A method and system for diagnosing gear condition by comparing data collected from each member of a set of coupled gears, including mating gears. Data containing vibrations or other signals from the set of coupled gears are collected. Condition indicators are calculated from the vibration data. The values of these condition indicators are compared for each pair of coupled gears. A divergence of the condition indicators as indicated by the comparison may indicate the presence of a faulted or otherwise anomalous condition. Such indication may be provided to a user. In one variation, the vibration data are used to calculate a synchronous average for each gear and the condition indicators are based on the synchronous average.