The dual master cylinder on my '48 has been having a problem. While driving around and occasionally using the brakes, the pedal will firm up and, eventually, the brake shoes will drag. After sitting all night, it goes back to normal.
I've studied the following illustration for a dual MC and propose one reason consistent with the symptoms. The pushrod is too long and will not let the "rear seals" go behind (or to the left) of the "fluid intake and return ports." The pushrod is adjusted to be as short as possible. It has no added valves in the lines.
What do you think?
Dual MC (My favorite MC diagram.)
