Depends, if your trying to lower the carriage and its going down slowly check the velocity fuse (safety protection device that is activated when the lift hose bursts or is cut off to slow down the free fall of the mast). This unit came with multiple options for masts but from the diagrams it should be located where the main lift line from the control valve is connected to the mast.
If its drifting down with no input from the control lever it can only be a couple things, a bypassing lift cylinder, a problem with the lift section of the control valve (bypassing spool or load holding device, not centering) or an external hydraulic leak.
To figure out if its a cylinder issue or a valve issue its best to install a ball valve inline on the lift hose in between the mast and control valve, lift the mast and close the ball valve.
If the mast stops drifting down you have a problem with your control valve. If it is still drifting down when closed you have an issue with one of your cylinders.
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