REMOVAL & INSTALLATION
See Figures 1 through 15
- Disconnect the negative battery cable.
- Remove some of the brake fluid from the master cylinder reservoir. The reservoir should be no more than 1 / 2 full. When the pistons are depressed into the calipers, excess fluid will flow up into the reservoir.
- Raise the vehicle and support safely.
- Remove the appropriate tire and wheel assemblies. For rear disc brakes, loosen the parking brake cable adjustment from inside the vehicle.
- Remove the caliper lock and guide pins and lift the caliper assembly from the caliper support. Tie the caliper out of the way using wire. Do not allow the caliper to hang by the brake line.
- Remove the outer shim, brake pads and spring clips from the caliper support. Take note of positioning of each to aid in installation.
- Install the wheel lug nuts onto the studs and tighten. This is done to hold the disc on the hub.
- Using a spring scale, turn the disc in a forward direction and measure the rotation sliding resistance of the hub.
- Clean the caliper piston. For front disc brakes, use a C-clamp or equivalent tool to press the piston back into the caliper bore. For rear disc brakes, use driver tool MB990652 or equivalent, to thread the piston into the caliper bore. Be sure at this point, that the stopper groove of the piston correctly fits into the projection on the replacement brake pads rear surface.
- Install the brake pads, shims and spring clip to the caliper support. Install the caliper over the brake pads.
Be careful that the piston boot does not become caught when lowering the caliper onto the support. Do not twist the brake hose during caliper installation.
- Lubricate and install the caliper guide and lock pins in their original positions. For front disc brakes, tighten guide and locking pins to 23 ft. lbs. (32 Nm) on vehicles built up to May, 1989. On vehicles built during and after May, 1989 to 1990 vehicles, tighten caliper guide and locking pins to 58-72 ft. lbs. (80-80 Nm). For 1995-98 vehicles tighten the front caliper guide and locking pines to 65 ft. lbs. (88 Nm). For rear disc brakes, tighten the caliper guide and lock pins to 36-43 ft. lbs. (50-60 Nm).
- For rear disc brakes, start the engine and forcefully depress the brake pedal 5-6 times. Apply the parking brake, then make sure the adjustment is within specifications. Adjust the parking brake cable, as required.
Check the disc brake drag force as follows:
- Start the engine and press the brake pedal firmly a few times to seat the pads.
- Once the pads are seated, shut the engine OFF.
- Turn the brake disc forward 10 times.
- Using a spring scale, measure the rotation sliding resistance of the hub in the forward direction.
- Calculate the drag torque of the disc brake by subtracting the value obtained in Step 8 (force required to turn hub alone) from the value obtained in Step D (force required to turn hub with caliper and pads installed). Compare calculated force with desired force of 15 lbs. (70 N) or less.
- If the calculated disc brake drag force is greater than specifications, disassemble and clean the piston. Check for corrosion or worn piston seal and check the sliding condition of the lock pin and guide pin.
- Install the tire and wheel assemblies. Connect the negative battery cable.
- Lower the vehicle. Test the brakes for proper operation.
See Figures 16, 17 and 18
The disc brake pads have wear indicators that contact the brake disc when the brake pad thickness becomes 0.08 in. (2.0mm) and emit a squealing sound to worn the driver.
Inspect the thickness of the brake linings by looking through the brake caliper body check port. The standard value of the brake pad is 0.39 in. (10mm). The thickness limit of the lining is 0.08 in. (2.0mm).
When the limit is exceeded, replace the pads on both sides of the brake disc and also the brake pads on the wheel on the opposite side of the vehicle. Do not replace 1 pad on a caliper because the wear indicator is hitting, without replacing the other pad on the same wheel as well as the brake pads on the other front or rear wheel, as applicable.
If there is a significant difference in the thickness of the pads on the left and right sides, check the sliding condition of the piston, lock pin sleeve and guide pin sleeve.