groovy rotor

[BennyM]

The other day I noticed a light, rhythmic scraping noise coming from the front right. I also have a very subtle shimmy upon braking at hwy speeds now. I Jacked up the car and turned the right front wheel by hand. It spins freely half a turn and then has resistance the other half, then it spins freely again. So, I took off the wheel, but was too lazy to disassemble the brake. There's plenty of pad left and the front of the rotor looks fine, but the back seems weird to me. It has a 1/4" groove near the outside, then a 1/4" of rust at the outermost edge. Isn't it supposed to be smooth metal all the way to the outer edge?

I've got a pic, though it's from my crappy cell phone camera:

Could this be caused by debris stuck in the pad or am I running out of rotor material?
Front brakes are 3 years old.

[Tiger]

That lip means that your rotors has worn down from original thickness... time to replace them. As for the front I am afraid you got warped rotors.... very common problem with solid rotors and mediocre pads... that the disc gets very hot and the rotors could not dissipate enough heat.... resulting in glazed and warped rotors.

[whiskychaser]

You normally get a lip of a couple of mm on the outer edge of the disc because the pads dont actually reach that far. Depending how worn they are, you might be due for a replacement anyway. The inboard pad only appears to be braking on about 1/4inch. And its been like that some time or it wouldnt have worn a groove. Its possible the pad is stuck in the carrier and while it looks to have plenty of meat on it, its actually shaped like a wedge. I'd suggest new discs and pads and make sure the caliper is sliding freely.
Dont know about your car, but on mine there is a handy little bracket at the bottom of the inner wing. I loop a piece of wire through it to hang the calipers on

[632 Regal]

The brakes on these cars tend to rust from the outer edge to inside. I have tried many combinations of pads and rotors with the same results. Time to replace the rotors sorry to say. You say the pads are fine, then sand them down to flat with sandpaper on glass or similar flat surface. Inspect them for heat cracks, if cracked replace! Have not figured a solution yet. I have painted the rotors to prevent the rust from creeping but even baking the high heat paint does not seem to help.

[Ross]

The reason it drags and has rust on only a portion is because it's warped. The outermost edge never sees the pad, hence the "lip".
Resurface or replace, clean all the attachment points and check caliper for sticking.

[BennyM]

Thanks guys. I figured that's what you were going to say, but it's good to get the confirmation. I hate having to replace rotors or pads when there's still material left to grab. I would say that over the last 10 years of E34 ownership, I've only had one set wear completely out and not warp. And yes I always do rotors and pads at the same time. I'll add the caliper seal kits to my order this time to be safe.

[Tiger]

I just took a look at my folk's brake... that I did about 20000 miles ago. I used the slotted ATE Prremium One and Akebono pads all around... Perfect wear on the rotors... zero mirror, zero glaze, rotor looks like dull surface which grabs well and zero lip.

[BennyM]

I just took a look at my folk's brake... that I did about 20000 miles ago. I used the slotted ATE Prremium One and Akebono pads all around... Perfect wear on the rotors... zero mirror, zero glaze, rotor looks like dull surface which grabs well and zero lip.

Yeah, that's the combo I was planning on ordering. Thanks.