i have a 99 buick park ave. 3800 eng supercharged, i have a vibration a highway speed avove 65mph, remains constant when speed increase does not stop until i get under 65mph, feel it in the seats and in the steering wheel, steering does not shake just vibrates, replaced front motor mount and had tires balance twice vibration still there, any help would be greatly appreciated, i just cannot figure out what is causing it. help if you can.

Very hard to pinpoint this type of problem, could be a bad tire relative to road force variation which requires a special type of wheel balance, could be a rear tire out of balance also, were they balanced?, could be a belt shift in a rear tire. All these things should be eliminated before looking at mechanical possibilities.

thanks for answering, the tires were balance twice the last time at a goodyear store as they are goodyear tires, what type of special wheel balance do i need? i remember they use to have a spin balance on car, i have been unable to find anyone that does it now. they just pull them off put them in a machine and balance. what do you suggest, how can i find out if it is a belt in th tire?

You need a Road Force balance done on the wheels and tires. Hunter 9700 wheel balance.

http://www.hunter.com/pub/product/balancer/4159T/index.htm

I'd guess the tire is your problem. Might be bent rim.. Goodyear is a brand my service manager mentioned when they were rebalancing my Michelins on my 03 due to road force variation causing a slight vibration.

You can move tires front to back and see if feel of problem changes. But I'd pay for a store that does Road Force and someone who knows how to work the machine--they don't all have knowledgeable techs. Do some looking and asking before paying.

I agree on tires..
I had that problem..
I think one can balance a tire with a slightly bent belt off car. When it gets put back on the car the weight and driving causes it to show up..

I hate those vibrations too. .LuV a smooth ride.

Good Luck.

I HAVE THE SAME VIBRATION PROBLEM WITH MY 94 PA (NOT AN ULTRA). I HAVE THE AUTO LEVEL CONTROL IN THE REAR. THE SPEED (USED TO START AT 65) AT WHICH THE VIBRATION BEGINS IS NOW DOWN TO 55 MPH. SO FAR I HAVE SWITCHED THE TIRES AND WHEELS WITH MY 99 REGAL TO TRY TO ELIMINATE THEM AS THE PROBLEM. THE CAR STILL VIBRATED AND THE REGAL ROAD JUST FINE TO 86 MPH. I WONDER IF THIS TRULY ELIMINATES THE TIRES AS THE SOURCE OF THE PROBLEM? I HAD THE TRANSMISSION CHECKED BY 2 DIFFERENT SHOPS AND I REPLACED THE 4 STRUTS WHICH HELPED BUT DIDN'T ELIMINATE THE VIBRATION COMPLETELY. :screwy:

ALSO, MY DIGITAL LIGHTS (RADIO AND HEAT CONTOL) GO OFF AND ON AT WILL. :evillol: WHILE THE OTHER LIGHTS STAY ON.

AND, MY ALTERNATOR LIGHT COMES ON (AND NEEDLE GOES TO ONE END OR THE OTHER) WHEN THERE IS NO DETECTABLE PROBLEM WITH MY ALTERNATOR OR BATTERY. :banghead:

ANY HELP WOULD BE GREATLY APPRECIATED

I HAVE THE SAME VIBRATION PROBLEM WITH MY 94 PA (NOT AN ULTRA). I HAVE THE AUTO LEVEL CONTROL IN THE REAR. THE SPEED (USED TO START AT 65) AT WHICH THE VIBRATION BEGINS IS NOW DOWN TO 55 MPH. SO FAR I HAVE SWITCHED THE TIRES AND WHEELS WITH MY 99 REGAL TO TRY TO ELIMINATE THEM AS THE PROBLEM. THE CAR STILL VIBRATED AND THE REGAL ROAD JUST FINE TO 86 MPH. I WONDER IF THIS TRULY ELIMINATES THE TIRES AS THE SOURCE OF THE PROBLEM? I HAD THE TRANSMISSION CHECKED BY 2 DIFFERENT SHOPS AND I REPLACED THE 4 STRUTS WHICH HELPED BUT DIDN'T ELIMINATE THE VIBRATION COMPLETELY. :screwy:

ALSO, MY DIGITAL LIGHTS (RADIO AND HEAT CONTOL) GO OFF AND ON AT WILL. :evillol: WHILE THE OTHER LIGHTS STAY ON.

AND, MY ALTERNATOR LIGHT COMES ON (AND NEEDLE GOES TO ONE END OR THE OTHER) WHEN THERE IS NO DETECTABLE PROBLEM WITH MY ALTERNATOR OR BATTERY. :banghead:

ANY HELP WOULD BE GREATLY APPRECIATED
SORRY, MY CAPS BUTTON STUCK!
94PA
:disappoin Please read the Community Guidelines (http://www.automotiveforums.com/vbulletin/guidelines.html), especially the section titled "POSTING EDIQUETTE".
It would also be better to Post a New Thread (http://www.automotiveforums.com/vbulletin/newthread.php?do=newthread&f=105), rather than posting in an older thread.:grinyes:
Thank you:p