Magnetite and graphite are very common phases present on the surface of polymer-matrix composite (PMC) and cast iron disc/drum couples in run in automotive brakes. Considering that some manufacturers use magnetite as raw material in their products this work investigates the generation of magnetite found in the third body as a process of tribo-reaction. Simplified brake pad and brake linings compositions without magnetite were produced and tested using the Brake Lining Quality Control Test Procedure - SAE J661 . After testing the surfaces were observed with Glancing Incidence X-ray Diffraction (GIXRD), Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray spectrometry (EDX) and Micro-Raman spectroscopy. Results showed regions containing magnetite on the steel/glass fibers.