# 790 loader lift isssue



## joshc (Aug 16, 2010)

Recently, I developed an issue where I am not able to raise the loader at any RPM's higher than idle. The tilt works just fine regardless. My thoughts are that I have a leaking in a seal/o-ring in the hydraulic control valve. I think rebuilding it is over my skill level. I called a local, reputable hydraulic shop about rebuilding it. They can do it, but he said some of the newer tractors have to have the pressure set on the control valve and they don't have a way to do that. Any idea is that's what mine would need?


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## BigT (Sep 15, 2014)

Howdy Josh,
Sometimes a quick connect becomes disconnected, even though it looks connected. Take the pressure off the system and disconnect/reconnect all of the QC's. 

If that doesn't work, try switching the lift and curl circuit hose lines at the quick connects to see if the problem moves from lift to curl. If you've now lost curl, then the problem is in the control valve. If lift is still a problem, its in the QC's, loader lines, or cylinders.


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## joshc (Aug 16, 2010)

Thanks T. I was going to try that, before I started to disassemble it all (switching QC) but I talked myself out of it. The reason was that if I had an issue with a QC, then it would have had to have been both of the lift QC. To have two fail at the exact same time seems very strange. I had another guy tell me to check the hoses to see if one had failed internally and thus creating a check valve. Same issue, I would have had to have had two hoses fail at the same time. Otherwise, one side would want to lift.

I should have added that, when the issue happens, I have to idle down, drop the loader a little and then I can lift again at idle. If I lift and curl at the same time, I have no issues with RPM.


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## jd110 (Nov 23, 2015)

Sounds like a faulty quick connect coupler to me that is flow checking at higher flow rates. I would change out both male and both female couplers on lift circuit. If the springs behind the poppets become weak, it allows this to happen.


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## joshc (Aug 16, 2010)

jd110 said:


> Sounds like a faulty quick connect coupler to me that is flow checking at higher flow rates. I would change out both male and both female couplers on lift circuit. If the springs behind the poppets become weak, it allows this to happen.


Both of them for the lift would have to fail, correct?


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## pogobill (Jan 31, 2012)

Not necessarily. The plumbing of the hydraulics should go through 2 quick connects (One Set) that then split to feed both lift cylinders. Same with the Curl function. The plumbing is interconnected for each bucket cylinder as well. If one quick connect is not functioning, it would affect both cylinders in the said system. If you've ever blown a bucket curl hose, you'll have noticed that the bucket will roll down as the oil shoots out the single hose... one cylinder will not try and keep the bucket up. I have a well stained pair of coveralls to attest to this theory!
Try what has been suggested. It will give you invaluable information on where to look for the issue, and to make sure the quick connects are in fact clean and connected properly may just solve your problem.


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## John Liebermann (Sep 17, 2018)

So what is happening? This an interesting issue.


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