2000 Mercury Mountaineer Shakes Bad past 55 MPH. Please Help!

Hello all,

I have a 2000 Mercury Mountaineer AWD. It started in the last few months. My truck also recently went over 130,000 miles.

When I drive under 55 MPH the truck drives fine. But, when I go over 55 MPH the truck begins to shimmy and vibrate. The faster I go the more the shimmy and vibration. It gets so bad that it scares me to continue at those speeds, so I slow down to under 55. This is very frustrating and dangerous when driving on the interstate or freeway.

I recently took it to a repair shop and had the tires balanced and rotated. After that, the truck shook more violently at high speeds than before the balance and rotation. They also said that the ball joints need replacing. I did not get them replaced yet.

After I left the repair shop I had some of my friends look at it. My friends are Army Certified and ASC Certified Vehicle Mechanics with years and loads of experience. They said that the ball joints don’t need replacing yet, and that they shouldn’t be the cause of the shimmy and vibration.

What do you think is the problem? Somebody please help.


It could be a defective tire (belt issue). Take the wheels off and try to roll them across the driveway. If one wobbles, you’ve found the problem.

I will try that. I will give you the results when it is done.


Explain in what manner were the ball joints inspected.


Have you had the transmission or cat. converter checked? I had the same issue with a different type of vehicle and that turned out to be my problem. If you have an Auto Zone in your area you can take it there and they can have their computer check you car for problems.

I second the bad tire as a likely source of the vibration. A tire with a belt separating may balance ok, but not drive well with the weight of the car on it. Still the tire shop should be able to see a tire going bad.

If you feel the vibration in your hands mostly it is a front tire. If you feel the vibration in your body, coming up from the seat then check the rear tires.

If it is not a tire, then some driveline component is failing. A U-joint, transmission mount etc.

I didn’t take the tires off and roll them, but I did take the truck back to the shop and had them road balance them (a more comprehensive balance). They said that they were now properly balanced.

Soon after I took it on the interstate. When I approached 60 MPH it shook and vibrated. But, unlike before, this time the shaking was in the seat and not so much in the steering wheel.

Based on this, I think there is a high probability that the problem is with my rear tires. The rear tires used to be on the front and are now on the rear. They are worn on the edges and practically new on the inside.

Just for its and giggles, does anyone have any ideas about other possible problems and solutions, or is the tire theory the only one there is?


The uneven wear on the rear tires (which used to be on the front) screams that the car needs an alignment. The rear tires are likely “cupped” as well. You can feel cupped tires as you rub you hand over the tire tread surface.

Cupped tires can’t be fixed. They are replaced. If you put new tires on and don’t do the alignment the new tires will end up where your current tires are now.

Worn suspension parts make it hard for a car to be aligned and to hold alignment. The age and mileage on the car indicate likely suspension parts are worn out and need replacing.