Muncie tail housing broken

[Too Many Projects]

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.

[69 Post Sedan]

Mitch, what are you running for motor mounts and transmission mount?

[Too Many Projects]

Originally Posted by 69 Post Sedan

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...

[69 Post Sedan]

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

[Too Many Projects]

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.

[dustinm]

Originally Posted by Too Many Projects

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.

[Too Many Projects]

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.

[big gear head]

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.

[Too Many Projects]

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... 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...

[rszmjt]

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