The rear pinion bearing is pressed onto the drive
pinion gear shaft at the gear end. The front pinion bearing
is often a slip fit on the smaller end of the shaft. The outer
races, or bearing cups, of both bearings are pressed into
the rear axle housing.
Either a solid spacer or a collapsible spacer (crush
washer) is used to set the pinion bearing preload. The
collapsible spacer is designed to be slightly compressed
when the drive pinion gear is installed in the rear axle
housing. The spacer maintains a mild pressure between
the front and rear pinion bearings, making it possible to
accurately adjust the bearing preload.
The differential pinion yoke/flange has internal
splines that fit the external splines on the drive pinion gear
shaft. See Figure 16-6. The rear of the yoke/flange, where
it fits into the rear axle housing, is machined smooth. This
is the sealing surface for the pinion seal. The yoke/flange is
held to the drive pinion gear shaft by a large nut and washer
that threads onto the shaft. This nut is a type known as a
jam nut. The top threads of the nut are deformed to tightly
grip the threads on the drive pinion gear shaft. This is an
interference fit. Tightening the nut also adjusts the pinion
bearing preload.
The pinion yoke is machined to accept the bearing
cups of the rear universal joint. The cups are either pressed
in and held with snap rings, or they are attached to the
yoke with U-bolts or bolted-on straps.
Pinion flanges are simply a two-piece yoke joined by
mating flanges. The outer section has the yoke; the inner
section has the external splines for the pinion gear shaft.
These companion flanges, as they are also called, would
be separated at the flanged section to remove the drive
shaft assembly, Figure 16-7.
The position of the drive pinion gear relative to the
ring gear must be set exactly. Otherwise, the gears will be
noisy and will wear out quickly. The position of the drive
pinion gear in the housing must be carefully adjusted so
that it contacts the ring gear at exactly the right tooth
depth. To make this adjustment to the ring and drive pinion
clearance, a pinion shim is installed in the housing, behind
the rear bearing cup. The thickness of this shim determines
the depth of the drive pinion gear in the housing. This shim
is installed at the factory when the rear end is assembled.
It must be checked for proper thickness whenever the drive
pinion gear is removed.
Figure 16-8 shows the position of the pinion shim on
most rear axle assemblies. This figure also shows the rela-
tive position of the collapsible spacer.
Ring gear
The ring gear, Figure 16-9, transfers power from the
drive pinion gear to the differential case. Both the ring gear
and the case are machined to fit together tightly. Bolts are
Chapter 16 Rear Axle Assembly Construction and Operation 313
Threads for
yoke nut
Drive pinion
splines
Collapsible
spacer
Drive pinion gear
Rear pinion
bearing
Drive pinion
gear shaft
Figure 16-5. A typical drive pinion gear. The rear pinion bear-
ing is pressed on the drive pinion gear shaft. A collapsible
spacer is used to aid in pinion bearing installation.Threads and
splines at the front of the drive pinion gear shaft are used for
installing the differential pinion yoke. (General Motors)
Differential
pinion yoke Differential
seal surface
Splines lock
gear to yoke
Drive
pinion gear
Drive pinion
gear shaft Flat washer
Pinion
gear nut
Hole for
U-joint
Figure 16-6. The differential pinion yoke slides over the drive
pinion gear shaft and is secured by the pinion gear nut. The
tightening nut also preloads the pinion bearings. The outer sur-
face of the drive pinion gear shaft seals against the front oil seal.
U-joint
Rear axle
assembly
Companion
flanges
Flange bolts
Drive shaft
Figure 16-7. Some differential pinion yokes are two-piece
flanged assemblies, as shown here. This type of design is
referred to as a differential pinion flange, or companion flange.
(Ford)