Probably been asked a trillion times before but what is the best method to repair play at the thread on the bottem of the spindle ?

The simple answer is to drill, tap and insert a helicoil. The difficult part is getting proper alignment with the top hole in the fork. Maybe someone who has done it can chime in.

Seems a rare problem ?

Like the helicoil solution but how do you align properly ?

Here is the tool I made to drill the bottom of the axle to use a Helicoil. Made a bushing to fit the top of the axle, acts as a guide, a drill bit extender and drill bit.

Slide extender through the top, install bushing, install drill bit, tighten set screws and drill.

Works for me.

Mike Bender
Tulsa OK

I wish I could help you but anything I can think of would require a specialized tool. That would be a good thing for someone to engineer and reproduce.

I made a set of tools but I'm not reproducing them. It's one of those tool sets that you use infrequently and the cost would be prohibitive to the average Model T'er. Not only do you have to drill the yoke in line, you have to tap the threads in line as well.

Mike's solution seems to work well and not difficult to make. Thx

One more question:

What size helicoil would I need to buy ?

The heli-coil would be for a 1/2-20 thread and the coil should be 1/2" long. Cut off any extra length that hangs out. You will also need a heli-coil tap for 1/2-20 and will have to pre-drill the hole to be coiled to 33/64 dia. Starting the heli-coil into the hole can be tricky, order extras. There are several installation tools available from cheap to expensive. The cheap ones work O.K. with care and patience.

If I remember correctly, the 1/2 helicoil tap drill is 33/64. The one axle I have installed a helicoil in was worn slightly larger than that. We mounted the axle upside down in a vise and then two of us eyeballed the tap straight and threaded it. It was tricky installing the helicoil, I installed it from the bottom, meaning the tang end was toward the top of the axle. When I went to cut off the tang, the tang and last thread popped out of the hole. I cut off the tang and used a pocket knife to work the end of the helicoil into the tapped hole.

To drill the hole precisely I think you could clamp the axle upside down in a drill press and use a 1/2 inch rod to line it up and then drill it oversize. A drill would follow the old hole, a milling cutter would pick up the exact center. Since I own a drill bit, I would use the drill bit. If the hole is to small for a 1/2 inch rod, use a 15/32 or 7/16 rod and wrap it with shim top and bottom. You might also consider reaming the bottom hole to 1/2 inch to facilitate using the 1/2 inch rod for alignment.

In short, if you "measure twice" and cut once, and don't get in a hurry you can do this without any specialized tooling other than that for the helicoil.