As a general problem by the construction and dimensioning of large drive trains, the possible conjunction of drive train and structure natural frequencies emphasizes. It is especially good to see in the field of wind turbines. Due to the system a complex, elastic and vibratory complete object results under turbulent stochastic input conditions (wind speed). The same tendencies can be found in other fields of application also. In the meantime even similar damages can be seen interbranch. This leads to the not new conclusion that it is absolutely necessary to have an exact knowledge of the dynamic behavior of the entire drive system and its surrounding already in the construction phase. However, that requires that for the illustration of the vibratory systems appropriate methods of modeling are used for the individual problem. At first, it seems as if a simple torsional model is enough for the determination of the first torsional natural frequencies, but at the latest when using an elastic MBS-model it can be seen that even this simple mode shape can be overlaid with further mode shapes (e.g. bending of the housing). To reach a complete and significant characterization of the dynamic system it is not enough to do a torsional vibration analysis by large drive trains with elastic elements. Instead, reduced FE-models after the method of the Guyan-reduction or the modally reduction are integrated in the MBS-environment and analyzed as elastic MBS-models [1,3].