Took my bike up and down the street yesterday and the rear brake would not close to stop the bike. It would eventually slow down but not any where near normal stopping power. I flushed and replaced the fluid today (with my new speedbleeders...awesome product). The old fluid was very dirty. However, it still will not stopping. It feels like pistons on the caliper are not closing correctly. If I tip it over on the side stand and spin the rear wheel, then put the brake on, it will stop fine. But not when it has riding momentum behind it. I do hear a clicking noise in the caliper when the brake is used. I Just started bleeding my brakes but I never have taken a caliper a part. Any thoughts on what may be the problem?