Hi, It's possible that the pistons inside the calliper are not returning properly. I am guessing that you get a rubbing or skreaching noise as well. The solution may be to give the calliper a jolly good clean. It only takes a small piece of muck to prevent it returning to its position after pulling on the break leaver.
You may have to take it off the bike to clean it properly, but try cleaning it on the bike first.
Gordo, April 2009
