Aw hell, since I just wrote an article on the subject for a mechanical forum, I'll go ahead and risk the controversy, and post it here:
Installation and Care of Brakes
There are very many DIYs and videos on installing new brake rotors and pads on a BMW. Some are good, some are terrible. They all seem to miss some really crucial points.
Firstly, you’ve GOT to buy good parts. Brakes are life or death. If you drive your car only on the street, however fast you drive, then OEM pads and rotors are truly excellent. I’ve never been able to fade BMW OEM pads on the street, once they were properly bedded, and you’ll be hard pressed to exceed the abuse I’ve given them…..
By the way, “DUST” is a byproduct of braking – SOMETHING has to wear, and this will create dust. If you don’t like dark front wheels, WASH THEM! Buying brake pads because they dust or don’t is like buying steak because it doesn’t get your grille messy.
Excellent rotors: BMW, Brembo, Balo, Zimmerman, Meyle, Textar, DBA.
Excellent pads: BMW, Jurid, Pagid, Textar, Akebono, Performance Friction, Hawk.
Avoid drilled rotors, especially if you intend to use the brakes hard. Drilled rotors crack much more easily, and are of no real advantage. Slotted rotors provide a very small advantage, in track or extreme autobahn use, without the drawbacks of drilled rotors.
Secondly, you must install the brakes correctly. Start by cleaning all “contact points”, after you’ve removed the old pads and rotors. Use a stiff wire brush, to clean rust off the wheel hubs (and the inside of the wheel, where it contacts the hub). Proceed to the caliper brackets, where the ears of the pads ride. Clean all the black deposits off of the caliper slide pins, too – brake cleaner works well here.
Throw away any orange gluey “anti-squeak” crap you bought. Metal-to-metal contact points need to be lubricated, NOT glued. These points will include where the brake piston(s) and caliper touch the backs of the pads, as well as the ears of the pads, and the caliper slide pins. Just before you install the new rotor, lubricate the hub, where the center of the rotor contacts it. Put on the rotor, and lubricate the rotor retaining bolt before installing it. Do not overtighten this bolt – just barely snug is plenty! Its only use is to hold the rotor while you assemble things, it is NOT structural!
Anti seize, (copper or aluminum) or a high-temperature synthetic grease, made for brakes and usually coming in a small black tube are fine lubricants for all of the above spots.
If you buy coated rotors, as signified by silver anti-corrosion paint, do NOT clean those rotors! If you buy rotors which are bare metal, you need to clean the faces with brake cleaner, because there’s grease on them.
The sensor should be replaced. The little spring clip usually loses tension, and the plastic sensor chips easily, when you try to reuse it.
If you use your car on the racetrack, I highly recommend that you have two sets of rotors, and two sets of pads. Mark them when you remove them…. Tape each corner’s pads together, and mark where they came from, mark each rotor….LF, RF, LR, RR. There is really no such thing as a dual-purpose pad, beyond your first few HPDEs.
Make absolutely sure that you bed your pads and rotors correctly! This process is to progressively cook the volatile resins out of the pads, and deposit a smooth layer of the pad compounds onto the brake rotors, to promote adhesive friction between rotor and pads.
Brake Bedding
For street pads, you’ll want to find a traffic-free area; bedding brakes will appear to be erratic driving to uneducated drivers, and police officers.
You’ll accelerate to ~50 mph, and brake extremely hard, just short of ABS activation, down to 5-10 mph. Then you’ll accelerate up to ~50 again, and repeat. And again. After 4 applications, give the brakes a half-mile or a mile to cool, without using them. Then repeat this process, preferably from ~65+ mph, five times, and then at least a full mile, to cool. {Most race pads require additional bedding, PM bmwdirtracer or ask pad manufacturer}
You must NOT stop completely, during the bedding procedure, while the brakes are smoking hot. If you do, you will deposit a big lump of brake pad material onto the rotors, and this will likely eventually result in ruined rotors, which everyone will tell you is because they’re warped, which is not the case.
When you have really hot brakes, even when they’re not new, you should studiously avoid coming to a complete halt…and, if you DO have to come to a complete halt, keep your foot off the pedal, when you’ve stopped. Try to let the car keep moving, a couple inches at a time
If you transfer a bunch of pad material onto one spot, this spot will continue to overheat, every time you drive the car…because it’s thicker.
If you overheat the cast iron rotor in one spot, you will transform the metallurgy of that iron into something called Cementite. Cementite has little adhesive friction, and every time the pad glides over this area during heavy braking, a “pulse” will be felt. Worse than a “warped “ rotor, this cannot ever be fixed. The iron isn’t iron anymore.
Some mechanics will tell you to “machine” the rotor, because it’s warped. It’s not warped, but it is trashed.
IF you’ve been lucky enough to feel this pulsing right away, you can maybe save the rotor, by sanding off the deposits, on the rotor, and the pad faces, with 100-120 grit GARNET paper. This is sandpaper without the silica. Just trust me here. It is available at the hardware store.
If the pulsation recurs, after scuffing the pad and rotor with this, and then rebedding., the rotor is trashed. You’ll likely see a pad imprint on the rotor, recurring after the rotor gets hot.
Remember that brake pads and rotors are wear items, just like tires. When this type of item becomes worn in a bad way which you can’t address, you throw it away, and start again with a new good part.
And this is why you don’t machine BMW rotors, .….either they’re good, or they need to be replaced.
