 This study developed a new method for measuring the thickness and breakdown ratio of oil films in elastohydrodynamic, EHD, line contacts within thrust needle roller bearings. Theoretical analysis showed that the electrical impedance produced by applying an alternating current, AC, voltage to these contacts could measure both parameters. This was verified experimentally, where the oil film thickness was found to be smaller than expected initially, but eventually matched the theoretical value. Additionally, the breakdown ratio was found to decrease over time, indicating that running in where had taken place. Thus, this method provides a reliable way to monitor the lubrication conditions of EHD line contacts, such as those in thrust needle roller bearings. This article was authored by Taisuke Maruyama, Fady Radzie, Tsutomu Sato, and others.