My son has a 73 f100 shorty. When did they stop the f100 and start the f150? What are the differences between the two?

 

I had an 81 long box f-100, had a 6cyl, 3 on the tree, I think it was just a light duty half ton

 

1983 was the last year for the F100 model. The difference between the F100 and F150 is that the F150 is considered a heavy-duty half-ton. The F150 had a slightly heavier suspension and up until 79 the F150s had less emissions stuff on the engine.