3 Point Hydraulics acting funny; L2950

[knightgang]

So my 3 point hydraulics are acting funny. When lifted all the way up with a box blade of the bush hog on them (maybe others but these are the only attachements I have used lately), they bouce and you can feel it in the entire tractor. (Video attached).
https://www.youtube.com/watch?v=9aGsq6V3UWc&feature=youtu.be

When I press on the feedback rod, it seems to lessen the impact, but it still seems to do it slightly. Problem is that my feedback rod almost has not adjustment left unless I make the rod longer with more thread to move the nuts further back.

Also, I am not sure of the fluid level. Both of the sight glasses (on the side of the tranny tunnel and on the rear at the PTO shaft, they have gotten cloudy or painted over by a previous owner. I will remedy this tomorrow, in the meantime, could this be bouncing be due to a low fluid level or a failing hydraulic pump?

Back to the feedback Rod, if I have it adjusted all the way out and need more adjustment, is there a valve that is severely worn and needs to be replaced? If so, how difficult of a task is this?

Any advice or direction at this point is very much appreciated.

Thanks

 

[rbargeron]

When any of my rigs hunt like that it usually cures it to lower the touch lever a bit. Even if you ignore it there is no damage being done by the slight bouncing.

On the fan drive the photos don't show whether the aluminum coupling is partly broken - there's a new one here if you need one. The flexible disk could be temporarily (or permanently) replaced by cutting a round piece of 3/8" or 1/2" reinforced conveyor belt material (cloth-inserted neoprene) and drilling some holes for bolts & washers. Or, there's an OEM part here. Pretty sure you can replace the coupling parts without taking anything else apart or taking the loader off - just raise it up out of the way.

 

[knightgang]

When I got the tractor a few months ago, I had to adjust the feedback rod to get the implements to stay in position. Now, there is no adjustment left in the feedback rod and it bounces at the top, still bounces even at say position 6, just not near as obvious.

It almost seems like the position control valve needs to be rebuilt or replaced.

It seems I can buy a new valve for $520 or buy new poppets and all new springs and prongs for a bit under $400 to rebuild it. I am just not sure if that is needed or a longer feedback rod.


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[rbargeron]

I didn't realize that the valve is never happy. I guess if it were mine I'd test the rod length idea by temporarily extending it. If that doesn't help, take the valve apart, clean & inspect and go from there. Does this tractor have draft control? Does its position have any effect on the hunting?

 

[North Idaho Wolfman]

Before you adjusted the feed back rod, would the implement raise then slowly fall? or did it raise, fall, then lift again, over and over?

If it was either, you need to rebuild the lift cylinder as it's leaking down.

With the feed back rod adjusted to the max, it is simply feeding fluid to the lift the entire time and the reason for the surge is the out of adjustment feed back.

 

[knightgang]

Before you adjusted the feed back rod, would the implement raise then slowly fall? or did it raise, fall, then lift again, over and over?

If it was either, you need to rebuild the lift cylinder as it's leaking down.

With the feed back rod adjusted to the max, it is simply feeding fluid to the lift the entire time and the reason for the surge is the out of adjustment feed back.

Wolfman, before the feedback rod adjustment it would raise then slowly fall. It would not stay in a lifted position unless it was all the way up. If I say, tried to set it at position 6, I could raise it all the way way up, and when I tried to lower it to position 6, it would fall all the way down. The only way I could keep it up was to let it fall to the position then tighten down the lowering speed knob.

Once I adjusted the feedback rod, it would stay in the desired position. Now, you see what it is doing. So, you are saying that the primary lift cylinder for the rear lift arms needs to be rebuilt?

I assume it is about the same as rebuilding any other cylinder, just that it is inside the housing under the seat, correct?

I have the Workshop manual, I will look through it to see if I can determine just how big of a job this is...

Any tips, how-to's or other advice is much appreciated.

 

[North Idaho Wolfman]

I'm not 100% convinced that it's the piston, piston rings, or cylinder wall issue but it sounds like it.
I would go through the valve while I was in there too as it's all in the same place.

Just curios what fluid are you using?
I had a problem with one surging / hunting / jumping when it was using generic universal fluid, changed it to Mystik JT-5 and it quit doing anything bad.

I would say on a scale of 1 (Easy) to 10 (Hard) it's a 2 to 3 job.
hardest part is popping the cover off as they are usually stuck on pretty good.

 

[knightgang]

Had the machine just a couple months. Have not changed the fluid, so not sure what's in it, level has not changed and this just started appearing in the last few weeks.


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[rbargeron]

......The only way I could keep it up was to let it fall to the position then tighten down the lowering speed knob.....

If it holds with the speed valve closed, then the lift cylinder is ok. If it had a bad seal or scored wall, it would bleed down from wherever it was set.

 

[knightgang]

If it holds with the speed valve closed, then the lift cylinder is ok. If it had a bad seal or scored wall, it would bleed down from wherever it was set.

I have not had to do this since I adjusted the feedback rod on the position control. I will have to see if this is still the case.

 

[knightgang]

Okay, it seems that the 3 point lift cylinder is leaking and that is causing the bounce issue. It is getting worse. In fact, I even closed the drop spped valve and the mower still hit the ground in less than 30 second after the tractor was shut off, from the full up position.

Wolfman, what all needs to come apart to have this cylinder repacked? Do I need to pull the 3 Point lift arms off the back, ir is everything under the seat and under the top cover?

I either need to fix this quickly or nurse it for another few weeks.

I assume that once the cylinder is out it is just a matter of having it repacked at any hydraulics shop, correct? Or do I need to go to Kubota for specific piston seals?

Being a 2-3 job in difficulty, about what is the labor time. I am mechanically inclined, but I know that it usually takes a little longer if you have not seen inside at the inner workings before.

 

[knightgang]

I rebuilding the lift cylinder really this simple???

I just thought that the mechanics of a tractor hydraulic system was more complicated than this. What is the manual not telling you?

Should I just get new piston seals form the Kubota dealer, or take the piston to a local hydraulic shop for repacking?

Also, what else should I do while I am in there? Rebuild position control valve?? Or is there really nothing else in there at all or that rarely needs attention?

Thanks.

 

[North Idaho Wolfman]

Sorry for the late response, computer (satellite) went down in a small but sticky wet snow storm last night.

Yes it is that simple.
I would get the seals from Kubota.
You could put new seals in the control valve while you're in there, I would also see about new seals/ O-rings in the speed control too.

 

[knightgang]

You think the poppets in the control valve would be ok and just do the seals, and not the entire rebuild?

Any idea when on an appr labor time?


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[knightgang]

I pulled the top cover of the rear end to take a look at the hydraulic piston. I discovered that the main o-ring was in tact but well worn. The backup ring (The stiff plastic one that wraps around the piston twice) was missing quite a bit of material in that it only went about 2/3 the way around the piston. Now that it has been resealed, I have not had an implement at the house to attach to it, but the arms are no longer falling overnight as they were before. I will know soon if this fixed it for sure or not.

Wolfe and others, thanks for the help.