944 S2 BRAKE SPECIFICATIONS
STANDARD FRONT BRAKES: The standard front brakes on the 944 S2 are taken directly from the '87 and on standard 944 Turbo. The pistons used in these 4-piston Brembo calipers are 36 and 40 mm in diameter (two each). The brake pad width is 98 mm, the same as that of the famous original 911 Turbo (model 930). The front rotors used with these standard calipers have a diameter of 298 mm (11.73 in) and a thickness of 28 mm (1.10 in).
M030 OPTION FRONT BRAKES: A 944 S2 equipped with the very rare M030 Sports Suspension option uses the same size front brakes as those used on the 1988 944 Turbo S or 1989 944 Turbo. These larger Brembo calipers first appeared on the 928 S4 so are routinely referred to as the "S4 brakes." The piston sizes are 36 and 44 mm and the corresponding brake pad width is a very substantial 132 mm. The front rotors used with these "S4" calipers have a diameter of 304 mm (11.97 in) and a thickness of 32 mm (1.26 in).
M030 cars use different steering knuckles and hubs. Different knuckles are required because the S4 caliper attaches using a radial mount as opposed to the axial mount for the standard caliper. Different hubs are used to accommodate the 4 mm increased thickness of the M030 rotor.
REAR BRAKES: The rear brakes on the 944 S2 also came from the 944 Turbo. The
piston sizes used in these 4-piston Brembo calipers are 28 and 30 mm in
diameter. The rear brake pads are exactly the same size as the standard front
"930" pads. The rear rotors have a diameter of 299 mm (11.77 in) and a
thickness of 24 mm (0.94 in).
928 GTS BIG BRAKE UPGRADE
When it comes to brakes, bigger is generally better :-) Fortunately, 944 Turbo and 944 S2 owners need only search as far as the factory parts bin for something that's even larger than the M030 S4 brakes. Note: this brake upgrade requires the use of 17" wheels or special modular 16" wheels to clear the larger calipers. Non M030 cars also require caliper mounting adapters to convert from axial mount calipers to radial mount calipers. I purchased mine from Broadfoot Racing. 1986 944 Turbo cars require modifications or a specially engineered adapter kit because of their different offset requirements.
BIG RED CALIPERS: The famous Porsche "big red" Brembo calipers from the late model 911 C2 Turbo or 993 Twin Turbo work well on late model 944s or 968s. Since these calipers were originally made to mount in the leading position in front of the axle they must be rotated around for use in the trailing position on the 944 or 968 series cars. Mounting the calipers in this location introduces three minor problems: 1) the location of the bleeder fittings and cross-over tube must be swapped, 2) the brake pad retention spring is now hinged at the top instead of at the bottom of the pad area, and 3) the brake line inlet is now at the top piston location instead of at the bottom piston location (not necessarily true anymore... the design may have changed)
BIG BLACK CALIPERS: The minor "problems" with the big red calipers are not usually a concern. However, in order to maintain factory reliability and improve brake fluid cooling I wanted to use the 2-piece combination steel and rubber brakes lines from the M030 944 S2 (see picture above). These lines use a rigid steel tube between the caliper and strut mount and this really helps cool the brake fluid. In order to use these lines a caliper with the fluid inlet location in the stock position is required. Therefore, I chose the 928 GTS "big black" calipers. These calipers are physically the same size as the big reds and use the same size brake pads. However, since they are meant to mount in the trailing position they are a true bolt-on option. They also don't show the brake dust!
The piston sizes used in the big red or GTS 4-piston Brembo calipers are the same size as those used in the M030 option S4 calipers, namely 36 and 44 mm. The brake pad width is also the same 132 mm. However, the brake pad depth is increased substantially to match the larger rotor diameter.
ROTORS: Three factory front rotor options are available for big red or big black calipers:
928 GTS — 1-piece, "non-drilled," same offset as '87 and on 944
Turbo or 944 S2.
911 C2 3.6 Turbo — 1-piece, "drilled," same offset as '87 and on
944 Turbo or 944 S2.
993 Twin Turbo — 2-piece (separate rotor and mounting hat),
"drilled," 5 mm less offset than above options. Not for use on cars
originally equipped with S4 calipers (M030 option) unless custom alloy hats are
All of the above rotors have a diameter of 322 mm (12.68 in) and a thickness of 32 mm (1.26 in). The 928 GTS rotors are reasonably priced and work well on the street, but are not as "sexy looking" as the drilled rotor options. The 3.6 Turbo rotors are similar to the GTS rotors but have cast-in ventilation holes made by a special process, as do the 993TT rotors.
I originally chose the C2 3.6 Turbo rotors because I wanted the look and added cooling the "drilled" rotors provided but didn't want the extra expense of fitting the 993TT rotors and custom hats. I'm now in the process of changing to the 993TT rotors and alloy hats... this should save about 4 lbs per side in unsprung weight... or so the vendors claim. We shall see when I weigh them.
Since I now had cool-looking "drilled" rotors at the front it seemed only reasonable to install them at the rear also :-) Though expensive, the "holy" rotors from the M030 968 were the perfect choice.
DUST SHIELDS: With the large front rotors it's necessary to remove or modify the stock brake rotor dust shields. I modified mine by essentially trimming away everything except the protective guard ring around the ABS sensor. A coat of black paint and they looked like factory. I also removed the rear shields for better cooling.
BRAKE BIAS VALVE: A 5/18 brake bias valve is used on the 944 Turbo and 944 S2. The '18' designates the pressure in bars where the slope of the pressure curve changes. Thus, when the pressure in the rear brake line reaches 18 bar, the slope of the pressure curve flattens a bit and any further increase in pedal pressure will result in less increase in rear brake line pressure. This is a safety feature designed to prevent premature rear brake lockup. Unfortunately, it also limits the effectiveness of the rear brake circuit. I replaced my stock bias valve with a 5/33 and this works well with the larger front brakes.
Two additional brake bias valves are available from Porsche: 45 and 55 bar (see parts list below). I would be extra cautious about using the 45 or 55 bar valve on a street car, especially one not equipped with ABS.
DRIVING IMPRESSIONS: This combination of calipers, "cross-drilled" rotors, and factory pads is very, very nice. There are no grinding noises and absolutely no squeal. Pedal feel is really excellent. In normal day-to-day driving you don't realize just how good these brakes are. However, one quick stop from high speed is all it takes to show how much braking power really is available. It is much better than the stock setup. For me, front tire traction provided by my 205/50-17 tires is now the limiting factor. I now have 225/45-17s up front :-)