Test Values/Wear Limits
Information
Depending on the wear of cast iron brake discs, two condition criteria can make replacement necessary:
- Cracking in the holed (perforated) brake disc friction plates is in an advanced state.
- Minimum brake disc thickness is not retained due to wear (material erosion due to friction).
| Location | Description | Type | Basic value | Tolerance |
|---|---|---|---|---|
| Pad thickness, front | Measured value | 11, 2 mm | ||
| Pad thickness, front (wear limit) | Measured value | 2 mm | ||
| Pad thickness, rear | Measured value | 10.3 mm | ||
| Pad thickness, rear (wear limit) | Measured value | 2 mm | ||
| Brake disc thickness, new (front) | Measured value | 28 mm | ||
| Brake disc thickness, new (rear) | Measured value | 20 mm | ||
| Brake disc minimum thickness after machining, front | Brake disc can only be reworked symmetrically, i.e. equally from both sides! | Measured value | 26.6 mm | |
| Brake disc minimum thickness after machining, rear, all | Brake disc can only be reworked symmetrically, i.e. equally from both sides! | Measured value | 18.6 mm | |
| Brake disc wear limit, front | Measured value | 26.0 mm | ||
| Brake disc wear limit, rear | Measured value | 18.0 mm | ||
| Peak-to-valley surface roughness of brake disc after machining (max.) | Measured value | 0.006 mm | ||
| Thickness tolerance of brake discs (max.) | Measured value | 0.02 mm | ||
| Lateral runout of brake disc (max.) | Measured value | 0.03 mm | ||
| Lateral runout of wheel hub (max.) | Measured value | 0.03 mm | ||
| Lateral runout of brake disc when installed (max.) | Measured value | 0.06 mm | ||
| Push rod play | Measured at brake pedal plate | Measured value | approx. 1 mm | |
| Diameter of parking-brake drum | Parking brake (electrically actuated, drum brake acting on the rear axle) | Diameter | 180 mm | |
| Diameter of parking-brake drum, wear limit | Diameter | 181 mm | ||
| Width of parking-brake shoe | Measured value | 24 mm |
Information on machining grey cast-iron brake discs
Possible complaints
- Damage due to lack of use (rusting). This causes vibrations in the steering wheel, noises and brake pedal pulsation.
- Brake disc becomes distorted as a result of serious driving, e.g. on a racing circuit.
- Too much lateral runout when new brake discs are fitted on dirty or distorted wheel hubs.
Procedure
- Check brake disc for cracks, minimum thickness, lateral runout, thickness tolerance, flatness and surface roughness.
- If necessary, (depending on the actual brake disc thickness and the brake disc wear limit) machine the brake disc using one of the disc brake dressing machines approved by Porsche. For a list of recommended disc brake dressing machines, see the appropriate Service Information .
- The brake disc must only be reworked symmetrically, i.e. evenly from both sides! Read the operating instructions for the disc brake dressing machine!