Evaluating The Cracks On The Grey Cast Iron Brake Discs

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The brake discs must be replaced (as a precautionary measure), if the perforation crack length is over 5 mm (as there is no mileage reserve in the event of further extreme load) and/or the friction plate rim is torn (less smooth braking and an increase in the likelihood that a disc will break)!
In the evaluation of damage, the following drawings must be used!

Corresponds to a disc exposed to above-average load. See Fig 1 .
- Need not be taken out of the vehicle!
Fig 1: Identifying Cracks On Grey Cast Iron Rear Brake Discs (1 Of 3)
Courtesy of PORSCHE OF NORTH AMERICA, INC.
In parts, perforation starter cracks are over 7 mm long. Conditions after shock braking 1,200 times (minimum desired: shock braking 200 times). See Fig 2 .

Fig 2: Identifying Cracks On Grey Cast Iron Rear Brake Discs (2 Of 3)
Courtesy of PORSCHE OF NORTH AMERICA, INC.
- Brake disc can no longer be used!
Brake disc with torn friction plate rim -arrow- . See Fig 3 .

Fig 3: Identifying Cracks On Grey Cast Iron Rear Brake Discs (3 Of 3)
Courtesy of PORSCHE OF NORTH AMERICA, INC.
- Brake disc can no longer be used!