Brake linings can become glazed from being overheated. That reduces their friction so you have to press harder and harder on the brake pedal, and that leads to even more overheating. A light sanding on the linings and the rotors or drums will remove that glaze but it often comes back. The resin binders in the lining material softens causing the glazing. Dust and road dirt get onto the linings and can help to grind that glazing away but it can also lead to a brake squeal.
One of the most common causes of that glazing is improper break-in procedures for new linings. Both new linings and new or resurfaced rotors and drums are microscopically very rough so there is only a small percentage of their friction surfaces actually making contact when they're new. That means your stopping ability is poor so you have to push harder than normal on the brake pedal. THAT leads to overheating and glazing. Conscientious mechanics will take your car on a test drive after replacing any linings, and they will perform a few very hard stops with plenty of time between them to let those new linings cool down. Those hard stops help to seat the new linings so they wear down to match the microscopic grooves in the rotors or drums. That increases the percentage of surface area making contact which increases braking power and leads to less heat buildup and glazing.
If that break-in procedure isn't done and the new linings are allowed to get hot in about the first 100 miles, that glazing will continue to be a recurring problem. You will find the brake pedal does not have to pushed further than normal; it has to pressed harder than normal to get the car to stop.
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Tuesday, December 20th, 2011 AT 11:00 PM