JLG 534D-10 - Manual (Page 106)

Hydrostatic Drive Pump
6.8 534D-9, 534D-10 & 544D
If charge pressure is not achieved, main pump is leaking
internally.
Note: Do Not stall pump for more than 15 seconds each
time.
6.6.6 Control Pressure
For the machine to move at proper engine speed, control
pressure should match engine speed.
Install a low pressure gauge (1,000 psi - 69 bar), hose
and adapter on the drive pump control pressure Ps port
(7). Remove the hose from the port and plug.
Note: Before starting, make sure the gauge can be
observed in the operator’s cab.
Apply park brake, start engine and run at high idle (2400
RPM). With the pump in neutral, the gauge should read
380 psi (26 bar). This reading may vary
+/- 15 psi (1,0 bar).
Use a tachometer to monitor engine speed. Start the
engine and run at 1100 RPM. While watching the
pressure gauge, move the shift lever to the forward
position. The gauge should read 100 psi (6,9 bar). Next
repeat the test for reverse. If the machine does not start
to move at 1100 RPM engine speed in both directions
equally at 100 psi (6,9 bar) control pressure, the stroking
piston needs centered mechanically.
To check this adjustment, install a clean hose between
control ports X1 and X2 (8). They are located on the top
of the drive pump. Remove and plug control hoses from
the top of the drive pump ports X1 and X2. Install two high
pressure (10,000 psi - 689 bar) gauges, hoses and
adapters in the drive pump ports Ma and Mb on the side
of the pump (9). Start the engine and operate at low idle.
Observe the gauges. Pressure at the Ma port must be
equal to the pressure at the Mb port. If the pressure is not
equal, loosen the locknut on the stroking piston
adjustment and turn the adjusting screw to equalize the
pressures. Tighten the locknut to secure the adjustment.
Repeat this procedure with low pressure
(1,000 psi - 69 bar) gauges to fine tune.
If the inching valve and forward/reverse valve work
correctly but adjustment does not produce the desired
pressure change, replace the control pressure (DA)
cartridge located on the left side of the drive pump.
6.6.7 Inching
Loss of control pressure can affect machine speed. Install
a low pressure (1,000 psi - 69 bar) gauge, hose, #6 run
tee and adapter between the hose and Ps port (7) on the
side of the drive pump. Apply the park brake and run the
engine at high idle. The gauge reading should be the
same as in previous control pressure test. Depress the
brake pedal. The control pressure should start to fall after
one-half inch of pedal travel. This pressure should drop
as the pedal travels farther and the service brakes apply.
The controlled linkage (10) length should be
12 1/4” (311 mm) from the centerline of the yoke pins.
The lever arm (11) position on the inching valve should
set 1/8 “(3,2 mm) off the pin as a starting point.
Another check for inching adjustment is to install a high
pressure gauge (10,000 psi - 689 bar), hose and adapter
on the Ma port (9) on the side of the drive pump. With the
park brake on, move the shift lever to the forward
position. At high idle, depress the inching/brake pedal
slowly. When the roller on the pedal touches the brake
valve plunger, the gauge should read 2,300 psi (159 bar)
+/- 100 psi (6,9 bar).
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