3-Pedals

Let me ask you the obvious question. Did you properly bed your brakes (first ones and second ones)? If not, it could explain this.

Carl Kunz

Yes, Always. Usually about 6-7 laps at 60-70% then let them cool down

Carl Kunz

No difference
.

Carl Kunz

The PFC rotors are not worn out in the traditional thickness sense, but they did develop this knocking clanking sound (like a bad cvc joint), and picked up this bad vibration when I approached speeds of 140+. When on the lift you could actually wobble them back and forth...

Carl Kunz

Hey Rick,
To answer your last question, I am still using the factory yellow calipers. I used PFC's PCCB brake conversion kit that I purchased through BBi Autosport, I requested brake pads that would be 70% for the track. I run Hoosier R7 Dot slicks since I don't know of any better rubber I can get for 20" rims. I'm sure you know that the OEM rims are staggered 20-21". Castrol SRF brake fluid, there are ceramic caps on each of the caliper pistons to help dissipate heat to the caliper. Tatum Racing who services my car at the track, and also just won the Porsche Sprint Cup Challenge a month or so at Indy. uses those piston caps on their cup cars. They are also working on coming up with a solution.
The PFC rotors are not worn down in the traditional thickness sense, but they have started to make this hideous clacking, clanking noise, (mostly rear) not unlike the sound of a bad CVC joint. On my last 4 laps I ran the car picked up this bad vibration, like I was driving on a gravel road. We recently inspected the rear rotors on the lift, and you could actually wobble the rotor... Our home track (Utah Motorsport Campus) is especially hard on right front tires, so I suspect the that same brake gets worked a little harder to. When we recently changed the front pads during the last running, the front right was almost down to bare metal and the metal backing plate was deformed, (not flat) and the caliper pistons had indented the metal almost 3/16". bad! The front of the brake pad was more worn than the back. The rear brake pads were just fine... All my brake sensors were cooked, crumbled like they were chaulk.
The original pictures I posted show the OEM PCCB brakes that were installed brand new everything, and that is what they looked like with less than 250 track miles on them. The thickness of the brake pads after did not show that much wear, not did the rotors. Even the carbon content in the rotors registered like new. They were jsut fried! I suspect the original incident the brakes were pretty close to new as well.
I use the car mostly for the track (80%), but I still drive it occasionally on the street.

Best, CK

38D

This sounds like the main issue to me. You are running the brake pads too thin for the speeds you are attaining. Same issue will be a problem for PFC steels or PCCB. Are you running the PFC thick pads (ie the double thickness ones)?

Hinz Motorsport

A few things here. It is clear you are running the pads too far past their recommended thickness on track, especially given your situation. I would recommend keeping 5-6mm of pad material left on the pad when you swap them out. The PCCB conversion kit you installed still uses stock-thickness pads (as do the same kits from Girodisc/AP). When the pads are only 17mm thick including the backing plate, that doesn't leave you much room but such is the cost of these things. Your car is too fast and Utah must obviously be very hard on brakes. What is likely happening is you are overheating the pads, which in turn causes you to add more brake pressure. Adding more brake pressure causes the caliper to deform slightly along with deforming the pad backing plate which is now incredibly hot. The caliper/pad deformation causes uneven pad pressure on the disc, which in turn introduces even more heat into the system. You now have a "runaway" brake issue and the problem will just get worse and worse and won't get better until you cool the brakes down. Even then, the pads are now deformed and everything will start all over again your next session out...this time only quicker.

One of the big reasons proper race calipers do a better job of managing heat is that they are much stiffer than OE calipers. That stiffness allows for more uniform pad pressure on the disc which helps reduce temperatures. The increased wear on the rear further suggests stability control is kicking in.

Regarding the noise, I have only heard of this issue one other time with PFC discs. What is happening is brake dust is getting packed between race hat and the snap ring and it is affecting the axial free float/preload between the friction ring and the hat. It is not hurting anything, it just makes noise. In your case, with everything being so hot you are going through pads at an accelerated rate, which in turn is generating more brake dust. You can resolve the issue by removing the disc (when you replace your pads) and pop out the snap ring and wipe out the brake dust that has accumulated in there, that will solve the issue. Oddly enough, this is also attributing to the wobble you are experiencing.

Now your car should really probably run the same size annulus that is used on the PCCB discs, but no one makes an iron rotor with that large of an annulus. The next best option is below...

I think based on everything you have said that it is time to upgrade your brakes to a proper race setup. The speeds you are seeing are simply too much for the stock brake system. PFC makes their track day packages for the 991 GT2/3/RS in both a 380 front and a 405 front. In your case, you need all the brake you can get so I would recommend the 405 kit. The 405 kit comes in two calipers types, the "S" and the "R". The "S" caliper uses 22/20mm thick pads. The "R" kits uses a wider caliper that requires 6-7mm of additional clearance to the spokes, the pads in this kit are 28/26mm thick (bingo). This is really what you need. However, depending on which wheels you are running the"R" kit may or may not clear. We can discuss that. The PFC kit uses massive Forged monobloc calipers that are lighter, stiffer, and feature thicker pads. This is an uncompromising kit that is full-on race, but based on your usage I believe it is what you need if you want to keep tracking the car.

The 405 kit should also clear most aftermarket 19" wheels, which would open up your tire selection a bit further as well.

Just know that your stock brake system was never really designed for repeated extreme abuse like you are using it. The Nurburgring is not that hard on brakes, and a lap is only 7-8 minutes. Your 20-40 minute sessions are just too much for those stock calipers.

If you have any questions on anything else I would be happy to discuss it further.

Pads shown below are 26mm thick, not the optional 28mm as mentioned above!

awew911

Listen to Rick... Sounds like your skills warrant next level up on performance and safety. 991.2 Cup for track duty. You won't miss the GT2 RS.

Hinz Motorsport

Can't argue with this either, I'm under the firm belief we should all have Cup cars... I'm gonna need you guys to buy a heck of alot more brake pads though!

In all seriousness Carl, there is no reason why you shouldn't be able to enjoy your GT2 on track. We can get this figured out. PM incoming.

thebishman

AP Radi-cal BBK

Quadcammer

What in the bloody hell are you talking about. 250 track miles is nothing. Literally one weekend worth at a decent hpde event. If you think that pccbs should be toast after that youre simply clueless

CX_GT3

I think the ideology of CCB's only last, very limited track miles comes from the 997 generation CCBs.

There are two types of CCBs on the market (correct me if wrong). High fiber CCBs are found on Ferrari and Mclarens; you can see very clear carbon weaves on the rotor, and they tend to have greater friction but doesn't last as long. Other types would be low fiber CCBs found on PCCB/Mercedes/BMW; low fiber CCBs last longer though tend to have a lower friction rate (which could be compensated by a higher friction coefficient pad).

Thrownaway

How long are your sessions?

Carl Kunz

Thank you everybody for some great insight to my braking issue. I think you have all contributed some very insightful thoughts and answers. Pretty sure I have what I need to go forward and resolve this problem.

Cheers, CK

shahrukh_bakar

This is a very interesting thread. Can you please post updates on how your next setup fares?