Brake Drum: Specifications

Maximum Diameter/Discard Diameter
- All brake drums are marked with the maximum allowable brake drum diameter. Refer to figure.


Maximum Lateral Runout/Thickness Variation
- The diameter variation of the drum braking surface must not exceed either 0.0635 mm (0.0026 inch) in 30° or 0.0889 mm (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 mm (0.006 inch).
- If either of these measurements are not within specification, reface or replace the drum.