my shifter used to shake really bad in 3rd and 4th, then i got the short throw and it solved my problem. Do you feel any othe vibration in the car at these speeds?
my cobra is in the shop as we write getting the tranny shimmed up at the crossmember. the drive shaft angle is off due to the new tranny and the car being lowered. does your shifter vibrate even if you push in the clutch at that speed, and doesn't go away until you scrub off the speed. the other thing is maybe its time for new uni's.
Yea sounds like a DS imbalance. Me on the other hand I'd get vibrations past 5k rpms or so regardless of the gear. I had a flywheel imbalance, but that when away when I got my fidanza aluminum one.
If you think that aftermarket gear sets vibrate, or vibration may be a "side affect" of having them installed, then someone has told you the wrong thing. There should NEVER be a vibration coming from the rear whether the gears are OE or not. They were installed improperly if they do indeed vibrate.
i rotated it 90* and nothin, im gonna keep spinnin it 90* every day until i do a full 360, and if its still vibrating im gonna go ahead and get an aluminum DS... hopefully that solves the problem cus the cars for sale