FAQ: Vibration under braking: warped rotors? NO!

[MerlintheMad]

Now the deposits are on the rotors themselves so these front pads won't alleviate the shuddering unless I get the rotors turned also correct? Then i'm assuming these ceramic pads will still require the proper bed in process after I get the rotors turned?

That will work as long as the rotors don't have cementite buildup on them: this only occurs if the rotor surface reached 1200-1300F degrees. Cementite is rough, a lousy heatsink and it grows worse with age, because it is much harder than the surrounding iron of the rotor surface, therefore it stands "proud" (higher) while the softer iron wears down. Brand new pads will not bed in on rotors with cementite: but rather will accumulate pad deposits on the higher cementite surfaces. You have to replace rotors with cementite.

 

[max2382]

That will work as long as the rotors don't have cementite buildup on them: this only occurs if the rotor surface reached 1200-1300F degrees. Cementite is rough, a lousy heatsink and it grows worse with age, because it is much harder than the surrounding iron of the rotor surface, therefore it stands "proud" (higher) while the softer iron wears down. Brand new pads will not bed in on rotors with cementite: but rather will accumulate pad deposits on the higher cementite surfaces. You have to replace rotors with cementite.

How do I know if there is cementite on the rotors?
Thanks

 

[itguy61]

How do I know if there is cementite on the rotors?
Thanks

If it comes back pretty quickly I would bet on it being there.

 

[MerlintheMad]

How do I know if there is cementite on the rotors?
Thanks

Short of an informed examination of the rotors, there isn't a one hundred percent diagnosis; but as @itguy61 says, lumpy braking shortly after bedding in would be cementite buildup as the cause. Turning the rotors will not get rid of cementite, because it goes deeper than the surface.

 

[Cyrus Duong]

Managed to take a picture of some funny looking stuff with my rotors. There are some dark spots that become very apparent when washing the car. I did it when the brakes were hot... In the closeups the water evaporated off.

Not feeling it yet but could this be the onset of the rotor build up?

https://photos.app.goo.gl/ASaajCz1JNtwmYBZA

I did bed my brakes in as soon as I got my car but perhaps this could be a visual indicator or something else? We'll see. I'll continue to drive normally and report if symptoms occur.

 

[MerlintheMad]

Not feeling it yet but could this be the onset of the rotor build up?

I don't think that cementite is visible until there is buildup from pad deposits. If you're not feeling anything, those spots are just discoloration.

 

[Helo58]

Managed to take a picture of some funny looking stuff with my rotors. There are some dark spots that become very apparent when washing the car. I did it when the brakes were hot... In the closeups the water evaporated off.

Not feeling it yet but could this be the onset of the rotor build up?

https://photos.app.goo.gl/ASaajCz1JNtwmYBZA

I did bed my brakes in as soon as I got my car but perhaps this could be a visual indicator or something else? We'll see. I'll continue to drive normally and report if symptoms occur.

You did a great job of capturing these photos. If you are not feeling the vibrations yet, I would suggest you switch to an aftermarket pad now. These photos look like just about every photo I have ever seen associated with "hot spots" that will ultimately become cementite.

 

[Helo58]

I don't think that cementite is visible until there is buildup from pad deposits. If you're not feeling anything, those spots are just discoloration.

My personal experience indicates that the discoloration precedes the vibration. The discoloration is the "hot spot" that will lead to cementite over several drive cycles. If you have one, it is only a matter of time until you have the other. A good deposition layer should be even as seen below.

 

[MerlintheMad]

A good deposition layer should be even as seen below.

If Cyrus has those same spots showing after driving and braking, then I agree with you. But I'm thinking that getting water on the discs while they were still hot, and having it evaporate, has produced temporary spots that will scrub away the next time he applies the brakes. "We'll see", as he said.

 

[Helo58]

If Cyrus has those same spots showing after driving and braking, then I agree with you. But I'm thinking that getting water on the discs while they were still hot, and having it evaporate, has produced temporary spots that will scrub away the next time he applies the brakes. "We'll see", as he said.

And that is what I love about you. Ever the optimist. I am not quite so optimistic in this case. "We'll see," said the Zen Master...

 

[Cyrus Duong]

And that is what I love about you. Ever the optimist. I am not quite so optimistic in this case. "We'll see," said the Zen Master...

Guess I'm the engineer, haha, testing my hypothesis...

Given it's evidence you've personally seen beforehand I see no harm in letting it happen (but thank you for your concern and sharing wisdom) considering the warranty for plenty for others has replaced them. If only to see if and how long it takes to happen from this state.

If they do end up getting worse I'll probably do it right and replace them and do it right with new pads and rotors. Wouldn't want to run only new pads on semi-defective rotors.

Currently closing in on 8k miles. As a reference for others.

 

[itguy61]

Helo has given some very good advice on being proactive and getting aftermarket pads BEFORE the problem manifests itself, that way you don't risk ruining your rotors before starting to resolve the pad issue. He is very wise on this issue as it seems he has had the worst luck on this issue!

 

[Cyrus Duong]

The lot of you are making me spend money! I have to use that warranty!

Well, I suppose I'll consider. Do we think the rotors suited for long-term use should the pads be replaced? Because there are some fancy looking rotors out there, not sure if they do a better job... But weight savings? :joke:

Edit - Considering I've gotta throw my winter shoes on the car soon, ideal to do it while those wheels are off (probably happening sometime nearing the end of this month).

 

[Helo58]

Given it's evidence you've personally seen beforehand I see no harm in letting it happen (but thank you for your concern and sharing wisdom) considering the warranty for plenty for others has replaced them. If only to see if and how long it takes to happen from this state.

I agree, no harm in waiting as long as you don't mind enduring the poor driving experience once/if it rears its head. In others areas of my life, I do similar things simply for the sake of "learning" or expanding my knowledge base. In this particular case, you are not reinventing the wheel so to speak. There are many photos that look almost identical to your photos. If you use the search terms "rotor" "brake" "hot spots" or "cementite" etc., and then go to images, you will see how well your photos match-up to others. But as you said, there is no harm in waiting. I'm a curious fellow myself.

Helo has given some very good advice on being proactive and getting aftermarket pads BEFORE the problem manifests itself, that way you don't risk ruining your rotors before starting to resolve the pad issue. He is very wise on this issue as it seems he has had the worst luck on this issue!

Thanks for the props, haha. However, "rarely does the one with wisdom encounter the worst luck." This is an ancient North Carolina proverb I think.

I have to use that warranty! Well, I suppose I'll consider. Do we think the rotors suited for long-term use should the pads be replaced? Because there are some fancy looking rotors out there, not sure if they do a better job... But weight savings? :joke:

I would encourage you to get new rotors through your warranty process and have them put on aftermarket pads of your choice at the same time. The Gyrodisc pads seem to be working out very well for many. The weight savings are a joke when considering the weight of the entire car, but many use the lighter rotors to better tune suspension movements. Lighter wheels, tires, and rotors go a long way in this regard. There are several discussions elsewhere that deal with "sprung" and "unsprung" weight that go into this further.

However, whatever your choice, keep us posted. More data helps! Given that the front rotors are back-ordered nationally, it seems that a significant number of folks are having the issue.

 

[Cyrus Duong]

However, whatever your choice, keep us posted. More data helps! Given that the front rotors are back-ordered nationally, it seems that a significant number of folks are having the issue.

Replacement rotors and pads seem ideal at the same time. Thank you for your kind words and advice. Shame the pads can cause something like this. I will report back. As you've said I can't help but add more data and evidence that something like this happens/is happening.

 

[Metalmania82]

Just had my front pads and rotors replaced under warranty along with a new head unit. This is after an initial visit where they stated they would not replace under warranty (even though the car only had ~3k miles at the time in less than 8 months of use). They offered to cut the rotors but I declined. We'll see how far these go until there's an issue again.

 

[djerickd]

Any other pad options released lately? Does no other platform use these calipers??

 

[Stinger Girl]

Yes I have read the posts, but what is this on my rotors? Yes, I can go to the dealership but if they are only going to give me a band aid fix I'm not interested. Tell me what I need to do to solve this problem and I'll do it!

 

[NS_Stinger]

Yes I have read the posts, but what is this on my rotors? Yes, I can go to the dealership but if they are only going to give me a band aid fix I'm not interested. Tell me what I need to do to solve this problem and I'll do it!
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Do you have any vibration when braking? If you don't you have nothing to worry about from what I can tell.

 

[Stinger Girl]

Do you have any vibration when braking? If you don't you have nothing to worry about from what I can tell.

Well that's not the response I was expecting but I'll take it!

I feel vibration in the brake pedal but not the steering wheel (no pulsing, only vibration) and was basically just ignoring it. Then yesterday the front passenger with me felt it which drew my attention to the rotors.