Hello everyone! I have a mechanical conundrum that I need your assistance with. Okay, here goes...

My Buick LeSabre shakes BAD at 60+ MPH. It'* the worst around 75 MPH and gets intermittently better / worse the faster you go from there. I have done the following (in order) trying to resolve the problem:

- Replaced original Yokohama tired with new Pirelli tires
- Replaced original steel wheels with new 16" alloys
- Checked motor mounts and struts
- Replaced front hub/bearing assembly on both sides
- Replaced front rotors and brake pads
- Replaced Pirelli tires with new Michelin'* Primacys (as I thought the Pirelli'* could be defective)
- Replaced the front two axles with new
- Machined rear rotors and checked rear bearings for play
- Put the vehicle on a lift for inspection - nothing abnormal was found

Despite all of the above the car continues to shake on the freeway. There has been NO change whatsoever. I thought that it may be the TQ converter or transmission but when dropped into neutral on the freeway the shaking continues as it did in drive. There is also no change going into or coming out of a curve at speed. The car only has 48k miles on it! I am completely stumped and very frustrated.

Any thoughts?

I should probably also mention that this is a 2004 model with the Custom package. No modifications have been made to the car aside from aftermarket speakers.

You didn't mention the tie rods.

How does the steering wheel feel when it goes to shaking?

Make sure the engine cradle is not ready to fall out. I had a recall on an old Ford once for the engine cradle bolts.

No mention of 4 wheel Alignment.
Wheel Balance re-check that for sure.
Are shocks / springs in good order?

The alignment has not yet been done. The car does not seem to pull. I will have it checked this week and advise the results.

The shocks? I have no idea what kind of condition those are in. Is there a way that I can test them? I didn't see anything obvious when the car was in the air.

The steering wheel feels okay to me in comparison to the rest of the car. I feel the shaking most in the floor and the front bench seat. It'* bad too. If there is a coffee in the cup holder the shaking will splash the liquid all over the center console.

My car also had a shimmy, but not as bad as you are describing. Wheel balance with new tires and a 4 wheel alignment shimmy gone at 65-75mph.
Has this car ever been in accident?
A good experienced alignment guy should also be able to check the steering/rod ends and also may be able to check the driveline angles/alignment.

The mystery has been solved! Apparently it was a combination of bad balancing and missing hub rings!

There is a slight vibration that occurs when the wheels are turned either left or right. The vibration occurs at any speed and is more pronounced the faster the car is driven. The tire shop suggested a bad engine / trans mount or perhaps a bad trans-axle bearing. Any thoughts or suggestions?