PackardDon wrote:
Do they both appear to be stainless? A 1953 Clipper that I once owned had a set of very rusty wheel covers while the replacements were stainless and could not have rusted. I suspect the rusty set had Korean War Chrome over steel, which was typically 1952, but I did not notice any subtle difference in manufacturing such as you showed so if you can determine if one of yours is steel and the other stainless it may provide a clue.

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.

HH56 wrote:
That appears to be the Electroboost system and a few have been installed on 55-6 models at the factory location and 1:1 ratio with the boost power set near maximum. I believe those master cylinders were all 1". If you go that route on a 53 you would need to convert to 12v and I cannot help but wonder with the low ratio about how well the brakes work if the boost unit failed. To the best of my knowledge no one using the 1:1 ratio has tried disconnecting power to simulate a failure or if they have, did not post the result.

I and several others would much like to see what would happen with a 3/4" or smaller cylinder at the 1:1 ratio. I don't remember the exact ram size in the BTV but think it is around 5/8". It can have a longer almost 4" stroke to displace or force fluid out of the cylinder in sufficient volume to fill the cylinders whereas a modern master cylinder has a comparatively short stroke large diameter piston and quickly pushes a fair amount of fluid ahead of the piston. If the brake shoes are adjusted properly not much volume is needed but discs and poor adjustment would need more. That is where the safety margin question of how much stroke for the reduced diameter cylinder is available to move the equivalent amount of fluid. Most modern boosters and cylinders seem to have a max stroke no more than about 1 1/2 - 2 inches

HH56 wrote:
Can't see the bottom of the brake pedal very well to say for sure which year it is but with the rod extending backward you are probably correct at 55-6 You can compare pedals in the parts manuals. Plates 62-63 in the 51-4 manual and plate 13C in the 55-6.