Century 612 wheel lift issues

[Matt Nugent]

We have a 1997 century 612 top kick wrecker. We just acquired it. When we operate wheel lift from ground it would lift a truck to max lift but if we had it only A few inches off ground then go to lift again,hydraulics will not lift. Drop it  to ground then it will go up to max again. We did have a pump input seal leak,which we replaced pump ,but it did it before also. That is why they sold it I believe. My question is ,do you think it’s leaking internally

in cylinder?previous owner had also replaced control valves  as they say. The cylinder that tucks wheel lift up stalls out and also the tilt or lift cylinder also. (Not sure of the terms for each,sorry)or are there relief valves in question somewhere. Thank you

[mooresbp]

You need to check pressures from pump and at control valves and cylinders.

[Matt Nugent]

Would you tee gauge in to the line powering cylinder back up or the opposite side to see if pressure is bleeding by?

[mooresbp]

Start with cylinder out first

[RIGGIO TOWING]

Have you checked the wear pads on the tower that the wheel lift slides up into? I had a Vulcan that would bind if you lifted from one height. If you start below it would power through the binding height but slowly. Just figured I’d mention it.