High Speed Vibration

I have a 1991 300 SL with 104,000 miles which vibrates when the cars is running between 60 to 75 mph. The vibration can be felt through the steering wheel and by a passenger. Above or below the range, the vibration
is not felt. I had the set of tires which had about 9000 miles, re-balanced and rotated, it didn't help; I had the steering damper replaced by my MB service garage, this didn't help but the mechanic recommended getting the wheels rebalance as he did agree there was a problem and didn't like the fact that the wheel weights were add only on the inside of the wheels; I next had MB Dealer rebalance this MAY have helped for a few miles but not for long. In frustration I replaced the tires with a well known National Brand with the series recommended by this Manufacture. The problem still persist. The MB garage I use for repairs has a lot of experience. I would think if there was a problem with the steering or drive train, one of the mechanics could identify the problem This is getting expensive. Looking for suggestions as to the next step?
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The symptoms are of tire imbalance. Yes, the same has happened with two sets of front tires - it shouldn't have - but here we are.
Two tire imbalances need to be addressed: static and dynamic. All tires have heavy spots; some will cause sufficient oscillation to bounce tires off the roadway at 55 mph! Dynamic balancing is to offset the tire's outside wall vs. inside wall imbalance for that oscillation will cause shaking in the steering. This is what you are feeling.
I've had personal experience of a tire shop's morons "balancing" new tires on the shop's "electronic machine" that only days later, and at the same shop, needed 1.5 oz weight corrections! No one batted an eye, they acted like nothing had happened - business as usual. So don't assume anything.
Finally, if the problem isn't solved by balancing one should not overlook the shock absorbers; worn out shocks could be involved, but first deal with balance.
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I suggest you find a shop near you who has Hunter Roadforce Tire Balancer.
http://www.gsp9700.com/pub/search/FindGSP9700.cfm
If this doesn't solve your problem, then you got problem elsewhere. This machine will tell the technician if anything is wrong with your wheel or tire.
Weight on the inside only is static balance... Weight on both side of wheel is dynamic balanced which is better, but the weight on the face side may be on the inner wheel as close to the outside as possible.
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Tiger wrote:

One thing I've not seen suggested is out of round tires, or is that much of a problem today? In the '60s I would take even Michelins to a shop and have them put it on a lathe, in some cases it would be "out of round" by as much as 1/16".
I've also seen air pockets under the tread, those you can't get rid of. True them on a lathe and they return as the tread decreases in thickness causing the effect to worsen.
I realize my experiences are as old as the hills, but I wonder just how prevalent they are today with people who buy cheap tires.
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Thanks to both T.G and Tiger for your comments. The dealer mentioned moving one tire on the rim for better balance but the weights were only on the inside. The wheels are Chrome, the original for the car. Maybe for appearance they only put the weights on the inside of the wheel, I bought the car in Nov ,2005 it had a set of top of the line Dean Tires, they had only about 9,000 miles when replaced yesterday with Goodyear's recommended for the car on the company's Web page. Any thoughts about the dust guards on the wheels? Thanks again to both of you as I resume my quest for a fix.

wheel
be
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Dust guard is okay... but not recommended. I'd rather swap out the brake pad for the dustless version.
I still don't understand why tire shop will simply do static balance when their machine can also do dynamic mag wheel balance... which put both weight on the inside that one is in the usual inside and one on outside but on the inner side that you don't see any weight at all.
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The reason you do a dynamic balance with the wheels on the car is the moving metal bits may not be PERFECT balanced themselves.
Around here there's exacly one "old guy" that does the on car balance.
He spins up the tires to 60 mph and puts his hand on the car and if he detects ANY vibration WHATSOEVER, adjusts the weights. It's a slow process, twice as much has a regualar balance and he's a crusty old fuck that often needs to be bribed to stop threatenig my life and car. A box of donuts foe "the guys in the shop" (in advance) works wonders as does a twenty in extreme cases (like when you know one rim is, uh, "problematical").
But my god does he do a good job.
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Keep in mind tires have an index mark to indicate the highest point on the tire an so di rims, these much be matched. This is not well understood.
Tires can be out of round as previously suggested.
I've never had a problem with weight only only on the inside. When the rare combination of every hard metal and soft rubber has been replaced and the tires and new and perfectly balanced and the alignment is perfect then even a 25 year old car can be as smooth as glass at 100 mph.
Uh, not that I'd admit to ever doing that of course. At least not till the statute of limitations expired.
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Have you considered worn prop-shaft bearings?
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MB
the
I
not
National
still
the
the car on the road. But, that said, not a bad ideal. I owned a Volvo that developed a bad vibration that turned out to be the drive shaft itself.
John
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John wrote:

Have you considered my suggestion? It's simple to do, if/when you get your tires balanced they can check that also.
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Ok, the fact that a decent balance changed the nature of the problem and was the only thing you've tried that had any effect would indicate to me that you're on the right track.
Before we go any further I'd ask were they balanced on a machine off the car or were the balanced ON the car? The latter is the only effective method IMO. I've never EVER been happy with an off car balance.
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On car balancing... I had this done with tires that are damn bad... drove me crazy... on car balancing will fix this. They are the best balancing but almost no one has it... and if they do, it is so old! The equipment is extremely old. Then if you rotate your tires... not balance anymore.
Off car balancing used to drive me crazy too... even with perfect tires... The reason it is bad is because they did not calibrate their equipment often enough or are too lazy to calibrate it to near perfection.
I now do my own mount and balance. I bought a tire mount machine... euro style... and parked it in my uncle's shop. And he has a balancer... nothing fancy but when calibrated... perfect!
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Where are you located again TIger? ;~)
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Maybe it's a bad rim. I had one rim on my '95 that was slightly askew (probably due to hitting potholes or a curb). I swapped it with the spare (which was never used) and it resolved a similar issue.
Josh
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