Clutch / Transmission issues in EP3
 

All, I'm looking for some feedback on issues I'm having with my EP3 (2005 Civic Si). If you could help rule out any simple repairs or identify any temporary fixes, that would be great.

While decelerating at an offramp the car made a "thunk" when I shifted into neutral. It then became difficult to shift into gear. If I shift deliberately and carefully the car goes into gear just fine. After 100 miles or so of driving, the car started "shuddering" when accelerating from a stop. Everything is fine once the car is moving...the car still accelerates like normal...but when starting from a dead stop it almost feels like the clutch is slipping. It's easier to take off a little more smoothly if you rev higher while taking off....which obviously isn't good for the failing (?) clutch. Regardless, the car is parked for the time being, I'll be driving the minivan to work until I figure out a solution, or just take the hit and trade the car in as-is.

The clutch fluid level is fine. Does that mean the slave cylinder / clutch master cylinder is also fine? Or, could one of those parts be causing the issue? Would it be a waste of time to replace the gearbox fluid? I suppose I could have a problem with both the clutch and the transmission...or even just the transmission. DIY clutch replacement on his car is probably outside of my comfort level.