ST recreation needs a master cylinder

[jessef7897]

Hello everyone,
Quick intro is in order. My name is Jesse, living in the greater Philly area, i've been working on porsche's for about 15 years. I've been bopping around the various forums for a while, mainly in a read only capacity. Currently working at a resto place in the Chester County area, but i've worked at a few places over the years so chances are i might have worked on a few of you local's cars. Anywho.

We're building a '72 ST recreation from scratch. It's somewhere between a recreation or reimagination or hot rod something. Aluminum front crossmember, aluminum trailing arms, heavy hollow torsion bars, period Koni's all around. And 908 brakes.

With the 908 front calipers, what size master cylinder should we be running? From what i understand, the 908 calipers are really close to S calipers but with a quick change pad feature. I assume that means that a standard 19mm master cylinder from a 72 car would work but i wanted to double check. I don't think we're opposed to "upgrading" if we need to as long as it works with the system.

Thanks in advance for any help, info, or direction and if there's anything i can help with, i'm hapy to be of service.

Jesse

[davep]

Not sure what they used in the race department in that period. The sports purpose manual only says the calipers are adequate, but to use competition brake pads and change fluid more often. However, the 1969 911S with the S calipers also used a 20mm master cylinder. How long these were supplied is not really known. Many racers needed to use larger master cylinders to have effective brakes. The 20mm MC has been NLA for a long time.

[blue72s]

the 1969 911S with the S calipers also used a 20mm master cylinder.
The 20mm MC has been NLA for a long time.

20mm? How do you know?
There's only two types of MC in the PET - one without warning function and one with the function (USA), and both are sized 19.05mm

[gled49]

Dave is right, 20mm was used for a short time. That MC will raise the brake pedal but also increases pedal effort. 19mm was used with warning in the USA and without in Europe. If standard brakes are used in the ST Repop, the 19 is perfect.

[davep]

It is noted in the "Service Information" booklet for technicians for the 1969 model year. Since all master cylinders are in inch sizes, the 19 is 19.05mm or 3/4" and the 20 is 20.64mm or 13/16"

[blue72s]

It is noted in the "Service Information" booklet for technicians for the 1969 model year.

OK thanks. Do you have the part number of the 13/16" MC ?

[gled49]

How is this for digging thru the archives. G

[blue72s]

Thanks so much.

[jessef7897]

Wonderful, thank you very much