Depending on the condition of the parts, the mechanic may need to do one or more of the operations. In any case. you must make sure the brake assembly is in sound operating condition.

Disc Brake Pad Replacement

Disc brakes have flat linings bonded to a metal plate or shoe. The pad is not rigidly mounted inside the caliper assembly; thus, it is said to float. These pads are held in position by retainers or internal depressions (pockets machined into the caliper).

A visual inspection on the condition of the pads can be made after the wheel and tire is removed. The inner shoe and lining can be viewed through a hole in the top of the caliper, whereas the outer shoe and linings can be viewed from the end of the caliper.

A good rule in determining the need for pad replacement is to compare lining thickness to the thickness of the metal shoe. If the lining is not as thick as the metal shoe, it should be replaced. The basic steps for disc brake service are as follows:

1. Siphon two thirds of the brake fluid from the master cylinder. This action prevents fluid overflow when the caliper piston is pushed back.

2. Remove the caliper guide pins that holds the caliper to the adapter. In typical applications, positioners and bushings will come off with the pins.

3. Lift the caliper off the adapter and away from the rotor. Do NOT let the caliper hang by the brake hose. Hook or tie the caliper to a suspension member. This will allow the rotor to be tested and inspected.

4. Remove old pads from the caliper and adapter. Note the position of antirattle clips because they may be reused if they are in good condition.

5. Using a C-clamp or large screwdriver. force the piston back into the caliper. This action will open the caliper wide enough for new, thicker pads.

6. Install the antirattle clips on the new pads. Fit the pads back into the caliper.

7. Slide the caliper assembly over the rotor. Assemble the caliper mounting hardware in reverse order of disassembly. Make sure all bolts are torqued to the manufacturer's specifications.

8. After new pads are installed, road test the vehicle to make sure that the brakes are operating properly and also seat the new pads. Several (3 to 3) heavy braking applications will work.

NOTE

It is acceptable to service just the rear or front disc brakes. However. NEVER service only the left or right brake assemblies; always replace both sets to assure equal braking action.

Since disc brake systems vary, consult the vehicle manufacturer's service and repair manuals for specific details on the type of disc brakes you are working on.

Servicing Caliper Assemblies

When a caliper is frozen, leaking, or has extremely high mileage, it is to be serviced. Servicing disc brake caliper assemblies involve the replacement of the piston, seals, and dust-boots. To perform this type of service. it is necessary to remove the caliper assembly from the vehicle. Basic steps for servicing the caliper assemblies are as follows:

1. Remove the piston from the caliper by using air pressure to push the piston from the cylinder. Keep your fingers out of the way when using compressed air to remove the pistons from the caliper. Serious hand injuries can result.

2. With the piston removed, pry out the old dust boot and seal from the caliper. Keep all parts organized on the workbench. Do not mix up right and left side or front and rear parts.

3. Check the caliper cylinder wall for scoring. pitting, and wear. Light surface imperfections can usually be cleaned with a cylinder hone or emery cloth. When honing, use brake fluid to lubricate the hone. If excessive honing is required, replace the caliper.

4. Check the piston for wear and damage. If any problems are found, replace the piston. The piston and cylinder are critical and must be in perfect condition.

5. Clean all parts with an approved cleaner. Wipe the parts with a dry, clean rag. Then coat the parts with brake fluid.

6. Assemble the caliper in reverse order of disassembly. Using new seals and boots, fit the