For 10 or 12 years now, can't really remember, my car would have a nasty vibration on the freeway. Anytime you got abouve 90km/h or 100km/h you'd feel a vibration in the steering wheel, accelerator pedal, driver seat, passenger seat, pretty much everywhere. I don't remember if came on suddenly or gradually.
I thought I'd give the experts one more shot at fixing it this summer and so far no luck.
So, far, the Dynotech driveshaft was balanced, and we tried a stock driveshaft, which made no difference. Balanced the rims/tires and even tried a different set of 4 rims/tires, which made no difference.
Put on a different rear differential assembly, a used one from a Super Coupe. That made no difference. Also put on a set of used read half shafts from a Super Coupe. That made no difference.
Put on new differential housing bushings made no diference.
Now, if it matters, there's also a clunk sound when the car drives over a large hump. Sounds like it's from the front-right suspension compressing. I've had this for many years too.
I also noticed a couple of times some nasty clunk going in reverse with the steering wheel turned to the limit. A mechanic also says the same vibration is felt when driving fast in reverse.
The vibration is present if you run the car on a dyno up to highway speed. You also feel it if you jack up the back end and drive the car up to highway speed with the rear tires hanging off the ground and the front wheels chocked.
Are there any other crazy Ideas I should suggest to the mechanic/shop? Rear brake rotors? Transmission rear mount?
FYI it's a 1996 Thunderbird 4.6, big bore aluminum block, Allen supercharger, awesome condition, no rust at all, paint looks new, but I feel like shooting the thing.