Chevrolet Silverado / GMC Sierra. Service manual — part 1499

Limited-Slip Function

Under normal conditions, when the differential is not locked, a small amount of limited-slip
action occurs. The gear separating force developed in the right-hand clutch pack is primarily
responsible for this.

The operation of how the limited-slip function of the unit works can be explained when the
vehicle makes a right-hand turn. Since the left wheel travels farther than the right wheel, it must
rotate faster than the ring gear and differential case assembly. This results in the left axle and left
side gear rotating faster than the differential case. The faster rotation of the left-side gear causes
the pinion gears to rotate on the pinion shaft. This causes the right-side gear to rotate slower than
the differential case.

Although the side gear spreading force produced by the pinion gears compresses the clutch packs,
primarily the right side, the friction between the tires and the road surface is sufficient to
overcome the friction of the clutch packs. This prevents the side gears from being held to the
differential case.

Locking Function

Locking action occurs through the use of some special parts:

A governor mechanism with 2 flyweights

A latching bracket

The left side cam plate and cam side gear

When the wheel-to-wheel speed difference is 100 RPM or more, the flyweights of the governor
will fling out and one of them will contact an edge of the latching bracket. This happens because
the left cam side gear and cam plate are rotating at a speed different, either slower or faster, than
that of the ring gear and differential case assembly. The cam plate has teeth on its outer diameter
surface in mesh with teeth on the shaft of the governor.

As the side gear rotates at a speed different than that of the differential case, the shaft of the
governor rotates with enough speed to force the flyweights outward against spring tension. One of
the flyweights catches its edge on the closest edge of the latching bracket, which is stationary in
the differential case. This latching process triggers a chain of events.

When the governor latches, it stops rotating. A small friction clutch inside the governor allows
rotation, with resistance, of the governor shaft while one flyweight is held to the differential case
through the latching bracket. The purpose of the governor's latching action is to slow the rotation
of the cam plate as compared to the cam side gear. This will cause the cam plate to move out of

2008 Chevrolet Silverado 1500

2008 Driveline/Axle Rear Drive Axle - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

its detent position.

The cam plate normally is held in its detent position by a small wave spring and detent humps
resting in matching notches of the cam side gear. At this point, the ramps of the cam plate ride up
on the ramps of the cam side gear, and the cam plate compresses the left clutch pack with a self-
energizing action.

As the left clutch pack is compressed, it pushes the cam plate and cam side gear slightly toward
the right side of the differential case. This movement of the cam side gear pushes the thrust block
which compresses the right-hand side gear clutch pack.

At this point, the force of the self-energizing clutches and the side gear separating force combine
to hold the side gears to the differential case in the locking stage.

The entire locking process occurs in less than 1 second. The process works with either the left or
right wheel spinning, due to the design of the governor and cam mechanism. A torque reversal of
any kind will unlatch the governor, causing the cam plate to ride back down to its detent position.
Cornering or deceleration during a transmission shift will cause a torque reversal of this type. The
differential unit returns to its limited-slip function.

The self-energizing process would not occur if it were not for the action of one of the left clutch
discs. This energizing disc provides the holding force of the ramping action to occur. It is the only
disc which is splined to the cam plate itself. The other splined discs fit on the cam side gear.

If the rotating speed of the ring gear and differential case assembly is high enough, the latching
bracket will pivot due to centrifugal force. This will move the flyweights so that no locking is
permitted. During vehicle driving, this happens at approximately 32 km/h (20 mph) and continues
at faster speeds.

When comparing the effectiveness of the locking differential, in terms of percent-of-grade
capability to open and limited-slip units, the locking differential has nearly 3 times the potential
of the limited-slip unit under the same conditions.

Locking Differential Torque-Limiting Disc

The locking differential design was modified in mid-1986 to include a load-limiting feature to
reduce the chance of breaking an axle shaft under abusive driving conditions. The number of
tangs on the energizing disc in the left-hand clutch pack was reduced allowing these tangs to shear
in the event of a high-torque engagement of the differential locking mechanism.

At the time of failure of the load-limiting disc, there will be a loud bang in the rear axle and the

2008 Chevrolet Silverado 1500

2008 Driveline/Axle Rear Drive Axle - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

differential will operate as a standard differential with some limited-slip action of the clutch
packs at low torques.

The service procedure, when the disc tangs shear, involves replacing the left-hand clutch plates
and the wave spring. It is also necessary to examine the axle shafts for twisting because at high
torques it is possible to not only shear the load-limiting disc, but to also twist the axle shafts.

REAR DRIVE AXLE DESCRIPTION AND OPERATION

Rear axles for this vehicle consist of the following components:

Differential axle housing

Differential carrier

Right and left axle tubes

Right and left axle shafts

These axles are either full-floating or semi-floating. These axles can be identified as follows: The
semi-floating axle has axle shafts with C-clips inside the differential carrier on the inner ends of
the axle shafts. The full-floating axle has bolts at the hub retaining the axle shafts to the hub
assembly. The axles can be identified by the stamping on the right side axle tube They may also
be identified by the ring gear size. The ring gear sizes include 8.60, 9.50, 10.50 and 11.50 inch
axles. The limited slip/locking differential information for these rear axles can be located in the
limited slip/locking differential section.

A open differential has a set of four gears. Two are side gears and 2 are pinion gears. Some
differentials have more than 2 pinion gears. Each side gear is splined to an axle shaft so each axle
shaft ; so each axle shaft turns when it's side gear rotates. The pinion gears are mounted on a
differential pinion shaft, and the gears are free to rotate on this shaft. The pinion shaft is fitted
into a bore in the differential case and is at right angles to the axle shafts. Power is transmitted
through the differential as follows: the drive pinion rotates the ring gear. The ring gear being
bolted to the differential case, rotates the case, The differential pinion, as it rotates the case,
forces the pinion gears against the side gears. When both wheels have equal traction, the pinion
gears do not rotate on the pinion shaft because of input force on the pinion gear is equally divided
between the two side gears. Therefore, the pinion gears revolve with the pinion shaft, but do not
rotate around the shaft itself. The side gears, being splined to the axle shafts and in mesh with the
pinion gears rotate the axle shafts. If a vehicle were always driven in a straight line, the ring and
pinion gears would be sufficient. The axle shaft could be solidly attached to the ring gear and
both driving wheels would turn at equal speed. However, if it became necessary to turn a corner,
the tires would scuff and slide because the differential allows the axle shafts to rotate at different
speeds. When the vehicle turns a corner, the inner wheel turns slower than the out wheel and

2008 Chevrolet Silverado 1500

2008 Driveline/Axle Rear Drive Axle - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

slows it's rear axle side gear (as the shaft is splined to the side gear). The rear axle pinion gears
will roll around the slowed rear axle side gear, driving the rear axle side gear wheel faster.

SPECIAL TOOLS AND EQUIPMENT

SPECIAL TOOLS

Illustration

Tool Number/Description

DT 47688 Pinion Bearing Remover

J 2222-C

Wheel Bearing Nut Wrench

J 2619-01

Slide Hammer

J 7818

Inner Bearing Race Installer

2008 Chevrolet Silverado 1500

2008 Driveline/Axle Rear Drive Axle - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado