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Shaking at High Speed

My 2003 Cadillac Seville starts shaking at speeds over 55 mph. It gets really bad at 70mph. It is not to the point that the wheel will come off but it is strong enough to annoy me. I can feel it more on the seat than the steering wheel. It does not get worse with breaking. I don’t feel car pulling to either right or left. Tires seem to be evenly worn. If I shift to neutral and coast, it is still there at the same intensity. I took it to local gas station. They think the problem is the no brand name economy tires on the car. They took them out and balanced them all. They said they had to shave a lot one of them to get to balance. After that balancing act, the shake is still there. The said they could not find anything else wrong with the car. They recommended that I buy new and better tires.



I’ve just bought this car recently. There is a small ding on the body above the right front tire. There are small scratches on right front bumper. The mirror on the right door is new. The car must have had a minor accident on that side (parking lot incident?). I was thinking that accident must have bended the rim or something else but my mechanic could not see anything.



Before, I go buy 4 new tires, does anybody have any other ideas?

Thanks,

Even before I read the part about the probable accident to the car’s right front area, I was thinking that the car needs to have its front end components checked by a competent alignment shop. (Please note that the category of “competent” does not include the likes of Midas, Meineke, Monro, Sears, AAMCO, or other chain operations)

The symptoms that you describe are likely the result of either defective tires or damaged/worn front end components like ball joints or tie rod ends. Either of these is a definite safety issue. Take the car for a front end inspection a.s.a.p. If the front end proves to be okay, then the problem is likely to be a damaged/shifted belt in those cheapo tires.

" They took them out and balanced them all. They said they had to shave a lot one of them to get to balance."

“Shave a lot” is a very interesting term. What does it mean? Whatever it means, I think you are getting close to finding your problem…Cheap or whatever, I think you have a defective tire…

“Shave a lot” is a very interesting term.

I was thinking the same thing. It sounds like maybe the tyres were unevenly worn. That would tend to mean there was a balance and/or suspension problem. If you don’t get the cause of that need for a shave fixed, you will just eat up whatever tyres you put on there.

Bias ply tires were often out of round enough to require shaving tread off to get them in balance correctly. But if the tires/wheels are the issue spin balancing should make that evident regardless the brand of tire. Check for liquid in the tires or a broken belt as suggested above. Rolling a mounted tire on a smooth and level floor will made a broken belt evident.

I appreciated everybody’s contribution.

Here is a quick update:
I’ve just bought 4 new Michelin tires. The ride is much more smoother at any speed. As for the high speed shaking, it is reduced 80%-90% in intensity. There is still a minor amount of it is still there. I can live with his but I prefer to get to the bottom of it. I would like to drive this car at least another 10 years.

When they were installing the tires, I asked them to take another look at the rods and ball sockets or anything unusual in the front end. They did not see anything. I am sure they did not care about my problem as mush as they cared to install the tires and move on to next customer.

Does anybody know a “competent alignment shop” in Washington DC or Montgomery County, MD area? I am not reading very good customer reviews about the local Cadillac dealer’s service department.