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I got couple of front rotors. They were used only one track day. Was gonna put them on my dd.
rotors developed small surface cracks around holes
Do you think they are fine to use? Thickness is there.
Rotors are junk. By the aparent depth of the cracks, too much material will have to be removed from rotors. Also if they were usable, those holes would have to be chamfered.
First of all, Guard Dad is correct. New rotors just aren't that expensive. You can get some Centric OEM replacements from Amazon for around $60.
That being said, these rotors look fine to me. If you subject drilled rotors to extreme temps on track, they will start to develop superficial heat stress cracks like those seen above. As a result, a lot of us who track our cars regularly will use blanks or slotted rotors instead of drilled ones. As a general rule, rotors like yours are fine as long as the thickness is still there, the cracks aren't deep enough to catch a fingernail, and they don't run all the way from one hole to another or to the edge of the rotor.
Close look at the rotors show significant localized hot spots, In these areas the iron is hardened. Resurfacing will temporarily restore flatness and the surface finish, but most hard spots extend deep into the metal and will return within a few thousand miles of driving. Hard spots cause uneven wear that results in pedal pulsations when the brakes are applied.
Rotors are toasted, and need to be thrown away for scrap metal only.
Light surface heat cracking on a none drill rotor, and the rotor can be saved by having it turned to get back to un-cracked metal.
On a drill rotor with the hair line cracks through the drilled holes, no saving the rotor, since the cracks will continue to run/get longer, and sooner of later, full crack through the entire rotor surface instead (read wheel just locks up sold, which just sears most of the hub/caliber/stud nuts off at the same time, as you are going down the highway instead).
Bluntly, you can get a set of new rotors for under $400, and no reason to run rotors that have already shown signs of failing. Hence when they do, going to do thousands of dollars worth of damage instead (not counting safety risk factors as well).
Other than the obvious overheated surface, those cracks are not a concern for a DD that will never see the same track conditions. The question of cost effectiveness needs to be answered. It'll cost ~$15 each to have these turned, just to see if they clean up to a workable condition. If they don't clean up, they're junk. If they do clean up, about half of their service life has been lost. Compare that to the cost of new rotors that have a service life of 50-75K of DD miles before needing turned.
IMHO - The cracking those rotors show is not something to get too too worried about. If you were doing a two day track event -would you have gone out the 2nd day with those rotors ???
Put another way - assume that you did about 30 laps the one day you tracked the car - do you think all the "damage" occurred on the last lap or two ??? I'd bet that the brakes rotors were already starting to experience cracking before half the laps were in the book - and you managed to not only do some more laps - but you also drove the car home.
But honestly - don't take the word of anyone here on this subject - next time you get an opportunity to get to a track - spend a bit of time walking around the paddock, and look at the brake rotors on the cars that are in the "fastest" groups - I fully expect that you will see rotors that look a LOT worse than what you are seeing on your car. And many of those drivers will go out and beat the heck out of those "already abused" rotors. What I worry about is not the presence of cracking, but the apparent depth of the cracking, and if you see any separation between the sides of the crack.
All of that being said - if the cracking is bothering you - spend the $150 and replace the rotors - and call it a day.
After talking to bunch of reputable shops and race/track guys i was assured not to worry about it for a daily driver.
I went ahead and installed these on my car
Will be monitoring them and if i notice more cracks or imperfections ill replace them
06-19-2015, 09:11 PM
Z06 rotors question.
