Lull 944E-42 Service Manual - Manual (Page 132)

Hydraulic System
8-16 944E-42
8.6 HYDRAULIC SYSTEM PUMP
8.6.1 Pump Description
Hydraulic system pressure begins at the pump. Various
factors are involved in creating the relatively high
pressure used in the hydraulic system. Pump rpm,
controlled via a transmission input shaft (and dependent
on engine rpm), the internal pump passageways and the
differential between pump inlet and outlet openings, all
contribute to pressure supplied.
For internal service instructions contact your local
authorized service distributor.
8.6.2 Pump Failure Analysis
The pump is the “heart” of the hydraulic system, and
whenever there is a problem in the system, the pump
often is blamed. However, pump failure is seldom due to
failure of pump components. Pump failure usually
indicates another problem in the hydraulic system.
According to pump manufacturer statistics, 90-95 percent
of pump failures are due to one or more of the following
causes:
• Aeration
• Cavitation
• Contamination
• Excessive Heat
• Over-Pressurization
• Improper Fluid
In the event of pump failure, investigate further to
determine the cause of the problem.
8.6.3 Pump Replacement
a. Pump Removal
1. Park the machine on a firm, level surface, level the
machine, fully retract the boom, raise the boom, place
the transmission control lever in (N) NEUTRAL,
engage the park brake and shut the engine OFF.
2. Place a Do Not Operate Tag on both the ignition key
switch and the steering wheel, stating that the
machine should not be operated.
3. Temporarily block up or support the raised boom.
4. Open the engine cover. Allow the system fluids to
cool.
5. Properly disconnect the batteries.
6. Drain the hydraulic reservoir. Refer to Section 8.5.1,
“Hydraulic Oil Reservoir Draining.”
7. Thoroughly clean the pump (1) and surrounding
area, including all hoses and fittings before
proceeding.
8. Label, disconnect and cap the hydraulic hoses
attached to the pump.
9. Remove the bolts, lockwashers and washers
securing the pump to the transmission. Remove the
o-ring located between the transmission and the
pump. Wipe up any hydraulic oil spillage.
10. Remove the hydraulic fittings from the pump to use
for later installation.
Note: Before removing any fittings from the pump, note
their orientation to ensure correct installation.
Note: DO NOT disassemble the operating pump. The
pump is pre-set from the manufacturer. Any adjustments
or repairs performed by anyone other than an authorized
dealer could void the warranty.
b. Pump Installation
1. Install the fittings on the pump in the same
orientation as noted during removal.
MU7460 1
MU7470
2
4
3