Lifting a 4WD almost seems mandatory these days. However, when changing the height of your vehicle from the factory ride height, your steering system can be affected. Thus, it is vital to ensure that this area is carefully considered and the proper changes made to preserve safe tracking of the vehicle.
There are two basic types of steering systems used on most live front axle 4WDs, and we will consider changes to each. The first type, typically referred to as crossover steering, is found on many live-axle Fords, Dodges, and Jeeps. The second type of system may be referred to as a push-pull system. These are often found on live-axle Chevys and Toyotas.
Live-axle steering systems use a drag link to connect the steering box's pitman arm to one side of the axle assembly to allow turning one of the knuckles on the axle. Then a tie rod is used to transfer the same steering input to the opposite knuckle on the axle. In both cases, a hydraulic steering stabilizer is often used between the tie rod and axlehousing to damp any unwanted steering oscillations.
In a crossover steering system, the pitman arm on the steering box rotates in a horizontal plane, or parallel to the ground. The drag link ideally runs parallel to the axlehousing and connects the pitman arm to a point on the passenger side, either to a point on the tie rod or to an arm on the knuckle itself.
The illustration on this page shows a simplified front view of a crossover steering setup. Note that in stock form the tie rod and drag link are very near parallel to each other and to the ground. This is important to prevent a condition known as bumpsteer. As the suspension cycles up and down, the drag link moves from its flat position to an angled position during compression or extension. When this happens, the effective horizontal length of the drag link changes and the front axle steers back and forth slightly, but insignificantly.
Whenever lift is added to the vehicle, the vertical distance from the pitman arm and axle increases. This causes the drag link to rise on the pitman end so that it is no longer parallel to the tie rod. Now, whenever the suspension cycles up or down, the change in the effective horizontal drag link length is greater, and the back-and-forth steering movement at the front axle increases. This bumpsteer can make your 4WD wander on bumpy, uneven roads.
Some companies offer S-link or curved drag links with lift kits. While these drag links can solve suspension clearance issues due to adding a lift and can help reduce tie rod end angles, they do nothing to correct the non-optimal steering geometry introduced by the lift. Since both ends of the drag-link swivel freely, drag-link shape has no effect on the tracking and bumpsteer performance.
One effective way to restore near stock steering geometry is by installing a dropped pitman arm. This is essentially a replacement pitman with a greater vertical drop than the stock arm. Installing such an arm drops the pitman end of the drag link lower so that the drag link is again close to parallel to the tie rod and axle.
Push-pull steering systems are affected by many of the same issues listed above. However, steering geometry changes may be more exaggerated, because the drag link in a push-pull system is considerably shorter than that used in a crosssover system. This means that the change in drag-link angle from horizontal is greater for push-pull than for crossover when given equal lift heights. Drag-link angle, again, should optimally be kept flat.
One method commonly used on push-pull setups to reduce steering geometry problems is that of replacing the stock knuckle steering arm with one that is raised. Raising the point of attachment where the drag link meets the steering arm effectively reduces the drag-link angle, bringing it back closer to our ideal horizontal condition. Depending on the type of arm used, this may be accomplished by providing an arm with a taller rise on it or by flipping the steering arm pivot ball to the top of the arm.
Adjustable S-link drag links are also sometimes available for push-pull systems. As in a crossover system, these will not correct the steering geometry caused by the lift-induced drag-link angle. However, they may be helpful when suspension component clearance is a problem or when a shorter or longer drag link is required.
When lifting a truck that uses push-pull steering, give careful consideration to the steering joint limits with respect to preventing bind under suspension compression or extension. Aftermarket-designed kits should have these factors taken into account. However, when deviating from proven sets of components, ensure that the drag link does not bind under any suspension cycling conditions. Long-term conditions where binding occurs could lead to steering component fatigue and possible failure.
For either steering system, there are several factors other than geometry that can affect overall stability. All bearings, tie rod ends, and ball/sockets should have no excess play. Additionally, proper wheel bearing adjustment is critical, along with proper knuckle bearing preload to prevent side-to-side wander and to minimize the effect of bumpsteer or front tire wobble. Finally, the steering box should be adjusted to eliminate any excessive free play, while making sure it is not adjusted too tightly and causing any bind at the neutral steering position.
Lifting a vehicle and installing larger tires can greatly enhance the look and performance of a vehicle. Proper geometry and components will help ensure your steering system provides safe and predictable response.
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