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Information on Steering Components
including Rack and Pinion and Steering Gear Boxes
Steering & Suspension
These two systems have the important job of controlling where your car
goes and how it rides. Here, in general terms, are how they work.
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.
(Please note that The Steering
many other companies use the terms Standard Mechanical and Steering Gear
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 degrees 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.
Rack and Pinion
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 &
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
& pinion steering system is that they are prone to leakage requiring
replacement of the rack assembly.
Rack & 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.
Rack & Pinion
The rest of this article
covers suspension, to read go to About.com
© By Vince Ciulla, March 26, 2001. (Autorepair.About.Com)
licensed to About.com, Inc. Used by permission of About.com, Inc.,
which can be found on the web at About.Com.
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