Since as a rotating machinery, the gearbox is an important source of vibration, the identification of signals and parameters of the component content of the gearbox is necessary for the monitoring of the system. Within the mechanism, the rotation of elements with pe riodic discrete geometries (bearings, gears, turbines, ...) is the origin for potential excitations which are commonly cyclic. These excitations are therefore characterized by frequencies that evolve with rotation speed that reconstructing them, is equivalent to an inverse problem or an identification problem. The main problem is to find the right external excitation conditions particularly in torque to reveal behaviors that are either resonances (a well-known linear problem and treated by identification) or internal excitations (less known and less well- treated). The difficulty here lies effectively in non-stationary operating conditions for a good exploitation of time and angular Fourier Transform framework