Troubleshooting Malfunctions (Cont)
Table 2-3. Troubleshooting (Cont)
Test or Inspection
MATERIAL HANDLING CRANE (M977, M985, M984E1)
Always support crane when disconnecting lines from cylinders when crane is not
in transport position. Check valves may be bad and allow crane to fall, causing
injury or death to personnel.
A common cause of crane malfunction is contaminated oil. Seals and packings
frequently break down in very hard use, and the small pieces of seals and packings
can travel through hydraulic lines into control valves, slowing or completely
blocking oil flow.
When troubleshooting the M977, M985, and M984E1 material handling cranes, refer
to foldout sheets, 3, 4, and 5 of Hydraulic Schematics, Wiring Diagrams, and Crane
M977 material handling crane is usually illustrated in this section. Location of
valves on cylinders, swing and hoist systems is very similar on M977, M985, and
M984E1 material handling cranes. Only important differences are illustrated.
CRANE WILL NOT OPERATE MANUALLY OR WITH REMOTE CONTROL.
(M984E1) Operate retrieval system (TM 9-2320-279-10).
If retrieval system works, (the pump, relief valve and oil filter are good), repair
crane controls (para 17-28.2 or 17-28.3).
If retrieval system does not work, go to Step 2.