I have a 1951 3600. My factory assembly manual shows that a spring is connected between a hole in a part of the frame crosspiece close to the end of the parking brake pull rod assembly and a metal tab on the back half of the rod assembly. I think the short beds have a one piece pull rod and the long bed like mine is a two piece rod assembly. I do not have that tab on the pull rod, and don't remember seeing one there during disassembly. Does anyone know where else the spring might be installed?