Attempt to raise train speed involves application of greater braking power i.e. braking systems rapidly absorbing and dispersing stored heat energy. Work instability arises from the occurrence of vibrations on friction element, which affects the lower efficiency of the braking process. In practice, this means that, during braking the vehicles currently alternative at a time of friction resistance may cause uneven braking process. The effects of these changes can manifest in the form of vibrations the high amplitude of the input. The purpose of this article is to present the relationship between the changes in instantaneous coefficient of friction of the disk brake and the changes in instantaneous accelerations of the vibrations of the friction pad during braking.