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 847 of 894
TROUBLE SHOOTING
Driver Training:
One of the major causes of bearing and gear failures
in the auxiliary unit is poor driving habits.
Driver should be taught to always use the lo speed or
reductions available in the auxiliary unit and keep the
front box in the higher ratios not vice versa.
Worn and pitted gears, as well as worn and pitted
bearings are usually caused by excessive use of the
auxiliary overdrive gears with the mainbox in lower gear
ratios.
Broken teeth in the auxiliary unit are usually caused
by drivers trying to start their vehicles with the auxiliary
unit in the high ratio while the big reduction is made in the
front box. Frogging or quick release of clutch gives a
jump start also noted for breaking teeth.
Noisy Operation:
Noise is usually very elusive and generally not the
fault of the auxiliary; therefore, mechanics should road
test to determine if the driver’s complaint of noise is
actually in the auxiliary. Remember that auxiliary units act
as sounding boxes and in numerous instances, drivers
have insisted that the noise was in the auxiliary; however,
investigations revealed the noise to be caused by one of
the following conditions:
(a) Fan out of balance or blades were bent.
(b) Defective vibration dampers.
(c) Crankshafts out of balance.
(d) Flywheels out of balance.
(e) Flywheels mounting bolts loose.
(f) Engine rough at idle producing rattle in gear
train.
(g) Clutch assembly out of balance.
(h) Engine mounts loose or broken.
(i) P.T.O. gear not fully engaged or housing not
properly shimmed.
(j) Universal joints worn out.
(k) Propeller shafts out of balance.
(l) Universal joint angles out of plane or at
excessive angle.
(m) Center bearings in drive line dry, not mounted
properly, etc.
(n) Wheels out of balance.
(o) Tire treads humming or vibrating at certain
speeds.
(p) Air leaks on suction side of induction system
specially with turbo-chargers.
Mechanics should try to locate and eliminate noise by
means other than auxiliary removal, or overhaul.
However, if the noise appears to be in the auxiliary try to
break it down into the following classifications. If
possible, determine what position the gear shift lever is in
when the noise occurs. If the noise is evident in only one
gear position, the cause of the noise is generally
traceable to the gears in operation.
(a) Growl and humming or, more serious, a grinding
noise. These noises are caused by worn, chipped, rough
or cracked gears. As gears continue to wear, the grinding
noise will be noticeable, particularly in the gear position
that throws the greatest load on the worn gear.
(b) Hissing or, more serious, a thumping or
bumping-type noise.
Hissing noises can be caused by
bad bearings. As bearings wear and retainers start to
break up, etc., the noise could change to a thumping or-
bumping.
(c) Metallic rattles within the auxiliary usually result
from a variety of conditions. Engine torsional vibrations
are transmitted to the transmission through the clutch,
which may be amplified and transmitted to the auxiliary
through the connecting propeller shaft. In heavy duty
equipment, clutch discs with vibration dampers are not
used, so a rattle, particularly in neutral, is common with
diesel equipment. In general, engine speeds should be
600 RPM or above to eliminate objectionable rattles and
vibration during the idle.
Always leave the main box in
neutral and the auxiliary unit in gear when idling.
A
defective or faulty injector would cause a rough or lower
idle speed and a rattle in the auxiliary. Rattle could also
be caused by excessive backlash in P.T.O. unit
mounting.
(d) Improper lubricants or lack of lubricant can
produce noises. Auxiliaries with low oil levels sometimes
run hotter than normal, as there is insufficient lubricant to
cool and cover the gears.
(e) Squealing, particularly when the auxiliary is
operating at higher speeds, could be caused by one of
the free running gears seizing on the thrust face or fluted
diameter temporarily and then letting go. In general, a
mild seizure will clear itself up and the auxiliary will
continue to operate very satisfactorily without this defect
being known. See .(g) below:
(f) Gear
seizure
at
high
speed,
usually
accompanied with loud squealing noise. This type of
seizure is readily apparent to the driver, since the truck
will suddenly slow down as if the brakes were being
applied. If the truck continues to move ahead, even
though the gear shift lever is placed in neutral, it would
indicate the floating gear on the mainshaft had seized.
Depressing the clutch should interrupt the driving torque.
The seized gear could be checked quite readily by
depressing the clutch and checking the action with the
gear shift lever progressively in all shift positions. If
releasing the clutch tends to kill the engine, then this gear
position has not seized. In other words, the auxiliary
would be in two gears at the same time. By a process of
elimination, the gear at fault can be readily identified. See
(g) below: (g) Vibration: Gear seizures on thrust faces or
fluted diameters are usually caused by vibrations in the
power train-this could be engine, propeller shafts, joint
angles rear axle, differentials, etc.
838
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