QUOTE--"Unless you like driving backwards at high speed, I would recommend abandoning this pursuit....Particularly since A/G GM rear brakes get really grabby in the wet...."
I'd never try to lock them up going more than 30 mph. But I can't even lock them up going 5 mph on the grass in my backyard. That's not right. I've got the proportioning valve ( Speedway.. on the rear brake line ) wide open. My goal is to be able to lock the rears up at 30 mph and then I can start closing the proportioning valve down until they barely squeal. This should give me about the shortest stopping distance with the setup I have.
One possible problem I might have is the master cyl is a disc/disc and I have a disc/drum. I don't know if the internals are different than a disc/drum. Guess I'll have to call one of the brake vendors and ask the tech dept