2004 g35 6mt

OK, here's the problem:

I recently installed a spec twin disk clutch and I sent the factory driveshaft to the driveshaft shop for them to build me a one piece aluminum unit. I received it back and it looked beautiful. After I put the car back together and broke the clutch in, i went on some highway runs. Around 120+mph i get a vibration in the drivetrain. I was thinking the driveshaft might have gotten damged during shipping and maybe threw it out of balance. I sent it back, and they checked it out and they found nothing wrong with it. So today i got it back form them and put it back on, and i'm still getting the same vibration. Did i mention it vibrated enough to make the tranny leak fluid out the tail shaft and there were aluminum deposits on the yoke (i'm guessing it vibrated against the bushing in the tailshaft). I'm lost, it didn;t due it before and i'm not sure what else to look at. any ideas?

sorry so long, thanks for any help

 

From what you are descibing it is the driveshaft that is causing the problem.

 

I have been planning on switching to a one piece driveshaft as well. Please keep us updated with anything you find out and whether you are able to resolve the vibration issue.