Hi,
I have a 2005 RX-8 GT 6 speed with 130 000km. 2 weeks ago the second gear started grinding when shifting over 6000rpm but only when the car was warm(running for at least 10 minutes). I changed the transmission oil but I still have the same problem. The garage told me it wasn't the synchro mesh because if that would be the cause, I wouldn't even be able to get into 2nd gear easily when the car is cold. I think it might be an issue with the clutch. Tomorrow I will bleed the clutch. What may cause this? It only does it when warm. I did the search, I only found that bleeding the cltuch and re-adjusting it might help so I will do this tomorrow!

 

if you cant shift without clutch, you have a transmission problem.

 

I can shift with no grinding into all gears without depressing the clutch.

 

Usually not true, unless the transmission is driven by a transfer gear set or chain, which the RX-8 is not. In most other manual transmissions with worn synchronizers, colder/thicker gear oil helps the synchronizers work, and hotter/thinner gear oil lets things slip and grind more.

If you aren't having significant problems with 1st or reverse engagement off of neutral at idle, it's probably not clutch drag. 2nd gear synchro is usually the first one to wear out in most cars. In the RX-8, the synchros are not particularly robust, and agressive driving (as you might expect with such a car) makes synchro life even shorter. There are many other accounts here of grinding synchros within a comparable range of KM / MI, so I would suspect that's what it is.

There is also the known weakness and breakage of the clutch pedal bracket, which can eventually limit and disable clutch disengagement, and cause gear grinding. I would check your clutch pedal freeplay, bleed the clutch hydraulic circuit, and check the clutch pedal bracket. Also, check to see if the clutch master cylinder holds pressure with the pedal depressed. If the seals are worn, clutch disengagement can be limited, temporary, or disabled.

But, because you do not mention gear engagement problems in any other gear or shift scenario, I would bet the root cause is a worn 2nd gear synchronizer.