yep, the rears get beaten up. most realize now that it's the electronics that might be the culprit

 

Cracks are not a good indication of wear on PCCB rotors, New PCCB rotors out of the box have cracks . Those little dime sized circles are supposed to be there... they werent from fixing "flaws" like the one poster responded.

A better indication of when to replace is the roughness of the surface and how much material is actually flaking off the wear surface. There is actually a certain permissible amount that will flake off... anything beyond that and they will need to be replaced.... Dont have the specs in front of me, but most dealerships should be able to provide that info.

 

Are these features a result of the manufacturing process? Or is there a specific function?

 

You are absolutely right on , that is one of the reasons I drive mostly with
PASM of .PASM and ABS system is what kilts rear rotors .

 

Did you mean PSM rather than PASM? In what way does ABS affect the rear rotors?

 

Conversation is getting interesting so can you explain a bit more what's going on with the electronics.

 

Yeas sorry I mean the PSM system.If you drive on the track or anywhere aggressively with PSM "on" and try to slow car fast before turns, your ABS and traction control will kick in way sooner then with the PSM "off". Majority of the break force goes to rear wheels ,and because the ABS is applied in multiply pulse signal and the bait of the break pads is not consistent rear rotors safer(it is almost like they are getting hammered).

 

Great thread. My understanding of the PCCB issue at the track is that the Stability system works by applying brake to a particular wheel when the parameters it's sensing indicate that the car is getting out of control. For example, if it's sensing rear of car oversteering out of control, it may apply brake to the outside rear wheel (don't know exact algorithm -- just giving examples).

Intuitively somehow I keep thinking controling a car spinning out of control most likely involves braking one of the REAR wheel (versus front), therefore it's the rear brake that gets killed, but I am not sure at all. Just speculating here.

I also recall reading someone (not me - no flame please ) claiming that smoother driver will wear out PCCB less.

 

That sounds more like the PTV (P Torque Vectoring) system that was introduced with the TT.2.

Your intuition is good because that's how M-B designed their stability management system BUT they use front and rear brakes selectively.

No flame here as that makes perfect sense.

 

Doing a little more research on PSM didn't answer why rear brakes would suffer more but I did find something interesting that sheds light on how PSM really works.

http://www.deter.com/porsche/PSM.txt

The Porsche website also indicates that PSM can apply SELECTIVE braking to any wheel as needed.

Still doesn't answer the question about rear brake wear.

And if rear PCCB's wear out, rear steel rotors must wear out at a faster rate too.

 

Ruf turbo, i'm not very technical and am very careful to not post things on topics like this unless im 100% sure I know what i'm talking about - that's why I used "might" in my post. I was hesitant to say anything at all because i'm far from an expert.

That said, I know i've read somewhere that even if the PSM light doesn't come on, it is still posssible that the rear brakes are being "applied" by the electronics. Or, something to that effect - similar to what Can also posted.

I'm going to stop now before I get myself into trouble LOL.

 

Quote:
Originally Posted by Porsche917
"Those little dime sized circles are supposed to be there... ."


We continue to be interested in this feature that has been reported at the start of this thread. We have now checked three full sets of PCCBs from the following cars: CGT, 07 Turbo, 11 Turbo S. None of the 12 rotors inspected have this feature.

Porsche917, can you please elaborate on your statement that these features are supposed to be there (agreed, as without them, there would be large holes), and that these are not the result of repair during the manufacturing process of some manufacturing imperfection?

Thank you.

 

You're not going to 'get yourself into trouble' for adding positively to the conversation. It's still helpful as it gives me another lead to research.

 

I"ve seen these on my car as well - can't go look at it now to give more details. I was also told they are some type of wear indicator as mentioned earlier in this thread.

 

Thanks for the very good info. This is what I will do then.