The decision to overhaul a brake caliper depends on the condition of the caliper and its components, and parts cost and availability. In many cases, a rebuilt brake caliper may be available at slightly more than the cost of overhaul parts, especially if the piston must be replaced. Many professional technicians simply exchange a worn out caliper for a rebuilt unit. This saves time and gets the vehicle back into service in the shortest amount of time. In addition, the rebuilt caliper generally has to pass a factory quality test so there is at least some sort of guarantee in case it leaks or there is some problem with the unit.
If the caliper is to be overhauled, compressed air is almost an absolute necessity to get the piston(s) out of the caliper body without damaging either component.
Removal & Installation
- Using a clean suction gun, remove approximately 2 / 3 of the brake fluid from the master cylinder. The reason for this is that the caliper pistons must be pushed back into their bores so the caliper can be removed from the rotor. This could cause the brake fluid to overflow from the reservoir onto painted surfaces or wiring.
- Raise and safely support the vehicle on safety stands.
- Mark the relationship of the wheel to the hub so it can later be installed in the same relationship. This helps retain the balance of the rotating assembly.
- Remove the front tire and wheel assembly. Install two wheel lug nuts to keep the rotor on the hub.
- Push the caliper piston(s) back into their bore(s) to provide clearance between the linings and rotor. Use a large C-clamp over the top of the caliper housing and against the back of the outboard pad. Slowly tighten the C-clamp until the piston(s) are pushed back into the caliper bore(s) enough to slide the caliper off the rotor.
- Remove the brake hose bolt from the caliper end of the hose. There should be copper seal washers on each side of the hose fitting. Plug the openings in the brake hose to keep the brake fluid reservoir from draining.
- Remove the caliper slide pin bolts and carefully work the caliper away from the rotor and caliper mounting bracket.
- Bottom the piston(s) in the caliper bore(s) using a C-clamp, if new brake pads are to be installed. Use a large C-clamp and a metal plate or wooden block across the face of the piston(s). Take care not to damage the piston(s) or caliper rubber dust boot(s). After bottoming the piston(s), carefully lift the inner edge of the caliper boot(s) next to the piston(s) and press out any trapped air. The boots must lay flat below the level of the piston face.
- Install the brake pad using the procedures found in this section.
- Install the caliper over the rotor and mounting bracket and work into place. Make sure the bushings in the caliper bracket are still in place.
- Connect the brake hose using new copper seal washers. Tighten the bolt to 32 ft. lbs. (44 Nm).
- Carefully lubricate the caliper mounting bolts (slide pins) using silicone grease. Do not lubricate the threads or the mounting bolts may tend to work loose. Install the caliper mounting bolts. Use a small flat-blade tool to push the pin boot over the shoulder of the mounting bolt. The pin boot must be securely in the groove of the mounting bolt. Torque the caliper mounting bolts to 80 ft. lbs. (108 Nm).
- Install the tire and wheel assembly, aligning the balance marks made at removal.
- Lower the vehicle.
- Fill the master cylinder reservoir to the proper level using only fresh, clean DOT 3 brake fluid. Pump the brake pedal firmly to push the pistons back out into operating position and to seat the lining.
- Bleed the brake system using the procedures found at the end of this section.
The following sequence shows a typical dual-piston front caliper being disassembled for inspection and overhaul. The overhaul procedure for a single piston front caliper and a rear caliper without a built-in parking brake mechanism overhaul is similar.
- The first step, even before removing the caliper from the vehicle, is to attempt to open the bleeder valve screw. This fitting is often seized in place in the caliper, especially on high-mileage vehicles or vehicles with aluminum brake calipers and steel bleeder screws. It would be wasted effort to disassemble, clean and overhaul a caliper only to find that it can't be bled because the bleeder screw won't open. It is also very common for a seized bleeder valve screw to snap off when attempts are made to loosen it. Getting the remainder of a seized bleeder screw out of a caliper without damaging the caliper body is very difficult and a job for an automotive machine shop. The fee to attempt to extract a broken bleeder screw will likely exceed the cost of a rebuilt or even new caliper. Try to open the bleeder screw first. If it loosens and brake fluid does flow from the bleeder screw, the caliper may be suitable for an overhaul. The final decision would depend on the condition of the piston bore(s) and he overall condition of the caliper. Remove the caliper using the procedures found in this section.
- With the caliper removed from the vehicle, place it on a clean work surface. Brake fluid in the caliper will tend to run out onto the work surface, where it can damage painted components. Placing some cardboard or other disposable covering on the work surface may save time at cleanup.
- Perform a visual inspection. If the caliper has an obvious crack or shows signs of collision damage, it may not be reusable. Check the tapped openings where the mounting bolts thread. In some cases, the threads can be damaged from corrosion or were cross-threaded during previous brake work. Sometimes threaded inserts can be used to save a caliper, but generally, if the caliper body shows signs of abuse, it should be replaced.
- Use clean shop cloths to pad the inside of the brake caliper during piston removal. Use just enough shop air to ease the piston(s) out of the bore(s). If the piston(s) is simply blown out, even with padding provided, it may be damaged. Dual piston calipers must have the pistons removed evenly and at the same rate. If one piston pops out before the other, it will be difficult to built enough pressure to remove the other piston. In the event one piston is seized and will not break free, is may be necessary to block the other piston with a piece of wood or C-clamp until the stuck piston can be freed. When working on dual-piston calipers, some technicians use a block of wood to limit the pistons' travel. Once the technician is assured that both pistons are moving, thinner blocks are used, allowing the pistons to come out evenly until both pistons are out. The piston(s) will come out through the piston dust boot(s).
- Inspect the pistons for scoring, nicks corrosion, and/or worn or damaged chrome plating. Replace the piston, if any of these conditions are found.
- Remove the caliper boots, being careful not to scratch the housing bore.
- Remove the piston seals from the groove in the caliper bore, using a small wood or plastic tool. These seals are usually "square profile" O-rings.
- Inspect the caliper bores, pistons and mounting threads for scoring or excessive wear.
- Use crocus cloth (an extremely fine abrasive cloth) to polish out light corrosion from the piston and bore. If the crocus cloth cannot remove the corrosion, do not use a more coarse abrasive. The caliper must be replaced.
- Clean all parts with denatured alcohol and dry with compressed air.
- Lubricate the threads of the bleeder valve with a thin coat of anti-seize compound and install just finger tight. It will be final-tightened after the hydraulic system is bled.
- Lubricate the new piston seals and bore with clean brake fluid or brake assembly lubricant (a special lubricant found in some brands of brake overhaul parts kits).
- Install the new seals into the caliper bore grooves, making sure they are not twisted.
- Lubricate the piston bore.
- Install the piston(s) and dust boot(s) into the bores of the calipers. Push the piston(s) to the bottom of the bores.
- Seat the dust boots in the housing using tool J 36349, or equivalent seal installation driver.
- Install the caliper onto the vehicle, as outlined earlier.
- Properly bleed the brake system as outlined in this section.