my 93 bonne is shaking when i go 50 mph and over, and i drive the highway for an hour to work each day! at first i thought i had a flat tire. my friend said it could be the wheel bearing in back, but that it'* hard to change by yourself. (True?) i need to know what it could be, how dangerous is it, how much to fix, and how long i can let it go. Please help with options, so i don't get screwed when i go to the shop!!

It sounds like you might have a tire out of balance. How old are the tires?

A bad wheel bearing wouldn't cause the shaking like you described.

i got the car a year ago from my uncle, and haven't had new tires. i don't know what he did to it before i got it, but he'* a pretty thorough guy. my friend shook the tire and it moved, (not that i know what that means), and said it didn't line up right, and that the tire was worn on the outside part. it would shake that bad just from old tires? it has 117,000 miles, and i drive on the freeway a lot. it feels like the tires are gonna pop off or something, and it'* hard to go over 55 mph because it shakes so bad.

A shaking at speed can be caused by quite a number of things. We'll start with the simpler and less expensive things and work our way up.

Physical inspection of wheels and tires. Make sure there are no imperfections in the sidewalls or distortions in the tread pattern. This could indicate a broken belt within the tire. Inspect for dings or cracks in the rim. Make sure the lugnuts are properly tightened and the tire pressure is correct.

Wheel balance. Weights can fall off. You could rotate the tires to see if the shaking has moved to a different corner.

Worn ball joints

Warpped rotors (if shaking ocurrs under braking)

Alignment (if the shaking is coming from the front).

randman- thanks much. obviously, i'm a chick who doesn't know too much about cars (although i can at least change a tire!), so can you tell me how difficult these are, and how much each might cost? I don't want to walk into a shop and have them do something unnecessary and charge me an arm and a leg.

My car shakes bad when i go fast, and it might shake too when i brake hard, and there'* some kind of thump noise from the back when i'm flying on the freeway. Are there things i can try to decipher while i'm driving to narrow down my options, or do i have to leave it all up to a mechanic?

Rotate your tires front to right on each side. While doing so, look for evidence of a missing wheel weight. If it'* a front tire out of balance, the shaking should be somewhat reduced if you move the wheel to the rear. If it feels like that'* what happened, consider getting new tires, or at the least, re-balance.

so it is possible that even though it feels like my car will literally fall apart, i might only need to balance or rotate my tires? is this something that happens a lot?

You are doing the right thing gathering information prior to having it looked at.
Personally, I do the free or inexpensive things first. Have a car buddy do the inspections, inflation and if possible, throw him a 6-pack to rotate the tires. If not, a tire shop would probably charge $30 or maybe less for this service.

Lets break down the additional information:
Uneven wear is usually caused be improper alignment. And improper alignment can cause a shake in the frone end too. My car would shake like crazy under acceleration starting about 48 MPH and continue until I let off of the gas. A $40 front wheel alignment cured this.

Jacking up the car and shaking the wheels is done here in MA during safety inspections to check for worn ball joints, tie rods and other outer suspension components. This could be the cause of the shaking but would think that other symptoms such as a wobble while steering would be present too. Nevertheless, if you do have worn suspension parts, it would be important to get that fixed for safety reasons.

thanks, randman. at least you're in MA and know about the snow like here in Michigan. My friend drove my car and the wheel bearing was what he came up with. My steering is off, but it has been for quite a while (i know, i'm a chick so i only deal with things that actually stop my car from moving). I would love for it to be something simple as rotating or alignment. thanks for the ideas, it helps. what you're saying makes sense, but i wonder why my friend wouldn't have came up with that?!

lower ball joints will cause the wheel to shake when it is up off the ground.

Balancing problems start off at speeds usually over 30 or 40
it will cause a continuous vibration.

If it is wearing on the outer or inner side of the tire more than the middle you probably need an alignment.