JLG 340AJ Service Manual - Manual (Page 242)

SECTION 5 - HYDRAULICS
5-84 – JLG Lift – 3121259
Troubleshooting
Table 5-17. Troubleshooting
Low or No Flow From Gear Pump
Item
1. Check oil level in reservoir.
2. Check input spline condition.
3. Check pressure at pump inlet. Recommended inlet
pressure: 0.8 to 3.0 bar absolute. 0.6 Minimum at
cold start.
4. Check condition of gear faces and bearing blocks.
5. Check bushings.
Description
Insufficient oil to supply gear pump.
Input shaft broken or stripped.
Clogged suction filter or inlet screen.
Scored bearing block and gear faces will reduce pump effi-
ciency.
Overpressure of gear pump will cause idler gear bushing to
fail.
Action
Fill reservoir to proper level.
Repair or replace gear pump.
Replace filter or clean suction screen.
Repair or replace gear pump.
Repair or replace gear pump.
Excessive Noise
Item
1. Check oil level in reservoir.
2. Check inlet line for leaks.
3. Check pressure at pump inlet.
Recommended inlet pressure: 0.8 to 3.0 bar absolute. 0.6
Minimum at cold start.
Description
Excessive air will cause cavitation sound.
Excessive air will cause cavitation sound.
Lower than normal inlet pressure causes excessive pump
noise.
Action
Fill reservoir to proper level.
Repair inlet line.
Return inlet pressure to recommended levels.
External Leakage
Item
1. Check for pinched o-rings or backup ring seal.
2. Check pressure seals.
Description
Pinched seal will allow leakage.
Damage to pressure seals is typically caused by reduced
"stack-up" in the pump assembly. This may be due to
under-torqued assembly fasteners, or more commonly is
attributed to excessive wear on the bearing blocks.
Reduced "stack-up" will affect seal efficiency possibly to
the point of seal extrusion.
Action
Replace pinched seal.
Inspect condition of bearing blocks. If they are found to be
worn, repair or replace the pump.
If bearing blocks are not worn, replace pressure seals and
re-torque pump assembly fasteners.