Why did my drive shaft just fall out of the transmission?

[centuryhouse]

I was driving my new 72 GMC (350, automatic, c15) at lunch and as I started off from a signal there was a loud clang and clattering and sudden loss of drive ability.

The drive shaft yoke (?) came out of the transmission and dropped on the ground. I had to get towed home.

On my initial post on this forum 2 weeks ago, I had noted that I could see splines showing on the driveshaft and asked if this was normal. No one answered so I assumed it wasn't a big deal.

Assuming the first pic is not normal, I was thinking the previous owner may have swapped out the transmission for a different type and then not put the correct length DS in place, or else replaced the DS with one that was the wrong length.

Thoughts? I don't even know what transmission I have or how to tell. Can someone get me going in the right direction on this? My GF just wrecked her car and is borrowing my Jeep, and now my backup transportation is down.

What I posted the other week:




Today: