In this paper, a mode selection method, useful in multi-body analysis and, in particular, in modal model generation of exible bodies, is shown. This method is based on so-called component mode synthesis and, in particular, on the Craig and Bampton approach. It is able to identify before any multi-body simulations which modes, among the so-called normal modes, could have a high participation factor in model dynamic behaviour. The idea is to evaluate the reaction forces that each normal mode generates on connection points (boundary degrees of freedom). The methodology and the implemented procedure are shown in the paper. The procedure was carried out in a particular simulation environment ( nite element and multi-body codes) using routines developed in Fortran language. Lastly, an automotive test case, used to verify the implemented selection method, is shown.