4.

TROUBLESHOOTING GUIDE

4. TROUBLESHOOTING GUIDE
4.1 TORQUE CONVERTER AND TRANSMISSION
The truck does not travel.

Does engine start? Check neutral switch. (See 5.2.)

• Check neutral relay and starter relay.
• Check starter switch.

Does torque converter operate? Replace any damaged input plate.

Do solenoid valves operate normally? Replace any damaged solenoid valve.

(See 5.4.)

Is converter oil level normal? Add torque converter oil.

Is oil clean? Is oil discolored?

Seized clutch: Replace clutch plates and

change oil.

Is inching adjustment proper? Readjust.

Is clutch oil pressure normal? Is charging pump operating?

1.08 - 1.47 MPa {10.6 - 14.4 kgf/cm2} Charging pump oil pressure:
[156.6 - 213.2 psi] 1.47 MPa {14.4 kgf/cm2} [213.2 psi]

Torque converter is damaged: Replace.

Charging pump defective.

Clogged filter: Replace.

Insufficient pump discharge: Air is sucked. Replace packing, gasket and
“O”-ring.
Charging pump is defective: Replace.
Clogged coin filter or choke plug inside control valve: Clean. (See 5.6 and
To next page 5.7.)

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Continued from
preceding page

Is converter inlet oil pressure normal?

0.39 - 0.69 MPa {3.8 - 6.8 kgf/cm2}
[56.57 - 100.08 psi]

Converter inlet relief valve seized or spring deteriorated: Replace.

Seal ring defective: Replace.

Both fwd and rev clutch packs operate at

the same time.

Clutch plates defective or seal ring damage: Replace.

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 4. TROUBLESHOOTING GUIDE

Poor acceleration or
insufficient power

Check oil leaks outside.

Is oil level normal? Add oil.

Does solenoid valve operate normally? Replace any defective solenoid valve.
(See 5.4.)

Is oil clean? Is oil burned or discolored?

Clutch pack defective: Replace clutch

plates and change oil.

Is inching adjustment proper? Readjust.

To next page

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4. TROUBLESHOOTING GUIDE

To be continued from
preceding page

Is converter inlet oil pressure normal?

0.39 - 0.69 MPa {3.8 - 6.8 kgf/cm2} Relief valve seized or spring
[56.57 - 100.08 psi] deteriorated: Replace.

Seal ring or “O”-ring defective: Replace.

Is clutch oil pressure normal? Regulator valve seized or spring

1.08 - 1.47 MPa {10.6 - 14.4 kgf/cm2}
[156.6 - 213.2 psi] deteriorated: Replace.

Seal ring or “O”-ring damaged: Replace.

Clogged oil passage: Repair.

Coin filter or choke plug inside control

valve is clogged: Clean. (See 5.6 and 5.7.)

Both fwd and rev clutch packs operate Clutch plates defective, piston or seal
at the same time. ring damaged: Replace.

Trouble with components other than

the drive unit.

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 4. TROUBLESHOOTING GUIDE

Oil temperature is too high.

Is cooling water level low? Add cooling water.

Is radiator clogged? Clean the radiator fin.

Is oil level is low? Add oil.

Oil passage is obstructed: Clean.

Filter clogged: Replace filter.

Charging pump is defective.

One-way clutch is defective.

(stator seized)

The truck moves when the

shift lever is in neutral.

Solenoid valve seized (See 5.4.). Replace solenoid valve.

Is oil discolored to brown or seized? Clutch plates defective: Replace.

Clutch piston does not return properly:

Replace piston.
Poor oil tightness inside clutch: Replace seal.

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4. TROUBLESHOOTING GUIDE

Noisy operation

Is oil level proper? Add oil.

Does oil contain bubbles? Oil is not good: Change.

Oil is deteriorated: Change.

Water is mixed in oil: Change.

Is inching adjustment proper? Readjust.

Is filter clogged? Replace filter.

Is air sucked into charging pump? Replace charging pump.

Is input plate defective? Replace input plate.

(with engine running at idle rpm)

Loose bolt or damaged gear? Tighten or replace.

Is bearing damaged? Replace.

Trouble with components other than

drive unit. Check wheel hub, wheel, and brake.

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Oil leaks

Problem and possible cause Remedy

Oil leaks may be caused by: blowing off of oil from the transmission gear case, a defective weld between the
converter case and pump wheel, cracked case, a loose connection of piping, damaged oil cooler, etc.

1. Torque converter
(1) Centering flange mounting area Replace torque converter assembly.

(2) Welded area between converter case and Replace torque converter.
pump wheel.

(3) Pump wheel boss oil seal Check seal lip and pump wheel boss sliding area for damage
or wear. If any defect is found, replace oil seal or torque
converter with a new one.

(4) Cracks in converter case Replace torque converter assembly.

2. Power-shift transmission
(1) Connections between torque converter Retighten bolts or replace gasket.
housing and transmission gear case

(2) Oil seal of output flange Check seal lip and pump wheel boss sliding area for damage
or wear. If any defect is found, replace with a new one.

(3) Piping connections Retighten bolts or replace seal washer.

(4) Oil cooler damaged Check radiator cooling water. Repair or replace any defective
oil cooler.

(5) Oil blows off from transmission gear case.

(a) Check for mixing of water. If oil gets cloudy, change oil.
(b) Check for suction of air. Check connections. Retighten where necessary or replace
seal washer.
(c) Check air breather for clogging. Check air holes for clogging. If clogged, clean the air holes or
replace breather with a new one.

(6) Drain plug Retighten.

(7) Cracks in transmission gear case Repair or replace the case.

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4. TROUBLESHOOTING GUIDE

4.2 REDUCTION GEAR AND DIFFERENTIAL

Problem Possible cause Remedy

1. Noisy differential
Problems with the differential will usually appear as a noise. However, you may confuse noise from the differential
with that from the engine, muffler, torque converter transmission, reduction gear, wheels, or wheel bearings. When
checking the differential, make sure that noise comes from the differential, not from other components.

(1) Noisy gear in driving Gear oil level is low or improper quality Add oil or change gear oil
(SAE90) API GL-4 or higher.

Ring gear teeth worn or damaged Repair or replace.

Bearing worn or damaged Replace bearing.

Drive shaft splines worn Replace shaft.

(2) Noisy gear during Pinion gear or side gear teeth worn or damaged Repair or replace.
traveling
Pinion gear or side gear thrust plate worn Replace thrust plate.

Spider worn Replace spider.

(3) Noise produced Pinion gear, side gear, or spider worn Replace worn part.
when the truck
makes turns

2. Malfunction of the differential

If the differential fails to operate normally, jack up the front wheels and check the differential from the front tire side
to verify that the differential is defective.

(1) The truck cannot Foreign matter such as metal pieces caught in the Clean.
travel or loud noise gears

Ball bearing damaged Replace bearing.

Drive shaft damaged Replace shaft.

Ring gear teeth damaged Replace ring gear.

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