8.5 rear end twisted tubes
 

I twisted the center section on the axletubes on the drag strip. Broke the propshaft aswell.
I see the common fix is to weld the axletubes to the center unit. But this requires special rods and tecnique. Any reason not to drill and tap the tubes with lets say 2,3 or 4 bolts instead?
3/8 bolts of high quality.

A picture.

What is your 60' time?

I would put time in it. Remove find another rear weld tubes and reenforce where arms meet housing.if you use that rear try to find a mandrel to keep tubes aligned. Someone may be able to do the work in the car. Grind old welds ,weld around.

You need to find out what the cast part is made of. If its cast steel, fine. You can weld it with whatever carbon steel rod/wire you want. If its cast iron, you need to use a dissimilar metal rod and the process is quite different. And risky.

Whenever I twisted up a leaf spring 8.5, I used it as an excuse to put in a 12 bolt or 9". You need to put it in a jig to get the tubes straight, then have a good welder take care of it. The time to weld the tubes is before it's twisted up. Once you figure in labor and expenses, cost to repair gets close to a 9" that will accept your current rear brakes. You said you twisted up the driveshaft anyway, so now would be the best time to switch to a rear that's more capable of holding your power level and get the correct length driveshaft for the swap.

But do the tubes automatically need to be twisted and need straigthning when this happens? The internals of the diff turn just fine with no noises. If I pull the housing down again and align it to where it was before, then drill and tap for set screws? Or weld.
The rear end is fresh built with new gears and bearings, but I did not know about this twisting issue. So would hate to throw it away.

At a minimum I'd check the housing in a jig. It may look fine, but could eat bearings or have other issues. Set screws won't be enough, and could potentially cause more alignment issues if/when things shift around again. End of the day, it's your car, and you can do anything you want to it. I just don't want you to put money and time into something that has a good probability of breaking again later. I like 8.5s, but I've wasted money trying to salvage one that would have been better spent elsewhere. The gears, posi, and axles are still good now and can be sold to offset the cost. Bare minimum, I'd get another bare housing, have the tubes welded, and build it with your existing parts.

I would not use set screws or bolts.The torque of the Pontiac engine will destroy it. Take the time and fix it right my 2cts. Those 8.5 are strong,if set up right. I ve run 9" slicks and 3.73- 4.56 gears in them. My 3800 lb 2nd gen will pull front wheels slightly off the ground.the only thing broke was the small bolt holding the crossshaft broke,allowing pin to come out,damaged pinion.I had one bent in my 65 Lemans it ruined tires always hummed. Took me awhile to find it ,axles came in and out ok. Bugger to diagnose.

Get yourself a Moser 12 bolt housing. Put some Caltracs on it. or weld your 8.5 10 bolt axles to center section.

There are plenty of you tube videos on how to weld. It’s a nickel Rod you need and you can buy it on Amazon. It’s not rocket science. You got to heat up the metal with a big torch and control how it cools down. The gap between the tube and housing will suck in the weld so you need to hit it with a few passes.

I'd try to find another 10 bolt 8.5 housing. If gor street occasionally raced. Strictly race I'd blueprint the 8.5. 12 bolts and 9" to me are $$$$.i guess I'm cheap. Another alternative is the older 9.3 Pontiac,olds rears. Depending on your location parts gears posi available. Another 8.5 first choice then have it jigged and welded. Old Pinion head here is the guy to talk too.

I've been 1.51 on my 10 bolt in the TA and the factory 28 splines! Tubes still good. I did upgrade to 30 splines when I dropped back to 3.42s

The 8.5 is more than capable.

Source another housing, forget about any bolting arrangement and weld the tubes.

Chalk it up to experience and move forward.

There should be plenty of housings out there heck even a 10 bolt 90s truck if you can;t find one cut the ends off for bolt ins and weld perches on it. Moser sells mono and multi leaf perches separately.

Not for everybody-
For my Pontiac powered GMC I eliminated all torque on the axle tubes of the '57 Chev rearend by building a torque arm on the center section linked to a frame crossmember. [Think later F-bodies]

Axle fixed. Straightened and welded the tubes. Built a new 3" driveshaft with 1350 joints.
Upgraded to Moser driveshafts aswell.
All good again.