Steering & Suspension
From About.com
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.
(Please note that Meridian and many other
companies use the terms Standard Mechanical and Steering Gear Box
interchangeably. Your car or truck only has one, never
both)
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
and pinion steering. The standard mechanical steering can be either power
assisted or non-power. Steering Rack and 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
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.
Steering Systems
Mechanical
Rack &
Pinion
The rest of this article covers
suspension, to read go to About.com
© By Vince Ciulla, March 26, 2001. (http://www.autorepair.about.com/) licensed to About.com,
Inc. Used by permission of About.com, Inc., which can be found on
the web at http://www.about.com/. all rights reserved. |
