I replaced my OEM rotors about 2000 miles, two track days and several autocrosses ago, because of the heat cracking. Nothing real serious, but I thought that it was time.

The right front rotor just cracked, all the way through, and accross the radius where the brake pad contacts the rotor, all the way to the edge. The rotor is toast. The crack occurred on the highway, driving legally, when I had to brake quickly (no ABS; just quick braking).

This brings up several questions:

I assume that this is not the normal behavior for a rotor. Was this likely just a faulty rotor?

Nobody has a replacement rotor, in either the Seattle area or the Portland area. I have an autocross tomorrow, and a track day Tuesday. I've put one of the OEM rotors back on to replace the cracked one. I'm not worried about the OEM rotor detonating, but I'm concerned about having a somewhat worn rotor (not badly worn, but clearly more worn than the other new one) on one front wheel, and an almost new one on the other front wheel. Is this an issue, or should I put the other old rotor back on, also?

And, while I'm at it, I'm curious about something else. The brakes never had the initial bite with the new rotors that they had with the old rotors. The brakes work fine with the new rotors, just less initial bite (Cobalt GTS pads on the street/autox; no difference noted with the full race pads on the track). Is there some sort of "bedding" process one is supposed to do for new rotors, analogous to the bedding of new brake pads?

 

I missed it: what did you replace the OEM rotors with?

 

This, from the S2ki marketplace.

 

Did you inspect it before you installed it?

 

Yeah; it was visually fine, and it worked just fine right up until it cracked. I know when it cracked.

It got through two track days and many, many autocross runs with no sign of any problem. This was not a latent crack that got bigger; it was a new crack all of a sudden, nuking the rotor.

 

Stoptach has an article regarding bedding in of pads and rotors: http://www.stoptech.com/whitepapers/...erformance.htm According to that article, the bedding in of new rotors isn't related to longevity but rather to seasoning a new rotor surface with a layer of pad material.

Rotors typically crack due to uneven heating or cooling.

 

Put back the matching pair of OEM rotors. OEM rotors are perfectly fine and as good or better than anything else for tracking. It's what I use.

 

Same thing happened to me on the same rotors. Only difference was it was 1 day at Thunderhill and 4,000 street miles. I still have the rotors here if you want to compare pics...

 

I assume that it was a faulty rotor. Some problem with the casting.

I have spares, if you need them. Some used rotors you could have for free as emergency spares. I also have a set of brand new rotors you could buy for what they cost me. I'd have to look up what that was.

Yes, new rotors are supposed to be "bed in".

 

I always carry at least 1 used rotor to track days, too. Just in case.