I've got a 2018 Canyon Exceed (XC mountain bike) that has recently developed alarming judder in the front brake (SRAM Level T), to the point that it makes the forks "twang" backwards and forwards, depending on speed and braking effort. The headset adjustment is fine, it's just that the forks are lightweight XC model (SID) and therefore a little flexy and they really don't like the brake pulsing.
Holding a constant, light pressure on the brake lever while rotating the wheel by hand reveals that the brake grabs as each of the rotor arms pass through the calliper. Inspecting the rotor shows that the pad coverage extends a surprisingly long way down the arm:
Same thing but different lighting:
I was surprised by the inconsistency of the pad surface too, which seems to correspond to which bits of pad the long cooling slots pass over:
The bikes got a little over 700km on it, most of them quite dry. The last 50 were wetter. The rotors are the originals, but are well away from their wear limit (1.55mm) and don't vary in thickness (1.87mm all the way around). I did wonder whether the calliper spacer was on the wrong way around, leading to the pads being closer to the wheel centre than they should be, but according to the direction arrow, it's correct (from factory).
I can't explain why this has suddenly become a problem. My trail bike has similar brakes (Level TL), also still on the original rotors, has lead a much harder life (3x the mileage, more severe terrain), pad also extends down the rotor arm, but it has never shown this problem. The same light-pressure, turn the wheel by hand test shows no hint of grabbing.
Is the solution just a new set of pads? Bedded in differently? How can I avoid this problem returning?