From the time I got my thirdgen nearly 2 years ago, it's had a BAD vibration from about 80MPH+. Of course, like most, I assumed it was the DS, so I started by changing the ujoints...no luck. I had also just put on new rims and tires...which I mounted and balanced myself, so I knew that wasn't the problem....so next I tried rotating the yoke 180* ...no luck. I tried everything I could think of. Well I just got my tranny rebuilt, and got a new case because there was a chip about the size of my thumb missing right next to the bolt hole. Turns out this was the problem. A small chip next to a bolt hole cause hella vibration. Well needless to say, I have no vibration problem now....so just to let those of you that cannot figure out this problem...my problem was in the tranny case.

 

Not to flame or anything but I dont see how that could be the problem. If the chip is on the bellhousing, I just cant see that being a problem. Did you replace the tq converter? a loose tq converter or slipping tq converter cluch would cause a vibration at high speeds or a loose input shaft.

 

I agree it could have been the TQC (yes I did replace it)...but like I said, i'd had the vibration since I had the car...and I've had the car now almost 2 years.....so I know that my TQC hasn't been slipping for that long a period if at all. At first I couldn't believe that the chip missing out of the case could cause that either....but it is RIGHT next to a bolt hole, causing that bolt to not stay torqued down....so It's pretty much like I had a bolt lose. The guy tells me that the crack more than likely cause a lot of vibration (he said this before I told him I had a bad vibration)....I get the tranny rebuilt w/ the case...then afterwards the vibration is gone. So if nothing else this proves that the crack was caused by something in the tranny. I'm not telling everyone that their tranny is cracked and is causing vibration....but I wrote this more for the archives....so that instead of assuming it's the driveshaft and going out and dropping the $$$ for an aluminum, they know there's more possiblities and will look deeper into the matter.

 

I had a similar vibration & went a similar route to correct. I just replaced my trans & converter & its gone. I found out something when bolting on the converter to the flexplate. You should start all 3 bolts before you tighten any of them. This centers the converter to the flywheel. If not centered... well you can guess, vibration. My vibration was first noticed after removing the trans to replace the crankshaft & got worse after my 9" rear was installed, causing me to think all kinds of bad things about the driveline.