Brake Drum Diameter Measurement

Brake Drum Diameter Measurement





1. Clean the brake shoe lining contact surface of the brake drum with denatured alcohol or an equivalent brake cleaner.
2. Using a brake drum micrometer calibrated in thousands of an inch, measure and record the largest diameter of the brake drum at four 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.
3. Compare the largest diameter measurement recorded to the following specifications:
Specification
^ Brake drum maximum allowable diameter after resurfacing 226.30 mm (8.909 inches).
^ Brake drum discard diameter 226.57 mm (8.920 inches).
4. If the largest diameter measurement of the brake drum is less than the maximum allowable diameter after resurfacing specification; the drum may be able to be resurfaced, depending upon surface and wear conditions, which may be present.
5. If the largest diameter measurement of the brake drum is equal to or greater than the maximum allowable diameter after resurfacing specification the drum may not be resurfaced.
6. If the largest diameter measurement of the brake drum is equal to or greater than the discard diameter specification; the drum requires replacement.