Checking Grey Cast-Iron Brake Discs - Evaluating Cracks

No need to remove from the vehicle as the perforation crack length is small (less than 5 mm). 

Fig 1: Identifying Perforation Crack Length (Less Than 5 mm)

Courtesy of PORSCHE CARS NORTH AMERICA, INC.

Some perforation cracks are over 7 mm long.

Brake disc cannot be used (maximum permitted perforation crack length is 5 mm)! 

Fig 2: Perforation Crack Length (Greater Than 5 mm)

Courtesy of PORSCHE CARS NORTH AMERICA, INC.

Brake disc with cracked friction plate rim -arrow-. Brake disc cannot be used! 

Fig 3: Locating Damaged Friction Plate Rim

Courtesy of PORSCHE CARS NORTH AMERICA, INC.