rbuswell

I've read most of the threads and consulted Grady Clay, my Porsche Mentor, and determined the benefits of a 930 23.8 MM master cylinder for my '82 SC with a 19 MM MC are worth the expense and trouble. Steve Weiner seems to agree with Grady on this upgrade.

Looks like a perfect trade-out except the aluminum tube/shaft that goes into the power booster is quite a bit bigger in diameter. The tube length looks identical. There is a smaller diameter inner section at the end of the shaft that looks like it is a perfect fit for my power booster. It goes on the shaft in the power booster fine from what I can tell.

My question; Is there an additional adapter I should be using or is the 930 MC a direct trade out/upgrade as the other threads seems to indicate?

Also, I've revived a thread on the MC bleeding/pressurizing procedure so if all of you brake experts would weigh in on that one too, I'd be forever grateful.


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loosecannon

I put a 930 master cylinder in my 911SC and it was a bolt in, no mods or adapters required. I've tried several self bleeding systems and so far the best bang for the buck has been a rubber hose with a one way valve in the middle. One end goes on the bleed nipple and the other end goes into a bottle of brake fluid. I start with the right rear, then left rear, then right front and finally left front caliper.

Peter Zimmermann

I'm not in total disagreement with the experts that have offered opinions on this thread subject. It's an interesting one, that's for sure, but I have to ask "why?" The SC uses a 7" booster, while Turbos, as well as 3.2 Carreras, use 8" boosters. The SC uses a 20.6mm master cylinder (not 19mm), and the SC system has to push front caliper pistons that total 96mm/front caliper (48mm x 2). The Turbo, with its 23.8mm master, has to push a total piston size of 152mm/front caliper (38mm x 4). The SC does not use a brake pressure limiting valve, but the 3.2 Carrera does. So, looking back, the factory retained the 20.6mm master for the 3.2L cars, but switched to an 8" booster with a pressure regulator. Pressure was limited to the same amount for both the 20.6mm and 23.8mm masters, until '85, when the Turbo system received more force. There is also a difference of 2mm in the operating stroke for the 20.6mm and 23.8mm masters, so a study would have to be done regarding brake pedal angle and push rod size. So, for there to be a gain, in my mind, if the Turbo master is used on an SC, then the 7" booster should be replaced with an 8" unit complete with a pressure valve. Then, to make that change worthwhile 3.3 Turbo front calipers, or similar, and perhaps suitable Brembo rears, should also be added. Again, perhaps I'm missing something here, but I think that putting a 930 master in an SC is like putting S pistons in a T engine. Each is part of an engineered system, and the resulting benefit, when used alone, is questionable. I also think, that leaving the 20.6mm master alone, but adding an 8" booster with pressure valve (i.e. bring the car up to 3.2L specs) might, maybe, be a better way to go when there is no intention of replacing/updating the calipers.

Naitove

This could get interesting...

Steve Weiner-Rennsport Systems

Rbuswell,....

I did indeed agree with Grady on this subject but only within some context,........

Pete is right on target here and simply swapping the SC's MC for the 930 one simply makes a higher and much harder pedal that many people might not like. Further, its more difficult to "feel" the onset of wheel lockup when the pedal requires a much more subtle touch to sense what happens at the tire patches. Personally, I happen to like this conversion but some of my clients do not, therefore I am very careful about who I recommend this MC swap for,...

I use 930 MC's when I install larger 4-piston calipers in lieu of the OEM 2-piston ones as one requires increased fluid displacement per stroke with these bigger brakes. There are several scenarios for these applications such as when using 930 calipers, or any of the Brembo GTP family of calipers.

I hope that clarifies my view on such things,...

Bill Verburg

The 23.8mm 930 m/s is not a good match for stock SC or Carrera calipers. For normal human beings to operate brakes the slave:master ratio needs to be kept in an acceptable range, for 911/964/993/996/997 that range is ~14.8 to ~21.5. The lowest # for a non-boosted app. w/ a very strong leg is ~16.1

The lower #s are desirable from a performance aspect because they provide higher, harder pedal w/ less travel. Ergonomically the human leg can modulate pressure at a fixed point better than over a range. The high harder pedal approaches zero.

A stock SC has a ratio of ~17.7(boosted of course) if a 930 23.8 is substituted that drops to ~13.2 well below the range of even strong boost. You can do it but it takes a lot of leg and will not be comfortable for most.

For normal street use #s at the top of the range are desirable to allow use by even the relatively frailest among us, they do give up some of the feel and controllability of the lower #s

911S3.6

As one who had the OEM S-calipers on my 1975 911S and converted to the Steve Weiner/Rennsport systems 930 brake upgrade>which includes 4-piston 930 calipers, steel brake lines, Brembo disks, and the aforementioned 23 mm Master Cylinder, i can tell you: the pedal is hard, there is no booster to compound the pressure upon braking-it is a very physical process...LOL! But, the results are a more linear, predictable and thoroughly confidence inspiring braking exercise. At no time have i EVER locked up the brakes no matter how much brake I've needed- it is threshold braking to the Nth power (chirp, chirp is all you hear). Nor have i ever run out of brakes, overheated them, boiled fluid etc. not even at Road America in 95 degree heat lap after lap (Kettle Bottoms at 150+MPH!) For track use , with Pagid Rs-4 pads, it is sublime. I was leery, but am now a convert. As a very wise man told me, if you are going to go fast, you have to be able to stop fast.

///Nick

///Nick

Bill Verburg

The slave:master ratio for 930 brakes w/ 23.8mm m/c is ~16.5 very near the lower limit for non-boosted brakes

KC911

Out of curiousity Bill, what would the ratio be for my Carrera (w/ booster) and a 23.8 m/c and 930 brakes? I love my setup, thanks Steve W!

Keith
'88 CE coupe

Bill Verburg

The same as Nick's(9113.6S) of course, but your vac boost takes the edge off the effort needed.

rbuswell

I've done the install and I really like it. It does require more pedal effort and it is very difficult to lock up the brakes but the car stops really well. It has a more linear feel and I can see why Grady recommended it. Further I may go with bigger brakes someday (maybe Steve's favorite setup) so since there doesn't appear to be any negatives I say "why not?" I have very strong legs by the way so once I got used to the feel and how much I needed to push, it was great.

I asked Grady to drive it and as soon as he felt the new pedal he got a big grin. Remember that Grady used to race.

Using my Motive power bleeder without doing any prep of the master cylinder was a snap. That is really a cool tool and I highly recommend it.