Inspecting and Refinishing Brake Drums

Whenever brake drums are removed, they should be thoroughly cleaned and inspected for cracks, scores, deep grooves, and roundness.

CRACKED, SCORED, OR GROOVED DRUMS
A cracked drum is unsafe for further service and must be replaced. Do not attempt to weld a cracked drum.
Light scoring of the drum surface not exceeding 1.0 mm (0.040 inch) in depth, which may result from normal use, is not detrimental to brake operation.
A drum with a grooved surface finish can be reconditioned using 80 grade sandpaper with drum mounted and rotating on a brake lathe. An inboard/outboard sanding motion will produce a multi-directional finish on drum.

OUT-OF-ROUND
An out-of-round drum makes accurate brake pad adjustment impossible and is likely to cause excessive wear of other parts of brake mechanisms due to its eccentric action. An out-of-round drum can also cause severe and irregular tire wear as well as a pulsating brake pedal. When drum exceeds out-of-round specification limits, the drum should be refinished or replaced.
Drum roundness can be accurately measured with an inside micrometer, fitted with proper extension rods.
When measuring a drum for out-of-round, take measurements at right angles (90 degrees) to each other.