Help: Stumped about brake behavior on track

[parsonsj]

I've got my car back from the Eyes on Design show in Detroit, and I want to get to the bottom of the odd behavior I experienced at Road Atlanta. The brakes work great for normal street driving; no complaints there. I've been blaming my pedal linkage ... but now I'm not so sure.

I'm using Wilwood 6 piston Superlites with 14" rotors in the font, and 4 piston Dynalites with 12" rotors in the back. The car has very little weight transfer during braking. (very low, 60% anti-squat, high rate springs).

Anyway, I've got a balance bar with separate masters and brake line pressure gauges. So I can see the line pressure, and easily adjust the ratio. Right now in my garage, I can push all day long on the pedal and get 1100 psi both front and back, with the front a bit higher than the back. I figured that would be a good starting point since the rotor and calipers are more capable up front.

(enough already, what's the problem?) During track events, the pedal gets soft and tends to stay low. If I pull it back with my left foot, the next brake will be very solid, but it will slowly go lower until I pull it back again. And the line pressure in the front is much lower: maybe 50-60% of the back.



This doesn't take long ... on Road Atlanta this started happening within 8 laps or so. So ... am I boiling fluid? Water or air in the front brake lines? Is there a secret to balance bar setup I might be missing?

Thoughts?

jp