3 point lift of 4000 Ford

I have a late '60s 4000 Ford with, what I believe to be, a gear type hydraulic three point lift pump.

My problem started when I added oil to the system. It had been cold, (40s that night and probably only 50's when I added). I noted that the lift was not lifting normally so I began adding oil. The engine was running and I foolishly left the position control lever in the full up position. As I added oil, the arms began to raise and obviously went to the full up position. When I had finished, I lowered the selector but the arms remained stuck in the full up position. By jumping up and down on the arms I got them to fall but now they will not lift a load.

By searching the archives I have noted that I could have stuck safety valve in the lift cylinder or a stuck relief valve in the pump. I also note the impossibly of a blown piston seal.

Are there any other things to look for if I don't see any of these as an obvious answer?

Thanks,

Art.

Thanks for your response.

I am having a difficult time coming to grips with the terminology for tractors. While I have worked with mechanical things all my life, the only tractors that I have worked on have been my own two. I'm not sure what the unloading valve is. I think the valve that you move up and down to raise and lower the lift arms is called, in my manual, the draft control lever or position control lever. Is this correct? There is another lever that is located in the lift cover that the manual calls a selector lever. I have only noticed this having two positions, down and the lift arms fall to their lowest point (below the level that they go to when the position control lever is at it's lowest point), and up, the lift arms seem to normally raise and lower with the control lever. Is this the unloading valve? Should it have a middle position?

Not knowing the correct terms and what everything is suppose to do when it is working properly is really killing me.

Thanks for your help,

Art.

Rod

Thanks for your advice.

I have an Intertec Shop Manual that seems pretty complete. It does include an exploded view of the lift cylinder assembly with the control valve(spool). And it does make reference to a Nuday tool for removal and re installation of the valve bushing. I don't have that tool so initially I will look for the kinds of things that you suggest ( a sticking or stuck valve). Hopefully when I get it apart, it will be easier to make sense of the pictures in the manual.

Now, back again to my lack of understanding about what the features of the hitch are for. I have been using the tractor to mow with a bush hog and to disc fire breaks. When doing either of those activities I normally have the small lever in the up position ( I think, I hope I'm not completely confused about what I was doing) and was able to set the big lever to different heights and have the arms maintain those positions. However, when I went to mow or disc, I just dropped the big lever all the way down and used it like that. There doesn't seem to be any down force from the lift arms. And the implement just rides up and down with the terrain. Is that normal? Am I using it properly?

Art.