Types of Brake Calipers
Brake Caliper Inspection.
In addition, the caliper boot should not show any signs of fluid leakage nor should the caliper boot appear hardened or cracked. The piston will eventually corrode and seize in place if a defective caliper boot allows moisture to accumulate between the caliper bore and piston.
Brake Caliper Service.
There are two schools of thought on preventing debris from being flushed into the anti-lock braking and master cylinder assemblies when the piston is seated in the caliper bore. The first “school” opens the bleeder screw to relieve pressure as the caliper piston is seated. The second “school” clamps the brake hose closed with a pair of hose-clamping pliers to prevent debris from back-flushing into the master cylinder. The first-school method is the most commonly accepted because there’s less chance of inadvertently damaging the hose.
Because the piston surface seals the brake caliper, the piston should be in like-new condition. If the piston is pitted or scored, it should be replaced.
The piston must be perfectly square with the bore before it will pass through the flat-cut O-ring in the caliper bore. The simplest method is to use a square bar to gently rock the piston from side-to-side until it drops into the caliper bore. A wooden 2×4 plank works well on larger bore caliper pistons.
Once the piston is installed, carefully remove the caliper guide pins and lubricate them with synthetic caliper grease or the OEM-recommended lubricant. When installing the caliper bracket bolts, apply thread-locking compound, if required. In other cases, lightly oil the bolts and torque them to specification. Always install new caliper hardware on the caliper bracket to prevent pad rattle and dampen pad squeal.