Gradall 534B (9020-7317) Service Manual - Manual (Page 89)

The 534B has a conventional front wheel drive, with
power from the engine. It has a torque converter and
transmission with a drive shaft and differential, and
a pair of planetary wheel ends. The rear drive uses
hydraulic oil to turn the motors and planetary hubs
at each rear wheel.
GRADALL LOED MATERIALS HANDLER 534B SYSTEM OPERATION
FRONT & REAR WHEEL DRIVE
The oil supply to the rear drive motors will vary
depending on the position of the gear selection lever.
The purpose of this is to coordinate the speed of the
rear wheels with the speed of the front wheels.
The 534B has a variety of options to control forward
and reverse, speed and power. An inching control
enables the operator to move the carrier slowly when
maneuvering or handling a load.
1. In first gear. A combination of low transmission
gear ratio to the front driving axle is used. The
rear drive uses parallel valving of hydraulics to
rear drive motors.
With the lever in Ist gear position, an electrical
contact is made at the sending unit (H) on the
transmission. The current activates the parallel
solenoid valve (F). This sends pilot oil to one end
cap of the series/parallel valve (C). The plunger
shifts into a parallel hydraulic mode and the
main pump oil is routed to the two drive motors
(D) equally. As the operator presses down on
the accelerator, the engine r.p.m. will increase
and so will the oil flow.
2. In second gear the gear ratios to the front axle are
changed to gain more speed and the hydraulic
valving is changed to series mode.
When the lever is shifted into the 2nd gear
position, an electrical current contact is made (J)
on the transmission. This activates the series
solenoid valve (G) and the opposite end cap of
the series/parallel valve (C) is pressurized. The
plunger shifts and the oil is routed in series to the
two drive motors. The motors turn faster to
match the speed of the front axle drive.
3. In third gear a higher gear ratio is used for
maximum speed in the front axle and the rear
drive is disengaged.
When in 3rd gear the rear wheel drive is not
functioning because the hydraulic drive can’t
keep up with the front wheel drive. Since the Ist
and 2nd gear solenoid valves are not activated,
the series/parallel valve (C) returns to neutral
and the oil in the drive motors simply circulates,
doing nothing. To reduce drag due to pumping a
full charge of rear motor oil, a cavitation valve
opens a direct line from the rear motors to tank.
It allows some of the oil to go to the tank,
therefore reducing the motor oil volume,
therefore reducing the drag.
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