Appropriate master cylinder for non-boosted upgrade

[techweenie]

I've put Carrera suspension and brakes on my '72 and I believe there are some upgrades for the master cylinder that could be worth considering.

Stock is 19mm. I believe I've seen a bored-out version with a bit more area -- maybe 19.5mm?

I feel the 23mm MC is too much...

Anyone have advice?

TIA

[MotoSook]

19mm should be just fine...

[palle7688]

No need for bigger dia. MC piston because your caliper pistons are not bigger, (does not displace more fluid)
I know, I know rear are bigger at 42 mm versus 38 mm but it's so little you can't feel the diff.
If you went to 4 pistons pr. caliper I would change it to 23 mm.
Perhaps Bill V. will jump in.

[AES]

Have you read this andthis

[techweenie]

You guys are great!

Thanks for the info. One less thing to worry about.

[Bill Verburg]

Hopefully you only put the Carrera brakes on the front of your car, where they will actually do some good. If so the stock 19.05mm m/c is fine because the master /slave ratio hasn't changed.

If you made the mistake of using the Carrera brakes on the back as well, replace them w/ stock.

[palle7688]

Bill, I've a second opinion of that.
I put Carrera rotors on front last year and rear this year, Carrera calipers on front and used the wider spacer from Carrera calipers on my stock calipers as you said. However my wrench was smiling a bit when I told him, asking why. Well I don't have 33 bar valve I said. After todays DE I noticed that my front wheels locked up quite early and rears didn't. I have to admit that I didn't really try to lock up the rears, but I feel that I could use more stopping power at the back.
So I going put the Carrera calipers in the back, try it for next DE and decide on valve for rear. Best thing would be an adjustable.
My wrench said that my SC with 3.2L engine, Turbo look and fat tires can easily handle Carrera calipers. And why not it's working fine on the Carrera.
I have to admit: why didn't I notice this last year, only diff is wider rear rotor.

[Bill Verburg]

First, you want the fronts to lock first, it's quite difficult to judge how early they are locking because the tendency is to back off or modulate them.

Second, the Carrera front and stock rear has exactly the same properties re braking as your stock setup, the only difference is the additional thermal mass fom the 4mm thicker rotors, bias and brake torque remain the same. It's impossible to judge from a distance but if the front is locking way early, I would suspect something amiss in the rear. Note if supension or tire changes were done that will also influence the braking charateristics.

Third, when cars are modified by design or age things change. First I would be sure that all components are working properly, second if additional rear brake is wanted I would try rear pads w/ a higher m

Then and only then if additional rear brake is wanted I would install an adjustable p/v. w/or w/o the Carrera rears. There is little need for bigger rotors in the rear of most 911s. In general the main reason that they are ever used is to balance out the fronts.

[palle7688]

Bill,
I know the fronts should lock up first.
I don't understand it either. There where no other mods made this vinter, same wheel, alignment, only diff is last years DE was on a prober race track while yesterdays DE was a slalom on a very small track.
I did install front Carrera rotors because of previous years heat problems last year.
After last years DE on a good race track I had problems with rear rotors warping.
So when replacing this year I choose Carrera rear rotors with stock calipers.
I will of cause check everything backthere.