Disc Brake Service Procedures
Safety Note: Asbestos has been used in brake linings for many years. Asbestos dust is a health hazard if inhaled. Do not clean brake parts with compressed air. Avoid breathing the dust off of brake parts.
Disassemble and Inspect
Remove the front wheels. Note: Before beginning this procedure, ensure that the vehicle is properly supported on axle stands.
Inspect the hydraulic hoses attached to the brake calipers for bulges or cracks.
Determine if the bleed screws can be loosened. Use a six-point socket or wrench to avoid damaging the screw.
Remove the brake caliper. The procedure for removing the brake caliper varies from one vehicle to another. Use the service manual to determine the correct procedure for the vehicle being worked on.
Note: Do not allow the caliper to hang by the hydraulic hose. Use a piece of mechanics wire to suspend the caliper after its removal.
Remove the brake pads from the caliper. Press the caliper piston back into the bore using a block of wood or equivalent and secure the piston with a c-clamp. The piston should move with moderate pressure on the clamp.
Inspect the caliper for signs of brake fluid leakage or damaged rubber boots.
Remove the brake rotors. On rear-wheel drive vehicles this usually requires the removal and disassembly of the wheel bearings. On many front-wheel drive vehicles the rotor is held in place by the wheel and will come off easily once the caliper is removed. Clean and inspect the wheel bearings.
Inspect the brake rotor for cracks, hot spots, or excessive wear. Measure the rotor with a micrometer to determine if it is thick enough to be reused.
Based on your inspection, create a list of recommended service and required parts.
Your work must be inspected by the teacher before proceeding to the next procedure.
Repair or replace parts as discussed with instructor.
If the rotors require machining, mount the rotors in the brake rotor lathe. Set up the cutter. Have the teacher inspect your machine set-up before starting the machine. Remove only enough material to true the rotors. Note: Safety glasses are required for this procedure.
Repack the wheel bearings with grease. Thoroughly clean any filings from the rotors before installing the bearings.
Clean and lubricate the pins or slides that allow the calipers to "float" on the rotors.
Install the rotors on the vehicle and adjust the wheel bearings. Lock the adjusting nut with the cotter pin and install the dust cap.
Install the brake pads in the caliper, ensuring that any anti-rattle springs or anti-vibration compounds are in place.
Install the brake calipers on the rotors. Use a thread-lock agent if required on the mounting bolts.
Fill the master cylinder brake fluid reservoir. Note: Avoid contacting skin with the brake fluid.
Check the brake lines for air. Have an assistant pump the brake pedal until the caliper piston moves out to firmly hold the disc pads against the rotor. While holding firm pressure on the brake pedal, open the bleed screw and check for air bubbles. Close the bleed screw before the assistant releases the brake pedal. Note: a commercially-available brake bleeding system may also be used for this procedure.
Check the brake fluid level in the master cylinder.
Install and torque the wheel nuts and reinstall the hubcap.