Wheel cylinders might need replacement when the brake shoes are replaced or when they begin to leak.
- Wheel cylinder leaks reveal themselves in several ways: (1) fluid can be found when the dust boot is peeled back; (2) the cylinder, linings, and backing plate, or the inside of a tire might be wet; or (3) there might be a drop in the level of fluid in the master cylinder reservoir.
- Such leaks can cause the brakes to grab or fail and should be immediately corrected.
- When looking at the tires for wheel cylinder leaks, the inside of the tire is often streaked with dirt and fluid. Occassionally the outside of the tire can even show signs of fluid leakage.
- Note the amount of fluid present when the dust boot is pulled back. A small amount of fluid seepage dampening the interior of the boot is normal. A dripping boot is not.
Hydraulic system parts should not be allowed to come in contact with oil or grease. They should not be handled with greasy hands. Even a trace of any petroleum-based product is sufficient to cause damage to the rubber parts.
- Cylinder binding can be caused by rust deposits, swollen cups due to fluid contamination, or by a cup wedged into an excessive piston clearance. If the clearance between the pistons and the bore wall exceeds allowable values, a condition called heel drag might exist. It can result in rapid cup wear and can cause the piston to retract very slowly when the brakes are released.
- Evidence of a scored, pitted, or corroded cylinder bore is a ring of hard, crystal-like substance. This substance is sometimes noticed in the cylinder bore in which the piston rests after the brakes are released.
- Light roughness or deposits can be removed with crocus cloth or an approved cylinder hone. While honing lightly, brake fluid can be used as a lubricant. If the bore cannot be cleaned up readily, the cylinder must be replaced.