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.

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