Note: Vehicles with diesel engines and model 5201 have massive brake discs 1. All models with more powerful engines have thicker brake discs 2 with internal blowing, which have better heat dissipation.
Remove the decorative wheel cap.
Mark the position of the wheel rims on the rear wheel hubs with paint. This will ensure that the balanced wheel is subsequently installed in the same position.
Loosen the wheel bolts of the corresponding rear wheel. The vehicle must still be on the ground.
Raise the car and remove the wheel.
Measure the thickness of the brake discs. At service stations, a special template or micrometer-bracket is used for this, since when worn, a protrusion forms on the edge of the disc. You can also measure the thickness of the disc with a regular caliper, but you should place pads of a known thickness under its cheeks, for example, 2 coins of 10 pfennigs. To obtain the true result, you should subtract 3.3 mm of the thickness of the two coins from the measured value.
Note: Take several measurements around the circumference of the disc.
Table 1. Front brake discs
1) M5, 540i, 525iX: new 28.0mm; wear limit 26.4 mm.
The rear brake discs have the same thickness of 10.0 mm on all cars. The wear limit is reached at a thickness of 8.0 mm.
When the wear limit is reached, the brake disc must be replaced. The wear limit is 0.4 mm less than the minimum thickness allowed when machining the disc. The maximum allowable runout of the surface of the removed disc is 0.05 mm.
If there are significant scratches or grooves deeper than 0.5 mm, replace the brake discs.
Information taken from this resource: «BMWMAN.ru»