Gus

wallra

sounds like you have air in the system. try blocking the front brake hose's and see If the pedal gets hard.

Gus

Bill Verburg

Here's pretty much what you have, thi is a 993 3 channel setup, 964 is mechanically very similar

To change to dual master the pedal, linkage, vac. booster & m/c are replaced, yes you can retain abs function


Most likely something like a Tilton 3 pedal floor mount is what you would use

here is what 997RSR uses, very similar to the Tilton but the Tilton has the m/c's in front of the pedal, RSR behind(under the drivers foot)


It's also possible that one form a 911 could be adapted


I'm curious as to what rotors and calipers you are using, w/ details I can run some #s on sizing m/c

The GT3s use a 27mm m/c but until 2010 they used pretty small rear caliper pistons, from 2010 they got w/ the program w/ decent piston sizing in back

Spyerx

Gus

Bill, Spyerx - Thanks for feed back and input - Bill the info you provide is great. The caliper information on the pistons is - Front 32mm' 36mm, 38mm and Rear is 28mm, 32mm. if you need additional information let me know. It would be great to get a good Master calculation. Would also appreciate the Dual Master info if you are going down that road.
General Info: Front - 6 piston Calipers on 345 x 32 mm rotors / Rear - 4 piston calipers on 345 x 28 mm rotors
I think answering Spyerx's questions will provide info to Bill as well ( except for the piston info )
!, What calipers in front and rear? --- I am testing some new Rolloface calipers and disk.
2. and you have the 993 mc already? --- Installed 993 MC setup some time ago when I changed to Big Red ( Blacks)
3. what pads and rotors? ---Right now Rolloface Pads/ rotors - Have looked at Pagid options as I normally run Orange front and Black rear. It looks like a Pagid 2127 works for the front and Pagid 8007 works for the rear.
4. what uprights in front? --- Stock 964 uprights with my own bump steer fabricated steering rods.
I have done some basic calculations on the difference between the Brembo's brake set up I had and the Rolloface units I am testing. First the brake set up i had was Big reds/Blacks with 332 mm rotors/floating Alum hat up front and stock 993 rear calipers and stock (964) disk in the rear. This set up worked very well.
The Rolloface vs the Brembo set up numbers are as follows - Brake area is the size of the brake sweep area on the disk.
Front
Brembo Rolloface Difference
Diameter 332 mm Diameter 345 mm Rolloface is 13mm larger
Brake Area = 28449 mm2 Brake Area = 27959 mm2 Rolloface has 490 mm2 less sweep area

Rear
Brembo Rolloface Difference
Diameter 298 mm Diameter 345 mm Rolloface is 47 mm larger
Brake Area = 21430mm2 Brake Area = 21366 mm2 Rolloface has 64 mm2 less sweep area
In both cases Rolloface rotors are larger diameter than the Brembo set up and offer a better braking factor.
You can feel the RF bit better than the B, even with the softer pedal I have now.
One thing that was really great about the Rolloface rear rotors is that the inner brake drum was made into the floating hat which allows you to keep the rear drum emergency brke set up without any modification.
Here are 2 picture of front and rear brake set up. FYI - I am running 18 inch wheels.

Spyerx

let me go check the math on my current setup on something...

Regarding your pedal feel, do you notice this when pushing the car, just driving slow, driving fast? Do you think it is pad knockback? Does a second application make the pedal much firmer??

For reference, this is my Brembo setup:

Brembo GT Kit, 993 - slotted, red, TS20 pads - 1M2.8001A - 6 piston, 355mm slotted
https://www.racetechnologies.com/pro...0?vehicle=9673
1M2.8001A – 355x32mm slotted, w/6p Monobloc: 28/30/36mm pistons

Brembo GT Kit, 964 - slotted, red, TS20 pads - 2C2.6017A - 4 piston, 328mm slotted
https://www.racetechnologies.com/pro...0?vehicle=9510
2C2.6017A – 328x28mm slotted, w/4p: 28/30mm pistons

993 C2 master cylinder. No proportion valve.

Bill Verburg

That setup gives a very front biased 2.082, w/ a pedal ratio of 39 the original 964 4/4 was 1.889 w/ a pedal ratio of 46, your bug red front w/ 993 rear was 1.713 w/ a pedal ratio of 32.786

Your 23.8mm m/c should be fine, the lower the pedal ratio the better for performance use(higher & harder) down to ~30 where the effort is starting to get a bit much, it does depend on boost and individual preference.

I suspect air in your system somewhere.

Too bad they don't have smaller front pistons, 28, 30, 38 ala GT3 would give a pedal ratio of 37.596 and a bias ratio of 1.414, 28, 32, 38 would be 38.472 & 1.481(this is about perfect

w/o different calipers a twin master is the only way to get your bias where you want it
w/ a 19.05 front and 17.78 rear & a typical balance bar your bias range is 1.626 to 2.421(still a bit front but at least in the ball park) and a pedal ratio of 32.82(this is great)
w/ a 20.64 front and 17.78 rear the bias range goes to 1.545 to 2.421 and pedal to 30.03

wallra

just to say this and I don't mean anything by it but are your bleeders on top. I've seen calipers put on the wrong side more than once.

Bill Verburg

Just for comparison purposes one of the best, IMHO, factory brake setup possible was introduced for the 2007RSR
front
28/30/38 on 380x32

rear 28/36 on 355x32

twin 18.8mm m/c

pedal ratio 29.47, these cars are set up for very fit and relatively young pros
bias 1.26 to 1.875

that said ew 964 or 993 will need those big rotors

Gus

Bill - thanks for all the data, I am taking a look at the numbers to see what we can do for better bias. One thing you said "w/o DIFFERENT CALIPERS a twin master is the only way to get your bias where you want it" has me wondering what caliper configuration you are referring to/or proposing. I do have the option of increasing the rear brake pad size by 8mm in height on the inside sweep area. But feel that from your numbers I would need a little more. If the changes were made to the rear calipers what configuration would /should be considered.

WALLRA - bleed nipples at top - thanks for the thought though -

Bill Verburg

The pad size has no effect on the bias
What does
#1 by a long shot is the ratio of front to rear piston sizes
#2 by a little bit is the effective radius of the rotors, in your case even if the f & r calipers have a difference it is so tiny as to be non existent as you have the same diameter rotors f & r

on 993 RSR there was an option of 380mm front rotors instead on the usual 322, That changed the bias from 1.426 to 2.032.
You bias isn't dangerous or anything and you are probably not even going to have heat issues because of the oversized front rotors, it's just that it isn't as efficient in utilizing resources as it could be. W/ a bias ratio ~2 the the front is doing more work than it needs to, while the rear is just loafing along not doing all it could be doing.

If you had a choice of front calipers on the same rotors you would want smaller pistons, I mentioned the GT3 which is 28, 30, 38, this would change the bias to a more favorable one and also lower the pedal ratio to a more favorable one. Alternately if you could use a caliper w/ larger rear pistons this would also make for a better bias ratio but it would make the pedal ratio worse.

The factory really got the all the pertinent ratios right on the 993RS, 993Cup and 993RSR, they didn't get the ratios that good again until the 2007 GT3 RSR, they instead relied on dual master setups in the race cars and oversized front rotors , up to 350x34 for street cars and eventually the PCCB brakes that are even more heat proof.

Peteinjp

Bill Verburg

That's a bandaid, The core issue w/ that is that friction coefficients are't a single #, they consist of a curve of values that vary w/ temperature, You loose the consistency of fixed bias ratios. But yes some people do use different pads front & rear

Spyerx

Ok, these are the piston sizes of my setup:
1M2.8001A – 355x32mm slotted, w/6p Monobloc: 28/30/36mm pistons
2C2.6017A – 328x28mm slotted, w/4p: 28/30mm pistons

Bill whats the maths on that? :-)

Looks like about a 1.77 split. I have no proportion valve, 993 master.

Here's what I notice in actual use: excellent pedal feel, strong/positive initial bite, good modulation, and at threshold minimal ABS intervention and good balance (ie doesn't feel tail light or nose heavy)