Re: 1955 Patrician Brakes

Posted by HH56 On 2021/9/14 14:49:01

I know the 3/4" master has been mentioned several times but don't remember anyone saying they have actually tried it or remember seeing any reports as to if or how well it works. As I recall, almost if not all of the installed conversions have been 1" diameter masters which seems to be a fairly standard size cylinder.

The reasoning behind the smaller diameter master discussion is the BTV ram is also relatively small but can do a long stroke to make up the volume. From an increasingly feeble memory, I think the BTV ram is just over 5/8" in diameter with a 4" max length stroke. It functions by the solid ram inserting inside a closed cylinder and displacing an equal volume of fluid out to the wheels. With the displacement method a considerable amount of force is generated hence getting away with the 1:1 ratio.

The theory behind trying a smaller diameter master is a belief it will require less force to move a smaller amount of fluid. If that is so perhaps a lower pedal ratio would work with a smaller cylinder as long as it still has an adequate size booster on a very heavy car. The vacuum section of a BTV is right at 6" in diameter with a single piston. The max size of a modern booster that will still fit the original space is 7". Craig used a 7" single diaphragm but for a bit of additional power a 7" dual diaphragm is available. Length is over an inch longer on the dual and will barely fit depending on the length of the master. Not sure if the 3/4" master is the same length as a 1" though and less would definitely be better.

On the reduced volume out, as long as the wheel cylinders and shoes are adjusted properly the BTV ram does not move more than about an inch so does not displace a large amount either. I do not think it would be a good idea if a disc conversion was also contemplated. I believe there is at least one disc conversion using the BTV but to me that volume capacity leaves very little margin for error. Almost as worrisome as those asking for trouble using the ElectroBoost setup with a 1"1 ratio with no margin for error if the power unit failed.

As to volume and force of a smaller master, In theory the smaller amount from a 3/4" piston might be sufficient but until someone tries it that force theory still remains to be proven.