•New stiffness and damping models are developed for oil film in normal and tangential directions.•Smaller lubricant stiffness is beneficial for alleviating gear meshing impact and shear vibration.•Meshing impact and friction heat is suppressed by either larger normal lubricant damping or smaller tangential lubricant damping.•Better combined stiffness and damping can be achieved by optimizing gear geometric parameters and operating conditions. Innovative stiffness and damping models for oil films are developed to account for the impacts in both normal and tangential directions. Given that these models are applied to a gear drive in line contact elastohydrodynamic lubrication (EHL), the combined stiffness is derived from the stiffness of both the oil film and gear tooth while the combined damping is established from the damping of these parts. The effects of three fundamental parameters (contact force, rotation speed, and tooth numbers) of the gear drive in line contact EHL on the combined stiffness and damping are then investigated. The results reveal that the small normal and tangential stiffness of the lubricant can alleviate meshing impact and shear vibration, while the impact and friction heat can be reduced by using an oil film with either a large normal damping or small tangential damping. Given that its amplitude and fluctuation are closely related to shear rate, effective viscosity, entrainment velocity, and curvature radii, the improved combined stiffness and damping can be obtained by rationally matching the geometric and operating parameters.