34 00... Assessing CFRP ceramic brake discs (CSiC) for wear

• For damage assessment, use the following service information.

Cracks (relaxation structures) in the brake disc friction surface 

Cracks in the brake disc friction surfaces are to be assessed differently from those in gray cast iron-brake discs. These cracks are not a wear criterion in carbon ceramic brake discs but production-related and already present in new condition.

For this, see also reference sample catalog of carbon ceramic brake discs in used condition. Refer to 34 00... REFERENCE SAMPLE CATALOG FOR ASSESSING VISUAL QUALITY OF CARBON CERAMIC BRAKE DISCS IN USED CONDITION  and 34 00... REFERENCE SAMPLE CATALOG FOR ASSESSING VISUAL QUALITY OF CARBON CERAMIC BRAKE DISCS IN NEW CONDITION 

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• Each brake disc is equipped with 6 tread wear indicators (3 each on the inner and outer side, see arrows in illustration).
• The tread wear indicators are attached near the outer diameter of the brake disc at an angle of 120° to each other. They are recognizable by their surface structure and color shading, which are different from the remaining friction surface.
• The size of each tread wear indicator is 2 cm²

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In the course of the use of the brake disc, the surface structure of the tread wear indicators (1) changes. The change of this surface structure allows for an initial assessment of the wear condition of the brake disc.

Graphic: Brake disc as new

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Illustration: driven brake disc

The tread wear indicators (3 pieces per friction side) provide only a first reference point regarding wear (initial assessment).

In connection with a one-sided driving profile (e.g. race circuit, short-distance driving), therefore deviations in the display accuracy of the indicators can result.

Under the effect of temperature and atmospheric oxygen, the brake disc loses up to approximately 200 g of its mass depending on the driving profile, mainly in the area of the carrier body. This material-specific loss of mass is to be determined by weighing the individual cleaned brake disc. The minimum permissible weight is marked on the brake disc chamber in a durable manner.

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Follow repair instructions 34 11 220 in the event of exchange.

If edge damage is present: see REFERENCE SAMPLE CATALOG for assessing carbon ceramic brake discs in used condition 

Courtesy of BMW OF NORTH AMERICA, INC.