1994 Ford Thunderbird Thunderbird Vibrates from Rear

I am sorry if this has been covered, I could not find any exact symptoms.

My car is a 1994 Ford Thunderbird 4.6L with the auto transmission and 60,000 miles. Car has vibrated from the back end since I bought it about 6 months ago and is steadly getting worse. This vibration can be felt at 5mph and nearly shakes you off the road at 70mph (I haven't attempted any faster than this).

I am positive it is the rear because I replaced the entire front end - upper and lower control arms, brakes, shocks, sway bar bushings, etc. Car was alligned immeaditly after all components were installed.

I have balanced the tires twice, replaced rear drums and checked the rear axle shafts, (by lifting, then blocking one wheel and running the car, and visa-versa).

I think it is either the driveline/u-joints or torque converter. My question is; Am I completely looking in the wrong spot? Should I be checking the motor and transmission mounts? Could the rearend possibly be binding? There is no noise other than a slight thumping noise when almost stopped while braking, (the "noise" can almost be felt in the seat better than being heard). I would hate to drop the fuel tank and find that everything with the driveline is in good shape.

Throttle does not seem to have any affect on this shimmy, braking increases the shimmy slightly (can be felt in seat, and wheel vibrates - but car tracks straight). The only reason I am considering the torque converter is because it seems like on the highway if you let off the throttle completely then barely touch it again, it is a good 1000rpm until you can feel the car pulling again.

Putting the car in neautral on the highway has no affect on the shimmy either. I am sorry for the length of this post, I wanted to make sure that you had all the information.


Thank you,
Ryan