Manitowoc National Crane NBT40 Series, Service Manual

Page: 60 / 220

HYDRAULIC SYSTEM NBT40 SERVICE MANUAL
2-24
Published 8-01-2017 Control # 287-11
Poor hydraulic system
performance (continued)
Valve spools not fully open.
Pilot pressure at valve bonnets should be 0.7 to 2.4
MPa (100 to 350 PSI) so valve has full throw.
Plugged diffuser Remove from tank and clean.
Boom holding valves out of adjustment or
dirty.
Adjust or clean as required.
Hydraulic oil too cold. Warm oil or use less viscous oil.
Line restricted. Check lines; clean and repair as necessary.
Plugged suction strainers. Remove strainers from tank and clean.
Internal valve crack. Replace valve.
Load too heavy. Check Capacity Chart and reduce load.
Oil temperature too high.
Reduce engine RPM or slow cycle time to cool oil.
Add oil cooler option if not equipped.
Turn moves erratic or
loosely (Glide Swing
System)
Loose swing bearing. Torque bearing mounting bolts.
Loose swing gearbox mounting bolts. Torque bolts.
Worn gears or bearing. Replace worn parts or adjust gearbox spacing.
Operator control of lever too erratic. Operate controls smoothly.
Park brake not releasing.
Check pressure in brake release line. Must be 2.1 -
3.4 MPa (300 - 500 PSI).
Dynamic brake not properly applying.
Check dynamic brake pressure. Must modulate
between 0 - 3.4 MPa (0 - 500 PSI).
Turn does not function
(Glide Swing System)
Attempting to swing up too much of incline. Level machine.
Turn circuit relief valves sticking. Clean and check circuit pressure.
Swing bearing drag. Lubricate thoroughly as upper is rotated.
Swing brake on.
Select swing brake control switch on and check
swing brake release pressure at 2.0 - 3.4 MPa(300
- 500 PS).
Swing speed adjustment set too low. Adjust valve on turn motor.
Turn moves erratic or
loosely (Standard system)
Brake not holding properly.
Check for no pressure in brake pilot line when turn
is in neutral.
Replace worn brake parts or shim brake to proper
torque.
Brake releasing at wrong time or erratically.
Bleed air from brake with bleed screw on side of
brake.
Turn does not function
(Standard System)
Attempting to swing up too much of incline. Level machine.
Turn circuit relief valves sticking. Clean and check circuit pressure.
Swing bearing drag. Lubricate thoroughly as rotating boom.
Brake not releasing properly.
Check for 1.4 MPa (200 + PSI) brake pilot pressure.
Clean pilot line or adjust motor counterbalance
valves.
Swing speed adjustment set too low.
Adjust or clean brake for proper release.
Adjust valve on turn motor.
CONDITION POSSIBLE CAUSE POSSIBLE SOLUTION
Reference Only