This cracked extension housing represents the 3rd in the last 3 years. It comes out of a street driven Hemi car that sees a little drag strip action (once or twice a year). Ironically, it is at the drag strip that this happens. It is a reasonable mild hydraulic cammed engine. The car has run in the 10.9 to 11.0 range. We have checked the driveshaft length and pinion angle (5 degrees nose down). This is a leaf spring car.

We originally thought it was due to the motor/transmission mount mismatch plus a rare thin k-member. The mounts were solid on the driver’s side, stock rubber on the passenger and polyurethane on the transmission. There was a lot of flex in the k-member, even after an attempt to stiffen it. This arrangement gave us 2 broken extension housings. In both cases, the transmission failed right at the lift of the throttle at the top end of the track (deceleration).

The k-member was changed out to a stock one to eliminate the flexing. The driver’s side stock rubber motor mount was replaced with a solid mount. The balance was left the same. This time the extension housing broke during acceleration. There was also some serious vibration experienced before hand. We thought it was a bent output shaft but initial inspection has not revealed this as the “smoking gun”.

Has anyone experienced this? Any ideas? We are frustrated.

Garth

Here is a 2nd picture showing the crack not quite going all the way around. The crack starts at the speedometer hole. All 3 have failed this way.

Garth

I question the poly trans mount, I would rather see a factory rubber mount there to give it some room to move around and not bind it up, especially if you have any body flex at all with a solid front mount.

I have 2 solid mounts and a poly trans mount and haven't broken a tail shaft like that.

I would look over the whole suspension,from spring bushings to center bolts to driveshaft length followed by transmission and driveline alignment.

Thanks guys for the feedback. Anyone else have comments or suggestions?

Garth

The K memeber might have been flexing enough to crack it..
The poly mount probably isnt allowing much trans movement or twisting..
So the trans is rock solid, and the front engine block/K member is flexing..something has to give which is the weakest link..The cast aluminum tailshaft housing.
Get the engine mounts off the think K member and get a motor plate..or atleast add some torque straps on each side off the frame rails to hold that engine still.