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In the development of noiseless brakes, investigation of actual vibration and knowledge of the operational deflection shape (ODS) is necessary in order to work out countermeasures methodically. Whereas great progress has been achieved in computer-aided simulation of brake noise, the measurement of the ODS is still problematic. The optical techniques usually employed for identifying the ODS have limitations in measuring all three spatial dimensions and are restricted to visible areas which must not be shaded or hidden inside. This paper presents an alternative method for measuring the ODS which uses miniature accelerometers placed in the cooling ducts of the disc and rotating with it. Together with a special evaluation procedure, this permits three-dimensional investigation and definite identification of both out-of-plane and in-plane vibration. Especially important is the part of the ODS in the region of the contact disc/pad, which was as yet inaccessible to other techniques.