Two Questions. And I welcome the diverse opinion and experiences.

1. How serious is the parking brake issue with big reds?
2. Do 993TT rear calipers work in a C4 narrow body?

Thanks

 

I think the only issue with Big Red 3.6 Turbo calipers on the rear is there is no disc appropriate for a narrow body car. The disc on the rear of a 3.6 Turbo is offset for a wide body car, and is 28 mm thick. The discs available for a narrow body car are all 24 mm thick. I think people are using the Big Red 3.6 caliper on the 24 mm discs but this may be dangerous as the pistons may fall out if pad becomes too thin.

The correct caliper to pair with the Big Red in the rear is the 993 caliper which has the correct piston sizes and will fit a 24 mm disc, but is painted black as supplied by Porsche. If one wants Red calipers, the correct thing to do is paint a 993 caliper red or to machine the Big red for a thin disc.

If one does not need red calipers then use the 993 caliper as it comes and pair it with 928 GTS front calipers which are same as Big Red but black color as supplied by Porsche but have the orientation of the pistons incorrect, the solution to this is to flip the brake line and bleeder screws.

 

Can anyone speak to experiences with adding Big Reds to the front and moving the front 964 calipers to the rear? I would assume that this would give 'most' of the braking advantages of going with Big Red's all around, without the cost of having to buy the rears also. My front and rear pad wear indicates that most of the heat/wear is on the fronts, so I would expect that there would be fewer gains from larger rear calipers/pads. Am I missing something? I mean, besides the fact that the color won't match.

Erick

 

The problem with using the C2 4 piston front caliper in the rear is that although the caliper looks the same from the outside, on the inside it has much larger pistons than required for correct brake bias if used on the rear.

The C2 front caliper has 40 and 36 mm pistons, the 3.6 Turbo Big Red and 993 rear calipers have smaller 30 and 34 mm pistons, this means with the same disc and master cylinder, the brake torque would be 40% more with the C2 front caliper than you need for the rear application. Not a good thing.

The brakes would be "biased" way too much to the rear, the ABS may bail the car out of this situation but it is not a good idea IMHO...............

 

I'm buying the kits from Brembo through Bob Brooks (RennTT) and can offer the following from my discussions with him. He had a number of conversations with Brembo in selecting my set-up.

Brembo told him that if I wanted to use some of my existing calipers (I had complete sets of 964 C2 and 993 C2 calipers), the best to use in the back would be the 964 fronts. (Of course I learned this the day after I sold and shipped the 964 fronts.) They did not recommend the 993 fronts or rears for use in the back as it would not provide the right torque.

I'm due to get the kits tomorrow and will post what size rotors and calipers were provided for other folks information.

 

Tom W- What front system does Brembo recommend with the 964 front calipers installed on the rear?

 

I was under the impression that the bias could be adjusted one of a couple of ways: By changing to the C2 Turbo bias valve; or by modifying the existing bias valve. No?

 

Cupcar: Brembo suggested the 964 fronts would be ok as the rear with the big red fronts. Bob said they did not like the idea of using the 993 brake options on the rear of the 964 with the big red fronts.

 

Cupcar, has corrrectly identified the correct caliper and rotor combinations for use on the 964. I can not believe that Brembo or any representative of Brembo would recommend a 964 front on the rear, Cupcar explained why.

Brake torque or bias is the result of the rotor diameter, the piston sizes and the pad material.

Generally when the Big Red caliper on 322x32mm rotors is used on a 964 the correct bias will come form 30/34(small 993rear) rears(big pistons/small rotor) on a 299x24mm rotor or from 28/30 993/S4 calipers(these are the midsize caliper) on 312x28mm rotors(small pistons/big rotor).

I think that the reason people get confused is that the 3 different sized multipiece Brembo calipers(lets ignore the monobloks here) come in different flavors w/ different mounts an pisto sizes

To recap what calipers are available[list=1][*] Big Red, use front, size large, pistons 36/44, mount radial, rotor 32mm, [*]993/S4 size medium, use front, pistons 36/44, mount radial rotor,32mm[*]993/S4 size medium, use rear, pistons 28/30, mount axial(can be machined to radial, rotor 28mm[*]993/S4 size medium, use rear, pistons 28/28, mount axial(can be machined to radial, rotor 28mm[*]993/S4 size medium, use rear, pistons 30/36, mount axial(can be machined to radial, rotor 28mm[*]basic size small, use front, pistons 36/40, mount axial, rotor 28mm[*]basic size small, use rear, pistons 28/30, mount axial, rotor 24mm[*]basic size small, use rear, pistons 30/34, mount axial, rotor 24mm[*]basic size small, use rear, pistons 30/34, mount axial, rotor 28mm[/list=1]

The bias or proportioning valve is only used to fine tune bias is is not intended for gross changes you need to be in the ballpark to start w/.

This is a 993/S4 axial mount (machined to radial mount) rear on 322x28mm rotor, it is a 911 rear appliction. Thom/ should be similar on a 10mm smaller rotor


This is the 993/S4 axial mount prioor to machining


This is a basic caliper can you tell where it came from or where it need to be installed

 

Bill, firstly - many thanks for all the helpful posts over the months on brakes and brake options. I was re-reading these last night and they are educational!

I do have a couple of questions regarding the suggested rear options:
-does a 312x28 rear rotor fit in a narrow body 964?
-do either of the suggested caliper/rotor combinations impact either ABS on the C4 or the parking brake functionality?

Regards

 

As Bill V. points out, the proportioning valve only comes into play at it's set point brake line fluid pressure, after which the pressure in the rear is reduced by 43% of the increase of the brake line pressure ahead of the valve.

For example a "60 Bar" valve will have its input pressure equal to its output pressure (front brakes = rear brakes) until the line pressure is 60 bar or 870 PSI. After 870 PSI the output pressure would, for example, be 913 PSI, if input pressure is increased 100 PSI to 970 PSI [913=.43 X (970-870)].

Point is the line pressure has to be pretty high before anything happens at all with the proportioning valve, so the basic bias has to be right. The valve is really there to taper off pressure in the rear as weight transferr occurrs to the front during hard braking.

 

Is there never a quality cheap alternative to anything?!?!

 

Yes

For the Brembo sourced kit I am refering to , No, you'll notice the rear rotor in my prior post? It is a 2 piece design that will accomodate different rear parking brakes and o/s. Steve sell these things!(I think?)

When used in the same sentance w/ "Porsche", No

 

For clarity, in the back, you can mount the black 993 rear caliper (same rear caliper as Carrera RS), which uses the same size pad as the C2/C4 front and the C4 and 92+ C2 rear, however with larger 34/30mm pistons. This uses the stock 24mm size rotor, which is available solid/vented or holey/vented.

FWIW, in front the black 993 S4 caliper (44/36 pistons) fits fine with the appropriate adaptor, on 304x32mm rotors (928 S4 or 968 M030 rotors are bolt on. 993 rotors do not fit as they have the wrong offset).

 

I did the upgrade long time ago to 964 Ruf Turbo brakes...which I think are the same Brembos on the 964 Turbo, but say "Ruf" instead of "Porsche". I could tell the master cylinder is on the small side by the peddel sensitivity. I think it'd be a better set up w/o the booster as well. I think the combination makes the ABS comes in a bit too early and doesn't work exactly as I'd hoped. The brakes do the job w/no fade. If I remember correctly you have to upgrade to 17s as well to clear the fronts as they are significantly bigger bit of kit.