Brake Drums

Inspection

PROCEDURE.

After removal, thoroughly clean and inspect the brake drums for cracks, scratches, and deep grooves, and check for out-of-round (ovality) and taper.

CRACKS, SCRATCHES, GROOVES ON BRAKE DRUM FRICTION SURFACE.

A brake drum with cracks must be replaced, as it does not provide safe operation of the vehicle. Do not weld cracks in the drum. Minor scratches and scoring should be smoothed. Deep defects on the drum friction surface greatly reduce shoe service life. In this case, the drum friction surface must be turned. If the shoes are only slightly worn and the drum friction surface has minor grooves, sand the drum with fine emery cloth. Do not bore the drum in this case. Complete removal of grooves from the drum surface and ridges on the linings may require removing too much material. However, drums and shoes that are run in together and have minor grooves and ridges provide satisfactory brake operation. When replacing shoes, a grooved drum must be turned. Otherwise, the new shoes will wear rapidly and brake system function will deteriorate.

BRAKE DRUM OVALITY AND TAPER.

Brake drum ovality and taper prevent correct brake adjustment and cause accelerated wear of parts. Brake drum ovality can also cause rapid and uneven tire tread wear and brake pedal pulsation during braking. If the drum exceeds the permissible ovality and taper limits, it must be bored to restore the correct shape. Drum ovality, taper and wear are checked with an internal micrometer. Measure the drum cylinder at two perpendicular sections, near the edge and near the disc.