Service Manual

HYDROSTATIC DRIVE SYSTEM
6-31Fixed Deck Mid-Size Service Manual
6
16. Bleed the hydraulic system. Refer to “Bleeding the
Hydraulic System” following.
Fig 817 PICT-6826a
15. Fill the reservoir with 15W-50 synthetic engine oil as
specifi ed. Note that there are fi ll level lines inside of
the reservoir (Fig. 817).
Bleeding the System
Due to the effects air has on effi ciency in hydrostatic
drive applications, it is critical that air is purged from the
system.
These bleeding procedures should be implemented any-
time the hydrostatic system has been opened to facilitate
maintenance or if the reservoir has been run empty.
Air creates ineffi ciency because it has compression and
expansion rates that are higher than that of oil.
Entrained air in the oil may cause the following symp-
toms:
1. Noisy operation
2. Lack of power or drive after short-term operation
3. High operation temperature and excessive
expansion of oil.
Before starting, make sure the reservoir is at the proper
hydraulic oil level. If it is not, fi ll to the proper level.
The following procedures should be performed with the
vehicle drive wheels off the ground and then repeated
under normal operating conditions.
WARNING:
POTENTIAL FOR SERIOUS INJURY
Certain procedures require the vehicle engine to
be operated and the vehicle to be raised off of the
ground. To prevent possible injury to the servicing
technician and/or bystanders, ensure the vehicle is
properly secured.
1. Raise the rear of the machine so the wheels are off
the ground. Support the machine with jack stands.
2. Open the bypass valves and start the engine.
3. Slowly move the directional control in both forward
and reverse directions (5 to 6 times). As air is purged
from the unit, the hydraulic oil level will drop.
4. Stop the engine and check the hydraulic oil level.
Add hydraulic oil as required.
5. Close the bypass valves.
6. Start the engine and slowly move the directional
control in both forward and reverse directions (5 to 6
times).
7. Stop the engine and check the hydraulic oil level.
Add hydraulic oil as required.
8. It may be necessary to repeat steps 1 through 7 until
all the air is completely purged from the system.
When the wheels move both forward and reverse at
normal speed, bleeding is complete.