It is known to provide a system to adjust the tensional force of the spring of a wiper assembly in order to adjustably vary the pressure exerted by the wiper blade on the window pane.
U.S. Pat. No. 3,366,989 to A. L. LUDWIG entitled WINDSHIELD WIPER ARMS and dated Feb. 6, 1968 describes such a system wherein the tension spring 25 is adjustably extended by a screw threaded tensioning rod 28 carrying an adjusting nut 29 which partially protrudes from a filler 18. Obviously, in this patent a specially designed filler 18 is required which is retained within the channel shaped portion 17 of the wiper arm by forming inturned flanges 21 along the inner edge of portion 17. It follows that the system in accordance with this patent cannot be used as a conversion kit for wiper assemblies already on the market and already in the hands of the automobile owners. Therefore, the latter would have to buy an entire new wiper assembly to obtain a wiper blade with an adjustable pressure capability.