Test No. 4: Charge Pump Flow And Implement Relief Pressure - Toro Groundsmaster 300 Series Service Manual

TEST NO. 4: Charge Pump Flow and Implement Relief Pressure (Fig. 11)
Using a hydraulic tester with flow meter
1. Engage the parking brake and block the front wheels
to prevent movement of the machine. Lower the cutting
unit or implement to the floor and turn the engine OFF.
2. Raise and support the seat or remove the seat and
seat mounting plate.
3. Put a drain pan below the transmission. Disconnect
the hydraulic hose from the charge pump outlet (pres-
sure) fitting on the transmission.
4. Connect the inlet hose of the tester to the fitting on
the transmission. Connect the tester outlet hose to the
hose that was disconnected in step 3.
IMPORTANT: Make sure that the oil flow indicator
arrow on the flow gauge is showing that the oil will
flow through the tester from the pump to the steer-
ing valve.
5. Make sure that the tester load valve is fully open
(counterclockwise). Start the engine and allow it to run
for approximately 5 minutes so that the hydraulic oil
reaches normal operating temperature.
6. Increase the engine speed to the FULL throttle setting
and use a tachometer to verify that the engine is running
at 3200 ± 50 rpm.
7. While watching the flow and pressure gauges, slowly
close the flow control valve (load valve) until the flow
gauge reads 1.0 GPM.
8. If the pressure is below 700 psi or 1.0 GPM could not
be achieved, adjust the implement relief valve by adding
the required amount of shims from the shim pack.
CAUTION
The implement relief pressure must not ex-
ceed 800 psi.
Testing
If adding shims to the relief valve does not increase the
pressure, inspect the condition of the charge pump
gerotor and internal housing.
If the charge pump is in good condition (no scoring,
scratches, or excessive wear), the general condition of
the transmission's piston pump and piston motor might
be suspected of wear and inefficiency.
A lack of sufficient implement pressure could be due to
the fact that the charge pump is having to direct most of
its flow to the main traction circuit (piston pump and
piston motor). When this occurs, oil pressure may not
increase to the 700 - 800 psi pressure necessary to raise
the heavy implement.
At this point, a traction pressure test could be used to
determine whether the hydrostatic transmission has
excessive piston group leakage and
repaired. (See Traction Pressure Test.)
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needs to be
Figure 11
1. Transmission
2. Tester
3. Load valve
®
Groundsmaster 300 Series