Checking Front Brake Discs - Evaluating Cracks

As different vehicle types have different brake disc sizes, there are also different maximum crack length limits.

The maximum crack length limit is calculated as follows:

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

Courtesy of PORSCHE CARS NORTH AMERICA, INC.

Friction surface width 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

Information 

Irrespective of the crack length, the brake disc must be replaced if the crack has extended as far as the outer and/or inner edge of the disc.

Replace brake discs as a precaution if:

• 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!