My buddy bought this 61 Studebaker hawk a month ago. Brakes were fine.
Front disc brake conversion, frame mounted dual reservoir master cylinder, residual valves and proportioning valve. It developed a brake problem, calipers wouldn't release. Definitley a bad master cylinder. Replaced it with an identical new, not rebuilt, unit. Couldn't get the brakes to bleed out properly. Found some single flare ends in the system and replaced every fitting and every brake line,basically built a new hydraulic system. Still won't hold pressure.
The only thing left are the calipers. But they show no signs of leaks and appear to be working properly. [He found the original problem when he touched a front wheel and nearly burned his hand, brakes were locked up] . Maybe the heat warped the seals?
Is it possible for the seals in the calipers to not hold pressure, and still not leak? Any other possibilities?