Brake Disc Wear Assessment - General

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

Cracks in the cross-drilled friction plate at advanced stage.
Brake disc minimum 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 after the thickness falls below the minimum. 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 Length (Too Big)

Courtesy of PORSCHE CARS NORTH AMERICA, INC.