Suspension system components couple to the steering linkage at the steering knuckles and the condition of the suspension system affects steering capability. Worn shock or struts, for example, contribute to front end wander.

Tie rod ends are bolted to the steering knuckles. A ball and socket joint in the tie rod end makes this a pivoting connection that is essential to steering.

In a parallelogram system, steering is transmitted to the linkage through a pitman arm, which converts steering wheel rotation into the back and forth motion of the linkage.

The two tie rods are connected to the center link and through adjusting sleeves to the tie rod ends. The sleeves are threaded to allow lengthening and shortening of the tie rod assembly when the toe angle is adjusted during a wheel alignment.

An increasingly popular type of steering system is rack and pinion. A pinion gear translates the rotary motion of the steering wheel into the linear motion of the rack. The rack acts like the center link, moving the tie rods back and forth to steer the vehicle. Rack placement varies from on car manufacturer to anther and from model to model.

Rack and pinion steering provides easy turning and fast steering response because of its low gear ration (8:1 to 10:1).

There are three basic types of front suspension systems: coil springs (double wish-bone), torsion bar, and strut. Coil springs and torsion bars were the traditional suspensions used on American cars until the recent popularity of strut systems. Strut suspensions are lighter weight, which helps save gas; and they take up less space in the engine compartment, which is very important with the transverse-mounted engines used in most front wheel drive cars.

All three types are independent front suspensions. When a wheel rolls over a bump or into a hole, the road shock is absorbed by that wheel's suspension. The other wheel is only minimally affected. This provides much greater stability and directional control than the old solid axle designs.

In all three suspension systems, each front wheel is connected to a steering knuckle and wheel spindle assembly.

Anti-roll Bars (Sway Bars/Stabilizers)

Anti-roll bars combat the roll of a car on it's suspension as it corners. They're also known as sway-bars or anti-sway-bars. Almost all cars have them fitted as standard. From the factory they are biased towards ride comfort. Stiffer aftermarket items will increase the road-holding but you'll get reduced comfort because of it. The anti-roll bar is usually connected to the front, lower edge of the bottom suspension joint. It passes through two pivot points under the chassis, usually on the sub-frame and is attached to the same point on the opposite suspension setup. It joins the bottom of the suspension parts together. With a good anti-roll bar, as the lower part of the suspension moves upward relative to the car chassis, it transfers some of that movement to the same component on the other side. In effect, it tries to lift the left suspension component by the same amount. Because this isn't physically possible, the left suspension effectively becomes a fixed point and the anti-roll bar twists along its length because the other end is effectively anchored in place. It's this twisting that provides the resistance to the suspension movement.

Springs

These come in three types. They are coil springs, torsion bars and leaf springs. Coil springs (coilded torsion bars) are what most people are familiar with.

Leaf springs are what you would find on most American cars up to about 1985 and almost all heavy duty vehicles. They look like layers of metal connected to the axle. The layers are called leaves, hence leaf-spring.

The torsion bar gives coiled-spring-like performance based on the twisting properties of a steel bar. Instead of having a coiled spring, the axle is attached to one end of a steel shaft. The other end is slotted into a tube and held there by splines. As the suspension moves, it twists the shaft along it's length, which in turn resist. As you press on the top of the coil, you're actually inducing a twisting in the shaft, all the way down the coil.

Shock Absorbers

They dampen the vertical motion induced by driving your car along a rough surface.
Shock absorbers perform two functions. First, they absorb any larger-than-average bumps in the road so that the shock isn't transmitted to the car chassis. Second, they keep the suspension at as full a travel as possible for the given road conditions. Shock absorbers keep your wheels planted on the road. Technically they are called dampers (velocity-sensitive hydraulic damping devices). They work in conjunction with the springs. The spring allows movement of the wheel to allow the energy in the road shock to be transformed into kinetic energy of the un-sprung mass, whereupon it is dissipated by the damper. The damper does this by forcing gas or oil through a constriction valve. Adjustable shock absorbers allow you to change the size of this constriction, and thus control the rate of damping. The smaller the constriction, the stiffer the suspension.

Strut Braces

When you corner, the whole car's chassis is twisting slightly. In the front (and perhaps at the back, but not so often) the suspension pillars will be moving relative to each other because there's no direct physical link between them. They are connected via the car body, which can flex depending on its stiffness. A strut brace bolts across the top of the engine to the tops of the two suspension posts and makes that direct physical contact. The result is that the whole front suspension setup becomes a lot more rigid and there will be virtually no movement relative to each side. In effect, you're adding the fourth side to the open box created by the subframe and the two suspension pillars.

Suspension Bushes

These are the rubber grommets which separate most of the parts of your suspension from each other. They're used at the link of an A-Arm with the sub-frame. They're used on anti-roll bar links and mountings and most OEM bushes are made from rubber. Rubber doesn't last, it perishes in the cold and splits in the heat. Replace them with polyurethane or polygraphite bushes - they are hard-wearing and last longer.

Air suspension replaces the springs in your car with either an air bag or an air strut made of high-tensile super flexible polyurethane rubber. Each air bag or strut is connected to a valve to control the amount of air allowed into it. The valves are in turn connected to an air compressor and a small compressed air reservoir. By opening and closing the four valves, the amount of air sent to each unit can be varied. By letting the same amount of air out of all the units, reducing the pressure in the bags, your car gets lowered, whilst increasing the air pressure by the same amount in each unit results in your car lifting higher off the ground.

Bags and Struts

Air bag systems come in two different types - air bags and air struts. The bags are typically used for leaf-spring suspension vehicles, but can easily be adapted to almost any swinging-arm type suspension system. Air bags are the most reliable systems because of their simplicity. Air struts are a little more complex and come in two types - simple struts and pivoting struts.

Ride Height Sensors

This is a mechanical lever linked to the suspension arm at one end, and to an electronic resistance pot at the other. The pot is connected to the chassis or frame so that the lever spins the pot as the suspension moves up and down. A computer can use this to read the height of the vehicle in that corner. New generation systems also incorporate air pressure sensors to add another level of feedback to the system.

Control Panels

In a factory-fit air suspension system, the control panel will either be integrated into the onboard computer, or be accessible via a ride-height adjustment control. For aftermarket systems, the control panel is normally a hand-held device with a series of control buttons and LED readouts on it.

In a coil spring suspension, the steering knuckle and wheel spindle assembly is connected between upper and lower control arms. The control arms are connected to the vehicle frame, and the coil spring is positioned either between the upper control arm and the car's body or the lower control arm and the vehicle frame. In either case, a shock absorber dampens the up and down oscillations of the spring. The weight of the front half of the car rests upon the coil springs.

The ball joint connects the steering knuckle to the control arms, allowing the steering knuckle to pivot between the control arms when the car is steered. They also permit up and down movement of the control arm. One ball joint is called the load carrier and the other is called the follower. Which is which, depends on the location of the shock: and spring.

When the shock and spring is positioned between the control arms, their bottom connects to the lower control arm and their top is connected to the vehicle frame.

When the shock and spring is ride on the upper control arm, their top is connected to the vehicle body.

In both cases, the weight of the car is transmitted through the spring to the control arm at its bottom...and through the control arm to the ball joint. That ball joint is the load carrier. Load carrier ball joints bear approximately one-half of the total vehicle weight. They are subject to severe wear and it is important to periodically inspect them.

Conventional shock absorbers, on the other hand, do carry weight. The purpose of shock absorbers is to control spring action and hold tires firmly on the road.

Tires are really just an air spring. And, like any spring, it will continue to bounce until the bounce energy is absorbed. Springs dissipate some of this energy, but it's the shock that absorbs excess energy from the spring. Shock absorbers transfer this motion energy into heat energy and dissipate it into the atmosphere.

Like ball joints, shock absorbers require frequent inspection.
When a shock stops dampening spring oscillation:

Steering and handling becomes more difficult
Braking action may be affected
There is excessive bouncing after stops
Springs can bottom out
Cupping begins to appear on tires

Other front suspension system components include the stabilizer bar and stabilizer links. The stabilizer bar and links join the two lower control arms to transmit cornering force from the outside wheel to the inside wheel during a turn. This helps equalize wheel loads and prevent the car from leaning or rolling outward when cornering. The stabilizer bar is also called the sway bar.

A strut rod is used in some systems to restrict the forward and backward movement of the lower control arm. It is attached between the lower control arm and the frame. Often, both ends of the strut rod are threaded to allow for the caster angle adjustment when performing a wheel alignment.

Stabilizer bars and strut rods do not wear out - they need to be replaced only when damaged or bent. Wear occurs at their connections, at the bushings. When the bushings wear, the connection is loosened. Vehicle handling gets a little sloppy and the wheels cannot remain in proper alignment.

There are no coil springs in a torsion bar suspension system. Instead, a torsion bar supports the vehicle weight and absorbs the road shocks. While a coil spring performs these functions by compressing, the torsion bar acts by twisting.

The torsion bar is connected between the lower control arm and the frame. The bar can be connected either longitudinally or transversely. Torsion bars can be used to adjust vehicle riding height. They are not interchangeable from side to side, because the direction of the twisting (or torsion) is different between the left and right sides.

Other than the difference between the torsion bar and the coil spring, this type of suspension is the same as the coil spring variety. Because the torsion bar is connected to the lower control arm, the lower ball joint is the load carrier. A shock absorber is connected between the lower control arm and the frame to dampen the twisting motion of the torsion bar.

A torsion bar is a solid bar of steel which is connected to the car chassis at one end, and free to move at the other end. The springing motion is provided by the metal bar's resistance to twisting.

In a strut assembly the shock absorber is a structural part of the vehicle's suspension. Strut suspension systems are more compact and weigh less than conventional suspensions, making struts ideal for the smaller, more fuel efficient cars of today and tomorrow.

With a strut suspension system, in most cases only the lower control arm is used. The upper control arm is replaced by the strut assembly, which supports the weight of the car. The strut is directly connected to the steering knuckle on one end. Sometimes, in fact, the strut assembly includes the steering knuckle and wheel spindle. On its top end, the strut is attached to the car's body through a strut bearing and rubber mount. The strut bearing acts as the upper pivot when the wheel turns. Since the strut carries the vehicle weight, the ball joint connecting the lower control arm uses the steering knuckle as a follower.

The similarity to conventional systems can be seen clearly to the modified strut suspension. Here, the coil spring is not part of the strut assembly; instead, it is connected between the lower control arm and the frame. In this case, the lower ball joint is a load carrier.

Rear suspension systems are as critical to ride control as front end systems. An automobile must be in optimum pitch and balance to ride right. There are two types of conventional rear suspension systems: coil spring and leaf spring.

Coil Spring Suspension

On a Coil spring suspension, the spring is mounted between the axle housing and frame. A lower control arm connects the axle housing to the frame. Some vehicles use an upper control arm for added stability.

Leaf Spring Rear Suspension

Control arms are not required on leaf spring suspensions. The leaf spring is connected to the axle housing with the U-bolts. The shackle assembly allows spring movement.

In both applications, shock absorbers connect between the axle housing and the frame and absorb excess energy from the system. If the vehicle is being used to carry heavy loads on trailers, load-assist shock absorbers are recommended.

Routinely inspect rear shocks whenever under-car service is being performed.

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