85
(4) Troubleshooting
Replace the HST main body, if defective, as an ass’y as a rule.
Condition Possible cause Remedy
1. Output shaft fails to rotate when
the HST pedal is set at forward or
reverse position.
1. Improper operation of HST pump
or motor.
Check the trunnion shaft movement
and replace the ass’y.
2. Damaged charge pump. Measure the charge pressure and
replace the ass’y.
3. Too low set pressure of low
pressure relief valve.
Measure the low circuit pressure and
replace part.
4. Too low set pressure of high
pressure relief valve.
Measure the high pressure circuit
pressure and replace parts.
5. Defective seat of HST check valve. Replace the part.
2. Output shaft fails to stop rotating
with the HST pedal at neutral
position.
1. Improper operation of neutral and
check valve.
Disassemble, wash, and them
reassemble (correction of valve).
2. Clogged throttle part of check and
neutral valve.
Disassemble, wash, and them
reassemble.
3. Damaged spring for check and
neutral valve.
Replace the part.
3. Insufficient speed of HST output
shaft or abnormal sound in the
HST unit.
1. High pressure oil leaking due to
wear at sliding part of HST pump
or motor.
Clean in the oil circuit and replace
HST unit.
2. Lack of oil by clogging oil filters. Replace oil filters.
3. The air is mixture in the HST oil
circuit.
Inspect the suction line of the charge
pump or lack of the oil in the sump.
4. Lack of discharge oil quantity by
abnormal oil temperature.
· When low temperature: Warm up
the tractor.
· When low temperature: Stop the
engine and restart the engine after
cooled.
4. Oil leaks at shaft and seal. Oil leakage due to damaged oil seal or
O-ring.
Replace damaged oil seal or O-ring
with new one. In this case, take
sufficient care not to damage the lip
when inserting the oil seal.
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