Re: GT Brake Shudder
Hope you won't take offence at this but it might be the way you use them. One thing that will, I have discovered, knacker discs and cause shudder is sitting stationary, with the brakes on when they're hot.
Can't remember the name but where I saw the info was on a very informative website on the technicalities of brakes and - amongst other things - how modern pad materials transfer compounds into the surface of the disc when hot. As you can imagine, this can give rise to variable friction coefficients around the disc rotor if one sits stationary with the brakes on, hence the shudder.
From personal experience I've had this problem on my GTA which was made worse by some iffy pads. Interestingly the shudder has decreased since fitting some ferodo pads and - after reading the article - keeping my foot off the middle pedal when stationary! Didn't cure it of course, that required new discs.
Also, bedding pads in is important in the higher performance brake set-ups. My way is:- a few miles of gentle use, then brake 60mph to 20mph at high deceleration, four times in rapid succession, then drive around until the've cooled right off.
TallPaul's comment about corrosion is valid - this would suggest a seized caliper if one pad is not contacting the disc face.
Hope you get it solved - bad judder at high speed is terrifying, to say the least!