Vibration when braking at certain speed

[quadslo]

After one track day, I am now noticing hard vibrations while braking. I have Clubsport S rotors and stock pads.

Weird thing is that it only starts to vibrate when reaching 70km/h and going really strong at 50km/h and then it is gone.

Braking in neutral (N) is the same.

When applying brake at 100km/h up to 200km/h, there is just louder noise from the brakes, but no vibrations.

I paid a visit to a mechanic who knows stuff around race cars and he said that he didn't see that kind of behaviour before. If rotors would be bend or pads burned on the rotors it should vibrate also at some other point, not just at 50Km/h.

Any ideas?


Update for Admin: Can you please put this post under the brakes section?

 

[NopeR]

Wheel weight fell off? Pad isn't making complete contact with the rotor?

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[quadslo]

I solved the problem. I did a few runs from 150km/h to zero, to really overheat brakes. Now the vibration is gone.

It is really weird that it was shaking only at 50km/h. On other cars I had shaking all over the place after a trackday.

 

[Paddler]

I solved the problem. I did a few runs from 150km/h to zero, to really overheat brakes. Now the vibration is gone.

It is really weird that it was shaking only at 50km/h. On other cars I had shaking all over the place after a trackday.

It sounds like you just needed to properly bed your pads.

I had this with my r. My issue was going from street pad to track pad for track days the brakes behaved as described. My fix was to have a set of rotors dedicated to the track pads and another for my street pads.

 

[Al_in_Philly]

Most people don't realize that the energy transfer during braking involves ultra-high speed vibration of the rotors. It's possible that the vibration that you noticed was at a harmonic of that vibration. The heating of the rotors from your high-speed braking likely altered the molecular structure of the rotors enough to alter the vibration frequency and thus the noticeable harmonics. That's my guess.


Most people look solely at ring seating/honing during engine break-in. There's an additional process going on within the pistons and other moving parts: a final settling of the molecular structure of the metal itself. Varying the engine speed during those initial heating cycles keeps the molecules within those parts from settling in one place aligned with a specific harmonic, making for an engine which runs smoother and wears more evenly. Brake rotors can have inherent variations in their molecular structure as well, even when they show no discernible differences in run-out.