In the first years of disc brakes, due to the higher line pressure the discs need to work and stop as expected, some sort of vacuum power booster was usually paired with them, even on some of the lighter European cars. In the USA, the '71 and possibly '72 Camaros had non-power disc brakes as standard equipment, with the power booster optional. In later model years, the standard equipment was "power front disc/rear drum brakes". I had a friend who had one of those cars. He said it stopped fine, but I'm not so sure I would want a non-power disc brake set-up myself. I remember the manual drum brakes on our '51 GMC 1/2 ton pickup, so any more pedal pressure to get the car to stop quickly with non-power front disc brakes might be more than I would like.
I was not aware of the Chrysler A-body non-power disc/drum brake set-up. Considering that power brakes were an upscale option everybody was used to back then, I suspect that not many non-power disc/drum set-ups were sold, unless it was a very low-option vehicle, but still with front disc brakes. Just my suspicion, not knowing of actual installation rates. BTAIM
Might the difference in the master cylinders be a "residual pressure valve" in the circuit for the front disc brakes? Which can re removed from an existing 4-drum master cylinder?
The power disc brake booster would also be a dual-diaphragm unit, as I recall, which means it'll stick out closer to the rear edge of the valve cover.
And, of course, you should have the particular valving related to the disc brake system.
For best results, to me, you should replicate the complete brake hydraulic system. PDB booster, PDB master cylinder, PDB line valving, etc.
Seems like there is an older thread on the perceived need of the specific dual-diaphragm booster rather than using a single-diaphragm booster from the C-body power drum brake system?
Just some thoughts,
CBODY67
