Jeep 1996 Grand Cherokee Service Manual page 121

3 - 76 DIFFERENTIAL AND DRIVELINE
DESCRIPTION AND OPERATION (Continued)
It is not necessary to remove the axle from the
vehicle for service. A removable differential cover is
provided for routine vehicle service. If the differential
housing is damaged, the complete axle assembly can
be removed.
For complete drive axle assembly removal and
installation refer to Drive Axle Assembly Replace-
ment in this Group.
IDENTIFICATION
Model 44 axle has the assembly part number and
gear ratio listed on a tag. The tag is attached to the
right side of the housing cover. Build date identifica-
tion codes on axles are stamped on the axle shaft
tube cover side. The Model 44 axle has a flat housing
cover gasket flange at the outer edge.
STANDARD DIFFERENTIAL OPERATION
The differential gear system divides the torque
between the axle shafts. It allows the axle shafts to
rotate at different speeds when turning corners.
Each differential side gear is splined to an axle
shaft. The pinion gears are mounted on a pinion
mate shaft and are free to rotate on the shaft. The
pinion gear is fitted in a bore in the differential case
and is positioned at a right angle to the axle shafts.
In operation, power flow occurs as follows:
• The pinion gear rotates the ring gear
• The ring gear (bolted to the differential case)
rotates the case
• The differential pinion gears (mounted on the
pinion mate shaft in the case) rotate the side gears
• The side gears (splined to the axle shafts) rotate
the shafts
During straight- ahead driving, the differential pinion
gears do not rotate on the pinion mate shaft. This
occurs because input torque applied to the gears is
divided and distributed equally between the two side
gears. As a result, the pinion gears revolve with the pin-
ion mate shaft but do not rotate around it (Fig. 1).
Fig. 1 Differential Operation—Straight Ahead Driving
When turning corners, the outside wheel must travel
a greater distance than the inside wheel in order to
complete a turn. The difference must be compensated
for, to prevent the tires from scuffing and skidding
through turns. To accomplish this, the differential
allows the axle shafts to turn at unequal speeds (Fig. 2).
In this instance, the input torque applied to the pinion
gears is not divided equally. The pinion gears now
rotate around the pinion mate shaft in opposite direc-
tions. This allows the side gear and axle shaft attached
to the outside wheel to rotate at a faster speed.
Fig. 2 Differential Operation—On Turns
TRAC-LOK OPERATION
In a conventional differential, the torque applied to
the ring gear is transmitted to the axle shafts through
the differential gears. During normal operation, the
torque transmitted to each wheel is equal at all times.
However, if one wheel spins, the opposite wheel will
generate only as much torque as the spinning wheel.
In the Trac-lok differential, part of the ring gear
torque is transmitted through clutch packs. The
clutch packs contain multiple disc. The clutch will
have radial grooves on the plates, and concentric
grooves on the discs or bonded fiber material that is
smooth appearance.
In operation, the Trac-lok clutches are engaged by
two concurrent forces. The first being preload force
exerted through Belleville spring washers contained
in the clutch packs. The second from separating
forces generated by the side gears as torque is
applied through the ring gear (Fig. 3).
The Trac-lok design provides differential action
needed for turning corners and for driving straight
ahead. However, when one wheel looses traction, the
clutch packs transfer additional torque to the wheel
having the most traction. Trac-lok differentials resist
wheel spin on bumpy roads and provide more pulling
power when one wheel looses traction. Pulling power
is provided continuously until both wheels loose trac-
tion. If both wheels slip due to unequal traction,
ZJ