I just got back from three days of running the '04 Z06 at Watkins Glen. I have upgraded the brakes to Wilwood 6 pot fronts, 4 pot rears, on 13" rotors. I was running Wilwood H pads up front, B pads on the rear. Also, bled the brake system with ATE Super Blue before going up to the Glen, and again during the first day at the track. The car got heavy use, as I drove it hard, and my gf drove it in the novice group.

Anyway, by the afternoon of the third day, the brake pedal started getting very spongy. It was not as firm as I remember from when I had done the upgrade on my '03 Z two years ago.

So, the question is this -- do I need to upgrade the master cylinder? Or should l just go to a higher boiling point fluid like Castrol SRF? Has anyone had this problem, and how did you solve it? I still have a good amount left on the brake pads, and the rotors have held up well. It's the spongy pedal that give me concern. I don't think I boiled the fluid, just a very soft feel in the pedal (initial push on the pedal took it most of the way to the floor, pumped it once and then got fairly firm pedal... does this mean a bad mc?).

And if anyone has upgraded the master, what did you switch to (part numbers would be greatly appreciated). I did a forum search, but didn't find any suggestions for an upgrade to the MC.

Thanks,
Steve

 

Sounds like it could be pad knockback.

 

I had been having soft pedal issues at the track, usually after the first heat. Preparing for PPIR (yes, they are open again) last week, I C-clamped the pistons to bottom them out before and during bleeding. I ran six sessions with no problem, so I'm pretty convinced there can be air entrainment between the piston and bleed screw. It's something I should have been doing all along.