Shibaura ST318, Workshop Manual

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8) Trouble Shooting
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 check
valve.
Disassemble, wash, and them reassemble
(correction of valve).
2. Defective seat of check and
high pressure relief valve
assembly.
Repair or replace the check and high pressure relief
valve assembly.
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 high 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.