A thumping or clunking sound when slowing down and possibly when accelerating, turning, or driving over bumps is always connected to one or more faulty suspension components. And depending on what exactly is causing the odd noises, the problem could have negative safety implications, so it’s best to take your car for an inspection as soon as you have some free time. Now, before we go into more detail on all the causes and fixes, here is what you can expect.
If your car makes a thump sound when slowing down, the most likely potential causes include worn-out sway bar/anti-roll bar bushings, worn-out top strut mounts, loose end links, and loose ball joints.
What Causes Car Makes Thump Sound When Slowing Down
In this part, we will cover each potential cause individually and include some of their other unique symptoms to make the thump sound easier to diagnose. Luckily, whichever of the following components turns out to be faulty in your car, fixing it will more than likely be less than $150.
Worn Out Sway Bar/Anti-Roll Bar Bushings
The anti-roll bar is nothing more than a metal rod that connects the left and right suspension arms to reduce body roll when cornering. However, the sway bar is fixed at two points on the chassis and on both control arms with metal clamps with rubber bushings.
When those rubber bushings harden and wear out, the anti-roll bar will become loose. That produces a thumping sound when braking and accelerating. Also, with worn-out sway bar bushings, the car makes a thump sound when turning in some cases. You will also notice that the car leans in corners much more than it used to, plus the leaning may not be linear.
Worn Out Top Strut Mounts
The top strut mounts sit between the strut assembly and the chassis of the car. The strut mounts are made of rubber to reduce vibrations when going over bumpy roads, but the rubber hardens and squeezes when it gets old. That means the strut will have vertical free play when the weight of the car is lifted from the front axle.
As a result, you will only hear the thump when hitting the brakes right after hard acceleration or even just backing off the gas pedal. Even more noticeable, you will hear thumping and clunking when going over bumpy roads, speed bumps, or potholes.
Loose End Links
We already explained what the anti-roll bar is and how it’s attached to the control arms. Well, in some cars, the anti-roll bar can’t be directly bolted to the control arms for practical reasons, so they use end links that extend the control arm reach to the anti-roll bar. That said, end links are pretty simple, too, as they are also a metal bar with two rubber bushings on each end.
And just like all rubber bushings, they will wear out and become loose, which makes a thumping sound when cornering, braking, accelerating, or driving over bumps. Also, the car will lean more in the corners and overall become more unstable, meaning the symptoms are the same as they are for anti-roll bar bushings.
Loose Ball Joints
The ball joint sits on the end of each control arm and essentially serves as a pivot point for the front wheels allowing them to turn left and right and some cases, in and out vertically. The ball joint is just that, a ball that sits inside a socket and can turn in all directions. Its design is almost identical to that of a human ball and socket joint found in hips, arms, knees, etc.
But with time, the socket will wear out, and the ball joint will become loose, which is what makes the thump sound when braking hard or driving over bumps. Also, you may notice the car is wandering left and right instead of going straight, vibrations, rattling, and possibly even some play in the steering wheel.
How Do You Fix Thump Sound When Your Car Slowing Down
If your car makes a thump sound when slowing down, the only way to fix it is to replace the faulty component. But as we already mentioned, all these components are fairly cheap to replace, save for some exceptions. Also, to replace any of them, you ideally need a two-post lift, so none of them are what you’d call DYI-friendly, but it’s not impossible to do it with a car jack, either.
Worn Out Sway Bar/Anti Roll Bar Bushings – Fixes
The only way to fix sway bar bushings is to replace them, which is pretty easy to do as long as they are accessible. A set of four sway bar bushings rarely costs more than $30, and it takes an experienced mechanic about half an hour to replace them. But in the worst-case scenario, you will pay for one hour of labor, which is $75 if we go by the national average, plus $30 for parts, bringing the total to $105.
Worn Out Top Strut Mounts – Fixes
Replacing the top strut mounts is a somewhat time-consuming job, plus it can be dangerous, and it requires special tools almost no household has lying around. That means taking the car to a repair shop is your best option.
Now, a set of strut mounts costs between $40 and $80, depending on the model, and it takes between one and two hours to replace them. That makes the average cost to replace strut mounts roughly $170.
Loose End Links – Fixes
Replacing sway bar end links is pretty easy because they are held with two bolts that are easily accessible in most cases. Moreover, a set of end links for a standard passenger car costs around $20 and around $35 for a full-size truck. And let’s say you pay for an hour of labor; in the worst-case scenario, the total cost to replace end links is roughly $100.
Loose Ball Joints – Fixes
Ball joints by themselves are pretty inexpensive components, plus it’s okay to replace them on one side only if the other one is good. A single ball joint costs roughly $30, and it takes less than an hour to replace it, bringing the total cost to an average of $105.
However, most modern cars have ball joints integrated into the control arm, so when a ball joint goes, you have to replace the whole unit. That drives both the parts and labor costs up. A single control arm with a ball joint costs around $100 on average, and it takes, and in the best case scenario, you will pay for an hour of labor, so about $200 to replace a control arm is what you can expect, plus or minus $50.
Q: Why does my car thump when braking and accelerating?
If your car thumps when braking and accelerating, it could indicate worn-out sway bar bushings, end links, or worn-out top strut mounts.
Q: Why do my new brakes make a thumping noise?
If your new brakes make a thump noise, it could mean the brake pads have not yet settled correctly, and it will take about 10 to 15 miles for them to do so. However, if the problem persists, it could mean something wasn’t installed right, or there are some loose bolts on the brake caliper.
Q: Why does my car make a thumping sound when driving?
Your car makes a thumping sound when driving, most likely because of old or unevenly worn-out tires. The other two possible causes are warped brake rotors and bad wheel alignment.
Q: Is it safe to drive with a thumping sound?
You are not in any immediate danger if you drive with a thumping sound, but the noise is associated with suspension and braking components, so you are not entirely safe either. If you hear a thumping sound, it’s best to take your car for an inspection and avoid long-distance driving.
Q: How much does it cost to fix a thumping sound?
How much it costs to fix a thumping sound depends on what’s causing it, but the average price is $150 with parts and labor. And again, depending on what’s causing it, it could be as little as $80 or as much as $300.
At the end of the day, very few components make a single distinct thump sound when slowing down or braking. Those components include worn-out sway bar links, end links, ball joints, or top strut mounts. And while there is no particular urgency to fix any of them, keep in mind that driving the car is at least slightly more dangerous than normal, and it’s a good idea to at least have your car inspected in a matter of a couple of days or a week.