Canadian 1950 GMC 1/2 . 3 in the tree and a 216. The truck has been up and running for some time now. 2500 miles or so. I had everything working down to the clock. And yes even the vac wipers and emergency brake. Well long story made short . My son came home and we went for a ride. He was doing well learning to double clutch. Motoring down the pavement around 50 mph. He decides to take a left. Slows a bit and [oh no] he abruptly shifts from 3rd to 1st. Well the gear went in. The clutch still to the floor the tires lockup and squeal on the pavement. Ok now engine keeps running but no power transfer to the back wheels. So the question is what is broken ? Feels like I can shift as always into any gear. In fact I got her moving under her own power in reverse only just enough to back her off the pavement . and onto the gravel side road. Thats all she had tho. Now nothing in any gear. Maybe a little chatter when releasing the clutch.Very little. I should just be happy she backed off the pavement. I'm guessing pressure plate troubles? What are your ideas? Thanks in advance.