Toro Groundsmaster 220-D Service Manual page 114

Charge Pressure Test
Using a low pressure gauge,
0 – 1000 psi (0 – 6895 kPa)
1. Engage the parking brake and block the front wheels
to prevent movement of the machine. Lower the cutting
deck or implement to the floor and turn the engine OFF.
2. Raise and support the seat.
CAUTION
Before opening hydraulic system, operate all
hydraulic controls to relieve system pressure
and avoid injury from pressurized hydraulic oil.
3. Thoroughly clean the area around the pipe plug lo-
cated on the top of the transmission between the charge
check valves (Fig. 11). Remove plug from the transmis-
sion.
4. Connect a 0 to 1000 PSI (0 to 6895 kPa) hydraulic
pressure gauge to the transmission opening. Use only
clean, hydraulic fittings.
5. Start engine and move the throttle to SLOW so that
the engine idles. Use a tachometer to verify that the en-
gine is running at 1700 + 50 rpm. The engine must idle
at this speed to provide sufficient charge pump flow and
pressure to lubricate the internal parts of the transmis-
sion. Check for any hydraulic leakage from test connec-
tions and correct before proceeding with test.
6. Allow engine to run for approximately 5 minutes so
the hydraulic oil reaches normal operating temperature.
7. Increase the engine speed to the FULL throttle set-
ting and use a tachometer to verify that the engine is run-
ning at 3200 + 50 RPM.
8. Observe the pressure measurement on the pressure
gauge. The pressure reading should be 70 to 150 psi
(453 to 1034 kPa). Record test results.
NOTE: A higher reading may be obtained due to the
back pressure in the system. This is acceptable.
9. If the pressure is below 70 psi (453 kPa), adjust the
charge relief valve in the transmission by adding the re-
quired amount of shims from the shim pack (see Charge
Relief Valve Service in the Repairs section of this chap-
ter).
NOTE: For every 0.010 in. (0.254 mm) of shim thick-
ness, there is an approximate 2 PSI (50 kPa) change in
charge relief pressure.
Groundsmaster 220–D
10.Perform a dynamic charge pressure test to identify
possible hydrostat (pump or motor) problems as follows:
A. With pressure gauge still connected, sit in the op-
erator seat, start engine and press the traction pedal
to forward.
B. While machine is moving straight ahead on level
ground (no turning or deck lifting), monitor the pres-
sure reading on the pressure guage. Record test re-
sults.
C. The pressure should drop no more than 15%
from initial test reading (Step 8 above). A pressure
drop of more than 15% may indicate a traction circuit
leak (e.g. check valve not seating, worn or damaged
hydrostat).
11. If adding shims to the relief valve does not increase
pressure or if charge pressure drops more than 15% in
dynamic test, inspect the condition of the charge pump
gerotor and internal housing (See Charge Pump Ser-
vice in the Repairs section of this chapter).
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 minimum charge pressure could be due to the
fact that the charge pump is having to direct all of its flow
to the main traction circuit (piston pump and motor).
When this occurs, charge pressure may not increase to
the 70 to 150 psi (453 to 1034 kPa) pressure necessary
to open the charge relief valve; therefore, no oil can flow
to the steering and implement circuit.
12.Disconnect pressure gauge from the transmission.
Install pipe plug back in the transmission. Check hy-
draulic oil level in reservoir (front axle).
FRONT
Page 4 – 16 Rev. H
PIPE
PLUG
Figure 11
Testing