727 Locked up while driving causes?

Today I was driving around my 72 Duster and pulled up to a stop sign, waited my turn at the 4 way and then took off in 1rst and got halfway through the intersection before my rear wheels came to a lock and that was all she wrote, it wouldnt go into neutral or anything.(not the parking brake or rear drums caused it) I had to wind up pulling the drive shaft so that the car moved freely and used my pickup with a tow dolly and come along to get it home. It seems to shift through the gears fine now, and the engine turns freely both in drive , neutral and reverse, along with the transmission. I did not mess with the linkage and hit very few bums so I am puzzled to its initial cause, and would not like to have it happen again. ANy thoughts or personal experience with this issue?



Bret