Originally Posted by M3PO
I just went to the track for the first time with Project Mu Club Racer pads and Castrol SRF. After 10-12 minutes, the brakes would start to vibrate. A few easier laps would reduce the problem and they were perfectly fine for the next session. I am overheating the rotors correct? The thermal expansion is creating temporary axial runout in the rotors?
No pad transfer on the rotors...
I use BMW M Sport pads and I've driven them to the point of absolute fade and have never had vibration under braking. I did however have significant vibration under braking when I tried the standard pads on track, which gradually disappeared (2 weeks after track day) as the uneven pad transfer wore off.
I'm inclined to think that yours is also due to uneven pad transfer. It's not something you can easily see. I'm fairly certain that most pads would overheat way before the OEM discs go beyond its maximum operating temperature. Also, once a disc is truly warped - not with axial runout due to pad deposits - it'll never recover, so by the fact that it gets better as you manage the brakes before the next session, points more towards uneven pad transfer.