AXLES-REAR
MOTOR TRUCK SERVICE MANUAL
Fig. 4-Pitted Bevel Pinion Teeth
The bevel drive pinion shown in Fig. 4 was in extremely
Occasionally in this type of trouble, the ring gear will
severe service.
appear to be undamaged. The reason for this: each
pinion tooth is contacted a number of times for a single
Note the pitted areas concentrated at the heel ends of
contact of a ring gear tooth due to the gear and pinion
the teeth on the drive sides indicating deflection in the
ratio. Gear damage is not noticeable to the naked eye,
assembly, resulting from abnormal pressures. Normally
but the tooth contour has changed. Running a used gear
pressures are quite evenly distributed over the entire
with a new pinion will cause early failure. Damaged
faces of the gear and pinion teeth. Under excessive
gears should be replaced only in matched sets.
loading, deflection throws the pinion out of its proper
position in relation to the ring gear, concentrating the
From the above discussion, it will be immediately
contact areas on the heel ends of the teeth. Unit
apparent, the more severe the service, the greater the
pressures build up to exceed the strength of the oil film.
need for quality lubricants. Use only recommended oils
The teeth contact without benefit of lubrication, the high
of a known brand and quality.
pressures break down the surfaces and the teeth are
pitted.
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