Which 7/8 master cylinder?

In 2012 I wanted to eliminate the power brakes in my '70 Charger. I tried 3 master cylinders that I had here, all 3 had different bore sizes: 1 1/8", 1 1/32" and a 15/16". ALL three gave the same results...firm pedal, minimal travel and brakes that were ineffective. I could barely skid the tires on gravel! The best was the 15/16" unit but it was still not great. I called and asked about a new aluminum 15/16" MC. It was no better than the iron one I had of the same size. I am not trying to talk trash on the sales guy but sometimes vendors are too fast to sell you something rather than to learn if their product will solve your problem. The $90 I spent made no difference and wasted my time.

When you deviate from a balanced stock setup, things can get screwy pretty fast. Several details factor into a well functioning brake system. The factory always made the front wheel cylinders or calipers larger than the rear. They had proportioning valves in a disc/drum system in the effort to have balanced braking. There are other factors such as pedal ratio, power VS non power and even the material used in pads and shoes.

4 wheel drum systems need NO proportioning valve. The front to rear brake proportioning is controlled by using smaller brake cylinders in the rear. The very same principal is in play with a 4 wheel DISC setup. The rear caliper BORE size must be smaller than the front.