MOTOR TRUCK SERVICE MANUAL
Fig . 7-Pitted Planetary Gear Teeth .
Here are idler pinions and a sliding clutch gea2 damaged
proved they had been correctly heat treated to sufficient
by abnormal pressures. Observe the pitted areas on the
hardness and strength to withstand all normal pressures.
idler pinion teeth near one end and the corresponding
It is therefore evident, normal pressures were greatly
mutilated areas on the gear. Excessive loading created
exceeded in operation and the failure may be readily
deflection in the assembly and the contact areas or
traced to abusive service. Very frequently when damage
bearing areas were concentrated at one end of the teeth.
of this kind occurs, other parts of the unit will be worn to
Consequently, pressures were sufficiently high to break
a point requiring replacement. Thorough examination
through the protecting oil film, permit metal-to-metal
and a complete tear down is the only way a lasting,
contact, and break down the tooth surfaces. Close
satisfactory repair job may be assured. Look for bearing
inspection of Fig. 7 will reveal some of the teeth have
wear, damaged bevel gears, mutilated differential gears
larger pitted areas than others. Merely because some of
and scored idler pinion pins.
these teeth happened to be in contact more frequently at
the instant of clutch ing and pressure application, they
Failures of this type may be easily avoided by loading
were most affected.
within the capacity of the vehicle in consideration of the
working conditions, and putting the trucks under the
Examination of all these gears definitely
control of only capable drivers.