The bead breaking unit for tire changing machines includes an arm having a first extremity associated turnable with a support structure and a second extremity having a bead breaking tool, the arm being suitable for oscillating between an away position, wherein the bead breaking tool is positioned substantially at a distance from the support structure, and a work position, wherein the bead breaking tool is positioned substantially close to the support structure, at least an actuator device having a mobile element associated sliding with the arm, at least a drive element for driving the arm, associated with the mobile element and suitable for operating during the movement of the mobile element from an extracted position to a retracted position to move the arm towards the work position and an apparatus of temporary coupling between the mobile element and the arm, suitable for operating during the movement of the mobile element from the retracted position to the extracted position to move the arm from the work position to the away position.