When my 540 used to feel like that I'd find a long straightish road and brake heavily from 60 mph to about 5 mph. I'd do this about 6 or 7 times. You'll smell the brakes at the end of it :-) Then let the brakes cool down to normal temperatures. It is important that after this cleaning process you don't sit at a stop with your foot on the brake pedal (at traffic lights for instance) when the brakes are hot as this can leave a pad imprint on the rotor, beginning the whole build-up problem again.
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