19-05-12, 09:35 AM
I agree with Gnasher, those calipers are superb. Mine are still performing brilliantly despite having covered an impressive mileage.
It can take a long time to get discs bedded in. I changed mine last October and opted for EBC discs and pads.
They were a bit grabby at low speeds at first and the discs rusted like crazy and would stick hard to the pads when parked overnight if there was any hint of dampness. Oddly, they're now fine, nice and progressive and they don't rust... but it took about 3000 miles of use before they started behaving themselves.
It sounds as though you've eliminated a lot of potential causes, though I do wonder how you can maintain the flatness of the disc to better than 0.001" when rubbing them down with sandpaper.
I'd more suspect the torsional rigidity of the front forks than the calipers. If there's something amiss with the inner surface where the axle clamps them together via the spacer/sleeve and speedo housing then they could rotate slightly in response to the torque applied by the brakes. Maybe that could provoke some sort of resonance effect that then buggers up the discs.