Dealing with high speed brake vibration

[noremaC]

So I've done quite a bit of searching on the Post and have consulted a Euro shop on this issue but would like to validate my thoughts.

I'm on OEM rotors, stoptech street pads and OE-spec fluid.

At higher speeds (80+), when I press firmly on the brakes I get:

- vibration in the steering wheel and pedal
- lack of performance, i.e. missing a lot of stopping power and initial bite

I recently took a trip into the mountains and pushed the car to the point where the brake pedal would basically go to the floor. I cooled down for 10 minutes. However, after this, I started experiencing this issue.

I believe my rotors are warped. I've already done a fluid change in hopes that would resolve the issue but no dice.

Question: should I start with replacing the front rotors, pads and sensors? The rotors only have like 10k miles with zero track days. I would think the rears are fine (also 10k miles).

Thoughts?

[noremaC]

Couple other thoughts: is it possible this is tire related or spacer related?

I would think with overheating the rotors in the mountains, it's likely brake related, however.

[Davisca455]

I have experienced vibration with high speed braking (145ish) in the past with my M3.
But then at lower speeds no vibration.
Original rotors/pads/19" wheels, no spacers.
I looked at the front tires and they looked fairly worn, so I replaced them.
Went out and repeated the high speed braking test, and no more vibration.

[Redd]

Possibly brake pad deposits. Since the rotors are still fairly thick, maybe get them resurfaced?

[Not Sure]

also consider replacing the LCA bushings with monoballs. definitely helps the car feel more stable under braking. i have the dinans but i think GAS are cheaper and functionally equivalent.

[noremaC]

Originally Posted by Davisca455

I have experienced vibration with high speed braking (145ish) in the past with my M3.
But then at lower speeds no vibration.
Original rotors/pads/19" wheels, no spacers.
I looked at the front tires and they looked fairly worn, so I replaced them.
Went out and repeated the high speed braking test, and no more vibration.

Thanks. I'm thinking it could be tire related. I have PSS up front and PS4S in the rear. Ideally I could find some ZCPs locally to test on fresher tires but odds are not in my favor. I wish there was a discernible way to determine tires vs. brakes.

Originally Posted by Redd

Possibly brake pad deposits. Since the rotors are still fairly thick, maybe get them resurfaced?

Interesting. Didn't think this was a recommended approach with modern rotors but will look into it. I've done multiple HARD stop and go's to try and remove any deposits but no dice.

Originally Posted by Not Sure

also consider replacing the LCA bushings with monoballs. definitely helps the car feel more stable under braking. i have the dinans but i think GAS are cheaper and functionally equivalent.

Great recommendation. When I begin to upgrade components, I will take these into consideration. Had my shop check bushing and components yesterday and all seems to be fine.

[trm0053]

Agree with Redd, this sounds like brake pad deposits on your rotors. Chances are you can see the deposits on your rotors.
It's very difficult to warp OEM rotors on these cars especially on public roads. So there is no need to replace them.
If pads are cooked, however, they need to be replaced.

Here's a great post by deansbimmer -> https://www.m3post.com/forums/showthread.php?t=1384226

If you don't have a more abrasive brake pads then you can try 3M paint and rust stripper disk or a wire cup brush to remove those deposits.

[Redd]

Unlikely tires. Tire vibrations will increase with speed, not just under braking.

[OldenburgerM3]

Another vote for deposits. I recently had to figure out the same issue on my car while on the track - i.e. warm/hot brakes. I could not reproduce this on the road despite numerous attempts, nor could I find any deposits visually.
I was against that diagnosis because I had recently replaced the rotors and pads, but when I did a session with my road pads then the next session on the track pads again, I had rubbed off the deposits and things were perfect.
Besides sandpaper (a method recommended to me by Hawk) I don't know how you'd solve it in the garage, but go with that diagnosis before spending money.

[noremaC]

Originally Posted by OldenburgerM3

Another vote for deposits. I recently had to figure out the same issue on my car while on the track - i.e. warm/hot brakes. I could not reproduce this on the road despite numerous attempts, nor could I find any deposits visually.
I was against that diagnosis because I had recently replaced the rotors and pads, but when I did a session with my road pads then the next session on the track pads again, I had rubbed off the deposits and things were perfect.
Besides sandpaper (a method recommended to me by Hawk) I don't know how you'd solve it in the garage, but go with that diagnosis before spending money.

I think the options are to either purchase some aggressive pads (Hawk Blues), run those for a couple of days and replace with street pads (re-bed those in).

OR

Try a hone disc drill attachment, in which I'd have to remove the rotors.

I feel like option #1 is the more effective approach.

[SAMM3Y]

Yes, pad slapping on none turned rotors will result in a lot of vibration... when I first tracked my car I pad slapped some EBC yellow pads on the rotors and by the end of the first session I left the track prematurely assuming they were cooked by the end of the second session they were bedded properly and were fine for the remainder of the day

[noremaC]

Originally Posted by SAMM3Y

Yes, pad slapping on none turned rotors will result in a lot of vibration... when I first tracked my car I pad slapped some EBC yellow pads on the rotors and by the end of the first session I left the track prematurely assuming they were cooked by the end of the second session they were bedded properly and were fine for the remainder of the day

Are you recommending those pads to help remove deposits?

[SAMM3Y]

Originally Posted by noremaC

Are you recommending those pads to help remove deposits?

They are noisy and bitey so could do the trick worked for me. I still have them somewhere if you're interested

[noremaC]

Update: so I've put on EBC Yellowstuff pads to "clean up" the surface of the rotors and after about 100 miles, there is still vibration under braking. It's been a mix of a few hard stops (down to about 20mph) and regular highway & city driving. I've just swapped out the front pads...not the rears.

The one thing I did notice when I took off the ceramic street pads was small "chunks" taken out of the face of the pad where it makes contact with the rotor, on both sides. Not sure if this is normal - have not seen this before.

The next thing I will try - which frankly I should have done first - is have the front tires balanced. I do have vibration in the steering wheel from 75-90 mph, so this could be contributing to the problem.

Finally, I'm wondering if the FCAB's could be an issue? I'm at 73k miles, no tracking as far as I know. Perhaps a good excuse for GAS monoballs?

[Redd]

EBC Yellows arent exceptionally abrasive so I'm not sure how good they will be as a 'cleaning' pad.

Pics of your ceramic pads showing chunking pls. Chunking is not normal.

The first thing you should have done is a full tire rebalancing.

FCAB failure results in noise more than vibrations. Doubt it's the FCAB, but if you need an excuse for monoballs, "I think it might be the FCAB, too".

[noremaC]

Originally Posted by Redd

EBC Yellows arent exceptionally abrasive so I'm not sure how good they will be as a 'cleaning' pad.

Pics of your ceramic pads showing chunking pls. Chunking is not normal.

The first thing you should have done is a full tire rebalancing.

FCAB failure results in noise more than vibrations. Doubt it's the FCAB, but if you need an excuse for monoballs, "I think it might be the FCAB, too".

See below. These "craters" are not very deep but definitely doesn't look normal. On both sides (only swapped out the fronts). EDIT: now that I'm looking at them, those are definitely from the "drill holes" in the rotors. Wonder what causes this?

Will likely get the wheels balanced in the next few days.

Yes on the monoballs

[Redd]

I have x-drill rotors (Brembo GT) and am on my 3rd set of brake pads and none of them chunk like that. Definitely not normal.

[noremaC]

Originally Posted by Redd

I have x-drill rotors (Brembo GT) and am on my 3rd set of brake pads and none of them chunk like that. Definitely not normal.

I'm wondering if this would indicate there are in fact deposits on the rotors. None that I can see on the outside but possible on the inside of the discs.

[SAMM3Y]

Are those craters from the ebc's? I'd do a full break In on them. 60-0 as hard as you can as fast as you can 10x in a row, let them cool to ambient then repeat. You want to get the rotors blued. Then if it still isn't better find somewhere you can do some hard braking from about 120mph. It worked on my old rotors.

When my car was new to me, I took it to Laguna seca bone stock and at the end of the sessions brake dust was exploding out of the rotor holes that was with stock pads, might be contributing to the marks in the pads? I think those ebcs are abrasive enough as evident by the noise and dust they create, when I had them bedded properly they bit pretty hard on the street.

[noremaC]

Originally Posted by SAMM3Y

Are those craters from the ebc's? I'd do a full break In on them. 60-0 as hard as you can as fast as you can 10x in a row, let them cool to ambient then repeat. You want to get the rotors blued. Then if it still isn't better find somewhere you can do some hard braking from about 120mph. It worked on my old rotors.

When my car was new to me, I took it to Laguna seca bone stock and at the end of the sessions brake dust was exploding out of the rotor holes that was with stock pads, might be contributing to the marks in the pads? I think those ebcs are abrasive enough as evident by the noise and dust they create, when I had them bedded properly they bit pretty hard on the street.

These are not the EBC's; those were the street pads as I pulled them off. What's strange is I don't have any noise with the EBC pads. Perhaps I haven't got enough heat into them?

[SAMM3Y]

Originally Posted by noremaC

These are not the EBC's; those were the street pads as I pulled them off. What's strange is I don't have any noise with the EBC pads. Perhaps I haven't got enough heat into them?

They felt/heard pretty gritty when I had them.. maybe the rotor is still glazed up

[nrubenstein]

So, brake vibration can come from:
1) Pad deposits on the rotors.
2) Bad wheel bearings (a big concern if you are also getting an intermittent long pedal, as this suggests pad knockback).
3) Balljoint or bushing failure. The thrust arm bushing, and the front lower link seem to be the weakest components in the E9x front suspension.
4) It is possible that the rotor is warped. I've had issues in the past with the BMW "floating" rotors. I wouldn't rule it out.