JLG 534D-10 - Manual (Page 107)

6.9 534D-9, 534D-10 & 544D
Hydrostatic Drive Pump
6.6.8 Front Motor Begin Point
The front motor begin point is when the motor begins to
stroke toward minimum displacement.
Without proper adjustment, machine speed on a flat,
smooth surface will not meet specifications. The motor
may not be shifting to a maximum speed position.
Install a digital or high pressure gauge (10,000 psi -
689 bar), hose and adapter on the Mb port (1) on the drive
motor.Adjust the reverse high pressure relief valve (2) to
3,000 psi (207 bar) by loosening the locknut. Install an
adapter, test port, #6 run tee and low pressure gauge
(1,000 psi - 69 bar) into the Ps port (3) on the pump.
(Ps port is the connection for the inching valve hose).
Set the parking brake and choke the tires to prevent
movement of the machine. The machine should be in
2WD.
Shut off machine and remove the plugs from the G port
(4) and M port (5) on the front drive motor. Install test
ports in place of each plug. Attach a digital or high
pressure gauge (10,000 psi - 689 bar) to each test port.
Note: During the next two steps, to prevent excessive
heat in the hydraulic oil and possible damage to
hydraulic components, do not operate for more than 30
seconds at a time.
Start the engine and raise the rpm until the gauge on the
Ps port is reading 240 psi (16,5 bar). Maintain this rpm
and pressure throughout the test. With the pressure on
the Ps port at 240 psi (16,5 bar), the pressure at G port
should read 3,300 psi (227,5 bar). Adjust the “begin” point
screw (6) on the drive motor so that the gauge on the M
port reads approximately 1,650 psi (114 bar).
Note: Begin point screw adjustment is very sensitive.
Note: The pressure at the M port will not be steady. This
is the pressure that shifts the motor to maintain minimum
displacement.
Under normal operating conditions, the 3,000 psi
(307 bar) at the G port required to shift the motor will not
be constant. When this pressure is reached, the motor
shifts. Since the pressure supplied is constant, the motor
will not stay in a partially shifted position. Reset the
reverse high pressure relief valve to 6000 psi (414 bar).
Use procedure in Section 6.6.9, “Drive Pump Pressure,”
to adjust this relief.
Note: Wrench size required: 4 mm allen and
10 mm box.
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