Abstract—As the silicone fluid inside of torsional viscous friction dampers (hereafter called “viscous dampers”) is non-Newtonian fluid, the effective viscosity in the actuation is different in the operation conditions and the dynamic characteristics are complex. The authors refer to the modeling and dynamic characteristics of torsional damping and spring of viscous dampers are experimentally investigation in the this paper by adopting simultaneous vibration measurement method at two points. Then, this method is very effective for a good grasp of the torsional behaviors of the damper inertia ring and the damper casing in order to clarify the effect of the silicone fluid on the torsional vibration of the engine crankshaft system. In the estimation of the torsional damping coefficient and spring constant of the viscous damper from the experimental results, the damper part is treated as one degree of freedom equivalent vibration system and its viscous friction part can be assumed to be replaced approximately with concentrated equivalent linear damper and spring between the concentrated equivalent masses consisted of the damper inertia ring and casing including the pulley part.