Brake Caliper: Service and Repair
REMOVAL1. Clean master cylinder reservoir and filler caps.
2. Remove reservoir filler cap and drain approximately 1/4 of fluid from reservoir. Use clean suction gun or similar device to drain fluid.
3. Raise and support vehicle.
4. Remove front wheel and tire assemblies.
5. Bottom caliper pistons in bores with large C-clamp. Position clamp frame on rear of caliper and clamp screw on outboard brake shoe.
Caliper Brake Hose Connection:
6. Disconnect brake hose at caliper. Discard hose fitting washers if worn, or damaged.
7. With a screw driver pry up on the caliper spring and pull the spring out of the caliper holes.
8. Remove caliper and brake shoes from caliper.
DISASSEMBLY
1. Drain old brake fluid out of caliper into drain pan.
Piston Dust Boot:
2. Remove piston dust boot. Use screwdriver to push boot out of groove.
3. Pad outboard shoe side of caliper interior with a minimum 1 inch thickness of shop towels. Towels will prevent piston damage when piston comes out of the caliper bore.
4. Remove caliper piston with short bursts of compressed air. Apply air pressure through fluid inlet port of caliper.
CAUTION: Do not blow the piston out of the bore with sustained air pressure. This could result in a cracked piston. Use only enough air pressure to ease the piston out.
WARNING: NEVER ATTEMPT TO CATCH THE PISTON AS IT LEAVES THE BORE. THIS MAY RESULT IN PERSONAL INJURY.
Caliper Piston Seal:
5. Remove caliper piston seal with wood pencil or plastic tool. Do not use metal tools as they will scratch piston bore.
6. Remove caliper slide pin bushings and boots.
7. Remove caliper bleed screw and cap.
CLEANING
Clean the caliper components with clean brake fluid or brake clean only. Wipe the caliper and piston dry with lint free towels or use low pressure compressed air.
CAUTION: Do not use gasoline, kerosene, paint thinner, or similar solvents. These products may leave a residue that could damage the piston and seal.
INSPECTION
The piston is made from a phenolic resin (plastic material) and should be smooth and clean. The piston must be replaced if cracked or scored. Do not attempt to restore a scored piston surface by sanding or polishing.
CAUTION: If the caliper piston is replaced, install the same type of piston in the caliper. Never interchange phenolic resin and steel caliper pistons. The pistons, seals, seal grooves, caliper bore and piston tolerances are different.
Fig 14 Honing Piston Bore:
The bore can be lightly polished with a brake hone to remove very minor surface imperfection. The caliper should be replaced if the bore is severely corroded, rusted, scored, or if polishing would increase bore diameter more than 0.025 mm (0.001 inch).
ASSEMBLY
1. Lubricate slide pin boots and bushings with GE, or Dow silicone grease. Then install the boots and bushings in caliper.
2. Coat caliper piston bore, piston and new piston seal with clean brake fluid.
Fig 19 Installing Caliper Piston Seal:
3. Install new piston seal in caliper bore. Press seal into groove with finger. Lubricate seal and caliper bore with additional, fresh brake fluid after seal installation.
4. Apply light coat of GE 661, Dow 111 or similar silicone grease to edge and groove of piston and dust seal. Grease acts as corrosion protection for these areas.
Sliding Boot Onto Piston:
5. Slide new seal boot over piston until boot lip seats in piston groove.
Snapping Boot Folds Into Place:
6. Push retainer part of boot forward until folds in boot snap into place.
Installing Caliper Piston And Boot:
7. Start caliper piston in bore with a twisting motion. When piston is started in seal, push piston only part way into bore). Maintain uniform pressure on piston to avoid cocking it in bore.
8. Press caliper piston to bottom of bore.
Seating Piston Dust Boot:
9. Seat piston dust boot with Installer 8248 and Handle C-4171.
Caliper Bleed Screw & Cap Installation:
10. Install caliper bleed screw and bleed screw cap if removed.
INSTALLATION
1. Install the brake shoes in the caliper.
2. Install the caliper and shoes over rotor and into ledges in steering knuckle. Be sure ends of brake shoes are properly seated on slide surfaces of ledges.
3. Install and tighten the caliper slide pins to 30 Nm (22 ft. lbs.). Start the slide pins by hand before tightening. Do not cross thread the pins.
4. Install the caliper spring into one caliper hole and under the adapter. Pull down on the opposite end of the spring and hold the end under the adapter. With a screw driver pry up on the spring to seat the spring into the other caliper hole.
NOTE: Verify the spring is seated properly into the caliper holes.
5. Install the brake hose to the caliper with new seal washers and tighten fitting bolt to 24 Nm (18 ft. lbs.).
CAUTION: Verify brake hose is not twisted or kinked before tightening fitting bolt.
6. Bleed the base brake system.
7. Install the wheel and tire assemblies.
8. Remove the supports and lower the vehicle.
9. Pump the brake pedal to seat brake shoes.
10. Fill the brake fluid reservoir.
11. Verify a firm pedal before moving the vehicle.