The current work intends to improve the cavitation erosion prediction methodology in hydro turbines by the use of onboard vibration measurements taken on the rotating shaft. For that, a measuring campaign in two similar Francis turbine prototypes has been carried out. In particular, one machine is a well known case of severe erosion on all the blades meanwhile the second machine does not present any erosion at all. A miniature telemetry system has been mounted on the shaft in both cases to transmit the signal from an onboard accelerometer to a receiving antenna. Simultaneously, measurements have also been taken on fixed parts of the machine such as the turbine guide bearing and the guide vane. First, the analysis of the results serves to validate the detection techniques applied to the onboard signals. Then, it is discussed whether the use of the vibrations from the shaft as an alternative to the bearing ones should be an advantage to infer the absolute erosive forces taking place on the runner blades.