So, this is a bit of horror story I just experienced with my rx8. So, for starters I purchased the car several months ago from a guy on Craigslist. The ad said fresh rebuild, new clutch, etc., etc.
Fast forward two months down the road, I start hearing a sort of chattering noise coming from the bell housing. It’s not crazy loud, the car drives fine. I check the forum, and see several posts about the throwout being noisy. I overlook it.
The noise persists and gets worse over the course of a few months, so I parked the car. I go to move it from where it was sitting to my house, and then the clutch gives out completely and the car will not come out of gear and I stall at the light. I somehow manage to get the car home.
I order a new clutch and have it towed to the shop to begin the replacement. A few hours later I had it apart and I’m about to remove the clutch. I go to loosen the bolts, and it’s ******* wobbling. Now I’m confused, but I progress. Moments later I’m looking st the flywheel, and staring me dead in the face is a massive 54mm nut. THE NUT IS ABOUT TO FALL OFF, it is so loose the wind gusted and it hit the floor. The needles on the pilot bearing had been WELDED to the input shaft.
Inevitably I had to replace the rear main seal, machine the flywheel, and very carefully grind the pilot bearing off of the input shaft.
Let this be a reminder that the small things make a big difference, and that, yes, you should put Loctite on that bolt.

So a little update. I got the car put back together and it will not go into any gear while the car is running. It will row through every gear with or without the clutch while it is off.

The slave cylinder is moving properly, and I’ve bled it many times.
I just put in a new clutch and it still doesn’t work.
I just replaced the transmission and it is giving me the exact same symptom.
The only part that hasn’t been replaced is the master cylinder, but it doesn’t leak fluid and engages the slave as it should.
The clutch pedal assembly does not appear to be broken. I’ve given it a thorough inspection, but have not removed it from the car.
I don’t know what else to do, so if anyone has some helpful insight it would be much appreciated. It’s been nearly 6 months, and I’d really like to drive my car again.

Obviously something ain’t working... that sounds very strange.

In for final results.

The clutch is brand new, 0 miles on it. (Exedy stage 1)
New pilot bearing, release bearing, pressure plate, machined flywheel as well.
I put in a used trans, with about 80,000 miles.
New slave cylinder.
Fresh gear oil in trans.
The clutch and pressure plate are installed correctly, I double checked everything when I swapped the trans.
If the car is running it will not shift out of neutral, as if there is a wall. If I try to force it, the engine will bog and then rev up to about 2k before dropping back to a steady 900.
Maybe I was sent a faulty clutch, or maybe my flywheel is too far gone even after machining?

I took it apart once again today to have someone double check my work, everything was tight, in place, and lined up.
I have adjusted the pedal, in and out with no change either way.
I did get the car into reverse and first gear, but it stalled both times with the clutch to the floor.
I’ve jumped the connectors, and plugged it up to a scanner.
The scanner is showing the clutch switch activating (whilst not jumped) and that it’s in neutral.
I’m hoping to find something soon.
The slave cylinder doesn’t lose any pressure with the pedal on the floor, I had someone watch it while I wa s inside the car.
(I just read something about the upgraded clutch, potentially, requiring more pressure than the factory lines can handle. Causing them to balloon when depressing the pedal, in turn not allowing the disc to completely disengage)

The slave cylinder moves a solid inch or more while the clutch pedal is depressed. The slave cylinder doesn’t lose any pressure while the pedal is depressed, either. I held it to the floor for a solid 30 seconds, and the slave didn’t move a centimeter until I let off of the clutch.

Master cylinder, clutch fork, and braided clutch lines will be my next move. I’ll probably pick up a clutch pedal, too.

I talked to an associate that works at a transmission shop, and he recommended changing the fork. They were chasing the same problem and it was a bent clutch fork the entire time (not an Rx8, though). Which I am skeptical of, since both transmissions had the same problem it would be crazy to think that they were both bent. With it only being a $30 part, it’s worth a shot.

I’ve also read that the extra weight of the upgraded clutch can cause the factory rubber hose to “balloon”, not allowing enough pressure through the line to completely disengage the clutch disc. Also a cheap enough part, and preventative as well.

I bought the clutch as a kit, which included a throwout bearing, pilot bearing, clutch, and pressure plate. (Exedy Stage 1 organic). Unfortunately, due to work, the clutch was out of warranty before I even got a chance to put it in the car. (60 days from date of purchase for non OEM replacement, manufacturer warranty). Also, you can see where the throwout bearing is making contact with the clutch.

I appreciate all of the advise, so far. This currently has myself, my peers, and other automotive professionals in my area stumped. Then again, half of the time their solution is “just ls swap it”.