I appreciate all the comments. As for 1958GMCnut's posting, I addressed the individual wheel performance in my original posting..I did exactly as you suggested. The master cylinder only has one output line for brakes so it could not be the problem. The failure you describe could only happen with a later model vehicle which uses a double piston. In this case the front /back separate downstream from the MC. I have seen the single brake flex hose for the rear stop up causing loss of rear brake action, but that has been checked.
I have noticed that the brakes seem to be more sensitive in reverse but can think of no reason for this. I would expect just the opposite.
meansam
