Platform (Mast) Won't Stay Elevated; Platform (Mast) Descends Too Slowly - JLG 15MVL Series Service Maintenance Manual

SECTION 6 - TROUBLESHOOTING

Platform (Mast) Won't Stay Elevated

Overview Of Procedure
The following procedure requests that the lift down, dump, and pump internal valves be checked to see if any are stuck
open, it also examines the lift down and dump valve circuits. Also suggests that the lift cylinder packing could be leaking
internally.
Check For These Obvious Conditions First:
• Manual descent valve is closed tight.
STEP
1. Is the lift down valve stuck open?
2. Lift down valves could be open due to incorrect electrical signal.
3. Oil could be passing around the lift cylinder bore packing.

Platform (Mast) Descends Too Slowly

Overview Of Procedure
The following procedure examines the mast some hydraulic components for obstructions and defects.
STEP
1. Check mast slide pads shimmed to tight.
2. Is there an obstruction in the mast?
3. The lift cylinder packing could be too tight in the bore of the cylinder barrel.
4. Check if the lift down valve is opening completely.
5. Is there a restricted hydraulic line (smashed)?
6. Check the flow valve in the cylinder valve block for a restriction, i.e. dirt.
6-42
Table 6-47. Platform (Mast) Won't Stay Elevated.
ACTION
Table 6-48. Platform (Mast) Descends Too Slowly.
ACTION
– JLG Lift –
SPEC YES
— Repair or Clean
Valve
— Check Pump Valve
Electrical Circuit
— Replace or Rebuild
the Lift Cylinder
SPEC YES
— Reshim Mast
— Remove
Obstruction
— Rebuild or Replace
Cylinder
— Clean or Replace
Valve
— Replace Hydraulic
Line
— Clean or Replace
Flow Valve
NO
Go to Step 2
Go to Step 3
—
NO
Go to Step 2
Go to Step 3
Go to Step 4
Go to Step 5
Go to Step6
—
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