2. Pinion bearing preload
3. Case bearing preload
4. Ring gear runout
5. Ring and pinion backlash
6. Ring and pinion contact pattern
PINION GEAR DEPTH.The pinion gear
depth refers to the distance the pinion gear extends into
the carrier. Pinion depth affects where the pinion gear
teeth meshes with the ring gear teeth. Pinion gear depth
is commonly adjusted by varying shim thickness on
the pinion gear and bearing assembly.
PINION BEARING PRELOAD.The pinion
bearing preload is frequently adjusted by torquing the
pinion nut to compress a collapsible spacer. The more
the pinion nut is torqued, the more the spacer will
compress to increase the preload or tightness of the
With a collapsible spacer, only tighten the pinion
nut in small increments. Then measure the pinion
preload by turning the pinion nut with an inch-pound
When a solid spacer and pinion nut are used, shims
control pinion bearing preload. The pinion nut is
torqued to a specific value found in the service manual.
To set pinion bearing preload, use a holding tool to
keep the pinion gear stationary. Then a breaker bar or
torque wrench can be used to tighten the pinion nut.
CASE BEARING PRELOAD.The
bearing preload is the amount of force pushing the
differential case bearings together. As with pinion
bearing preload, it is critical.
If preload is too low (bearings too loose),
differential case movement and ring and pinion gear
noise can result. If preload is too high (bearings too
tight), bearing overheating and failure can result.
When adjusting nuts are used, the nuts are
typically tightened until all of the play is out of the
bearings. Then each nut is tightened a specific portion
of a turn to preload the bearings. This is done when
When shims are used, a feeler gauge is used to
check side clearance between the case bearing and the
carrier. This action will let you calculate the correct
shim thickness to preload the case bearings. Refer to
the service manual for special equipment and
RING GEAR RUNOUT.The ring gear runout
is the amount of wobble or side-to-side movement
produced when the ring gear is rotated. Ring gear
runout must not be beyond the manufacturers
To measure ring gear runout, mount a dial
indicator against the back of the ring gear (fig. 5-20).
The indicator stem should be perpendicular to the ring
gear surface. Then turn the ring gear and note the
indicator reading. If the ring gear is within
specifications, locate a position on the ring gear that
indicates ONE HALF of the maximum runout on the
gauge. Mark the gear at that point. Then rotate the ring
gear until the teeth on the opposite side of the gear from
the mark are in mesh with the pinion gear.
If ring gear runout is excessive, check the ring gear
mounting and differential case runout. If not a
mounting problem, replace either the ring gear and
pinion or the case as needed.
RING AND PINION BACKLASH.The ring
and pinion backlash refers to the amount of space
between the meshing teeth of the gears. Backlash is
needed to allow for heat expansion
As the gears operate, they produce friction and
heat. This makes the gears expand, reducing the
clearance between the meshing teeth of the gears.
Without backlash, the ring and pinion teeth can jam
into each other and fail in a very short period of time.
However, too much ring and pinion backlash can cause
gear noise (whirring, roaring, or clunking).
Figure 5-20.Measuring ring gear runout.