Dark Spots on Front Rotors

[Go_Habs_Go]

Hi guys,

Last week I went for an oil change and decided to switch off my winter tires for my summers. When they took the wheels off I looked at my brakes/rotors. The rear rotors seemed fine but when I looked at my front rotors I noticed spots on both of them (driver and passenger side). They weren't rust spots or anything like that. They were more like dark smudgy spots across the rotor, almost like ink spots. There were several of these spots on both of the rotors. I touched the spots with my finger but I didn't really feel anything, it was like they were part of the rotor.

I asked the tech who was working on my car about the spots and he said they were probably heat spots. He said the rear rotors didn't have the spots because most of the braking is done by the front brakes. He asked if I felt any vibration when I braked and I said no, it feels perfectly smooth when braking. He said if I wasn't feeling any vibration then not to worry about it. He also mentioned the rotors would get resurfaced when I changed my brakes so the spots would be removed.

Frankly I wasn't so impressed with the tech's explanation. Is this normal to get heat spots on my front rotors (if that's what they actually are?). I've had my car for less than 2 years (20 months) and I have about 30,000 kms on it. Should I be worried about this and look into asking the dealership to replace the rotors under warranty? Or is this all perfectly normal? Does anyone else have spots like this?

Thanks for your replies!

[condor888000]

Hum....no idea. Sounds odd though man.

[Go_Habs_Go]

Yeah I definitely find it a bit odd, I've never seen spots like that on the rotors of my other cars. I'm also pretty sure they weren't there when I put on my winter tires in November. It's almost like the rotor got stained somehow?? I'm a little bit concerned about it but at the same time my braking seems fine (car stops in normal distance, brakes respond normally, there is no noise when I brake).

The only thing I noticed that may somehow be related to the spots is that I noticed some black inky stains on my front rims. I wiped it with my finger and it seemed to come off easily so I wasn't too concerned about (I figured I would give it a good wash soon) but now I am wondering if those stains are related to the spots on the rotors. E.g. either the spots on the rotors are giving off a dark brake dust that is now staining my rims or I got some sort of dark liquid splashed on my rims and rotors and it somehow made the spot on my rims?

I will try to take one of the wheels off this weekend so I can get a picture of it.

Anyone with any ideas in the meantime?

[taz4432]

Well, you said so yourself that everthing is working as it should. So I'd say to keep driving in the meantime and if there is any sign of deteriorating/unusual performance, get it checked out.

[Go_Habs_Go]

I've been doing some reading about this and it looks like what may have happened is that some of the material of my brake pads may have come onto the rotors. This actually occurs "normally" especially when braking hard (and heating up the pads and rotors to really high temperatures). However it may also lead to spots being left on the rotor and eventually what they call "cementite". This is not a good thing to have on your rotors!

So is this normal wear and tear on my rotors? I don't usually brake hard (just in emergency situations when there is no other choice) otherwise I usually downshift and slow down way before I need to brake. So far I am not getting any vibration when braking but I'm wondering if the spots will eventually turn into cementite and "warp" the rotor, causing vibrations to occur.

Will mention it to my dealer next time I go back...I want them to at least mark it down that this happened before the 24 month period of ownership passed (I think that's how long they cover brakes?)

[Go_Habs_Go]

FYI here is a great posting on the physics of braking and the materials involved.

http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml#