Most of today's automobiles have disc brakes on the front wheels, and many also have disc brakes on the rear wheels. Disc brakes preform better than drum brakes, and their mechanical simplicity makes them more reliable. The components of a disc brake are open to the surrounding harsh environment, and even though the disc rotation will allow the brake to expel most dirt and debris, it sometimes happens that contamination gets caught on the disc and rotor. Keeping the disc brake clean will keep braking performance at the optimum and will eliminate irritating brake squeal and other troublesome problems.
Park the car on a level surface and set the parking brake. Put automatic transmissions in the "Park" setting, and place manual transmissions in either first or reverse gear. Slightly loosen the lug nuts and then jack the car up. Support the car on an axle stand. Now completely remove the lug nuts and pull the wheel off.
Remove the two caliper retaining bolts. Firmly grasp the caliper and slide it up and off the disc. If the caliper is stubborn then firmly rock it back and forth a few times to force the piston to retract a little, and try again. Hang the caliper out of the way using a wire or bungee cord, taking care not to stretch or kink the flexible brake hose.
Slide the brake pads out of the caliper. If retaining clips are present, these can be pried off the caliper with a screwdriver or pulled off with pliers. Take care not to damage clips during removal.
Open the bonnet and loosen the cap on the brake fluid reservoir. The reservoir is usually located at the rear of the engine compartment on the driver's side. On recent model vehicles the reservoir is usually made of semi-clear plastic, making the fluid level visible from the outside. Retract the caliper piston by placing the spindle swivel of a large C-clamp on the edge of the piston face, hooking the frame end of the clamp on the back of the caliper, and tightening the clamp to push the piston into the cylinder. Keep an eye on the brake fluid reservoir to make sure it does not overflow as the piston retracts and brake fluid backs up into the reservoir. If the reservoir looks like it might overflow, use a baster or syringe to remove some of the brake fluid.
Clean the brake disc, or rotor. The friction surface of the disc should be clean and relatively smooth. Most contamination can be removed by applying brake cleaning fluid and wiping the disc with a rag. A ring of rust around the disc rim is normal, as is a thin coating or light rust on the non-friction surface of the disc. Any mild pitting or scoring on the disc friction surface can be addressed by having the disc turned on a lathe at a brake shop or auto parts store. If heavy pitting or scoring is evident, then the disc should be replaced.
Clean the brake pads. Pry and scrape off the old shims, and then clean the pad by applying brake cleaning fluid and wiping with a rag. Stubborn dirt can be removed with a wire brush or emery cloth. Look closely at the lining surface and scrape off any visible contamination. If the linings are worn out, unevenly worn or damaged, replace the pads.
Clean the caliper. Apply brake cleaning fluid and wipe with a rag. Use a wire brush to remove stubborn dirt and deposits. Be very careful not to damage the rubber piston seal. Also clean the brake slides and caliper slide bolts.
Lubricate the caliper pad slides and slide bolts generously with brake grease. Be careful not to get grease on the disc or pads. Apply new shims to the backs of the brake pads. Reassemble the brake by following the steps in reverse order. Lower the car and check the brake fluid level in the brake fluid reservoir to be sure it is at, but not above, the full mark. Test the brake operation before driving.
Do not inhale brake cleaning fluid fumes or brake dust. Work in a well ventilated area. Do not use emery cloth to clean the brake disc. The aluminium compounds in the emery are not compatible with the cast iron disc. Catch all used brake fluid in a metal catch pan and dispose of in accordance with local regulations.