Since the piston travel in the wheel cylinder changes when new brake shoes are installed, it is possible for previously good wheel cylinders to start leaking after new brakes are installed. Therefore, to save yourself the expense of having to replace new brakes that become saturated with brake fluid and the aggravation of having to take everything apart again, it is strongly recommended that wheel cylinders be rebuilt every time new brake shoes are installed. This is especially true for cars with high mileage.
Most wheel cylinders can be rebuilt while mounted in position on the brake backing plate. However, if the cylinder must be removed, disconnect the brake line and unbolt the cylinder after the brake shoes have been removed.
- Remove the brake shoes.
- Place a bucket or some old newspapers under the brake backing plate to catch the brake fluid that will run out of the wheel cylinder. Disconnect the brake line and remove the cylinder mounting bolts. Remove the cylinder from the backing plate.
- Remove the boots from the ends of the wheel cylinder.
- Push one piston toward the center of the cylinder to force the opposite piston and cup out the other end of the cylinder. Reach in the open end of the cylinder and push the spring, cup, and piston out of the cylinder.
- Remove the bleeder screw from the rear of the cylinder.
- Inspect the inside of the wheel cylinder. If it is scored in any way, the cylinder must be honed with a wheel cylinder hone or fine emery paper, and finished with crocus cloth if emery paper is used. If the inside of the cylinder is excessively worm, the cylinder will have to be replaced, as only 0.08mm of material can be removed from the cylinder walls. Whenever honing or cleaning wheel cylinders, keep a small amount of brake fluid in the cylinder to serve as a lubricant.
- Clean any foreign matter from the pistons. The sides of the pistons must be smooth for the wheel cylinders to operate properly.
- Clean the cylinder bore with alcohol and a lint-free rag. Pull the rag through the bore several times to remove all foreign matter and dry the cylinder.
- Install the bleeder screw and the return spring in the cylinder.
- Coat new cylinder cups with new brake fluid and install them in the cylinder. Make sure they are square in the bore or they will leak.
- Install the pistons in the cylinder after coating them with new brake fluid.
- Coat the insides of the boots with new brake fluid and install them on the cylinder. Reinstall the wheel cylinder. Install and bleed the brakes.