I have a 97 Riviera with 130k and a bad vibration in the front end, left side at about 70 mph. It'* not the tires/wheels because I've checked them all on the front left, with the tires off the ground, and I can see the tire / wheel vibrating. When I look directly at the center of the axle shaft/nut, I can see it shaking up / down and left / right. When i look at the passanger side it is solid and stable.
I have already changed the wheel bearing / hub assembly but it did not help at all. The brakes are brand new and the rotors were turned and no change either.
Lower ball joint looks and feels ok and also tie rod end ok. No play at all when I try to rock the tire in any direction.
I do however have a bad rear trans mount that i plan to change asap.
Has anyone experienced this and what was the fix.

I appreciate the help.

First, please start a new thread (next time) of your own instead of asking a question in someone else'* thread. I split this thread from the one you dug up. When you search, pay attention to the date of threads you read, and don't dig one up that is old. Next, please put your year and trim level car in your signature so we know what kind of car you have every time you post.

Vibration while driving can be caused by a wide variety of problems; axle shafts/joints, bad engine mounts, old struts/shocks, warped rotors, tires, other loose suspension parts like ball joints, tie rod ends, etc. Because of all the possibilities, it'* rare that we can diagnose a vibration before you check all of these things. Do you notice any noises or vibration while turning the wheels? eg - Bad axle joints may have a clicking noise while turning and can also cause a bumpy ride.

Your trans mount may be an issue.

Honestly it sounds like a tire/wheel imbalance. Switch it to the rear, and see if the problem moves.