Front

Checking front brake discs (wear assessment)

Normally, brake disc replacement is necessary after the thickness falls below the minimum. In rare, isolated cases (of very high loads for long periods) replacement may be necessary due to crack formation. To a certain extent these cracks may be rated as not important. A description is given in the following sections of when to replace brake discs.

Cracks arise through material fatigue due to frequent and extreme thermal expansion fluctuations. Particularly in cases of very high loads for long periods, these the rmal expansion fluctuations produce internal stresses. The result may be cracks in the friction surface.

These cracks allow relaxation of the friction disc, so that the speed at which the cracks develop is very slow. The cracks run from the centre of the friction surface to the (inner and outer) edges of the brake disc. As different vehicle types have different brake disc sizes, differences arise for the maximum crack length limits.

The maximum crack length limit is calculated as follows:
0.75 x a (-a- = width of friction surface in mm).





Width of friction surface a
Larger cracks impair braking comfort and reduce brake disc strength, therefore making brake disc replacement necessary as precaution.

Bedding in the brake pads and brake discs
New brake pads require a bedding-in period of approximately 200 km! Not until then do they achieve their best friction and wear coefficient. During this period, the brakes should be subjected to full stress when traveling at high speed only in emergencies. The slightly reduced braking effect must be compensated for by increased pressure on the brake pedal. The same also applies after replacing or machining brake discs.