Subaru 2009 IMPREZA, Service Manual

Page: 2153 / 3619

5MT-81
General Diagnostic Table
MANUAL TRANSMISSION AND DIFFERENTIAL
2. DIFFERENTIAL
Symptoms Possible cause Corrective action
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.
(a) Insufficient or improper oil Disassemble the differential and replace
broken components. At the same time
check other components for any trouble,
and replace if necessary.
(b) Use of vehicle under severe condi-
tions such as excessive load and
improper use of the clutch Readjust the preload and backlash of the
bearing, and the contact surface of gear.
(c) Improper adjustment of taper roller
bearing Adjust.
(d) Improper adjustment of the drive pin-
ion and the hypoid driven gear Adjust.
(e) Excessive backlash of a vehicle under
severe operating conditions due to worn
differential side gear, washer or differen-
tial pinion. Add recommended oil to the specified
level. Do not use vehicle under severe
operating conditions.
(f) Loose hypoid driven gear tightening
bolts Tighten.
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. (a) Insufficient oil Lubricate.
(b) Improper adjustment of hypoid driven
gear and drive pinion Check the tooth contact.
(c) Worn teeth of hypoid driven gear and
drive pinion Replace as a set.
Readjust the bearing preload.
(d) Loose roller bearing Readjust the backlash of the hypoid
driven gear to drive pinion, and check the
tooth contact.
(e) Distorted hypoid driven gear or differ-
ential case Replace.
(f) Worn washer and differential pinion
shaft Replace.