'98 M3 rotors - can/should they be re-machined?

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feeling vibration in my '98 M3 during braking.
Can / should I have the rotors machined to remove run out? Or just replace?

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BTW only 55000 miles on the car, and less than 20000 miles on the current rotors & pads.
derek snipped-for-privacy@hotmail.com wrote:

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derek snipped-for-privacy@hotmail.com wrote:

google is your friend
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well the thing is if you have cross drilled or slotted rotors, i would say that you need to replace as i have never come across a shop who cuts those and i would also see the the slots and or cross drill holes presenting a problem to the lathe. If you have standard rotors, check the service manual, or perhaps even the manual to see what minimum rotor thickness is. If there is severe warp replacement may be the only option. If you have standard rotors and after cutting, they still fall within guidelines for your safe driving id say go for it because replacement rotors should not be the cheap sort, not on that car. Happy motoring.
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Yes, they are drilled - it is an M3. So no machining then. Ah well. Cha-ching!
varan wrote:

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How did you bend them? Hard stop from speed and then hold on brake?
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R. Mark Clayton wrote:

I wouldn't be convinced that they've warped anyway. Did '98 M3s come from the factory with cross drilled brakes???
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If the rotors are not warped, what else could cause vibration only during braking?
I don't think I drive or brake excessively hard compared to other people - but then most cars I've driven end up with warped rotors so maybe I do. Isn't rotor warpage inevitable?
What would cause a rotor to warp prematurely - as I said these have <20k miles? I know the root cause is ultimately heat, but if the rotor warps, the heating (or cooling) must be non-uniform if it causes metal to warp. What can cause that?
adder1969 wrote:

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mcquarrie wrote:

Not much.

Maybe you do. Where do you drive? How often do you brake from high speeds? How often do you have to sit in traffic with the brakes held after doing so? How many steep downgrades do you have to brake on? All subjective and also influenced by your personal braking habits. No; it's not inevitable, but if you tend to warp them on other cars, the BMW will be little different.

You can warp rotors in a half day on track. Or on a mountain road. Or maybe even a bad day on the interstate. It's more of an 'incident' thing than a cumulative mileage thing. -- C.R. Krieger (Been there; warped that)
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OK. So I did it . I confess.
Whatever the cause, the consensus is my rotors are warped because the vibration only happens during braking.
So, on the question of purchasing new rotors and pads for an M3;
Is the OEM rotor cross drilled? someone expressed some doubt about that. my existing rotors are.
BMW dealer prices are stratospheric, but that's what I get for being married to a woman who wants an M3. I want equal-to-OEM performance but a lower cost. What are some of your experiences regarding aftermarket rotors/pads?
I would prefer pads that didn't squeal quite as much as my current ones do. Other than that I'm happy with my current braking performance.
E28 Guy wrote:

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I wouldn't guarantee it. Worn bushes can give the same symptoms - slight run out that would otherwise go unnoticed sort of excites them into a wobble. It's been a characteristic of strut suspension for ever.
--
*Letting a cat out of the bag is easier than putting it back in *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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New BMW rotors are not all that expensive. I've found them to be one of the cheapest options. And performance is just fine. BMW dealer labor is pretty high, though.
For brake pads there are a number of good options that produce less dust and squeal than OEM. I like Axxis Ultimates, although they are still a little "dusty." I've run Porterfield R-4S pads on other cars (not BMW) and they are very low dust, although they don't last as long as the Axxis pads. Both have great braking performance, by the way.
By the way, the most common reason for warping rotors that I've seen is unevenly torqued wheels/excessively torqued wheels. Modern aloy wheels are much harder than cast iron rotors. Torque the wheels too tight, add a little heat from a brisk ride with heavy braking, and those rotors will warp every time. Buy a torque wrench and torque your wheels yourself, if you don't want warped rotors.
Original M3 rotors drilled? Call the parts department of your local BMW dealer and they'll be happy to clear that question up for you. I'm pretty sure that OEM BMW M3 rotors are not drilled, but check to be sure.
-bill w. in loveland, oh "B On Trak"
mcquarrie wrote:

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true overtightening will lead to warpage. MAny tools dealers like snap on or matco or mac have torque sticks that are appropriate for your car. ask if your shop has them, if not try to order the one specific to your car and bring it into the shop each time your wheels come off, they use the torque stick instead of the regular socket (17 mm probably for your beemer) and will use it to put the wheel bolts back on. ..... i wish i had a 98 m3....
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Thanks for the tip about the torque stick.
yes, it is a nice car, but it does have it's flaws. The grass is always greener....
varan wrote:

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snipped-for-privacy@gmail.com wrote:

Try http://www.stevehaygood.com/ Steve is a well-known quality aftermarket parts supplier to the BMW community. A good guy who's willing to offer advice, as well. And, front pads are a 20-minute job to install yourself. Learn it; do it; get instant gratification.

I've always been a fan of PBR (fka Axxis, fka Repco) Metalmasters. I know a lot of folks like the slightly less aggressive PBR Deluxe for the street. Both dust light grey, about the same color as your alloys. They also dust less then OEM pads.

So what's the most common reason for warped rotors on a car that *always* has its wheels cross-sequentially torqued to the proper specs? One like mine ...
It's almost invariably *heat*. Even your theory requires it. Although I'm known for going easy on my brakes, I can feel incipient warping sometimes when on track (and Road America can be very nasty on brakes). At that point, there are two choices. Get them even hotter and 'drive through it' or get off the track and into the paddock (where one stops *without application of the brakes!*) to let them cool. Either way, it takes them a few days to get back to normal street feel. -- C.R. Krieger (Been there; dodged that)
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E28 Guy wrote:

That's what the cool-off lap is for. One lap with light braking should bring the temps down to street-driving levels.
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Rex B wrote:

Two or three laps might do that. If you've got 'em *really hot*, one cool-down lap usually isn't enough. I never stop the car with the pads when parking after coming off track. That's just askin' for trouble. That's also what the parking brake is good for. -- C.R. Krieger (Been there; warped that)
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E28 Guy wrote:

Next time I'm at TMS I'll have to check the rotor temp after coming off track. We get them real hot at that track. Cracked rotors are common, but warped ones are rare. This on a 1st gen RX7. I haven't tracked my Z3.
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Is what you're feeling warpage, or glazing? The latter would wear off, but would the former straighten back out?
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Thanks for the advice. Why are PBR deluxe less "aggressive" than metalmasters?
E28 Guy wrote:

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