MOTOR TRUCK SERVICE MANUAL
Fig. 8-Shock Fracture.
When shock loads greater than the maximum strength of
as small cracks may be obscured by oil film or be small
the gears are applied to the planetary unit, failure such
enough to pass unnoticed.
as that shown in Fig. 8 is the result.
Note the grainy appearance of the break in the idler gear,
in severe operations such as construction work, oil field
without any of the progression found in fatigue failures.
hauls and logging service. Many times abusive handling
This indicates the part was sufficiently stressed by an
is responsible rather than payload or operating
instantaneous load to cause immediate fracture. In this
conditions. The two-speed axle equipped vehicle does
case the other planetary parts should be very carefully
not need to be "frogged" or "bucked" when handling
checked, as they have been damaged by the high
heavy loads. There is sufficient power in the low range
stresses and may have small cracks in them that are
to move the truck under almost any condition without
almost impossible to see with the eye. If any of the four
idlers have broken, it is indeed advisable to replace all,