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Old 05-15-2017, 11:51 AM   #1
Roosters
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JD 850 Hydraulics

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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Old 05-15-2017, 12:32 PM   #2
rhino
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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.


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Old 05-15-2017, 05:42 PM   #3
RC Wells
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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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Old 05-15-2017, 08:23 PM   #4
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The motor runs fine with no change when valve is actuated. There just is no pressure to lift
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Old 05-15-2017, 08:38 PM   #5
RC Wells
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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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Old 05-16-2017, 04:35 PM   #6
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Any Idea where to get the rockshaft valve seal repair kits?
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Old 05-16-2017, 07:01 PM   #7
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John Deere
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Old 05-17-2017, 10:22 AM   #8
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Quote:
Originally Posted by RC Wells View Post
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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Old 05-17-2017, 10:38 AM   #9
RC Wells
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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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Old 05-18-2017, 08:12 PM   #10
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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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