A couple of weeks ago a took my RS to Sebring for the first time. Going into T9 in dry conditions I had a very similar experience to what Mitch236 reported regarding his steel brakes. namely, when coming hard on the brakes there was less than full retardation rate and the ABS was pulsing. I ended up missing the apex by 20 feet or so. Pedal was firm. Did anybody else had this happen with PCCB yet? When I was applying the initial braking more softly, braking was very good. This happened a few times.
Since practically all the brake system hard components are different between steel and PCCB, I think that the problem is rather in the ABS controll software. My theory is that since the brake rotors are huge and cooling is improved over earlier cars, when the brakes are hit hard when not fully to temprature, the initial braking is not quite even left and right. The ABS mistakes this for a lockup condition, and therefore regulates pressure i.e. does not allow full braking force. If this is the case the solution may be in a software upgrade from Porsche, but they need to admit there's a problem first...

 

hate to tell ya but it's not a Porsche problem. was this the first time with the car on track? had brakes been thoroughly bedded in prior? was the track surface bumpy? how 'bout your braking technique...stab vs squeeze?

After the initial "green fade" first time on the track, no problems with my PCCB brakes.

 

It's possible, even though i did not have any fade issues. It was the first track even for the car, but I have done Sebring many times before with my (steel brakes) GT3 and C2 prior to that, and never experienced this phenomena, even on fresh sets of brakes that were installed at the track.

 

This phenomenon is Normal. Prior to my first track event with the RS I had attempted to bed-in my brakes but obviously I didn't eliminate the green fade. At the first event, first session pedal and brakes felt firm. Somewhere in the second session the pedal felt mushy and I thought Oh sh*t we got fade. But it was OK. Third session and subsequent track events no problem. Pedal is firm, modulation is good and now no problem heel/toe on street either since the firmness and pedal height of when they were new is gone. Also make sure you have replaced the stock brake fluid with a higher wet boiling point like Castrol SRF.

And remember on a bumpy surface you Will invoke ABS. Cheers!

 

This would happen to me on my 2004 GT3, but not on the track. It always happened on off ramps when I came to a stop from a highway, I would test my brakes and the first intial hard stop would always generate the ABS pulsation way before I thought it was necessary.

 

Again, it's your braking technique and/or the surface. I've driven mine for 6k miles and have not yet had ABS kick in. My Turbo S (also with Gen2 PCCBs) with 33k miles...ABS used to kick in the first 5k miles until I learned to squeeze the brakes hard but smoothly. When you "jump" on them ABS is likely to kick in more often. Just my 'ol 2 cents.

 

I agree with BobbyC. I had the same issue with my brakes...I thought I had bed them in pretty well but didn't seem to get those ceramics hot enough on the street. I incurred some green fade on my first few laps but I had enough track in-between braking zone that the green fade went away after 5 laps or so. I did notice the pedal will travel a bit more when the brakes get hot, but I am impressed how the pedal feel returns to normal once you drive it on the street for a few days.

 

Not in my experience. I have a fair amount of Sebring laps on my PCCB car, and I haven't had any issues like yours. With PCCBs, I've found that rates of slowing depend on the brakes' operating temperature. That is, when the brakes are fully up to temp after a few laps, it's very easy to gauge the ABS intervention threshold as well as projected braking distances.

 

I guess it comes down to brake temp and how hard you stab them. I still feel that the ABS program can be improved to allow for more pressure as the threshold braking continues and heat is being built up. For now it seems that the initial pressure that the ABS allowes is fixed until ABS is deactivated. The net result is that stopping distance is needlessly longer with ABS vs no ABS under these conditions. Imagine you are on the highway, crusing at 80 MPA, brakes cold, and all of a sudden you need to emergency brake. This would not be the time to finesse the brakes - they better work perfectly (max retardation limited fy friction coefficients) rater than by ABS logic (or lack off).

 

in my experience there are 2 issues:

1) is some type of green fade - how the car first stops on the street with the pccbs (instant on / instant off) will change when you first really light it up on the track and you will initially get that pedal to the floor feeling but it will go away

2) on bumpy tracks in the braking zones (limerock on the back straight), the abs unit just freaks out and dramatically lenghtens the real threshhold braking time to stop - on smooth surfaces, the abs unit is asleep - and thereore, stopping distances are shorter

 

997gtnorth - I agree with your #2 remark - "the ABS unit just freaks out". This I think is a software glitch. I hope Porsche will address it.
As for 'green fade' - I am yet to experience it. The pedal never went soft - never mind getting to the floor.

 

That's what I'm saying! +1

my911rs - seems like you have yet to bed-in your brakes...

 

I'm sure you mean T10......T9 is a pedal to the metal high speed turn.....T10 is a hard braking try not to spin turn (ask me how I know-LOL)

Sebring track map: http://www.sebringraceway.com/pdfs/06-Raceway-Map.pdf

 

Thanks Mark, Turn 10 it is.

 

As others suggested, it may be a that you are hitting the brakes initially to hard. Even on a straight line the energy transfer to the front in terms of the pitch and oscillation has to be managed. For threshold braking the front wheels need to be turning at 80% speed of the car's actual momentum. If you stab on the brakes too hard the front tires won't hold it and ABS will engage; this is particularly apparent with street tires.