My car has OEM clutch disk/PP/TO bearing/tranny, and Spoon flywheel. Disk/PP/TOB has about 15K miles (2K track) miles, the rest has 35K miles (5K track).

Until my most recent track day, the clutch pedal was engaging/disengaging closer and closer to the top of its travel (something I've associated with normal disk wear -- is that right?), but was otherwise fine. At the last track event, it got harder and harder to shift, until ultimately I was using nearly my whole arm's strength to get the shifter out of one gear and into the next (this with the clutch pedal all the way in). It was the same even with double-clutching/rev-matching, so I tend to think it's not synchros.

Now, it was an *extremely* hot day (108F ambient, higher on track), but I've run in similar conditions with no problem before.

After pitting and letting the car cool down for a couple hours, I tried again and found that the clutch was now engaging/disengaging near the *bottom* of its travel. But otherwise it seemed fine (no slipping once in gear), and shift effort was near-normal. Went back on track, and after a couple hot laps the symptoms returned.

And finally, since then, the car drives on the street seemingly normally, only with the engagement point remaining near the bottom of the pedal travel.

Any thoughts as to what would cause this specific behavior (stiff shifting when hot, change in engagement position)? Could it be just the clutch fluid (2-3 years old, DOT4)? Or TO bearing? Disk wear seems irrelevant, though if I have to open it up of course I'd replace it. Could the pressure plate be playing a role?

Cheers and thanks,
John

 

A friction disk that gets thinner and thinner should IMO make it easier to shift at all times.
(and make it engage/disengage at the top of pedal travel)
The stroke of the slave & vork & TO bearing and PP doesn't change, so more play available for the FD.

The change in engagement position would make me think: Pressure plate.
The slave cylinder hasn't moved.
(assuming the stroke of the slave is still ok, have you checked the slave for leaks?)
The shift vork's pivot point hasn't moved.
The TO bearing hasn't moved.
Only thing that could make a difference is PP.

Let us know what you find

 

Start with a thorough clutch bleed and flush. Depending upon where you live (humidity), you may have picked up quite a bit of water in the fluid. This could result in the symptoms you described on the track. Water in the fluid can also promote some rusting in the master or slave cylinders. If this happened, then you are destined to replace those. Try new fluid first and see what this does for you. It's the cheapest initial route to take. If this doesn't do much, then look forward to some further diagnosis.