An experimented investigation of the coastdown characteristics of a two-rotor system consisting of a variable-speed d.c. motor driving a flexible rotor on two journal bearings is presented. The characteristics are plotted in terms of decelaration versus speed for various operating conditions (speed, lubricant type, misalignment and commutator carbon brushes). The coast-down curve resembles the classical Stribeck friction diagram and hence can be used to evaluate the transition speed of journal bearings of rotating systems. The results confirm that this simple technique provides a measure of the friction present and indicates the mechanical condition of the rotating assemblies. © 1983.