These belts will breakdown if not tracking properly on sheaves. I have seen them hug one side I one direction then return to centre in the other direstion! Need to level all sheaves to correct, It puts more strain on fewer air cords causing damage. I have seen individual cords strands break through belt and short to any sheave and cause it to shut down at next floor. It's a pain but inspect every inch possible ( I run my whole arm up and down all the belts ). Also have found lots of rubber between belts and keeper plate on car and cwt, if you use magnet I found lots of bits of steel from aircords with rubber! Also we have noticed belts have a crazy edge curl when not under load during replacement (bacon curls)