Why Is My Car Shaking?

Vehicles shaking or vibrating while accelerating, driving down the highway, braking or idling are among the most frustrating and common automotive complaints. A shaking car is scary, especially if you don’t know why it’s shaking. Understanding and recognizing the causes and what you can do to fix it are critical to your safety and the overall health of your car.

Why Do Cars Shake?

Many things can cause a car to shake because vehicles contain lots of parts that spin (tires, wheels, axles) and move (brakes, suspension, transmission, engine). Each requires a different fix, and it can take some detective work to determine exactly what you’re dealing with.

When Do Cars Shake?

Car shaking when idle

A car will shake when idle when the engine isn’t running smoothly. Depending on the specific cause, some shaking can be more severe than others. You may also notice or feel the revolutions per minute (RPM) randomly changing.

Due to greater engine load and lower engine speeds, rough (shaking) idle is usually more pronounced in “Drive” when sitting at a stop light. Consequently, higher RPM when idling in “Park” can help smooth out a rough idle. Depending on the severity of the problem, you may also experience stalling or backfiring.

What to do?

A smooth-idling engine indicates your engine’s air fuel mixture, fuel, ignition and emission systems are working exactly right. If that’s not the case:

• Check, inspect and replace a dirty air filter and PCV valve that can starve the engine of air or fuel.
• Check for vacuum leaks.
• Replacing worn spark plugs, defective or damaged ignition coils, ignition wires or the distributor cap — all DIYable fixes.

A dirty fuel filter or clogged fuel injectors can also cause rough idling and shaking.

• Try replacing the fuel filter and add fuel injector cleaning treatment to your fuel tank yourself. Filters are inexpensive and easy to swap out. Check your owner’s manual and be sure to replace filters and spark plugs at the manufacturer’s recommended intervals.
• If this doesn’t fix the shaking, it’s time to bring your car in for service.

On acceleration

Low automatic transmission fluid (or a slipping clutch disc on a manual transmission) can cause a shudder and shaking on acceleration. See if the Check Engine Light (CEL) is on when your car begins to shake during acceleration. If it is, it most likely means a dirty, failed or failing mechanical component, or one of many engine sensors is sending haphazard or intermittent data to the computer (ECM).

What to do?

• Pull over and determine if your car is safe to drive.
• Check the automatic transmission fluid and clutch master cylinder levels. Your owner’s manual will show you where the transmission dipstick and clutch master cylinder are and which specific fluids your make, model, and year vehicle needs.
• If the CEL is on, do a visual under-hood inspection. Check for loose, cracked or damaged wires, hoses or electrical connectors.
• Stop driving if the CEL is flashing. A flashing CEL indicates a serious drivetrain problem. Sensing a problem, the ECM puts the car into “Limp Home Mode” which greatly reduce engine power and allows you to drive to a repair shop.
• Use common sense. Leave CEL repairs to the pros and call for a tow, if in doubt.

While driving

Tires and wheels

Worn, damaged, under/over-inflated or out-of-balance tires cause vibrations and shaking at medium to fast (highway) speeds. There are some common causes for this. A damaged tire, or a bent or cracked wheel from bouncing into a curb or getting walloped in an accident, will cause your car to shake when driving.

What to do?

• Check tire pressure. Under- or over-inflated tires quickly overheat and wear abnormally, leading to low and high-speed vibrations.
• Inspect your tires for sidewall damage and bulges, along with excess wear on the edges or the middle of your tires.
• Have your tire service center rotate and balance your tires and wheels. Check if an out-of-spec wheel alignment or a worn or bent suspension part aren’t causing unusual tire wear (cupping, scalloping, feathering).
• Driving safety depends on basic tire maintenance. Pick up tread depth and air pressure gauges online or at your local auto parts store and use them regularly. Replace any tire that has tread measuring 4/32-in. or less.

Suspension, hub bearings and axles

Loose, worn or damaged suspension parts (bushings, tie-rod ends, ball joints, mounting hardware), wheel hub bearings or CV (constant velocity) joints will all cause shaking and vibrations at any speed. They tend to be more pronounced when the wheels are fully turned and traveling at lower speeds. A bent or worn drive axle, hub bearing or out-of-balance driveshaft will also cause shaking while driving.

What to do?

• Check if the CV joint rubber “boot” seals are cut or ripped. Water entering through a torn CV joint seal will quickly damage the joint, causing grinding and shaking.
• Worn or damaged suspension parts, wheels or wheel hub bearings can lead to irregular tire tread wear, causing your car to shake. Damage can happen in an accident or from simply hitting a curb or pothole.
• When in doubt, rely on a repair shop to diagnose and correct the cause of abnormal tire wear and shaking.

While stopping

Brakes

If shaking happens only when braking and stops when your car does, the brake system is the likely offender. Common problems include worn, loose or contaminated brake pads and warped or cracked disc rotors. Rotor warping may be due to overheating. Harsh driving or rusty/corroded brake caliper hardware allows the brake pads to drag against the rotors while in motion.

What to do?

• Replacing pads and rotors can be a DIY project, but brake hardware or caliper repairs are best left to the pros.

Other less-likely causes

Loose or missing wheel weights, snow jammed into the back side of a wheel, road tar or a plastic bag wrapped around a drive shaft or axle can cause shaking while driving. Although unusual, collapsed engine mounts or a damaged crankshaft damper can cause your car to vibrate and shake at idle.

What to do?

Carefully clear the snow from the wheel, cut off the plastic bag, or scrape off the road tar yourself. If a wheel weight came loose, let the pros rebalance your tires. Leave motor mount and damper problems to the experts to diagnose and repair.

Even if the shaking is subtle or only occurs occasionally, don’t ignore it. Diagnosing a shaking problem as soon as it begins is important. Although fixing a shaking car may be simple and inexpensive, it could also become considerably more costly if neglected.

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