Master cylinder piston size differences, manual and power.

[375instroke]

Why is a power disc master cylinder for a '73 Dart (for disc brake swap) 15/16", and the manual master 1-1/32"?  I would think the smaller cylinder would give less pedal effort.  What's up?

[John_Kunkel]

I believe it has to do with the pedal ratio, manual brakes typically have a 6-1 pedal ratio while power is 4-1; the larger diameter MC will keep the manual pedal travel within certain limits. Even though the smaller MC would give higher pressure with less effort the increased travel would put the pedal closer to the floor.