Clean all grease, brake fluid, and other contaminants from the brake drum using a suitable brake cleaner. Visually check the drum for scoring, cracks, or other damage and replace, if necessary.
Check the drum inner diameter using a brake shoe clearance gauge. There are 2 important specifications when discussing rear drum diameters. The refinish diameter is the maximum diameter to which the drum may be machined. This diameter allows room for drum wear after it has been machined and returned to service. The discard diameter is the point at which the drum becomes unsafe to use and must be discarded. NEVER refinish a drum to the discard diameter. If after refinishing the drum the diameter is within 0.030 in. (0.76mm) of the discard diameter, the drum MUST be replaced.
After removing the brake drum, inspect the inner braking surface for excessive wear or damage. If it is unevenly worn, streaked, or cracked, have it resurfaced or replaced. The standard inside diameter of the brake drum is 7.087 in. (180mm). The maximum allowed diameter is 7.165 in. (182mm).