JLG 4394RT Service Manual - Manual (Page 135)

SECTION 4 - HYDRAULICS
3121133 – JLG Lift – 4-11
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.
4.8 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 insure 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 dur-
ing 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.
3. Using light clamping pressure on the ears of the
front cover, secure unit in vise with shaft side down;
remove cap screws (14) and washers (9).
4. Separate rear cover (6) from the body (13). The
static seal (8) may remain either with the body or the
cover. In either case, remove the static seal and dis-
card.
5. Lift out the rear bearing block (2), drive gear (12),
and driven gear (11).
6. Separate body (13) from front cover (5). Dowel pins
(7) and the front static seal (8) may remain with
either the body (13) or the front cover (5). In either
case, remove the static seal and discard.
7. usually the front bearing block (2) will remain in the
body (13), so invert the body and lift out the bearing
block.
8. Invert front cover (5) with shaft seal up. Remove the
shaft seal (1) by prying it out with a large screw-
driver.