Subaru 2009 IMPREZA Service Manual page 2153

2. DIFFERENTIAL
Symptoms
1. Broken differential (case, gear, bear-
ing, etc.)
NOTE:
Noise will occur, and eventually the differ-
ential will not be able to operate due to
broken pieces obstructing the gear revo-
lution.
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
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 the fol-
lowing 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 misadjusted bear-
ings and incorrect shim adjustment.
• Bearing noise when driving or coasting:
Cracked, broken or damaged bearings
• Noise mainly when turning:
Noise from differential side gear, differen-
tial pinion or 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 the clutch
(c) Improper adjustment of taper roller
bearing
(d) Improper adjustment of the drive pin-
ion and the hypoid driven gear
(e) Excessive backlash of a vehicle under
severe operating conditions due to worn
differential side gear, washer or differen-
tial pinion.
(f) Loose hypoid driven gear tightening
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-81
MANUAL TRANSMISSION AND DIFFERENTIAL
Corrective action
Disassemble the differential and replace
broken components. At the same time
check other components for any trouble,
and replace if necessary.
Readjust the preload and backlash of the
bearing, and the contact surface of gear.
Adjust.
Adjust.
Add recommended oil to the specified
level. Do not use vehicle under severe
operating conditions.
Tighten.
Lubricate.
Check the tooth contact.
Replace as a set.
Readjust the bearing preload.
Readjust the backlash of the hypoid
driven gear to drive pinion, and check the
tooth contact.
Replace.
Replace.