Backhoe boom rotation cylinder creeping

Drunkwater · Jul 5, 2017

I have a new-to-me 1990 JD 970 with an 8A backhoe on the back. I made a quick intro thread here.

This backhoe has a pair of single-acting cylinders which pull on chains to rotate the boom. The cylinder which rotates the boom left (operator left/tractor right) is leaking down while in operation. I was working on a side-hill this weekend removing a stump, and after rotating 'up' the hill to dump the bucket, the boom would coast back down hill on its own. It would cover 90ｰ of rotation in 10-15 seconds. I also heard a hydraulic flow 'squeeking' sound from below me while rotating in that direction (either the spool or the cylinder). I initially thought it might be a relief valve opening, but could have been a bad check valve or...? It wasn't a metal on metal noise, definitely hydraulic. At no other time would the sound occur except when rotating left.

There was no puddle of fluid on the ground, so I'm assuming the seals on the cylinder are fine? The backhoe was definitely under powered when trying to rotate that direction, as it wouldn't budge the stump once I got it free. It took the full throw of the control lever to get the bucket to rotate over when dumping heaping loads (on the occasions I actually managed to get a full load!)

I'm hoping to get some advice for troubleshooting. The tractor is located at a seasonal residence, so I want to have a plan of attack for my next visit in a few weeks. Cheers!

Sysop · Jul 5, 2017

Best/cost-free troubleshooting method would be, on the valves, switch the hoses for the right and left swing. It will make the controls operate backwards, but it will allow you to narrow down where the issue is through process of elimination.

If the issue changes sides when you swap hoses around, the issue is in the valve. If the issue stays the same with the hoses switched, it is the cylinder.

Just because it isn't leaking out of the system, doesn't mean it isn't leaking internally allowing flow when flow there should be none.

I don't think there is a check valve, but I could be wrong.

chriswheeler · Jul 6, 2017

Sounds like we have the same setup, 970 TLB. ( mine is a 92 ) When I got mine several years ago, I ended up rebuilding both swing cyl. from kits I bought off ebay. Can't remember exactly what I paid, somewhere around $60 per kit. While rebuilding I noticed lots of crud inside the non-pressure side of these. Think the crud killed the cups and seals, rings inside. I cleaned everything up, installed the kits on both sides and replaced the non-pressure hose and added new clamps. What a difference !! I noticed the rings and seals removed were in very poor condition. Yes, my valves up at the sticks do leak some, not enough to matter when I'm using it. When I'm done using it, I do install the boom pin lock and swing pin lock to store it, so it's not a issue for now. I'm sure that at some point those valves are going to need rebuilding, but it's fine for now. I've got about 1500 hours on it, and I'm sure that the hoe was the tool most often used on this machine. Good luck with yours, mine worked out to be a great machine.
Chris

Drunkwater · Jul 6, 2017

Thanks Sysop, that's a good plan to narrow down the issue. Any idea where fluid would go if it's leaking past the internal seals? (for my learning, this is my first foray into hydraulics) I'm assuming that since these are single-acting cylinders, it would pool up on the back side then eventually spit out a breather.

Hi Chris, I think you're right, mine's the '90 TLB, sitting at 2033 hrs right now. Both the boom and swing pin locks go in whenever it's not digging. I'll keep an eye out for the rebuild kits - sounds like a good wintertime project to tinker on. Did you have to do any work on the inside bores of the cylinders? hone or...? Or was it just a matter of replacing the various seals and wipers.

Higher up on the list right now is dealing with a stuck PTO clutch. The prev. owner didn't do much if any PTO work, and sold all his implements a year ago, so the PTO wasn't used much and now the clutch is seized. I need to find a good heavy PTO implement to try and break it free with. I was thinking a wood chipper or big bush hog with lots of rotating mass might do it by aggressively revving up and down.

chriswheeler · Jul 6, 2017

The cylinders were in great shape, just lots of dirt and crud inside on the low pressure side. Didn't need to hone, both had a good bore. Seller said mine was used to maintain irrigation ditches, could be mine got used under water. The low pressure hose on mine had a crack in it, I replaced the hose and clamps. Looked at the pic in your other post, ours are identical except for tires, I have R-1's. Stuck PTO clutch has me scratching my head ?? I don't know what implements you have, but I'd mount a brush hog or a tiller if you have one of these ( something that will apply a load to the PTO ) and engage the lever ( yellow ball behind your left leg ) and see if it powers up the implement. A tip to engage the PTO, let it idle and engage, don't engage above idle speed. If it does spin up, I'd apply a load ( start mowing with a brush hog, start tilling with a tiller, think a tiller might provide a better load ) While under load, fully depress the clutch, see if the PTO disengages. I have never heard of something with a live PTO having a stuck clutch, but that sure could be the case. If you end up buying a brush hog, have confidence that this tractor will power a 6' with ease. I have a 5' and during heavy cutting, no noticeable load on the tractor. I'd sure try to get the PTO to work before splitting to replace the clutch pack. I've split a couple of tractors, this one looks like it could be the hardest yet. Clutch pack is expensive as well. Good luck and enjoy, I sure like mine.
Chris

Drunkwater · Jul 20, 2017

I've got myself a copy of the tech manual (2 pages attached). Anyone know the purpose of the crossover relief on the swing cylinders? I can make sense of the rest I think. The restrictors and check valves on the main spool look like they keep a bit of tension in the chain attached to the cylinder opposite the rotation.

A bit of research says these are used to protect from pressure spikes - is it just because you can get a lot of momentum while swinging the bucket?

I suspect these crossover valves may be the issue, and my initial gut feeling/intuition was a relief valve opening early.

Any help/insight much appreciated!

View attachment 8A backhoe hydraulic schematic.pdf

chriswheeler · Jul 20, 2017

Thanks Drunkwater, I didn't have that diagram. The low pressure side of these should just have air, no hydraulic, no oil. Only way oil gets in is leaking by the seals on the pressure side of the piston. Now that I know that these crossover valves are there, I'd suspect with all of the dirt I removed from mine, that valve could be contaminated as well and needing a clean out at the least. Doesn't look hard to do. Because mine works fine as is, thinking I'll save that for this winter when the snow falls. But it's a sure thing something will need cleaning in that valve with all of the crud I removed from mine. Going to print this diagram and save it, thanks,
Chris

Drunkwater · Jul 21, 2017

Thanks Chris, I think I will take it apart and see what's up. Hopefully there's a bit of crud stuck under the ball or something similar that's easy to fix. Let me know if you need any pages from the backhoe or 970 service manual, I can scan and send them over. I picked up both because not knowing bugs me too much, and I've got limited time to tinker on the machine.

Cheers
John