Maybe you remember being pushed along in a wheelbarrow during childhood. The ride was bone-jarring - even with an air-filled rubber tire cushioning against the rough ground. Because there was no additional insulation, vibrations that made it past the tire traveled directly through the metal tub and into your body.
Of course, automobile suspensions are built with shock absorbers and springs designed to flex and absorb irregularities of the road. While these items reduce the severity of the bumps, you can be sure that noise, vibration, and harshness levels would still approach that of a wheelbarrow without specially-shaped rubber cushioning pieces fitted to each suspension component.
These "cushioning pieces" are formally known as suspension bushings - and there are different types of them specifically fitted for control arms, shock absorbers, springs, trailing arms, sway bars, and other components. While these bushings serve as flexible mounting points, their primary role is twofold. First, they absorb and isolate the car's body and occupants from shocks and vibrations. But secondly, they also serve to eliminate loose play in the suspension components - keeping everything aligned snugly and firmly in proper position - helping to ensure that all four tires stay firmly planted on the ground.
Since rubber bushings in your suspension take a pounding any time your vehicle is in motion, they must be extremely robust and durable in order to last. And, generally, they do last for quite a while under most normal driving conditions - so much so that automakers don't specify any kind of replacement interval. However, rubber bushings in your suspension do eventually succumb to wear, tear, and dry-rot over time. When one or more suspension bushings give up the ghost, you've got metal-on-metal contact creating noise, vibration, and harshness.
In this article, we'll discuss the different types of bushings you'll find in a typical automotive suspension, and how to recognize signs of wear that tell you it's time for replacement. A key point we cannot emphasize enough is that replacing old rubber bushings with new ones goes a long way toward improving the ride quality of your vehicle - restoring the supple cushioning it had when driven out of the showroom.
Glossary Of Suspension Bushing Types
Axle Support Bushings
Typically found on vehicles with front or rear solid axles, these rubber bushings are found on the arms that connect the axle carrier assembly and the vehicle's frame.
Body mounts are essentially rubber doughnuts that fit in between the body and frame of a vehicle (if those items are separate) to further isolate road noise, vibration, and harshness.
Control Arm Bushings:
Also known as A-Arm bushings or wishbone bushings, these dampen vibrations between the vehicle frame and control arms which pivot up and down with wheel movement.
Lateral Control Arm Bushings
Usually found on a vehicle's rear, lateral links are hollow metal tubes that connect a wheel hub to the midpoint of the vehicle body in order to keep the wheel hub assembly upright and centered while driving. At each end of the link is an eyehole where round bushings are located.
Radius Arm Bushings
Typically found on solid axles, a radius arm connects the axle housing assembly to the frame of the vehicle - and is intended to reduce front-to-rear shifting of the axle and wheel.
Shock Absorber Bushings
At each end of a shock absorber are round "eyeholes" that serve as a mounting point to attach the shock to both a suspension control arm and to the vehicle frame. Within the eyeholes are specially-shaped rubber bushings.
Spring Plate Bushings
On vehicles with torsion bar spring setups, a radius arm connects the rear wheel hub assembly to the round end of the torsion spring. Covering the end of the torsion spring on select makes is a "spring plate". A round spring plate bushing wraps around the end of the torsion spring underneath the spring plate.
On vehicles with struts installed, strut bumpers fit in between the strut body and the strut mounting plate(s) that forms the very top of the strut assembly.
Positioned at the top and bottom of strut assemblies, these wide (and sometimes flat) bushing pieces slot in between the very top of the strut frame and the metal of the vehicle.
Strut Rod Bushings
On a control arm setup with struts, a strut rod is positioned to limit unwanted fore-aft shifting of the lower control arm. A strut rod also allows caster to be fine-tuned during a wheel alignment. Bushings that surround both ends are round in shape. These serve a similar function as tension rods.
Sway Bar Bushings
Also known as stabilizer bar bushings, these are positioned inside of metal brackets bolted to the vehicle frame or crossmember.
Tension Rod Bushings
Similar in function to a strut rod bearing, a tension rod limits unwanted fore-aft shifting of the lower control arm during braking or steering. Tension rods also allow caster to be fine-tuned during a wheel alignment. Bushings that surround both ends are round in shape.
Track Bar Bushings
A track bar is a lateral locating link, attached to a live axle at one end and the vehicle frame at the other. Bushings at the mounting points eliminate any jarring vibrations.
Trailing Arm Bushings
Widely used at the rear of front-wheel-drive vehicles, a trailing arm is a suspension arm that pivots in a plane parallel to the longitudinal axis of the car. The wheel is fixed to and trails behind the fixed pivot point on the chassis. With this type of independent rear suspension, the wheels are always upright relative to the body, and they lean with the body in a corner.
Causes Of Wear
Perhaps the most influential factor determining how long suspension bushings will last is the condition of the roads you drive on. Naturally, poorly maintained and unpaved roads will chew up rubber bushings faster than smooth highways. Another less obvious factor is the quality of the original equipment (OE) bushings as chosen by the vehicle manufacturer. A costlier vehicle from a manufacturer that puts high emphasis on engineering and quality will likely be equipped with longer-lasting bushings made from a more expensive rubber blend. On an entry-level economy car with a mega-low sticker price, that's not as likely.
Oil and fluid leaks are the next biggest cause of suspension bushing deterioration. Unlike parts such as ball joints, steering tie rods, and some driveshafts which have metal parts designed to be lubricated with grease, rubber bushings need to remain dry. Petroleum-based fluids will cause rubber to change chemically - reducing its strength to a soft, mushy consistency that can tear apart. Heat and cold cycles will also adversely affect rubber. Heat from nearby exhaust pipes can be detrimental, and outside frigid air will stiffen the rubber to the point where it may crack or tear.
Low-profile tires on large, heavy rims can also have a repeated bludgeoning effect on all the rubber bushings in your suspension. When you compare the superior level of cushioning that traditional, higher-profile tires provide vs. low-profile tires, keep in mind that such a choice becomes a compromise. Finally, something as simple as over- or under-inflated tires can wreak havoc on your suspension bushings, so check those pressures.
Signs Of Wear
When rubber bushings wear, the effects are similar to bone cartilage that has deteriorated. Stress on joints and related parts increases, and painful groaning noises may result. Components can shift out of their firmly-mounted, proper positioning as wear increases - allowing play and slop that causes a vehicle to wander and behave erratically at speed.
What You'll Notice Behind The Wheel
If you're experiencing banging noises, creaks, or frame-rattling vibration from the front or rear suspension, a good road test with a range of twists and turns at various speeds may help you isolate where the noise is coming from.
Worn control arm bushings will have the biggest influence on incorrect wheel alignment. On the highway, this will show up as wandering more than a steering wheel that's permanently off-center. It may be difficult for a technician to successfully perform a proper alignment because parts won't hold the position to which they've been adjusted. Small bumps may seem extremely harsh if there isn't enough rubber to keep metal from bouncing off metal. You'll also experience steering wheel vibrations. Sudden braking-while-steering maneuvers at parking lot speeds will bring out a worn control arm bushing.
Loose stabilizer bar bushings will reduce the effectiveness of the bar itself. More body roll will be noticeable around corners, and you may hear an arthritic creaking noise when vehicle weight shifts if the bushings are worn enough to allow metal-on-metal contact. Approaching a driveway entrance or speed bump at an angle is a good way to bring out noise from worn stabilizer bar bushings.
Strut rod bushings, strut bumper bushings, tension rod bushings, trailing arm bushings (rear), or radius arm bushings (including spring plate bushings if applicable) that prevent a vehicle wheel from shifting fore-aft may or may not cause noises when worn, but wear in these areas can cause erratic pulling to one side during sudden braking or acceleration. Loose steering around corners can also result, especially if the areas affected are at the front of the vehicle.
If you experience a clunking noise over bumps with no other symptoms, that can indicate the bushings located at the ends of the shock absorbers are worn.
What You'll Notice Upon Inspection
Since body mounts are positioned between body and frame, they naturally have an effect on how high a vehicle's body sits. A compromised mount bushing can cause the body to sag in the affected area. The sagging may not be a lot, but it can be enough to create misaligned doors and fenders. If a door drags against its sill considerably when opening or closing, check the hinges for sagging. If they're okay, a body mount bushing could be the issue.
If you see tire wear along one side that would normally indicate an improper wheel alignment setting, but the vehicle shows alignment specifications "within range" on a professional alignment rack, the issue can very well be caused by compromised suspension bushings. If this is the case, all three alignment settings (toe, caster, and camber angles) can temporarily shift out of specification when the vehicle is moving.
If you have access to a lift, or you've got two jack stands to get both front wheels in the air, have a second person turn the steering wheel back and forth while you get underneath and listen for noises. It's worth a try, because you may be able to hear where the issue is.
While you're underneath, use a pry bar to see how much play there is at the connecting points of the control arms. Generally, you shouldn't see more than 1/8th of an inch of free play from the bushing. If you do, it's time to replace.
Opportune Times To Replace Suspension Bushings
Typically, we like to help our customers by making recommendations about when it makes sense to replace one or more components when related parts need to be removed for any reason. However, doing so for suspension bushings as a whole is not easy. Because the labor to install new bushings on some components can be extensive, labor costs to replace bushings by themselves can be high. And with suspension designs varying from vehicle to vehicle, what makes sense on one model may not make sense on another.
With a few exceptions, metal suspension components are durable and don't need replacement unless they've become bent or damaged. However, wear items such as shock absorbers typically come with new bushings included. If your vehicle has stand-alone shock absorbers that are otherwise in good conditions, removing and installing them does not involve a great deal of labor - whether you replace individual bushings (if available for your vehicle) or the entire shock. Sway bars and rear track bars are relatively easy to unbolt, so replacing bushings there is easy. We also recommend replacing any end link pieces while those bars are off the vehicle.
If strut assemblies need to be removed or replaced for any reason, there's minimal labor involved with replacing strut bushings and strut bumpers. Replacement struts may or may not come with these pieces - so check carefully. Suspension components such as radius arms, trailing arms, and strut rods may be easy to remove separately depending on individual suspension design.
If the vehicle in question is very old or has significantly higher mileage, it may be worth the investment to perform a complete rebuild of the front and/or rear suspension. In cases like this, it is best to plan to replace all the suspension bushings at the same time. We find it unwise to decide, for example, to replace control arm bushings but not stabilizer bar bushings. Take advantage of the fact that all components are disassembled. The price of individual bushings is a miniscule portion of the total repair. This is clearly a case where it's best to proceed with everything while it's all apart.
To help guide you through the selection of all types of suspension bushings we offer, we've set up our website to provide you with all the choices that will fit your vehicle. It's possible to enter specific make, model, and year in drop down boxes before beginning your search. Or, input vehicle information after entering an individual page. With new rubber in place, you'll really enjoy the improvements in ride quality - and, you'll regret not doing it sooner!