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Spidery cracks on my drilled discs.....

robbosliding

robbosliding

PCGB Member
Member
One other point of concern which I have had reassuring advice about- I showed the car some hard use of the brakes. I noticed whilst cleaning that some spidery cracks had appeared around the drilled holes on the centre two rows of vents on the front discs. I have been advised that under 5mm in length is tolerable, anyone else had any similar experience or have any advise to offer? The discs/pads are OEM for the record.
 
To quote the manual:

  • Perforation starter cracks arise through material fatigue due to
    [*][FONT=verdana,geneva"]frequent and extreme heat elongation fluctuations. These fluctuations[FONT=verdana,geneva"][*][FONT=verdana,geneva"]in the disc temperature, which generally arise in racing[FONT=verdana,geneva"][*][FONT=verdana,geneva"]conditions, tear the friction plate perforations in a radial direction[FONT=verdana,geneva"][*][FONT=verdana,geneva"]due     to material fatigue (changing heat elongation conditions).[FONT=verdana,geneva"][*][FONT=verdana,geneva"]For their part, these starter cracks allow a partial[FONT=verdana,geneva"][*][FONT=verdana,geneva"]relaxation of the friction plate, so that the speed at which the[FONT=verdana,geneva"][*][FONT=verdana,geneva"]cracks develop is very slow.
    [FONT=verdana,geneva"]
    [*][FONT=verdana,geneva"]    The maximum permissible perforation crack length is 5 mm.
    [FONT=verdana,geneva"]
    [*][FONT=verdana,geneva"]    The growth of the perforation starter cracks or a tearing of the[FONT=verdana,geneva"][*][FONT=verdana,geneva"]rim of the friction plate worsens the smoothness of braking,[FONT=verdana,geneva"][*][FONT=verdana,geneva"]decreases the disc strength and therefore makes a precautionary[FONT=verdana,geneva"][*][FONT=verdana,geneva"]parts replacement necessary.[FONT=verdana,geneva"]
​


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Thanks for the reply Richard.

Are the cracks likely to be through the disc or just surface cracks? I am hopeful they are the latter and may disappear with normal use of brakes. Your views and experience please?

Cheers
 
Wishful thinking I'm afraid - I don't think they will disappear with use. If/when they exceed the dimension shown - replace them.
 
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