Chapter 7 Disc Brake Fundamentals and Service
Introduction • Disc brakes have been in use since the 1970s on the front wheels. • Now many new vehicles have disc brakes on all four wheels.
Disc Brake Advantages • Light weight. • Dissipate heat better than drums. • Brake dust is not trapped. • Less prone to pull. • Self-adjusting.
Disc Brake Disadvantages • Noisier than drum brakes. • Disc brakes are not as effective as a parking brake.
Wear Indicators • Audible – tab mounted on brake pad that contacts the disc and makes noise when wear becomes excessive. • Electronic – sensor or simple electrical contact with disc when wear is excessive • Tactile – contact with metal backing plate causes a pedal pulsation.
Fixed Calipers • Caliper does not move on application. • Pistons are on both sides of caliper. • No longer installed.
Floating Calipers • Also called a sliding caliper • Brake piston only located on inboard side of the caliper. • Caliper must be able to slide to engage pad on outboard side.
Caliper Variations • Pin • Center Abutment • Pivot pin
Four-Wheel Disc Brake • Same basic design on rear brake calipers as front. • Provision has to be made for parking brakes. • First used on American cars in 1965 on the Corvette
Road Test • Check fluid level and pedal height before driving. • Drive in a deserted area. • Make note of pulls, pulsations, and noises that may help diagnosis.
Disc Brake Inspection • Check the thickness of pad material. • Check for uneven wear. • Make certain caliper slides are operational. • Check for heat damage and cracks.
Rotor Inspection • Check for visual wear and heat damage. • Ensure rotor is within thickness specification. • Check for excessive runout.
Is machining always necessary • Rotors do not have to be machined if • They are not worn beyond the manufacturers specified limits. • They do not have excessive runout. • If rotors are re-used: • Insure that BOTH the rotors on the axle do not need to be machined. • Note: Used rotors may actually have better braking function that new/machined rotors.
Replacing Front Disc Linings • Usually necessary to remove calipers. • Pay attention to mountings and ant-irattle clips for reinstallation. • Loosen the bleeder screw and retract the piston. • Make sure caliper slides are clean. • Replace pads.
Rear Disc Linings Rear lining replacement is similar to front except: • Most rear disc brakes have a special procedure to retract the piston due to the parking brake. Consult service literature.
Disc Caliper Rebuilding • Disc brake calipers can be rebuilt. • May be more cost-effective to replace, especially on rear. • See the text for details on caliper rebuilding.
Noise Prevention • Make sure the pad fits tight in the mounting. • Ensure shims and clips are installed. • Aftermarket insulator materials may help.
Installing Caliper • Install caliper to proper torque. • Make sure caliper slides are clean and lubricated. • Torque wheels to specification. • Be sure to apply brakes to seat linings before driving.
Disc Brake Noise • Glazed linings • Hard spots on rotors • Not cleaning rotors after machining
Pedal Pulsation • Rotor has excessive runout or thickness variation. • Improper or uneven torque on wheels. • Loose wheel bearing.
Brake Pull/Uneven Wear • Sticking caliper piston • Defective brake hose • Caliper slides not free
Test Drive after Brake Service • Make certain to test drive thoroughly. • Use proper procedure to “break in” linings.