What are these lines on my brake rotor?

[rationull]

I did an oil change and tire rotation on my Civic today and noticed some lines on my driver side rear brake rotor that I hadn't noticed before:

They don't appear to be cracks, and they don't feel like ridges when I rub my finger across them. I tried to wipe them off with brake cleaner on a shop towel but they didn't come off. I didn't rub all that vigorously, though. There are similar lines in a few places on the rotor. I have not noticed any strange brake behavior.

I'm guessing this is just some kind of pattern caused by the e-brake (which actuates the calipers -- not a drum in the hat) somehow.

Anyone recognize this? Does it look like a problem? The car has the original pads/rotors with 49k miles on them. Pads have plenty of thickness left.

 

[JustinC25]

I've only see this when a car doesn't get driven much, and sits a lot. This is just an outline of the pad that imprinted onto the rotor. Nothing to be concerned about.

Does your car sit for any period of time ?

 

[Johnny]

+1

 

[toyota62]

+1

 

[OLAFF]

Here it is you ready?

You drive down the road and you lay on the brakes, so you come to a stop... then you let off the brakes and you move on untill you do it again...

So when you step on the brakes. a bunch of material gets scraped off the pad and it piles up on the front of the pad itself... then when you let off pad separates from the rotor leaving that junk behind... so you must have inched forward after the inital stop... as the second time around the pad didnt wipe the first line.

So then that stuff can start rusting and eat away at the rotor unless you go drive in it...

I say go lay on the brakes 2-3 times and it will go away.

 

[Kestas]

Does this pattern size match the pad size?

 

[willix]

Originally Posted By: Kestas
Does this pattern size match the pad size?
Thats is the question. Is it a vented rotor? Have they been machined before? if the car sat for a period. If so, I would dismiss the markings and not worry. They will go away after time and won't cause braking issues. If you put the brakes to extremes, surface cracking will devolope but start out small on the surface and never look that straight unless it is a vent rib in the casting. I really looks like a leading edge pad marking left after sitting.

 

[rationull]

To answer the questions:

- The rotors have never been machined.
- Solid rotor (not vented).
- The car doesn't sit for more than a couple days at a time in general.
- The pattern size does generally match the pad size in places but there is at least one line that's all alone.

I definitely don't push the brakes to extremes, but I try to give them a minor workout every now and again. Maybe I haven't done that for a while, though. I'll try a good firm stop or just pull up on the ebrake when stopping next time I can and see if they rub off that way.

 

[Kestas]

Brakes don't like to sit unused. Nor do they like to sit in one spot after a high-speed brake event.

Don't worry about it. Good picture, by the way.

 

[mechtech2]

Sure looks like the pad caused it.
Sitting, especially in wet/humid weather with the e-brake on can do this, as can any extended rest.

 

[OLAFF]

This is a crack, and you dont want to see that on your rotors...

What you got is nothing more then some brake dust from the pad.

 

[HTSS_TR]

The rear rotors are not too expensive and you got 50k miles out of it which is not too bad, I would change the two rear rotor for peace of mind. You don't want the rotor dis-intergrated while driving in city streets or on highway, $100 or so for 2 rear rotors to avoid serious accident is worth every penny.

 

[mechtech2]

Catera - Another failure of a drilled rotor!

 

[OLAFF]

Originally Posted By: mechtech2
Catera - Another failure of a drilled rotor!


Not my rotors, just a picture off google, to illustrate what a crack looks like. His stuff is not cracked.

BTW a solid rotor is the best rotor for any generic vehicle.
Drilled rotors if not done right can cause severe failures.
Solid rotor has more mass then drilled rotor and more surface area and in fact can slow don a vehicle faster then say a drilled or slotted rotors.

Brakes are devices that convert kinetic energy to heat, so the rotors are nothing more then heat sinks. The more heat they take the better they can work.

I was in a Mustang with drilled rotors on a road course when under heavy braking for one of the corners the right rotor blew up, sounded like an explossion and the piece that separated piered through the rim and then proceded to bounce and tear various stuff under the car. We of course hit the tire wall at a good amount of speed and wrecked the car.

Since that day I have sworn never to use such rotors on a car again.

I have a friend who is a braking engineer at FORD, that fella refuses to even hear about drilled rotors.

 

[mechtech2]

Vented rotors are good. I call them 'solid' rotors even though they really are not. It's all we can get for replacement front rotors.

 

[rationull]

Originally Posted By: HTSS_TR
The rear rotors are not too expensive and you got 50k miles out of it which is not too bad, I would change the two rear rotor for peace of mind. You don't want the rotor dis-intergrated while driving in city streets or on highway, $100 or so for 2 rear rotors to avoid serious accident is worth every penny.


Sounds like overkill. Braking action is still perfectly smooth on smooth road, and the rotors are plenty thick.


After some driving today some of the lines are faded but a couple of stronger ones are still there. If the opportunity comes up tonight I'll hit the ebrake to slow myself down to exercise the rears a little more and see what effect that has.

 

[rationull]

The lines are still on the rotor, after the last month of driving and even using the e-brake by itself to slow down a couple times.

Oh well, brakes still feel fine!

 

[Texan4Life]

stress cracks IMO

First time to see them on a disc though. Otherwise I have just them on brake drums.

I would run it, or if your paranoid you could put new rotors and pads on and not worry about it.

 

[rationull]

I really don't think they're cracks. They don't feel like anything, perfectly smooth. Not to mention there are small gaps in the pattern. It's just discoloration.

 

[chrome]

As other have pointed out, they are corrosion lines caused by moisture mixing with the metallic dust at the edges of the pad. The accelerated corrosion caused by the fine metal particles etches the disc along two neat lines. If you look at the lines under a magnifying loupe, you will see small shallow pits.