so its like clock work. As soon as I hit 85mph I feel crazy vibrations in the center console steering wheel and the dashboard shakes like hell. Its so loud to. It sounds like the tires are just going to give out. I have had the tires and wheels balanced and all. Have wheel weights on but I'm starting to think its else where. I was thinking maybe drive shaft or steering linkage. It kills be because its a great car super clean and drives very well. Rear gear is 373 but I do know these gears are loud in the highway.

 

If you let off the throttle at 85mph does it still vibrate? Or is it only when you are on the throttle at that speed?

 

it will vibrate if I'm on or off the throttle.

 

I'm having this sort of vibration issue as well, only mine starts at about 70 and then the car wont accelerate. It stops when you get under 70. Is a front end rebuild in order?

I was reading around a bit and... could a bent rim cause this vibration problem?

 

my money is on front end parts...but could be bent rim, bent axle, out of balance or miss aligned drive shaft. those would all be speed related not rpm. were the tires spin balanced?

 

I would have the tires re-balanced. I have had wheels balanced terribly and got similar issues. I have also had wheel weights come off. But if you go to a place and have them check/re-balance every wheel it may solve the issue for cheap. That's where I would start.

 

Mine does similar to this, but starts usually closer to 70. Then again, my suspension is shot so until i get that fixed that would be my guess as to my problem.

 

In my experience, I've had a bad tranny mount (replaced with prothane mount which fixe that), i've had an un balanced stock steel driveshaft which I replaced with inland empire 3" alumiunum driveshaft (ZERO vibrations at any speed that i've gone which is yp to 120MPH so far), and a bad alignment can possibly cause this.. Alignment specs on my car are as follows:

Camber: -1.2 on both sides
Caster: 4.3* on driver's side, and 4.8* on passenger's side
Toe: 3/32 toe in.. total toe is 0.09

Check wheel bearings, front end linkage looseness, ball joints, etc.. BTW the tranny mount is cheap and I would start there if I were you.. It's a poly upgrade as well so it can't hurt. Just don't get the energy suspension one, that created more vibrations for me on my car.

 

Im having the same issue. right around 70. I just replaced my transmission mount (energy suspension one). I have 2 driveshafts and after testing both I cant pinpoint the vibration.

 

I would say to anyone with vibration check driveshaft then check tires/rims, next would be rotors, unless the steering wheel jumps around alot when you hit bumps its not front end.

 

Driveshaft vibrations are much higher frequency than anything wheel/tire/suspension-related. A driveshaft that's out of balance will vibrate like you're inside an old electric razor. Bzzzzzzzzzz!

Other problems are much more low-frequency. A "shake", not a vibration.

The stock driveshaft on my old 94 Formula was one of the "known bad" ones from the factory. Around 90 MPH or higher it would vibrate your fillings out. Replaced with an LPE 3.5" unit and everything was smooth as a baby's butt out to 140+. Sometimes you can also make a noticbably difference in driveshaft vibration simply by flipping it 180* on the reear end yoke. It should be "neutral balanced" so that kind of change shouldn't make a difference, but it often does nonetheless.