Haudraulic oddity that has my local dealer stumpped

[JWR]

Of course if it happens again, KennyV is right. Obstruction still in there.
However, it seems to me we only know about 90% of the relevant facts here, hence the puzzle. A few questions: 1) What is/was the temperature ? 2) Any way water could have gotten into one of the lines ? Is the fluid loss of 3/4 gal a clue ? Here is a wild guess at the sequence you experienced: In the off-season with things apart, an obstruction got in one of the lines somehow. There was some obstruction in a line (maybe an ice plug? Something else?) When you tried initially to open the grapple the obstruction stopped flow and repeatedly stopped it at the same point when the obstruction reached a narrow spot. Then when you started taking connectors apart, movement of the cylinder or cylinders occurred while a connector was off & that would have sucked air in. Inadvertent cylinder/grapple movement [maybe while you were bleeding the lines? With a double acting cylinder when you force fluid out one side it must suck fluid or else air on the other side] could have sucked air into any line having a connector off. You put it all back together. Now you have BOTH an air pocket and an obstruction. First guess is the time that the grapple closed SLOWWWW was because air, not oil, was getting past the obstruction or else the obstruction had partially melted by that time. Or the obstruction had become "less perfect" due to movement. When the break-thru came and you expelled a lot of air, the obstruction either melted or moved to a much different place. Just can't be sure I'm following every step of what was done in which order and what might have been happening when the connectors were off. Too many unknowns to be sure. Interesting !

 

[Logginsteve]

Of course if it happens again, KennyV is right. Obstruction still in there.

Yeah, very likely. Especially if it is the ring. In that case it would no doubt be "tethered" and just looking for another opportunity to cause me frustration. For sure I need to try and figure out which one has the problem and get it fixed. Fortunately that is a lot easier/cheaper to do than moving the whole tractor 45 miles away to get it tinkered with!

However, it seems to me we only know about 90% of the relevant facts here, hence the puzzle.

I'd be surprised if I even know 90% of what's going on with this thing, so thanks for being generous I turned over the situation in my head last night and I think we're both headed down the same track...

A few questions: 1) What is/was the temperature ? 2) Any way water could have gotten into one of the lines ?

Temperature both days was in the 60s. Over the winter we had very mild, by Maine standards, temps but a LOT of free moisture (i.e. rain vs. snow). I'll get to that in a sec.

Is the fluid loss of 3/4 gal a clue ?

Given that I can't find any source of leakage anywhere on the tractor itself, I believe this is a critical part of the equation.

Here is a wild guess at the sequence you experienced: In the off-season with things apart, an obstruction got in one of the lines somehow. There was some obstruction in a line (maybe an ice plug? Something else?) When you tried initially to open the grapple the obstruction stopped flow and repeatedly stopped it at the same point when the obstruction reached a narrow spot. Then when you started taking connectors apart, movement of the cylinder or cylinders occurred while a connector was off & that would have sucked air in. Inadvertent cylinder/grapple movement [maybe while you were bleeding the lines? With a double acting cylinder when you force fluid out one side it must suck fluid or else air on the other side] could have sucked air into any line having a connector off. You put it all back together. Now you have BOTH an air pocket and an obstruction. First guess is the time that the grapple closed SLOWWWW was because air, not oil, was getting past the obstruction or else the obstruction had partially melted by that time. Or the obstruction had become "less perfect" due to movement. When the break-thru came and you expelled a lot of air, the obstruction either melted or moved to a much different place. Just can't be sure I'm following every step of what was done in which order and what might have been happening when the connectors were off. Too many unknowns to be sure. Interesting !

Here are the steps I took and then my theory follows:

Thanks for the follow ups!

The hoses aren't the problem, neither are the couplings. I switched out one set of couplings and no difference. Reversing the hoses produces no difference either. So it's definitely one of the cylinders. I came the the same conclusion that you all have which is something is in there and interfering with the restrictor hole. There are no adjustments on the grappler.

To be clear on a couple of things:

1. Original problem was 100% the same thing every time, no matter how much power I put to the pump or how many times I hit it.

2. Lifting manually the first time, with the house couplers removed, apparently increased the range it was getting stuck at, but otherwise when hooked back up it was same behavior as #1.

3. Lifting manually the second time, but now making sure I went to maximum open position, produced a large burst of air out of the line.

4. Hooked it back up and it now opens to max position at full speed. However, closing seems to be slower than it should be.

My theory is that a seal on one of the cylinders is defective in some way. During last Fall's work I lost small amounts of fluid as a result. Small enough that I didn't notice (i.e. no jet/spray), but large enough over time to deplete 3/4 gallon of fluid. As it sat over the winter moisture got into the cylinder the same way the fluid got out. The dozens of times we had free moisture in the air and then freezing temps hours later caused internal damage to one of the seals. I'm still puzzled about how this caused the exact symptoms I had, but it's the best I can come up with as a layman with limited experience with these things. Usually when something hydraulic of mine fails it's very straight forward.

I think it is quite possible the air was already in there because the fluid drained out over the winter. When I did my initial bleed I left the lines in the fluid and so when I moved it around it did suck the fluid back into the lines. Granted, I wouldn't doubt that I introduced some air into the system, however since I didn't move it all that much the first time and things improved after I don't think I introduced all that much air. But who knows I was focused on getting the thing open, not trying to figure out the finer points of my problem.

In the end, I'm happy that I figured out roughly what is wrong and can pursue a cost effective fix. Next thing I'm going to do is disconnect one of the cylinders from the jaws so that I can figure out which one is causing it to close too slowly. Then I'll switch and look at how the other one goes. I expect one will move correctly in both directions, the other won't and that's the one that needs to be broken into.

Does that sound like I'm on the right track?

Steve

 

[JWR]

Yep, sounds good to me. Time will certainly tell if you need to do anything else. I think an informative test would be to hook the grapple up to some else's tractor or a handy skid steer & see if it acts the same.

 

[Logginsteve]

Yeah, it would be good if I could do that or if I had another attachment for the front circuits (which I don't). Unhooking one cylinder at a time should tell me something!

Steve

 

[rScotty]

In the hydraulic forum a guy had some odd hydraulic happenings on his M59 Kubota when he tried to run his front remote circuit while the auto bucket leveling function was engaged. Cure was to turn off auto leveling and then cycle all the hydraulics.
rScotty