Subaru Impreza 3 / Impreza WRX / Impreza WRX STI. Manual - part 447
6MT-125
General Diagnostic Table
MANUAL TRANSMISSION AND DIFFERENTIAL
2. DIFFERENTIAL
Symptoms
Possible cause
Corrective action
1. Broken differential (case, gear, bearing,
etc.)
NOTE:
Noise will occur, and eventually the differ-
ential will not be able to operate due to bro-
ken pieces obstructing the gear revolution.
(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 conditions
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 pinion
and the hypoid driven gear
Adjust.
(e) Loose hypoid driven gear clamping
bolts
Tighten.
2. Differential and hypoid gear noise
Troubles of the differential and hypoid gear
always appear as noise problems. There-
fore noise is the first indication of trouble.
However, noise from the engine, muffler,
tire, exhaust gas, bearing, body, etc. are
easily mistaken for noise from the differen-
tial. 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, incor-
rect gear engagement, damaged gears,
etc.
• Gear noise during coasting: Damaged
gears due to misadjusted bearings and
incorrect shim adjustment.
• Bearing noise when driving or coasting:
Cracked, broken or damaged bearings.
(a) Insufficient oil
Replenish or replace with the specified
amount of recommended oil.
(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 differen-
tial case
Replace.