Turning the barrel adjuster on the rear brake cable of my older Cannondale touring bike doesn't seem to have any effect. No matter which way I turn the barrel, the cable doesn't appear to lengthen or shorten, and hence, the brake pads don't move either nearer to or farther from the rims. Do these simple adjusters break or perhaps I have turned too much at some previous time and it needs to be "rethreaded"? Do you typically need to replace them over the years? Most important, is there a good site with instructions for learning how to remove, inspect, and repair/replace barrel adjusters? Thanks. I'd rather be riding than posting, but brakes are getting bad!