xschop

Has there been a definitive answer whether the 78-80 brake MC is adequate for the Big Black piston volumes?

I'm not sure of the actuation volumes between a 78 and 1995 MC. The info I have shows the 78 being capable of more volume than a car with 4-pots. Doesn't make sense.

GlenL

I'm not following the data in the charts.

I would think the area of the master cylinder would be larger in proportion to the areas of the pistons in the calipers.

Then again, a lot of the volume moved is to pressurize and expand the brake hoses and the pistons themselves aren't moving much at all. That'd lead me to think that the piston size is less important and that the extra travel to push them out (flex caliper back) 0.1mm (guessing) isn't significant. If the multi-piston calipers are more rigid than the sinlge piston "fist" version then maybe having all those pistons to pump into is a wash in term of fluid needed.

Jadz928

A little armchair here, but would the later 10" booster help w/the bigger brakes?

And if so, is a later MC needed for the later booster?

xschop

I also find it odd that the front driver's side crosses with the rear passenger and each circuit has a regulator to the rear. I guess I can throw on what I have and see how it all feels with this MC and maybe plumb in a Wilwood adjustable bias valve to the rears. I like the 16" 993 wheels that are on here, but the 330mm rotors don't fit, however the Boxster S rotors (318mm) can squeeze right in with the 6-pots.

WallyP

The idea on the early brakes was to have two independent systems that give equal braking, and reasonable controllability with one system.

Later systems (front/rear split) give better controllability wth one-system use, but very little braking with rear wheels only...

jon928se

The 95 MC has a stepped bore - 23mm for the front circuit and 20mm for the rear. The 78 has equal bore -23mm thus for the same piston stroke it displaces more fluid than the 95.

In theory the 95 displaces less volume to the rear calipers compatible with the smaller diameter of the rear caliper pistons . But Porsche regulated this with a pressure regulator.

Depending upon how the brake circuits are setup in your 948? - if split diagonally you do NOT want to use the 95 MC. If split front to rear you can use either MC and add in the Wilwood adjustable regulater to limit rear braking force.

IcemanG17

great thread

My experience.....both my 1979 racer (9" booster) and Seans 84 (10") have full GTS brakes....the only other difference is pads....his race pads are more aggressive than mine....

In short.....his pedal feel is WORLDS lighter than mine and has much more POWER....You much push my pedal quite a bit harder to get equal stopping power....

Its also interesting about the straight bore MC......I do have issues with rear brake lockup when tires are anything but fully warm....

xschop

I will be installing 1.375" 4 pots in the rear and 1.62x1.25x1.25 6 pots up front. If the 2 separate bias valves don't allow enough pressure to the rears, then how would I plumb in the Wilwood adjustable bias valve, or would I have to plumb in 2 adjustable bias valves for each crossover circuit?

IcemanG17

When Mark Anderson installed the 14" F50 brakes on the front of his racer....he took out the bias bar......he found the rears could barely keep up....

xschop

Are the inputs to the 2 individual bias valves m10 x1.0 bubble flare?

IIRC I saw an adapter that would allow removal of those valves and just tie the line together.

Lot of work done today, it's ready for the General.