1978 John Deere 850 Project

wct097 · Dec 4, 2018

So the milky "overfull" fluid looks normal, clean, and at the proper level now. I think that indicates air/foam in the fluid when running. Going to check the o-rings where the hard lines meet the pump, swap the filter, and check the connections. If that doesn't improve things, I'll be looking to replace the pump.

I think I have the 9cc pump. Will try to upgrade to the 11cc model since I have a loader and power steering.

Thaduck · Sep 18, 2019

My Dad gave me his old JD 850. Been sitting a little while. Would you mind sending me the tech manual? It Run hot, then I realized There is steady bubbles in coolant tank even when just starting up. Along with black water sprinkles put exhaust. Hopefully just a leaking head gasket.

beenthere · Sep 18, 2019

Would you mind sending me the tech manual?

Thaduck: :welcome: to TBN

To whom are you addressing that question about the tech manual??

thepumpguysc · Sep 19, 2019

I would imagine, anybody that has 1..

Thaduck · Sep 19, 2019

Thank you! I clicked reply on 1 of the first few post of this thread. Should have clicked “reply with quote”. But yes I would love to have a pdf of JD 850 tech/service manual from anyone.

wsguerin · May 26, 2020

I know this is an ancient thread but what jd110 described, about the rusted snap rings, is exactly how my 850 SCV valve failed. about ten years ago, I managed to fix the one piston (controls the bucket) but sheez, what a dumb design that a $.05 part causes such a drastic failure. I tried to fix it again last year but the snap ring was more like a wire that the "C" clip I used last time and the cap passed right by it. It's a huge pain to take it off the tractor, a real head banging knuckle scraper. Any tips on fixing the snap ring?

RDJD850 · Aug 18, 2020

Is anybody still following this thread? I'm a brand new 850 owner and new to this forum. I'm having the same issues with the SCV. I've been looking everywhere for an AR88090 or an Eaton 30922-DSC. Haven't found anything yet. Waiting on a call back from All States about finding one from a dismantled tractor, but I don't know what condition it would be in. Any suggestions on where to find one. I'm also thinking on buying the interior parts and trying to rebuild it. I've found all of the parts except for a "Cap" AM38628 and washers M46768. Any suggestions on where to look? Under a load, hydraulic oil is leaking out of the top of the two cylinders, which don't have plugs. Under a heavy load, the oil will squirt out. Any suggestions on how to repair this instead of complete replacement of the SCV? I am definitely not a mechanic, but I'm fairly handy.

beenthere · Aug 19, 2020

RD
:welcome: to TBN
Let's hope you can get some help for the problems, and TBN usually can come through.
If you can, get some pics (we like pics) pointing out the problem(s) and focus members attention on the location and parts you mention. Hang in there..

Pics pointing to the problem wsguerin mentions may draw some help too.. The "wire" mentioned might be the part in the hyd. cylinder, but don't know that for sure.
Sometimes descriptions don't help much without a good pic or two.

RDJD850 · Aug 19, 2020

Thanks beenthere. I’ve got a few pics but can’t figure out how to post them from the app. Help?

RDJD850 · Aug 19, 2020

Here are 3 pics. The first is the top of the SCV showing the two open middle cylinders without a plug in the top. The parts diagram shows plugs should be in the top of both. The second pic is a close up of the 2 cylinders showing a hex opening. A hex wrench can be used to tighten or loosen them. The 3rd pic is showing the two loader control levers that are attached to the SCV. You can see that the far right lever extends well beyond where it should stop. I think it blew out about 2 gallons of oil/fluid when I pulled that lever back too far and it stuck in that position. Is the SCV repairable or do I have to find a new one from a salvage yard? The SCV unit is obsolete and I can't find it anywhere, but I haven't called salvage yards yet. I can find all of the internal parts (o-rings, clips, plugs, bushings, etc), but the left side cap is obsolete and the actual pistons are part of the SCV unit (AR88090). Any help or advice would be appreciated!

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