1949 Allis Chalmers B - 3 Point Hitch Fabrication

This tractor came with parts of a crude hitch. It kind of appears to be a 3 point setup but parts are missing so I don't know what is actually from Allis Chalmers. This first photo is of the finished project.

I'll try to describe the parts I have to work with. There is a solid cross bar (rockshaft) 1-1/4" in diameter behind the seat, with two arms welded to it. One end of the bar is roughly cut with an acetylene torch and the other end is the mill-sheared end. It is hard to believe that Allis Chalmers would make something so poorly finished but there are parts of the bar and mounts that look factory made. Hanging off the rockshaft are two vertical lift arms. They look to be factory made but it's anyone's guess which factory made them. The curved drawbar down between the two tires on the tractor has two 1/2" thick "tabs" welded to it that are what I'm going to use as the anchors for the draft arms (red bars in the photo below). I bought the Ford 8N draft arms from a fellow tractor club member.

I bought two 7/8" link pins off Amazon, drilled 7/8" holes in the two tabs (that was fun, using an ancient Milwaukee Wrist Wrecker 3000 1/2" drill motor), and mounted the link pins.

The next step was to remove the top rockshaft that was bent, and attempt to straighten it. Of course to get the rockshaft out, I had to remove the seat back.

I used my Harbor Freight 25 ton press and it seems to have done the job fairly well. It was difficult to see how straight I got the bar because of the various things welded to the bar.

It's not perfect but is much better than it was.

Here is another photo of the top assembly.

Next I made some bushings for the (unfortunately non-adjustable) leveling/lift arms. I made them from bronze so they would wear instead of the lift arm castings.

OD of the bushings was slightly less than an inch to fit the lift arm bores and the ID was 5/8".

The photo below shows where the bushings go in the bottom holes of the lift arms.

The only thing left to make is a top link. The mounting point on the rockshaft is very strange, so I can't just use a standard top link. I ended up modifying an old top link I had laying around that had had a hard life.

I cut two 5/16" pieces of flat bar and drilled a 5/8" hole through each.

Below shows a mock-up of the top link with the two pieces of bar stock clamped in place.

Here is the finished product. Yes, it hangs quite a ways out the back. If the length becomes a problem, I may need to shorten things up. All in all though it works well.

One thing I learned about this tractor's lift cylinder is that it is called a "displacement" cylinder. A normal double acting hydraulic cylinder has a rod that extends out, and the end of the rod inside the cylinder has a piston with seals. Hydraulic fluid presses on the the full diameter of the piston to extend (and retract) the cylinder. With a displacement cylinder, there is no internal piston on the end of the rod. Instead, the one and only seal is at the end of the cylinder where the rod exits the cylinder. When pressurized hydraulic fluid enters the cylinder, it acts on the rod's diameter, since the only area that is exposed to outside ambient pressure is the diameter of the rod. This depiction below shows the two types of cylinders.

Below is a video I put together of the build process.