An unexpected behavior of space bearings lubricated with new substitute grease at low speeds was investigated. The complex discontinuous tribological behavior of such a biphasic grease was investigated by combining numerical and experimental approaches. From a numerical point of view, using the Discrete Element Method, the grease tribological behavior seems to be controlled by both the thickener particle size and physico-chemical parameters associated to the interactions between the different grease components (PTFE, oil / surface, volume). From an experimental point of view, the influence of the controlling parameters was investigated on a bearing test bench by using different greases composed of two sizes of PTFE particles and two base oils. The considered grease behaviours were discriminated for a given protocol in terms of bearing torque evolution (presence or not of torque peaks) and of surface morphologies (grease cluster formation, grease structural changes,…). Correlations between modelling and experiments are then proposed.