Komatsu PC138USLC Operation & Maintenance Manual page 305

MAINTENANCE PROCEDURE
4. Bleeding air from swing motor
(Carry out only if the oil inside the swing motor case has been drained.)
NOTICE
If the air is not bled from the swing motor, the motor bearings may be damaged.
1) Remove cover (4) between the hydraulic tank and the
operator's cab.
2) Run the engine at low idling, loosen mouthpiece (2) at the
motor S port, and check that oil oozes out from mouthpiece
(2) of the motor S port.
NOTICE
Do not operate the swing under any circumstances.
3) If no oil oozes out, stop the engine, remove mouthpiece (2)
from the motor S port, then fill the inside of the motor case
with hydraulic oil.
4) After completing the air bleed operation, tighten mouthpiece (2) of the motor S port.
5) Run the engine at low idle, and slowly swing the upper structure at least 2 times uniformly to the left and right.
5. Bleeding air from travel motor
(only when oil inside travel motor case has been drained)
1) Run the engine at low idle, remove hose (3) from port C,
then when the oil has flowed out, tighten it again.
2) Run the engine at low idle and swing the work equipment
90° to bring it to the side of the track.
3) Jack up the machine until the track is raised slightly from
the ground.Rotate the track under no load for 2 minutes.
Repeat this procedure on both the left and right sides, and
rotate the track equally both forward and in reverse.
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MAINTENANCE