I recently acquired an 87 t-bird with the 3.8 that I am really starting to like. One problem I just can't seem to figure is it has a vibration that comes and goes. It almost has the feel of warped rotors but it sometimes comes in when I am just cruising on the freeway. Seems to be centered under the center of the vehicle. Almost always happens when I take my foot off the accelerator. I had the trannie flushed and have tuned the engine which runs very smooth. I wonder if it might be u-joint? Any help?
It could be,does it do it when your on the brake?If not it probably is.
Reach under and grab a hold see if theres any play.
Stepping on the brake seems to make the vibration worse. the vibration is more intense when braking, but does vibrate without the brake. Maybe it is rotors and u-joints. I don't know, could it be somthing in the trannie?
abs maybe? idk i dont have the abs system on my bird.. but thats my first guess if you dont have ABS, then it points to a wheel bearing.. or u-joint