Porsche 996 TT, Руководство по ремонту

Страница: 1394 / 2099

46 50 02 Checking front gray cast iron brake discs
(wear assessment)
General
1. Visual inspection for cracks and evaluating cracks
2. Checking brake discs for minimum thickness
Notes on bedding in the new brake pads
Includes:
1. Visual inspection for cracks and evaluating cracks => 1. Visual inspection for cracks and evaluating cracks
2. Checking brake discs for minimum thickness. => 2. Checking brake discs for minimum thickness
top of page
General
The condition of the parts can make replacement necessary under two criteria, depending on the wear of
perforated brake discs:
1. Cracking in the holed (perforated) friction plate is in an advanced state.
2. Brake disc minimum thickness is not attained due to wear (material erosion due to friction).
In practice, both forms of disc erosion occur.
Usually, it is necessary to replace the brake discs when they fall short of the brake disc minimum thickness.
Only in rare cases (for long−term race driving brake loads / very high temperature fluctuations in the friction
surfaces), the cracking and perforating can proceed so quickly that a premature disc change has to be
performed. Both criteria governing acceptable disc condition will be described separately in the following
sections.
top of page
1. Visual inspection for cracks and evaluating cracks
Note
Perforation starter cracks arise through material fatigue due to frequent and extreme heat elongation
fluctuations. These fluctuations in the disc temperature, which generally arise in racing, tear the
perforations in a radial direction due to material fatigue (changing heat elongation conditions). For
their part, these starter cracks allow a partial relaxation of the friction plate, so that the speed at which
the cracks develop is very slow. •
The maximum permissible perforation crack length is 5 mm. •
The growth of the perforation starter cracks or a tearing of the rim of the friction plate worsens the
smoothness of braking, decreases the disc strength and therefore makes a precautionary parts
replacement necessary. •
46 50 02 Checking front gray cast iron brake discs (wear assessment) 1331