3 point hydraulic won't lift properly

Lawnranger · Jul 23, 2019

Just checking to see if anyone has any other ideas, so here is the problem: My JD 3120 3 point will lift as long as it is in the lifting mode, but when you stop and hold position or go all the way up, the hitch jerks up and down. It powers up to the last position then the hydraulics turn off, it drifts down and then the pump engages and it raises again. Worse with more weight. I was lightly grading ( 2 inches at a time) a load of gravel into some horse stalls when it started. I was using a box blade with no scarifiers.

I read every post I could find on here about similar problems and have checked everything. Fluid is good, loader works fine, hydro works fine, steering works fine. I can lock out the 3 point with the rate of drop valve and it will hold. If I leave it open then the hitch will drift down even with no load. I pulled the relief valve under the seat and it looks fine. I cannot depress the ball bearing and the o-rings are intact, so I am assuming it is good. I also pulled the screens in the power beyond circuit. One at the back of the seat and one at the fitting where it goes back into the transmission. I didn't pull the main filter, as I serviced it about 100 or so hours ago, and because all the other functions are not affected I assume it wouldn't be an issue. There was a small amount of debris in the first screen so I cleaned it out and back flushed it with some brake clean. After I dried it off and put it back in the problem was still there. I also checked the feedback rod and it is intact and seems to be set correctly.

I put the backhoe on and it functions fine. With that said I think if I had a hydraulic issue the backhoe wouldn't function correctly. I believe the power beyond circuit bypasses the three point hitch when you use the backhoe. If this circuit is functioning it would only stand to reason my rockshaft piston is bad. Unless I am missing something else?

I read on one of the other posts on here about JD having an issue with water getting into the rockshaft. My dealer said there were no tech bulletins on the 3120 three point that he could find. I did notice some corrosion around a bolt under a plastic cap under the seat area. I am the original owner of this machine and it has very rarely stayed outside, almost always garaged. I do use it to snowblow and plow, so it does get covered with snow. I have also changed the fluid a few times over the years and have never noticed it being cloudy. It looks clean and clear now as well.

The tractor has just over 1200 hours on it. Any ideas? Thank you all for taking the time to read my post. I always learn a lot on this site and appreciate the time the members put in to make it what it is. Hoping I am missing something easy to fix..........not sure if I can take on the rockshaft piston.

Agvg · Jul 24, 2019

Leaking valve or leaking pipe between valve and drop valve, it holds when you close it then the lift cylinder is fine.

oosik · Jul 24, 2019

MANY years ago my new Ford 1700 had a spell of jerking while raising/lowering the 3-point. I have NO idea what the cause was. I cycled it full up/full down with a rear blade attached. After doing this for about 40 times - it just quit jerking and never did it again. My guess - air trapped somewhere.

I would guess that Agvg has hit upon the cause. Hydraulics are somewhat like a "black art" to me.

Lawnranger · Jul 24, 2019

Agvg said:
Leaking valve or leaking pipe between valve and drop valve, it holds when you close it then the lift cylinder is fine.

Thank you. Makes sense when you say it like that. I don't have any leaks externally, so I reason my lift valve is the culprit. Or the relief valve and although I can't move it by hand, maybe the spring is still bad.

Lawnranger · Jul 29, 2020

Just an update in case anyone else searches this problem. Sorry it took so long for me to update it. In the end it was my three point hitch pilot valve. I followed all of the advice posted here and advice from my dealer. In summary it was as follows, the 3 point hitch would jerk up and down with any weight on it:
1) No weight, no issue.
2) Add weight and close the rate of drop valve, no movement and no drop overnight. Means the rockshaft piston is good.
3) Checked and cleaned one way filters in the power beyond circuit, just in case one was plugged and cavitated the system.
4) Hooked up power beyond circuit, (backhoe or wood splitter) no problem with operation. Ruled out pumps and main circuit as culprit, now must be the 3 point circuit but not the rockshaft.
5) Checked adjustment on the 3 point, theaded rod with stop nut on the left side. (From the dealer, raise it all the way up and you should be able to lift it another inch by hand), adjusted properly.
6) Took out pilot valve, left hand side inside housing below the seat. Found very small piece of green painted metal inside one of the valvel seats,
removed it and cleaned the valve. John Deere said this valve was not rebuildable, but I replaced all the O rings and reinstalled it. The jerking was gone, but now it sounded like it was always in bypass mode when holding weight up. If I turned it off, the 3 point would drift down within an hour unless the rate of drop valve was closed. As someone else pointed out in this thread, the parts are machine fit so most likely it was leaking by the port I found the debris in.
7) Ordered and replaced the valve, new O rings again, new filters and fluid,(again) and problem solved.

I never located anything to indicate the orgin of the debris, but I suspect it was either brake material, or possible differential from using the rear lock er. It was small enough to get by the inline screen filter.

Back in operation, hope it helps the next member who might have an issue.