It's the proverbial twenty miles of bad road. The potholes are worth it, however, for the great weekend of backwoods hiking and exploring. Then you hit the pavement and the rattling starts. Maybe you couldn't hear it on the unpaved road, but every expansion strip on the Interstate makes your car sound like a tin can full of bolts. Something's loose in your suspension.
While there's little chance that your car is going to lose something essential as it goes down the road, chassis and suspension noises definitely have to be checked out for safety's sake. Plus, who wants to drive a vehicle that sounds like it's about to drop to the pavement?
If your car has lots of miles on it don't be surprised if some portion of the heavy metal supporting it over terra firma starts complaining. Unfortunately, finding the cause of the noise isn't so easy. The dynamics of a rolling vehicle, the complex nature of modern suspensions, and the way sounds echo through the chassis and body make it hard to pinpoint the location of a problem.
If you hear a clunk when the suspension works over bumps, you may have excessive clearance in a joint due to wear. It might be as simple as a loose nut on the strut, or something more subtle such as a shrunken, dried-out rubber bushing.
Check If the Clunk Is a Known Issue
First, search online for any Technical Service Bulletins (TSBs) for your car that pertain to the noise. These bulletins are issued by automakers for known problems and often include options to fix your car, such as redesigned suspension parts. There are several sites online where you can search by your car’s make and model or VIN for outstanding TSBs. Alternately, you can always call your dealership as they should have all of the up-to-date TSBs for the marques they sell.
Suspension clatter is a common problem which generates quite a few TSBs. Some of these entitle you to get the clunk fixed for free, while others may say that the noise is simply a characteristic of the vehicle and should be accepted as normal. Regardless, this is a good place to start.
Time to Bounce
If no clues are forthcoming, it's time to go hands-on. Rope in the strongest friend you can to assist. For frontend noises, pop the hood and have your comrade press down on the bumper or fender. Release and lift repeatedly until the suspension is really working. While doing this, listen carefully and use a good light to examine the upper strut or shock mounts and the control arm joints.
If you hear anything strange, but can't pinpoint the source, place the end of a broomstick or long screwdriver against your ear and touch the other end to suspected areas. This works almost as well as a mechanic's stethoscope. Nothing obvious? Then lie down and look underneath with your light.
The "dry park check," which checks for free play in the steering mechanism, is less physically challenging. Have your helper sit in the driver's seat, turn the key to unlock the column, then rock the steering wheel vigorously from side to side while you watch the steering components. There should be next to no visible play.
By the way, if you raise the car by the frame, the suspension and steering parts will be hanging at an unnatural angle, which may hide the looseness you're looking for. So, place your jack and jackstands under the control arms or the rear axle to keep the weight on the suspension components.
You can pinpoint bad upper A-frame or control arm bushings by having a helper hold the brakes firmly with the engine idling while shifting from Drive through Neutral to Reverse repeatedly. Look down over the fender as your helper does this. Some vehicles have substantial horizontal struts that position the lower control arms fore and aft. These are mounted in large rubber bushings, and you can hear these bushings move around if they have any extra clearance here. Mounting points on the frame can rust away, but this causes steering symptoms far more noticeable and worrisome than a mere noise.
Older rear-wheel-drive vehicles with a live rear axle and coil springs may have what's called a panhard rod that runs diagonally from the chassis to one side of the axle housing. The rod's bushings are a likely source of a clunking noise.
Worn-out shocks or struts are also common culprits here. When the internal hydraulics wear out, the piston will move without the proper resistance and stop short when you hit a bump. With shocks, another thing to check for is loose or dried-out mounting bushings. A groaning noise when you turn the wheel typically means there's a dry joint, likely at the idler or pitman arm.
Another potential source of noise is the husky stabilizer bar (also known as a sway bar). This bar helps keep your car level in a curve. The links that attach it to the chassis have rubber bushings at both ends, which can rot and dry out just like any of the other rubber components we’ve mentioned here.
Unibody cars that get driven frequently on salted winter roads can also develop the rusted-out suspension pickup points. This is the worst-case scenario for these kinds of clunks where the only real fix involves a trip to the frame shop where new metal can be welded on.
If this is your vehicle's problem, you have real trouble. If one point is rusted, the suspension point on the opposite side is probably also rusted. Your car may have rust in other places as well. At that point, you have to decide how much money you want to spend on a slowly self-destructing car. It may be time to send such a heavily rusted car to the great crusher in the sky—err, junkyard.
Alternate Sources of Noise
Sometimes what you think is a suspension clunk could be something else entirely. For instance, take the exhaust system—the muffler, headpipe and tailpipe, plus the catalytic converter. If everything is in the right place, but the hangers are loose or broken, it's likely that there will be occasional contact that clunks between these components and the chassis or driveshaft. Once your exhaust is cool to the touch, try forcing the system from side to side to see if you can duplicate the sound.
A broken motor mount can also cause a solid thump. Motor mounts can delaminate after they’ve been soaked repeatedly in hot engine oil. Alternately, you may just have a couple of loose bolts. You will notice this problem more often when you get on or off the throttle, but it won't be detected over bumps.
Restoring The Peace
While we've seen people fill the gap left by a deteriorated bushing with shims made of sheet metal, or use a screw to tighten a mount around a loose bushing, the only real fix is replacement. This can be more involved and expensive than you might expect, but it's worth it for the peace and quiet, not to mention less wear and tear on your vehicle.
On the other hand, some repairs are free, or nearly so. It costs nothing to tighten a strut gland nut that may have backed out over time. (If you tighten this nut, you should put a drop of anaerobic thread locker on it to keep it from backing out again.) Likewise, it costs very little to replace shock mounting or stabilizer bar bushings.
Stef Schrader routinely breaks and attempts to take project cars on race tracks. She enjoys fancy cheeses, good coffee, fast Porsches, traveling to new places and rare, weird cars. She lives with a large collection of Fisher-Price Puffalumps and an overloaded parts shed.