HH56 wrote:
Question I have is where are you going to mount and what type pedal? If there is enough room and you mount in the engine compt down toward the original location and adapt to use the bottom of the original PB pedal that will be 1:1 and converted by the new mechanism to 4:1. If you mount up higher near the air vent and connect to the pedal arm that might not provide enough stroke the way the stock pedal assy is suspended. If you install the 55 manual pedal and mount under the floor that will be around 6:1 and you would not need the extra linkage in the new bracket.

JeromeSolberg wrote:
You can think of the master cylinder/slave cylinder relationship as a lever, with the lever ratio being the ratio of the areas. The smaller the area, the larger the pressure, but you have to make that up with a long stroke, just like in a long lever arm.
The Bendix Treadle-Vac has a 0.652" (some say 0.655") bore diameter, with a very long stroke, from what I can measure around 3". This is what allowed it to work with the small diameter vacuum booster, and be (marginally) acceptable in the case one lost vacuum.

I tried a Ford Courier dual master cylinder with it's 7" booster. It has a 3/4" bore size. The 7" booster barely fit down there, but all in all the installation looked great. I put some pictures up somewhere on another thread, I need to find it.

However, the pressure ratio is proportional to the square of the bore diameter (area=pi D^2/4) that means it has a pressure ratio of (0.655/0.75)^2 which comes out to about 75% of the original brake pressure.

It was NOT ENOUGH! I drove it and I had to push HARD on the pedal, and my neighbor was of the opinion it was not safe.

I have recently evaluated using the Wildwood TM1 externally mounted dual master cylinder. It has a 0.625" bore, but only a 1.3" stroke, so I don't think it would be acceptable, though I have thought about it.

Wilwood TM1 Master Cylinder, 0.625" bore

JWL wrote:
May be a bit off topic, but is anyone familiar with brake master cylinders being boosted by the power steering pump? I recall seeing one of these boosters being installed on one of the car restoration programs. Maybe it was on one of the Restoration Garage episodes? One of these boosters may solve the space problem if the car already has power steering.