Subaru IMPREZA 2004 Service Manual page 63

2. DIFFERENTIAL
Symptom
1. Broken differential (case, gear, bear-
ing, etc.)
NOTE:
Abnormal noise will develop and finally it
will become impossible to continue to run
due to broken pieces obstructing the gear
revolution.
2. Differential and hypoid gear noises
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, bear-
ing, 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 the following four kinds of noises.
• Gear noise when driving: If noise
increases as the vehicle speed increases
it may be due to insufficient gear oil,
incorrect gear engagement, damaged
gears, etc.
• Gear noise when coasting: Damaged
gears due to maladjusted bearings and
incorrect shim adjustment
• Bearing noise when driving or when
coasting: Cracked, broken or damaged
bearings
• Noise which mainly occurs when turn-
ing: Unusual noise from the differential
side gear, differential pinion, differential
pinion shaft, etc.
General Diagnostic Table
Possible cause
(a) Insufficient or improper oil
(b) Use of vehicle under severe condi-
tions such as excessive load and
improper use of clutch
(c) Improper adjustment of taper roller
bearing
(d) Improper adjustment of drive pinion
and hypoid driven gear
(e) Excessive backlash due to worn dif-
ferential side gear, washer or differential
pinion vehicle under severe operating
conditions.
(f) Loose hypoid driven gear clamping
bolts
(a) Insufficient oil
(b) Improper adjustment of hypoid driven
gear and drive pinion
(c) Worn teeth of hypoid driven gear and
drive pinion
(d) Loose roller bearing
(e) Distorted hypoid driven gear or differ-
ential case
(f) Worn washer and differential pinion
shaft
6MT-131
MANUAL TRANSMISSION AND DIFFERENTIAL
Disassemble differential and replace bro-
ken 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.
Adjust.
Adjust.
Add recommended oil to specified level.
Do not use vehicle under severe operat-
ing conditions.
Tighten.
Lubricate.
Check tooth contact.
Replace as a set.
Readjust bearing preload.
Readjust hypoid driven gear to drive pin-
ion backlash and check tooth contact.
Replace.
Replace.
Remedy