Boom won't stop on it's own

[Scotty Brown]

Hey everyone, in my constant effort to fix the leaks on my old telehandler, I've run into an issue where the boom and fork tilt won't stop moving when I release the handle. It will stop if operating down, but not going up and if I tap the handle the other direction, it stops. This is a 1999 Terex SS1048. The main control valve was leaking so we took it apart and replaced the O-rings. This is a 3 part control valve with the top section controlling the boom in/out, middle controlling the tilt and the lower controlling the boom up/down. My thinking is that I have something, like an old O-ring piece, stuck in a port between the middle and bottom sections. But, before I start pulling it apart again, I wondered what others think. Is there a possibility that it's something else altogether. Everything worked great before taking it apart. Thanks!

 

[Vetech63]

You need to determine what part of the system is faulting. Do you have a joystick with hydraulic pilot hoses?

 

[Scotty Brown]

You need to determine what part of the system is faulting. Do you have a joystick with hydraulic pilot hoses?

I do. We took the main valve assembly apart again (impatient) and found that one of the O rings was deformed. I replaced it, very carefully, and it fixed the problem, mostly. The boom up/down will now stop when I let off on the joystick, but the fork tilt still continues to move, albeit very slowly. Slight movement of the joystick in the opposite direction and it too stops. The tilt is activated by a button on top of the joystick and I confirmed that the relay is working correctly. So, I think I'm convinced that the issue is in the hydraulics and probably the main valve assembly. Now, what to do about it, I have no idea.