Tools Required
J 8001
Dial Indicator, or equivalent
Caution: Refer to Brake Dust Caution in the Preface section.
- With the brake drum removed, clean the brake shoe lining contact 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 one or more of the Braking Surface Conditions listed, the drum requires refinishing or replacement.
- Using a brake drum micrometer calibrated in thousandths-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, or scoring depth recorded to the following specification:
Specification
Brake drum maximum allowable scoring: 1.5 mm (0.059 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 (0.75 in)
from the outer edge of the drum.
- Measure and record the radial runout of the brake drum.
9.1. | Rotate the drum until the lowest reading is displayed on the indicator dial, then zero the dial. |
9.2. | 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: 0.03 mm (0.001 in)
- If the brake drum radial runout exceeds the specification, the drum requires refinishing or replacement.