clearify your vibrations. where do you feel it like front, rear, middle like tranny tunnel, does it vibrate through the steering wheel, come on at a certain speed and go away. this helps. what brands tires do you have? I had set of kumhos once that wouldn't balance for nothing, they did alright on the machine but on the highway the would shake, the tire shop was confused wasn't the wheels so they tried new set of tires.. shake gone. a driveshaft can cause vibrations, some have smal weights on them if they where balanced from the factory, also if they dented by hitting something this will cause and out of round condition and make them vibrate but this really unusual for a mustang.
describe your vibration better and others will chime soon enough.
Vibration starts to come in at 75ish, vibrates from the rear, but into the steering wheel. My center console also vibrates. I have bfg comp t/as, and also just took off the nitto 555r's that also vibrated.
Keeping my eyes open on this thread. I got about the same thing. The car shakes at high speeds (75 or so) and I can really feel it through the steering wheel.
possible bad u joint on the driveshaft, possible rear end or rear suspension issues as well. is it just high speed or high rpms? RPM's would be indicative of something wrong with the driveshaft.
A tire can have a condition called "Out OF Round". It will balance out all day but will always vibrate because it is like an egg rolling end for end. Goodyear (Good for A Year) and General tires are known for this. Also a bent wheel is a likely cause of this vibration. You dont have a driveshaft problem because it is not all the time and doesnt change with accelleration or decel. This is a ROTATIONAL vibration because it changes with vehicle speed, if you feel it in the steering wheel it is in the front, if you feel it in the seat its in the back. Have a well trained tire guy check the balance, its either in the tire or the wheel.
Yes wheel bearings being loose can effect ride quality but shouldnt cause this type of vibration. He can easily check wheel bearings by grabbing the tire and trying to force movement up and down. If they are tight they can also be bad but would be accompanied by a noise. Hell loose tie rod ends are very common on foxbody especially inners, and these can cause bad vibrations. Jack the front end up and shakedown the steering system and check for any loose components. I still think you have a bent wheel or out of round tire.
The only thing i can think of is on the bottom of the rear end there should be a good sized piece bolted to it. My mechanic told me a lot of people take it off to reduce weight but some people get bad vibrations at high speeds when they take it off. I cant really explain it well but he said i'd be tempted to take it off