JLG 400CRT ANSI Service Manual - Manual (Page 49)

SECTION 3 - TROUBLESHOOTING
3121111 – JLG Lift – 3-7
Table 3-3. Hydraulic System Troubleshooting
TROUBLE PROBABLE CAUSE REMEDY
Hydraulic pump noisy
Air entering system through broken line or fitting Repair or replace line or fitting
Air bubbles in oil Replenish oil as required
Faulty pump coupler Replace coupler
Defective pump bearing Repair or replace pump
Oil filter(s) dirty Clean and/or replace filter(s) as necessary
Pump cavitating (Vacuum in pump due to oil star-
vation
Restricted suction line Clean, repair, or replace line
OIl in reserve low Replenish oil to proper level
Restricted reservoir air vent Clean vent
Oil viscosity to high Drain system and replace with recommended oil
(Refer to hydraulic oils)
Leak in suction line or manifold Repair or replace line or manifold as necessary
System overheating
Oil viscosity too high Drain system and replace with recommended oil
(Refer to hydraulic oils)
Restricted or blocked hydraulic line Repair or replace line
Machine overloaded Check weight in platform
Main relief valve set too high Reset valve as required
Hydraulic system oil low Replenish oil as necessary
Pump not delivering oil
Restricted suction line Clean repair or replace line
Air entering system through broken line or fitting
(suction side) Replace or repair line or fitting
Oil level too low Replenish oil to proper level
Plugged strainer in tank Clean strainer
Pump coupling defective Replace pump coupling
Broken pump drive shaft Repair or replace pump
System pressure too low
Main relief valve set too low Reset valve as required
Main relief valve stuck in open position Clean, repair or replace valve (Check system oil for
contamination)
Hydraulic pump not functioning properly Repair or replace pump
Leak in component, line or fitting Repair or replace component, line or fitting
Scored valve spool; Scored cylinder Replace valve; Replace cylinder
System(s) operate erratically
Sticking or binding valve spools, piston rod, etc Clean, repair or replace components as required
Hydraulic oil not a t optimum operating tempera-
ture Allow oil sufficient time to warm up
Pump drive slipping Repair or replace drive