Note: Vehicles with diesel engines. as well as model 5201 have massive brake discs 1. All models with more powerful engines have thicker brake discs 2 with internal airflow, which have better heat dissipation.
Remove the wheel trim.
Mark with paint the position of the rims on the rear wheel hubs. Thanks to this, the subsequently balanced wheel is set to the same position.
Loosen the wheel bolts of the corresponding rear wheel. In this case, the car 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. It is possible to measure the thickness of the disk with a conventional caliper, however, pads of known thickness should be placed under its cheeks, for example, 2 coins of 10 pfennigs). To obtain the true result, subtract 3.3 mm from the measured value of the thickness of the two coins.
Attention: Take several measurements around the disc circumference.
Table 1. Front wheel brake discs
1) M5, 540i, 525iX: new 28.0mm; wear limit 26.4 mm.
The brake discs of the rear wheels have the same thickness of 10.0 mm on all vehicles. 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 a disc. The maximum allowable runout of the surface of the removed disk: 0.05 mm.
If there are significant scratches or grooves deeper than 0.5 mm, replace the brake discs.