Service Manual User Manual

The Gradall Material Handlers, Models 544 and
534B have unique 4 wheel drive systems. The drive is
a design between independent mechanical front drive
and hydraulic rear drive systems, accomplished
through an electric interface. This guide covers the
hydraulic drive system and the electric interface
between it and the mechanical drive. (Trouble shoot-
ing the mechanical drive proper is not covered.) In
order to trouble shoot one must have basic tools and a
basic understanding of how the drive works:
The front wheels are driven through a powershift
transmission. This transmission is the “master” drive
system. By “master” we mean the hydraulic rear
drive senses what the mechanical drive is doing and
reacts accordingly. The rear drive signal for forward
and reverse is obtained from two microswitches
located under the dash near the transmission control
cable. This signal ultimately drives the spool of the
forward/reverse valve. The sigual for first gear for
the rear drive comes from a pressure switch connected
to the first gear clutch port on the transmission.
Likewise, the second gear signal originates at the
second gear clutch port. Both of these signals control
the series/parallel valve spool, i.e., parallel flow in
first, series flow in second. During third gear opera-
tion the rear drive automatically free wheels, this
means that in third the machine is two wheel drive
which yields a fuel efficient system during long high
speed runs. This free-wheel signal comes from the
third gear transmission clutch pressure port. The
free-wheeling signal actuates the cavitation valve.
NOTE: When roading over two (2) miles the rear
hubs shouid be disengaged.
Inching is accomplished by disconnecting the me-
chanical front wheel drive and powering only with
the rear wheels. When depressing the clutch/brake
pedal, an electrical signal is sent disconnecting the
front drive transmission, further movement of the
clutch/brake pedal varies the flow to the rear drive
through the utilization of the hydraulic controller.
GRADALL
®
MATERIAL HANDLER
TROUBLE SHOOTING FOR
544 & 534B DRIVE SYSTEM
REAR WHEELS DRAG ENGINE DOWN
PROBLEM PROBABLE CAUSE REMEDY
CAVITATION Loose wire at cavitation valve
VALVE NOT or third gear pressure switch............................ Repair
OPERATIONAL
Too much back pressure in pilot
SERIES PARALLEL drainline at series/parallel valve.............................Repair
SHIFTED IN
THIRD GEAR Faulty third gear pressure switch ....................... Replace
Faulty cavitation valve...........................................Check wiring from pressure switch. eck valve.
Faulty series/parallel valve
(broken springs, sticky spool)............................... Check solenoids and wiring. Clean spool.
Replace spring, O-Rings.
CONTROLLER Controller stuck ................................................... Check valve and wiring
ONLY PARTLY
SHIFTED IN FIRST Low pilot pressure ................................................Reset pilot pressure, 350 psi
& SECOND GEAR
Form No. 8360r
1