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.

 

[Mr. OAM]

Have your tires balanced again but tell them you want a "fine" balance. This is done with a tighter tolerance and works better at faster speeds. I wonder if they noticed a rim was a little bit too out of round or had a bend in it and they didn't say anything about it? Ask to watch the spinning of the assemblies as well.

Rare case, it could be a brake disc causing it. I don't know if it can still be done but some places used to be able to balance your tire assembly while still on the car to take the brake drum or rotor into account.


Steve