Gradall 534C-10 (2460-4129) Service Manual - Manual (Page 71)

Reason for Drive Pump Pressure Check
Drive pump pressure determines the drive power of the machine. Low drive pressure will result in less power.
Install a high pressure gauge (10,000 PSI), hose and adapter on the MA port (located at the bottom of the
drive pump). Apply the park brake and put the 2WD/4WD switch in the 2WD position. Move the shift lever to
the forward position and run the engine at full throttle (2500-2700 RPM). The gauge reading should be 6,300
PSI. Adjust the POR valve located on top of the pump as necessary. To adjust this relief valve, loosen the lock-
nut and turn the adjusting screw clockwise to increase pressure and counterclockwise to decrease pressure. Move
the gauge to the MB port of the drive pump to repeat the procedure with the shift lever in the reverse position.
See Figure 20 and Figure 20A.
There are also high pressure/anti-cavitation relief valves on the drive pump. These could influence drive system
pressure with a low setting or missing O-ring. On machines with 6,300 PSI drive pressure, adjust these valves to
6,800 PSI. Normally, these high pressure relief valves do not require checking. However, if there is a drive power
problem and adjustment of the POR valve on the main pump does not change the pressure, these valves may
have to be adjusted. Install a high pressure (10,000 PSI) gauge hose and adapter on MA port on the pump. To
check these high pressure relief valves, raise the setting on the POR valve on the drive pump. Loosen locknut on
POR valve and turn the adjusting screw clockwise one turn to increase pressure. With a high pressure gauge
(10,000 PSI) hose and adapter on MA port, set the park brake, put the shifter in forward and run engine at
full throttle. Adjust the forward high pressure relief to 6,800 PSI. The forward high pressure relief valve is on the
bottom of the pump. Install the high pressure gauge (10,000 PSI), hose and adapter on the MB port and
repeat the procedure for reverse. Adjust the reverse high pressure relief to 6,800 PSI. The reverse high pressure
relief valve locates on top of the pump. Leave high pressure gauge (10,000 PSI) hose and adapter on MB port.
Reset the POR back to original position. With park brake on, put the shifter in reverse and run engine at full
throttle. The pressure should be 6,300 PSI. Adjust POR valve as required.
See Figure 20 and Figure 20A.
The traction lock valve also has two high-pressure/anti-cavitation relief valves. Normally, these require no
adjustment. However, they can adversely affect drive system pressure if, say, they are set too low, or an O-ring
is missing. To check these valves, raise the POR valve pressure setting above 6,800 PSI. Set the forward high
pressure relief valve on the pump to 6,800 PSI. Then lower the forward high pressure relief valve on the traction
lock valve under 6,800 PSI. Turn the valve in 1/8 turn and secure locknut. Repeat the procedure for reverse.
Then reset the POR valve to 6,300 PSI.
See Figure 21.
FIGURE 20
MAIN PUMP ASSEMBLY
(SIDE VIEW)
534C-9 & 534C-10
HYDROLASTIC DRIVE PERFORMANCE CHECKS MANUAL
Form No. 29633 3/97
IX. Drive Pump Pressure
19