Automotive diesel engines have been developed with the aim of achieving higher performance and lighter weight. Since the torsional vibration stresses of the crankshafts have become severer with increase of specific power, torsional vibration rubber dampers of shear-type have been widely used in order to reduce the vibrations. However, the dynamic characteristics of the dampers depend on amplitude, frequency, temperature and secular change effects. Therefore, the dynamic characteristics should be separately investigated with every influence factor. This indicates that it is difficult for the damper designers to predict the dynamic characteristics of the torsional vibration dampers in engine operation.This paper refers mainly to the dynamic characteristics of shear-type torsional rubber dampers with rubber vibration isolator hardened by secular change. For the purpose of this work, rubber test specimens have been designed, the rubber materials of which are the same natural rubber as used on the test torsional vibration dampers. Static and dynamic tests were carried out in order to investigate the properties of the rubber test specimens hardened by secular change. Furthermore, their dynamic properties were analyzed on the basis of the three-elemental Maxwell model which has been adopted as a rheological model.As a result of the characteristic investigation, it is confirmed that the rubber hardening by secular change has a great influence on the dynamic characteristics of the rubber part of the torsional vibration dampers.