Go BottomBackhoe spool valves stuck leaking - HELP
 | Norm
Join Date: Posts: 1 
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2001-05-05 27783
I went to attach my JD 7 backhoe to my 755 today. Everything started out fine, then as I was raising and leveling the backhoe, suddenly the hydraulics sounded like there was a valve stuck open and there was oil leaking out of the spool valve assembly. I stopped the engine and found one of the valves, the right stabilizer to be specific, was fully extended and when I pulled it back to center (requiring a bit of a push) more oil leaked out from the underside (side of the valve assembly opposite the levers). The engine was still off at this point. I would appreciate any input from you out there with more experience with hydraulics than I have. Is this caused by a failed relief valve? If so, how do I go about replacing it? Thanks.
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| Roger L.
Join Date: Jun 1999 Posts: 0
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2001-05-05 27788
I don't know that particular set up, but maybe some general info will help. Off hand it doesn't sound like a failed relief valve. It just sounds like one or more of the O-ring seals in the spool valve gave way. This happens sometime for no reason at all. You can take the spool valve apart and replace them, although getting the O-ring+spool back into it's cylindrical housing is a difficult without hurting the O-ring. The trick is to compress the ring with some flexible shimstock and a hose clamp.....same type of tool as is sometimes used to get a piston and rings into a bore - if you don't use the finger and screwdriver trick.
Relief valves almost always fail "open" (low pressure all the time) rather than "closed" (hydraulic bomb!). They are designed that way. A relief valve that stuck in the closed position could be dangerous.
Keep in mind that I am just guessing. It could be lots of other things. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley 
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2001-05-06 27797
It would be good to have some more information. Were the stabilizer extended and the control valve stuck before the hoe was mounted, or did it extend after the hoe was connected? Was the relief valve sound present during the entire time the tractor engine was running, and was the sound just 'suddenly noticed?' From the description, it seems like the hoe was connected with the stabilizer spool closed, but the 3ph was used during this time for 'raising and leveling.' I'm curious how the hoe is plumbed. My hoe connects ahead of the 3ph, so if any control valve is operated, the 3ph won't lift. If the relief valve sound wasn't present when the hoe was first connected, did it happen when the 3ph was used? Finally, was the amount of oil leaked consistent with a seeping fitting or more like something broken? In the situation, I think I'd verify that the hoe connections to the tractor hydraulics were correct. Input from a pressure line, and output to a return line. I'd also want to see if the stabilizer control valve operates freely without pressure to the hoe. If the amount of leaked oil seems like seepage from fittings, I'd tighten them and perhaps use some liquid hydraulic fitting sealant. ....
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| Jim Reichard
Join Date: Posts: 1
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2001-05-06 27799
Looking at the manual for the # 7 backhoe they show a cap on the bottom of the valve. Under this cap is the return spring and a "O" ring. I'm wondering if you lost or damaged this cap and lost your return spring and O ring. there is also a posibility that the spring retainer could have come loose in the cap that would cause it to jam and if you tried to move it .it would put pressure on the cap causing it to leak.
JIM ....
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| Norm
Join Date: Posts: 1
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2001-05-06 27800
Let me try to answer each of you questions. First of all, it is not a 3ph BH - it is a subframe. When I speak of raising and leveling, I am referring to lifting the entire unit up for mounting - hydraulics connected and using the stabilizers and boom to position the unit. There is no way to misconnect the hydraulics - one hose in, one out with opposite genders so they can't be confused. The sound was not present from the beginning of the mounting operation - it was working and sounding correctly as a began. After a couple of minutes the sound occurred and I noticed that the valve had been extended. The amount of oil leaking was *definitely* a 'something broken' and not just weeping. Once the pressure was stopped, and the valved returned to its normal position (as I said, taking a bit of force and squeezing more oil out the bottom) it then operated freely with no sign of hanging up. Having done this, the valves at that end of the gang make a sort of 'squishing' sound when you move them through their range. ....
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| Norm
Join Date: Posts: 1
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2001-05-06 27801
Jim - the caps are all still there - nothing visibly wrong at the valve gang. Once the oil pressure is relieved, there is no obvious problem with the way the valve moves through its range. ....
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| Roger L.
Join Date: Jun 1999 Posts: 0
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2001-05-06 27810
I'm sticking with the internal O-ring theory. Either way, it sounds like it is time to take the offending spool valve apart and fix it. Or just replace it if the stabilizers use a separate and independent dual valve. If it is a portion of a 6-valve gang, a reasonable and cheaper alternative might be to block off the ports on the bad spool and add an outboard dual spool valve to work the stabilizers. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2001-05-07 27836
Seem pretty clear now, and I'm sorry to agree. It's better when something can be straightened out without a repair bill. I might be tempted to try it again to see if the valve now works. Guess there's always the chance of something like a 'displaced' o-ring that might reseat. However, even if it did, I'd have little confidence in it and would keep wondering when it was going to fail again. I have a tough time living with equipment I don't trust. ....
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| Norm
Join Date: Posts: 1
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2001-05-07 27839
Thanks for all the help - any additional thoughts will also be most welcome. I will be pricing out the parts to replace the o-rings and seals today. It looks like I have to do alot of un-plumbing (is that a word??) as well as dealing with corrosion around the hose connections to the cylinders so I will price out a set of hoses as well since it is going to be all apart. It's an old unit I purchased used, so it just might be time for a full overhaul. ....
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| Jim Reichard
Join Date: Posts: 1
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2001-05-07 27868
If it intrests you I will be putting a # 7 backhoe parts manual and a technical manual on e bay this week. the parts manual is 185 pages and the tech is about 70 pages. I also have a 70 -70A loader parts book and a 790 parts manual.
THANKS
JIM ....
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| Norm
Join Date: Posts: 1
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2001-05-08 27879
What are you asking for the #7 manuals? ....
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| Jim Reichard
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2001-05-09 27954
I have the starting bid on the manuals at $10.00 each.I included the link to the tech manual. to get to the parts manual look at sellers other actions .it will show you the other manuals I have up for bids.
THANK YOU!
JIM ....
Link:
Click Here
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| Norm
Join Date: Posts: 1
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2001-07-07 29867
I just wanted to follow up and thank everyone for their help. The problem was found to be a blown seal on the bottom of the spool, just as had been described. It's an old bh (1987) which was very well used when I got it so I decided to take the opportunity to overhaul the whole thing. I cleaned up the whole valve assembly and replaced all of the o-rings. I replaced all of the hoses. I broke down the whole bh, degreased, scraped rust and painted. It is all now back together, working fine, no leaks. Thanks again for all of the help. By the way, I got the hoses from www.hydraulichosefittings.com. They were incredibly helpful and the prices were seriously lower than anything I could have gotten locally. The only problem was that the crimps where larger than original equipment which nearly didn't fit on the top row of the valve. Changing the angle of the fittings gave me just enough clearance to get them connected. This is not a reflection on the Co., rather my inexperience with different configurations. I would definitely buy from them again - just make sure that the fittings I choose will fit in the required space. ....
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| Roger L.
Join Date: Jun 1999 Posts: 0
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2001-07-07 29868
Congratulations on getting it all done and back together! Glad that the problem turned out to be what we all thought. Did you have any problem getting the spool valves with their new O rings to slide back into the bores? Sometimes the fit is so close that the sliding parts tend to snag or rotate the O rings. Thanks for the hydraulic hose site. I'll definitely put that into my group of good web sites. That sure could be the way that small businesses are run in the future. ....
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| Norm
Join Date: Posts: 1
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2001-07-07 29869
Roger - no problems what so ever reassembling the valves. The backing washers for the o-rings where bent into cups - which is why the o-ring blew in the first place. There was so much of a cup that the o-ring just popped out. thanks again. ....
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| Richard Harburn
Join Date: Posts: 1
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2001-07-10 29967
One additional comment. I don't know what your valves look like but I frequently rebuild a bank of 5 spool valves with spacer blocks between the valve bodies and an inlet and outlet section. There are three threaded rods (used as tie rods) that pass end to end thru the entire assembly and have a lock washer and nut on each end. Because of the O rings and mylar spacers that my assembly uses, I have to be very careful to torque the whole assembly to specifications. Even bought another torque wrench because I didn't have one that would work for inch pounds of torque. Just something for you to consider. ....
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