Shibaura ST330, Workshop Manual

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114
7. Troubleshooting
(1) HST Troubleshooting
Usually replace the HST main body as an ass’y when it is defective.
Condition Possible cause Remedy
1. The output shaft does not
rotate even though the HST
pedal is depressed in
forward or reverse
direction.
1. Improper operation of HST pump or
motor.
Check the trunnion shaft for operation
and replace the ass’y.
2. Damaged charge pump.
Measure the charge pressure and
replace the ass’y.
3. Dropped set pressure of low-pressure
relief valve.
Measure the pressure of the
low-pressure circuit and replace parts.
4. Dropped set pressure of high-pressure
relief valve.
Measure the pressure of high-pressure
circuit and replace the parts.
5. Defective HST check valve seat. Replace parts.
6. Air is mixed in the HST oil.
Inspect the suction line and oil level of
transmission.
(need air breeze from in the HST)
2. Output shaft does not stop
rotating even though the
HST pedal is set at the
neutral position.
1. Improper operation of HST link system or
defective return spring.
Disassemble, link system and
reassemble.
2. Defective thrust plate of pump side. Replace part.
3. Too low speed of HST
output shaft.
1. Leak of high-pressure oil due to worn out
sliding part of HST pump or motor.
Replace the HST ass’y.
Replace the mission oil and filter.
2. Air is mixed in the HST oil.
Inspect the suction line and oil level of
transmission.
(need air breeze from in the HST).
3. Lack of HST oil of HST system.
Check the oil level and replace the oil
filter and strainer.
4. Lack of charge pump discharge quantity
by abnormal HST oil temperature.
At too cold : Warming up
At too hot : Stop engine and restart after
cold.
4. Oil leakage at shaft and seal
Oil leakage due to broken oil seal or O-ring.
Replace the broken oil seal or O-ring
with new one. At this time, be careful
not to damage the lip of the oil seal.
Drain piping is clogged with foreign matter
or the like and oil seal is broken and oil
leaks. (Oil seal pressure withstand : Normally
0.098MPa {1 kgf/c
㎡
}
Remove the clogging of the drain
piping to avoid pressure exceeding the
normal 0.098MPa 1kgf/c
㎡ and replace
the oil seal with new one.
At this time, be careful sufficiently not
to damage the lip when inserting the oil
seal.