Beck TD, Part 53: A Special Transmission Tool

I've been enjoying this project to rebuild an antique Volvo M41 transmission - it has been quite the learning experience. The M41 is an overdrive transmission, and that is a very different beast from the M40 trans that I recently rebuilt. One of the interesting aspects is that the overdrive shift action is done with hydraulics at very high pressure (over 500 PSI), using an oil pump built into the overdrive unit.

Of course, when you're rebuilding, you want to inspect and repair that high-pressure pump, and it turns out it has a part that requires a special tool to remove. It's called the "non-return body" and it's down in the bottom of a hole. This photo is a bit hard to read, but you can see the non-return body at the bottom of the hole, and the part itself is shown in the inset at the top right. It's not a normal hex head. Instead, it is sort of an oval with flat sides:

The official Volvo repair manual calls for a special tool, and it has apparently disappeared off the face of the earth. Even Google doesn't seem to know of it.

However, I found a good video of how to rebuild the unit (link) and it showed a different tool used for the job. Here's a composite of two screens from the video, showing the tool in use (left) and the "business end" of the tool (right):

Of course, I still have no idea where to buy the tool, so I decided to make one of my own. Fortunately, I suppose, the non-return body in my overdrive was very loose and easy to extract - probably because some previous "mechanic" didn't have the tool either. Once out, I could see that the oval was nominally 7/16" wide and 1/2" long.

I started by finding a likely steel rod, and after turning down a bit so it would fit in the hole, I cut off a chunk in my horizontal band saw:

After cleaning up the cut end on the lathe, I mounted the piece in a collet block in the milling machine vise. I carefully centered the spindle over the piece, and installed a 7/16" end mill.

I plunged the end mill to 0.150" depth, and then moved the Y axis to create the oval slot. This photo shows the slot and the piece I hope to fit into it:

Of course, it didn't fit right away because I made the slot exactly the same size as the piece. I proceeded to carefully enlarge the slot in length and width until the non-return valve was a snug fit.

Once that was done, I reversed the workpiece and installed it in my new ER32 Spin Indexer. This is the first real work I've done with it, and cutting a 9/16" hex head was a real joy compared to my previous way with a hex collet block. Quicker, safer, more accurate. I like it!

And here's the finished tool with the non-return valve beside it:

In use, the valve body is installed in the tool, and a 9/16" wrench is used to tighten it in place.

If I was going to do this every day, I would have sourced a steel rod that could be hardened and tempered to make it tough and long-lasting. But I'll be using it once or twice, and without significant torque applied, so this should be just fine. Certainly better than leaving it loose, which is what the last guy did!

Continue on to Part 54....