03 6r' Massive shuddering under braking. Warped Rotors?

[Octonauts]

Hi guys,

Bought an old 03 6r to serve as a track bike. I've spent a couple months rebuilding it, and finally had the chance to take it to QR on the weekend.

Unfortunately, braking from speeds higher than ~110km/h turned the front end into a mini jackhammer - quite unsettling given the nature of QR. I had so much shuddering from the front of the bike my eyes and jaw were feeling it!

I'm 90% certain the issue is warped rotors , but i'm wanting to confirm before spending the money on new rotors. I am only 90% certain, as I never noticed issues braking from lower speeds. That doesn't mean it's not the rotors though. I had brand new pads on the bike as well (I bedded them in the car park before the day started) but i've never had this issue with new pads on any of the other bikes i've ridden before.

Could anything else give massive shuddering under that much braking? I checked for loose/ worn head bearings, but the bike handled / steered fine on the day, and there is no play in the forks. If it was wheel bearings or an out of balance wheel, I would've noticed it at lower speeds, or under acceleration too, wouldn't I

I have maxed out the preload on the front to give me 28mm of sag. Is it possible this is causing issues? I can't see anyway in which it would, but just wanting to confirm suspicions.

Thanks for your help, this is an awesome community.

Octonauts.

[Mitch]

couple of questions?

1. when you brake are you feeling any pulsing thru the lever?
2. have you had the front wheel off the ground and spun it? does it spin freely and grab at one point?

[smithy5]

Lift up the front wheel and secure it, then spin the wheel with a can or something next to the rotor. Should give you an indication.

[pkay]

Mate if you can't lift the front wheel go for a ride and gently apply the brakes - if your rotors are worn you'll feel the grab ungrab friction sensation - you don't need to do a stoppie to feel it. The braking will not be a linear force.

[javaman]

Unfortunately, braking from speeds higher than ~110km/h turned the front end into a mini jackhammer - quite unsettling given the nature of QR. I had so much shuddering from the front of the bike my eyes and jaw were feeling it!

I had 2000 zx6r which shudders under heavy braking on the track. I knew it was warped because of a previous crash.

Interestingly it never felt it on the road.

I replaced them with those $300 a pair ebay discs and all went well.