The material of the wheel in a worm-gear has to be non-rigid due to very high sliding velocity. Such gears are currently made of plastic in the case of a small module. The present paper describes an original method for studying the quasi-static loaded behavior of a worm gear, with a steel worm and a nylon wheel. Plastics are viscoelastic materials and do not obey Hooke’s law. This paper describes an elaborated method that is a generalization of Kelvin’s model. The computation also uses experimental tests to obtain data relating to the plastic. The computation of the load sharing is described and uses the equation of displacement compatibility. The history of previous deformation and the effect of the nylon’s structural damping are taken into account. At a given constant temperature, the load sharing. meshing stiffness and loaded transmission error depend on the driving torque and time, that is to say speed of rotation.Copyright © 2005 by ASME