Rear brake vibration when bakes are hot.
 

I have had an odd problem pop up on my last track day.

After about 3-5 hot laps, the car starts to shake under braking. The harder I push the car into the braking zone, the worse the vibration gets.

I know its coming from the rear brakes. Nothing comes through to the steering wheel. The rear pads were recently changed from ECS Yellows to HAWK HP Sport pads just a week prior to the track day.

Yes, defiantly feels like warped rotors, but they were fine just a couple weeks prior to the pad change.
Plus, in the time the car cools down between heats, it goes away until I put 3-5 laps on it on the next heat.

Anyone experience this? Don't want to waste too much time figuring this out before the next event.

Thank you!

If it were me I think I would replace the rear rotors, I have never been a fan of changing pad compounds with out at minimum cleaning the rotor surface up with a light cut, ( I am not a fan of cutting rotors anymore so if I change compound I change rotors as well ).

A buddy mentioned something similar.
He said that it could be incompatible brake compounds on the rotor where I would need to resurface the rotor to fix that.
Do not know how true that is, but I did only run EBC compounds before switching to the HAWKs. It seems a resurfacing is needed.

If they are OEM and never been cut you can probably cut them with out much risk of them re warping quickly, But one cut is probably all you will get out of them. I am not sure what a shop will charge you to do it and honestly there are probably quite a few shops that don't even offer this service anymore.

Do you have steel brake lines? A buddy who tracks his car a lot said that as the fluid and lines heat up they constrict causing the shudder.

Maybe someone else that made the change to steel lines can comment.

I got steel braided lines all around.
Only happened after a pad change.
Had no luck finding a place to resurface them before my next event.
Trying to just get more miles on the pads and get them more bedded in, hopefully that helps.