Checking Grey Cast-Iron Brake Discs - Minimum Thickness
Information
Normally, brake discs are used until the maximum wear dimension is reached. Only in a few exceptional cases is it advisable to skim the brake discs (if there is deep scoring or corrosion of the friction surface). In this case, only the brake disc dressing machines approved by Porsche AG must be used (see appropriate Service Information ).
- Only "as new" brake discs may be reworked!
- Only rework the brake discs symmetrically, evenly from both sides!
Information
As the pressure force of a brake piston on the brake pad varies in magnitude, different areas of wear arise on the friction surface. The brake disc can basically be divided into two areas of wear:
- Outer wear areas. > Outer wear areas
- Central wear area. > Central wear areas
Outer wear areas
Central wear areas
The natural balance between stronger and weaker braking ensures that in almost all cases the typical wear profile of a perforated (cross-drilled) brake disc (friction plate) arises.
This means that the inner and outer smooth friction edge zone is most worn.
Information
Unlike smooth brake discs, on which the minimum thickness is measured in the middle of the disc, the minimum thickness of perforated (cross-drilled) brake discs must always be measured on the inner and outer friction surface track that is most worn -arrows- .
Wear areas A and B
- A Central wear area
- B Outer and inner wear area
- Measure brake disc thickness.
- 1.1 Measure the brake disc thickness -X- close to the outer or inner friction surface track -arrows- at least three different points -A, B, C- offset by 120°. A commercially available micrometer screw or a brake disc gauge is a suitable measuring tool.
Measurement points for brake disc thickness
- Compare measurement with wear limits.
Non-S models:
> 4600TW TECHNICAL DATA/BRAKE WEAR LIMIT
S models: