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 (Too Small)

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: Identifying Perforation Crack Length (Too Big)

Courtesy of PORSCHE CARS NORTH AMERICA, INC.

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

Fig 3: Locating Cracked Friction Plate

Courtesy of PORSCHE CARS NORTH AMERICA, INC.