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I just got back from a two day trip and for the last 30 miles or so, I felt a grinding metal on metal sound when I applied the rear brake. Sure enough, the brake pads are completely gone and the rear rotor is pretty scratched up. Are minor scratches OK or do I need to replace the rotor? The front rotors are super smooth - I can't believe the rears wore out that quick (8k), but I should have caught it and changed them before the trip. I'd rather not buy a rotor right now, but if having a scratched rotor is a bad thing, I'll bite the bullet.

I've done some searching here, but I didn't really see anyone mention metal on metal scratches - more discussion about thickness, warping, and undulations in the rotor.

At a minimum, you will have to have them machined (turned) before installing new pads. I believe the minimum thickness is embossed on the rear disc. If the scratches are deeper than the minimum thickness, then the rotor must be replaced.

The above said, I always replace rotors on my autos since a thinner rotor will heat up faster and allow the caliper pistons to extend out farther towards the end of the pad life, both of which I am sure is taken into consideration when BMW establishes the minimum thickness spec, but nevertheless can only diminish the performance. Whether the rear rotor's (slightly) diminished performance will limit the overall bike braking is hard to say since the fronts work so much harder.

spenserj87 wrote:I just got back from a two day trip and for the last 30 miles or so, I felt a grinding metal on metal sound when I applied the rear brake. Sure enough, the brake pads are completely gone and the rear rotor is pretty scratched up. Are minor scratches OK or do I need to replace the rotor? The front rotors are super smooth - I can't believe the rears wore out that quick (8k), but I should have caught it and changed them before the trip. I'd rather not buy a rotor right now, but if having a scratched rotor is a bad thing, I'll bite the bullet.

I've done some searching here, but I didn't really see anyone mention metal on metal scratches - more discussion about thickness, warping, and undulations in the rotor.

I didn't think the rotors could be turned. I've also seen pictures of rear rotors in the some of the replacement DIYs and they don't look any worse than mine. I just don't want to be stupid. Maybe I should post a pic:

In years of searching - I've never found anyone who can grind/turn/refinish motorcycle rotors. I heard through a Ducati owner that such a thing existed, but he came up blank when asked to give a name/email or any other contact info.

As far as your rotor - it will probably be fine after some miles on it with a new set of pads, but it will eat up the new pad rather quickly, so you may want to keep a close eye on it. Most "experts" would suggest replacing it - which isn't a bad suggetion until you price the new rotors.

Thanks for the insight - I figure a $30 pair of pads is worth trying if there isn't a safety or other issue. If it eats them up or I notice any other problems, I can do the rotor. I'd rather save the $ right now. Lesson learned on watching the pad wear.