Unscrew three M12x1.5 bolts and secure the hub in a vice using aluminum pads (see fig. 251).
Fig. 251. Removing the brake disc.
1 - hub,
2 - socket wrench with extension,
3 - brake disc.
Using a socket wrench with an extension, loosen the self-locking bolts securing the brake disc to the front wheel hub.
Check the wear of the working surfaces of the brake disc; if grooves deeper than 0.5 mm or cracks form, the disc must be replaced.
The brake disc is installed in the reverse order, tighten new self-locking mounting bolts. Install the hub on the steering knuckle and check the runout of the outer working surface of the brake disc, as shown in Fig. 252. If the runout is large, it is necessary to rotate the brake disc relative to the front wheel hub. Install the caliper and, if necessary, bleed air from the brake hydraulic system.
Fig. 252. Checking the brake disc runout.
1 - brake disc,
2 - indicator mounting stand,
3 - hour indicator
(Information copied from the website: www.mercedesman.ru)