The location of the pool pump impeller is shown in this cut-away of a pump. The spinning action of the impeller when driven by the pump motor generates the water pressure in your pool system. Sometimes debris will get into the pump and will crack the impeller. In other cases the threads that hold the impeller to the motor shaft become worn causing the impeller to wobble and rub against the diffuser. This guide explains how to replace a bad pool pump impeller.