JD 310A Backhoe Hydraulic Problem

[Jason_E]

Hello! Back to the site again, hoping you fine folks can lend your brains.

While running my '81 JD310A backhoe the other day the controls suddenly became jerky (cavitation?), then the right-side stabilizer (passenger side in a car) suddenly extended down to the bottom of the cycle. Tried other controls, and loader suddenly raised up to max height. When trying to lower the loader, the valve wouldn't depress but it felt normal when trying to raise it. Same on the stabilizer, they felt like they were bottomed out. I shut the machine down to check for any leaks or obvious problems, none.

Next day I switched the two hoses on the stabilizer so it would lift up so I could move the machine to my garage. The loader moved up again to max height on its own, the stabilizer moved all the way up. Moved the machine with no issues with steering or drive, though I was in 2nd low gear and only 1000 RPMs, basically idled my way home. The engine is not laboring to lift the loader or stabilizer, when they got to the end of their cycle the RPMs returned to normal. Usually when the backhoe is sitting overnight or a couple days with the stabilizers up, they'll drop to the ground. I don't normally park that way of course. It took a week for the stabilizer to fall to the ground, definitely not how it normally operates. It took several days for the loader bucket to come down as well.

After the pressure was off the loader bucket for a couple days, I tried raising the bucket while the machine was off. Still stuck, so I tried to lower the bucket and the valve felt normal in that direction. The I tried raising it again and the valve worked and felt normal. Did not have the same result with the stabilizer, no movement of the valve when pushing away from me as if I'm lowering it. Used a jack to raise the stabilizer a bit to relieve pressure thinking that would loosen the valve but it had no effect and is still stuck today. All these tests were done on a cold machine that was off. Firing it up caused the loader and stabilizer to lift again.

Easy tests first. I drained the oil and replaced the two hydraulic filters, the oil and filters look fine. Also pulled the sump screen and it was clean. Found some pieces of metal in the hydraulic filter bowl (not the transmission one), they look like pieces of a washer or something, doesn't appear to be spring steel. They're about 1/16" in diameter, ~2mm, a bit flattened, not a completely round cross-section. They're quite chewed up and may have been moving through the hydraulic system a while as none of the pieces are sharp.

Opened the relief valve and found that the "plug", part #AT26171, had the shaft snapped off and the valve was loose. Ordering a new plug, spring, valve and o-ring so that should fix the relief valve, assuming it was broken by the pieces of metal. I have not yet refilled the oil since I need to repair this valve first.

And now for the questions.

Does the stabilizer/loader issue sound like a result of the failed relief valve? I don't know what the symptoms of a failed relief valve would be.

Any idea what those metal pieces are?

Thanks for any help you can offer. I have the service manual, owners manual and parts catalog for this machine but no hydraulic testing tools. Lots of big wrenches and sockets.

 

[Tx Jim]

Welcome to YT
Your 310A has closed center hyd's. Do you understand the differences between closed & open center hyd's?

Hyd cylinder rod extending/retracting at their own will is normally caused from failed control valve or valve control handle not returning to
neutral position. If control valve is leaching internally between spool & housing the only solution is replacement of complete valve assembly.

Hyd filter relief valve is designed to open in cold weather when oil is thicker then close after oil warms up. If this filter relief valve is
stuck open then that lowers amount of oil available for frt hyd pump therefore slowing hyd function reaction times of BH & FEL.

 

[Jason_E]

Thanks for the welcome to the forum Jim. I've posted here a few times over the years since I purchased the backhoe 15 years or so ago, couldn't recover my pword and made a new account (old account name was "Jason E" instead of "Jason_E").

You asked if I know the difference between open- and closed-center hydraulics. I have a rudimentary understanding of the differences, hopefully enough knowledge to carry on a conversation. I can follow flow control logic easily enough.

I'm ordering the parts today, I'd hoped there would be some guesses regarding the metal parts in the hydraulic system filter as acquiring parts is a monumental and expensive endeavor here in rural Canada. I'm hopeful that the relief valve replacement and hydraulic oil/filters replacement will fix the problem, though the mystery metal is a concern. Thanks again for your help, will post a response when I have additional information and I welcome any additional assistance from you and the community.

 

[Jason_E]

An update on this. I was unable to source relief valve parts so I fabricated my own successfully. Removed the stabilizer valve assembly, the spool had a piece of the metal I mentioned in OP stuck in one of the openings. I was able to remove it.

I attempted to remove the valve spool from the body but was unable to unscrew the spool plug on the end of the spool. The service manual says to remove the spool cap (which I did) and then remove the spool. [b:84c22d64c3]Is there something else holding the spool in?[/b:84c22d64c3] I removed the spool cap, then the valve spool screw with the washer, spool spring, spacer, washer, bushing and then an o-ring. The spool plug is the next part inside the valve assembly, it's slotted with a threaded hole in the middle for the valve spool screw. I am unable to unscrew the spool plug, I don't know which way it turns or if I even have to remove it to pull the valve spool out the bottom. The spool does not come out easily and I was concerned about damaging parts in my ignorance.

I reassembled the valve and installed it on the backhoe, put everything back together and refilled new oil and fired it up. Everything is working properly (where did those metal pieces come from!?!). The only issue right now is the stabilizer valve is extremely stiff, I have to smack it with my hand to free it up and can then raise and lower the stabilizer. When I reinstalled the spool screw and spring, I tightened it all the way. [b:84c22d64c3]Did I overtighten? Does this need to be backed off and the spool spring put under specific tension so the valve can return to center properly?[/b:84c22d64c3]

I can post the exploded parts diagram as well as a photo of the mystery metal pieces if this board supports it.