Visual inspection for cracks and crack assessment


Perforation cracks are caused by material fatigue due to severe, repeatedly fluctuating heat expansion. Disc temperature fluctuations of this nature that occur especially under racing conditions produce radial cracks in the perforation holes of the friction disc due to material fatigue (alternating themal expansion). These cracks, on the other hand, will reduce tension of the friction disc to a certain extent, i.e. crack grwoth continues only

The maximum admissible perforation hole

Further growth of perforation hole cracks or cracks at the edges of the frictions disc impair braking comfort and reduce disc strength. For this reason, the components affected should be replaced as a precautionary measure.

Checking brake discs for cracks

The brake discs have to be replaced (as a precaution) in the following cases: Length of perforation hole cracks is more than 5 mm (this means that no service life reserves remain if brakes continue to be subjected to severe loads) and/or if cracks appear at the edge of the friction disc (reduction of braking comfort

For example of crack assessment, refer to page 46-22.

1996 Porsche 993 Starter Wiring Diagram
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