Disc brakes operate by applying friction between pads and a rotating disc, offering stronger braking forces compared to drum brakes. They are equipped with advanced components like calipers and hydraulic systems, providing advantages such as rapid cooling and ease of maintenance, while facing challenges like noise and warping. The performance of disc brake pads depends on their materials, which influence friction and efficiency across various temperature ranges.

1. 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. 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. 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. 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.