Factors contributing to the dynamic instability of ball retainers in precision bearings were investigated. A real-time, rolling-element bearing dynamics simulation was written (PADRE - Planar Analysis of a Dynamic Retainer) for rapid evaluation of key bearing design factors. This code permits economic screening of a large number of bearing geometric parameters as a prelude to other more comprehensive dynamic bearing codes. The simulation uses a recently-developed integration package to increase computational speed and accuracy, and also employs a simplified lubricant traction model due to Johnson and Tevaarwerk. Tests with precision angular-contact ball bearings verified important features of this analysis including friction threshold for instability, retainer motion, and the instability frequency. Retainer instability was found to be highly sensitive to retainer-ball friction and exhibited a constant characteristic frequency, which was independent of speed, external vibration, radial load, and preload.