Ford 4000 power steering issue

[DenB216]

I have a 72 Ford 4000 tractor with a 3-cylinder gas. It has the later style power steering setup with a power steering pump and and the control valve and cylinder inside of the steering box. The steering shaft seal was leaking out the column so I took the box apart and replaced the seal and all the seals inside the box. I never took the cylinder out or did anything with the rings. Just replaced all the o-rings and gaskets. I put everything back together and checked tolerances and all the shims are within specs. Now the problem I have is that once you start turning the steering wheel with it running it will turn by itself all the way to the lock. It doesn't matter which way you go. It does the same thing turning left or right. You can stop it with your hand with reasonably little effort. Sitting there running it won't turn by itself you have to turn the steering wheel. It does seem like it takes a little bit of effort to get it moving but once you do it turns all by itself all the way to lock. Nothing has changed except for taking the box part and putting it back together. And it worked fine before, it just leaked. It doesn't feel like anything's binding or catching. With the tractor off I can turn it all the way either way with no drag or binding. I've had the box apart five times now checking everything, cleaning it all out and trying to figure out what the problem is. So far I've not been able to change anything. I'm also not entirely sure how the fluid is valved to turn one way or the other. There are no check valves or moving pieces, just a center spool valve with ports. Hopefully somebody here has experience with this type of box and can give me some direction. I am at a loss.

 

[DenB216]

Here are some pics of the steering box so you can see what type it is.

 

[Bern]

See link below. Is this the box you're working on? Because a late-model 4000 could have 2 different boxes depending on which front axle you have.

If that's the box you're working on, it sounds like something happened to the torsion bar inside the control valve. The torsion bar is responsible for centering the control valve when you release the steering wheel. If it really is broken, that part is not serviced separately.

The torsion bar is #23 in the image below.

Intergral PS Box

 

[DenB216]

Yes that is the box I have. That makes sense. Is there a way to know if it is twisted or distorted? I know it isn't snapped.

 

[Bern]

If you grab the input shaft with one hand, and twist the splines with the other, it should snap back to center each time you let go of the splines, on either side of center. You can get a sense of the internal movement by looking in the area of reference #19 in the picture.

 

[DenB216]

Ok I will try that. As it sits right now it is stuck all the way to one side. Not centered in the notch at all.

 

[Bern]

Either the torsion bar is broken, or else some contamination got in there and it's sticking.