Buick Riviera

I have a 1997 Buick Riviera 3.8 ltr front wheel drive automatic has 177,000 miles. When I am driving down the highway between 60 and 70 miles an hour the front end begans to shake and gets worse after 70 and beyond feels like the frontend is going to fall off. Everything feels tight when I jack the car up and shake the tires there is no play. The struts are orginal I am not sure what is causing this so any help would be great.
September 2, 2007.

Sounds like a wheel balance problem.

Thanks I thought that to so I rotated the tires and still had the same problem at the same speeds does this car have an idler arm

Sep 3, 2007.
No Idler arm on it. RAck and pinion gear with tie rod ends.

When you shook the wheels, did you move your hands around to different clock positions? Sometimes the 3 & 9 (tie rod, steering) or the 6 & 12 ( suspension/ball joint) positions don't always uncover play.

I don't know the history of the tires on yours but, if the fronts are out of balance, fair chance the rears would be also. Rotating may not be the best check on that.