Table 2-1.--Allison Four-Speed Automatic Transmission Troubleshooting Chart--Continued
TROUBLE
PROBABLE CAUSE
REMEDY
Add oil to proper level
1.
Oil level low
High stall speed
1.
Refer to low main pressures above
2.
Clutch pressure low
2.
Replace transmission
3.
Forward clutch slipping (forward)
3.
Replace transmission
4.
First and reverse clutch slipping
4.
1. Refer to engine manufacturer's
Low stall speed
1. Engine not performing efficiently
manual or vehicle service manual
(may be due to high altitude)
2. Replace converter assembly
2. Broken converter parts
1. Adjust linkage
Rough shifting
1. Manual selector linkage out of
adjustment
2. Control valves sticking
2. Replace transmission
3. Modulator cable binding or
3. Replace cable or adjust to
improperly adjusted
specification
1. Replace transmission
Engine overspeeds on full throttle
1. Piston seals leaking or clutch plates
upshift
slipping in range involved
2. Forward clutch piston seals or clutch
2. Replace transmission
plates slipping (all upshifts)
3. Broken sealrings on front support hub
3. Replace transmission
4. Sticking governor valve
4. Clean or replace governor
1. Replace transmission
Excessive slippage and clutch chatter 1. Clutch slippage in that range clutch
in one range (not in all ranges)
2. Replace transmission
2. Excessive oil leakage in range piston
seals
3. Oil leakage in valve components for
3. Replace transmission
that particular range
Change oil; install new filter
1.
Failure to change oil at proper interval
Dirty oil
1.
Check oil cooler lines
2.
Excessive heat
2.
Replace transmission
3.
Clutch failure
3.
Replace filter
4.
Damaged oil filter
4.
Oil leak at output shaft
1. Faulty or missing seal at output flange 1. Install new lip-type seal in bearing
retainer
Slippage in all forward gears
1. Low oil level
1. Add oil to proper level
2. Low clutch pressure
2. Refer to low main pressures above
3. Forward clutch slipping
3. Replace transmission
1. Replace transmission
Slippage in fourth and reverse gears
1. Fourth clutch slipping
only
2. Broken sealrings on support assembly
hub
2. Replace transmission
Slippage in reverse and first gears;
1. First-and-reverse clutch slipping
1. Replace transmission
proper function in other forward gears
1. Adjust linkage
Vehicle moves forward in neutral
1. Range selector linkage out of
adjustment
2. Forward clutch failed and dragging
2. Replace transmission
2-68
