unusal hydraulic setup

Turning my attention to the hydraulics on my 770. Was going to start by draining the fluids but am confused at this setup. I haven't been able to get a hold of my uncle to ask if he remembers why his father had this configuration, perhaps someone on here can help me.

Why would they run a line from the drain to a brass valve that's also connected to the return port, and why would there be a male fitting below? The right side goes to the rear of the tractor in the normal fashion.
Also, fluid that is leaking from the male hydraulic fitting is red, ATF maybe? What's the recommended fluid today for these units, regular hydraulic fluid? Hopefully my uncle returns my call, I'm real curious because I've never seen a setup like this on any other Oliver I've looked at.

rich, i saw your post on the other forum about a 3-point hitch for your 770, i think the Saginaw unit mounts to the axles and i don't think this would be good for the 770.the axle housings are not that hard to break. other 3-point hitches mount where the oliver hitch mounts to the tractor, that's where you should be pulling from, not the axles. I've had a 3-point on my 77 for about 30 years that i got from central tractor, now CT farm and country. they have them for sale and it looks to be the same as the one i have. you can put pins in it for down pressure and will easily lift the rear wheels off the ground, great for post hole diggers, york raking and back blade work. it also works good with a 3-point plow. you can easily pull a 3 bottom plow with no ballast on the tractor, and for plow day you can just drive it on and back it off the trailer. i think but don't know that the wierd plumping on your hyd. may have been for a bucket loader or a one way cylinder. you can remove it and put a plug in the hole, i think, and plumb like the other side. you should have regular hydraulic fluid in the pump. here's a pic. of my hitch and plow. hope this helps, chuck

Thanks for the help Chuck. I hadn't thought of the stress placed on the axle housing from mounting a 3pt hitch. Thankfully others on here think of things I haven't. I can use the drawbar for doing just about everything, main things I'd like a 3pt for is eventually getting a 4 row cultivator and maybe moving round bales, once I get ready to make another go at the farming thing. That looks like a real strong hitch you have on your 77 and looks sharp in the second picture plowing. How does your tractor handle the plow without draft control? What do you do when you need to pull a drawn implement, since you don't have the factory drawbar.

From what I've heard from my uncle, my 770 was used mainly as a field tractor and doesn't appear to have ever had a loader on it. I will be plumbing it like the other side. Advantage of having the hose on the drain hole is when draining the hydraulic fluid it won't make a mess all over the platform, I may keep that short hose on just for that.

rich, i have the original hitch that bolts to the 3-point hitch, as far as plowing i just keep my hand on the hydraulic lever and listen to the tractor and watch the plow and adjust accordingly. a gauge wheel would be nice, but are very hard to find. the tractor handles it very good. chuck

Do you mean you have the original hitch from the tractor and you just swap it with the 3pt when you one or the other? I can see a 3pt plow being real handy and sounds like you have a good sytem worked out until you find a gauge wheel.

Rich, it bolts directly to the 3-point hitch. chuck

I'm gonna have to save that picture because what I think you have there is a quick way to go from a one way to a two way remote cylinder.