And, goldfinger, don't overlook getting a second opinion at another shop (balance, etc), preferably, not a tire chain store. My favorite place is an independent brake and alignment shop with a good balancer. They don't depend on tire sales.

my tire store has 3 Hunters and the one is a brand new Computerized model. We did the balance on that one then cross referenced to the others untill all 3 said they were zeroed out.

We check each rim for runout too. I just cant believe after 2 sets of brand new comfort treads its the tires.

Chceked the ignition coils, no problem. Again ALL the plugs looked the same too , exactlly the same ???? After cleaning the throttle body and MAF it is smoother at idle but the slight seat vib is still there.

Since they have Hunter balancers, did they use a 9700 RoadForce balancer to compensate for the variation in the springiness in the tires?

If you do, I suspect you'll find the tires are not actually rolling round because of the difference in the crush in different parts of the tires. That causes a hop just the same as if the tire is not round--and a lot of them aren't.

If you want to cure your problem, put Michelin tires on and have them balanced with a Hunter 9700 and get the alignment front and rear set perfectly to the recommended spec. Close enough to spec or within the range isn't it; get it set to spec.

They do NOT recomend road force balancing and they told me that it is recognized form of balancing by ANY tire manufacturer ????

He said he would put the Michelin Smeterys on but I have had excellent luck with the Comfort treads in the past ????

I'm not sure who they are? The tire dealer? And what tire manufacturer doesn't want their tires balanced other than the ones making donuts that won't balance well.

As for Symmetry tires, I had those as OEM on my LeSabre and they were good, but I replaced them with Harmony by Michelin. They have been good WITHOUT being RoadForce balanced. But the tire chain from whom I bought the tires has RoadForce balancers in some of their stores so I can go get them rebalanced if I wish under my lifetime balance guarantee.

The Park Avenues had a slight stiffness problem transmitting the uneven tire movement through the car. BM'* solution was to replace the tires with Michelins and to have the wheels and tires RoadForce balanced. What tire store doesn't want them RoadForce balanced?

Go to a quality Buick dealer and ask them what they do.

I'm not sure what brand Comforttread is, but my service manager back in 03 was showing me he GoodYears they were putting on a GM car and how bad they were with the RoadForce balancer--how much they were off from rolling round. He commented that the Michelins were still the roundest rolling of them all.

I wish you luck but you can't believe everything the tire store may say. A friend shopping for a new car was told he better buy a new XXX brand car because the independent truckers are likely to go on strike and that means no new cars at the dealers to be available. I pointed out to him the trucking of cars from transfer drop lots is done by companies with fleets of trucks, not by independent truckers driving the car haulers.

Goodyear is the compny that said they do not recomend RoadForce, they recomend match mounting the tires to the rims.

The tire store said he doesn't have a problem putting on the Michelins but I am not convinced that is the best idea. These Comfort treads have the best reviews of any tire I have seen ??

I am not even 100% that its a tire...

oh comfort treads are Goodyears

Ok took the car back to the tire dealer, put 4 brand new Michelins on and problem seemed worse, more vibration than with the GoodYears. So we switched them back and recheck all the rims for run out and they were all true and balanced right up.

So I then took an indicator against every wheel inside and out while mounted on the car and spun them to check runout. All seemed perfect. I had the 4 wheel alingment re-check, on the money.

So... If the tires are not the problem, all new tie rods and rotors and rear air shocks. Wheels are balanced and true but I still have a shake and slight vibration felt in the seat and seen in the passenger seat when noone is sitting there.

CV shafs and wheel bearing all check out good... So is this just one of "those" problems ???

You haven't done front shocks?

nope they are struts and seem fine, no bouncing and no front end vibs just in the seat. The steering wheel doesnt move a all. Even if the struts were shot I can see it having a seat vib it would be in the wheel one would think