Top 3 Reasons Why Cars Vibrate

Here we’ll review the top three reasons why cars vibrate while driving. The key words from the last sentence are while driving. An automobile can also vibrate at idle or all the time. This article addresses the situation, when the car runs smoothly in park, but as it begins to roll down the road a vibration develops. Often this vibration worsens with road speed.

With that said, if you have a vibration all the time some of the leading causes include worn out motor mounts, rough engine idle or an engine misfire situation. You can read up on those articles to solve car vibrations felt while standing still.

Why Cars Vibrate While Driving

Auto Facts Repair Manuals
Auto Facts Repair Manuals

For the mechanic diagnosing the reason cars vibrate starts with a road test. Experienced technicians reduce a lot of diagnostic effort by driving the car at varying speeds and conditions.

Motorists seeking to solve this common car problem efficiently should go along on the road test with the mechanic.  This prevents any miscommunication between the service writer and the person actually working on the car.

In the following article we’ll point out what each problem feels like while driving. In addition, we’ll review how professional mechanics can eliminate possible causes using the actual symptoms of the problem. Finally, in each section we’ll talk about what it takes to repair these common conditions that drive motorists crazy.

Vibration from Tires and Wheels

The most common reason cars vibrate often points to a wheel or tire problem. They do an excellent job of balancing the wheels and tires at the factory when the automobile is new. This high-speed precision balancing can lose its effectiveness over time. Some of the reasons include normal tire wear and slamming into potholes.

Tire and Wheel Balancer
Tire and Wheel Balancer

As the tires wear they can change their shape and no longer match the precision balancing from the assembly line. However, one of the most common things mechanics find when a tire goes out of balance is a missing wheel weight. If an automobile slams into a pothole the jarring action can knock factory installed wheel weight from the original installed location.

Even if all of the weights maintained their original position it’s possible for the wheel itself to suffer damage. This becomes especially true for vehicles with sporty aluminum wheels. A steel wheel and a hubcap hold up much better against the blunt force trauma of a pothole collision. The aluminum sport wheels aren’t as strong.

In either situation of a bent wheel or a tire needing re-balance, the symptoms often become more severe when the car increases speed. In fact, drivers often complain that they feel the car vibrate at 30 mph and above. Also note that when you have a tire and wheel vibration applying the brakes and accelerating have no effect on the level of the disturbance. In order to solve this problem it’s necessary to mount the wheel on a tire balancing machine. Not only can the technician diagnose the out of balance, but they can also see if the wheel is bent.

Vibration when Applying the Brakes

reasons cars vibrateAnother common reason why cars vibrate relates to brake system problems. We separate this problem from a tire balance or a bent rim issue with a simple road test. If the vibration only occurs when the driver applies the brakes, then we can take the rims and tires off of the possible causes list.

Since most of the weight of the automobile is supported by the front wheels, problems with the front brakes remain more common than problems with the rear brakes. More specifically, front rotor warping issues usually cause a driver complain of vibration while stopping or slowing down from highway speeds.

Mechanics separate front brake rotor issues from rear brake rotor problems in two ways. If the front brake rotors are warped enough to generate a driver complain of vibration, you’ll often feel this in the steering wheel. However, when the rear brake rotors cause the vibration issue you won’t feel it in the steering wheel at all.

Mechanics slightly apply the emergency brake while driving and see if the vibration worsens. Using this method they’re only applying the rear brakes and therefore distinguish front and rear rotor problems from each other. Solving a brake system vibration usually requires a brake job that includes replacing the rotors.

Common Drive-line Vibration Problems

Bad driveshaft u-joint
Bad driveshaft u-joint

In some cases an automobile that vibrates under certain circumstances can point to a drive-line vibration problem. On rear wheel drive automobiles, we’re talking about the driveshaft that runs from the transmission to the rear differential. On front wheel drive automobiles this refers to front drive axles, CV and tripod joints.

The important thing to remember about drive-line vibration problems is how they feel on the diagnostic road test. In both a front wheel drive and rear wheel drive set up these drive-line vibrations become more evident when applying power. More specifically, drivers feel the vibration while accelerating. In fact, after they reach highway speeds and take their foot off the gas the vibration might disappear completely.

On rear wheel drive cars and trucks problems with the front and rear universal joints become common on high mileage units. However, in rare cases, the driveshaft itself can become out of balance. This is often attributed to physical damage to the driveshaft from road debris. Mechanics diagnose these rear wheel drive problems by hoisting the vehicle in the air and checking for play in the universal joints while looking for damage along the driveshaft.

On front wheel drive automobiles loose, worn out or binding constant velocity joints can be another reason why cars vibrate. The driveshaft on the front wheel drive automobile has a CV joint out toward the wheel and a tripod joint close to the transmission. These flexible joints allow for smooth power application, regardless of wheel position. Mechanics can raise the automobile and check for looseness in these components.