In this work, the wear and failure mechanism of polytetrafluoroethylene (PTFE)/SiO2/epoxy composites with a high concentration of SiO2 particles under dry sliding is examined. In the composite with 12.5 wt.% PTFE, a significant rise of the coefficient of friction (COF) appears after sliding over several kilometers and under a load of 60 N against balls made out of Al2O3 and steel. It is attributed to an accumulation of back-transferred Al2O3/steel and fractured SiO2 on the worn composite surfaces as well as a reduction of PTFE on worn SiO2 surfaces. The TiC/a-C:H coated ball yields the most stable COF. It is also observed that the loading capacity of the composite decreases with increasing PTFE concentration. Massive wear of the composites is seen after few kilometers sliding when the normal load rises above the loading capacity. The increased wear is due to a high concentration of PTFE which lowers the hardness as well as the compressive strength of the composites.