25th Apr 2011, 21:35

From what I understand about these cars, the driveshaft reaches a resonant frequency around 65 mph (mine does). It is something the Ford engineers knew about, and for whatever reason, just ran with. If you look on your driveshaft, there is a big balance weight... perhaps it came off. Just google Thunderbird driveshaft vibration, and you should get a good explanation.

4th Apr 2012, 23:15

If you have rear drum brakes, the drums don't fit the axle shafts correctly. They have too much clearance between the axle shaft O.D. and the drum I.D..

You will need to shim the space around the axle to align.