Measuring Front Brake Discs

Measuring front brake discs





Measuring brake discs/wheel hubs

Information
Fasten dial gauge set with ball joint arm to wheel bearing housing.

Measuring the brake disc includes: measuring the brake-disc thickness tolerance and measuring the lateral runout of the wheel hub.

Enter measured values in the brake disc measurement sheet.

- Remove wheel.

1. Measure the lateral runout of the brake disc (with adapter plate fitted).
1.1. Fit special tool -1- adapter plate 9510/1 with standard wheel bolts on the wheel hub. Tightening torque: 130 Nm (96 ftlb.).
1.2. Fit the measuring equipment -2- dial gauge set with ball joint arm Nr.147-1 at a suitable position on the wheel bearing housing (schematic representation of the Cayenne).
1.3. Fit the dial gauge -2- with some preload and measure the lateral runout at the greatest external diameter of the brake disc.

Max. permitted brake disc lateral runout = 0.06 mm.





Dial gauge on brake disc (schematic representation of the Cayenne)

2. Measure the wheel hub lateral runout
2.1. Remove the brake disc.
2.2. Fit the measuring equipment dial gauge set with ball joint arm Nr.147-1 at a suitable position on the wheel bearing housing. Fit the dial gauge with some preload.

Information
The front face of the wheel hub must not be corroded. If necessary, clean with fine emery cloth.

2.3. Measure the wheel hub lateral runout at the front face of the wheel hub. To do this, always take measurements at the external and internal diameter of the wheel bolt area -arrows- (5 measuring points each).





Measuring points on wheel hub

Max. permitted wheel hub lateral runout = 0.03 mm.

3. Measure the brake disc thickness tolerance
3.1. Measure the thickness tolerance using a suitable micrometer within the braking surface at approx. eight points.

Thickness tolerance of the brake disc, max. 0.02 mm. (New brake disc = max. 0.01 mm).

4. Procedure in the event of different lateral runout measured values:
4.1. Wheel hub lateral runout is too large: Replace the wheel hub.
4.2. Wheel hub lateral runout is OK, but lateral runout on brake disc (measured with brake disc fitted on wheel hub) is not OK:

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.
Offset the brake disc radially with respect to the wheel hub (matching/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.
Repeat the measurement with adapter plate 9510/1 fitted. If the lateral runout is still greater than 0.06 mm, replace the brake disc.