If vibration occurs under thermal load, it is usually caused by "brake disc deformation. If, in addition, different measured values are obtained when measuring the brake disc thickness, the following diagnostic results seem to be confirmed: brake disc twisting, brake disc "wobbling", brake disc out-of-round, brake disc deformation, etc.

But the real cause of this phenomenon is different: the current generation of brake linings is designed for friction. When the brake disc/brake lining system is correctly engaged, a very thin and homogeneous layer of brake lining material is formed on the brake disc friction surface due to diffusion processes. As a result, more or less of the same material is present in the edge regions of the two friction surfaces (brake disc and brake lining); it is possible for a hierarchical transition (diffusion) of material particles to form in both directions. As a result, the chemical bond between the casting material and the brake lining material may be broken or re-formed.

The process is uninterrupted because the transition area of the boundary between the brake disc friction surface and the brake lining friction surface is smooth.

If the braking process is not followed or the running-in phase is not followed, an uncontrolled and uneven deposit of friction material will form on the braking surface, which will lead to local excessive thermal loading of the braking surface; The temperature of the uneven deposit protruding from the surface of the brake disc will be higher than that of the cast iron around it. Each time the brake lining comes into contact with the deposit front (once per revolution), the temperature at this location increases. When the temperature reaches 650°C to 700°C, the cast iron under the deposit will transform into cementite, forming a cementite deposit (Fe3C) with extremely high hardness within the cast iron lattice. When the mechanical load of the brake is extremely high and causes its thermal load to increase sharply, the process will continue and the brake will start to vibrate. As the temperature increases, the cementite will penetrate deep into the brake disc material while its total amount increases.

Eventually, the process will lead to the above-mentioned signs, such as brake friction, bounce or shaking. In this case, the problem can only be solved by replacing the brake disc and the brake linings.

It must be clear that the real cause is not a defective brake disc. Errors in assembly, failure to follow the running-in regulations, etc. will trigger the above-mentioned change process, which will lead to the damage of the brake disc without any defects.

Additional Notes:

If it is intended to remove these deposits, which are usually difficult or not visible at all without optical aids, by abrasive means (for example, abrasive cloth, sandpaper, etc.), this leads to a further deterioration of the condition of the brake disc, since particles of the grinding tool itself, in particular aluminum oxide, can thus penetrate into the surface of the brake disc friction surface. For the same reason, these deposits must not be removed by sandblasting.