PontiacBonnevilleClub.com

I've read about all I could find on the 65 to 75 mph "shimmy". I've got it. Today I shifted into Neutral and while the shaking did lessen a bit, it was still present so I can't help but think a balance would be in order. Luckily there's a shop in my town that offers road force balancing...for $20 per wheel, so $80 total. That's a bit much to spend with no guarantee it will fix anything.

I just can't see why there would be something inherent in 50 to 60% of all 2000+ Bonneville wheels and/or tires that would make them shake at a certain mph...but I won't start pulling at that thread...from what I've read nobody has been able to figure it out. About 85% of my driving is at 70 mph+ so I want this fixed.

Give me your opinion...would you drop $80 on a road force balance? My rims are stock 17'' and my tires are Firestones...not the RSA's.

I wouldn't do it. 90% of my driving is at or above 70 mph and it does not seem to be that big of an issue. I would recommend trying to stay off of 70 exactly.

Road force will more than likely not fix the issue. There are so many other issues that should be addressed first, such as the ISS that might cause the wheel to feel lose or shaky. Plus, the age of these cars with higher miles it might not be worth it.

I would focus on preventative maintenance and follow the recommended maintenance list that has been put together for the 2000+ Bonnevilles.

There is not a definitive reason or fix for the shake at this point.

mthedude wrote:Give me your opinion...would you drop $80 on a road force balance? My rims are stock 17'' and my tires are Firestones...not the RSA's.

How many miles on the tire? What quality are they?

How many miles on the car? What has been replaced in the suspension?

If the tires are not fairly high-priced quality tires, you will likely find that there is more than 18 lbs of road force in the rim and tire combinations. If you are not willing to get tires that are more likely to be round and stay round, then you will be wasting your money if you are concerned about the $80.

I'd start with checking the play in the hubs: if they have more than .005 in movement directly in and out along the axis of the axle, then replace them with a quality hub. Many people check by rocking the top and bottom of the tire and looking to be sure the movement is in the bearing and not the ball joint.

I'd check the tie rod ends for play. These are apparently known to wear and the free play can exacerbate the unbalance in the tire.

Are you getting any unevenness in the brake rotors when they're applied? If so, have those turned or replaced. A little lateral runout in the rotor can give a repetitive vibration that feels like balance.

Check for wear in the A-arm at the bushings attaching it to the subframe.

I just replaced the sway bar links when one of mine broke while jacking the car up to replace a hub bearing. The new bushings give a different, tighter feel to the ride.

Be sure you have a good alignment on all 4 wheels. This can exacerbate the unbalance in the tires.

Be sure you have a shop that is balancing the wheels carefully as closely as they can using regular dynamic balancing. Rotate the tires front to rear and see if the imbalance changes and seems to move from front to rear. My experience is that an unbalanced tire on the rear can give a vibration that feels like it's from the front. Front tires feel like they're definitely from the front.

Then you may want to try the road force balancing--but I'd ask how thorough they are. If the balance is out over the 12-13 my dealer service manage recommended in the early days of road force, will they check the rim and then rotate the tire to try to minimize the total force from the combination unit? Or are they only going to be willing to troubleshoot if there's more than 18 lbs. In other words, do they use the 9700 Hunter road force balancer as a money maker where they throw the tire on, run the road force part and say "See, it's 17 lbs," and then just do the separate spin balance and you're done? Or is it a troubleshooting tool.

I have a shimmy at 43mph. Its a dented wheel. I mount my own tires and ballance statically with an old crappy coates unit with a dull tip and a missing foot. My point? My balance is fine well over 100mph. Same with my race bike, only thats tested to 170mph. I see no benefit to paying extra for fancy balancing techniques.

I've read in some Mercedes and Acura forums that 65-70mph shimmies occur on those cars too. The first thing they suggest as a solution is road force balancing.

When I bought new tires recently, I went ahead and got the wheels road force balanced. My shimmy is not gone completely, but it is about 90% better and occurs within a narrower range than before. As someone mentioned above, there are other factors that can contribute to a shimmy. If you are confident that those are not to blame, and that the problem is solely within your wheels, and you have newer tires, then I would suggest considering a road force balance.

Ken_W

You will have to road force balance again when you rotate. It takes into all spinning parts that the wheel is attached to.

I think people have come to the conclusion that the shimmy in internal in the trans.

Thanks for all the ideas....I just got the car 2 weeks ago so I have no clue about what parts have been replaced, but I do know the tires are a Firestone, I'll look at the model name next time I drive it. They have really good tread on the fronts and at least 65 to 70% on the rears. Mileage is 89k and unfortunately I do most of my driving at 70mph.

Quick thought....if it IS in the trans, why doesn't it shimmy when the RPM's are the same at a lower speed?

I don't really know how to diagnose suspension wear and I really don't want to walk into my mechanic's garage giving them a wild goose to chase, because $600 will fall out of my wallet if that happens.

also, do any other GM Cars with this motor trans experience the same shimmy? If yes, that would point more toward the trans analogy I suppose.

I still suspect control arm bushings for the shake but have no proof. I think that is the issue as I have seen people replace everything that rotates and they still have the shake even after a road force balance, only other thing I can think of being able to cause the issue is those bushings.

crash93ssei wrote:I still suspect control arm bushings for the shake but have no proof. I think that is the issue as I have seen people replace everything that rotates and they still have the shake even after a road force balance, only other thing I can think of being able to cause the issue is those bushings.

The bushings in the control arms or on the frame...or both?

Just my ¢.02, my brother's 01 LeSabre's trans locked up one day leaving work, he did have the front end shake, which went almost completely away after the rebuild...

my car does it too,sometimes its perfect and then my seat is shaking at 60-80 i changed front tranny mount and rear shocks and i balanced the tires myself..