Brake Drum Refinishing Specifications

All brake drums are marked with the maximum allowable brake drum diameter.

When machining, make sure the final finish feed cut is fine in order to avoid a screw effect on the brake shoes when the brakes are applied. This final feed cut specification varies from lathe manufacturer to lathe manufacturer.

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 0.0635 min (0.0025 inch) in 30° or 0.0889 min (0.0035 inch) in 360°.

Measure brake drum runout. Brake drum runout should be checked with the drum mounted on a brake lathe. Brake drum runout should not exceed 0.1524 min (0.006 inch).

If either of these measurements are not within specification, reface or replace the drum. Refer to Brakes and Traction Control, Brakes, Drum Brake Systems, Brake Drum Machining for refacing procedures.

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