Disc Brake Hold Off & Prop Valves

[QUOTE
However I also tend to believe they help in keeping air out of the system which could enter at the wheel cylinders or calipers.

,,,don't you think that if air could leak in, brake fluid could leak out,, especially at the 700 to 1400 psi at the wheel cylinder - caliper with the brakes engaged,,

My 68 Barracuda was a 4 wheel drum car, converted to 4 wheel disks, used the 73 and up mopar A body disks / calipers on the front, a Dr Diff disk kit on the back, using a 68 A body distribution block in the brake line system, no proportioning valve, no hold off valve,, stops fine.[/QUOTE]
Cool, so just lines from the MC straight to the calipers? No valving at all?
Thx for the reply