For 1990-2009 cars

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 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.

3. The maximum allowable diameter :

Specification
Maximum allowable measurement 296.5 mm (11.673 in)

4. 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.
5. If the largest diameter measurement of the brake drum is equal to or greater than the maximum allowable measurement, the drum requires replacement.