Cylinder binding can be caused by rust deposits, swollen cups due to fluid contamination, or by a cup wedged into 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 hand, crystal-like substance. The substance is sometimes noticed in the cylinder bore in which the piston rests after the brake 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.Care must be taken when installing new or reconditioned wheel cylinders on cars equipped with wheel cylinder piston stops. The rubber dust boots and the pistons must be squeezed into the cylinder before it is tightened to the braking plate. If this is not done, the pistons jam against the stops causing hydraulic fluid leaks and erratic brake performance.