I purchased a 2006 m3 with the Alcon 6 piston front and 4 piston rear bbk. The brake pedal feel was terrible with a low sinking pedal and a lack of modulation as just breathing on the pedal caused way too much deceleration. I upgraded to a Porsche 997 carrera booster and 997 gt3 master, part # trw : pmn166. I’m pretty sure all 997’s use the same master . You will need to fabricate a small adapter from the pedal to the threaded booster shaft. And shorten the hollow threaded part on the booster to use the long m3 bolts . Now the pedal is as firm as a 997 gt3 with no travel .
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Sounds like air in the system coupled with a low torque pad compound like PFC08.
No air and street/track pads. The fluid displacement from a 2 piston front to a 6 piston front , 1 piston rear to 4 piston rear Calipers is substantial. The stock master is designed for stock Calipers and does not have the volume to fill all those pistons without pushing the brake pedal down. That is why production cars with these huge Calipers have bigger masters to preserve a firm pedal.
That's interesting, as I have a Z3 3.0i brake master cylinder in my car on Porsche Brembo 993TT big red front calipers and 998 rear calipers without any issue.
Maybe its your pad compound, I've never had good luck with PFC08s. Worst pads I've ever put on my evo and my E92M.
Piston count has nothing to do with pedal feel. overall piston displacement is what can change how the pedal feels. How much surface area do your alcon calipers have compared to stock? E46 M3 has single piston calipers at all 4 corners by the way. I think you already know that but your 2 -> 6 front 1 -> 4 rear statement doesn't support my assumption.
Last edited by S14; 10-27-2020 at 08:31 PM.
I know a 6 piston Stoptech ST60 for my E90M3 has slightly less total piston area than the factory 1 piston sliders.
You’re right, same issue on my 2001 M3 E46 with Apracing 6+4 all around.
The piston area increase too much for the stock pump, which is even narrower on diameter than the 2002+ M3.
It seems I could solve with a Z8 brake pump, whick is 27 mm at the front.
I couldn’t swap the 997 pump because I need a 3 port pump to connect the precharge pump which MK60 brake system on 2002+ does not have.
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