Dotie:
If you find it is not
cowl shake, another TBird owner had this issue:
"Since I've owned the Bird, there has been a pronounced "body shake" or vibration whenever I go over 70 mph. It seems to shake the most behind the seat--sometimes vibration in the steering wheel.
I've had 3 different wheel balances at different places--different set of wheels--tires checked for flat spots and roundness, etc. I've had the crossbars checked and torqued to 46 ft lbs. Nothing seems to help so far.
A friend of mine at my car club suggested taking it to a place that uses a Hunter Dynamic Balancer. I went to their website and read about their equipment--seems impressive. I contacted their service manager and he recommended using the Hunter GSP 9700 Road Force Measurement System.
He found a Lincoln dealer who had the right eqiuipment and here's the resolution:
"Got it fixed today. Went to a Wheel Specialty House who had the Hunter equipment and very experienced, trained personnel. It took them about 2 hours, but the wheels were out of balance big time (despite what others had told me and after 3 wheel balances). They also had to reset the tires on the rims. The Road Force Measurement System really does a great job. So, for those of you who have vibration problems at higher speeds (not
cowl shake), I would go to the Hunter website
www.gsp9700.com. It will explain how the sytem works and you can
search for the facility nearest you that uses their equipment. Give it a shot--it worked for me! The locator is
www.gsp9700.com/pub/search/findgsp9700.cfm "