I have 996 GT3 350mm brakes on my Cayman S 3.8 w/ Deman rotors, PFC 08 pads, PFC fluid, GT3 brake ducts. One would think that I'd have all the brakes I could want. Not true. I've tried different rotors, pads, fluid, etc. but still have fade and long pedal travel after a few hard laps. I think the problem is heat. After observing a drop-off in highway gas mileage I'm wondering if the pistons aren't fully retracting? The seals are long gone and last time I changed pads one of the ceramic pucks came off. How can I test this hypothesis? Or any other thoughts? (Aside from not braking so much? Working on that.)

 

Are you saying the brake piston seals are shot? Replace them first before you do anything else.

 

Have your calipers rebuilt....which includes pucks and seals, fresh fluid and a bleed. I had to do this last year. ALL my pucks had essentially disintegrated along with the seals. Be prepared for a long wait for the pucks. I eventually had to give up waiting and bought new calipers. Which I was not happy about. 3 or 4 months later the pucks came. Rebuilt the original set and they are now sitting on a shelf ready to go for the next time the pucks disintegrate. I found it rather ridiculous Porsche did not have pucks readily available and that PNA told my shop to "just have your customer buy new calipers"

Best of luck...

PS: When the seals are gone a lot of grit & sand ends up in the caliper it self which could cause binding. Also, I would recommend Endless 650 fluid.

 

Yes, the piston seals are fried. My first thought when I saw how bad they were was that I needed to replace them but a bit of forum research led to the conclusion that w/ track use they will just end up that way again pretty soon anyway. I.e. don't bother. However I think they do provide some spring to help the pistons retract.

The pucks look OK, one just fell off because there was no more seal to hold it. Again, forum research said it is an annoyance to have to hold them in place when replacing pads but, otherwise, no problem.

Is there any way to test if the pistons are not retracting? I think the falloff in highway gas mileage could be a clue.

FWIW I have also used SRF and it was the same. I'll give Endless a try next time.

 

The pistons should move freely if you push on them with your fingers. If not, then the seals are bad. Yes, the seals need more frequent replacement with track use but that's the price of driving on the track.

 

FWIW, here are several racers who say that the seals are not necessary:
http://rennlist.com/forums/porsche-c...yes-or-no.html


How hard are they to replace? I used to have an RX-7 race car and they were a PITA.

 

First find out if you have a heat issue. Try those stick on temp strips. More cooling is better. Make sure you have good flipped. Endless or motul or castrol

Have a shop inspect if needs to repair. These are wear parts. There are 2 seals. Inner and outer. Go to a shop that can get the porsche Motorsport rebuild kits. This come with piston inner seal and puck. About 150-200 per caliper. Order puck clips. These keep pucks from separating from piston. 997 504 864 00 about $5 each. Outer seals should be used unless your car is 100% track and you have service schedule for brackets. Outer seals can be ordered from porsche.

Check rennlist for thread I posted with PDF of Motorsport rebuild kit numbers a while ago

 

Could not find that thread.

I ordered some stickers and will probably just go ahead and order seal kits from Zeckhausen. Can the outers be installed w/o removing the pistons?

I suppose I'll switch back to SRF as it has the best wet boiling point.

However, the fade has not changed regardless of fluid, rotors, pads, lines, master cylinder, GT3 ducts.

 

I had an issue on an 09 Cayman S which felt like fade but turned out to be something else. Under hard braking the pedal would go to the floor. I still had brakes but it wasn't a good feeling. On inspection by the dealer what they found was the rod going into the accumulator was not set properly and there was a plastic tip on it which had cracked. They replaced the accumulator, tip and recalibrated the rod after which I had normal brakes again. Odd combination of problems.