Brake Caliper Disassembly
Most often, calipers are replaced rather than rebuilt. The old caliper is sent back to the manufacturer as a core.
If the caliper must be rebuilt, it should be taken to the workbench for servicing. Drain any brake fluid from the caliper by way of bleeder screws. Remove the bleeder valve protector, if so equipped.
- To disassemble the caliper, the piston and dust boot must first be removed.
- Place the caliper face down on a workbench.
Using air to remove a piston. Courtesy of General Motors Corporation - Service Operations.
- Insert the used outer pad or a block of wood into the caliper.
- Place a folded shop towel on the face of the lining to cushion the piston.
- Apply low air pressure (NEVER MORE THAN 30 PSI) to the fluid inlet port of the caliper to force the piston from the caliper housing. If a piston is frozen, release air pressure and tap the piston into its bore with a soft-headed hammer or mallet. Reapply air pressure. Frozen phenolic (plastic) pistons can be broken into pieces with a chisel and hammer. Be careful not to damage the cylinder bore while doing this. Internal expanding pliers are sometimes used to remove pistons from caliper bores.
- Inspect phenolic pistons for cracks, chips, or gouges. Replace the piston if any of these conditions are evident. If the plated surface of a steel piston is worn, pitted, scored, or corroded, it also should be replaced.
- Dust boots vary in design depending on the type of piston and seal, but they all fit into one groove in the piston and another groove in the cylinder. One type comes out with the piston and peels off. Another type stays in place and the piston comes out through the boot, and then is removed from the cylinder. In either case, peel the boot from its groove. In some cases it might be necessary to pry it out, but be careful not to scratch the cylinder bore while doing so. The old boot can be discarded since it must be replaced along with the seal.
Peeling off the dust boot.
- Remove the piston's and the cylinder's seal by prying them out with a wooden or plastic tool. Do not use a screwdriver or other metal tool. Any of these could nick the metal in the caliper bore and cause a leak.
Removing a piston seal with a wooden stick.
- Inspect the bore for pitting or scoring. A bore that shows light scratches or corrosion can usually be cleaned with crocus cloth. However, a bore that has deep scratches or scoring normally indicates that the caliper should be replaced. In some cases, the cylinder can be honed.
- Check the service manual before doing this. If there is no mention of honing the bore, the manufacturer probably does not recommend it. Black stains on the bore walls are caused by piston seals. They do no harm. When using a hone, be sure to install the hone baffle before honing the bore. The baffle protects the hone stones from damage. Use extreme care in cleaning the caliper after honing.
- Remove all dust and grit by flushing the caliper with alcohol. Wipe it dry with a clean lint-free cloth and then clean the caliper a second time in the same manner.
Brake Caliper Reassembly
- Before assembling the caliper, clean the phenolic piston (if so equipped) and all metal parts to be reused in clean denatured alcohol or brake fluid.
- Then, clean out and dry the grooves and passageways with compressed air.
- Make sure that the caliper bore and component parts are thoroughly clean.
- To replace a typical piston seal, dust boot, and piston, first lubricate the new piston seal with clean brake fluid or assembly lubricant (usually supplied with the caliper rebuild kit).
- Make sure the seal is not distorted. Insert it into the groove in the cylinder bore so it does not become twisted or rolled. Install a new dust boot by setting the flange squarely in the outer groove of the caliper bore.
- Next, coat the piston with brake fluid or assembly lubricant and install it in the cylinder bore.
- Be sure to use a wood block or other flat stock when installing the piston back into the piston bore. Never apply a C-clamp directly to a phenolic piston, and be sure the pistons are not cocked.
Spread the dust boot over the piston as it is installed. Seat the dust boot in the piston groove.With some types of boot/piston arrangements, the procedure of installation is slightly different from that already described. That is, the new dust boot is pulled over the end of the piston.
Some installation procedures require the dust boot to be pulled over the end of the piston.
- Lubricate the piston with brake fluid before installing it in the caliper.
- Then by hand, slip the piston carefully into the cylinder bore, pushing it straight, so the piston seal is not damaged during installation.
Use an installation tool or wooden block to seat the new dust boot.
Seating a dust boot with a boot installer.
- Another point to keep in mind is that some caliper designs have a slot cut in the face of the pistons that must align with an antisqueal shim.
- Make sure that the piston and shim align. It might be necessary to turn the piston to achieve proper alignment.
- To complete the caliper assembly job, install the bleeder screw.