Vibrations of a thin-walled cantilever rod of a box-shaped profile were studied. The natural vibrations frequencies of a rod with a crack of different depth and located in different places of the rod were determined. The method of conducting an experiment using a vibration analyzer is given. A variant of determining the location of the crack depending on the change in the natural vibrations frequency is proposed. The resulting expression for estimating the location of the crack has an error of no more than 2.7 percent of the length of the rod, which makes it effective in practical application. The puchnost points of each oscillation form of the cantilever rod are determined, taking into account internal friction, which allowed us to specify the locations of sensors for maximum efficiency in evaluating the influence of crack parameters on natural frequencies. We found that when the crack is located in the places where the puchnosty for the corresponding vibration form causes noticeable energy dissipation due to friction in the crack.