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General E46 Forum
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Old 06-17-2011, 02:31 AM   #1
WheyArea
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When to replace rotors?

I've done a ton of searching but couldn't find a definite answer (subjective to the model and Google gave me the phonebook from 328 - M3 unfortunately). I own a 2001 330ci and purchased some new brake pads. What is the recommended spec to change rotors? I believe the ones I own are the original OEM but as I understand it, our cars can take 2-3 brake replacements before needing a rotor change.

Also, when measuring in mm do you measure the rotor as a whole or each lip?
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Old 06-17-2011, 02:33 AM   #2
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huh, i've had to change mine at every pad change....
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Old 06-17-2011, 02:36 AM   #3
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huh, i've had to change mine at every pad change....
That's kind of my point. What made you do so?
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Old 06-17-2011, 02:43 AM   #4
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cuz they were either warped or worn beyond a recommended thickness and they cant be turned.

new ones aren't that expensive, so it's worth it just to do it right and not have to worry about it.

breaks are more important than almost anything else on the car IMO.
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Old 06-17-2011, 02:57 AM   #5
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I agree, but sometimes what is recommended vs. what is necessary can be very far apart for these cars unfortunately. Money is tight and before I make the purchase I would like to know where my current rotors fall. I don't think it's impossible to use to the same rotors if they're indeed up to standard. I just don't know what that standard is as of now
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Old 06-17-2011, 04:22 AM   #6
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i usually go by the appearance. if there is any rust on the top or center of the rotor they are done.
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Old 06-17-2011, 04:25 AM   #7
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The standard is in Bentley and stamped on your rotor.

If you're above minimum thickness, you can use rotor again.

When I replaced my pads in the front after 60K miles, the rotors were maybe halfway between new and minimum...and you measure across the entire disk...excluding the lip, of course.

Then, your rotors should, of course, be currently stopping smooth. They say you can't turn the rotors, but I'm sure you could if someone who knew how to do it properly was doing it, but the expense of doing it is probably what new rotors would cost!

Be sure to clean all mating surfaces really well--the pad only sits about 5/1000" off rotor, so needs wheel, rotor, and hub all fitting perfectly flat--be sure to remove all dirt/gunk. I use a sanding disk on my drill and then blow/rinse off with a cleaner...then lightly coat one side of mating surface with anti-seize, being careful on the rotor hat not to get it too near the lug nut holes...you do not want anti-seize on lugs.

While down there, instead of just 'slapping' pads on in 15 mins., clean, and then also, might as well remove caliper guidepins and clean them and inside the bushing (whether you use brake grease inside the bushings is up to you. I go against the TIS and currently have grease in it...as it came with it when I got them remanned recently...but technically, you don't grease).

You can, though, grease caliper where the pad slides on it...after also brushing it off.

Can you tell I like clean? lol So do cars!
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Old 06-17-2011, 05:14 AM   #8
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Quote:
Originally Posted by WheyArea View Post
I own a 2001 330ci and purchased some new brake pads. What is the recommended spec to change rotors?

Front 20.4 mm
Rear 17.4 mm
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Old 06-17-2011, 06:12 AM   #9
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BMW does allow turning rotors, just not on the M models. You can use one more set of pads when the rotors are at the min thickness.
If you run more aggressive pads than stock, it might be wise to change the rotors when they get to min thickness as they may wear the rotor more than the stock BMW pads.

In general, the rotors will last through two sets of BMW pads.

BMW TIS procedures - replace pads-
http://tis.spaghetticoder.org/s/view.pl?1/04/54/66

Replace rotors-
http://tis.spaghetticoder.org/s/view.pl?1/04/35/41

Fine grinding rotors-
http://tis.spaghetticoder.org/s/view.pl?1/04/54/69
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Old 06-17-2011, 09:17 AM   #10
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If you determine that you do need rotors, we have replacements available below...

Click HERE for more information.


Please let us know if you have any questions! Feel free to shoot me a PM or email.

Best,
Joe
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Old 06-17-2011, 09:53 AM   #11
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ECS overcharges. Period. They do have good pictures and "kits" though. Also I can't thank them enough for my spacers.

Example?

Front Brembo rotors for a 330 @ ECS: $74 each side

bmaparts.com for the SAME Brembo rotors for a 330 $54 each side. (free shipping)

'nuf said.
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Old 06-17-2011, 11:03 AM   #12
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I replace my rotors with each pad change.
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Old 06-17-2011, 11:35 AM   #13
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Bermbo makes great rotors but I'm sure there is extra $$ in the name. I buy after market ones from a local auto part store here for $26/each and have had no problems with warping or premature wear on any of my vehicles - I don't track them, just daily drivers. If you are a DIY'er, reasonable rotors and pads can be purchased for less than $200. Well worth the investment if you ask me. I agree with DEMAX though, there's more to a good brake job than slapping new rotors and pads on...
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Old 06-17-2011, 11:38 AM   #14
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use the min thickness stamped on the rotors as guides. If you are close to the min thickness, you can reuse it one more time. If you are on the min thickness, you should probably replace.
All this talk about not being able to turn the rotors is BS. You just have to find a shop that knows what they are doing. Most brake shops will not turn them because they are in the business of REPLACING THEM; there are exceptions.
If your rotors are scored/grooved/warped and these markings are deep, you should replace them.
I have had cross-drilled (not actually drilled but forged drilled) turned. Find a race shop; I mean a real race shop and they should be able to do it.
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Old 06-17-2011, 11:40 AM   #15
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The rotors for our cars are spec'd at 25mm (for the 330) and min spec is 23mm. That gives you 1mm on each side. If you've worn your brake pads, you've worn your rotors. Make sure your wheels aren't torqued by a gun too because this CAN warp your rotors/hub.
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Old 06-17-2011, 11:42 AM   #16
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Whatever you guys do stay away from cheap aftermarket rotors. Bad experience with the brand new OPParts rotors the dealer installed on my car before I bought it. Vibrations up the @$$. Put the Brembos on and the car is smooth as glass
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Old 06-17-2011, 12:54 PM   #17
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Thanks guys!
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