12 bolt

Beef'ed up TA's with 1/8" plate both sides. Was also going to add a 1/4x1/4" safety loop, but decided not too. These were welded 360deg and small plates filled in the sides. IMG_1073.jpeg

Have to get back on the cars, got sidetracked for a while.

I plan to do all the machining and posi tuning myself. After that, it is a repeat of last time.
Yeah, the fixture is kind of red-neck, but had seen someone else doing this so went for it. I used a transfer punch that was a tight fit in the original threads to line up the chuck and verify it was straight.

Saw a post on another forum where a guy showed a photo of a boring bar jig he used to cut the case for ring gear clearance. Started making something like that. Here's the main spindle and below is the 0.5" boring bar.IMG_1387.jpeg

I ground the first one by hand and got a bit too thin at one spot for my liking. But, there was a rib there, so probably no issue.
It seems like you're working on an interesting automotive project. I'll do my best to provide assistance. Regarding your issue with the 12-bolt, this is a rather complex matter that requires some in-depth knowledge and experience to address.
Open to any suggestions. This is my second one. Gary jumped in the old thread and gave me some help. Suggestions are welcome. :)

Tom set up the posi and fitted axles on the first for a real fair price, like $250 if I remember right.


It doesn't have many mile, and the TA's have been off a couple of years (ready to go back in). But, it is a 3:73 and I'd like a 4:11 option. :)

I must have over $10k in rear end parts including all my 10 bolt stuff.
Last edited:
Bushings and shaft finished. Had an old set of side yoke roller bearings and installed those. The tricky part will be to set it up perpendicular to the table.

I had some old brass scraps for the bushings. Also got the flange machined in the mill.

This might actually work. 15/32 drill bit works perfectly for the 0.47" boring bar. Now fixturing. I'll slow down the mill, low feed rate, and small cuts. Need to make two tools to measure the radius and advace the cutter.

A bit of progress on this. Made a bracket that bolts to 4 holes for the strut rod bracket. And, that clamps to one right angle. The other right angle clamps to the flange. If my boring bar snaps (wearing a face shield for machining) I will machine a 6 inch dia disk to hold a cutter. That disk would have a hub I could cross bolt to the shaft. Sort of like a lot of fly cutters.

To my surprise, this actually works. I'm making very small cuts each pass. I've got to make a gage that lets me know when I'm at ring gear radius + 0.05".
I missed that you were cutting ring gear clearance. Nice setup, clever solution.
Yeah, copied the idea from a photo at CF. I ground the first case by eye and kept installing my mock up posi case to check clearance. It ended up being thinner that I expect this one to be.
Well, if anyone tries this, use a tool that is more pointed than this rather blunt boring bar. My HF mill needs the bar to be swinging freely before making your cutting pass. Hence the grinding on the center line. Below center line the cut is smooth. Still need to blend it in a bit to get rid of the sharp edge. But, as the walls taper in, not going too deep away from center line is important. IMG_1767.jpeg
Yeah, that has to be slow going. I've never made an interrupted cut that big on cast iron but your cut looks really clean.
Yeah, 5 to 10 thou cuts. Slow going for sure. If I would have had a pointed cutter, the clearance grinding strip would have been narrow.