98 / 105
97
Improper lining friction
rating.
Drum resurfaced with too
fine of a micro-finish.
Light contact of linings to
drum.
Consult vehicle or lin-
ing manufacture for an
alternate lining material.
Micro-finish should be
150-200 RMS. Check
condition of return
springs, camshaft bush-
ings, air system and shoe
to drum contact. Remove
the gloss with eighty (80)
grit emery cloth.
Recognized from a mirror-like finish on the
braking surface.
Polished Drums
Heat distortion
Drum has been dropped
or stored on its side.
Improper chucking when
turning drum.
Turn brake drum if within
limits or replace.
Variations in drum diameter at different
points on the braking surface
Out-of-round Drums
Normal wear condition
(age).
Replace brake drums
and brake linings.
Uneven lining wear, or braking surface diam-
eter measures in excess of allowable limits.
Oversize Worn Drums
Problem
Probable Causes Recommended
Actions
Brake Drum Failure Analysis
TMC RP 608A © 2003 – TMC/ATA – Reprinted with Permission