Rob S

Jake 951,

I had a very similar problem years ago on a 944S2. I wrote about the problem -- and the solution I found (see post #19). It essentially involved a process that I wouldn't have believed would work. Until it did...

http://forums.pelicanparts.com/porsc...low-pedal.html

It essentially involved installing the pads after first extending the pistons to the point where the pads just barely were able to fit. I had to literally tap them in with a mallet. This consumed the "slack" normally created by the piston seal square O-rings during brake release. Amazingly, it was a permanent fix. Even after significant pad wear from track use, the low pedal never returned.

Rob

Jake951

What you experienced is exactly the problem I'm having. I've also heard from other motorsports "authorities" that piston seals can be stiff when new and the stiffness can pull the pistons back into the calipers. This creates a feel that is similar to knockback but should more properly be called "pullback". The solution, as you found, is to break in the seals by forcing them to hold the pistons up against the pads. I did this with the broomstick that you see in the photo at the start of this thread.

The broomstick improved things dramatically on the street after rebuilding the calipers with new seals, but I'm still getting the "long" pedal on the track when the brakes get hot. When this occurs, you can see by eye that a gap opens up between the pistons and pads when you let off the brake pedal, even with the car standing still. A quick tap on the brake pedal temporarily closes the gap, but you have to get on the brakes immediately after the tap to get normal braking. Otherwise the pistons will retract again and you are back to a long pedal. If you let the brakes cool down for several hours or overnight, the gap goes away and the brakes are rock solid again.

I have to assume that I have extraordinarily stiff seals and I need to break them in some more, or find a different seal that is not so stiff. I've tried both Brembo and StopTech seals and they both exhibit this problem in my calipers. Porsche will not sell you seals for these calipers, but want you to buy an entire caliper assembly.

KA MOTORSPORT

It is very important to soak the seals in conditioner over night before installing them.

modoz61

I am not certain if the OP answered this anywhere else in the thread but

What is your pad wear like?

even or tapered?

After 5 years and lots of track days and great road trips I replaced my calipers as I was getting excessive tapering on pad wear. While elongation of piston bore / poor seals can explain a little of this

our suspicion was caliper flex - new calipers fitted and everything back to rock solid, the calipers refurbished and seals had been replaced on the previous set once so it was deemed end of life

just a thought

Jake951

What exactly does the conditioner do? Does it soften the seals so that they aren't so stiff when you install them?

Jake951

My pads are pretty uniform in wear, with a mm or two. I do know the OEM calipers in the GT3 do flex. You can see this with the car standing still and having an assistant step hard on the brakes while you watch the calipers. There is a "monoblock" Brembo caliper that has a solid bridge across the top that provides resistance to flexing. The OEM caliper does not have this bridge.

I have considered upgrading to the monoblock calipers but that would be my solution of last resort if I can't find a less expensive solution.

KA MOTORSPORT

The Brembo SCF Seal Conditioning Fluid ha been developed to give the best initial surface conditioning to new Brake Caliper seals before assembly. When used correctly the seals will not require any bedding onto the pistons and the correct seal friction and optimum design performance is achieved immediately.

mm450exc

RESOLVED!!!!!!!!!

Just to close this thread...

PFC08 sorted the problem for me. Can go all day long now!

Jake951 installed a StopTech kit I believe and all sorted as well.

bergx7

Good to see. Definitely need to keep track of pad wear, especially when using two different pads on the same set of rotors (e.g. swap track pads and street pads). Sometimes they don't quite mate right when you go from one to the other.