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Chris in IN
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2001-04-30          17413

The link below has pictures of the bent cylinder. If the link works. There are some things I do not understand from the posts above. If the cylinder was hardened why did it not break? It bent alot and does not have a crack of any kind in it. If it was not hardened properly why did it not fail before? I have done alot heaver diging in the past than I was doing when it failed. My dealer service manager says that air in the fluid would not cause the relief valve to fail. Well than what caused it to bend? I do remember one day after using the tractor that the fluid looked milky in the sight glass. A few minuts later it looked fine. With the backhoe on I can not see the sight glass. I will be checking with the dealer tomarrow to see what they have come up with. ....

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Loaders Back Hoes How the he   did this happen
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Chris in IN
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2001-04-27          27306

I went out after supper today to dig out some 4" & smaller tree stumps with my JD4400 & 48 hoe. It was just getting dark and I was about to quit but decided to do one more. I was reaching over and digging behind the stump trying to pull it out. I went to tilt the bucket back, it made a loud squall and stopped. I got off to see what the problem was. I could not believe what I saw. The bucket cylinder shaft is now bent in an L shape. Has this happened to anyone else? I knew I should have gone back to the shop and worked after supper.

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JerryGoucher
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2001-04-27          27309

Yes, Chris,
I have had it happen. I had a hose clamp on the suction side of the hydraulic pump under the tractor behind the loader frame that didn’t fit right. Air was being sucked in and the fluid was aerated. Sense the fluid was aerated, the relief valve wouldn’t work. Know telling what kind of pressure it was running. Had a real chore trying to find the problem. My dealer checked and tried everything. I wound up finding it myself. The simple things are some times the hardest to find.
JerryG
....

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Roger L.
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2001-04-28          27319

Chris, that bent cylinder rod sure does sound familiar. In fact, I remember a thread about two years ago on this board where someone bent a cylinder - I believe it was on a new JD hoe, too. If I remember right, his dealer knew somehow (tech bulletin?) that they were having a problem with some defective cylinder rods and it was replaced for free. You might search the archives or post a question with the words "JD hoe" and "bent cylinder" in the subject and see if the original poster is still around.
I'll have to remember that one on the aerated fluid, I've not heard of it happening before. You are right that sometimes it is the easiest things that are hardest to find. I can remember some real odd ones in my years as a mechanic....things that I stumbled on by accident and never would have found by looking. ....

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Chris in IN
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2001-04-28          27322

Thanks Roger. I found the old posts. I tried to find them last night before I started this thread. I did not enter the right key words. ....

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dsg
Join Date: Jun 1999
Posts: 528 Franklin, Maine
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2001-04-28          27329

Chris, It was me that had that problem. JD did replace it under warranty. I was doing the same thing you were, but I hurd a big BANG (the cylinder hitting the dipper stick) I was sick to my stomach thinking I'd done something stupid, Not so, the JD rep. said some cylinder rods were not Heated prop. in the Factory.
Call them, I did. David ....

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JeffM
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2001-04-30          27374

Chris, sorry to hear about your misfortune. Please let us know how you make out. I was out digging with my 48 yesterday and kept worrying about hearing the "big bang", seeing as how we have the same setup. And Jerry's problem with aeration causing the relief valve not to work makes me wonder if I shouldn't rig up a pressure gauge as described by Roger Loving to give some warning on this type of problem. Would that help? ....

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Roger L.
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2001-04-30          27376

Jeff, If I somehow gave the impression that a pressure gauge would detect aerated fluid then it was a mistaken one. Though I like a pressure gauge and it tells a lot, I do not believe that a pressure gauge would help in gas/fluid mixtures at all. Technically we call these "two phase fluids". The pressure within the bubbles will be the save as the pressure in the surrounding fluid. The only gross exception is in the overall areas where cavitation is taking place. And even there the pressures are equal at any specific microscopic level. It would be the volume of the air bubble which changes....not the pressure relative to the surrounding fluid.
So what bent the cylinder rod? I am not so sure that it had anything to do with the relief valve, which should work just as well with bubbly oil as any other kind. My suspicion is that something caused the cylinder's end restraint to either flex or bend enough so that the load on the cylinder wasn't straight along it's long axis anymore. And that load coupled with questionable heat treat on the cylinder rod caused the cylinder to bend itself.
I had a bucket pin slip its moorings last Fall when I was pulling on a big rock. The cylinder pushed at an angle hard enough to rip the supports loose and tear the bucket almost in half. The cylinder was fine. The relief valve did not trip. In fact, it was easy and noiseless. It also happened at dusk and I wouldn't have noticed if I hadn't seen the outline of the ruined bucket against the sky when I lifted it out of the hole. ....

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JeffM
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2001-04-30          27377

Roger, thanks for the explanation. Your theory as to the bent cylinder sounds plausible, but it is so hard for me to imagine a bucket tearing up like you describe. As to how the cylinder gets to where it is not operating along its long axis: if the bucket end pivot were not lubricated well or if it was binding for some reason, couldn't that cause lateral forces to be generated? And couldn't this contribute to the type of cylinder failure described? ....

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Roger L.
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2001-04-30          27400

I don't think that binding could cause enough off-axis force to bend a rod unless the rod was otherwise weak. What happened with mine is that the pin that pivots the bucket on the end of the dipper boom came adrift. It worked its way sideways and out until only one side (ear) of the bucket was pivoted to the boom. The next time I curled the bucket real hard against that rock the forces on the bucket were trying to force it sideways as well as pivoting on one ear. What happened next was that the seam next to the ear on the bucket gave way and as I continued to apply pressure the tear continued on around about half way to the teeth. This also bent the back of the bucket like a tin can lid as well. This was all because the pivot pin that slid sideways was the one that the bucket rotated on - so the off-axis force was mostly on the bucket. If the pin that slid sideways the other one that connects the cylinder to the bucket, then the bucket could still rotate just fine, but I think that the off-axis force would tend to bend the cylinder.
As I see it, the forces are large enough that mere binding one end of the pin wouldn't do it. All that would happen is that the rotation would stop. It would need to be that the pivot pin is only connected at one end instead of both ends.
If you did not find this, then I think the best explanation is a defective cylinder rod that was too flexible under compression and the rod flexed sideways until it moved enough to provide its own off-axis geometry. This is a very typical failure of a steel rod or any column under compression: it moves sideways until a slightly larger off-axis force causes it to buckle. ....

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JeffM
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2001-05-01          27610

Chris, thanks for the pictures. Sure is scary looking. Looks like soft steel, but potentially you do get soft steel if not hardened properly, right? I try to forget all that strength of materials stuff about steel transformations that I had to learn in engineering school a hundred years ago. ....

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Chris in IN
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2001-05-03          27731

I got my tractor & backhoe back from the dealer today. They covered the cylinder under warranty. I had to try it out tonight, so I dug stumps for 2 hours tonight. I worked it hard, I wanted to be sure it did not happen again. Not a single problem and I think it dug better tonight than it did the night it bent. Thanks for the help. ....

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