It is easy to get distressed when you hear a knocking noise coming from the back of the car. It can even force you to visit a mechanic, yet you can fix it yourself.
Your car can make this noise when accelerating, braking, or even when it is just idling. Many factors can cause it, and knowing how to diagnose and fix them can save you a lot of money and even time.
So, let us go straight to the causes of this knocking noise from the back of the car when driving and how you can fix them, either at home or in a mechanics shop.
1. The Back Tires Could Be Misaligned
The back tires tend to get misaligned over time, and when they do, they tend to move sideways, thus resulting in knocking noise coming from the back of the car when driving.
Therefore, you should get them realigned now and then, especially when installing new tires. You can also use your car manual to know how often you should realign them.
However, it would help if you were careful not to depend too much on the manual since this routine maintenance can be affected by how often you drive in rough terrain.
2. Impaired Rear Ball Joints
The nylon sockets in the rear ball joints can wear out due to abuse, such as driving the car at high speed over speed bumps or pools of water. They can also wear out due to a lack of lubrication.
When the nylon sockets wear out, they make the ball joints malfunction. It will make it hard for the suspension to move freely.
Therefore, the knocking noise from the back of the vehicle could be due to the suspension trying very hard to move and turn due to impaired rear ball joints.
If this issue is not diagnosed early, the ball may end up detaching itself from the socket completely. It could also make the wheels break from the vehicle, which can be dangerous.
To diagnose if the noise is due to an impaired rear ball joint, check if the car moves sideways no matter how much you try to control it.
If so, you can suspend the wheels with the problem and inspect the joints. After confirming the problem, you can fix it or call a mechanic if you don’t have the skills to do so.
3. Damaged Struts
Struts are essential components that act as shock absorbers in a suspension. They have a piston and a hydraulic fluid in them.
As the car movers over speed bumps, harsh terrains, or potholes, the piston will push against the fluid, thus damaging the strut. It will make the car produce a knocking sound as it moves.
You can quickly diagnose damaged struts by checking if they let out the hydraulic fluid. However, if you cannot spot the fluid, you will have to use the bounce-back test.
If the car bounces back several times after you have released it, then it means the struts are damaged and need to be replaced.
4. Damaged Wheel Bearings
The wheel bearings play a vital role in a vehicle since they enable the wheels to move smoothly. However, as the bearings stroke one another, they create friction.
This friction can damage the bearings, especially when they are not appropriately lubricated.
The damaged wheel bearings will make your car produce a knocking noise, especially when the car is moving at a speed of more than 35 kilometers per hour.
However, since not every wheel bearing will get damaged at once, this noise will only be coming from the damaged bearings.
For instance, if the rear wheel bearings wear out, you will hear a knocking noise from the back of the car when driving.
The damaged wheel bearings will have to be replaced since they might cause the wheels to stop moving. It can be dangerous and stressful.
5. It Could Be Due To Loose Lower Lug Nuts
The knocking noise coming from the back of the car when driving might also be caused by the loose back lug nuts. The lug nuts are components used to attach the wheels to the vehicle.
These lug nuts could get loose due to regularly driving on rocky surfaces and over speed bumps. They might have also not been adequately tightened when replacing the wheels.
The good thing is that this issue can easily be fixed without incurring any cost. All you have to do is use a screw to tighten the notes.
6. Problem With Your Car Back Brakes
If you only hear the knocking noise coming from the back of the car when applying brakes, it means that your car back breaks have a problem.
For instance, the bolts or calipers might have gotten loose. Also, the joints or shock absorbers may be worn.
Here, you will have to fix or replace them to remove the noise.
7. Damaged Rear Sway Bar
The car suspensions cannot function probably without the sway bars. A sway bar is a component that prevents your car from rolling when it turns in a corner.
They are under a lot of pressure and can even break. So, a broken rear sway bar can make the car produce knocking noise coming from the back.
You can fix the broken sway bar by welding it. However, this method tends to be unreliable, especially when done unprofessionally.
Therefore, driving your car to trusted mechanics experts is essential to ensure a lasting solution.
8. Faulty Rear Bushings
The bushings enable your vehicle to stay aligned by stabilizing the suspensions. They also absorb the shock caused by moving wheels.
But since they are made of rubber, they tend to wear out over time, primarily when used to driving your car in harsh terrains.
The rear metals will freely rub against each other when this happens, producing the knocking noise.
Unlike the other components in your car, you cannot repair the bushings. Therefore, you will have to buy and install new ones.
9. Broken Rear Axle
Your car’s rear axle supplies torque to the rear wheels. They also hold the back tires and carry your car’s back weight.
But even though it has been designed to last for the entire lifetime of your vehicle, sometimes it breaks down due to stress.
For example, hitting a pothole or driving over speed bumps at high speed can damage the rear axle. A broken rear axle will prevent the tires from hitting the road evenly.
Therefore, the tires will make a knocking noise as the car moves.
Like bushings, the axle cannot be fixed once it breaks down; hence the only way you can get rid of the knocking noise is to install a new one.
There are many reasons you hear a knocking noise coming from the back of your car when driving.
Some of them have to do with faulty components such as broken rear axle, defective rear bushings, damaged struts, and impaired rear ball joints, while others have to do with misaligned or loose parts such as back tires and lug nuts.
Therefore, you must understand the significance of each component in your car to attend to their problems whenever you hear this noise.
James has been a car enthusiast since his childhood when he learned the differences between a ford and a chevy from his father. He loves to drive and restore old cars with a special drive for Italian marvels. Currently, he has a 1968 Alfa Romeo. He has studied aeronautics and civil aviation in his college and still gets smitten by Galant SS and Lancer GSR.
He is a New York-based product training director working with a giant automotive retailer. He loves to review and uncover the vehicles and their fascinating stories. He believes in keeping it legitimate with a keen passion for research on the latest technological upgrades in cars. While reading his articles or blogs, you can sense the extensive research and dedication backing the piece of text. He loves fried chicken, music, and spending quality time with his pet dog.