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What is acceptable as far as rotors cracking? If you see hairline cracks at an HPDE should you stop and replace Asap? Is it cause for major concern? I am on Canada cast Napa rotors but have my brembo rotors available.
 

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I'm no expert on brakes, but as far as I know hairline cracks on the rotor face are normal. Once those cracks extend to the edge of the rotor, its time to replace. I'm sure people with more brake experience can give you a little better info.
 

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That's correct. The small surface cracks are also known as "heat checking" and are common and normal.
 

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Discussion Starter #4
Gotcha, there was a corvette guy here that helped me out and said the same thing. After looking at his rotors I knew I was fine. Only small hairline surface cracks a couple of millimeters long.
 

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General rules of thumb for rotor cracks:

  • If you catch a fingernail in it, it's trash.
  • If any crack is longer than 1", it's trash.
  • If it reaches the edge of the rotor (inside or out,) it's trash.
 

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I saw this rotor on a NASA CMC car in the pits - he kept driving on them the remainder of the day.

 
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