Jeep 1996 Grand Cherokee Service Manual - page 63
driving condition. These conditions are acceleration,
deceleration, coast, or constant load.
When road testing, accelerate the vehicle to the
speed range where the noise is the greatest. Shift
out–of–gear and coast through the peak–noise range.
If the noise stops or changes greatly, check for insuf-
ficient lubricant. Incorrect ring gear backlash, or
gear damage can cause noise changes.
Differential side and pinion gears can be checked
by turning the vehicle. They usually do not cause
noise in straight–ahead driving. These gears are
loaded during vehicle turns. If noise does occur dur-
ing vehicle turns, the side or pinion gears could be
worn or damaged. A worn pinion gear mate shaft can
also cause a snapping or a knocking noise.
BEARING NOISE
The axle shaft, differential and pinion gear bear-
ings can all produce noise when worn or damaged.
Bearing noise can be either a whining, or a growling
sound.
Pinion gear bearings have a constant–pitch noise.
This noise changes only with vehicle speed. Pinion
bearing noise will be higher because it rotates at a
faster rate. Drive the vehicle and load the differen-
tial. If bearing noise occurs the pinion rear bearing is
the source of the noise. If the bearing noise is heard
during a coast, front bearing is the source.
Worn, damaged differential bearings usually pro-
duce a low pitch noise. Differential bearing noise is
similar to pinion bearing. The pitch of differential
bearing noise is also constant and varies only with
vehicle speed.
Axle shaft bearings produce noise and vibration
when worn or damaged. The noise generally changes
when the bearings are loaded. Road test the vehicle.
Turn the vehicle sharply to the left and to the right.
This will load the bearings and change the noise
level. Where axle bearing damage is slight, the noise
is usually not noticeable at speeds above 30 mph.
LOW SPEED KNOCK
Low speed knock is generally caused by a worn
U–joint or by worn side–gear thrust washers. A worn
pinion gear shaft bore will also cause low speed
knock.
VIBRATION
Vibration at the rear of the vehicle is usually
caused by:
• Damaged drive shaft
• Missing drive shaft balance weight
• Worn, out-of-balance wheels
• Loose wheel lug nuts
• Worn U-joint
• Loose spring U-bolts
• Loose/broken springs
• Damaged axle shaft bearings
• Loose pinion gear nut
• Excessive pinion yoke run out
• Bent axle shaft
Check for loose or damaged front-end components
or engine/transmission mounts. These components
can contribute to what appears to be a rear-end
vibration. Do not overlook engine accessories, brack-
ets and drive belts.
All driveline components should be examined
before starting any repair.
Refer to Group 22, Tires And Wheels for additional
information involving vibration diagnosis.
DRIVELINE SNAP
A snap or clunk noise when the vehicle is shifted
into gear (or the clutch engaged), can be caused by:
• High engine idle speed
• Loose engine/transmission/transfer case mounts
• Worn U–joints
• Loose spring mounts
• Loose pinion gear nut and yoke
• Excessive ring gear backlash
• Excessive differential side gear–to–case clearance
The source of a snap or a clunk noise can be deter-
mined with the assistance of a helper. Raise the vehi-
cle on a hoist with the wheels free to rotate. Instruct
the helper to shift the transmission into gear. Listen
for the noise, a mechanics stethoscope is helpful in
isolating the source of a noise.
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DIFFERENTIAL AND DRIVELINE
ZJ
DIAGNOSIS AND TESTING (Continued)