Glazed brake pads are a common cause of weak, noisy braking - and they often come from a fixable habit rather than a defect. Glazing is when the pad surface overheats and hardens into a slick, shiny layer that grips poorly. Here is what causes it and how to deal with it.
What causes glazing
Glazing happens when pads get too hot for too long and the friction surface hardens. The usual causes: riding the brakes down a long hill, dragging a lightly-stuck brake, aggressive stops on a cheap pad, or - very commonly - skipping the proper bedding-in when the pads were new; see how to bed in brake pads. A sticking caliper that keeps a pad applied will glaze it too.
Signs of glazed pads
Tell-tale signs are reduced stopping power despite plenty of pad material left, a high-pitched squeal, and a hard, glassy, shiny look on the pad face when you inspect it. The rotor may develop a matching glazed sheen. The brakes feel like they need more pedal to do the same job.
Can you fix glazed pads?
Sometimes. Light glazing can occasionally be scuffed off by sanding the pad surface and re-bedding the brakes with a series of firm stops from speed to lay down a fresh, even transfer layer. But heavily glazed pads are usually best replaced - the hardened layer runs too deep. If the rotor is glazed, it may need resurfacing or replacing too.
Preventing it next time
Prevent glazing by bedding new pads properly, not riding the brakes on long descents (downshift to engine-brake instead), and fixing any sticking caliper promptly. Quality pads resist glazing better than bargain compounds; install them with fresh hardware and bed them in right.