Brake Judder on Track
 

I had a really bad brake judder last year at Mallory Park and ended up swapping the brake discs out after that, and have also refurbed the front and rear calipers since. Given the temperature of the discs at the time, I figured some brake ducting was probably in order. Got the parts together and given I'm waiting the bumper scoops from Bearo.tech later this month, I rigged the ducting underneath the front tray to get some improvement. I also looked at hub and disc run-out and ended up using some wet & dry paper to reduce the hub run out from the already quite reasonable amount (0.0008" / 0.02mm) to a trivial one (0.0004" / 0.01mm).

Out at Bedford Autodrome in the UK today with the ghetto ducting and running DS2500 pads and OEM-style Bremtech vented fronts from Brakes International, I was getting some pretty significant brake judder - although not as bad as I was seeing at Mallory Park last year. What I found interesting was the pattern on the brake disc:

https://cimg3.ibsrv.net/gimg/www.s2k...4d6ff7963b.jpg
Pattern on the disc

That looks like pretty consistent spacing of the marks. Prior to the track day the disc runout didn't fluctuate in any manner which would explain that patterning. Any ideas? I wondered if it could be the ABS pulsing under sustained heavy braking when the disc was already hot? I want to check the runout over those areas at the weekend assuming I get the chance.

Run pads meant for track use.

This is caused by pad smear. Unless your rotors are mechanically distorted (improper torque, cracks, etc), they are not the root cause. They do not "warp" from heat from braking.

I was assuming accretion not a warped disc. Ferodo DS2500s have come well recommended from a number of people for track use - if the solve is simply chucking some Dixel ES/Z or going up to DS3000 pads for track then that's all good :)

Put some oem new discs on.