Terex T780 - Telescope Circuit

Boom Hoist Circuit
BOOM DRIFTS DOWN
CAUSE REMEDY
Hold valve not seating properly Replace hold valve
Hoist cylinder by-passing See section on “Cylinder Leakage”
BOOM HOIST ONLY - INOPERATIVE OR ERRATIC
CAUSE REMEDY
Boom will drift down Repair or replace hold valve
Boom won’t lower Repair, replace, or backflush hold valve
Boom hoist cylinder binding Repair or replace
Load is too great Consult capacity chart, check RCI.
Piston packings damaged Replace packings
Low oil level Add oil as required
Hose plugged or liner collapsed Replace hose
Air in cylinder Bleed cylinder
BOOM DROPS SLIGHTLY AS RAISE CONTROL IS RELEASED
CAUSE REMEDY
Air in cylinder Bleed cylinder
Boom hoist hold valve free flow check not
seating properly
Replace hold valve
BOOM HOIST AND TELESCOPE INOPERATIVE OR ERRATIC
CAUSE REMEDY
Pump disconnect not engaged Engage pump disconnect
Main relief valve malfunctioning See section on “Relief Valves”
Low oil level Add oil as required.
Rotary manifold leaking internally Reset rotary manifold
Tandem pump faulty See section on “Pumps”
T300-1_T500-1_T780
Troubleshooting
406 P/N 12261-683
REVISED: January 2015