How to Troubleshoot Rear Suspension Noise

by Richard Rowe
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Suspensions are complicated things, and finding problems in them can be a real ordeal if you don't know what you're looking for. Or, more accurately, what you're listening and feeling for, because sight is often just the final confirmation of something you've already figured out. Tracking suspension problems down means knowing the suspension components, what they're supposed to do, and the ways they can break. But if nothing else, remember that anything that moves is suspect.

Test Drive

The first step to diagnosis is a test drive, and for that you'll need a smooth and empty road, a parking lot and preferably an assistant to help you listen. Start by rolling down all of the windows, and put the rear seat back down if you have the type that folds down. Next, start your test drive on a smooth, flat section of parking lot or road. Note if the noise starts at low speed, whether it's accompanied by a thunk or vibration you can feel, if it goes away or gets worse when you speed up, and what type of noise it is: squealing and thumping are common. Go to the parking lot, and start driving around in large circles at 15 to 20 mph. See if the noise gets better or worse when the car starts to lean. Go around the other way, and listen again. The goal is to reproduce the noise, and the conditions under which it occurs.

Constant Noises -- Wheel, Tire or Wheel Bearing

Constant noises don't usually mean a problem with the suspension as much as the wheel, tire or wheel bearing. These problems typically manifest as both noise and vibration that start at low speed, and get worse with higher speed. Wheel bearings tend to be fairly noise when they go, sometimes squealing, but more often grumbling and growling. If you have a bad wheel bearing, it will typically get louder while you're turning and the vehicle's weight starts leaning on that bearing. So, bearing noise that gets louder when you turn left means a problem on the right, and vice versa. Wheel bearings can also emit a clicking noise, but so can rear drum brakes and failed drum brake shoes. If you have drums and hear clicking, check those out before you assume a bad wheel bearing.

Noises Over Bumps and While Turning

Actual suspension problems will manifest when the suspension suddenly has to move, either because of a bump or because the weight of the vehicle shifts onto that side while cornering. The classic symptom of bad ball joints is a hard thumping over bumps, and while entering a corner. Rear suspensions, though, are more likely to have problems with the control arms and linkages that connect them. Sway bar end-links are also suspect, as are strut mounts. Generally speaking, the deeper the thud or thunk, the bigger the problem. A light rapping noise might only be a sway bar end-link, whereas a heavy thump is more likely a control arm, control arm bushing or strut mount. If you get a loud thump from one side going over large potholes or speed bumps, and the car seems to roll excessively while you're turning the other direction, you may have a blown shock. The thump you're hearing is the suspension bottoming out on the bump stop at the top or bottom of the spring.

Parked and Rocking -- First Inspection

Once you've got an idea of where the noise is coming from and what it might be, park the car, set the parking brake and start bouncing the rear end while you and your assistant listen around the vehicle. Bounce the car repeatedly as hard as you can. Go to the side, brace your hands on the top of the roof or fender, and then try pushing it laterally back and forth. Go to the rear and rock the car back and forth. Creaking or grinding noises usually mean something metal is rubbing against something else that's metal, indicating a bad ball joint, end link, or rubber coil spring isolator. Sharp popping noises may indicate that something is either broken or so worn that it's causing the suspension to bind up. These kinds of failures will be more common on vehicles with complex, multi-link, independent rear suspensions with lots of smaller links and joints.

Lifted and Shaken -- Deeper Inspection

To get visual confirmation, you'll eventually need to jack the vehicle up, support it on jack stands, and take a look for loose, broken or worn-out components. Start by grabbing the wheel at the 3 o'clock and 9 o'clock positions, and try rocking it back and forth while you listen and look for components moving and wiggling relative to each other. Grasp it at the top and bottom and do the same; a second set of eyes is very helpful here. Anywhere any moving component bolts to or touches any other is suspect. Look for cracked, squashed and leaking grease boots around links, which indicate a failure there. The rubber bushings at either end of your control arms should be complete, soft and pliable, not cracked or squashed. Look for rust rings around bolt heads, which indicate loose bolts and potentially worn-out or broken parts. For some suspensions, you may need to support the control arm or axle with a jack to unload the suspension. Once the suspension is level, you can use a small prybar to check all of the joints for free play that you might not have seen just looking at it.

Tire Wear

Tire wear can be a vital indicator of suspension problems, and can help get you pointed in the right direction if you can't track down the noise or see anything wrong. Check your tires for hard wear along one edge, a softer "feathering" wear that starts at one side of the tire and goes to the middle or further, or "scalloping," or dips in the tread. Edge wear means the top of the tire is leaning in or the bottom is leaning out. Feathering usually implies a broken or severely worn toe bar linkage, which is the bar that connects the wheel on one side to the other. Scalloping means something is wobbling or vibrating in the suspension, often the result of bad ball joints, bad suspension bushings or worn-out end links. Loose strut mounts and broken struts are a possibility with all of these, but are more likely with scalloping.

Just a Thought

If you hear a banging when you're going down the road, and a light tapping when you do the bounce test, check your exhaust system. Exhaust pipes are suspended by rubber hangars, which can wear out or break over time. The sound you're hearing could be the exhaust pipe or muffler hitting your suspension -- it's more common than you might think.

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