Go Bottom2004 John Deere JD 790 hydraulic problem
 | tpike35
Join Date: Aug 2004 Posts: 9 greer sc 
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2007-07-18 143839
2004 John Deere 790 w/419 loader and #7 backhoe ..just turn 200 hrs .One week after backhoe was removed 3ph just drop when I was doing some loader work . 3ph was working fine earler that week (scraping the driveway). This tractor is keep out of the weather ... all service has been done by me inclunding 50 hr ...this tractor was bought new in July 2004 ,backhoe w/powerbeyound was added last year I've had the backhoe off twiced makeing sure that lines were clean and cliped together each time ...I changed hyd fluid w/filter and clean the screen (even thought it didn't need it ) hyd fluid is on the full mark...Loader, power steering and backhoe all work fine .... speed /drop valve is open and no bent hyd lines under or on tractor. I've looked at both bypass valves for trash(system,rockshaft relief)I pulled the rockshaft unit off to look inside for something wrong everything looked fine John Deere dealer was not much help only bring in and we will look at it said that it sounds like the rock shaft valve, about $1000.00 to replaces If that is the case I can order parts to rebuild it myself for under $100.00... any help would be appreated ...
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| jd110_1963
Join Date: Feb 2002 Posts: 87 westminster, md
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2007-07-19 143881
I assume you have looked at all of the linkages? If the rockshaft just dropped while you weren't using it, I would suspect a broken or disconnected piece of linkage. I believe there is a feedback rod that connects to the left rockshaft arm. I would look there first. ....
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| tpike35
Join Date: Aug 2004 Posts: 9 greer sc
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2007-07-20 143894
Thanks JD110 for your reply Yes I have looked at all the linkaged and it's all in good working order I guess that I'm just going to rebuild the rockshaft valve and replace all seals,o rings and inspecting the seats and springs ,It seemes to me thats all it can be when the loader,powersteering and backhoe all work fine ..They all run off the same pump and system .... I can order the parts for about $20.00 when JD want's $550.00 for the valve...It will be monday before I can order the parts and about 2 weeks getting them so in the meantime if you know something eles that I could have overlooked please let me know tpke35 ....
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| tpike35
Join Date: Aug 2004 Posts: 9 greer sc
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2007-07-20 143895
The tractor has a hose that loops on the power beyound. Which I have inspected and seems to be working fine ... the loader,backhoe and power steering are working right .After alot of inspecting of the overload,rockshaft and main relief valves and hyd lines on the tractor .I pulled the rockshaft housing (thought something might have came loose inside it) everything looked good inside it .... (going by the parts and tec manuals) I did however notice the main spool in the rockshaft valve was not touching the feedbackarm ( not sure if that is right) and the pistion was all the way back also... when I would move the leaver only the feedbach arm would move not touching the spool later on when I went to put it back on( hours later) the feedback arm was touching the spool , pushing it in and out when I would move the control arm , after puting it on and starting up the tractor it sounded like the main spool was pulled right back in so it could not touch the feedback arm I hope this infor will help... ....
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