Dynahoe 190-4

[erich boehm]

I performed R&R on left stabilizer cylinder. The cylinder moves the stabilizer down to lift the machine, but will not return it to a raised position. Any advise would be much appreciated.
Thank you.
 

[DGH]

Some machines have lock valves built into the end of the cylinder so you have to have pressure to retract the cylinder. This is a safety feature so the machine does not drop if a hose breaks. There could be something stuck in there or it was not reassembled correctly.
 

[erich boehm]

I have the original service and parts manual, which has a nice exploded view drawing of the check valve group. I verified the correct assembly of the stabilizer thermal relief check valve and still the problem persisted. I then switched the check valve group from left to right and right to left and I still have the same problem of the left side cylinder failing to retract. Thanks for your quick response and advise. EB
 

[DGH]

Ok, There could also be restrictors in the lines from the control valves. Usually located in the outlet of the valves. They are just a disc with a small hole in them. They are there to control the speed of lowering the machine. I have seen bits of rubber from a failed hoes get stuck in them causing your type of problem.
 

[NCWayne]

If it has a lock valve in the line , and the seal on the piston fails it will do exactly what you are talking about. I just repacked an outrigger cylinder on a customers bucket truck that was doing exactly what you are describing, and a bad piston seal was the culprit.

It can go down because there is more surface area on the back side of the piston than the rod side (due to the rod taking up space). As a result of the extra space the fluid going into the cylinder will pressurize it enough to push it down, and displace fluid from the rod end to the tail end. There is just enough pressure differentialgoing that direction to make it move out and displace the fluid past the piston. Going the other way, because of the different size area the pressure has less area on the rod end to act upon vs the tail end, and unfortunately the displacement of fluid, and lack of differential pressure, keeps it from building enough pressure to cause the lock valve to unlock and allow the cylinder to raise.

If you need to get it up you can break the lines loose and use a jack, another machine, etc to put pressure on the cylinder in the up direction. This should unlock the valve and allow the cylinder to rise with the applied pressure, but it will usually drop right back down when the pressure is taken off of it, but at least the cylinder is no longer pressurized and can be removed to be rebuild. Good luck.
 

[Stabilizer]

Could you have a blocked or collapsed hose. You could have a bad check valve as well.
 

[erich boehm]

First and foremost, thank you all for your responses. The reason I removed the piston to begin with, was to have it refitted with new seal, packing, O-rings, back-up O-rings and rod wiper. All the components are brand new. I will try the suggestions that all of you made. Thanks again. EB
 

[erich boehm]

I tried the suggested remedies from all of you, but unfortunatly, no luck. By the way, I neglected to mention that the machine has been sitting with it's left rear quadrant up in the air with an approximate 4" of clearance between the bottom of the tire and the floor. So, I decided to get radical. I jacked up the left rear axle just enough to neutralize the weight exerted on the stabilizer. I disconnected both hydraulic hoses from the cylinder, the check/stop valve and the thermal valve. I then tried to lower the stabilizer very slowly, but it still did not move. The machine still sits there with the left rear tire 4" off the floor. Thanks, EB
 

[DGH]

So, if I understand correctly you took the weight off the cylinder, then disconted the lines took out valves etc then tried to mechanically push the rod back into the cylinder and could not. If that is the case, it would seam that the cylinder is jammed in that position, like something came apart inside and wedged the piston. Correct??
 

[erich boehm]

I tried to push the piston into the cylinder by slowly opening the valve on my jack, which is supporting the left rear part of the machine. Unfortunatly, this did not work. I am now concerned that I may have distorted the cylinder in the process of removing the head nut, which was rusted in place. I had to use a tremendous amount of force to unscrew it. Thanks for your continued advise. EB