Gears installed... vibration, where to look?

[666ws6]

I installed my 3.90s and everything looked good... backlash .007 (and within 0.002 all around the ring). Pattern good, centered on the tooth and little toward the heel.

There's a small amount of whine but only a little beyond stock gears.

Problem is there is a vibration at 40 mph and up. Feels like a rotational vibration. At higher speeds, more like a high frequency thudding.

Any thoughts on what I should check? My thoughts lead toward driveshaft or how tightly I have the differential shimmed. I did change the u-joint on the DS at the rear too.

[ArleneJ]

If you changed your rear u-joint, the driveshaft may be out of balance - you should have it checked and re-balanced.

[666ws6]

I was thinking the same thing, so I flipped the DS 180 to see any change in the vibration .... and it fixed it.... vibration gone! Smooth as ever!

[ArleneJ]

Glad to hear you solved your problem!!