Well, 4.10's are definitely the way to go. Can't believe I was actually considering 3.73's!! Thank you 1LOW03GT!!! Now the bad. Had my steel driveshaft re-balanced and new u-joints pressed in, vibration lessened but still there. Shortened a Ford Al driveshaft ("J") model by one inch and installed. Again, vibration lessened but still present around 130KPH (mellows out a bit at 150-190KPH). Any other suggestions or am I going to have to live with a vibrating rear view mirror??

The vibration started after you had the gears installed?

Did they put the limited slip additive in?

My buddies 06gt with an aluminum drive shaft and 4:10 gears also vibrates. It drives him nuts Fix dunno

Yes. Vibration free with the 3.27's and stock steel driveshaft. Re-balanced the steel (new u-joints) and got a bit better. Installed aluminum and got a bit better yet again. I used new flange bolts each time. I'm wondering about pinion flange runout as the shop I used for the gear install has a good rep. so I'm giving them the benefit of the doubt. It's enough to vibrate the rear view but certainly not as bad as with the stock driveshaft.

As an aside, there are a lot of posts out there on various boards about people running the Ford Racing 'J" aluminum driveshaft on 2001 IRS Cobras with T3650 as a direct fit. I decided to take a chance knowing there was at least 0.7" difference in length. Some may have had success but my personal experience is the Al shaft is 1" (44.5" stock vs. 45.5" centre line of u-joints) longer so food for thought anyone is thinking about that swap.

Yes, it was added.

Is he using a Ford Racing Al shaft or from elsewhere?

Glad you like the 4.10's,but it's to bad about the vibration!!!
If everything checks in,how about the halfshafts?Could there be any chance that the joints on those be a little worn?

I do believe it's a custom piece

I know this is an old thread, but wondering if the issue was ever solved?