Checking brake disc minimum Notes

Along the innermost and outermost friction disc tracks that have no holes, wear of the corresponding brake pad friction area is lowest - compared to the center hole area -if the brakes are subjected to high contact pressures. As a result, less severe braking will lead to a corresponding increase of surface pressure in these areas and, hence, to increased friction disc wear. The natural ratio of heavy to light braking will produce the typical wear profile of a perforated friction disc in virtually every case (inner and outer, smooth friction edge zone shows greatest wear / refer to Fig. 19791-46).

Arrows = area of greatest wear on brake

A = perforated friction area B = smooth friction edge area

As opposed to smooth brake discs where the smallest thickness is measured in the disc center (effective frictional radius), the minimum thickness of perforated brake discs must always be measured at the inner or outer track of the friction disc that is worn

Example for area of greatest wear

The figure below shows the typical wear groove pattern (arrows) of a perforated 993 brake disc that was driven up to the wear limit under severe long-term operation (test opera-

Checking minimum brake disc thickness

Use a suitable micrometer to measure the smallest brake disc thickness at one of the two smooth friction edge zones (at the friction edge zone that is worn to the greatest extent).

For the wear limit (minimum thickness), refer Observe important note on new brake pads

Micrometer Check Brake Disc

Important note on new brake pads

Due to the relative high abrasive action of perforated friction discs, the wear pattern of newly fitted brake pads will adapt itself relatively rapidly to the wear pattern of the used brake disc. After introduction of optimized perforation patterns, the service life of perforated Porsche discs as well as of brake pad materials is now almost equal to the service life of smooth discs.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

Don't pay hundreds of dollars to find out what is wrong with your car. This book is dedicated to helping the do it yourself home and independent technician understand and use OBD-II technology to diagnose and repair their own vehicles.

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