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?
if it only does it during cerain speeds (like 40-60 mph) i'd balance your wheels, but if the tires arre newit may also be a slaightly egg-shaped tire, like a manufacturer defects. im not excactly sure what it'd be if it only does it when u let off the gas tho.
I'd have to check those U-joints right away (before one breaks at speed). You might wanna check the pinion bearing while you have the U-joint out (just see if the pinion has any up/down slop)
my vote is for the pinion bearing. u joints are also part of it id bet
I'm going to have the u-joints and pinion bearing replaced over the weekend.
U-joints most likely....