In order to isolate vibration transmitted to a machine from the floor and to reduce the vibration caused by shock force applied directly to the machine, a new method of ON-OFF control for the spring support is suggested in this work. The end of the spring is designed to control the clamping friction force by means of a brake mechanism. The clamping friction force is varied according to the switching law which is deduced using the variable structure systems (VSS) control theory. The switching law takes into account the energy dissipation due to friction. In the numerical simulations and experiments, the reduction of the impulse response and the displacement transmissibility are investigated. The results show that the method is effective for suppressing shock motion and isolating vibration.