Service manual

Rev. A
Groundsmaster 3280--D/3320Hydraulic System Page 5 -- 20
Charge Pressure Test (Using Pressure Gauge)
A charge pressure test should be performed to identify
if a worn or damaged hydrostatic transmission is caus-
ing a hydraulic system problem.
NOTE: Before conducting charge pressure test, deter-
mine counterbalance pressure setting for the machine
(see Traction Unit Operator’s Manual).
1. Make sure hydraulic oil is at normal operating tem-
perature.
2. Park machine on a level surface with the cutting deck
(or implement) lowered and P.T.O. switch off. Make sure
engine is off. Set the parking brake and block the front
wheels to prevent machine movement.
3. Read Precautions For Hydraulic Testing.
CAUTION
Before opening hydraulic system, operate all
hydraulic controls to relieve system pressure
and avoid injury from pressurized hydraulic oil.
4. Thoroughly clean the area around the 1/8 inch pipe
plug located on the top of the transmission between the
two check valves (Figs. 16 and 17). Remove the plug
from the transmission.
5. Connect a 1000 PSI (70 Bar) hydraulic pressure
gauge to the transmission opening.
6. After installing pressure gauge, start engine and run
at idle speed. Check for any hydraulic leakage from test
connections and correct before proceeding with test.
7. Run engine at full speed (3200 +
50 RPM).Usea
tachometer to verify that engine speed is correct.
8. Observe pressure gauge. The pressure reading
should be approximately the same as counterbalance
pressure.
9. Turn off machine. Record test results.
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.
11.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).
If charge pressure drop is more than 15%, inspect the
condition of the charge pump gerotor and internal hous-
ing (See Charge Pump Service in the Sauer--Danfoss
(Sundstrand) 15 Series Service Manual at the end 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.
12.Disconnect pressure gauge from the transmission.
Install pipe plug back in the transmission. Check hy-
draulic oil level in reservoir ( front axle).
Figure 16
2
1. Seat base opening
2. Check valve
3. Pipe plug
1
2
3
Figure 17
FRONT
PIPE
PLUG