A gear evaluation system which includes means for measuring gear rotational speed and gear case vibrational displacement associated with gear mesh action. A signal is displacement associated with gear mesh action. A signal is developed that represents the time series average signal synchronized to the relevant gear shaft speed. This signal is passed through a bandpass filter set to pass a signal at the gear mesh frequency (for the particular gear under evaluation). After rectification the output signal provides information relating to average vibrational levels associated with gear mesh action and deviations from the average levels.
