drum brake proportioning valve

Tincup said
A Residual pressure valve is generally only used where the master is low in the car (I.E. frame mounted in a Hot rod ) to prevent bleed back.

crlush said
Residual valves are for hotrods that have the master cyl mounted on the floor, .

This seems to be a trend passed around the www but the fact is that for YEARS manufacturers used residual valves, and long after 67 when they went to tandem cylinders. I'm not sure I understand why they were used if not needed, because as we all know, manufacturers are not known for adding stuff that isn't needed.

I think we are focusing too much here on the presence / lack of a residual valve. I don't believe this issue has beans to do with the problem