Quote:
Originally Posted by spectrepig
(Post 1303380)
My brakes are screeching, but it is only the last bit of a stop, or pulling into my garage. Any ideas?
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This is the hardest squeal to get rid of in a brake system with opposed-piston calipers (versus standard sliding calipers with rubber bushings). Here's what pros do -- some of which has been mentioned already:
1. Chamfer the leading edge of each pad at a 30° angle for about 1/3 of the pad depth. This will eliminate the vibration caused by an abrupt 90° edge being excited by the rotor.
2. Use a high-temperature brake lube, such as Permatex Ceramic Extreme brake parts lubricant (the purple stuff). The lower temperature stuff works for a while, but it dies off the first time you are out having a little fun. Smear a thin layer on the back plate where it contacts the caliper abutment surface and the pistons. Of course, do NOT get any on the friction material!
3. Once installed, re-bed the pads. This helps promote a smooth and even pad transfer layer on the rotor friction surface. Pads do not like rubbing up against naked iron. They prefer to rub against their own kind (sounds really bad, but that is just how they are!). To do this, go find a country road or industrial area on a Sunday. Do some .3-.4g slowdowns (light to moderate braking) from 45 to 25mph, 5x in a row. This will start to warm up the mating surfaces. Step up the speed to 65mph and brake to 35mph, harder for this round -- .6-.8g. This is harder than you would normally brake in stop and go traffic, but not so hard as to activate the ABS. Accelerate briskly between each brake application. You should start getting some "green fade" at this point if the pads are still fairly new. You will notice the pedal getting softer and brake distances getting longer. You might even start to smell the pads as the rubber content is being converted into carbon. If they haven't started fading yet, do a few more higher speed runs.
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THIS IS KEY! << Once the pads are definitely fading, get off the brakes! Drive a mile or two without using them at all, if you can.
DO NOT stop with your foot on the brake pedal until the rotors have cooled down or the pad might "print off" onto the friction surface. This is the leading cause of brake judder, often misdiagnosed as a "warped rotor". If cooled down properly, there will now be a smooth and even layer of pad material frozen to the rotor friction surface. It is normally a dark gray as opposed to the lighter metallic color of a bare iron rotor. You might even see small areas of golden or even slight bluish coloring on the edge of the rotor or near the hat or heat dam area. This is normal.
After they have cooled overnight, you will likely have a better performing brake system that makes less noise. However, the square-ish pads in the Brembo calipers are more prone to noise than with longer pads loaded in sliding caliper with soft rubber bushings to soak up the vibes. As a result, they may squeak from time to time no matter what you do.
4. Cleanliness seems to help. Pad dust buildup will promote noise, so keep those wheels and brakes clean.
5. Go out and use the brakes hard every once in a while. Slow speed rubbing eventually wears off the pad transfer layer. Take the car out and have some fun every now and then -- the brakes will be a lot happier.
Chris