I ran my M3 at Laguna Seca a week ago at a Touring Car Club event, and I quickly got a very spongy brake pedal. The car is completely stock (except for a Sparco seat and HMS harness bar) running Turner's Cool Willy pads and Motul 600 brake fluid. In addition, I've done the bend-the-backing-plates trick.

I've run Motul 600 in my Z28 and the stuff is awesome. In the M3, however, I would get a spongy pedal after only 3 or 4 hot laps. The brakes never went away, just got really soft.

Any ideas? (yeah yeah, I'll get a Mov'it kit as soon as I can afford it)

Thanks,

Chris

The assumption here is that you don't have air bubble's in your brake fluid and you have fresh fluid installed.
Maybe that you are boiling the brake fluid in the line at the caliper. Bleed some fluid at each line for eyeball inspection. Or your stock rubber brake lines are flexing and expanding due to heat and age and need to be upgraded to stainless steel brake lines.

I don't think you really want to bend your brake pads backing plates. You will not get full performance of your pads entire surface getting full and equal surface contact performance against the rotors. To solve a brake pad chattering issue you are putting your safety at risk by reducing your braking performance. There are other methods to reduce brake pad chatter. Or just live with it.