May be some twisting happened.

I used to have this happen on Liberty borg Warner super T 10s w steel cases and mid plates but aluminum tail shafts .

My solution for the problem at the time was an exo skeleton. I could never find the culprit for the problem
But it would happen on the 1/2 shift . Never happened again after the exo skeleton . My drive shaft had plenty of space for movement .
Was the exact same break your Muncie has.

Now that you posted that I might make one for my pro shifted Muncie.

Hello Mitch..

I have now had this exact thing happen to me 2 consecutive times at the track. My car is an original LS6 with M22 that I am tinkering with for participating in Pure Stock events.. You may of seen it at SCR last year.

1st time I just figured it was old aluminum that fatigued. Found another 3978764 Tail housing, Had the entire thing gone thru and installed a billet mid plate while it was apart.. There was no signs of DS impact to the seal or any other witness marks that would indicate an alternate reason for the failure.

So put it back together an took it for about a 8 mile drive (drove perfect), went to the track last night and Same Exact thing happened again on my second pass and right after the 1/8 shifting into 3rd it broke.

Take in mind I am running on F70 polyglas tires with 2.0-2.3 60's. Curious to know if you got a chance to investigate yours any further and found the potential root cause.

Thanks, Dave

The consensus was the drive shaft was not able to handle the rotational rpm and was bowing in the center, like a jump rope and the vibration caused the break. I have a solid motor mount on the left side and a urethane on the right. The trans mount is rubber, to allow for any slight twisting that could occur. Twist isn't the issue here, as the breaks we've experienced are happening behind the trans mount. As a result of the replies here and talking with driveshaft builders, I now have a 3.5" heavy wall aluminum driveshaft that is balanced to 6,500 rpm with solid 1350 u-joints and yokes.
Your driveshaft is a little shorter and you should be able to get a heavier wall steel shaft that still meets the critical rpm rating. Hopefully that is allowed in pure stock. If not, have the stock shaft checked for high speed balance.

Dave, I don't know of you have the 27 or 32 spline Muncie. I've been told that the tail housing on the 32 spline transmissions was weak. I have one that I bought with a busted tail housing. When I tried to find a replacement I was told that this was common. I replaced mine with one from AutoGear. They are much stronger that the originals.

Thanks Mitch, Great info and I will be looking into that.. Its a new driveshaft and have over 20 passes on the car prior with no issues.. Something must of changed in the geometry and will be going over it all with a fine tooth comb this time.

Besides checking over all the geometry, u-joints, and adding a left side steel mount.. I will be in the process of sourcing an AutoGear tail housing. Thanks!

So this was the aftermath…. Finally got one of my best 60 ft’s and the car was on its way to run its best pass ever..

Wow, that was going to be a good pass.