Brake Drum

With the drum off the vehicle, measure the drum for diameter variation (oval shape). The diameter variation of the drum braking surface must not exceed either 0.0025" (0.0635 mm) in 30 degrees or 0.0035" (0.0889 mm) in 360 degrees.

Measure the brake drum runout. Brake drum runout should be checked with the drum mounted on a brake lathe. Brake drum runout should not exceed 0.006" (0.1524 mm). If either of these measurements are not within specification, reface or replace the drum.

Always replace the drum if refacing will cause the diameter to exceed drum maximum diameter. All brake drums are marked with the maximum allowable brake drum diameter.