Express Parts

By Ron Henningsen

“But as the body roll increases, the front tires are tilted farther outward and the tire grips even less.”

“If we install a heaver front anti-sway bar, we will increase the load on the outward front tire and thereby increase under steer in this manner.”

“By the addition of a firm rear bar we effectively balance the drift and eliminate up to 50% of the body roll.”

These quotes should give you some insight into anti-sway bars, their function and their purpose. The world’s foremost expert on stabilizer bars, in my opinion, is Ronald deMarcellus, who founded ADDCO Industries, Inc. He published a book in 1993 titled “Handling: What It Is and How to Get It.” I believe it is the “bible” regarding stabilizers and their influence in handling.

An entire encyclopedia could be written on this subject, but in essence, transverse stabilizers or anti-sway bars are attached to the frame of the vehicle and have their ends connected to a suspension component such as the control arm. They allow vertical movement of the individual wheel suspension.

When a vehicle is being driven straight ahead, both wheels will move in a similar manner up or down over bumps and dips. The anti-sway stabilizer bar twists when only one wheel moves vertically. If both wheels move in a similar fashion no twisting takes place. The bar simply pivots on the bushings where it is attached to the frame.

Stabilizer bars come in a variety of designs. They may be solid, hollow or partially hollow ends. They may have ends that attach directly to the suspension components, or they may be attached by links. They may be attached at either the upper or lower control arm.

The generally accepted theory of operation is that the higher the bar is attached to the upper control arm or the more responsive a ball joint is, the more force the bar puts into the opposite wheel when the twisting action takes place. So, the question may be asked, “why are stabilizer bars more frequently attached to lower control arms?”

The answer, generally, is that it is easier to engineer. You may recall that on some of the early ‘90s Fords, the stabilizer bars were literally attached to the upper ball joint stud. This method of attachment of the stabilizer bar made in much more responsive for a given bar diameter.

For stabilizer bars to work efficiently, they must be attached correctly and the mounting must be maintained. This is true for the frame attachment bushings as well as the end links. A recent innovative design on frame attachment bushings is the “grippy” type of bushing used on some of the larger Ford SUV’s and trucks. Instead of a round hole on the inside, this type of bushing actually has a hole with flats on it. These flats engage flats on the stabilizer bar and create a moderate torselastic effect of the bushing when one wheel moves and the other doesn’t. This in effect, changes the operating efficiency or rate of the stabilizer bar.

End links on stabilizer bars are critical components. With the older type of end links that were nothing more than a long bolt with a metal sleeve and shock absorber type washers, normal deterioration of the bushings occurred because of the vehicle being driven on roads covers with salt and various contaminants. This meant that considerable wheel movement would take place before the bar twisted and applied a force to the opposite wheel. The result was poor handling.

GM made a design change many years ago, moving away from soft covered bushings to a urethane blend. This was nothing new. As far back as the ‘60s GM had an option on its early muscle cars of original or replacement non-rubber, bronze-alloy bushings that attached the link to the bar in the lower control arm. These bushings provided some lubricating qualities and prevented squeaking, and they provided a much more responsive reaction when one wheel moved, causing the bar to twist.

On today’s suspension designs you’ll find a wide variety of stabilizer-link connections. Some are molded polymers or nylon-blended units with ball sockets. Some are the older style solid metal links. Some have a bushing on one end and a ball socket on the other.

Think about some of the link designs you find and how the force is transmitted. If you have a vertical stabilizer link attached to the lower control arm, and the lower end is a standard bushing arrangement with a couple of washers but the upper link is a ball stud arrangement, when the ball stud is allowed to move through some degree of travel, what is your reaction force going to be? It won’t be as great as it would be if it were a solid link, since the link tends to rotate in the ball socket first. This may provide ease of transition into the bar reaction, but it does little or nothing to provide responsive handling.

It would take an engineer to figure out all the specifications necessary, but vehicles with only front stabilizer bars are usually not as responsive or don’t have the handling the vehicles with front and rear bars have. It is generally understood that the rear stabilizer bar balances out the overall system, is supplemental to the front and fine-tunes handling characteristics. Changing the diameter of a vehicle’s front stabilizer bar can provide more reaction but may radically disturb the vehicle’s overall handling and balance.

The generally accepted procedure for testing stabilizer bars is to grasp the end links and snake them, and if they don’t rattle they are OK. This is not a valid test.

On stabilizer end links that contain ball-socket connections, you must be careful not to have the lower control arms extended or to have enough force on the links to allow them to seem tight when they actually are not. It is best to check the end links with the vehicle’s load on its tires. Grasp the links or use a pry bar to apply force while you feel for any looseness. On the older type of links, a visual inspection, along with grasping the links with the wheels on the ground, will enable you to detect any looseness.

The frame-attachment bushings on stabilizer bars often are overlooked and their condition mis-judged. Some people believe that as long as they are there and not protruding from the mounting bracket they are OK. Raise the vehicle, allowing the wheels to hang, and look at the shape of the hole. If it is severely elongated under load with both wheels hanging, what do you think happens to the bar when the vehicle is driven?

Rather than causing the bar to rotate as it should, a stabilizer bar frame contact bushing that is soft or deteriorated will allow the bar to rotate in the bushing. This means that more body roll and loss of vehicle handling will take place before the bar reacts or twists. I believe that you should always replace stabilizer bar bushings in complete sets. That means replace both frame attachment bushings and both end link bushings. Although it is not normally done this way, this is what will really restore your vehicle’s handling.

Stabilizer and sway bars are integral parts of overall chassis system. Certain vehicles have experienced high stabilizer bar failure rates in the past 20 years because of inadequate bar or link design or a load that exceeds the amount for which the system was designed. Many technicians in the field have little or no technical understanding of stabilizer bars. Obtain deMarcellus’ book and read it. You may only understand 20% of the information the first time you read it, but you will understand more with each successive reading. It is perhaps the best-written, most practical accumulation of technical information regarding vehicle handling and stabilizer bars available today.

All the procedures for inspection and determining serviceability will at least allow you to have the vehicle deliver the handling and operating characteristics of the stabilizer bars found on them. Several years ago, stabilizer bars almost disappeared from vehicles. They have found their way back into modern design chassis systems and continue to be used. However, they must be maintained with correct bushings and mounts or the benefits they were designed to provide will not be available to the vehicle operator.