TM-5-3805-254-14-P-2
TRUCK, DUMP, 20 TON, 6X4, ON-OFF HIGHWAY 71,000 GVW, IHC MODEL F-5070 (CCE)
TECHNICAL MANUAL; OPERATOR’S, ORGANIZATIONAL, DIRECT SUPPORT, GENERAL SUPPORT AND DEPT MAINTENANCE MANUAL (INCLUDING REPAIR PARTS INFORMATION AND SUPPLEMENTAL MAINTENANCE INSTRUCTIONS)
JUNE 1980
TM-5-3805-254-14-P-2 - Page 859 of 894
TRUCK SERVICE MANUAL
WHEELS, RIMS, TIRES
CHAPTER II
BRAKE DRUMS
INSPECTION
The friction surface of brake drums must be
smooth, true and concentric whether for air or hydraulic
brakes.
Make certain with a visual check that drums are
not barrel shaped, bellmouthed, scored or eccentric. A
barrel shaped drum (Fig. 1) results from overheating.
If
this barrel shaped condition is not corrected, the braking
surface is reduced and uneven lining wear results.
Fig. 1
Extreme pressure which over a period of time will create
a bellmouthed drum is shown in Fig. 2. Brake linings on a
bellmouthed brake drum will make contact only on the
inner surface of the drum.
In addition to cutting the
braking surface to a minimum, it will also cause uneven
and rapid wear.
Fig. 2
Scored drums are the result of worn linings to the point
where the drum-to-shoe contact is made or an
accumulation of small steel particles imbed themselves
in the brake lining (Fig. 3). The steel particles form a
tough scale which is sometimes harder than the drum.
As a result deep grooves are formed in friction surface of
drum.
Brake drum scoring never improves but continually gests
worse until both lining and brake drum are useless.
Attempting to reline brakes without turning scored
Fig. 3
brake drum surface will quickly destroy new lining and
make effective braking impossible.
Brake lining in an eccentric or out of-round drum
cannot make full contact with the drum resulting in rapid
or uneven lining wear and could even cause brakes to
seize or chatter. Maximum allowable out-of-round or
eccentricity should be .10 mm (.004").
If inspection shows that any of the preceding
conditions exist, brake drum should be either turned or
replaced. To assure a balanced braking system, always
install turned or new brake drums in pairs on each axle.
Any time a new brake drum is to be installed on
a vehicle, the runout should be checked as follows. Place
the new brake drum with hub and wheel assembled in
lathe making certain drum is centered.
Mount Dial Indicator SE-1848 on lathe and check runout
about 12.7 mm (.5") in from end of drum as shown in Fig.
4. Runout must not exceed .38 mm (.015").
NOTE: Before assembling drum, hub and wheel, all
parts must be clean and free of foreign matter.
If runout exceeds .38mm (.015") remove drum
from hub, rotate drum 180° and reinstall on hub. Check
runout again; if runout still exceeds .38mm (.015"),
remove drum from hub and rotate drum 1/4 turn.
Reinstall drum on hub and recheck runout.
REFINISHING BRAKE DRUM
On brake drums manufactured after January 1,
1971, the maximum diameter to which drum can be worn
is stamped or cast into drum. Drum should be discarded
if worn beyond this limit. Minor scores on brake drum can
be removed with fine emery cloth or steel wool, but
always clean
850
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