Hey guys im new here but i just bought a used G37s with 80 or so thousand miles and it drives great but when im in 6th gear and i try to speed up the rpms get shaky like they go up to about 3000 then go down to 2800 then back up. it also does this if im in 4th going up to about 5000 it'll go down to like 4700 then ill shift. but does anyone know what might be happening?

2008 G37s 6-Speed
only mods:
Invidia Exhaust
Stillen air intakes
short shifter

 

If the engine speed is increasing when floored, and the car isn't picking up speed at the rate of the engine increasing, then usually that means your clutch is slipping. If your flywheel is warped that would explain the vibration....

 

like soundkillr i am also leaning to a slipping clutch to by the culprit of your concern. have a tech check it out on a road test. btw when you step on the clutch pedal does the engine rpm drop immediately as it is depressed? a good clutch will react in this way, every time you step on the clutch pedal the engine rpm should drop immediately because the the pressure plate is clamping down on the clutch to slow down the engine so the trans can be shifted smoothly to the next gear.

 

Not necessarily. If the flywheel is slightly warped, and depending on his slip techniques on take off he wouldnt feel it. Now when the engine is spinning at say 5000 rpm, it is greatly exaggerated and as the clutch slips it's grip, the vibration from a warped flywheel will be more present.

 

So pretty much what happened is while i was driving in traffic and my clutch kept getting stuck to where i couldnt shift so i took it to an infiniti dealer and they said that it was either the throwout baring or the flywheel but they want to charge me 1225 just to tell me which is it. even tho i bought a warranty through the dealership i got it from. but thank you everyone who replied.

 

according to your current description now in regards to the clutch getting stuck it sounds like either theres an issue with the throw out bearing or perhaps the fingers/vanes on the pressure plate. if they are going to drop the trans to look at everything you might as well have them replace the clutch, throw out bearing, pressure plate, and resurface the flywheel. btw i have never seen warranty coverage on a clutch or other related components attached to a clutch. its no different than your brake pads and rotors, those components never get warranty coverage because it is considered wear items.

 

I'd try some simpler solutions before going straight in to change the clutch and what not. I would get the rear dif serviced and the trans fluid flushed and replaced. Also maybe check/change the spark plugs and wires because if those are starting to go they can cause a little stutter too. I have had my differential flushed before and once it was done the car felt much smoother under acceleration. Do what you want and how you want, but imo. don't just jump into the deep end. Good luck

 

My money is on the worn clutch. At 80K, depending how it was driven, it's likely due.