used to hold the ring gear to the case. The bolts pass
through holes in the case and are threaded into tapped
holes in the back of the ring gear.
Since the ring and drive pinion gear teeth must mesh
accurately to transmit motion without noise or damage,
the position of the ring gear is important. Automotive tech-
nicians should be familiar with gear terminology that will
be encountered while adjusting the differential assembly to
obtain correct gear positions. The convex side, or drive
side, and the concave side, or coast side, of the ring gear
are pointed out in Figure 16-9A. These terms will be used
when differential gears are adjusted. The tooth parts that
must be carefully adjusted are identified in Figure 16-9B.
The terms heel and toe will be used extensively for ring
and pinion gearset adjustment.
Differential Case Assembly
When a vehicle makes a turn, the outer wheel travels
a greater distance than the inner wheel—the arc (or
radius) of the turn is greater at the outer wheel. If the rear
drive axles were simply connected together, both wheels
would have to travel an arc of the same length during a
turn. Since this is impossible, one of the tires would lose
traction, or slip, during the turn. If the tire did not slip, it
would skip over the road surface. This condition is called
wheel hop.
The purpose of the differential case assembly is to
allow the vehicle to make turns without slippage or wheel
hop. It does this with an arrangement of gears that allows
the rear wheels to turn at different speeds. Two basic types
of differential case assemblies used to accomplish this task
are the standard differential and the locking differential.
Standard differential
The standard differential, also called a single-pull
differential, is composed of meshing spider and side gears
enclosed in a differential case. See Figure 16-10.
The standard differential case is usually a one-piece
unit. The ring gear is bolted to the case. The case is usually
made of cast iron. Occasionally, it is made of aluminum.
Side bearings are usually pressed onto the case.
The spider gears are made of hardened steel and are
held in place by a steel shaft called the pinion shaft. The
pinion shaft passes through the differential case and the
center of the spider gears. It is attached to the case with a
bolt. Spider gears are also called pinion gears.
Spider gears mesh with side gears, which are also
made of hardened steel. When the ring gear and differen-
tial case turn, the spider and side gears also turn. Power
flow is through the case, into the spider gears, and on into
the side gears. The side gears are splined to the drive axles.
314 Manual Drive Trains and Axles
Rear U-joint
Front pinion
bearing Pinion
shim
Pinion
gear nut
Differential
pinion yoke
Collapsible
spacer
Rear pinion
bearing
Figure 16-8. Pinion shim and preload spacer locations. Proper
pinion adjustment is critical. The adjusting nut, preload spacer,
and depth shim are all critical to proper pinion adjustment.
(DaimlerChrysler)
Correct
pattern
Toe
Concave side
(coast)
Convex side
(drive)
Heel
Top land
Profile
Root
Toe
Heel
Lengthwise
bearing
arc
A B
Figure 16-9. When installed, the ring gear is bolted to the differential case and meshes with the drive pinion gear. A—The ring gear
has convex and concave sides. The convex side is the drive side. It contacts the drive pinion gear when the vehicle is accelerating.
The concave side is the coast side. It contacts the drive pinion gear when the vehicle is decelerating. B—Gear terminology will be
important when the differential assembly is serviced. Proper heal and toe contact is critical to quiet operation and long life.
(General Motors, DaimlerChrysler)