# JD 850 Hydraulics



## Roosters (May 15, 2017)

I bought a late 70's 850 that would not raise the arm or bucket. After cleaning the fluid it still would not raise. I then bought a new pump on Hoye and rebuilt the rams. It will operate the rams in and out until I put a load on them. It will also lift the 3 point with no load. I'm thinking the pump from Hoye just is not enough. Any help would be much appreciated. Thanks


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## rhino (Jan 9, 2017)

When the tractor is just setting there with engine running at low rpms, does it sound all right or does it sound like its against a load. Try this with it just running push the 3 point hitch lever forward and listen to hear if the engine changes it sound, like it relaxes. Or if there is a remote in the rear make sure that the levers are centered. Hope it helps.:usa:


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## RC Wells (Dec 26, 2008)

The seals on the rockshaft piston must be good or the tractor will dump all its hydraulic pressure back into the sump.


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## Roosters (May 15, 2017)

The motor runs fine with no change when valve is actuated. There just is no pressure to lift


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## RC Wells (Dec 26, 2008)

Check the seals on the rockshaft piston, that is what activates the three point and on these tractors if those seals leak you will have very low hydraulic pressure to the loader. Three point may lift without any weight but stalls with weight, or may just do nothing.


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## Roosters (May 15, 2017)

Any Idea where to get the rockshaft valve seal repair kits?


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## RC Wells (Dec 26, 2008)

John Deere


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## Rock_knocker (Apr 12, 2017)

RC Wells said:


> Check the seals on the rockshaft piston, that is what activates the three point and on these tractors if those seals leak you will have very low hydraulic pressure to the loader. Three point may lift without any weight but stalls with weight, or may just do nothing.


I thought the 3PH was downstream of the loader, but in any case if the 3PH valve is not being operated, then all the fluid should be shunted to the loader and the 3PH does not enter this equation at all.


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## RC Wells (Dec 26, 2008)

Rock Knocker,

It is a design issue with all the Yanmar built tractors, they pressurize the rockshaft gallery then the loader taps into that gallery. Full pressure is delivered to the auxiliary port as long as the three point is not moving upward or the rockshaft piston is leaking back into the sump. 

The same general design is true of all Japanese tractors that do not use an add on priority valve or have a manual flow selector built in. It is likely that design is common because tractors equipped with loaders are not used in their primary market.


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## Roosters (May 15, 2017)

So appreciate your help. Talked with JD service today, he suggested to check the rockshaft relief valve. Since I am new to this i don't want to tear everything apart. You folks sound more confident on the rockshaft piston. Unless anything else I'll try that first.


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## Roosters (May 15, 2017)

*Success!*

I took apart the rockshaft, pulled the gear shift lever, and the other top cover. There was gunk in the case and the rockshaft piston cylinder. New seals, o-rings & gaskets,
and the loader and three point are back in business. Thanks for the help to all!


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## Roosters (May 15, 2017)

So I was a little premature on my results. The bucket and loader work fine but the Rockshaft won't lift with weight on it. Should i now rebuild the relief valve?


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## mph45 (Nov 8, 2008)

I put a HIGH pressure guage with a HIGH pressure tee fitting on my load lines at the spooler valve and I always can tell if I am getting the correct pressure. I had to connect to the BYD (power beyond) connection.


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