Home    Contact Us      

Content on this page requires a newer version of Adobe Flash Player.

Get Adobe Flash player







AUTO THEORY

How Automotive Suspension and Steering Works

Front Suspension

Note: Unless your classic car is a Cord, Morris Minor, Olds Toronado, Jeep, or a mid-70s GM X-Body, it is almost certainly a rear-wheel-drive vehicle. We want to make that clear, since this article will only deal with the most common layouts you might encounter in old cars. Also, no mention of McPherson Struts is made, since these devices are generally found on more modern vehicles.

Since the beginning, cars have been suspended by some sort of road shock-cushioning system that smoothes out the irregularities of the road surface and maintains stability. Otherwise, driving them would be so uncomfortable and dangerous that some other form of transportation would be in use today.

Suspension systems use springs to accomplish this task. Spring steel is simply steel that, when bent or twisted, returns to its original shape. In doing so it absorbs the energy created by the movement of the vehicle. On the front end of the car the general suspension systems employed by manufacturers were - and still are, in two cases - leaf springs, torsion bars and coil springs:

Spindle Assembly. Uses solid I-beam axle. Spindle swivels on a kingpin (spindle bolt).
Spindle Assembly. Uses solid I-beam axle. Spindle swivels on a kingpin (spindle bolt).

Leaf Springs were hand-me-downs from the carriage trade and are still used today on a few rear axles, trailers and trucks. They are easy to manufacture, inexpensive and relatively effective, although more difficult to "fine tune" to a chassis. The last cars to utilize front leaf springs were the British AC Bristol and Ace sports cars. The AC Cobra was derived from the Bristol.

Torsion Bars were widely used by some foreign manufacturers as well as Chrysler during the 50s, 60s and 70s. The chief advantages of torsion bars are their adjustability and "compactness," when it comes to space considerations. Stabilizer bars, used in virtually all vehicles today, are torsion bars.

Coil Springs were found early on to provide the best combination of ride, control and cost of manufacture and are used in some form on nearly all cars today.

Suspension Components

The coil spring, mounted between the upper suspension arm (control arm) and the car's body, is a very common method of arranging the front suspension. Another common method is the mounting of a coil spring between the upper and lower suspension arms, henceforth called control arms. Upper and lower control arms are almost always of unequal length. The reason for doing so is to provide a way to keep the wheel as close to vertical as possible during its up-and-down travel as it moves along the road surface.

The control arms are connected to the car's body at one end by moving joints that are supported by rubber bushings, their purpose being to help locate the arms in space, allow movement and to help cushion road shocks that would transmit through the car body if only bolts were used.

Ball Joints

At the wheel end of the control arms are normally found ball joints. Ball joints are used to carry the loads on the wheel while allowing it to move up and down in space. Depending upon design, ball joints can be under tension or compression - an important consideration when attempting to remove them - because spring tension must be properly relieved to prevent serious injury.

Ball joint steering knuckle assembly. Steering knuckle swivels on two ball joints. Red line indicates alignment of ball joints.
Ball joint steering knuckle assembly. Steering knuckle swivels on two ball joints. Red line indicates alignment of ball joints.

As they move ball joints wear, causing looseness in the suspension system that in turn causes steering problems and tire wear. All ball joints have "play," or clearance specifications, beyond which they should be replaced or (in some designs) rebuilt.

Older cars, especially ones with leaf spring front suspensions, generally were not equipped with ball joints. Instead, manufacturers utilized a pivoting metal assembly fitted with bushings to tie the control arms together.

PAGE 1 2