I've been chasing a highway speed vibration for some time now. In the midst of it (and with 170K miles) I have rebuilt the suspension due to a bunch of worn parts. The vibration still plagues me. I have replaced the following:

all 4 struts
all 4 bearings
all 4 springs
front control arm bushings
front ball joints
front tie rods (inner and outer)
front strut bearings
both half shafts
and tranny was just rebuilt
4 new tires
4 new rims
tires have been balanced numerous times (on the car-before the new rims, off the car, in several different shops and states)
new rotors, drums, calipers, wheel cylinders, pads and shoes
all 4 motor mounts (2 were broken, 2 were worn)

Most parts were replaced due to wear. Although the suspension feels incredibly tight and responsive, nothing seems to impact the vibration. If I walk into any shop, the first response is always "tire balance". And yes, I had them balanced again today, they were only slightly off.

The vibration starts slightly around 65mph and is most severe at 80mph. If I run up to 100mph, pop her in neutral and coast down, it'* still there. We had it up on the rack today and everything looks and feels perfect. Except for the steering rack. From side to side, there is no play. However, there is about 3/4" slop in the rack itself. Is this normal? Can a failing rack produce a high speed vibration?

I suppose it'* possible. I'm going to go toss this one around with some gearheads ...

I'm no Gearhead, but it seems to me that this is the only piece of the puzzle that has not been replaced. You did not mention how many times you tried to align the front end.

Go Gearheads Go!!!!

Alignment is true. We have aligned it twice and doublechecked again today. It was well within specs.

If alignment is in, that rules out a loose subframe or damaged subframe bushing as well.

That sounds like a TON of slop in the rack. I've yet to see one actually fail here, but you may have it there. Be advised that your rack is very trim-level dependent. And the SSEi rack will be 2 or 3 times the cost of the SE/SLE rack.

I'd definitely look for a wrecker unit on this, particularly since they don't fail often.

Does this look like an option? Or is their selection too vague?

www.steeringrack.com

Have you checked the tires for round? doesn't happen too much, but when it does, it acts just like you're describing.

Is it possible to put another "Set of Wheels" on the car to possibly disspell the Tire/Wheel/Balance issue(*). Also, how do you tell if you have a Rack with 3.0 or 3.2 turns lock to lock when you have lots of play in the steering wheel???

He mentions different rims, tires etc.

This is looking like the rack to me as well. It'* the only thing that hasn't been replaced at least once.

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This must be torture, but I'm in favor of The Rack!!!