Nothing is more unpleasant but especially worrying than driving a car and it starts vibrating for no apparent reason. It is, therefore, better to find the origin of this symptom and to fix it as quickly as possible to prevent any further potential damage or, even worse, a car accident. Let’s see what are the most common causes and solutions in case of a car vibration under acceleration.
First things first: locate the problem
First of all, you will have to try your best at isolating the probable cause of the problem while trying to detect if it’s rather coming from the engine, the powertrain, the suspension, the direction system or the wheels. Most vibration problems at high speed are related to the wheels in some way while vibrations happening under acceleration are usually related to the engine or powertrain.
To help you with that, first try to notice if the vibrations are related to accelerating or braking, if it happens when it’s cold outside or not and if it’s a frequent occurrence when changing gears or not. Have you hit a pothole recently? Are your tires excessively worn out? All these hints will help you find where the problem is originating from and allow you to bring your investigation a little further.
If you notice vibrations when a gear is engaged, if it disappears when the clutch is depressed or when you put the transmission in neutral, you’ll need to focus primarily on the transmission components next and so on. Vibration problems related to the engine will usually vibrate according to the vehicle’s rpm. Make sure you don’t mix up rpm and speed though. If the vibration reacts linearly and according to the speed of the vehicle instead of the rpm, the problem has probably more to do with the wheels or anything connected to it.
Most common causes of vibration under acceleration
I’d rather warn you. Because most components inside the powertrain and drivetrain systems move at a really high speed, any incorrectly balanced part can cause a vibration. An engine with bad combustion, worn parts inside the transmission or even a slight misalignment in the wheels can also cause a vibration. This list is pretty exhaustive and following it point by point and eliminating them one by one to find the cause of your problem may be really time-consuming. Trying to at least locate the problem first by performing a test drive to pinpoint the problematic system first is highly recommended. For now, let’s focus on the major causes and we’ll talk more about troubleshooting a little later in this article.
Incorrect wheel balancing
The first thing any mechanic will think about when having to deal with a vibration problem is the wheel balancing. And a quick check-up on the wheel balancer will usually give them a good idea if this one will be a quick fix or if it will need a more advanced diagnosis.
An incorrect wheel balancing can happen for numerous reasons.
- Lost wheel weight: Wheel weights sometimes fall off when you hit potholes and bumps. If you have two sets of rims and tires for winter and summer, the fact that you are not switching the tires on the same rims every season and thus get new weights installed, they can rust and fall out. It happens sometimes. If your car is equipped with mag wheels that don’t have a rim lip, the wheel weights are usually stuck to the inside of the wheel using a sticker-like material and water and snow can often cause the weights to fall off. Stick-on wheel weights don’t always last as long as standard ones but I guess it’s the price to pay for having badass chrome wheels on your ride.
- Deformed wheel: If you hit a big enough pothole, one of the wheels could bend and cause a misbalance. This happens even more with bigger aftermarket mag wheels. RTX models from a couple of years ago are a good example as they were widely known by car enthusiasts to bend pretty easily. The cheaper your wheels are, the easier they will bend but a big enough hole can make any wheel bend no matter how good they are.
- Deformed tire: Just as for the wheels, potholes can also crack the inside metal layer of tires and make them either wavy or create a bump on the sidewall of the tire. Both of these situations will cause an improper balance of the tire and will definitely create vibrations while driving.
- Snow, mud or dirt inside the wheel: This one is pretty frequent and people don’t always think about it before bringing their car to the repair shop. If you were just stuck in a snow bank or drove in a mud pit and your car starts shaking at high speed, think about stopping the car on the side of the road and inspect the inside of your wheels for dirt. If losing a 0.75oz wheel weight can make your car shake, imagine what a 0.5lb of mud stuck inside your wheel can do!
When a mechanic performs an alignment job on your vehicle, he is basically making sure that all 4 wheels are parallel to each other. I say ‘basically’ because a correct alignment is a lot more complicated than that since most vehicles require a slight toe-in, i.e. front wheels pointing slightly inwards, to help the vehicle drive in a straight line even when you are not holding the steering wheel. The camber and caster also need to be correctly set and only one or 2 degrees out can make a big difference in your vehicle’s handling.
All this is really hard to put in layman’s terms and you may be a little lost if you aren’t a full-fledged mechanic. Simply remember that an improper wheel alignment can cause an annoying vibration at high speed and that there’s is no way to verify it by yourself. All those backyard mechanic tricks like using a rope or a level or anything else than a laser alignment machine is simply worthless.
The only incorrect alignment sign you can visually notice is unevenly worn tires. When one or more of your tires is worn out only on the inside or the outside of the tread, it usually indicates an incorrect toe or camber setting. The vehicle might also drag to one side or the other when you let the steering loose. The only drawback to this is that until the time you are able to detect uneven wear on your tire, you may well rush to the shop to get an alignment job but it will be too late and you will still need to replace the defective tires.
And tires are expensive.
To avoid that, get your car aligned at the same time as you get your winter tires on or at least once a year. Paying for an unnecessary alignment every year or so is still a lot cheaper than having to buy a new full set of tires.
Worn or loose suspension component
Ball joints, as they wear out, will create a space between the actual ball and its seating which will ultimately make the wheel shake while driving. The vibration will get worse and worse according to the vehicle’s speed. A knocking sounds when driving over potholes is a good indication that one of your ball joints needs to be replaced.
Just as with ball joints, time will leave its mark on control arms too. Bushings used to mount the arms to the vehicle are made out of polyurethane and will not last forever. They tend to dry out and crack and will become loose after a while. If they are not replaced quickly, the vibration can become a real problem and cause more damage to other suspension components. Do not take this one lightly and get it fixed as soon as you can.
I know, wheel bearings aren’t really part of the suspension system but I decided to include them here since they are placed inside the knuckle and consequently, will often be heard and felt through the shock absorbers and coil springs.
Wheel bearings don’t typically cause vibrations though, or at least not until they are totally destroyed to the point where the ball bearings start to come out of it, creating a loose between the inner and outer cups. I strongly recommend that you replace a noisy or loose bearing way before that. The small ball bearings are pretty much the only thing holding your wheel to the spindle and you really don’t want to lose one while driving at high speed.
It’s safe to say that almost any faulty component inside the gearbox can make it vibrate, jerk or stutter, and transfer the vibration to the rest of the car.
Improperly balanced input and output shafts, worn out drums, incorrect oil level can all cause added restriction, vibrations, and incorrect gear shifts.
Typically, the best way to find out if the vibration is coming from the transmission or not is to put the car in neutral or shift gear as soon as it starts to vibrate. The vibration should stop, change or at least slow down. If the vibration stays the same, the problem is probably coming from somewhere else.
On a manual transmission, a spotted or uneven flywheel can provoke significant vibrations but can also damage the clutch in a few months. The vibrations will be felt when the clutch is not in use and when changing gears.
Bent or improperly balanced driveshafts can also cause vibrations at high speed. On FWD cars, it’s pretty rare but it happens a lot on RWD and 4WD vehicles. Stuck or seized universal joints can do the same thing. The vehicle will start to shake at about 50km/h and the condition will only get worse the faster you go.
Most driveshafts are balanced from the factory and balancing weights are welded to it to achieve a perfect balance. Just like with wheel weights, they can fall off when they begin to rust so the older the vehicle is, the more likely it is to happen. Also, any foreign object hitting the driveshaft with enough strength can bend it and it will need to be replaced.
Injection and fuel delivery
On pretty much any internal combustion engine, 2 strokes, 4 strokes, gas or diesel, if the air/fuel ratio is not perfectly maintained because the injectors are not working properly or a gas line is leaking for example, it will create misfires and misfires will make the engine stutter and vibrate.
An injector problem will cause the engine to shake whether you are parked or not. Faulty injectors rarely are an intermittent condition. They either work or they don’t.
Fuel pumps, on the other hand, tend to be intermittent at first, until they ultimately fail completely. If your car stalls or start stuttering, try carefully hitting under the fuel tank with a rubber hammer. If the problem goes away, you probably need to replace fuel pump.
Defective spark plugs may prevent one or more of the cylinders from operating correctly. If your spark plugs are worn or dirty, they won’t be able to create a nice and powerful spark and will not ignite the air/fuel mix contained in the cylinders. Without that much-needed explosion, the crankshaft will not turn at the proper speed for the whole revolution and the engine will run erratically., transmitting vibrations to the whole car.
Same thing for any of the other components of the ignition system. Distributors, rotors and ignition wires may well be a thing of the past now but the coil-on-plug system still needs to work correctly for the spark to light up the fuel. A bad or missing sensor reading can also cause the PCM to not send the firing signal to the coils too. Most of these problems should make the check engine light to light up so make sure to always check your DTCs first. Any of the p0300 to p0308 diagnostic trouble codes will let you know if there’s something wrong with your ignition system and misfires are happening.
There may also be other compression or firing problems such as carbon deposit in the combustion chamber or an incorrect timing sequence of the intake and exhaust valves. A leaking engine head gasket could also cause misfires and make your engine vibrate.
These problems are difficult to identify and also sometimes difficult to fix. Compression tests will be needed as well as an internal check-up using a small camera or the removal of the engine head will be required to perform a thorough inspection. If you don’t know what you are doing, leave this one to professionals. This one is not for beginners.
Air intake problems
A clogged air filter will obviously prevent enough air to reach the engine but a leaking air intake can also bring false sensor readings. In fact, any leak in between the air filter and the engine head will bring more air to the engine than what the mass air flow sensor is measuring and will cause engine misfires.
A malfunctioning mass air flow sensor can also create the same symptoms without any air leaks so be warned. Always use an OBD-II scanner to verify that the data sent by the MAF sensor is outside the normal threshold before replacing it. If the data seems normal, the problem is probably caused by an air leak instead of a malfunctioning sensor.
Recorded DTCs can also help you find out if your mass air flow sensor is in good working condition as a code will be set if the data goes out of a normal operating threshold. Worth mentioning, MAF codes can take a while to be set so if you car just stutters and dies as soon as it’s started, it may not have been running long enough for a code to be set. Further bench-testing of the MAF sensor will then be required.
A loose or cracked vacuum hose will also make the engine stutter and vibrate. If air can enter the intake system anywhere after the MAF sensor, it will add to the volume of air measured by the sensor and will create an incorrect air/fuel ratio, once again leading to more misfires. Look out for anti-pollution systems and purge valve codes, like a p0402 for example, as signs of a leaking vacuum hose.
An old trick to identify air leaks leading into the intake system is to keep the engine idling and spray the air intake pipes and hoses with brake cleaner. Brake cleaner being extremely flammable, the RPM of the engine should rise quickly if there is a leak somewhere. As soon as the engine’s sound starts to change, stop spraying, wait about 30 seconds and repeat until you have correctly located the leak.
Car vibration: good maintenance to avoid risks
To reduce the risk of experiencing unwanted vibrations on your vehicle, it’s recommended to have your car regularly and thoroughly inspected by a professional but, ideally, the owner should take as much care of it as possible. Always keep your tires inflated at the appropriate tire pressure to ensure your tires last as long as possible without deformation and uneven wear. Buying and replacing suspension and direction parts with quality ones and not only the cheapest ones available will definitely help too. No car will ever last forever and components will always end up needing to be replaced at some point but with a little love from its owner and extra care provided by a trustworthy mechanic, it could last a lot longer while keeping the total cost of repairs to a minimum.