Checking Front Brake Discs - Evaluating Cracks

Different vehicle types have different brake disc sizes. This produces differences for the maximum crack length limits.

Maximum crack length limit is calculated as follows:

0.5 x a (-a-  = width of friction surface in mm).

Courtesy of PORSCHE CARS NORTH AMERICA, INC.

Width of friction surface a

The length of a crack can be measured with a steel rule, for example. > Brake discs 

Courtesy of PORSCHE CARS NORTH AMERICA, INC.

Brake discs

As a precaution, brake discs must be replaced when:

Information 

• Irrespective of the crack length, the brake disc must be replaced if a crack has extended to the outer and/or inner edge of the disc. 
• The brake disc must also be replaced if chipping/breakages in the surface coating exceed 3x3 mm. 

• the > Maximum crack length 0.5 x a mm  (a = friction surface width in mm) is exceeded!
• the > Maximum crack width 1 mm  is exceeded!
• the > Maximum crack depth 1.5 mm  is exceeded!