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10 U-Type Hydrostatic Unit Service
Testing
TESTING
General
Testing the U-Type Hydrostatic Unit is limited to check-
ing the charge pressure and implement relief pressure.
This is checked at the charge pressure gauge port
(Figure 9).
NOTE: Use a snubber or needle valve between the port
and the gauge to dampen pulsations.
Test Procedure
1. Make certain the tractor engine is off.
2. Remove the seat deck and tunnel assembly. Refer
to sections 14 and 15 for procedures.
3. Locate the charge pressure gauge port (Figure 9).
4. Attach a pressure gauge with a snubber to the
charge pressure gauge port.
5. Turn the PTO off, and engage the parking brake.
Start the tractor engine.
6. Set throttle control to FULL. Check the charge pump
relief pressure. The gauge should read read a mini-
mum of 50 psi.
If the pressure is not within this range, perform the
checks listed in Troubleshooting. If these checks do
not correct the pressure, install a relief valve shim kit
to increase or decrease charge pump pressure (see
appropriate parts book).
Add shim washers (B, Figure 10) to the charge pres-
sure relief valve to increase the pressure. If the pres-
sure is too high, replace the current washers with thin
washers, or remove the washers to decrease the
pressure.
7. Check the implement relief pressure. Set throttle
control to FULL and fully lower the attachment lift.
Once the lift cylinder is completely extended, keep
depressing the pedal. The gauge should read 850-
1000 psi.
If the pressure is not within this range, perform the
checks listed in Troubleshooting. If these checks do
not correct the pressure, install a relief valve shim kit
to increase or decrease charge pump pressure (see
appropriate parts book).
Figure 9. Check Pump Pressure
Figure 10. Relief Valve Shims
A. Implement Relief Valve Shims
B. Charge Pump Relief Valve Shims
A
B
WARNING
The following procedure requires tests to be
performed in close proximity to a moving drive
shaft. Stay clear of the shaft. Do not wear loose
fitting clothes. Keep hands, hair, and clothing
away from the moving shaft.
Add shim washers (A, Figure 10) to the implement
relief valve to increase the pressure. If the pressure
is too high, replace the current washers with thin
washers, or remove the washers to decrease the
pressure.
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