Re: brake pedal drops at autox track.
Do the brakes still function properly or is there a loss of any braking at all? If they start to fade and get hot, the fluid if old can boil which results in the pedal getting spongy which will take more pedal pressure to compress. A flush and fresh fluid can help. Also DOT-4 has a higher boiling point than DOT-3 so that can help. Usually fading with good fluid will still give a hard pedal but greatly reduced braking. Also old rubber lines can start to swell and require more pedal travel.
You can check the booster by shutting the car off then pumping the brakes several times to bleed the booster down. Then hold the pedal down and start the car. The pedal should rise against your foot.
I have had a check valve be bad right out of the box before. The car stopped fine in my case but something didn't feel right. You can check it by just pulling it out and blowing in it. You should only be able to blow through the side that plugs into the booster, not the side that connects to manifold vacuum.
It's possible that you're just not able to rebuild booster pressure fast enough between applications when you're autocrossing but it sounds like a fluid issue. Usually no vacuum manifests itself in a hard pedal.
Do you have good stainless hardlines, braided flex lines, fresh pads, and fresh fluid?
Dart 400-AFR 195-224/224 HR-Powerjection III TB with F.A.S.T. Sportsman XFI
TKO 600-Moser 3.42-Detroit Truetrac
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'69 Camaro Beater-SFT 327-M20-Moser 4.10-sold
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