In this paper the application of spectral and wavelet analyses in power train system diagnostics were shown. The main goal of investigations was a comparison of changes of selected values measured by accelerometer installed in the car body during particularly designed road test. The investigation object was passenger car and the experiments were performed with use of special measuring device. The logged data were analyzed using amplitude spectrum and short time Fourier transform (STFT) algorithms implemented in Scilab software. The transformed data were compared with continuous wavelet transforms (CWT), which were obtained with use of Morlet's and Mexican hat analyzing wavelets. The advantages and disadvantages this transforms were discussed. As main effect of investigations it can be concluded, that the STFT and CWT algorithms can provide more diagnostics information then the other transforms.