Broken 727 Housing

[e.barojas]

Howdy

Just finished my epic build, (4 slow years)... A multipoint fuel injected 5.2 Magnum engine on my 1972 dodge charger...
I had it running for a week, transmission freshly rebuilt btw... There were some hard vibrations at idle which usually settled at medium throttle, At WOT you could feel them as well, but not excessively. Eveything was OK at slow speed, but during my first freeway run, at 70mph the vibrations were almost unbearable, it felt strange until suddenly: bum! Really loud bang, my center console was ejected in the air and power lost. I thougt i had blown the engine but when i stopped it was still running.
I looked under the car and all i could see was a loose driveshaft, the front universal joint failed, apparently one of the sockets in the cross thing broke. I fixed that, and when i got it running again i heard a strange whining sound... I looked closely and the transmission housing was broken! From where it bolts to engine block, torn apart! attached only by two screws and separated by a few cm's.

The question is, what couldve caused this? Theres a big chance the driveshaft was not properly balanced, but could this have caused such damage?
Any experience on things like this?

thanks.
everardo

[acelondon]

Sounds like the shaft was out of balance. Physics tells us that those vibrations can only go on so long before the metal can't take any more.

Im looking to put a 4speed in my charger. My 727 will need a home when that happens. i have a 318 also. My tranny runs great. PM me if ur interested.


Can't explain the idle vibe tho. unless your torque convert was out too. My car has a idle vibe, but its bad carb tuning. i think ur MPI should be better than that.

[e.barojas]

No one has ever seen this kind of problem before?
Do you really think a misbalanced driveshaft can make this happen? I mean, that diagnosis is only from me, not really from a pro.

common, i want some more feedback, i really want to avoid this next time.

[mikepmcs]

Tranny not bolted in correctly, u joint failure, or driveshaft out of balance.

Welcome aboard

Mike

[e.barojas]

Would you exclude torque converter completely?

If it were a driveshaft issue, should it vibrate at idle when in Parking or neutral? (I don´t see how could it anyway)

[mikepmcs]

Wait, it was vibrating when the car was in park while at idle?  The first post didn't read like that to me,  I took the way you wrote idle to mean like you weren't on the gas that much but still in motion.

[e.barojas]

Just got that tranny fixed...
Using a very short driveshaft, so cant hammer it or go fast. Anyhow, the vibration at road-speed seems to have disappeared. It vibrates a little but seems normal for a 40 year old car. I havent pushed it to 70mph yet, I hope the tranny doesnt bold off or something.
At Parking or neutral, with the car not moving there is a strong vibration, which lessens and at some point disappears completely when i rev the engine, when it goes into drive, with load its also lessened quite considerably, its almost not noticeable, however, just as you pop the lever into N the car rattles like theres no tomorrow.

I wish its not the torque converter.

Anyhow, Im inclined to think that this vibration is different from the one that caused the housing to break. As at that moment, it all seemed very related to the speed at which i was travelling, and this vibration when the car ain´t moving just seems different, and not strong enough to break a u joint.

cheers

[mikepmcs]

Motor mounts??? tranny mount? 

[acelondon]

Maybe the motor needs re-balanced?

[e.barojas]

Both tranny and engine mounts are new. The engine was just rebuilt, has less 1000 kms probably.

[BROCK]

Counterweights on the torque converter must match the engine

[e.barojas]

OK... How can i know which torque converter will fit both my engine and my tranny?
Is there a special one sold to adapt magnum engines?

Also, you think this can break the tranny housing, before even breaking the tranny shaft seal?
thanks mates...