Shaving Rotors

[tglazed]

Do any of you guys shave rotors. It's about time for new pads and rotors but they are thick enough where they can be shaved. Anybody have an opinion on shaving rotors? Not sure what to do.

[135TX]

Advised from my local German auto mechanic "these rotors are not to be cut. If someone were to offer to do that run the opposite way fast"
I don't remember why but that's what I'm told... GL

[Freon]

If BMW has a published minimum thickness I'd be fine with it.

You say "they are thick enough" but what leads you to that belief?

[Pig Farmer]

Just a thought... The front rotors are two piece and allow for thermal expansion. You can see the pins around the rotor hat (about the size of a dime) that hold the rings in place. Just the slightest amount of play between the ring and hat when resurfacing the rotor could affect runout. I'm guessing this is why it is not recommended?

I don't think you would have an issue with the rears since they are one-piece.

[tglazed]

Bmw has a published minimum thickness for front and rears. That's why I asked.

[Solo_M_Tech]

Thinner Rotor= more prone to warping. They are cheap enough. Just buy new ones.

[BEAR-AvHistory]

Originally Posted by tglazed

Bmw has a published minimum thickness for front and rears. That's why I asked.

Pretty sure that's just to tell you when they are too warn to reuse, not a how much you can cut thing. Replace them if they are scored or too thin.

[darkrom]

Fair question, but the honest answer is it is pretty ghetto and not worth it. High performance cars deserve good brakes over everything else.

[Elsabor67]

No German auto shop (in Germany) even offers shaving rotors here. Just replace them.

[EM58NDS 135i]

Not worth it. Just buy new ones, they are not expensive, and certainly not something you should bodge on a high performance car.

[tglazed]

I understand where everybody stands on it but does anybody have first hand experience with it. They take off not even a half a millimeter. My rotors are all about 3mm above minimum thickness that BMW published. I say first hand experience because most of these replies are just hearsay. "So and so told me". I don't disagree with not going cheap on brakes but why spend 500 bucks on new rotors when you could shave less than a half a millimeter off and not be able to tell a difference?

[tglazed]

In all honesty, pig farmers reply was the only reply worth reading, no offense... I will end up purchasing new brake rotors but I definitely think someone should look more into resurfacing brake rotors on our vehicles

[inline sex]

Obviously it's recommended to replace rotors along with pads. But if you prefer to machine them make sure it's w/in spec.
There is usually a min thickness and a 'min. thickness to machine'

[EM58NDS 135i]

I don't see why anybody would go to the effort. It's more hassle than just fitting new ones. Perfect chance to upgrade too. I just fitted ECS drilled & slotted rotors all round, with EBC Red Stuff pads & HEL Performance lines. I could not be happier, the improvement over stock rotors & pads is like night & day, and my old rotors/pads were not even worn out.

[Speed25]

Guess I'm in the minority, but mine have been turned (same as "shaved" I guess). Less than $20 each and they still do great on the track. In fact, I have another set of fronts that go back on with the street pads when I change them; I don't have to bed either set anymore. I know lots of track addicts that have used turned rotors for years and I've never heard of a single issue. Nothing wrong with buying new ones, but I'd keep the tire/gas money!

[Freon]

Resurfacing rotors is in no way "ghetto."

If BMW publishes a minimum thickness I say go for it. That in my mind means a competent engineering team did the work to confirm a safe thickness from structural standpoint.

Just realize they'll wear further from when you have them machined as you use them. If you'll end up hitting the minimum point before your new pads are worn it may not be worth the bother.

[tglazed]

Awesome, thanks for the replies. Does anyone know the thickness of BMW rotors when they are brand new?
As of right now mine measures;
Front drivers side-25.45
Front passenger side-26.17
Rear drivers side-23.79
Rear passenger side-23.73

[MightyMouseTech]

95% of the time here at Acura we machine the rotors when we change pads. Unless the brakes are not serviced on time/properly, the rotors are usually still above min. thickness for nearly the life of the vehicle.

[BEAR-AvHistory]

Originally Posted by MightyMouseTech

95% of the time here at Acura we machine the rotors when we change pads. Unless the brakes are not serviced on time/properly, the rotors are usually still above min. thickness for nearly the life of the vehicle.

Different metal composition. Pretty much the opposite at BMW. Even under the 4 year 50K free maintenance program they chuck the rotors on a pad change.

[fe1rx]

Originally Posted by tglazed

Awesome, thanks for the replies. Does anyone know the thickness of BMW rotors when they are brand new?
As of right now mine measures;
Front drivers side-25.45
Front passenger side-26.17
Rear drivers side-23.79
Rear passenger side-23.73

Front nominal 26 mm, minimum 24.4 mm
Rear nominal 22 mm, minimum 20.4 mm

I think you measured your rears incorrectly.

[fe1rx]

Originally Posted by BEAR-AvHistory

Different metal composition. Pretty much the opposite at BMW. Even under the 4 year 50K free maintenance program they chuck the rotors on a pad change.

Its the pads not the rotors. BMW rotors stay nice and shiny because they are continually being polished and turned into dust by the pads. All rotors are cast iron, with some hair splitting regarding carbon content.

[fe1rx]

Originally Posted by Freon

Resurfacing rotors is in no way "ghetto."

If BMW publishes a minimum thickness I say go for it. That in my mind means a competent engineering team did the work to confirm a safe thickness from structural standpoint.

Just realize they'll wear further from when you have them machined as you use them. If you'll end up hitting the minimum point before your new pads are worn it may not be worth the bother.

I agree it is sometimes appropriate, but given the aggressive wear characteristics of OE pads, probably only if you are using a pad that is much easier on the rotors. In my experience, one set of OE pads wears a bit more than half the usable rotor thickness away (given my driving), so a second set would take the rotor very close to or below the minimum, even without turning. If that is your situation too, it would be better to replace them rather than turn them.

Also, the concentric texture of a turned rotor is not ideal. Rotor faces should have a random texture, hence new rotors are ground not turned. Turned rotors shouldn't be used "as turned", they should be given a random texture with a sanding disk.