Car shakes at 55 mph. What service do I need?

July 30, 2009 1:37 PM

Car shakes at 55 mph. What service do I need?

I own a 2002 Pontiac GrandPrix. It generally rides pretty smoothly. But when I start to go faster than 45 mph or so, the car starts to feel wobbly and the steering shakes a little bit, and the ride can feel bumpy/rocky.

I'm certain that I've ran over a pothole or two this past winter.

What type of service does my car likely need? Alignment? Tire balance/rotation? Other?

posted by capitalist.pig to travel & transportation (21 comments total)

Probably alignment; that's what caused a similar effect on my car when I went over ~65.
posted by Tomorrowful at 1:40 PM on July 30

How are your tires? If they're badly worn, then that's the most likely culprit, and getting them replaced will fix the issue.
posted by yorkie at 1:40 PM on July 30

Sounds like you may have a flat spot or a misalignment of your tires. Usually becomes more noticeable at that speed. Does it make a pronounced noise? How old are your tires? When was the last time you had them rotated or had your alignment fixed
posted by stratastar at 1:40 PM on July 30

Try balancing first - much cheaper than an alignment, and that's what caused shaking in my old Saturn.
posted by peep at 1:41 PM on July 30

Tires are about 15,000 miles old. They don't seem very worn. The last time they were rotated or aligned was when they were first put on the car, 15,000 miles ago (two summers ago).

There is no pronounced noise.
posted by capitalist.pig at 1:44 PM on July 30

Balance the tires. To balance tires they put little weights on the rims (go out and look at your tires now, you'll see them). It's not that hard for them to fall off, and when that happens they'll shake the car at certain speeds.
posted by spikeleemajortomdickandharryconnickjrmints at 1:49 PM on July 30

Agreeing with peep - several years ago our car did the same thing at 55-60 mph. Guy at muffler shop that also does most of our other repairs suggested balancing the tires, which he did, and voila - problem solved.
posted by Oriole Adams at 1:50 PM on July 30

I say balance and rotate and see if you then need alignment (my tire shop doesn't even do alignments, they send them out to someone else only when necessary, which apparently isn't often enough to generate revenue). Goodyear says:

Tire Balancing

If your tires are unbalanced, you'll notice vibration. This can lead to driver fatigue, premature or irregular tire wear and unnecessary wear to your vehicle's suspension. Your tires should be balanced when they are mounted on wheels for the first time or when they are remounted after repair. Check your tire balance at the first sign of vibration or shimmy.

Vehicle Alignment

Your vehicle is properly aligned when all of its suspension and steering components are working smoothly and when its tire and wheel assemblies are running straight and true. If you notice uneven tread wear, it could be due to a misalignment and your vehicle should be serviced by a professional.

Tire Rotation

While many people are knowledgeable enough to rotate their own tires, the procedure is especially quick and easy for a professional. Your vehicle's owner's manual will specify the proper rotation pattern and schedule for your vehicle. If no specific schedule is indicated, a good rule of thumb is to rotate your tires every 6,000 to 8,000 miles
posted by Lyn Never at 1:50 PM on July 30

Unbalanced tires or bad alignment.

As peep points out, getting the tires balanced is far cheaper than getting an alignment. So start there.
posted by Netzapper at 1:51 PM on July 30

The cause, then, is almost certainly that you've not rotated the tires, which should probably be done every ~5000-7500 miles. The fix may involve a simple rotation of tires, or a full replacement, depending on just how funny the wear of the rear tires has become.
posted by u2604ab at 1:51 PM on July 30

I have the same issue with my car. Balancing usually helps but in my case it did not, one of my rims is bent from an accident I had months back and I didn't notice it until I had my tires rotated and could feel the vibrations through the steering wheel.

Keep this in mind if balancing the tires doesn't solve the issue.
posted by hellojed at 1:54 PM on July 30

Balance and rotate before alignment job.
posted by hellboundforcheddar at 1:55 PM on July 30

Sounds weird but I have personal experience: check your lug nuts. If they're even a little bit loose you might experience that vibration.
posted by tommasz at 1:57 PM on July 30 [2 favorites]

In my experience, suspension related concerns are the result of the following, in order from most to least likely:

1: Tire balance or wear
2: Dented rim.
3: Suspension damage like worn tie-rod, ball joint, or shocks/struts.
4: Worn CV joint.

Just a vibration isn't enough to condemn an alignment. An alignment will also have symptoms like strong directional pull or drift as well as extremely accelerated tire wear.

My money is on shocks or struts in this instance. Your wobbly and rocky feeling could be the car hitting the suspension bump stops and not being able to dampen normal shocks. If you car is simultaneously kind of pudding-y and clattery, the culprit is shocks/struts. In this case, your vibration could be the result of the irregular tire wear caused by bad shocks and that's feeding back through your steering wheel.

Run your hand over the surface of the tire (longways). If it's cupped and choppy, you've probably got bad struts. If it's feathered or worn excessively on the inside or outside then you need an alignment. If three wheels are fine and one exhibits irregular wear, then there's suspension damage local to that wheel.

If you walk up to the trunk or the hood and push down (with all of your weight) and the car reciprocates several times before coming to rest, you need new shocks/struts.

Most strong vibrations felt through the steering wheel are originating in the front wheels (where the steering system attaches.) Use your jack to raise the car like you're changing a tire. Give each front wheel a shake. Holding the tire at 3 and 9 o-clock and shaking will illuminate a bad tie-rod end. Holding the tire at 12 and 6 will help determine if a ball joint is bad. If the wheel is loose in every direction and makes a grinding noise when you spin it, you've got a bad wheel bearing (also a possible culprit).

Good luck!
posted by Jon-o at 1:58 PM on July 30

When checking lug nut tightness, don't just run around with a wrench. Jack up, brace with a stand, undo all the nuts, and dislodge the wheel. Make sure no debris lives on the mating surfaces between axle flange and wheel. Put the wheel on and tighten, take care to see the wheel seats right and tighten opposing nuts in sequence. Especially on an older car, using a hand wrench, it can be surprisingly easy to put a wheel on crooked even though it feels tight.
posted by maniabug at 2:40 PM on July 30

A mechanic once told me their rule of thumb for front end vibration was: Begins around 55mph = balance tires. Begins higher than 55mph = alignment. YMMV.
posted by Thorzdad at 2:55 PM on July 30

Check to see if your tires are screwed in tight. Also, you may want to investigate whether there is tire rot.
posted by reenum at 2:55 PM on July 30

Tires can look fine and still have incipient tread separation that manifests in this way.
posted by fourcheesemac at 3:08 PM on July 30

You probably hit a pothole and slighty bent a one of your wheels (what Americans call "rims").
posted by Zambrano at 5:43 PM on July 30

I agree with Jon-o. Could be bushes too.
posted by luckypozzo at 8:20 PM on July 30

Thank you, everyone, for your help! I had a mechanic balance and rotate the tires. While doing this, he discovered that one of the rims had been dented (probably from a pothole). Replacing the rim (and also the tire) finally resolved the problem.

I highlighted those who suggested a dented rim might be the culprit. Thanks again.
posted by capitalist.pig at 12:37 AM on August 2