I understood they were put in to prevent squealing — story back in the day .those brakes often were loud. I often wondered how they did effectively did that . Maybe friction between drum and spring damps high frequency vibration , like those devices you sometimes see on utility wires in air. Some of those look
Like springs . The wires vibrate and fatigue at the pole end fastening , eventually breaking off . Cannot believe it does anything for cooling the brakes ? Thermal connection to drum bulk metal too poor?
Over the past 40 years I have found drums with them missing and have had a few break from rust. Didn't seem to make a difference if the shoes were matched to the drums and all lube surfaces were rust free and greased.
