Just bought an '01 s type, 4.0, 79k. Sweet ride! I've noticed a vibration from 45 mph and up. Increases with speed. I can feel it in the seat and kinda rumbles through the whole car. Steering wheel doesn't shake. She just got new tires, same concern as before them. Stops fine no pulse. Whats most common to fail? Figuring driveshaft as it makes no diff whether in gear, under load, or coasting in neutral. Rear diff fliud is clean and full. Doesn't change when cornering, or side loading, ie quick side to side steering inputs. Rules out wheel bearings least in my mind. Has she an old school u joint on her driveshaft? Or perhaps a carrier bearing I should be looking at? Appreciate your inputs.
Dan

 

Either a bent wheel or unbalanced or a universal joint on the driveshaft. Thats what I would think...I am sure others here may have other advise. .....Maybe a broken bolt on the flywheel also.

 

thanks achysklic,
Spun the new tires when balancing myself. Rims fine and minimal runout. Worst tire if you call it that took 2 ounces to balance. Have heard about rear wheel bearings failure common, but mine dont growl while driving nor on the lift. Still investigating this vibration, I'll update as possible. Figure next step is to drop the driveshaft and check the ujoint. Sidenote, my 2 yr old niece saw my car for the first time this eve, and said "pretty!" Then tried to pet the "kittie" hood ornament. Guess it crosses all ages. lol.
Dan

 

Actually I had to replace my rear drivers side wheel bearing. It didn't vibrate at all, but it growled like a mad Jaguar!

 

was the u-joint gone now