Information On Brake Disc Wear Assessment

The condition of the parts can make replacement necessary under two criteria, depending on the amount of wear on cross-drilled (perforated) brake discs:

1. Cracks in the cross-drilled friction plate at advanced stage. 
2. Minimum brake disc thickness is not attained due to wear (material erosion due to friction). 

   In practice, both forms of disc erosion occur.

   Normally, brake disc replacement is necessary if the thickness is less than the minimum thickness. In rare, isolated cases (of very high loads for long periods) replacement may be necessary due to crack formation. To a certain extent, these cracks may be rated as not important.

   The maximum permitted perforation crack length is 5 mm. 

   Fig 1: Identifying Perforation Crack Big Length (Greater Than 5 Mm)

   Courtesy of PORSCHE CARS NORTH AMERICA, INC.