Went to take the G up to the navy base this morning and it made a weird clunking noise when I dropped it into reverse. After that, any shifting was really difficult. While at a stop or driving I would have to press really hard to get it to shift. There would be audible clunks when it did. At a stop, clutch engaged, in first, the whole car would shake until I gave it gas and let the clutch go. Has anybody seen this before/know what it could be?

06 g35 MT sport edition, NA but with all the bolt ons and a BC cam. No previous issues, but currently throwing a code for O2 sensor (not an issue, sensor works...) and brake, vdc, and slip lights turn on while driving (pretty sure cuz my brake fluid level is looking a little lean).

 

Sounds like Synchronizers

 

New twist, I went to drive the car again 3 hours later and it shifted just like normal. Like nothing ever happened.

 

Try resetting the ECU... I don't really know to be honest but our cars with 6mt are just Wierd when it comes to shifting in my opinion.. I'd just get used to it, and wait for somthing catastrophic to happend and just fix it.. Easiest way out bro.

 

Syncros shouldn't be goin bad unless your shifting like **** **** or the previous owner was... I'd just keep it real and not try beating on it every time you drive it...

 

Sounds like you may need to bleed your clutch hydraulics. Check the clutch fluid to make sure it's not low. If air was introduced into the system due to it being too low, the clutch might not completely disengage when you push the pedal down. Maybe the temperature change from the 3-hours later situation caused the fluid in the car to expand enough that it was now full-enough not to have a problem and maybe you were also fortunate enough for the air bubble in the system to float to the top and bleed itself out.

Definitely start by checking the level of the fluid in the reservoir. Make sure you put in the right kind too if it's low.