JLG 4394RT Service Manual - Manual (Page 176)

SECTION 4 - HYDRAULICS
4-10 – JLG Lift – 3121249
inlet of the pump during operation in order to verify
that the pump is not being asked to draw an inlet
vacuum higher than it is capable of.
Be certain to fill the pump and/or motor housing with
clean hydraulic fluid prior to start up. Fill the housing by
pouring filtered oil into the upper case drain port.
NOTE: It is highly recommended to use the highest possible
case drain port, this ensures that the housing con-
tains as much oil as possible and offers the greatest
amount of lubrication to the internal components.
In initial start-up conditions, it may be convenient to
fill the housing, just prior to installing the case drain
line. Component, (especially motor), location may be
such that access to the case drain port after installa-
tion is not realistic.
Make certain that the oil being used to fill the compo-
nent housing is as clean as possible. Store the fill
container in such a way as to prevent it from becom-
ing contaminated.
Install a 60 bar (or 1000 psi) pressure gauge in the charge
pressure gauge port in order to monitor the charge pres-
sure during start-up.
It is recommended that the external control input signal,
(electrical connections for EDC), be disconnected at the
pump control until after initial start-up. This will ensure that
the pump remains in its neutral position.
DO NOT START THE ENGINE UNLESS PUMP IS IN THE NEUTRAL
POSITION (0 DEGREES SWASHPLATE ANGLE). TAKE PRECAU-
TIONS TO PREVENT MACHINE MOVEMENT IN CASE PUMP IS
ACTUATED DURING INITIAL START-UP.
"Jog" or slowly rotate the engine until charge pressure
starts to rise. Start the engine and run at the lowest possi-
ble RPM until charge pressure has been established.
Excess air should be bled from the system lines as close
to the motors as possible.
NOTE: With the engine on low idle, "crack", (loosen-don't
remove), the system lines at the motor(s). Continue
to run the engine at low idle and tighten the system
lines as soon as oil is observed to leak from them.
When oil is observed to "leak" at the motor, the line
is full, the air has been purged, and the system
hoses should be retightened to their specified
torque.
Once charge pressure has been established, increase
speed to normal operating RPM. Charge pressure should
be as indicated in the pump model code. If charge pres-
sure is inadequate, shut down and determine the cause
for improper pressure.
INADEQUATE CHARGE PRESSURE WILL AFFECT THE OPERA-
TOR'S ABILITY TO CONTROL THE MACHINE.
Shut down the engine and connect the external control
input signal. Also reconnect the machine function(s), if
disconnected earlier. Start the engine, checking to be cer-
tain the pump remains in neutral. With the engine at nor-
mal operating RPM, slowly check for forward and reverse
machine operation.
Charge pressure may slightly decrease during forward or
reverse operation. Continue to cycle slowly between for-
ward and reverse for at least five minutes.
Shut down engine, remove gauges, and plug ports.
Check reservoir level and add filtered fluid if needed.
The machine is now ready for operation.
4.7 HYDRAULIC GEAR PUMP
Overhaul pump only in a clean, dust free location, using
clean tools and equipment. dirt and grit will damage the
highly machined surfaces and will result in leakage or pre-
mature failure of the pump.
Before beginning disassembly, scribe "match marks" on
the body (13) and covers (5 and 6) to ensure that the
pump will be reassembled in the same manner as it was
shipped from the factory. If the body or rear cover is
replaced during overhaul, scribe a match mark on the new
part in the same location as on the part it replaced.
Pump Disassembly
1. Clean outside of pump with a good grade solvent
and dry thoroughly.
2. On models with a splined drive shaft, proceed to
step 3. On models with a keyed drive shaft, remove
drive key (10) from drive shaft. Using a file or stone,
remove burrs from shaft end of keyway.