Measuring Front Brake Discs

Information 

Measuring the brake disc includes: 

• Measure the brake disc lateral runout.
• Measure the wheel hub lateral runout.
• Measure the brake disc thickness tolerance.

Enter measured values in the brake disc measurement sheet.

> 4X00IN BRAKE DISC MEASUREMENT SHEET

1. Measure the brake disc lateral runout.
   1. 1.1  > 9510/1 - Adapter plate-1-  must be fitted on the wheel hub using standard wheel bolts. > Tightening torque 160 Nm (118 ftlb.) 
   2. 1.2  > VAS 6079 - Dial gauge-2-  must be fitted at a suitable position on the wheel bearing housing.
   3. 1.3  Fit dial gauge -2-  with slight preload and measure the lateral runout at the greatest external diameter of the brake disc. > Measured value 0.06 mm 

      Courtesy of PORSCHE CARS NORTH AMERICA, INC.

      Dial gauge on brake disc

2. Measure the wheel hub lateral runout.
   1. 2.1  Remove front brake discs.

      > 465019 REMOVING AND INSTALLING FRONT BRAKE DISC 

   2. 2.2  Fit dial gauge with slight preload at a suitable position on the wheel bearing housing using > VAS 6079/1 - Dial Gauge Holder for Brake Discs  .

      Information 

      The front face of the wheel hub must not be corroded. Clean it using fine emery paper if necessary.

   3. 2.3  Measure the wheel hub lateral runout at the front face of the wheel hub.
      1. 2.3.1  Take measurements at the external and internal diameter of the wheel bolt area -arrows-  (5 measuring points each). > Measured value 0.03 mm 

      Courtesy of PORSCHE CARS NORTH AMERICA, INC.

   Measuring points on wheel hub

3. Measure the brake disc thickness tolerance.
   1. 3.1  Use a suitable micrometer screw to measure the thickness tolerance at 8 points within the braking surface. > Measured value 0.02 mm 
4. If the wheel hub lateral runout is too high:  Replace wheel hub.

   > 405719 REMOVING AND INSTALLING FRONT WHEEL BEARING

5. If the brake disc lateral runout - measured with brake disc fitted - is too high, but the wheel hub lateral runout is OK:  Rework and take measurements again.
   1. 5.1  Clean the levelling and centering surfaces on the brake disc and wheel hub. Then apply a very thin coat of Optimoly TA (aluminium paste) to the centering surface on the wheel hub.
   2. 5.2  Offset/match the brake disc radially with respect to the wheel hub (secure on the wheel hub at a different position than before). One of the two M6 countersunk screws can be left out in this case.
   3. 5.3  Repeat the measurement with > 9510/1 - adapter plate  fitted. > Measured value 0.06 mm 
   4. 5.4 If the lateral runout is still is too high:  Replace brake disc.

      > 465019 REMOVING AND INSTALLING FRONT BRAKE DISC