Drum braking systems use a hydraulic wheel cylinder to press twin shoes into the interior of a drum, stopping the vehicle. The rubber seals on both sides of the wheel cylinder can become worn and eventually fail, requiring replacement. The average backyard mechanic can replace the seals on drum brakes in about an hour.
Raise the vehicle at the brake to be repaired using the floor jack, then remove the wheel by turning the lug nuts counterclockwise. Set the wheel aside, and away from the vehicle.
Remove the drum by turning the keeper bolt in a counterclockwise direction, if applicable. Pull the drum free from the brake assembly and set it aside, away from the work area. Place the drain pan underneath the brake at this time.
Locate and inspect the wheel cylinder, usually at the top of the brake assembly. The cylinder is a small, round steel or plastic device capped with black rubber gaskets. These gaskets should not be visually leaking, or appear kinked or damaged.
Remove the wheel cylinder by turning the rear wheel cylinder retainer bolts counterclockwise, then pulling the cylinder away from the assembly. Some automobiles may require the removal of the brake springs to access the wheel cylinder; lever a screwdriver into the spring hook and disengage it from the shoe. The rear of the wheel cylinder will have a gasket sealing it to the brake assembly. Collect any brake fluid in the drain pan.
Replace the wheel cylinder gaskets by prying them off with a screwdriver, then positioning new gaskets in their place. Some models will have more than three gaskets, but typically there are two rubber cones on the outside with a central gasket protecting the small piston within.
Reassemble the wheel cylinder by pressing it back into place and securing the rear retainer bolts in the back in a clockwise direction.
Replace the springs (if applicable) and drum, then secure the keeper bolt by turning it clockwise until snug.
Replace the wheel by turning the lug nuts clockwise until tight, in an alternating pattern.
Lower the vehicle from the jack, and repeat the entire procedure on the remaining drum brakes.
Once all brake seals are replaced, bleed the brake system by turning one bleeder nipple on the back of the brake plate counterclockwise, then continually pouring fresh brake fluid into the master cylinder while the brake pedal is depressed. This could require two people. Close the bleeder nipple and move to the next brake's nipple and repeat the process until all lines have been purged.
