Subaru XT 1988 Service Manual page 514

MANUAL TRANSMISSION AND DIFFERENTIAL 3-1
Condition and possible cause Corrective action
4. Broken differential (case, gear, bearing, etc.)
Abnormal noise will develop and finally it will become impossible to continue to run due to broken pieces obstructing
the gear revolution.
(a) Insufficient or improper oil.
(b) Use of vehicle under severe conditions such as
excessive load and improper use of clutch.
(c) Improper adjustment of taper roller bearing.
(d) Improper adjustment of drive pinion and crown
gear.
(e) Excessive backlash due to worn differential side
gear, washer or differential pinion.
(f) Loose crown gear clamping bolts.
5. Differential and hypoid gear noises.
Disassemble differential and replace broken components
and at the same time check other components for any
trouble, and replace if necessary.
Readjust bearing preload and backlash and face contact of
gears.
Add recommended oil to specified level. Do not use
vehicle under severe operating conditions.
Troubles of the differential and hypoid gear always appear as noise problems.
Therefore noise is the first indication of the trouble.
However noises from the engine, muffler, tire, exhaust gas, bearing, body, etc. are easily mistaken for the differential
noise. Pay special attention to the hypoid gear noise because it is easily confused with other gear noises. There are
following four kinds of noises.
(1) Gear noise when driving:
If noise increase as vehicle speed increases it may be due to insufficient gear oil, incorrect gear engagement,
damaged gears, etc.
(2) Gear noise when coasting:
Damaged gears due to maladjusted bearings and incorrect shim adjustment.
(3) Bearing noise when driving or when coasting:
Cracked, broken or damaged bearings.
(4) Noise which mainly occurs when turning:
Unusual noise from differential side gear, differential pinion, differential pinion shaft, etc.
(a) Insufficient oil
(b) Improper adjustment of crown gear and drive
pinion.
(c) Worn teeth of crown gear and drive pinion.
(d) Loose roller bearing.
(e) Distorted crown gear or differential case.
(f)
Worn washer and differential pinion shaft.
81
Lubricate.
Check tooth contact.
Replace in a set.
Readjust bearing preload.
Readjust crown gear to drive pinion backlash and check
tooth contact.
Replace.
Replace.