Why Is My Car Shaking? (Top 8 reasons)


A shaking and vibrating car can be alarming, and you are correct to investigate the cause. The root of the problem may be simple but could have a more serious outcome if not repaired.

A car commonly shakes and vibrates for the following 8 reasons:

  1. Engine misfire
  2. Loose exhaust system
  3. Flywheel / torque converter fault
  4. Wheel imbalance
  5. Brake rotor imbalance
  6. Faulty tire
  7. Bad wheel bearing
  8. Motor mount faulty

In this post you’ll learn about the most common causes of a car shaking, you’ll learn how to diagnose them, and what you can do to fix it.

Your car may offer us some clues as to what’s going on, for example if the shake happens:

  • Only when you reach a certain speed – See wheel imbalance below
  • Only when breaking – See Brake rotor below
  • Only when the engine is idling – See misfiring below
  • Shakes all the time – See misfiring below

Engine Misfire

Coil over plug

Your engine is a synchronized series of controlled explosions. The energy from these mini explosions is transformed into forward movement by the pistons, crankshaft and transmission.

Most cars will have four cylinders with one combustion (explosion) per cylinder.The even number of cylinders, makes for a smoother sounding engine, odd cylinder engines do exist but aren’t quite as smooth.

Cylinder combustion doesn’t happen simultaneously, they’re sequenced for optimum momentum of the crankshaft.

Each cylinder has it’s time to shine. On every forth turn of the crankshaft (known as a four stroke cycle aka four stroke engine), an explosion forces the piston down the cylinder and doing so turns the crankshaft.

If a cylinder doesn’t combust (fire), that cylinders power is missing from the cycle and causes the engine to run roughly. Often experienced as a shaking or vibration.

The shaking is caused by the uneven number of cylinder combustion’s. Crankshafts are highly engineered bits of kit, they’re finely balanced around the number of firing cylinders.

Any interruption in the firing order and the crankshaft is off balance which transfers into flywheel imbalance (manual transmission), Flex-plate and torque converter (auto transmission).

What Causes A Misfire

Coil

There are many reasons for a car engine to misfire. Luckily for us there are also some very common reasons which we’ll cover right here. As you probably know, your cars engine is ran by a computer. It’s called a PCM (Power-train Control Module) it makes all the decisions about fueling and timing, cooling etc.

It’s other clever function is self diagnoses, it won’t quite fix itself, however they are working on that, but it will flag anomalies and faults. Reading the PCM requires a scan tool and the information is displayed as a code, the code is unique to a circuit or component fault.

It makes sense to read your codes now, before examining the car. The code will point you in the right direction, but also working on the car may cause spurious codes to set which will send you down the wrong track.

A cars engine needs three systems to work in harmony. A misfire is caused by a fault in one of these three systems. You may have a single cylinder or multiple cylinder misfires. A single cylinder suggests a localized cylinder fault and multiple misfires suggest and system fault.

  1. Air/fuel mix
  2. Spark
  3. Compression

Common Causes Of Misfires

Scan tool

Here’s a list of the most common causes of a misfiring engine, and what you can do to fix it. However you will need a scan tool at the very least and only higher end tools will have command “On” functionality. That said scan tools aren’t very expensive, you can pick up a good model for about $35, and about $200 for a scan tool with command test features and oscilloscopes.

Check out the tools I recommend here on the Mechanics tools page.

  • Faulty spark plug – Remove plugs for inspection, misfiring cylinder plug may be wet, dry or oily
  • Faulty coil – Swap coil to adjacent cylinder, check if misfire follows the coil or remains with the cylinder (Coil Over Plug) or check resistance
  • Bad gas – Fill the tank with fresh gas
  • Bad fuel regulator (older cars) – Fuel pressure test
  • Bad fuel pump – Check resistance
  • Faulty injector – Check Resistance
  • Vacuum leak – Test common leak areas, brake booster pipe, split vacuum lines etc.
  • Lazy O2 sensor – Test with scan tool or DVOM
  • Egr valve stuck – Command on with scan tool test
  • Evap purge valve open – Command on with scan tool test
  • MAF – Check flow readings with scan tool
  • Faulty knock sensor – Tap and check readings with scan tool
  • Turbo fault – Check inter-cooler pipes, waste-gate and actuator, vacuum lines and compressor wheel.
  • Head gasket fault – Compression test
  • Valve train fault – Leak down test
  • Piston ring fault – Dry & wet compression test

Loose Exhaust System

Exhaust

Your exhaust system runs the full length of your car, funneling the spent gases to the rear of the vehicle. The exhaust system is fixed to the engine and as such is a source of vibration. Your engine is mounted on rubber blocks (motor mounts) to help absorb movement and the exhaust too is suspended by rubber mounts.

The mounts suspend the exhaust system a few inches away from the car floor, in an effort to absorb the vibrations and prevent exhaust to body contact.

It’s not uncommon for the exhaust rubber mounts to become perished and break. If the exhaust comes in contact with components such as the sub-frame, transmission, linkages etc. The driver may experience the vibration or shake through the steering wheel, pedals or seat.

Have the system checked, replacing the exhaust mounts isn’t complex, however if one has broken the others likely aren’t too far behind.

Flywheel/ Torque Converter Fault

Dual mass flywheel

Symptoms of a flywheel or torque converter fault include shaking at idle and usually less noticeable on the road.

A loose or damaged flywheel or pressure plate can easily cause an imbalance. The dual-mass flywheel is fitted to manual transmission cars and is designed to help smooth out power application. The flywheel is under a ton of stress and is a common failure.

They’re connected to the crankshaft and cause shaking most noticeable at idle.

Wheel Imbalance

Tire condition

Symptoms of a wheel imbalance include a shaking of the steering wheel or a general vibration felt inside the car, but only when moving down the road and usually only at a certain speed.

Your cars wheels aren’t in perfect balance, small lead weights are stuck on to create balance and they must be maintained. Trouble is the weights fall off and create a shake or tremor which can be felt in the steering or in the seat. A tire shop will take care of this without any fuss.

Incorrectly tightening the wheel rim can likewise set up an imbalance. So if the shaking coincided with a flat wheel of a recent wheel off repair, release the wheel and tighten again in a star pattern. See the info-graphic below.

Wheel torque sequence chart

Driving off road can also create an imbalance, it’s worth checking the inside wheel rim for muck buildup. Cleaning the muck usually solves the problem. Worn steering or suspension ball-joints will also cause car shaking in the steering wheel.

Warped Brake Rotor

New rotors

Symptoms of warped rotors include, shaking in the steering wheel under braking. Your brake rotors are at the business of your cars brakes. The rotors are attached to the wheels, the calipers push the pads against the spinning rotors and convert motion into heat energy.

Trouble is, all that friction causes wear. The rotors become thin, overheat and bend out of shape. A brake shop will check the rotors for run out, but if you’ve got pulsing in the brake pedal, you can bet your rotors are warped.

Warped rotors is a common problem. A new set will fix the problem, but you’ll also need a new set of brake pads.

It’s worth noting that incorrectly tightening the wheel can cause brake rotors to warp.

Faulty Tyre or Rim

Damaged Tyre

Symptoms of a bad tyre include a shake in the car which maybe worse at a certain speed. A tyre is mission critical kit, since it’s what keeps you on road.

A tire that’s faulty goes out of shape and creates a horrible imbalance. Tyre flat-spots are also common in a car that’s laying up. It causes, the tires to develop flat areas. Driving on flat-spot tires is like driving a car with square wheels.

Flat spotted tires may come good after a few miles driving, but if they don’t come back into shape when warm, a new set of boots are needed.

A buckled or damaged rim is also a common cause of steering shake, check your wheels for wheel rim damage.

Worn Wheel Bearing

Symptoms of a worn wheel-bearing include vibration and shaking together with a roughness and a humming noise relative to speed. You may also notice the sound changes when turning a bend or corner.

The wheel bearing is attached to the axle and it allows your wheel spin freely. The bearings simply wear out as a car ages and wheels turn enough times. It’s usually the front bearings that wear first as their doing the heavy lifting.

Replacing the bearing will fix the problem.

Motor Mount Faulty

Engine mount

Symptoms of a faulty motor mount include vibration rough noise creaking or knocking especially at take off or changing gear.

Your engine is vibration central, and without effective cushioning it would shake your teeth out. Motor mounts are blocks of rubber that the engine sits on, the rubber absorbs most of the harshness. Higher end cars may have oil filled motor mounts or dynamic mounts which are PCM controlled.

A broken engine or transmission mount is pretty common.

John Cunningham

John Cunningham is an Automotive Technician and writer on Rustyautos.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write articles that help fellow gear-heads with all aspects of classic car ownership, from tires to roof aerials and everything in between.

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