Brake piston mechanism of rear brake calipers

A brake piston mechanism of rear brake calipers comprises a piston body, a travel adjusting nut, a waveform spring and a clamp spring. The front end of an inner cavity of the piston body is provided with a small cylindrical first cavity capable of holding the head end of a travel adjusting screw stem when in an early installation state, the middle of the inner cavity of the piston body is further provided with a conical second cavity capable of holding the travel adjusting nut, the head of the second cavity is connected with the tail of the small cylindrical first cavity, a cylindrical third cavity capable of holding the waveform spring and the clamp spring is arranged on the middle rear portion of the inner cavity of the piston body, and a large cylindrical fourth cavity is disposed at the tail of the inner cavity of the piston body. The brake piston mechanism removes a structure of an assisting piston and a gripping mechanism of the assisting piston and the adjusting nut by aid of structural change of the i