Gradall 534D-10 Service Manual - Manual (Page 75)

Reason for Charge Pressure Check
To ensure proper park brake operation, charge pressure needs to be at proper specification. Since temperature
can affect results, make certain to test system with warm oil (minimum 100°F). Control pressure is modified
charge pressure. If charge pressure is low, control pressure may be low and machine speed reduced. Thus, drive
performance is adversely affected by low charge pressure.
Install a low pressure gauge (1,000 PSI), hose and adapter on the charge pump test port. It locates near the
front inside of the hydraulic reservoir. NOTE! Before starting, make sure the gauge can be observed in the
operator’s cab and apply the park brake. Start the engine and run at low idle (800-900 RPM). The gauge
should read approximately 380 PSI. At full throttle (2500-2700 RPM), the gauge should read a maximum of
480 psi and never less than 380 PSI.
See Figure 9.
Throughout test operation, charge pressure should not drop below 380 PSI and should move toward
480 PSI as RPM rises, regardless of how many functions are being operated simultaneously.
The charge pump relief (located at the left side of the main drive pump) adjusts as necessary. To adjust the
charge pump relief, loosen the locknut and turn the adjusting screw clockwise to increase charge pressure; turn
counterclockwise to decrease charge pressure. Be sure to note the amount that the relief turns in either direction.
When finished, tighten the locknut and install a blue plastic cap.
To pinpoint the loss of charge pressure, start at the pump. Make sure the machine is in 4WD when testing rear
motors. Remove the hose from the G port (charge pump output port) on the pump, install a low pressure gauge
(1,000 PSI) on the fitting and plug the hose. Check the charge pressure again and observe the gauge. If the
charge pressure comes back to specifications, the loss of pressure is in one of the auxiliary valves. These valves
include the 2WD/4WD valve, traction lock valve, park brake solenoid valve and the joystick. Isolate each of
these valves to check for the loss of charge pressure.
See Figure 10.
Another test to determine the loss of charge pressure is to cap off lines to the drive motors. Reinstall hoses
from previous test. Install low pressure gauge (1,000 PSI) on the charge pressure test port. Check each motor
separately. Start at the left rear motor. Remove the hoses to the motor at the tubes and plug with ORS #12
plugs (P/N 8471-4002). Cap motor work ports also to prevent dirt from entering the motor with ORS #12 caps
(P/N 8471-4006). Start the machine and observe the gauge for charge pressure. Engage drive forward and
reverse against the park brake and observe gauge for charge pressure simultaneously. Record the findings. If
See Figure 11.
Isolate the front drive motor from the circuit if the rear motors are not defective. To isolate it will require two
blocking plates (P/N 9108-1667). Install these plates between the front drive motor work ports and the drive
hoses. Remove the flange halves and place the blocking plates on the ports and reinstall the hoses and
flanges. Again, start the machine and observe the pressure gauge for charge pressure. If the charge pressure
recovers, the motor is defective. To confirm, check charge pressure with drive against the park brake. Charge
pressure should remain at 380 PSI.
See Figure 11A.
The charge pump efficiency also needs to be checked if the previous tests prove inconclusive. Check charge
pump flow out of T1 port on the side of the pump.
(See Figure 12). At 850 RPM, there should be 4 GPM.
At 2500 RPM, there should be 12 GPM of flow. Disconnect run tee and plug. Measure charge pump flow out
of fitting against above specification. The flow readings are checked at 480 psi. If the test is positive on flow,
proceed to the next step.
To check internal leakage of the main pump, block off ports A and B at the main pump. If drive motors have
already been isolated, continue testing. Install two high pressure (10,000 PSI) gauges, hoses and adapters in drive
pump ports MA and MB. Start machine and operate at low idle. If the pump is good, pressure at MA and MB test
ports should read 380 PSI. Adjust relief valve to see if pressure responds. Engage forward drive with park brake set,
raise engine speed to full throttle and record drive pressure and charge pressure. Repeat this procedure for reverse.
Drive pressure should be 6300 PSI in each direction. Charge pressure should remain at 380 PSI and rise to
approximately 480 PSI near full throttle. If charge pressure is not achieved, main pump is leaking internally.
See Figure 12.
NOTE! NOTE! NOTE! NOTE! NOTE!
Do not stall pump for more than 15 seconds each time.
V. Charge Pressure
Form No. 29633 3/97
10
NOTE! NOTE! NOTE! NOTE! NOTE!
charge pressure recovers, the motor is defective.If charge pressure does not recover, repeat test for right rear motor.