jmgtp

I have brand new pads and rotors on the car. I also rebuilt all 4 calipers. Probably around 300 miles on everything. Yesterday, I noticed a groove appearing on the rear passenger rotor. As you can see in the image the brakes are so new that the crosshatching is still visible as well. What is important to note is that I cannot feel the groove at all with my fingernail - at least not yet. It is just a visual mark for now.

Still, doesn't seem normal. Apart front something foreign between pad and rotor what can cause this?

Car is a 94, non J55. I'd have to lookup the brand of rotors that I bought, if relevant. The pads are Autozone duralast gold. They are a ceramic pad that I had read positive reviews on from the c6 crowd so I tried them for the C4. Braking performance is good, pedal is firm, there is no noise.

Whaleman

I assume you removed the pad to check for a piece of metal or something else embedded in the new pad.

drcook

Somehow mark your pad so you can look in a radial arc to see if something is there as Whaleman said. A piece of hard material could be anywhere on the arc causing that. Put a mark on both sides of the pad where the groove is and when you take it out follow a radial line that matches that line. Make sense ?

If the pad is OK, it could just be how the rotor was turned. I had a rotor that looked fine until the gloss was wore off and you could see that it wasn't machined correctly. The gloss and anti-rust coating hid the defect.

jmgtp

I'll admit I haven't pulled it apart yet. Maybe tomorrow but more likely weekend. Hope it's not a bad rotor.

jmgtp

I just finished pulling it apart. I didn't find much. There was a tiny ridge on the edge of the pad and I used a file to smooth it out. I do not believe it to have been the cause because where it is on the pad is not lined up where the mark on the rotor is. I used 00 steel wool over the face of the rotor but as it sits it's only a visual mark and I cannot feel it with my fingernails.

Bottom line is that I found no evidence as to what caused this mark. My best guess at the moment is that foreign debris was caught up in there, made its mark and is now long gone. Will keep an eye to see if the mark on the rotor develops into a groove.

Hard to see in the pic because I couldn't get my phone to focus this close but the ridge that I filed is blurry but barely visible.

Whaleman

That "new" pad looks 100 years old. Dan

jmgtp

Effect of the extreme closeup. It's 4 moths old with a few hundred miles.

hcbph

Those pads don't look right to me, are they semi metallic or what?

Here's some instructions on breaking in new pads I found online:

Here are the basic steps on how to bed your brakes:Brakes on Car
1.The bedding-in process requires lots of accelerating and quick decelerating. Perform this process early in the morning and in a low-traffic area so that you avoid other vehicles.
2.From 60 MPH, apply the brakes gently a few times to bring them up to their usual operating temperature. This prepares your pads and rotors for the high heat generated in the next steps.
3.Make a near-stop from 60 to about 10 MPH. Press the brakes firmly, but not so hard that the ABS engages or the wheels lock. Once you've slowed down, immediately speed up to 60 MPH and apply the brakes again. Perform this cycle 8-10 times. Do not come to a complete stop! If you hold the brake pedal down while stopped you will leave excessive pad material on the rotors and ruin your braking performance.
4.Once you've performed that final near-stop, accelerate and drive a bit more, trying to use the brakes as little as possible so they can cool down. Again, do not come to a complete stop while the brakes are still hot. (Avoid traffic!)
5.If you are bedding in performance/racing brakes, you may have to perform extra near-stops from a higher speed.

Some more notes about bedding:
•Brand new brake pads and rotors will have very little braking power on their first few applications. Gently apply your brakes from low speeds a few times to establish some grip before you take your vehicle onto the highway or busy roads.
•Don't immediately bed your brakes if you have brand new rotors with phosphate, cadmium, or zinc plating. Do some normal driving to polish the plating off the rotors before bedding in your brakes.
•After you perform the break-in cycle you should see a light gray film and a slight blue tint on the rotor face. The gray film is material from the pads transferring onto the rotor face, and the blue tint indicates that the rotor has reached the proper break-in temperature. These are good signs that you have bedded your brakes properly.
•Some brakes, such as big brake kits or new pads installed onto old rotors, may require a second bed-in cycle. Let the brakes cool down fully before performing the second cycle.

jmgtp

The pads are ceramic. I bedded them per the FSM. They look pretty much like every other ceramic pad I've used before. Don't get too caught up on the pic, I had a very bright led work light shining on them and it's a bit deceiving looking. All the pads look just like this one but it is only the rear rotor, outboard side, that has the mark on the rotor.

drcook

you can see the "arc" where the grooving on the rotor was mirrored on the pad. follow that groove with your fingernail and see if you can feel a hard spot

jmgtp

I didnt notice that when I had the pad in hand. Certainly is there in the picture. I'll pull it apart again in the next few days. If I can feel it would sanding the pad down to flat be ok? Sucks to have this problem on new parts.