Lightweight Brakes

[Flieger]

Hello,

My car is a 1971 911S with the appropriate "S" Aluminum front calipers and "M" steel rear calipers. The fronts are beautifully rebuilt by Eric Shea but I can see that the rears are going to need attention in the not-too-distant future.

I am considering all my options at this early stage. My basic plan is to buy some rebuilt M calipers and swap the originals out.

I also have some big dreams about lightening the rear of the car.

What are the options for Aluminum rear calipers? I know 986 calipers work but they need adapters, right? What about the C12 calipers?

I want to take weight off but retain the correct brake balance.

Can you experts give me some guidance?

Thanks

[Flieger]

Eric, Do your Aluminum 3" Brembos do not fit the rear? I have 8Jx16 Fuchs in the rear so wheel clearance should not be a problem.

[davep]

There are few light rear caliper applications. There may be a 930 caliper that will fit. However, the Brembo caliper has a 48 mm piston as opposed to the 38mm piston you currently have. In my opinion that would unbalance the braking, front to rear, too much.

[Neunelfer]

I'm with Dave,

While these calipers may fit, or can be made to fit, they all carry the 48mm pistons. On the 908, that didn't seem to be an issue as they used the basic S-Caliper front to rear. On a 911 I would want the brakes to be biased properly "out of the box".

You could entertain the alloy arm issue but, on a 71 tub I feel there are major drawbacks in the shock/tub geometry. One year later and you and I would be in the clear, literally, there. Doable but a pain.

How about we try this set of Porterfield R4S pads I have sitting here with your name on them? Your calipers are fine.

[Flieger]

Thanks for the replies. I will put my fantasies away.

[TRE Cup]

There is the alloy caliper from the alfa 164. it bolts right up on the back of your car, has larger pads. But i don't remember piston sizing. You would most likely have to install an adjustable bias valve to limit its performance.

[Flieger]

Are there brake bias valves that proportion fluid pressure between front and rear throughout the whole range of pedal pressure? I know the Carreras had the pressure limiting valve that just put an upper limit on rear braking. Below that threshold, the rear had the same pressure as the front. I know a dual master cylinder with adjustable bias bar would be the hot setup but I would be fine with a fixed, correct bias if it saved money and meant less installation work.

[TRE Cup]

you have a 19 mm master with separate circuits front and rear. A wilwood, summit, or similar dial adjustable knob unit goes for about $60-$80. You can get some -3 hose with fittings to interrupt the rear circuit where it exits the master. Then run the to/from lines to the valve where you can mount it inside the cockpit. If i remember correctly, some of these valves reduce pressure as much as 30% (linear) with it full open.
so best to read the the specs before buying. Its a little tricky to set up, especially on light cars with large torsions. Best to find a set of tires that you can sacrifice to flat spotting while you explore the limits

[Flieger]

Thanks for the info, these are all still just thoughts in my mind, way off in the future projects timeline.

[Scott Clarke]

Eric-
Would it be possible to sleave down the Brembos to 38mm? I would love to match my fronts.