As my 04 6MT, is the one and only 8 I've ever driven, I'm trying to figure out if the transmission's quirks are "normal" or signs of a problem.

I haven't found any similar occurrences posted via searching.

The biggest notice is when you come to a stop light (most noticeably if you put the gear shift into neutral and roll to a stop) and when the light turns green and you push the clutch in, and put it into first.. the transmission kind of "jerks" into gear. The same sensation is occasionally felt while shifting, just a bit of a jerk/thud as it goes into gear. There has been no grinding or rough sensations felt through the shifter. The shifter slides into gear smooth, it's just a bit of a thud, felt through the car as a whole, when it gets into gear. Has nothing to do with the clutch engaging, it happens as soon as its into gear, has no bearing on whether or not you're releasing clutch, etc. Sometimes if you downshift through the gears as you're coming to a stop, it appears to allow you into first more commonly without that 'thud' sensation, but not all the time.

Relatable specs; New clutch/TOB (+/- 3k miles ago). Just did a transmission fluid flush with Redline synthetic (old oil was quite dirty/black with quite a bit of build up magnetized to the drain plug). I have only owned this car for 500ish miles so I have no idea if/when it was ever flushed previously. Car has just shy of 84k miles.

Any input is appreciated.

 

My gut is telling me that it may have something to do with the clutch hydraulics. When a thud is heard changing gears it's usually indicative of the pressure plate not dis engaging enough, making it difficult for the gears to change. The 8's have a clutch peddle problem, they become weak and sometimes break. Although my 06 has not seen this "yet". So I would start looking at the clutch assembly.
From the peddle to the slave cylinder. But fwiw, I'm not a mechanic, just someone that loves cars and enjoys diagnosing and fixing problems.
Give it a whirl and check back!
P.o.

 

Thanks for the input. I suppose you could be on to something, maybe... I do have a chirpy squeak sound, and as soon as you touch the clutch pedal it goes completely away (far before actual engagement). Definitely not the TOB/input shaft bearing. I lubed up the slave where it pushes against the clutch fork, it seemed to help a hair, though not entirely. It's definitely not as loud. Maybe the slave is a little on the fritz??

My clutch pedal bracket was already visited at some point (by one of it's prior owners). While it's ugly, I don't believe it's going anywhere.

 

I should also add, it's not leaking anything at all.

 

Based on what I've read about some other cars (as I can't find anything Rx8 related) it might be normal... but was hoping to confirm that 8s tend to do this (no other manual car I've owned has ever done it).

Good descriptions here, and appears to be what I'm experiencing, but again, not specific to the RX8

Clunk when going into first gear? - Scion FR-S Forum | Subaru BRZ Forum | Toyota 86 GT 86 Forum | AS1 Forum - FT86CLUB

 

Ok cool, so I'm not crazy. Although my shrink might raise his eyebrows and lower his glass to that one. So it's just in first gear? I know that clunk, I just got so use to it that I forgot about it. If I recall I would just blip the gas slightly then push it in first. It helps to rev Match the gear. So at a crawl, you only need to raise the rpm 2-300 rpm. That should smooth out the clunk. And I side note, my second gear is bit loud going in when the car is cold. I would shift from first to third until the gear oil warms up, then it's gone. Again it's about learning what your car likes and dislikes.
Another thing to try is bleeding the clutch line and put some fresh dot4 or whatever it calls for
I can't remember exactly, but ya
That's all I can think of. Cheers!