What do folks here use as a rule of thumb for replacing rotors with crazing / cracking. Crack to edge, catch a fingernail, wait until it breaks into 2 (or more) pieces?
I'm on the fence about whether to give the rotor below another day or two or not (no cracks to edge, but crazing evident across rotor, can catch my nail in the larger ones).
i would replace those asap.
To prevent that failure in the future, dont buy cross drilled rotors! really there is no reason other than looks to get a drilled rotor.
there used to be a reason for drilled rotors ... not now.. slotted if you just have to have something different.
I would say that they are done. You could wait until a crack has traveled to the edge of the rotor but I wouldn't.
Also why drilled rotors? All the holes do is give a crack a place to start. Look at the cracks almost all of them start at a hole.
I worked on Trans Am cars back in the 80's & 90's and we used to use drilled rotors but stopped and ended up with the same braking performance and longer rotor life. In fact we lost a 3rd place finish due to a rotor letting go and taking out the brake line and causing the car to spin and hit the wall.
when? About now.
Whelp... on a race car those are done.
On a road car - you "could" probably wait longer but why risk it?
Oh and +1M on the "Stop buying rotors with holes" unless you get them for free.
+1 to each of the posts above
Interesting that the "replace 'em" posts here are at odds with the reports from the track-day regulars at corvettefourm (pic is of my C6), where the response was "run 'em". Interesting. Was hoping for uniform results across my polling of my two fav racing-related forums.
For trivia's sake, they're the factory rotors-- GM didn't give me any choice. Whenever they're done I have blanks ready to go on. I suspect GM drills them because that's what the country club vette buyers whose car will never see WOT expect to see.
Thanks for the feedback above and additional thoughts!
They wouldn't be on my car in the first place
Oh, every one sort of said that already.
In reply to NOSLO6:
If you're still under warranty I'd take it in for a try for warranty replacement, then immediately swap to the blanks and sell the like-new drilled rotors to someone else. Just don't mention the word "track" there 
^What they said^.
In my M3 track rat I do a lot of my catching up on the brakes. I go pretty late and deep and the car is on Toyo RA1s in 255/40-17 and about 3200#, so they're getting worked pretty hard. I'm using Performance Friction 01 pads now - used to use Hawk HT-10s. For rotors I'm using aftermarket iron blanks like Balo or Centric. The car stops fine, they hold up, and they're very cost effective.
I tried a set of slotted rotors on my IT2 Neon. Shocked, I was, when they developed cracks in the bottom of the slots, where the material is thinnest.
doesn't porsche use drilled rotors too?
the slotted rotors aren't much good either with the latest technology in brake pads.... they're just not as bad as drilled...
as for the 'Vette drivers.... the ones I see at the track are either replacing rotors between sessions or are going to after the next session... and non of them are running expensive drilled / slotted ... all are running blanks
I'm not sure that I would let those pass an autocross tech inspection.
I've got some cheese-grater rotors on my turbo FC. They aren't cracked, but I plan on replacing them once I get the car up and running with Brembo or Centric (Stop-Tech's parent company) blanks. I don't think they are worth the risk or the added pad wear, and the FC's stock brakes are pretty damn good to begin with.
belteshazzar wrote: doesn't porsche use drilled rotors too?
I know quite a few Mercedes Benz use drilled rotors as OEM. I just removed a drilled pair from my SAAB c900, no cracks, but one of them insists on being warped just enough to cause a vibration. I've cut it twice now, and I might try one more time just for stubbornness sake (if it is still above minimum spec). Am I right in guessing that once they (rotors) warp they want to stay that way?
Back to the OP: if it was my car I would loose those rotors as fast as possible. I might be willing to try a different brand of drilled rotors, but I wouldnt be surprised to see more cracks at some future time.
Replace them with good solid units (my thought before reading all the other posts).
Use Carbotech XP10's and thing will stop on it's nose all session long. Best pad I ever used for cars under 3,500 lbs.
porsche, mercedes, corvette... seems like if it didn't work, they wouldn't bother. not to say that they do or don't. i've never even had any.
HappyAndy wrote: Am I right in guessing that once they (rotors) warp they want to stay that way? .
If they warp right away, I think its usually a mis-shapen casting- too much meat on one side, not enough on the other. Had a new J-hook rotor on the SLM race car that warped quite badly right away, and the edges were quite different in thickness as the rotor turned.
I'm going to err on the cautious side and put my new NAPA blanks on.
For those who are interested, a tech from DBA posted a really good pictoral guide to crazing in a recent thread. He, like the crowd here, thought these were on the way to being done.
THX for the feedback!
fornetti14 wrote: Use Carbotech XP10's and thing will stop on it's nose all session long. Best pad I ever used for cars under 3,500 lbs.
That's exactly what I'm running-- I love them too.
Just as an FYI, these factory rotors did a decent job-- the wear you're seeing is after about 8 track days, most at NJMP where both tracks have very heavy braking zones at the end of the main straight. Serious track rats who carefully log their track time and replacement costs have generally reported getting similar life out of the factory rotors, the popular and higher dollar DBA-replacement slotted or blank rotors, and the lower dollar but surprisingly durable NAPA blanks.
Again, thanks for the thoughts. GRM rocks. 
belteshazzar wrote: doesn't porsche use drilled rotors too?
Yes, but the holes are cast in, not drilled.
Gearheadotaku wrote:belteshazzar wrote: doesn't porsche use drilled rotors too?Yes, but the holes are cast in, not drilled.
And I've heard they still crack.
Yes, but the holes are cast in, not drilled.
lawlz
You'll need to log in to post.
