JLG G12-55A Telehandler S/N: 0160069309 Had an issue with this machine where there was a leak coming from what I thought was the seals on the fork compensation cylinder. It's the cylinder located in the center of the boom between the boom lift/lower cylinders. Removed the cylinder and attempted to remove the gland when I noticed that the rod was bent. Sent the cylinder to a remanufacturing facility. Received the cylinder back, reinstalled on the machine and sent back to service. The machine went 800 or so hours without issue until total havoc. The eye broke off the rod, and the rod broken into pieces after it got wedged in the boom. I'm 100% certain that the weld on the reman rod was really poorly made at the eye. I can see the voids and porosity. All that being said I am ignorant to the purpose of this cylinder. The shop manual calls it a compensation cylinder, and I know it is used for the tilt circuit of the attachment. But I don't know why it's needed or what it does in laymen. When the cylinder is repaired or replaced I plan on doing a "Tilt Circuit Port Relief Adjustment" to make sure the pressures are correct. All of the pins and bores and boom and frame look to be in great shape. I am confused on what caused this cylinder to bend in the first place. Any insight is appreciated.
Generally, If its the cylinder I think it is- Telehandlers will have one cylinder mounted with one end/ eye on the frame of the machine, the other eye will be attached to the boom. The hoses are then paired up with the cylinder on the mast, that controls the fork tilt function. So as the boom goes up, the boom and frame movement on this cylinder, flows a equal flow of hydraulic fluid back and forth from both sides of the fork tilt cylinder, which allows the fork tilt cylinder to stay level to the ground. It basically controls the self leveling on the forks. So you could have something wrong on the upper cylinder, so the boom/ frame is pushing this cylinder, and the upper isn't moving. You could have guys using the fork tilt to smash dumpsters or generally being rammy with it, and if the pressure relief isn't working correctly, the fork tilt cylinder is trying to move this cylinder when they are ramming, and there's no where for this cylinder to move to. So it bends the rod. You can also control fork tilt with the lever in the cab, which overrides this cylinder. There could be a problem in that valving, so that when you use hydraulic power to tilt the forks, its not allowing this fluid to travel, i.e. blocking flow, which could also bend the rod. Either way, something is not allowing this cylinder to move the way its supposed to, so if for instance, the operator is moving the boom down, which moves oil in this cylinder, its supposed to tilt the forks up. If something is causing that oil not to flow- the boom movement is going to bend this cylinder. You could even have a crushed hose in the boom.