The complaint we hear from Shelby almost always starts the same way: a grinding or clunking sound as the door moves, sometimes a visible jump where the roller leaves the track for a fraction of a second. On original steel rollers this often shows up worse in the cold, since this area sits in a severe-cold climate band and steel doesn't flex the way nylon does when the metal contracts. A worn roller stem lets the wheel wobble side to side inside the track, which chews the galvanized rail a little more every cycle. Left alone, that wear eventually reaches the point where the door binds hard enough to stress the opener or the cable, and what started as a $20-a-roller fix turns into a track replacement. Catching it at the grinding stage, before the jump becomes a full derail, is the cheapest place to be in this repair.