Centric Slotted Rotors: It's not pad transfer I have, it's flaking/pitting!

[Torsion]

Wanted to share since I haven't seen any threads discuss this.

I'm using Centric Slotted rotors and Carbotech XP20 front pads. After two track days, the wear on the rotors is really splotchy... which I don't like very much.

I *thought* most of the splotches around the area of the slots was pad transfer... but today when I looked more closely in the right lighting I noticed it was actually flaking and pitting of the outside layer of metal.

I asked CT about them, and here's what they said... which now makes more sense:
"Those rotors have one of those special coatings that is being used from time to time. I am referring to the contact surface of the rotor. Rotor manufacturers are applying different coatings to help longevity and thermal capacity. The problem with that is the coating only lasts so long and causes issues like you are seeing now. "

What do you think?





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[VoodooBoss]

Can you feel that with your finger nail? I'm not convinced what they told you is correct in this situation. Your rotor surfaces should be solid iron.

 

[Torsion]

Maybe you're right... it was surprising to me too... but this was straight from Carbotech, so I figure they deal with this stuff all the time and must know one rotor from the next.

Looking again at the photos, it's *possible* that the black areas are caked on pad material (and/or dirt)... and that it's flaked off in some areas.... I'm really not sure.

 

[steveespo]

Bob
What does Centric say? Do they advertise a wear surface or treatment of the rotor face that may explain what Carbotech said? That does look like the top layer of cast iron flaking away. The heat generated by race pads can carborize the iron causing rapid oxidation. This is how acetylene/oxygen torches burn through steel. If they surface harden the rotor surface, maybe they make it brittle and it breaks away as the heat penetrates to the untreated iron. A metallurgist is what we need to decipher this condition. That isn't pad transfer though.
Steve

 

[Torsion]

Good advice Steve, I just sent an email out to StopTech.

I also did a little scraping on the rotors with a small blade... as far as I can tell those truly are pits in the metal rather than in a thick layer of pad material.

 

[Centri5.0]

I have the same setup. Mine do not look like this. Willt take pictures tonight.

Sent from my DROID4 using Tapatalk

 

[Torsion]

Here is the reply from StopTech:

We have seen this issue before, also with Carbotech pads and feel this is due to the metallic content of their pad formulas.
Here is the response provided by our director of engineering after reviewing a previous instance of this issue as seen on one of our big brake kits:

“It seems like this pad formula has a lot of iron being deposited and it is in a valance state to readily start oxidizing (rusting).

The oxidized iron transferred from the pad will flake off under these conditions.

The deposits of course will cause the judder.

I would recommend new rotors, a new friction formula chosen based on the application and then the friction material needs to be bedded in properly and watched to keep it bedded in”

It is possible that your pads may be running too hot or too cold, so I would recommend working with the pad manufacturer to see if a different compound would suit your setup better given your recorded rotor temperatures.

 

[pufferfish]

i use the centric rotors with XP12 and no such issues. i have used the XP16 and XP20 before with factory rotors and they both ended up looking a lot like yours. i feel like i beat this to death, but i believe braking style and brake cooling efficiency determines if you will do well with the higher heat range pads or not. i suggest you replace your rotors with new centrics and XP12 up front. i believe they will perform better for you. just my 2 cents.

 

[Torsion]

Thanks for the advice guys. pufferfish, perhaps you are right and XP12s might suit my situation better... but I seriously can't afford to keep messing up my rotors and pads like this.

we're gonna find out one day that I have squirrels living in my brake ducts or something.

 

[drano38]

I had a similar issue with Carbotech.
Started with XP12. Sent pics to company, and they said I might be over temping them, and try RP2. Same thing. Tried XP16. Same thing. Maybe I was eroding rotor rather than pad transfer onto rotor also. But I got very bad shudder while braking on track.

So last summer I switched to PFC 01, and they work great. More expensive, but I don't waste track time trying to clean off my rotors.

 

[Torsion]

How long do they last, drano38?

 

[drano38]

PFC 01? Three days at Brainerd MN, and 2.5 days at Hastings NE took them down about 1/2 to 1/3 material remaining.
This summer I'll try PFC 08, their endurance pad.

 

[Torsion]

Good to know, I'd love to try a set of PFC pads. If those don't work for me I'll give up and buy a Prius.

 

[drano38]

I'm sure PFC 01 or 08 will work great for you.
ArizonaBOSS, 2012YellowBoss, and others have tracked them extensively and really like them.
I've still got Carbotech XP8 on the backs (and they stay on for street driving). Not sure if I'll use them again, or move to PFC 97 when needed.

When you're ready for PFC, look to the right for KNS Brake's ad.

 

[ArizonaBOSS]

I use PFC01s on Centric blanks and the pads typically last about 4 events before needing to be replaced. I am very happy with their longevity and performance.

 

[Torsion]

Can I drive to and from the track with PFC01s on the front?

 

[ArizonaBOSS]

Can I drive to and from the track with PFC01s on the front?

Yes but it may be noisy

 

[Torsion]

Update for posterity: I took a wire brush and cleaned the rotors up a bit. Then I put on another set of XP20 pads. Then I did a track day on NT01 tires (not PSS like last time).

Here's how the rotors look afterwards, much better. The pitting is still present, but looks less pronounced. And the pad material seems to be more or less well distributed across the rotor, rather than splotchy like last time. Braking performance was fine all day.

So, I'm happy that I didn't have to scrap these rotors.

I don't know why they look better after this track day than after the last, though. Maybe they were hotter with the NT01 tires, and thus working within range? Maybe my other XP20 pads were glazed, but these were not?

 

[Theviking]

Can I drive to and from the track with PFC01s on the front?

I've used the PFC08's for two track days so far (Shenandoah) and they worked very well paired with a new set of Centric rotors. Granted it's not really a high speed track (115-120mph in my case) and I do have brake cooling ducts. I would sometimes get a little bit of chatter towards the end of a session but it would clean up quickly during the follow session. The pads look like I could easily get several more days out of them.

Also ran them on the street for a brief period. In my case they made next to no noise and stopped just fine even when cold. But you will get tired of cleaning the dust off your rims.