Muncie tail housing broken
 

What would cause this to break here ?
In 4th gear at 5,500 rpm. Felt a vibration and then heard a bang and trans jumped into neutral. Drove back to the pits and loaded on the trailer. I could only get 1st gear, but it moved under it's own power.
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Mitch, what are you running for motor mounts and transmission mount?

Left is solid, right and trans, urethane. It broke behind the trans mount, where it shouldn't have any stress on it. Pretty sure I'm not strong enough to break it shifting...:grin:

I run solid engine frame mounts and rubber trans mount…..never had an issue. That’s what everyone told me to run. I personally think your current setup is not optimal…..too much flex. But that’s my opinion, take it with a grain of salt.

Kurt

If it broke in front of the trans mount, I can see that happening. The only thing I can think caused the break behind the mount is the yoke seizing in the bushing and twisting the housing. I think that was the violent vibration right before it snapped.

Did you pull that driveshaft yet? Your engine mount setup is pretty standard, the solid left just keeps the engine from rising, as a normal mount would do under acceleration.

No, I put it on the top bunk of the 4 post to nap for the winter now. The yoke looked a little rough when I swapped the rear axles before SCR, but it's been in there for several years and 2,000 miles before the swap. The snapped off section rotates easily by hand on the yoke now too. I did drive the car a short distance after the swap and felt a vibration then too. Probably should have left the car home at that point, but you know how that goes. Must be something in the axle ?? It all looked good when I changed the axle seals. Front u-joint is the same, I had to install a conversion joint in the back for the larger axle yoke and that seemed to go fine too.

I had a rear end shop for 15 years and most of the time when I would swap gear ratios in a car from a 2 something to a 4 something the customer would complain about a vibration caused by the rear end. It was not the rear end causing the vibration. A drive shaft is designed to run at a certain RPM. When you change gear ratios the drive shaft RPMs change, and a 4.10 will spin the drive shaft a lot faster than a 2.73. When you exceed the limit of the tube it will develop a bow, which causes a bad vibration. The cure is a thicker wall tube or a larger diameter tube. If your drive shaft bowed at that speed then it could have easily broke the tail housing.

Ah, ha, an answer that makes sense of this. I never had the vibration with the 3.31 gears but it was bad with the 4.56's...:eek2: Getting them changed to 4.11 in the Spring, so I guess I better be getting more than just a new input yoke. THANKS Freddie ! Helping me spend my money...:laugh:

I would be checking the transmission mainshaft in a lathe between centers to make sure it is straight also. JMO

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.

Question: do you have solid engine mounts on this?

No, but I will be putting one on the Drivers Side now..

Currently has Original Style Rubber Motor and Trans Mounts.

I've seen solid mounts do that. Also, I've had to center most bell housings especially blowshields.

Hard to tell from the picture but.. is something broken here on the crossmember.

Attachment 258818

I've been using solid Moroso mounts on my Camaro since '84. I had a solid transmission mount on it for many years. It's had 3 Muncie transmissions, a AutoGear and now a G Force and I've never broke a tail housing.

Good Eye.. I thought the same thing at first then went back under to realize it was only a shadow.