I just acquired this 1982 Series iii lightweight. All was going well until I left an intersection in first gear, hear a sound from below (like a piece of metal broke or dropped out) and then the engine just revved as if in neutral. I can shift it into all gears but the gears won't engage, in other words there is no drive to the rear wheels. If I put it into 4wd then I can drive it with front wheel drive only but still nothing to the back. Anybody have any ideas what happened before I start taking things apart?

 

Most likely a broken axle. They are cheap. They break routinely. If it broke at the wheel end it’s a very easy change. But they usually break at the diff end. Still not difficult but you need to remove the 3rd member (doughnut) to get the broken piece out.