The influence of different sets of friction and diffusion coefficients on the dynamics of a nuclear system is investigated. Taking as an example a dinuclear system we show in a c lassic investigation that with zero diffusion in the coordinate, the uncertainty relation can be violated during short initial times. Sets of diffusion coefficients are found for which the c lassic and quantum diffusion equations give close physical results. The tunneling through an energy barrier is sensitively influenced by the friction and diffusion coefficients in coordinate in the diffusion equation.