This paper studies the effect of manufacturing errors on predicted dynamic factors of spur gears. Three dynamic factors are defined and studied: dynamic load factors@ dynamic tooth force factors@ and dynamic bending moment factors. Three computer programs for predicting dynamics are discussed; a forced vibration analysis using six degrees of freedom@ a multi-degree Dynamic Transmission Error Program (DYTEM) using a six degree of freedom model@ and a Geared Rotor Dynamics Program that uses a finite element method. Using experimental data provided by National Aeronautics and Space Administration the DYTEM program is used for dynamic factors prediction.