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Suspension Dictionary

Ken Brubaker
| Senior Editor, Four Wheeler
Posted February 1, 2013

What It Is, How it Works, What Can Go Wrong

The theme of this issue is suspension systems, so we thought it would be appropriate to create a list of major, commonly used suspension components, define what they do, and address some things that can go wrong with each.

For those of you that are newbies to four-wheeling, you’ll soon learn that much of the mechanical action of interest takes place underneath your rig. That’s where the magic happens, whether its lockers, axleshafts, and yes, the suspension. For this reason it’s a good idea to know what the major suspension components are, what they do, and what can go wrong with said item. In the end, the understanding of how your suspension works will help you choose what mods you need to make and even what spare parts you may need to carry. Oh, and you’ll be able to join in on the suspension conversation around the campfire.

A-arm
What it does: A pair of these (an upper and a lower) are typically found on each side of an independent front suspension (IFS) and independent rear suspension (IRS). The inside of these arms attach to the vehicle’s frame and pivot up and down via bushings. The outside of these arms are fitted with ball joints that allow the attached knuckles to pivot with steering input. Typically, most A-arms are made from steel, though aluminum is sometimes used.

What can go wrong: Short of a collision, A-arms hold up pretty well and it’s usually the ball joints that fail in the event of a gnarly tire-to-obstacle impact. It’s rare, but the stock rubber bushings can wear out, which can affect the alignment and overall drivability. Aftermarket A-arms often use polyurethane bushings, which require regular lubrication. Shown here is a stock GM A-arm (left) next to an upgraded Rough Country (www.roughcountry.com) A-arm, which features beefier construction and larger, greasable ball joints.

Airbag
What it does: Sometimes called an air spring, this air-filled device can be used instead of a standard suspension spring to offer a range of adjustability. Geby Wager’s Top Truck Champions’ Challenge rig is an example of an airbag-equipped machine. The current Ram 1500 is an example of a vehicle that is available from the factory with airbags in the front and rear suspension. These types of airbags are designed to compensate for heavy loads like towing or hauling, automatically. They can also be used to increase the vehicle’s ride height to improve off-road performance. Several aftermarket companies like Firestone (www.firestoneindustrial.com) offer airbag kits that supplement leaf springs for hauling or towing (shown). Air Lift (www.airliftcompany.com) is one of the companies that offer air springs that fit inside coil springs to help handle heavy loads. Some of these airbags require the use of a compressor and auxiliary air tank, while others can be filled manually via a Schrader valve. They work great for leveling a vehicle used for towing and hauling and they can also add stability.

What can go wrong: Over time airbags can dry rot, leak, or suffer a puncture. Airbags require the use of air lines, which can leak or break. Control units and compressors can also fail. In rust-prone environments, the steel end-caps found on some airbags can rust and fail. It’s also worth noting that more pressure in the bags equals a stiffer ride and less wheel uptravel.

Ball Joint
What it does: Ball joints are basically spherical bearings that fasten the knuckle to the A-arm or “C” on a solid axle and allow the steering knuckle to pivot, which allows you to steer your vehicle. Most modern 4x4s have upper and lower ball joints on each knuckle. So what do ball joints have to do with suspension? Well, in a solid axle application ball joints have nothing to do with the suspension, but in an IFS suspension the ball joints have the additional duty of moving in a vertical plane with the A-arms.

What can go wrong: It’s worth noting that adding larger/heavier wheels and tires and increased wheel backspacing can cause ball joints to wear at a much faster rate than normal in both solid axle and IFS applications. If ball joints are worn the result may be steering wander and/or clunking. If the ball joints fail, the knuckle can even detach. There are heavy-duty ball joints available for some applications from companies like Dynatrac (www.dynatrac.com) and Omix-Ada (www.omixada.com). In an IFS application the ball joints can be a limiting factor in regards to suspension travel because their range of motion is designed for stock wheeltravel. Long-travel IFS suspension systems often include A-arms that are fitted with replaceable uniball bearings that have an increased range of motion and are heavier-duty than a standard ball joint. Camburg Engineering (www.camburg.com) is one of those companies that offer such a joint.

Bumpstop
What it does: A bumpstop cushions the last few inches of suspension uptravel, eliminating a harsh “bottoming out” event where the suspension can slam into the vehicle frame or unibody. Bumpstops are typically made of rubber, though the aftermarket often replaces them with polyurethane. When a vehicle is lifted, a longer bumpstop or a lowering bracket needs to be installed to ensure that the suspension’s final uptravel is cushioned correctly.

What can go wrong: Bumpstops that are well used or old can crack or break. They can even just fall out in the case of OE-style push-fit bumpstops. Oil leaks can cause rubber bushings to soften and become ineffective. It’s important to replace a damaged or missing bumpstop immediately to ensure that the suspension isn’t damaged during full compression. There are many sources for bumpstops from suspension companies including Skyjacker (www.skyjacker.com), BDS Suspension (www.bds-suspension.com), and Rancho (www.gorancho.com). Hydraulic bumpstops, like the adjustable and rebuildable JounceShock from Light Racing (www.lightracing.com) are the pinnacle of bumpstop performance and are basically small shock absorbers that gradually damp the last few inches of uptravel.

Bushing
What it does: Bushings made of rubber or polyurethane are the most common bushings found at pivot points in a suspension. For example, where the IFS A-arms mount to the vehicle frame, where the leaf springs mount to the shackles and hangers, and in the ends of link arms. Basically, the bushings allow the component to move in a pivoting motion without allowing side-to-side movement. Shown here is a metal sleeve being inserted in a large polyurethane bushing in a link-arm assembly.

What can go wrong: Rubber bushings typically hold up well, but will dry out and crack with age. An engine oil leak can saturate the rubber, causing it to soften and fail in short order. Heat is also a bushings enemy. If a bushing does fail, you’ll know it because whatever component they’re in will usually move in ways they’re not designed to and make noise and/or affect drivability. Aftermarket polyurethane bushings like those available from Daystar (www.daystarweb.com) are impervious to oil, but they’re harder than rubber and they need to be lubricated regularly.

Coilover
What it does: Instead of utilizing a separate coil spring and shock, a coilover shock is both of those items constructed as a unit with the coil spring mounted onto the shock. This setup combines ride height and damping in one package. A coil-on-shock strut, as found on many late-model ½-ton IFS pickups, is similar to a coilover, but struts don’t offer the height, compression, and rebound adjustment of a coilover. Fox (www.foxracingshox.com) is one of the companies that offer coilovers with an external shock reservoir to improve cooling and wheeltravel. Shown here is a Skyjacker (www.skyjacker.com) coilover shock assembly on a Toyota Tacoma pickup.

What can go wrong: A coilover can wear out over time, but the beauty is that they’re rebuildable. Typically a strut is disposed of and replaced. If you live in a salt-prone environment the coilovers threaded adjusting mechanism can rust and become inoperable.

Coil Spring
What it does: The coil springs under a typical 4x4 are designed to set the ride height of the vehicle as well as have a rate that isn’t too hard or too soft. Vehicles that carry heavy loads typically have a higher spring rate. Some coilover shocks use two or even three coil springs of different rates and sizes to enhance the performance of the suspension. Some suspension systems set the coil spring by itself, some place it over the shock absorber, and some connect it to a shock (a coilover).

What can go wrong: As a vehicle ages the coil springs can sag. This allows the vehicle to ride lower to the ground, which decreases the amount of usable suspension compression. A heavy winch and bumper or snowplow can hasten coil spring sag. Installing an adjustable airbag like those from Air Lift (www.airliftcompany.com) to help support the extra weight and decrease the stress on the spring, may lead to longer life, but can limit the travel of the suspension. We’ve had numerous coil springs crack and break from just normal use and age, necessitating a replacement. Sometimes we’ve used OE replacements, while other times we’ve used the broken spring as an excuse to install a lift kit.

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