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Steer Clear

Posted in How To on October 17, 2002
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Precise and responsive steering is a must on any vehicle, but it's especially important on an off-road machine. After all, a truck that's steered a few inches off line on the street is usually no big deal, but when the road is a washed-out trail, a pit of sticky mud, a collection of boulders, an off-camber slope across a rugged hillside, or no trail at all, accurate steering is a must, lest you put a tire wrong and you and your ride suffer the consequences.

Besides steering the truck where the driver wants it to go, the various components of a steering system must be durable because they're subjected to huge loads produced by rugged terrain and large wheels and tires. Another steering factor to consider is geometry and the manner that a steering system's linkage is setup and adjusted. This is especially crucial because lifted suspension systems require altered steering components and special alignment procedures that are not OE-style nature.

With this steering story, we're going to take a look at the aforementioned steering characteristics, OE as well as modified steering systems, performance aftermarket steering upgrades, basic and advanced steering geometry, and all of the accessories and components that make for a highly functional and robust steering system.

Steering Systems: From Steering Shaft to Steering Knuckle

Fundamentally, a steering system takes the rotational input of the steering wheel and routes it through a series of gears, links, and rods and turns that motion into a lateral movement that steers the wheels and tires from side to side. More specifically, the steering wheel turns a steering shaft that turns the input shaft of a steering box that's connected to a worm gear and a piston rack. The worm gear and piston rack multiplies the input shaft's rotational motion and ultimately sends this movement through a 90-degree turn and onto the steering box's output or pitman shaft. The steering box's output shaft takes the rotational motion and changes it into a lateral -- or in some cases, a longitudinal -- movement via a steering arm, a drag link or a pitman arm, and the steering knuckles.

Steering Geometry and Alignment

Although it's unlikely that you'll be performing a complete frontend alignment at home, it's an excellent idea to familiarize yourself with the various components involved in wheel alignment because wheel alignment has a tremendous effect on steering response and feel. One aspect of wheel alignment that has a huge effect on steering is the caster angle, known to old-timers as a kingpin angle.

Basically, caster refers to the vertical angle of the steering knuckle, whether that knuckle is on a solid front axle or on an IFS (2WD or 4WD). When viewed from the side of a knuckle, caster is usually seen as the rearward angle of the knuckle; that is, the top of the steering knuckle is angled slightly toward the rear of the truck. The caster angle increases a truck's straight-line stability and is usually set between 2 and 6 degrees for a solid front axle; as much as 8 degrees for an IFS.

With the caster set as described, the steering will exhibit a self-centering action, especially when exiting a corner. On the other hand, with the caster set near zero, drastic changes occur, such as twitchy steering at highway speeds and the absence of a self-centering effect. Excessive caster is also a problem because it causes the steering response to become heavy and less responsive, and the steering system resists turning into corners, although straight-line tracking is maximized.

Now that we've looked at caster, let's analyze the effect lifted leaf spring packs have on caster angle. Again, viewed from the side, consider the installation of a new lifted set of leaf spring packs may position the axlehousing slightly ahead or slightly behind its original location. Imagine a lifted spring pack that places the axlehousing closer to the front spring hanger or shackle. Such a position would rotate the axlehousing and the top of the steering knuckle rearward because of the curvature of the spring pack and would create additional caster. The opposite would hold true if the lifted spring pack positioned the axle slightly closer toward the rear of the truck than the steering knuckle's caster would decrease.

Staying with the subject of unintentional caster changes, we find that many lifted aftermarket leaf packs employ a thin 1-3-degree shim at the bottom of the spring pack, which is intended to keep the driveshaft's U-joints from binding when the ride height is increased. However, when the thick end of the shim is placed toward the front of the truck, the steering knuckles are rotated forward, with the resulting loss of caster angle. Also keep in mind that caster changes occur when a multi-link equipped solid-axle suspension is lifted.

If taller than stock coil springs are installed, the increase in ride height will position the locating links at a new angle that will change the caster angle. If longer locating links are installed, they too may change the caster. Steering system's toe setting controls the angle of the front wheels. Viewed from above the frontend, toe is the distance between the leading and trailing edges of the front wheels. When the front of the wheels are closer together than the rear of the wheels it's referred to as toe-in; toe-out is the opposite. On any truck the toe adjustment is crucial to straight-line stability. Improper toe adjustment will result in noticeable wandering or drifting at highway speed as well as uneven tread wear.

Camber is the inward (negative) or outward (positive) angle of the top of the tires viewed from the front. The camber angle of an IFS truck is important to proper handling, steering, and tire life because it determines how the tire contacts the road surface. With a truck at ride height, camber is usually close to zero, which places the tire tread flat against the road. Negative or positive camber will change (decrease) the tire contact patch. The best scenario would be to have the tire at zero camber throughout the suspension's travel, but that's not possible because of the arc an IFS suspension travels through. Often 1 or 2 degrees of negative camber is set into the alignment at the truck's static ride height so the tire is flat against the road surface when the vehicle is cornering. Excessive negative camber will cause excessive wear on the inside edge of the tread and create more heat in the tire because a smaller portion of the tread is carrying the vehicle's weight. Excessive negative camber also will reduce the steering feel, response, and tracking.

An interesting aspect of steering geometry is the Ackermann angle. When a truck is steered into a corner, its outer front wheel must travel a longer path than the inside wheel. Therefore, the angle of steering for the outside wheel must be less than the inside wheel that is steered in a noticeably tighter arc. Setting the steering geometry to effect the proper Ackermann angle ensures the front tires maintain contact and don't skid laterally during cornering, whether that cornering is on dirt or pavement. The Ackermann angle is not truly adjustable: its parameters are set at the factory and adjustment would require extensive mods to the steering linkage.

* This illustration shows the major components of a Toyota solid-axle steering system. The pitman arm takes direction from the steering box (not shown) and sends the input to the drag link then onto the steering knuckle arm. The input then moves to the tie rod that links the left and right steering knuckles together.

* Ford's Super Duty truck uses a slightly different approach to solid axle steering. The steering box moves a steering arm (A) that moves a lateral drag link (B) that moves a steering knuckle on the passenger side (C). The knuckle is attached to a tie rod (D) that connects to the driver-side steering knuckle (E).

* GM 2WD IFS illustrates the steering layout of most IFS trucks. The steering arm (A) is attached to the steering box's output shaft and moves the centerlink (B) in a lateral path. An idler arm (C) supports the centerlink on the passenger side and tie-rods (D) transmit steering movement to the steering knuckles.

' Caster is easy to understand. Take a look at this diagram and you'll see how the top of the steering knuckle is tilted back in relation to the bottom of the knuckle. Proper caster angle helps with steering stability and response and enhances the steering's self-centering trait.

* Camber is crucial to the tire's contact with the road surface and has an effect on steering stability. Most trucks use a small degree of negative camber (the top of the wheels angled inward) at static ride height. Too much negative camber will cause a loss of steering response and feel and will decrease a truck's straight line tracking because the tire's contact patch isn't fully planted.

* The toe setting is illustrated with these two diagrams. Illustration A shows toe-in where the leading edges of the tires are closer together than the rear of the tires. Toe-out is the opposite. For proper steering, straight-line tracking, and tire wear, the steering should be set up with a slight amount of toe-in because the truck's forward motion actually pushes the wheels to a zero toe attitude.

* The Ackermann steering angle describes the difference in steering angle between the two front wheels and tires as a truck corners and turns. Because the truck's inside tire covers less ground than the outside tire when rounding a corner, the steered angle of the inside wheel is more than the outside wheel. The outside wheel and tire have a longer path around the corner, so its steering angle is less. The Ackermann angle effectively minimizes a vehicle's tendency to skid or scrub the front tires when cornering.

Steering Shafts and U-joints

Because many of the trucks popular with enthusiasts are more than 20-years-old, it stands to reason that steering components of suspect strength should be upgraded for safety's sake. One such item is the OE steering shaft that connects the steering column to the steering box. When a truck is used in a heavy-duty application such as towing or for rough 'wheeling, or when fitted with oversized tires and wheels, the OE steering coupler receives a lot of stress and can show signs of wear in a little as 5,000 miles. It may exhibit symptoms such as vibration through the steering wheel and excessive steering play.

The best way to cure steering shaft problems is to install a performance aftermarket shaft such as the units manufactured by Borgeson Steering System Components. The Borgeson Replacement Truck Steering Shaft is available for Dodge, Ford, and Chevy fullsize trucks as well as for Jeep CJs and Wranglers. The Borgeson units feature a telescoping shaft, a needle-bearing U-joint, and a true bolt-in design. Select models of the Borgeson Truck Steering Shafts include a vibration reducer and a second U-joint.

* The recirculating ball steering box has been used for decades to steer trucks. Its use continues, although manufacturers have started to equip certain 2WD trucks with rack-and-pinion steering systems. In function, steering input from the driver turns the worm shaft (the drive gear), which is fitted with a spiral-threaded worm gear. The driven gear is the sector gear that has corresponding gear teeth in a semi-circular pattern. The worm gear is threaded into a ball nut that has an internal spiral groove and a set of ball bearings between the worm gear and the ball nut. The outside of the ball nut has teeth that engage with the teeth on the sector gear. As the worm gear rotates (from steering shaft/wheel input), the ball bearings transmit turning force from the worm gear to the ball nut, which moves in and out. That movement turns the sector gear and shaft, which rotates the output shaft.

' Hydraulic fluid flows through a steering pump and box is an important factor in both component's performance and longevity. In particular, large tires and tough terrain place a huge amount of stress on the hydraulic fluid, which will often cavitate or foam, thus causing a loss of steering response and often a loss of lubrication to the pump's gears. When the gears lose lubrication, they seize and then the pump is junk. Howe Performance Power Steering maximizes fluid flow through the pump and steering box with the installation of a larger than stock hose fitting on the pump's return line. This allows the fluid to return to the pump with far less restriction than a small standard fitting. In the photo, the return line from the steering box to the pump (left) is fitted with a -8 fitting while the pump outlet/box inlet fitting (right) is a standard sized -6.

' As you may have surmised, the power steering pump is crucial to a steering system's function. On the left is an OE-style Saginaw pump that can be used in a high-performance application after a few upgrades to its hydraulic system. On the right is a late-model OE Jeep pump, which is unreliable for use with huge tires and is replaced with a Saginaw truck box on performance applications.

' Hydraulically assisted steering is an upgrade from a manual steering box, and it's virtually a requirement with big tires. A hydraulic power system includes a pump, a hydraulic fluid reservoir, hydraulic lines, and a hydraulic steering box. The hydraulic pump and the pump reservoir are mounted to an engine bracket and are powered by an accessory drivebelt. The lines carry hydraulic fluid to and from the steering box. The hydraulic box is similar to the manual box, but the ball nut also functions as a hydraulic piston separating the steering box into two chambers. When the steering wheel is turned, a control valve directs hydraulic pressure to one side of the ball nut (left or right, depending on which way the steering wheel is turned) which helps push the ball nut, thus reducing steering effort.

' If you need the ultimate steering pump feast your eyes on this special Howe unit. Originally designed for industrial use on heavy-duty (5-ton) trucks, the pump is overkill for an OE-style steering system, but required on the Trophy Truck-style full-hydraulic steering system Howe manufactures. The complete ultimate power steering system includes the big pump, a 2- or 2.5-inch-diameter hydraulic cylinder, a scratch built steering rack, and a remote hydraulic fluid reservoir.

' Howe Performance Power Steering fabricates this slick aluminum canister that holds an additional two quarts of hydraulic steering fluid and reduces fluid aeration through the use of special internal baffles. The remote canister is fitted with a fullsize engine oil filter to keep the steering fluid clean, and a twist-on top-mounted filler cap for easy access to the fluid.

* The latest trend in steering is the addition of a hydraulic ram. Upgrading to a hydraulically assisted steering system is straightforward: The pressure and return lines to and from the steering box are tapped into, and lines are run to the hydraulic ram, which is attached to the steering linkage and either the frame (IFS) or axlehousing (solid axle). Howe builds custom hydraulic cylinders in any length and diameter to accommodate any type of steering system from OE-based to full custom. The front cylinder is a 1-inch diameter and 6-inch stroke model; the center cylinder is an 8-inch-stroke and 1.5-inch diameter unit; and the rear is a 2-inch diameter and 10-inch stroke cylinder.

Steering Linkage: Make the Connection

The various linkage of a steering system are often the weak link in a high-performance steering system. Honestly, it's a testament to the quality of the OE parts that the stock steering linkage survive when subjected to the amount of stress created by extreme use and oversized tires. Of course, why use stock steering linkage when there are aftermarket upgrades? Replacing various steering links with aftermarket components is an excellent upgrade because performance and durability are each enhanced. Here are just a few of the options for stronger than stock steering linkage.

' Full-size 2WD GM trucks running large tires often experience failure or extreme wear of the idler arm, which leads to sloppy and inaccurate steering response. Moog has developed a line of replacement steering parts designed specifically to remedy such problems. The Moog M2 components include ball joints, antisway bars, tie rod ends (left), and idler arms (right). Each features a metal pivot stud in a full-ball configuration which provides 360 degrees of rotational movement for highly responsive steering, an all-metal gusher bearing design for improved lubrication of the bearing surface, and a unique double bearing for reduced steering effort.

0212or Steering18 Photo 8515966

* Owners of IFS trucks have probably looked at the OE tie rod adjusting sleeve and wondered if it's up to the task of off-roading. In extreme cases, the answer is no. Large tires, aggressive driving, and a suspension lift can all conspire to cause the slotted sleeve to lose its adjustment which changes the steering and alignment. If the sleeve breaks outright, the tie rod end will separate from the suspension linkage causing a dangerous condition. Fabtech manufactures a steel adjusting sleeve for many truck applications that is best described as a solid metal rod that's internally threaded and hell for strong.

* Autofab's Steering Box Gusset Kit for '73-'87 GM full-size trucks and '73-'92 Blazers and Suburbans is a tried and true method for strengthening the frame section where the steering box mounts. The frame flexing problem begins with the steering box's mounting position on the outside of the framerail, which places a lot of stress on the open channel framerail. This is compounded by the use of aftermarket springs and large-diameter tires, which focuses additional stress in an area that's already marginal in terms of strength. Also, time can take its toll on the framerail, as rust will further weaken the area where the box is attached. The Autofab Steering Box Gusset Kit (available for 4WD and 2WD trucks) addresses all of these concerns except the rust problem. If the frame is rusted through you'll have to weld in a replacement frame section before installing the Autofab brace. The brace's triangulated design is well thought out as it ties the framerail and steering box to the frame's front crossmember. To maintain the OE steering box's stock location the brace is installed inside the open framerail with Grade 8 fasteners.

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