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Discussion Starter #1
i have a 2008 cobalt special edition with 40 thousand miles, my problem is that when i exceed past 50 mph until 70 mph the steering wheel shakes and gets worse when i get on the brakes but once the speed drops below 50 it stops, ive changed front rotors and brakes and all i can get from mechanics is that i have worped rotors which cant be true if i put new ones on and it did the very same thing as soon as i drove it out of my shop. Any thoughts on the subject would be greatly helpfull.
 

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Classic symptoms of an alignment issue. Get it fixed quick because you will wear your tires unevenly and be forced to buy new sooner than later. I purchase the 3yr plan at my local Tires Plus for $170 and any time I take the car apart or every 10k (I commute for work) I get it realligned. Probably a bit much but at least I know I'm drving straight.
 

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Sounds like you might have a broken belt in one of your tires or you might have lost a balance weight. Bent rim will also manifest itself the way you describe, hit a curb lately or a real bad pothole?
 

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the tires are brand new and i just had the alignment done, this is why im at a loss right now... I have a buddy that thinks its something to do with the abs system or something along those lines so i'm curious of your guy's thoughts on this
 

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It's a small shake while driving but between those speeds if I get on the brakes its a rather vigorous shake but the car dosent pull any while I'm on the brakes
 

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New tires doesn't mean they're good. I even had an out of round brand new Michelin "X" once. Get them roll tested.
 

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Where did you get the roll test done?

To eliminate the tires rotate front to back, if you get the exact same vibration you have eliminated the tires and the rims. Warped rotors alone will not make your car shake at high speeds.

Are these steelies? Are you using the proper lug nuts for your type of rims? Does your rim have proper eccentric ring?
 

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thats what i thought you meant by roll test is to rotate the tires front to back, same vibration. the rims are stock same with the lugs
 

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A roll test is done with a machine similar to a balancing machine except it has a roller that applies pressure on the tire belt as it is rotating. It has sensors that produce a printout of how round your tire is. If there is a broken belt or a defect in the tire it appears as a bump or a blip on the graph. If it falls within certain parameters the tire is qualified has good. In my case it was a front Michelin and it was brand new but it still had a big bump on the graph that showed it clearly out of specs. Even with the graph in hand the Costco guy was still arguing with me. I just screamed louder until he changed it.
 

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Discussion Starter #14
that would b understandable about the tires if it didnt do the same vibration before i got new tires so unless two sets of tires have the same issue then i dont think thats it
 

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I think that's the first time you mentioned that it did that before the new tires. This can't be a big mystery. Not the tires, not the rotors only leaves the rims....
 

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it started right after i went down a steep grade the first time which was about a month after i got the car and has just gotten worse sence then
 

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Did you hit a puddle of water at the bottom of the hill with hot rotors? This will warp even new rotors if lug nuts aren't torqued equally.
 

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this happened to me, took it in to the dealership, they did a wheel alignment cost was around 100bucks, and it was fine after
 
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