Determining the Causes of Vehicle Vibrations

Steering Wheel Vibrations

This is probably the most common vibration people deal with. There’s an important distinction to be made with steering wheel vibrations. Does the vibration happen all the time while you’re driving, or just when you step on the brakes? If it happens all the time, it’s likely to be a tire or tire balance problem, especially if it occurs around the 55 to 60 mph range. It could also be a driveline issue, but the most common causes of this type of vibration involve the tires or tire balance.

If the vibration only happens when you step on the brakes, then the problem likely is the brakes. This does not necessarily mean that your brakes are about to fail, but rather the brake discs (or brake drums) have become out of round, or warped. When this happens and the brakes are applied, you get a vibration. You can deal with this vibration in one of two ways. You can have the brake parts machined true again, which should get rid of the vibration. Or, if the brake discs or brake drums don’t have enough metal material left to be machined, they’ll need to be replaced. Here’s a video covering this topic in more detail.

As stated in the video, this test won’t work for all vehicles. It depends on the type of parking brake setup you have. See the Brakes article for more details on this topic.

Isolating Brake Pulsations

You can find out if the vibration is coming from the front or back wheels with a simple test. You need to do this safely, so find a road that’s not busy, or, better yet, a parking lot where you can safely drive at speed. While driving the vehicle at the speed that the brake vibration normally occurs, activate the parking brake or emergency brake. Don’t fully apply it. You only need to apply it a small amount to get a result. When you do this, you isolate the rear wheels from the brake system. Most parking brakes lock the rear wheels using the rear brakes. When you activate the parking brake, you’re often working the same components in the rear brakes that are activated when you depress the brake pedal, but during your test, they are the only brakes being applied. So, if you have a vibration when doing this test, you have warped rear drums or rotors. If you don’t feel the vibration, the problem is likely with the front brakes. Here’s a video about the specifics of the test.

As stated in the video, this test won’t work for all vehicles. It depends on the type of parking brake setup you have. See the Brakes article for more details on this topic.

Tire and Wheel Problems

If the steering wheel vibration happens at low speed, it’s a tire or wheel problem. Low-speed wobbles or vibrations are almost always caused by this. You might have a tire with a bad belt that causes it not to be round, or you might have a wheel that’s bent due to a collision or some other trauma. Come to think of it, it could also be that the wheel is loose on the hub. Don’t laugh, I’ve seen it happen. Remember this is at low speeds, less than 30 mph or so.

If your steering wheel vibration is at a higher speed, such as 55 to 60 mph, it’s almost always tire balance. Vibrations mean that something is out of balance. Things that rotate, such as tires, crankshafts, and axles, all have a certain resonance at a given speed. Engineers deal with this resonance by balancing the component by adding or removing weight at strategic points. This helps prevent a vibration at a given RPM.

You might have noticed that if you go at a slower or faster speed, the vibration goes away. This is due to the resonance effect I’m talking about. There’s a given speed at which a vibration will show up. Hit that speed and the vibration will be pronounced. Go faster or slower, and no more vibration.

Wheel Alignment, Loose Suspension Parts, and Vibrations

It’s a common misconception that a wheel misalignment or loose suspension parts can cause a vibration. This is false. Your vehicle’s alignment is the angle at which the wheels hit the road. It’s not really possible for these angles to cause a vibration. If the alignment is way out, your tires will wear badly. This tire wear can get bad enough to make a vibration begin to develop, but understand that it’s the tire that’s causing the vibration at that point, not the alignment.

Loose suspension parts are another frequent suspect. People sometimes ask me if they have a loose ball joint or some other component causing the vibration they’re feeling. The answer is always, “Loose suspension parts can aggravate a vibration, but they are not the cause of the vibration.” Remember, vibrations are caused by rotating assembles, not necessarily loose parts. In fact, when a wheel is up to speed it acts like a gyroscope. This means that even with loose suspension parts, at speed, you may not notice the loose parts at all. Vibrations can actually create loose parts, sure, but that misses the point. Vibrations are almost always the result of something spinning that’s out of balance. This imbalance is what causes the vibration. I’ve seen vehicles with very loose suspension parts drive smooth as glass down the road. I’ve also seen one wheel weight come off a wheel and it felt like the front end was about to fall apart.

The moral of the story is that you should put loose suspension parts and alignment at the very bottom of the list of things to check when dealing with a highway-speed vibration. They are very rarely, if ever, the cause of such things. Just to be thorough, I’m going to post a video here on how to inspect your suspension.

Vibrations at Idle, Engine Mounts

I cover much of this in the Idle Problems article. I’ll do a brief summary here. If you have a vibration at idle, focus on engine performance first. There might be a cylinder that isn’t putting out an equal amount of power, causing the engine to not run smoothly, or a mixture problem, or some other mechanical cause.

Don’t assume right off that if you have a vibration at idle, your engine mounts are bad. New engine mounts bolted up to a poorly running engine means you still have a vibration; it’s just muffled by good engine mounts. Start with engine performance and perform any necessary repairs. After you’ve done that if you still have a vibration at idle, then look to the engine mounts.

A lot of people tell me they’ve replaced all the engine mounts in their vehicle and they still have a vibration. Then I go through the speech above, and the cause ends up being a vacuum leak or something. Save yourself some time and money and look to engine performance before going for engine mounts if you have a vibration at idle. Some engine mounts are a real pain to replace and expensive; don’t go there unless you have to.

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