vibration woes

[white95]

i know that vibration comes with the territory of owning a Mustang with aftermarket exhaust, lower gears, stiffer suspensions, etc.. I get this vibration that seems to come in waves [so to speak] at speeds of 70 mph or higher. dip the throttle and the vibration subsides somewhat but if i let off the throttle and slow down in gear the vibration worsens until i get around 60-65 mph. this is kinda annoying so ive taken these measures to kill it:

A] installed an aluminum driveshaft
B] rebuilt my rear end
C] had my tires remounted and rebalanced
D] changed harmonic balancer

The only other things I believe it could be is:

1] i have bent fingers on my pressure plate, i go thru throwout bearings every 3 months... this problem will be addressed in the next few weeks, im swapping out motors, have new clutch/pressure plate..

2] Ive been told that when i installed my tremec i should've had my driveshaft shortened 5/8" and theres some necessary modifications to the crossmember i also havent done. so the driveshaft must be in a bind? anyone know about the crossmember mods?

3]the upper rear control arm bushings are shot, i have new ones to replace em

4] I'm really out of ideas, my car is lowered 2", i have tubular upper and lowers, none of my exhaust is in contact with my body/chassis, already bent the tabs on the gas tank down to remedy that.

 

[MORDENENOUGH]

I have the same problem, my car is lowered 1 1/2 inches, with exhaust and suspension mods. My vibration comes on around 2200 -2400 rpm in 5th gear while cruzing on the highway. My clutch setup is new and I had the factory flywheel surface machined. I'm running poly motor and tranny mounts... I didn't notice an issue until I did the clutch work and mounts... did it at the same time. I still run the factory driveshaft. I was told that when I installed the driveshaft, I didn't bolt the flange up in the same position as it came off. Does that make sense... only if its out of balance. The other thought I had was maybe a problem with the machine work or clutch set up, its a Borg Warner Cobra replacement. Is it possible that the pinion angle is out of wack now that the cars are lowered? I know this doesn't help your cause but would appreciate any clues as well.
Thanks

 

[95-stang]

First thing to try is rotating the driveshaft through 180 bolt it back up and and see if that helps. [unless you tried that]

 

[Stangbangin]

with your car being slammed like it is, it could be your pinion angle is so extreme it's mking the driveshaft your whole car....maybe, maybe would be my guess specially since it should have been shortened.