Steering and Suspension

Suspension Systems

The purpose of the suspension system is to provide a smooth ride in the car and to help maintain control of the vehicle over rough terrain or in case of sudden stops. There are two basic types of suspension used in most cars today. Strut suspension and Conventional suspension. Suspension systems control the movement of the car and keep the tires in contact with the road, providing a better and safer ride.


















Shock Absorber
Shock absorber's are attached to the car's frame near each wheel on most cars with conventional suspension systems. Shock absorbers are either housed inside coil springs, or mounted beside them.
When your car hits a bump, the spring contracts. The shock absorber works with a piston and thick fluid inside it to keep the spring from rebounding too quickly, making your car ride smoother, improving control and reducing tire wear.



Coil Spring
Coil Springs are a component in both Strut and Conventional Suspension systems. When your car goes over a bump or has to stop quickly, the coil spring contracts then rebounds. It is the job of the Strut or Shock Absorber to keep the coil spring from rebounding too quickly.

Strut Assembly (Strut and Cartridge)
Most front wheel drive cars have some kind of Strut Suspension. The strut is a special type of shock absorber that helps to minimize the motion of the suspension. The coil spring surrounds the strut assembly. Struts and shock absorbers work in very similar ways. However, struts function as a structural part of the Suspension System, and therefore also affect things like wheel alignment, vehicle control and suspension wear.

Strut Suspension System
Most front wheel drive cars have some sort of Strut Suspension System. In the Strut Suspension System, a coil spring with a bearing plate at each end supports the car. The spring assembly rests on a seat. The Strut Suspension System helps to cushion the movement of the coil spring when a car hits a bump or a pothole and works to hold the tires to the road and provide better vehicle control.

Conventional (Shock Absorber) Suspension System
In conventional (Shock Absorber) Suspension Systems, two control arms are attached to the frame of the car and a coil spring and shock absorber are attached to the frame and one of the control arms. The spring and shock absorber work together to smooth the ride of the car over the roughness of the road. This suspension system works to hold the tires to the road and provide better vehicle control.





Steering System Mechanisms
The steering system on an automobile starts with exerting force on the steering wheel. This turning force is passed on to the pinion gear and is transferred to the rack. The tie rod on the end of the rack pushes or pulls the spindle to make the wheels turn.








Power Assist Piston
The power assist piston is a hydraulic unit that helps transmit force from the rack to the tie rod making it possible to steer the car while exerting less force on the steering wheel.

Pinion Gear
The pinion gear is attached to the steering wheel by the steering shaft. When the steering wheel is turned, the pinion gear turns. The teeth in the pinion gear mesh with the teeth on the rack, transferring the rotating motion to a side-to-side motion.

Rack
The rack is moved side to side by the motion of the pinion gear. The rack pushes or pulls on the tie rods which transmit the motion to the wheels. In a manual steering vehicle, all of the motion is controlled by the pinion gear moving the rack. In a power steering vehicle, there is a piston attached to the rack to help transmit the movement to the tie rods.

Tie Rod
The tie rod connects the key parts of the steering mechanism. They pass on the movement from the rack and pinion unit to the spindle connected to the wheel.

Spindle
The spindle is attached to the wheel and causes the wheel to turn when it is pushed or pulled by the tie rod, thereby turning the vehicle.

Rack and Pinion Unit
The rack and pinion unit houses the rack and pinion gear assemblies as well as the power assist piston.

Tire
The tire provides traction for steering and stopping the vehicle.




Steering & Suspension

The steering and suspension systems of a car are not only important for safety reasons but also enhances the comfort level of the vehicle. The two systems are directly related to each other, which is why they are always referred to together.

First lets look at the steering system. There are two basic types, standard mechanical steering and rack & pinion steering. The standard mechanical steering can be either power assisted or non-power. Rack & pinion is almost always power assisted although there are rare cases where it is not.

Standard mechanical steering uses a series of links and arms to insure both wheels turn in the same direction at the same time. It hasn't changed much in all the years it's been used and is quite simple.

Basically this is how it works; the steering wheel is connected to the steering box through the steering column. The steering box turns the rotation of the steering wheel 90° and, in the case of power steering, uses high-pressure fluid to help actuate the steering.

The steering box has an arm attached to the output shaft called the pitman arm. This connects the steering box to the steering gear. The pitman arm is connected to one end of the center or drag link. In the other end of the center link is an idler arm. Between the idler and pitman arms, the center link is supported in the proper position to keep the left and right wheels working together.

The inner tie rod ends are attached to either end of the center link and provides pivot points for the steering gear. From there it goes to the outer tie rod ends through an adjustment sleeve. This sleeve joins the inner and outer tie rod ends together and allows for adjustment when the front wheels are aligned. The outer tie rod ends are connected to the steering knuckle that actually turns the front wheels. The steering knuckle has an upper and lower ball joint that it pivots on and creates the geometry of the steering axis.

As you can see, it's pretty simple. It is just a simple mechanical connection from the steering wheel to the front wheels. The weaknesses of the system are at the pivot points. The pivots are ball and socket joints that do wear out over time and will require replacement. Loose steering parts will make a car difficult to handle and will cause the front tires to wear out prematurely. That's why it's important to have the steering checked at least once a year. A great time to do it is when you're in for an oil change. I always instruct my mechanics to check the steering and suspension while the car is up in the air and they're waiting for the oil to drain out.

Rack and pinion steering is somewhat different. Basically it combines the steering box and center link into one unit. The steering wheel, through the steering column, is directly connected to the rack. Inside the rack is a pinion assembly that moves a toothed piston to move the steering gear. One end of the inner tie rod ends is connected to either end of this piston and the other end is connected to directly to the outer tie rod end. The inner tie rod end is actually threaded into the outer tie rod end and can be rotated to make adjustments during a wheel alignment.

The advantage of rack and pinion steering is that it is more precise than the mechanical system. By reducing the number of parts and pivot points, it can more accurately control wheel direction and is more responsive. The down side of a rack and pinion steering system is that they are prone to leakage requiring replacement of the rack assembly.

Rack and pinion steering is almost always used with a MacPherson suspension system. The bottom of the steering knuckle still pivots on a lower ball joint, but the top of the knuckle is connected to the MacPherson strut. In this system the outer tie rod end is connected to an arm on the strut housing itself.

The MacPherson strut assembly replaces the upper control arm, front shock absorber and ball joint, increasing handling and responsiveness. It controls ride much the same way as a standard hydraulic shock absorber. It also keeps the front end aligned and eliminates, in some cases, the need for caster and camber adjustments. In most cases it also contains the front coil springs so care must be taken when you are replacing them.

The down side is that they will eventually start to leak and will require replacement. They generally last longer than a conventional shock absorber and that may offset the greater cost of the MacPherson strut assembly. As far as replacement goes, some struts have an internal shock assembly that can be replaced separate from the rest of the housing and others have to be replaced as a unit.