i bought a trojan 1900 wheel loader when i got it the bucket cylinder was leaking oil so i took it to this hydraulic shop and they ended up making a new tube & rod when i installed the cylinder i notice the control valve was missing a piece that the dealer doesnt make any more so i bought a used valve from the dealer and when i installed it now the cylinder is bypassing(when i lift it up it does down by itself) what can be the cause the cylinder or the valve?
Drifting of the cylinder could be the valve or the cylinder. One way to test for bypassing in the cylinder would be to disconnect the hose hooked to the end of the cylinder opposite the one the ram comes out. Then have a good cap able to take the full pressure of the hydraulic system to cap off the hose and another to cap off the port on the cylinder. Like I said these have to be able to withstand the full pressure of the system not just some plastic caps to keep dirt out. Now if you have this cylinder capped run machine and operate the control to put pressure to the end of the cylinder the rod is connected to, rod should move in at least a short amount. If instead the rod starts coming out it would mean oil has bypassed the piston seals and is now working on the piston to push it in the wrong direction.