Abstract: The invention is a device which can be screwed into the rod string near or at the downhole pump for the purpose of shaking the pump with each stroke of the sucker rod in order to free a stuck or obstructed ball valve located in the pump. The device is formed from three metal parts, two of which fit together forming a compartment having a ceiling and a floor. The floor is formed by sides of the square opening which communicates between the compartment and the well. The metal parts forming the compartment attach to the rod string leading to the wellhead. The third part comprising the device is a piston having a cylinder head which is movably confined within the compartment and having a square neck which extends through the square opening and attaches to either the pump or a sucker rod located near the pump.