I have owned an 03 G35 sedan 6MT for a short time. The car has 93K miles. The last couple of days I have had a problem with 5th gear. When I am decelerating in 5th gear, and get to approx. 1,500 RPM's, the shifter will pop to neutral either on its own or as soon as I depress the clutch pedal, with no effort on my part to move the shifter.
The clutch was replaced at about 84K, before I bought the car. Could this be the sign of a serious problem? Thanks in advance for any advice you can provide.

 

Popping out of gear is usually a sign of the dog teeth on each individual gear wearing. They are beveled teeth that interlock and physically mesh the gears together. When they were out through grinding the trans, or the clutch not fully disengagingnduring shifting, they sometimes get damaged and don't lock properly and tends to pop out of gear. Fixing this involves replacing the gears and synchro sliders which aren't normally considered wear items.

Teeth in question are the small teeth on the front pf this gear
http://www.supplierlist.com/photo_im...0407/Gears.jpg


Of course, this is a theory based on what youve stated. It could be a clutch issue as well, or something else. Hard to tell sometimes without opening up the trans