I'm experiencing hydraulic cylinder drift on multiple cylinders at the same time. Its primarily the main boom elevation and telescoping, maybe also carriage tilt. It doesn't seem like a check valve thing to me since it started at the same time on both.
Is there a counterbalance valve in the setup? Could be the cause if it's broken or not set right.
I don't know. Right now I'm thinking the control valve connected to that joystick might be involved. That joystick controls both of those functions.
I have a hard time believing that both counterbalance valves went bad at the same time. I think you are on the right track with the joystick. ISZ
Well it appears to be 50% fixed. I got o-ring kits from Web Equipment for the two identical main counterbalance valves, one on the main boom cylinder and one on the extension boom. Had a hydraulic repair place put the kits in for me since there was about a dozen o-rings each. What a pita removing the valve from the main cylinder. After putting them back in, I left it overnight extended and elevated with a half-ton concrete block on the forks. The main boom didn't drop an inch,but the extension boom came down all the way. Now i see that there is another smaller counterbalance valve on the extension boom. On mine it's on a manifold at the rear of the cylinder along with the other valve and hose attachments. The parts diagram shows it out at the other end of the cylinder, prolly why I missed it. Its smaller but there's a kit for it, too. Just have to verify with Web Equipment.
The local repair place repaired the other counterbalance valve for $58 including the o-rings. It only dropped 1 inch overnight, so I'm considering that a complete success, for less than $200.