tial case is supported in the housing by two bearings
located on either side of the case. The differential
cover contains two integrated frame mounting brack-
ets. The Hydra-Lok

t differential has a two-piece dif-

ferential case which contains the gerotor pump
assembly and the clutch mechanism. The axle is ser-
viced as an assembly.

OPERATION

The axle receives power from the transmission

through the propeller shaft. The propeller shaft is
connected to the pinion gear which rotates the differ-
ential through the gear mesh with the ring gear
bolted to the differential case. The engine power is
transmitted to the axle shafts through the pinion
mate and side gears. The side gears are splined to
the axle shafts.

HYDRA-LOK

T DIFFERENTIAL

A gerotor pump and clutch pack are used to pro-

vide the torque transfer capability. One axle shaft is
splined to the gerotor pump and one of the differen-
tial side gears, which provides the input to the pump.
As a wheel begins to lose traction, the speed differ-
ential is transmitted from one side of the differential
to the other through the side gears. The motion of
one side gear relative to the other turns the inner
rotor of the pump. Since the outer rotor of the pump
is grounded to the differential case, the inner and
outer rotors are now moving relative to each other
and therefore creates pressure in the pump. The tun-
ing of the orifices and valves inside the gerotor pump
system includes a torque-limiting pressure relief

valve to protect the clutch pack, which also facilitates
vehicle control under extreme side-to-side traction
variations. The resulting pressure is applied to the
clutch pack and the transfer of torque is completed.

Under conditions in which opposite wheels are on

surfaces with widely different friction characteristics,
Hydra-lok

t delivers far more torque to the wheel on

the higher traction surface than do conventional
Trac-lok

t systems. Because conventional Trac-lokt

differentials are initially pre-loaded to assure torque
transfer, normal driving (where inner and outer
wheel speeds differ during cornering, etc.) produces
torque transfer during even slight side-to-side speed
variations. Since these devices rely on friction from
this preload to transfer torque, normal use tends to
cause wear that reduces the ability of the differential
to transfer torque over time. By design, the Hydra-
lok

t system is less subject to wear, remaining more

consistent over time in its ability to transfer torque.
The Hydra-lok

t also benefits from using the same

lubricant supply as the ring and pinion gears.

NOTE: Differential is serviced as an axle assembly.

DIAGNOSIS AND TESTING - REAR AXLE

GEAR NOISE

Axle gear noise can be caused by insufficient lubri-

cant, incorrect backlash, incorrect pinion depth, tooth
contact, worn/damaged gears, or the carrier housing
not having the proper offset and squareness.

Gear noise usually happens at a specific speed

range. The noise can also occur during a specific type
of driving condition. These conditions are accelera-
tion, deceleration, coast, or constant load.

When road testing, first warm-up the axle fluid by

driving the vehicle at least 5 miles and then acceler-
ate the vehicle to the speed range where the noise is
the greatest. Shift out-of-gear and coast through the

REAR AXLE - 226RIA

3 - 11

peak-noise range. If the noise stops or changes
greatly:

• Check for insufficient lubricant.

• Incorrect ring gear backlash.

• Gear damage.
Differential side gears and pinions can be checked

by turning the vehicle. They usually do not cause
noise during straight-ahead driving when the gears
are unloaded. The side gears are loaded during vehi-
cle turns. A worn pinion shaft can also cause a snap-
ping or a knocking noise.

BEARING NOISE

The axle shaft, differential and pinion bearings can

all produce noise when worn or damaged. Bearing
noise can be either a whining, or a growling sound.

Pinion bearings have a constant-pitch noise. This

noise changes only with vehicle speed. Pinion bearing
noise will be higher pitched because it rotates at a
faster rate. Drive the vehicle and load the differen-
tial. If bearing noise occurs, the rear pinion bearing
is the source of the noise. If the bearing noise is
heard during a coast, the front pinion bearing is the
source.

Differential bearings usually produce a low pitch

noise. Differential bearing noise is similar to pinion
bearing noise. 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 shaft bore will also cause low speed knock.

VIBRATION

Vibration at the rear of the vehicle is usually

caused by a:

• Damaged drive shaft.

• Missing drive shaft balance weight(s).

• Worn or out-of-balance wheels.

• Loose wheel lug nuts.

• Worn U-joints or CV joints.

• Loose/broken springs.

• Damaged axle shaft bearing(s).

• Loose pinion gear nut.

• Excessive pinion yoke run out.

• Bent axle shaft(s).
Check for loose or damaged front-end components

or engine/transmission mounts. These components
can contribute to what appears to be a rearend vibra-
tion. Do not overlook engine accessories, brackets
and drive belts.

All driveline components should be examined

before starting any repair.

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.

• Transmission shift operation.

• Loose engine/transmission/transfer case mounts.

• Worn U-joints or CV joints.

• Loose spring mounts.

• Loose pinion gear nut and yoke.

• Excessive ring gear backlash.

• Excessive 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.

DIAGNOSTIC CHART

Condition

Possible Causes

Correction

Wheel Noise

1. Wheel loose.

1. Tighten loose nuts.

2. Faulty, brinelled wheel bearing.

2. Replace bearing.

Axle Shaft Noise

1. C/V half shaft

1. Inspect and correct as neces-
sary.

2. Bent or sprung axle shaft.

2. Inspect and correct as neces-
sary.

3 - 12

REAR AXLE - 226RIA

REAR AXLE - 226RIA (Continued)

Condition

Possible Causes

Correction

Axle Shaft Broke

1.Vehicle overloaded.

1. Replace broken shaft and avoid
excessive weight on vehicle.

2. Erratic clutch operation.

2. Replace broken shaft and avoid
or correct erratic clutch operation.

3. Grabbing clutch.

3. Replace broken shaft and
inspect and repair clutch as neces-
sary.

Differential Cracked

1. Improper adjustment of the dif-
ferential bearings.

1. Replace case and inspect gears
and bearings for further damage.
Set differential bearing pre-load
properly.

2. Excessive ring gear backlash.

2. Replace case and inspect gears
and bearings for further damage.
Set ring gear backlash properly.

3. Vehicle overloaded.

3. Replace case and inspect gears
and bearings for further damage.
Avoid excessive vehicle weight.

4. Erratic clutch operation.

4. Replace case and inspect gears
and bearings for further damage.
Avoid erratic use of clutch.

Differential Gears Scored

1. Insufficient lubrication.

1. Replace scored gears. Fill differ-
ential with the correct fluid type
and quantity.

2. Improper grade of lubricant.

2. Replace scored gears. Fill differ-
ential with the correct fluid type
and quantity.

3. Excessive spinning of one
wheel/tire.

3. Replace scored gears. Inspect
all gears, pinion bores, and shaft
for damage. Service as necessary.

Loss Of Lubricant

1. Lubricant level too high.

1. Drain lubricant to the correct
level.

2. Worn axle shaft seals.

2. Replace seals.

3. Cracked differential housing.

3. Repair as necessary.

4. Worn pinion seal.

4. Replace seal.

5. Worn/scored yoke.

5. Replace yoke and seal.

6. Axle cover not properly sealed.

6. Remove, clean, and re-seal
cover.

Axle Overheating

1. Lubricant level low.

1. Fill differential to correct level.

2. Improper grade of lubricant.

2. Fill differential with the correct
fluid type and quantity.

3. Bearing pre-loads too high.

3. Re-adjust bearing pre-loads.

4. Insufficient ring gear backlash.

4. Re-adjust ring gear backlash.

REAR AXLE - 226RIA

3 - 13

REAR AXLE - 226RIA (Continued)

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