2002 Buick Century • 433,000 miles

I have over 400k miles on my 2002 buick century-I hadn't had to replace much on it, but for the last few weeks, I'm feeling vibrations while driving. It doesn't matter at what speed I'm driving at. The only thing that is constant is it's more pronounce as I depress the accelerator. If I easy back on it, it will quiet down. What causes this and how can I fix it?
March 24, 2012.

It's impossible to diagnose things like that over a computer but to start the process, where do you feel the vibration, the seat, steering wheel, or entire car? If the steering wheel shakes, a worn inner cv joint housing is somewhat common. They will cause the steering wheel to vibrate when under load as in accelerating, and it will go away when cruising and coasting.

Vibrations felt in the seat are often due to a broken belt on a rear tire. Bent wheels will do that too. Broken tire belts that aren't real bad yet often are more noticeable on high-speed corners like on highway off-ramps.

If you feel the vibration when the car isn't even moving, that leaves out everything related to wheels, tires, and drive train. There's a misfire in the engine, the outer cast ring on the vibration damper has turned and is coming apart, or, on some engines, the balance shaft is out-of-time. That balance shaft doesn't usually get out-of-time on its own. That happens from being assembled improperly.

Mar 24, 2012.
I should of been specific in my problem. The steering wheel doesn't shake, it's more like under the seat. I just gotten new rims and tires. You feel it more when pressing on the gas. As soon as you take your foot off the pedal or ease off on it, it either stops completely in city driving or barely noticable on the highway. I don't feel any vibation when sitting still. Could it be a loose motor mount?

Mar 24, 2012.
The first thing I would do is rotate the two right side wheels front to back, then drive it to see if it's the same. Then switch the two left wheels and drive it again. Wheels can get bent on older types of tire changers and unless the mechanic has reason to suspect that, he won't see it on the spin balancer.

The next course of action would be to use a dial indicator to measure "lateral runout" by spinning each wheel when it's off the ground. Some brand new wheels will have excessive runout that causes a shimmy. If you find one that's excessive, there are other things to check before condemning a wheel. While they're removed, rust and scale can break off and fall behind a disc brake rotor, or a piece or scale can get stuck between the wheel and hub. Either of those will cause that wheel to wobble but you often won't feel it under all conditions.

Mar 25, 2012.