Brake Drum Diameter Measurement
- Clean the brake shoe lining contact surface of the brake drum with denatured alcohol or an equivalent brake cleaner.
- Using a brake drum micrometer calibrated in thousands of an inch, measure and record the largest diameter of the brake drum at 4 or more points, equally spaced around the drum. Ensure that the measurements are only taken within the brake shoe lining contact area and that the micrometer is positioned the same distance from the outside edge of the drum for each measurement.
- The maximum allowable diameter : Specification: Maximum allowable measurement 296.5 mm (11.673 in)
- If the largest diameter measurement of the brake drum is less than the maximum allowable diameter, the drum may be able to be resurfaced, depending upon surface and wear conditions which may be present.
- If the largest diameter measurement of the brake drum is equal to or greater than the maximum allowable measurement, the drum requires replacement.
Tools Required
J 8001 Dial Indicator Set, or equivalent. See Special Tools .
| CAUTION | Refer to Brake Dust Caution . |
- With the brake drum removed, clean the braking (friction) surface of the brake drum with denatured alcohol or an equivalent approved brake cleaner.
- Inspect the braking surface of the brake drum for the following braking surface conditions: Heavy rust and/or pitting Light surface rust can be removed with an abrasive disc; heavy surface rust and/or pitting must be removed by refinishing the drum. Cracks and/or heat spots Excessive blueing discoloration Missing balance weights
- If the braking surface of the brake drum exhibits 1 or more of the braking surface conditions, the drum requires refinishing or replacement.
- Using a brake drum micrometer calibrated in thousands of an inch, measure and record any grooves present on the drum braking surface. Ensure that the measurements are only taken within the brake shoe lining contact area.
- Compare the groove, scoring, depth recorded to the following specification: Specification: Brake drum maximum allowable scoring 1.5 mm (0.06 in).
- If the brake drum scoring depth exceeds the specification, or if an excessive amount of scoring is present, the drum requires refinishing or replacement.
- Mount the brake drum on a brake lathe.
- Mount a dial indicator, J 8001 or equivalent, and position the indicator button so it contacts the braking surface of the brake drum at a 90 degree angle, approximately 19 mm (0. See «Special Tools»(ref-238260-S42045467462006072400000) .75 in) from the drum's outer edge.
- Measure and record the radial runout of the brake drum. Rotate the drum until the lowest reading is displayed on the indicator dial, then zero the dial. Rotate the drum until the highest reading is displayed on the dial.
- Compare the radial runout of the brake drum to the following specification: Specification: Brake drum maximum allowable radial runout 0.06 mm (0.0024 in).
- If the brake drum radial runout exceeds the specification, the drum requires refinishing or replacement.
J 41013 Rotor Resurfacing Kit
| IMPORTANT | DO NOT refinish the brake drums in order to correct any of the following complaints: Brake noise (growl/squeal) Premature brake lining wear Cosmetic or superficial corrosion of the drum braking surface Drum discoloration Refinish the brake drums ONLY when 1 or more of the following conditions exist: Severe scoring of the drum braking surface (groove depth in excess of specification) Brake pulsation caused by the following: Brake drum out of round (runout in excess of specification) Corrosion or pitting that is deeper than the drum braking surface |
- Use a micrometer in order to measure the largest diameter of the brake drum. If the largest diameter of the brake drum exceeds the brake drum maximum refinish diameter, DO NOT refinish the brake drum. Replace the brake drum.
- Use the J 41013 or an equivalent tool in order to THOROUGHLY clean the rust from the brake drum flange.
- Refinish the brake drum. Refer to the brake lathe manufacturer's operating instructions.
- After machining the brake drum, use 120 grit aluminum oxide sandpaper in order to create a non-directional braking surface.
- Clean the braking surfaces with GM P/N 12377981 (Canadian P/N 10953463) or equivalent brake parts cleaner.
J 21177-A Drum to Brake Shoe Clearance Gage. See Special Tools .
| CAUTION | Refer to Brake Dust Caution . |
| IMPORTANT | The rear brakes must be adjusted manually after replacing the rear brake shoes. |
- Remove the rear tire and wheel. Refer to «Tire and Wheel Removal and Installation»(ref-238261-S35716783552006072400000) .
- Remove the rear brake drum retainer, if necessary.
- Loosen the adjuster nut for the park brakes. IMPORTANT: Before removing the brake drum, apply a small amount of penetrating oil around the wheel studs, axle shaft hub and brake drum.
- Remove the rear brake drum.
- Using the J 21177-A (1), measure the inside diameter of the brake drum. See «Special Tools»(ref-238260-S42045467462006072400000) .
- Using the J 21177-A (1), adjust the brakes shoes until there is approximately 0. See «Special Tools»(ref-238260-S42045467462006072400000) .76 mm (0.030 in) clearance between the rear brake shoes and the rear brake drum.
- Install the brake drum.
- With heavy force, apply the brake pedal 2 times in order to center and adjust the brake shoes.
- Inspect the drums again for light drag. If necessary, repeat the above steps for adjusting the brakes.
- Lower the vehicle. Refer to «Lifting and Jacking the Vehicle»(ref-238215-S26215505352006072400000) in General Information.
- Adjust the park brake. Refer to «Park Brake Adjustment (w/Rear Disc)»(ref-238208-S27340836472006072400000) or «Park Brake Adjustment (w/Rear Drum)»(ref-238208-S13087910742006072400000) in Park Brake.
