Brake Suggestions

I'm about to change the pads on my 2001 330xi. I'm pretty much a mechanical newbie so I had a few questions:

-Any recommendations on pads I should get? This is a commuter car only and while I do like to zip around, I don't think I'm particularly hard on the brakes. I got two years out of my last set. That said, I'd like to get the cheapest pads that would offer the best "good enough" performance for back road commuter joy riding.

-What's the minimum width on the rotors? I have 17" wheels.

-Any recommendations on rotors?

-Should I change both front and the back while I'm at it or should I just check both sides and replace as needed?

-Any reason why I might want to replace the pad sensor wires?

-Any "gotchas" with changing my brakes?

Thanks for any info you may have!

Don't do that. Brake pads are cheap enough, if you aren't buying dedicated track or race pads, that you can buy the best ones for very little more than the cheapest ones. I've always liked PBR (fka AXXIS, fka REPCO) Metalmaster pads. They also made a 'Deluxe' pad, both of which are excellent and not expensive. What's best about them is that they dust less, and light grey, so your wheels stay cleaner looking.

OEM rotors will work fine for you. No reason to go for anything more exotic if they worked for you up to now.

Fronts usually wear faster than rears, so check the rears, but don't plan on replacing them immediately unless your inspection reveals too much wear.

Not a wire, but a whole sensor unit. No reason to replace these unless your brake wear light came on. In that case, you do need to replace them because their function requires they be destroyed to give you the light warning. If you're keeping them, just be careful removing them from the old pads because they can be a bit fragile because they're plastic and the clips bend easily.

Yeah. The rotor retaining screw. These things seize up all the time. Don't hesitate to grind the head off with a big drill bit if it gives you the least bit of trouble. Leave the stub in there as a locator pin, but don't worry about replacing it. If your rotor falls off because that screw isn't in there, you've got a much bigger problem.

Don't forget to use a little anti-seize around the centering hub.
And check the brake fluid level after you finish.

Thanks a lot!

dittos on all prior suggestions - axxis/PBR metalmaster pads, or oem should be just fine for you. The first braking on a freezing or sub-freezing winter morning, particularly say, backing down a driveway, with metalmasters might find you going deeper into the brake pedal than you expect. Otherwise, metalmasters are pretty good all around. The axxisPBR deluxe pads will do better cold, but won't offer the fade-resistance of the metalmasters, particularly when pushed.

Kudos on being willing to tackle one of the basic BMW maintenance tasks - get the Bentley manual for your car, it details basic maintenance procedures and then some, can be very helpful; worth the expense, in my opinion. It will also (at least it should, I'd be _really_ surprised if omitted) your rotor wear specs. Get yourself an appropriate mouth-width micrometer if you want to measure rotors accurately.

Chock your wheels; work on a level surface, ideally concrete; if on asphalt, use a piece of plywood under your jack, and jack stands. ALWAYS use jack stands - ALWAYS; (corollary: never trust a jack). NEVER place yourself or any body parts under a car that is only on a jack. The BMW-provided jack for changing flats could be used to get a wheel off the ground, but stability & safety wise, is less than ideal, so consider using a more robust floor jack of some kind. There are cheap jacks everywhere that, by & large, will work fine for quite awhile - almost all are made in China (or roundabouts); don't expect them to last forever. Depending on usage, you might get 2 or 3 years before a cylinder seal leaks or whatever. You get what you pay for; if you want a jack with a long service life, expect it to be really expensive, and that sounds like overkill for what you'd likely be doing. Local auto-parts stores, Sears, Harbor Freight, or even Costco/Sam's Club should have something that'd be just fine. I'd recommend not getting the smallest floor jack possible.

Rotor set-screws can strip easily, particularly if rusted (as mentioned). As CR says, you can drill it out - you don't have to drill it out to the last nth degree. Once you get it almost completely drilled out, you can knock the rotor off with a good thwack (I've used a 4lb deadblow hammer for that). Make sure you have sharp drill bits good for steel.

Generally relevant threads; you can search the forums for others -

http://bmwcca.org/forum/showthread.php?t=6201
http://bmwcca.org/forum/showthread.php?t=6268

Thanks for all of the helpful replies! They really were helpful. I bought the Metalmasters for all four wheels. I measured all four rotors with a micrometer. The front driver-side rotor was just below spec so I replaced both front rotors with OEM rotors. I bought a little hydraulic jack with jack stands. Replaced both sensor wires.

I don't have any really fancy tools (I borrowed the digital micrometer) so taking off the caliper and caliper bracket involved a wrench and a mallet, heh. Still, everything went pretty smoothly. The rotor retaining bolts came out pretty easy with a hex key and a little bit of tapping from a mallet.

I didn't torque anything down to any sort of spec other than the lug nuts. Everything else I just tightened as well as I could. I hope that's okay.

I have a few questions I thought of while doing this brake job:

-What's the real difference between semi-met pads and ceramic pads? From what I could gather, ceramic is less dirty and quieter while semi-met provides more stopping ability. Is this about right?

-I don't have them but what exactly is the point of cross-drilled rotors? I'm sure there's something about them I don't understand but if a brake system is going to turn motion into heat then a rotor is a heat sink, yes? As such, wouldn't MORE surface area be better?

The theory behind cross-drilled rotors is better heat dissipation and escape of "gasses" during extreme braking. They also come with the possible downside of the "possibility" of cracking due to the weaker strength of the rotor, though most people don't have that problem.

Personally, I'd skip the cross-drilled and just use OEM plain rotors. The difference seems to be minimal based on user opinions I've read.

And yes, bigger surface area is better; more of a heat sink, with less fade and better heat tolerance due to the larger area. The calipers make more of a difference though; more pistons = more stopping power!

If you have a torque wrench, then you should use it for anything within it's range - it would be better to torque the caliper bolts to spec. For all but perhaps very experienced mechanics, there's no way to feel exactly the correct torque. Over-tightening is not great, although perhaps not as bad as under-tightening. All too easy to over-torque or even break a bolt, and brake caliper bolts are, as part of the braking system, fairly critical to safe operation.

Unless you become a professional racer, I'd avoid cross-drilled rotors. To address your query, I suspect the idea behind cross-drilling is to improve heat dissipation.

Hey, congrats on doing the brake job