Typically you’ll always first experience the car shaking when on the highway with the car loaded and a few hours of driving ahead of you. Not that there’s ever a convenient time for the car to go wrong; this is always one of the worst.
The good news is this article has all of the possible causes.
Although 13 potential reasons your car is shaking when driving fast might sound like a lot. Everybody describes fast and shaking in different ways; to one person, 40 mph is fast, yet to another, 70mph is fast, so I wanted to include all scenarios and variations of shaking.
Reasons your car is shaking when driving fast
Even though each issue below can cause the car to shake when driving fast, they all have unique other symptoms to listen to or feel for.
1. Tire defects
A problem with car tires is one of the most common causes of a car that shakes when driving at any speed. But, in this instance, it could be the first noticeable sign of a collapsed tire belt.
When a steel belt (ply) that runs through the tire snaps, it allows the air to push a bubble out of the tire, in this case, on the tread section. The tire becomes slightly egg-shaped instead of perfectly round. Sometimes it can take quite a while for a broken belt in the tire to get bad enough that car becomes completely undrivable. So when this type of issue first happens, you may only experience shaking or vibrating when getting up to higher speeds. You may also experience a lot of road noise with a tire defect.
2. Wheel balance
Most of the time, the wheels out of balance can be felt at speeds of around 50 – 60 mph, and then when driving faster, the issue tends to disappear. However, it does depend on what you call driving fast; if it is at speeds of around 60 mph and the steering wheel vibrates, it’s probably just a front wheel needing rebalancing.
One thing to be aware of is the rear wheels can sometimes be felt at higher speeds, such as 70+ mph through the car seats. For these reasons, you should always rebalance all four wheels simultaneously instead of just doing the fronts.
3. Buckled rim
A buckled rim causes the car to shake, similar to the wheel balance. Defects in the rim usually appear from potholes in the road, which causes the rim to be out of balance. Depending on how bad the buckle is, it may not be possible to rebalance the wheel and get it right. A repair or replacement is the only way to solve the shaking in these instances.
Another problem with rims is if the buckled wheel was previously straightened and the rim cracked. Repairers often weld these cracks, leaving a giant metal blob on the wheel, causing a balance problem. This can make it incredibly difficult to balance the wheel correctly, and you may only solve the issue by replacing it.
4. Bent or damaged driveshaft
Although a driveshaft is part of the transmission, I wanted to keep this one separate. It’s surprising how often I see cars I’m working on that have been driving around with a bent or damaged driveshaft, which are challenging things to damage.
Most commonly, they get damaged from debris in the road or a side impact to the wheel (although this has to be a pretty hard impact), causing the driveshaft to either be missing a good chunk of metal or bend. You will also experience other issues, such as clunking and squeaking noises alongside the vibrations when driving. Depending on how bad the damage is, it might only be noticeable as a shake once you go fast. But now the vibrations are causing further damage to the transmission and the engine.
5. Wheel alignment
Most would associate a wheel alignment problem with the car pulling off to one side when holding the steering wheel straight. While that is true, when you get up to high speeds, you can get a scenario where the toe angles of the wheels are fighting against each other.
Imagine your two front wheels pointing towards each other and each wheel trying to pull the car in a different direction. It can make the vehicle feel unsteady and has been known to cause cars to shake at high speeds.
6. Suspension problem
There are so many parts to a car suspension that absorb vibrations and keep the car planted on the road. Usually, when suspension components are causing a problem, you will experience knocking noises; however, the car will also feel unsteady and may shake when driving fast. The most common issues to look out for are:
- Worn bushes
- Worn ball joints
- Bent or damaged suspension arms
- Broken coil spring
- Worn shock absorbers
- Bent rear axle
7. Brake issues
Brake issues when driving fast are usually only relevant if you experience shaking when you are braking. However, there is one specifically; brake binding, which will cause the car to vibrate at high speeds, even when the brake pedal isn’t pressed.
What’s happening is either the brake caliper has seized, or the hose has collapsed, and the brakes are being partially applied. You drive the car at higher speeds; the brake heat rises, and the rotor warps.
You will feel this as shaking through the pedals or steering wheel, depending on which wheel is causing the binding. You may also experience brake fade. If you stop the car and get out to look through the wheels, there should be a strong burning smell if this is the case. Alongside some smoke and a glowing red or blue-tinted brake rotor at one of the wheels.
8. Wheel bearing
The cause of a wheel bearing failure is often wear and tear. The inner and outer components of the bearing can become loose or worn, resulting in excessive play and misalignment of the track the bearings spin on.
When driving, the wheel is unstable and moves around from side to side when it should be firmly in the same position. The issues are most noticeable as shaking when driving quickly and a humming noise that gets louder the faster you drive. If left unaddressed, a faulty wheel bearing can lead to the wheel falling off with the hub still attached.
9. Spark plugs
Spark plugs can cause engine shaking at high speeds for various reasons. One common cause is a misfire, which occurs when the spark plug fails to ignite the air-fuel mixture correctly or on time. This will lead to the engine vibrating or shaking. This can happen at higher speeds because the coil pack provides energy to the spark plug, struggling to cope at higher speeds, or the spark plugs are loose or damaged.
Fouled or worn-out spark plugs can also contribute to engine shaking. Deposits on the electrodes or eroded electrodes can weaken the spark, again leading to misfires and the associated shaking. Fouling is most commonly caused by oil soaking the tips of the plugs. This happens at any speed, but when an engine is hot and you are traveling fast, the oil becomes thinner, and if there is a weak piston ring, the chances of oil leaking into the combustion chamber are much higher.
Incorrect spark plugs for the engine can also cause engine shaking if they have the wrong heat range. If the spark plugs cannot dissipate heat correctly or are not suitable for the engine or driving conditions, overheating or pre-ignition will occur. These are more noticeable when driving fast because of the rise in engine temperatures.
One thing to note with spark plugs is sometimes it’s not the spark plugs directly causing the issue. Spark plugs rely on the coils or coil pack converting low voltage into the high voltages spark plugs need to operate. It could be a supporting component causing the illusion that the plugs have failed.
10. Engine mounts
The engine can move around excessively with worn motor mounts, as its vibrations and movements are no longer absorbed. Instead, vibrations can be felt through the body of the car. It’s not common to experience shaking from worn motor mounts when driving along. Most commonly, you will experience a shake when starting the vehicle or switching the engine off for a second or two.
However, when driving at high speeds and changing gears, there will be a second or two of extra movement until it settles into place. Also, if you apply more gas, then let off, and reapply, like when driving in traffic, the engine will be thrown backward and forwards. You won’t feel this when the motor mounts are good as they absorb this movement.
The transmission is often an overlooked area of a car that causes vibrations and shaking. However, it’s much more common than you might think.
Low transmission fluid levels or dirty, contaminated fluid are specific problems that can result in improper lubrication causing the transmission to overheat. This can lead to gear slippage and vibrations. Vibrations typically mean that driving with a low fluid level has caused damage to appear on gear teeth or moving components in the transmission.
One thing to note is low transmission fluid level means there is a leak. No combustion process is happening inside the gearbox, so the fluid is not consumed.
Additionally, a failing torque converter or differential can cause shaking. The torque converter transfers power from the engine to the transmission. At the same time, the differential is responsible for equally splitting that power from the transmission to the drive wheels. Any slight issues with either will cause unusual shaking at vibrations at all speeds but will be more apparent when driving fast.
12. Fuel supply problems
Problems with the fuel system or related component can also cause the engine to shake. Essentially, the faster you go, the more fuel the engine needs, so if there are any interruptions in the fuel pressure or the amount of fuel getting to the engine, you can expect to feel such problems. The most common issues you can expect to experience are defects with the following:
You can expect to feel like the engine is stuttering or shaking with any of the above issues. Common other symptoms you’ll notice include the engine refusing to accelerate when you get to a certain speed and feeling the engine jerking when driving at a constant speed.
Curing these problems can sometimes be done with a good quality fuel treatment.
13. Engine internals
Inside an engine is several perfectly balanced rotating components. An engine doesn’t lose balance weights like a wheel can. Typically when a part is out of balance, it is damaged beyond repair. Usual causes are driving an engine low on oil or when a motor is modified well beyond a component’s limits. Damage from driving low on oil happens because of friction causing a rise in temperatures. Friction between moving metal components is due to a lack of lubrication normally provided by the engine oil.
Crankshaft or connecting rods are the components susceptible to get damage, usually bent. They will create vibrations as they rotate when damaged. These vibrations strengthen as you rise through the rev range or drive faster.
Avoid driving if you do suspect engine damage. Eventually, one of these components will ultimately fail, and the engine will grind to a halt. Not cool when driving at speed!
How to diagnose a car that shakes when driving at high speeds
When diagnosing the exact cause of a car that shakes when driving at high speeds, first, you should conduct a road test. You may need to find the right road which will legally allow you to get up to the speeds necessary to experience the problem. Stay within the speed limit! An excuse of trying to find out why a shakes at 90mph will not sit well with a police officer.
When carrying out a road test, you need to hone your senses and pay attention to where the fault is coming from, i.e., is it louder on one side of the vehicle, is it coming from the front or rear, any warning lights on the dashboard and what other symptoms are you experiencing, which will give you a good indication on what you need to look at first. The engine management light is always good to look out for, even if it flashes on for a few seconds and goes away. The fault code will be stored in the ECU fault memory so that a code reader will tell you precisely the issue.
Is it safe to drive when the car is shaking?
Honestly, you should avoid driving with any fault on a car. When deciding if the vehicle is safe to drive with any fault, specifically when shaking at high speeds, you must first know the issue.
For example, if the issue is the wheels out of balance, then you carry on like this forever, in theory. However, the tires will wear out unevenly, and your arms will hurt after a long drive. But if the issue is caused by an engine or fuel supply problem, for example, you could drive for 5 minutes, the car completely shuts off, and the engine seizes.
Using the information in this article and my methods for diagnosing a car that shakes when driving at high speeds, you can quickly identify the issue and then make the necessary repair. However, these problems can sometimes be tricky to self-diagnose without experience. Having a mechanic take a look may be the best cause of action, typically a 5-minute test drive, and they will probably say x is the problem.