Clutch slipping

I mentioned on a different thread that i just started to have my clutch slip on my 2004 C2 with 70K miles. I thought I would get a few more miles out of the clutch but evidently not. But before I start tearing it down, i wanted to take a step back and make sure I'm not overlooking any other potential causes. I don't have much experience with symptoms of a clutch going bad but a basic test which i have read and experienced is to put the car in a higher gear at a lower speed and floor it to see if the clutch is slipping under torque. My car will slip when doing this but I also notice that the engagement when not under load is different. As an example, I can release the clutch at low rpm's and there is a definite difference from the last time I drove it. Prior to this weekend (I've had it on a lift for the last couple of weeks working on a few other things), when I would release the clutch there was a very positive engagement of the clutch. Now when I release the clutch, the engagement is not crisp or it feels a little "mushy" (I'm describing the movement of the car forward not the pedal feel). This happens even at low rpms. Could another potential cause be something preventing the clutch from re-engaging fully? I need to educate myself on the design of how the clutch engages and disengages but I thought I would ask the question.

Very smart to check other possible issues. One thing you might want to try is bleeding your clutch hydraulic system. Worth a shot. However, based on what you described, I'm confident your clutch is bad. The clutch disk is worn. My friend's Civic Si did exactly what you described.

70k miles on the original clutch? That's pretty excellent life for these cars. They have so much grip on acceleration that they wear the clutch quickly.

Given the mileage, its certainly likely you just need a new clutch. I've only had 1 clutch go bad in a car and it started with high gear slips as you mentioned, and within a week it was slipping in 1st gear and un-driveable. As far as other things that would prevent it from engaging. Basically the way that it works is the pressure plate has springs that apply pressure and pinch the clutch plate between the flywheel and pressure plate. When you push the clutch pedal a hydraulic piston pushes against a lever that, in turn, pushes against a throw out bearing / release bearing that rides on a series of teeth on the pressure plate. When force is applied, they release pressure against the clutch disk. It takes a considerable amount of force to do this - but I guess just a light force would be enough to result in slipping under heavy loads. Pretty much anything that would be causing it to hang up would need to be diagnosed with the transmission pulled - so my advice would be to assume its the clutch and proceed, but once you have it open if the clutch doesn't look shot, you can check everything else.

60K is about the average for these cars. Make sure to check/test the flywheel too.

I bought my car with 102.4k on the clock, original clutch from what I could tell. Very close to hitting the rivets but wasn't slipping. Clutch life is all over the map according to the driver and how the car is driven. Of course get it wet with oil/fluid and all bets are off.

110k on my 1st clutch. 2nd one has done 60k, and looked in good nick when we had a look at it whilst changing the RMS earlier this year.

My clutch was the original but it was around 50K miles when I had it changed out with the IMS solution install. When the shop owner first test drove my car he said, "Your clutch is shot!". I just presumed that all 996 Porsches had stiff clutches. I was wrong. It was considerably hard to depress. When I went to test drive the car after the service, the clutch pedal was light ... almost effortless. The clutch plate was worn down to the rivets.

Stop and go traffic vs highway miles will play a big part in the lifespan of many parts...