This paper describes a dynamic model for gear transmissions acting around a static working point, and taking into account the complete mechanical components. Gearbox casing behavior is introduced by using substructure analysis, and a tangent stiffness matrix is defined for each roller body bearing element. This model is used to compare the pullup and pulldown dynamic behavior of a five speed medium size automobile gearbox where the gear meshing phenomena are assumed to be identical. The eigenmodes of the pullup and pulldown models are compared and frequency responses to meshing excitation are studied. Substantial differences between pullup and pulldown behavior are observed and associated with to the orientation of static load.