What causes vibration in a car
A car has many moving or rotating parts that could cause vibration. Finding the source of vibration is not always easy; however, there are few common causes that we will look at in this article. The key to diagnosing a vibration is to match it to other events. For example, is the vibration only present during braking? Does it disappear when brakes are not applied? Does the frequency of vibration matches the tire rotation speed? Does the vibration get worse with the transmission in Drive? Does it change with the engine speed? And so on. When you bring your car for repairs, this type of questions will help your mechanic to find a problem faster.
Wheels and tires vibration
An out-of-balance tire can cause a vibration or 'shimmy' at highway speeds with the frequency matching the tire rotation speed. For example, a 215/50 R17 tire that is out of balance will produce a vibration with a frequency of about 13-14 Hz at 60 miles per hour (96.6 km/h). When a new tire is installed on a rim at a repair shop, it's balanced on a tire balancing machine. The process involves attaching small weights to offset variations in weight distribution across the wheel. Over time, as the tire wears, the weight distribution can change. Similarly, when the dirt or ice sticks to the wheel, the weight distribution across the wheel changes causing a vibration. See the example: Ice on the wheelIce on the wheel.
Another common issue with the tires that can cause vibration is out-of-roundness. An out-of-round tire can also cause vibration that is usually more pronounced at highway speed (60-70 mph or 96-113 km/h) and it feels like minor front-to-back shudder. Weight-balancing an out-of-round tire won't help with the vibration - a tire could have uniform weight distribution, but if it's out of round, it will still cause vibration.
Hunter GSP9700 Road Force Balancer
Photo: Hunter Engineering Company
A tire could be out of round for many reasons, including a manufacturing defect, improper installation, damage after hitting a curb, excessive wear, etc. A fairly common example is when tires develop flat spots after a vehicle has been parked for a long time, especially in cold weather.
Sometimes, tires with this type of flat spots can round out by itself after a car is driven for a while and the tires are sufficiently warmed up; typically after a long highway drive. In other cases, flat spots can stay permanently. Your mechanic will be able to see if any of your tires is out of round by spinning them on the tire balancing machine. An out-of-round tire can be easily detected on a newer tire balancer that has a feature called Road Force that measures radial and lateral tire forces. In some cases, the out-of-roundness can be minimized using this type of tire balancer by match-mounting or matching the tire and rim runout, placing the 'high' point of the tire on the the 'low' point of the rim. Balancing tires with Road Force could cost from $80 to $150.
A bent rim can cause a very similar vibration. Usually alloy rims get bent on the inside, so it's difficult to see if the rim is bent unless a car is lifted on a hoist or the wheel is spun on the tire balancing machine. If an alloy rim is bent, it must be replaced. A new alloy rim could cost anywhere from $180 to $650 depending on a car.
Vibration caused by brakes
Bad brake rotors or drums can cause a vibration that is present during braking. Typically this type of vibration is more noticeable when braking at high speeds, for example, when exiting the highway. This type of vibration could also be accompanied by shaking of the steering wheel and pulsation of the brake pedal. Commonly this issue is caused by run-out or thickness variations across the rotor braking surface, although other reasons are also possible.
Sometimes, this issue could be caused by unevenly-distributed rust spots on the brake rotors, especially if a car was parked outside in a rainy weather for a few days without moving. The brake rotors could also be warped due to excessive heat or other reasons. Depending on the diagnosis, the repair could involve a brake job with machining or replacement of the brake rotors or drums. The cost of repair could range from $250 to $480. Machining means cutting a thin layer from a brake rotor or drum on a special brake lathe to make the surface smooth and uniform across the rotor or drum. When doing a brake job, it's better to use the OEM or other high-quality brake pads and rotors; many problems with brakes including vibration are often caused by using inferior quality parts.
An engine inherently produces a vibration, as it has a lot of moving and rotating parts. To isolate the engine vibration from being felt inside the car, the engine and transmission are attached to the car body with shock-absorbing rubber engine and transmission mountsLiquid-filled engine mount. Typically there are three or four mounts holding the engine and transmission unit. Some of the engine mounts are filed with liquid to better absorb the vibration. Here are some of the examples of engine vibration causes:
A bad engine mount can cause the engine vibration be felt inside the car. Often this type of vibration is more noticeable at idle, with the transmission in Drive or Reverse. A bad engine mount could be diagnosed in a repair shop; replacing an engine mount typically costs from $150 to $400. Another common situation is when the engine mounts are misaligned or installed improperly, for example, after an accident repair. This also could cause more engine vibration to be felt inside a car.
An exhaust pipe that for some reason touches a car body can also cause the engine vibration to be felt inside the car. An exhaust pipe is connected to the engine and isolated from the car body by rubber hangersExhaust hanger. If an exhaust hanger breaks or an exhaust pipe gets bent when hitting a bump or backing up into a curb, the exhaust pipe can directly contact the car body transferring the engine vibration to the body at the point of metal-to-metal contact. The repair depends on the damage.
A misfire, or when some of the engine cylinders don't work also causes vibration. When the engine misfires, it runs unevenly, shakes and lacks power. Typically when the engine misfires, the "Check Engine" or the engine-shaped light comes on or flashes on the instrument panel. The repair depends on the cause of misfire.
Many engines have a balance shaft to reduce the vibration. Often a balance shaft is driven by the timing belt or chain. A balance shaft must be properly timed to reduce the vibration. An improperly timed balance shaft will cause increased vibration of the engine. This typically happens if during replacement, the timing of the balance shaft wasn't set properly.
The term drivetrain vibration is usually refers to vibration caused by components connecting the vehicle engine to the wheels, including a transmission, drive shafts, CV joints and a propeller shaft in a rear- or four-wheel drive vehicle. Here are few common examples:
A bad u-jointFront u-joint of the rear propeller shaft of the 4WD truck, which is a part of the propeller shaftPropeller shaft in a rear- or all-wheel drive vehicle, can cause a vibration that is mostly noticeable under medium acceleration or less often, deceleration. The frequency of vibration caused by a bad u-joint is higher than that of tire vibration because the propeller shaft rotates about 3-4 times faster than the tires. A u-joint has four needle bearings that are packed with grease and sealed. Once the seal is damaged, the grease comes out and water gets in causing corrosion. Typically a bad u-joint looks rusty and might be jammed or have excessive free play. Replacing a bad u-joint is not very expensive.
Some cars use rubber flex joints on a propeller shaft. A bad flex joint will cause a similar vibration with the frequency matching the rotation speed of the propeller shaft.
Some automatic transmission problems or using wrong transmission fluid could cause shudder on acceleration. Automatic transmission is very expensive to repair or replace.
A bad CV-joint in a front-wheel drive car can cause side-to-side vibration, mostly noticeable at acceleration. The CV-joints are usually replaced as a complete driveshaft, which could cost $350-800.