I've had a couple of moments on track when the brake pedal goes hard (ie you can't depress it much and the brakes don't slow the car down). A bit disconcerting. Lifting off and pressing the pedal again and it works normally.

Anyone else found this? Any guesses what the problem might be?

It sounds like you the vacuum assist (power brakes) isn't there when you first press the pedal, but returns. Do you get any braking with first (hard) press? Does more pressure bring more brakes? On the second press is it perfectly normal (no fade at all)?

This is certainly something to be concerned about. I would have your service tech check it out and stay off the track until the cause is found and fixed.

Doug

That sounds very scary. Could it just be air in the lines? If so, I think a simple brake flush would cure it. But have it checked by someone that knows brakes. That would really concern me.

It can't be air in the lines. If that was the case the pedal would be VERY soft, not hard. And the problem would not go away.

Okay, makes sense. I just can't imagine what it is then. Doesn't sound like brake fade because the second time they work. Unless that's a perception issue: the second press occurs when the car has slowed and so it feels like the brakes are now working normally. Not second guessing the OP, but it might be hard to tell when you're scared, going into a corner too fast and don't have any brakes ...

willr, when you find out, please let us know!

Well, I got some braking on the first (hard) press, but very little - not the best feeling going into a corner! To be honest I didn't have time to figure out if more pressure would eventually have worked - just came off the brakes and had another go and it was OK. No fade on brakes as am using uprated fluid and pads.

I've experienced soft pedal and pad fade before, but in both cases the pedal performs normally, you just don't get the braking. This was something different...

Loss of vacuum assist sounds like the best explanation. Anybody who has tracked with Tilton master cylinders and big calipers knows exactly what you are describing. Your right quad gets quite a workout in those setups.
The question is why this is happening. Has it occurred during useage offtrack? Did any dash warning lights come on? The event might have triggered a stored failure in the diagnostic center.
Bottom line- get it checked out.

It hasn't happened off track, but I'm extremely light on the brakes for normal road driving. On track it happened about 10 minutes into the session.

I'll certainly get the brakes checked before tracking it again... So far I must say I've been less happy with the Cayman pedal feel compared to my 996. Apparently Porsche changed the brake design for 987/997, using a vacuum pump run off the cam rather than relying on the inlet manifold. The 987/997 cars I've tested have all had softer feeling brakes, which I don't like...

I'm with you. I find the CS' soft pedal disconcerting, especially on the track. It also interferes with my heel/toe since the brake pedal needs more travel than I'm used to. Perhaps I'll get used to it, but I'd rather improve it. Anyone have any ideas?

__________________
Dan