I just installed 3.80's (posi) in my mustang and now I notice that when I hit 80mph it vibrates like crazy. The gears don't make any noise before then so I am guessing that is not my problem. Could this be my driveshaft? Thanks.

 

try flipping the driveshaft 180*

 

did you happen to upgrade the trans as well at the same time?

Remember now that you have 380s the DS RPM is much higher at the same MPH

what were your old gears 2.70s?

 

I did the t5 first, and my vibration went away, now with the new gears, its worse then ever. Yes, I had 2.79 before. It used to vibrate with the auto, but not near this bad

 

you might want to get it balanced if it did it before and check the u-joints for play

 

Most likely the U-joint installed incorrectly

 

if that doesnt work dennys damnit http://www.dennysdriveshaft.com/

If it did it before its the same thing now driving at 80 as it would have been driving at 130mph with the 279s

 

Yes, I am pretty sure its the driveshaft, just wanted to make sure it wasn't the gears, thanks guys.