Why is my car so sensitive to wheel balance?

I have a 99 Maxima SE with about 130k on it. Recently I noticed the front wheels vibrates slightly at 80+ mph speeds. On my local commute
the vibration seems to come and go, and since my commute isn't too long, I've just ignored it for a while.
On a recent road trip, the vibration is more consistent at 80+ miles, and I had to drop the speed to about 75 to get rid of it. At the destination I decided to look up a shop with the Hunter GSP9700 road force balance machine, and had them balanced it. They remounted the tires, claiming the heavy spot of the rim is too close to the heavy spot of the tire and now "everything is within spec".
Unfortunately it made it worst. The vibration is more consistent now, and occurs at 70mph+, and I have to drop the speed to 65mph to get rid of it.
The tires are Michellin Energy Plus MXV4 and has about 70K on it. It's getting close to need replacement but I can still drive it for a little bit. When I got it 4 years ago, I had a big headache with wheel balance. The wheels would shake at normal highway speed no matter how many times Costco and America Tire Co balanced it. It's only when I found a GSP9700 and did the road force balance did the vibration went away, and it's been fine since.
Could the sensitivity of the wheel balance be an indication of a different problem with my car? The SE is the sports edition, with firmer suspension than the regular Maxima.
Raymond
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Did you buy this car new? I had a car that had symptoms like this once and after years of trying to fix it, we finally found a out-of-round wheel.
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snipped-for-privacy@none.com wrote:

Poss out of true tires.
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On Dec 30, 6:02 pm, snipped-for-privacy@none.com wrote:

it could be an out of balance axle shaft causing problems.
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snipped-for-privacy@none.com wrote:

Most sport suspensions are more sensitive to vibrations because of out of balance / out of round problems because the harder bushings do not isolate the suspension from the chassis as well as the standard spongy bushings. Vibration is often evident near a resonant frequency, and is not nearly as noticeable at higher or lower speeds. If the vibration is bad at 80 mph it may not be bad at 70, or 90 mph. Things as simple as tire pressure can change the resonant frequency.
--
Mike Walsh

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On 12/31/08 12:17 PM, in article snipped-for-privacy@bellsouth.net, "Mike

I'll add to that the bushings might be starting to fail as well. '99 is getting to the age where its worth taking a look.
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snipped-for-privacy@none.com wrote in

Do the tires spin DEAD TRUE when rotated?
Put the car up on a hoist, with the tires maybe a foot off the ground. Start the engine, let it idle, then put the transmission in first gear/Drive. One front wheel will spin on its own, the other may require a push with your hand to start it going.
Now squat down at the front of the car and watch the tread spin. ANY wobble, hop, squirm or combination of those will render any balancing useless.
Repeat for the rear wheels. But you'll need to spin them as fast as you can by hand then study carefully before they stop. Might be easier to have somebody else keep them going while you watch.
The tires must spin dead true before attempting a balance. I have personally found that most vibrations of the sort you describe are simply due to tires that are poorly mounted.
--
Tegger


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On Dec 30, 6:02 pm, snipped-for-privacy@none.com wrote:

_______________________ Perhaps - and you would need to do some research on where it could be done - you need an "on-the-car" balancing of your wheels. This would take into account not just your wheel+tires, but the hubs and axles also.
It does exist, and is probably more pricey than traditional shop balancing machines, but it may be the only course in your case.
Best regards for a Happy New Year!
-CC
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snipped-for-privacy@none.com wrote:

Thanks everyone for your suggestions and input.
I went to my local Nissan dealer (since they also have a GSP9700) to try to get the 2 front tire rebalanced. They looked at the tires and said it's almost down to the wear marks and said it'll be difficult to balance it properly and it's probably not worth the money to do it. He's probably right.
I am going to just use it for local drive for a little bit, and then replace the tires. Going to request a road force balance on the new tires when I get them, and see how my car behaves with the new tires. If I still feel vibration at highway speed, then I'll take it to a mechanic to have them take a look.
Raymond
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snipped-for-privacy@none.com wrote:

Finally bite the bullet and got new tires for my Maxima SE. Michelin Primacy MXV4 and the tire shop, a local America's Tire Co, road force balanced it on the GSP9700.
The front steering shake is completely gone. I can bring the car to 80 and it's still quite smooth. This probably means the old tires, having about 65K on them (Michelin Energy MXV4 Plus) and 4.5 years old, had some problems that balancing could get rid of, and shows up as vibration on my sensitive car.
The car also tracks more straight. I had a small pull to the right side with the old tire. Now it tracks more straight. Not perfect, but much better.
On a different note, I do noticed a very subtle humming type of noise from the rear. I thought they messed up the balance and asked them to road force the rears again. It's still there. I don't really feel a vibration from the rear before and after the rebalance.
Don't know why I didn't notice it before. Maybe the old tires are more noisy. Perhaps the rear bearing is on its way out? The tire place said it could also be the sound of the tire when it is new, and suggested drive a few hundred miles to see if it improves. We'll see.
I had the car since new (99) and the current bearing has about 135K on it. How long are bearings supposed to last? Do they needs to be replaced periodically, or are they usually good for the life of the car?
Raymond
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