I have been experiencing an increased problem with brake gabbing when first starting out in the morning. While this has always been a problem, it is getting worse. I checked wear on the front pads (at 39K miles) and have decided I don't know when they need replaced. They still have about 1/4 inch left. How do I tell when they need replaced, other than wait for the tell-tale noise? Does the taper on the top edge of the pad indicate the minimum thickness before replacement? Any suggestions as to the best brand/type of replacement pads? Many thanks!