steel backing plates.

22. Disc Brake Pads and Friction Materials (2 of 11)
Backing plate has lugs that correctly position the pad in the caliper assembly and help the backing plate maintain the proper position to the rotor
Brake pad locating lugs.

23. Disc Brake Pads and Friction Materials (3 of 11)
Amount of friction expressed as ratio
Coefficient of friction
Kinetic energy (motion) of sliding surfaces converts to thermal energy (heat).

24. Disc Brake Pads and Friction Materials (4 of 11)
Composition of friction material affects brake operation
Materials that provide good braking with low pedal pressures tend to lose efficiency when hot
Wear out quicker
Materials that maintain stable friction coefficient over a wide temperature range
Generally require higher pedal pressures
Tend to put added wear on disc brake rotor

25. Disc Brake Pads and Friction Materials (5 of 11)
Disc brake pads and drum brake linings are made from materials that have a moderate coefficient of friction.

26. Disc Brake Pads and Friction Materials (6 of 11)
Brake friction materials:
NAO materials
Low-metallic non-asbestos organic (NAO)
Semimetallic materials
Ceramic materials

27. Disc Brake Pads and Friction Materials (7 of 11)
Combination of weighted qualities:
Stopping power
Heat absorption and dispersion
Resistance to fade
Recovery speed from fade
Wear rate
Performance when wet
Operating noise
Price

28. Disc Brake Pads and Friction Materials (8 of 11)
Coefficients of friction:
C: ≤0.15
D: 0.15–0.25
E: 0.25–0.35
F: 0.35–0.45
G: 0.45–0.55
H: >0.55
Z: Unclassified

29. Disc Brake Pads and Friction Materials (9 of 11)
Disc brakes more prone to squealing
Due to vibrations between brake pad and rotor
Shims and spring-loaded clips help reduce squealing.

30. Disc Brake Pads and Friction Materials (10 of 11)
Anti-noise measures:
Softer linings
Brake pad shims
Springs to hold in place
Example of brake pad retainers.

31. Disc Brake Pads and Friction Materials (11 of 11)
Anti-noise measures:
Contour and groove linings
Bendable tangs
Noise-reducing compounds

32. Wear Indicators Inspect brakes at regular intervals. Wear Indicators
Spring steel scratchers
Warning lamps
Messages on dash

33. Disc Brake Rotors (1 of 7)
Brake disc or rotor is main rotating component of disc brake unit.
Withstand high temperatures
Made of cast iron
Two-part rotor
Composite rotor

34. Disc Brake Rotors (2 of 7) Rotors can fail in two ways:
Parallelism
Lateral runout
Dust shields help to shield the rotor from dust, water, and debris.

35. Disc Brake Rotors (3 of 7)
Types of rotors
Solid
Ventilated

36. Disc Brake Rotors (4 of 7)
Some ventilated rotors are directional, meaning they are designed to force air through the rotor in one direction only.

37. Disc Brake Rotors (5 of 7) Some rotors are slotted and drilled
Better dissipation of heat
Better removal of water from the surface of the pads

38. Disc Brake Rotors (6 of 7)
Most rotors have the minimum thickness stamped or cast on them.

39. Disc Brake Rotors (7 of 7)
Worn rotors cannot absorb as much heat and therefore are subject to brake fade much sooner.

40. Parking Brakes (1 of 3)
Parking brakes are designed to hold vehicles stationary when parked.
Holds vehicle on specified grade in both directions
Separately active from service brake
Mechanically latches into applied position.
Foot or hand operated

41. Parking Brakes (2 of 3)
Two types of parking brakes used in standard disc brakes:
Integrated
Top hat drum

42. Parking Brakes (3 of 3) Electric parking brakes:
Pull on a conventional parking brake cable
Mounted on caliper and directly drive caliper piston
Electric motor to apply disc brake assemblies
Automatically released by electronic control module (ECM)

43. Diagnosis (1 of 12)
Diagnosis starts with understanding customer’s concern.
Communicate directly.
Diagnosis should identify any and all issues.

44. Diagnosis (2 of 12) Tools used for diagnosis:
Brake lining thickness gauge
Brake wash station
Caliper piston pliers

45. Diagnosis (3 of 12) Tools used for diagnosis:
Disc brake rotor micrometer
Dial indicator
Parking brake cable pliers

46. Diagnosis (4 of 12) Tools used for diagnosis:
Caliper piston retracting tool
C-clamp
Off-car brake lathe

47. Diagnosis (5 of 12) Tools used for diagnosis: On-car brake lathe
Caliper dust boot seal driver set

48. Diagnosis (6 of 12)
Disc brake tools. A. Brake lining thickness gauges. B. Brake wash station. C. Caliper piston pliers. D. Disc brake rotor micrometer. E. Dial indicator.

49. Diagnosis (7 of 12)
F. Parking brake cable tool. G. Caliper piston retracting tool. H. Off-car brake lathe I. On-car brake lathe. J. Dust boot seal/bushing driver set.

50. Diagnosis (8 of 12)

51. Diagnosis (9 of 12)
To diagnose stopping, noise, vibration, pulling, grabbing, dragging, or pulsation:
Verify the customer concern by operating the vehicle if safe to do so.
Remove and inspect calipers.
Inspect caliper mountings, slides, and pins.
Inspect brake pads and wear indicators.

52. Diagnosis (10 of 12)
To diagnose stopping, noise, vibration, pulling, grabbing, dragging, or pulsation:
Check brake pads.
Disassemble caliper.
Reassemble calipers.

53. Diagnosis (11 of 12)
To diagnose stopping, noise, vibration, pulling, grabbing, dragging, or pulsation:
Retract and readjust pistons.
Inspect and measure disc brake rotors.
Remove and reinstall rotors.

54. Diagnosis (12 of 12)
To diagnose stopping, noise, vibration, pulling, grabbing, dragging, or pulsation:
Refinish rotors.
Inspect and replace wheel studs.
Install wheels and torque lug nuts, and make final checks.

55. Summary (1 of 7)
Disc brakes create braking power by forcing flat friction pads against the outer faces of a rotor.
The vehicle’s kinetic energy is transformed into heat energy by the disc brake components, which slow the vehicle when applied.
Disc brake assemblies consist of a caliper, brake pads, and a rotor.

56. Summary (2 of 7)
Caliper pistons use hydraulic pressure to create a clamping force of the brake pads to the faces of the rotor.
Disc brake pads require much higher application pressures to operate than drum brake shoes because they are not self-energizing.

57. Summary (3 of 7)
Advantages of disc brakes over drum brakes: more effective at transferring heat to atmosphere, self-adjusting, resistant to water fade, and easier to service.
Disadvantages of disc brakes compared to drum brakes: more prone to noise, more prone to pedal pulsations due to warpage, and more difficult to use as an emergency brake.

58. Summary (4 of 7)
Disc brake calipers come in two main styles: fixed and floating/sliding.
In disc brake calipers, the piston is sealed by a square cut O-ring.
Floating/sliding calipers require clean and lubricated pins, bushings, or guides for proper operation.

59. Summary (5 of 7)
Brake pad lining is either riveted or bonded to the pad backing plate.
Brake pad lining is available in a variety of materials with varying amounts of coefficient of friction.
Brake pads may use shims, spacers, guides, and bendable tangs to help minimize squealing.

60. Summary (6 of 7)
Brake pad wear indicators, if used, can be of the mechanical or electronic type.
Rotors rotate with the wheels and are usually made of durable cast iron with friction surfaces that run true and parallel.
Brake rotors can be solid or ventilated.

61. Summary (7 of 7)
Disc brake parking brakes can be of the integrated caliper style, top hat drum style, electric pull-cable style, and integrated electric motor caliper style.
Diagnosing brake faults requires good information from the customer, an adequate test-drive when possible, and a good understanding of brake theory.