I'm chasing a drive line vibration which I suspect could be caused by the pinion angle being off. I have the lower arms with the eccentric adjustable oval bushings. When I rebuilt the entire rear end suspension and added lowering springs, I may have not set the angle correctly. Any one have pinion angle specs for an 84 Cougar?
Should be between 0 and 4 degrees IIRC.
Check the driveshaft for weights...that could be causing rotational vibration.
What speed or RPM is the vibration happening at? When I went to 3.73 gears I never got the stock driveshaft to balance. I ended up having to replace the stock driveshaft with a 3.5" diameter aluminum driveshaft.
It's more harmonic than vibration. I thought it was the front tires, but after upgrading to sport comps, its still there.
Did the vibration start with the 4.10s? Does it only happen at a certain speed? Can you go faster and the vibration/harmonic goes away?