Checking Front Brake Disc - Minimum Thickness

Information 

Normally, brake discs are used until the maximum wear dimension is reached. → WM 4650TW TECHNICAL DATA/BRAKE WEAR LIMITS  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 disc brake dressing machines approved by Porsche AG are to be used .

• Only as new brake discs may be reworked! 
• Only rework the brake discs symmetrically, evenly from both sides! 

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:

1. -A-  Outer and inner wear area.
2. -B-  Central wear area.
   Fig 1: Identifying Front Brake Disc Minimum Thickness Wear Areas

   Courtesy of PORSCHE CARS NORTH AMERICA, INC.

The central wear area -B-  is the area with the highest degree of wear.

Fig 2: Identifying Central Wear Areas

Courtesy of PORSCHE CARS NORTH AMERICA, INC.

• Measure the brake discs using a suitable micrometer at least three different places (-A, B, C-  ), offset by 120°.
  Fig 3: Measuring Brake Discs Using Suitable Micrometer

  Courtesy of PORSCHE CARS NORTH AMERICA, INC.