Brake Drum Surface and Wear Inspection: Notes

Whenever the brake drums are removed, they should be thoroughly cleaned and inspected to see if the drums are cracked, scored, deeply grooved, or beyond the specified out-of-round limit.

• Inspect the inner race. If the inner race is separated from the wheel bearing inside the drum, replace the drum and wheel bearing assembly.
• A cracked drum is unsafe for further service and must be replaced. Do not attempt to weld a cracked drum. Smooth out any slight scores.
• Heavy or extensive scoring will cause excessive brake lining wear and may require refinishing the drum braking surface.
• If the brake linings are slightly worn but are still reusable and the drum is grooved, polish the drum with a fine emery cloth but do not refinish it. Eliminating all grooves in the drum and smoothing the ridges on the lining would remove too much metal and lining. If left alone, the grooves and ridges match, and satisfactory service can be obtained. If the brake linings need to be replaced, refinish a grooved drum. A grooved drum, used with a new lining, will not only wear the lining, but also will make it difficult, if not impossible, to obtain proper brake performance.
• An out-of-round drum makes accurate brake shoe adjustment impossible and is likely to cause excessive wear of other parts of the brake mechanism. An out-of-round drum can also cause severe and irregular tire tread wear, as well as a pulsating brake pedal.
• The extent to which a drum is worn or out-of-round can be measured accurately with an inside micrometer fitted with the proper extension rods. When measuring a drum for wear or the radial runout, take measurements from the inside edge to the outside edge of the machined surface at 90 degree intervals around the circumference of the drum. When the drum exceeds the maximum radial runout, refinish the drum.