Subaru 2004 Impreza Service Manual page 49

MANUAL TRANSMISSION AND DIFFERENTIAL
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 vehicle speed increases it
may be due to insufficient gear oil, incor-
rect 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 differential side
gear, differential pinion, differential pinion
shaft, etc.
General Diagnostic
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
5MT-118
Remedy
Disassemble the differential and replace
broken components and at the same time
check other components for any trouble,
and replace if necessary.
Readjust the bearing preload and back-
lash and face contact of gears.
Adjust.
Adjust.
Add recommended oil to specified level.
Do not use the vehicle under severe oper-
ating conditions.
Tighten.
Lubricate.
Check tooth contact.
Replace as a set.
Readjust the bearing preload.
Readjust the hypoid driven gear to drive
pinion backlash and check tooth contact.
Replace.
Replace.