This manual discusses vehicle wheel alignment and track alignment for construction equipment. For automotive vehicles and trucks, wheel alignment is a process of repositioning the suspension and steering parts and components for normal wear and effects of replacing parts. Track equipment is altogether different from wheeled vehicles, but the principle of track alignment is the same to ensure the track maintains proper alignment and adjustment to prevent wear and stress on the equipment.
The manual begins with steering geometry and understanding that wheel alignment involves checking and adjusting a complex series of interrelated angles, covering camber angle, caster angle, kingpin inclination, toe-in, turning radius, and tracking.
The next topics include safety and tools for front-end alignment, and alignment procedures.
The subsequent topics break down the adjustable and nonadjustable angles and cover them in greater depth, discussing what to perform for each.
The following topics cover the various steering and alignment problems stemming from defective parts, bent frame, defective tires, road crown and road irregularities, vehicle load and acceleration, braking, and turning forces.
When you complete this manual, you will be able to:
Camber is the inward or outward tilt of the top of the wheels when viewed from the front of the vehicle, as shown in Figure 1. If the centerline of the tire is exactly vertical, the tire has a camber setting of zero degrees. If the top of the tire tilts outward, it has positive camber, and if the top of the tire tilts inward, it has negative camber. Positive and negative camber is shown in Figure 2.
Figure 1 - Camber is the inward or outward tilt of the tire when viewed from the front of the vehicle.
Figure 2 - Positive and negative camber.
Camber settings of +¼ degrees for the curb side and +¾ degrees for the driver side wheels are typical. The amount of camber used depends on the kingpin inclination (KPI) setting. Kingpin inclination is the inclination of the steering axis to a vertical that is the equivalent of steering axis inclination (SAI) in automotive front ends.
Incorrect camber angle results in abnormal wear on the side of the tire tread. Excessive positive camber causes the tire to wear on its outside shoulder. Likewise, excessive negative camber causes the tire to wear on its inside shoulder. Unequal camber in the front wheels also can cause the steering to lead to the right or left. The vehicle will lead to the side that has the most positive camber.
Camber adjustments are not often made on heavy-duty truck axles. Some service facilities with specialized equipment adjust camber by cold bending axle beams, but, generally, axle manufacturers do not approve this practice. Bending an axle can damage the structural integrity of the beam, increase the risk of metal fatigue, and lead to the axle breaking. Heating and bending the axle should never be attempted as it removes the heat-tempering camber.
Look at a furniture caster and note that the caster can swivel around its attachment point. This attachment point can be thought of as the center about which the caster swivels. When the furniture is moved, the center moves before the caster wheel. If the center is behind the caster wheel, the wheel will swivel and follow behind the center. This occurs because the wheel has less resistance if it follows the center than if it attempts to stay ahead of it. Even when the wheel starts out directly ahead of the center, it will quickly move to one side or the other. This increases the friction on the wheel because it is trying to turn at an angle to the direction of movement. The wheel will continue to turn around the center until it reaches its point of least resistance, which is directly the center.
The principle that makes the caster work is applied to vehicles to make steering easier. The upper and lower ball joints or the lower ball joint and strut mounting form the steering axis, as shown in Figure 3. The steering axis is an imaginary line between the upper and lower ball joints or the lower ball joint and the strut mounting. The caster angle is usually referred to as caster. As with camber, caster is usually small. Common caster specifications range from one half degree to three degrees, with a maximum of about seven degrees. Caster can be positive or negative.
Figure 3- Steering axis.
Positive caster. If the imaginary line of the steering axis strikes the ground of the point at which the tire contacts the road, the tire and wheel will follow behind the steering axis (Figure 4). This keeps the wheel and tire assembly from wandering, since it wants to follow behind the centerline set up by the steering axis. This is positive caster. To get positive caster, the lower ball joint must be ahead of the top ball joint or the strut mounting. Like the furniture caster, the tire finds the path of least resistance by following behind the steering axis line. This tendency of the wheels to continue to move in a straight line is called tracking.
Figure 4 - Positive caster.
Positive caster causes the wheels to travel straight ahead and increases steering ability. Positive caster also assists in recovery. Recovery is the tendency of the wheels to turn back to the straight- ahead position after the driver completes a turn.
There are some disadvantages to positive caster. Positive caster makes it hard to turn the wheels from the straight-ahead position when entering a turn. On vehicles with power steering, this is not usually a problem. Positive caster also contributes to body roll. During a right turn, positive right wheel caster will cause the right steering knuckle to rise slightly, while the left side knuckle will drop slightly. This causes the vehicle to rise on the inside of the turn, reducing cornering ability. When the wheels are turned to the left, the left steering knuckle rises and the right knuckle drops.
Negative Caster. To ease turning, vehicles today have negative caster (Figure 5). Negative caster is obtained by placing the upper ball joint or the strut mounting ahead of the lower ball joint. With the steering axis behind the tire contact point, there is no caster force causing the wheels to track forward. Other alignment angles compensate for the lack of tracking to ensure steering stability is not compromised. Negative caster also helps compensate for body roll when the vehicle is turned. During turns, negative caster causes the outside steering knuckle to raise and the inner steering knuckle to lower. This compensates somewhat for body roll, making the vehicle more stable.
Figure 5 - Negative caster.
Caster has almost no effect on tire wear, but improper caster can cause wheel pull and other handling problems. Wheel pull is the tendency of the vehicle to drift to one side when the driver releases the steering wheel when the vehicle is moving. A large difference in caster between the two front wheels will cause pulling to the side with the least positive caster. If one wheel is more negative than the other (even if both are negative), the vehicle will pull toward that wheel. Excessive negative caster can also cause bump steer. Bump steer is a condition in which the vehicle tries to steer away from the driver when it travels over the road irregularities. Since caster primarily affects steering and front wheel tracking, it is not measured on the rear wheels.
Kingpin inclination (KPI) is the amount in degrees that the top of the kingpin inclines away from the vertical, viewed from the front of the truck. Kingpin inclination in conjunction with camber angles places the approximate center of the tire tread footprint in contact with the road. KPI reduces steering effort and improves the directional stability. KPI cannot be adjusted on trucks. Once set, KPI should not change unless the front axle has been bent. Corrections or changes to this angle are accomplished by replacement of broken, bent, or worn parts.
Toe is the tracking angle of the tires from a true straight-ahead track. If a line were drawn through the centerline of each tire and compared to the centerline of each tire and to the centerline of the vehicle (the true straight-ahead position), the amount of deviation between the two lines indicates the toe angle of the tire. When the centerline is exactly parallel with the vehicle centerline, the toe angle is zero. When the front end of the tire points inward toward the vehicle, the tire has toe-in. When the front of the tire points outward from the vehicle, the tire has toe-out. You can see toe-in and toe-out by looking a Figure 6, which you are observing from an overhead viewpoint.
Figure 6 - Toe-in (left) and toe-out (right).
The ideal toe angle, when a vehicle is running loaded down a highway, is zero. We set toe angles statically. The objective of setting toe at a specified angle when aligning the front end is to have zero toe at highway speeds. Incorrect toe angles not only accelerate tire wear, but also can have an adverse effect on directional stability of the vehicle. In fact, incorrect toe angles have the potential to cause more front tire wear than any other incorrect alignment angle. Too much toe-in produces scuffing, or a featheredge, along the inner edges of the tires. Excessive toe-out produces a similar wear pattern along the outer edge of the tires. In extreme cases of toe-in or toe-out, feathered edges develop on the tread across the entire width of the tread face of both radial and bias-ply tires.
Because the objective is to have a zero toe angle under running conditions, most truck specifications require a zero or a slight toe-in setting. When a fully loaded vehicle is moving at highway speeds, there is a slight tendency of steering tires to toe-out. Any looseness in the steering linkage and tie-rod assembly also will contribute to the toe-out tendency. On newer vehicles, most radial steering tires are set with zero toe angle and bias-ply tires are set with a fractional toe-in.
Toe is specified in either degrees or fractions of inches, depending on the type of alignment instruments you are using. When a toe-in setting is required, settings of 1/16 inch ± 1/32 inch are usually specified. The toe specification usually depends on whether radial or bias-ply tires are used. Adjustment of toe angle or dimension requires lengthening or shortening the tie-rod dimension. This is achieved by loosening the tie- rod end clamp and then rotating the cross tube.
To determine the cause of excessive tire wear that you suspect to be related to toe angle, you should first check kingpin inclination, camber, and caster. Correct, if necessary, in this order. You should not make an adjustment to toe angle until the other factors of front-wheel align are known to be within specifications.
When measuring toe angle, the front suspension should be neutralized. To neutralize the suspension, roll the vehicle back and forth about half of a vehicle length. This relaxes the front suspension and steering linkages. Neutralizing the front suspension is important before making front-end adjustments, especially if the vehicle has been jacked up on either side to scribe the tires. This operation causes the front wheels to angle as each is returned to the floor. When possible, use a scissor jack that cradles both sides of the front axle when working on front ends.
If you begin by neutralizing the front end, both front wheels should at this point be in the exact straight-ahead position. Toe-in measurements should be taken across the hub centerline, front, and rear on each tire (Figure 7. Make sure that the wheels are on the ground and fully supporting the vehicle weight. Measure and record the measurements. The difference between the front and rear measurements is the toe specification.
Figure 7 - Determining toe.
After measuring toe, you can use the following procedure to adjust toe angle:
Recheck the toe setting after any change in caster or camber angle.
Turning radius or angle is the degree of movement from a straight-ahead position of the front wheels to either an extreme right or left position. Two factors limit the turning angle: tire interference with the chassis and steering gear travel. To avoid tire interference or bottoming of the steering gear, adjustable stop screws are located on the steering knuckles (Figure 8). Turning radius or angle should be checked using the radius gauge described earlier. If turning angle does not meet specifications, it should be corrected.
Figure 8 - Stop screw determines the maximum turning angle.
To make an adjustment to the turning radius, use the following procedure:
A stop screw is located on each end of the axle housing for the purpose of limiting the amount of the turning angle of the wheels. These screws are not adjusted in accordance with the frame and tire interference, as in conventional steer axles. The stop screws in front drive axles limit the operating angle of the universal joints in the drive axle shafts. You should reference the OEM service manual before making adjustments.
Ackerman geometry is the means used to steer a vehicle so that the tires track freely during a turn. During a turn, the inboard wheel on a steer axle has to track a tighter circle than the outer wheel. In other words, the outer tire has to travel just a little further because of the wider arc it has to follow. Ackerman geometry is also known as toe-out during turns. It allows the inner and outer wheel to turn at different angles so that both wheels can negotiate the turn without scrubbing, as shown in Figure 9.
Figure 9 - Ackerman geometry.
To achieve the required Ackerman angle, the steering wheels intersect on the axis of the rear axle again (Figure 9). On single drive axles, the centerline of the drive axle is the rear axis. On tandem drive axles, the intersecting axle is centered between the two drive axles, as illustrated in Figure 10.
Figure 10 - Measuring wheel base for single and tandem drive axles.
The Ackerman angle built into the steering geometry actually provides perfect rolling angles or both front wheels at only one turning angle. Anything other than this turning angle introduces an error, the size of which depends on the length and inclination of the tie-rod arms. As a result, the lengths of the cross tube and tie-rod arms have to be selected so as to minimize the error throughout the full range of steering angles possible on a particular front end. In trucks, the Ackerman steering error has to be smallest at low turning angles, where the most steering corrections are made and at the highest speeds.
Toe-out on turns is accomplished by having the ends of lower steering arms (those that connect to the tie-rods) closer together than the kingpins, as shown in Figure 11. Actual toe-out during a turn depends on the length and angle of the steering control arms and length of the cross tube.
Figure 11 - In a toe-out condition on turns, the inside wheel turns at a greater distance than the outside wheel.
Even if the toe-in setting with the wheels in a straight-ahead position is correctly adjusted, a bent steering arm can cause the toe-out to be incorrect, causing tire scuffing.
Turning radius angle should be checked using radius plates. To check the turning radius angles, you can use the following:
When a vehicle is running on the highway, all of the axles should be tracking perpendicular to the vehicle centerline; that is, the rear wheels should track directly behind the front wheels when the vehicle is moving straight ahead. When this happens, the thrustline created by the rear wheels is parallel to the vehicle centerline, as shown in Figure 12, View A.
Figure 12 - Correct and incorrect thrustline.
However, if the axles are not running perpendicular to the vehicle centerline, the rear wheels will not track directly behind the front wheels, and the thrustline of the rear wheel deviates from the centerline of the vehicle, as shown in Figure 12, View B. The steering controls fight the vehicle thrustline, resulting in an uncentered steering wheel and accelerated front tire wear, which causes the vehicle to oversteer when turning in one direction and understeer when turning in the other direction. Oversteering is an overresponse to steering input, which in vehicles yaw or lateral tracking off the intended turning radius. Understeer is an underresponse to steering input, most often causing steering tire slip at high speeds. Incorrect directional tracking can occur on single-axle vehicles, tandem- axle vehicles, and trailers. On a single-axle vehicle, the rear axle thrustline can be off if the entire axle is offset or if only one wheel has an improper toe angle. On a tandem axle, there are a number of different combinations that can cause incorrect tracking. Figure 13 illustrates some of these combinations.
Figure 13 - Typical incorrect tracking of tandem-axle vehicles.
One method of checking a single axle for misalignment is to clamp a straightedge across the frame so that it is square with the frame rails on each side. Then measure from the straightedge to the center of the hub. The distance on each side should be within ½ inch of each other. If not, the axle must be aligned.
It is also possible for the trailer axles to be out of alignment and cause a tracking problem. Depending on the severity of the trailer misalignment, it might be possible to see the effects of the misalignment as the trailer travels down the road. Usually, the trailer will travel at an angle to the tractor. Misalignment also makes it very hard to back up the trailer.
There are two basic ways that drive axles can be misaligned. In one case, if both axles are parallel but are not perpendicular to the vehicle centerline, then a resultant thrust angle is created. As shown in Figure 14, the drive axles try to push the vehicle away from the centerline.
Figure 14 - Incorrect tracking of trailers.
If the drive axles are not parallel, then the situation is described as a scrub angle problem, as shown in Figure 14. In this case, the drive axles are trying to turn the vehicle. In either case, to bring the truck's travel back into a straight line, the driver has to provide an opposing steering input. This need for continual correction can induce driver muscular fatigue as well as increased tire wear and reduced fuel economy.
Essentially, trailer alignment involves adjusting all components in such a way that the trailer tracks straight and true, and is a matter of adjusting how trailer components line up according to three parameters-axle orientation, axle toe, and axle camber. While trailer wheels can be out of alignment relative to camber and/or toe, according to some industry experts, the most common problem is axle offset. Axle offset, or dog-tracking, is displacement of the rear of the trailer to one side of the tractor when the trailer is being towed. Axle offset is expressed in degrees based on variance with the geometric driving axis, or thrust angle. Thrust angle is the angle between the longitudinal center plane and the geometrical axis.
- To Table of Contents -
The pad must be positioned under an area of the vehicle's frame or at one of the manufacturer's recommended lifting points. Your owner's manual will list safe jacking points in a few different areas, but is usually included in the spare tire section.
Never place the lifting pad under the floor pan or under steering and suspension components. These areas may look strong enough to hold a lot of weight but are not. Not only can these parts be damaged by the weight of the vehicle, but they can also cause severe injury to you when they let loose.
Never use a hydraulic floor jack to move something heavier than it is designed for.
Always check the rating of the floor jack and also the jack stands to be used on the vehicle.
Then, verify that the vehicle weight is below this rating. The (GVW) gross vehicle weight is in your owner's manual and also on the driver's side front door jam on most automobiles.
Safety stands, also called jack stands, are supports of various heights that sit on the floor. Make sure the surface they sit on is strong, flat, and level.
Concrete is preferred, and blacktop areas could be unsafe due to softness. Use 1½- inch thick lumber under the jack stands on blacktop areas so they do not sink into the surface.
Safety stands are placed under a sturdy chassis member, such as the frame or axle housing, to support the vehicle's weight.
Once the safety stands are in position, the hydraulic pressure in the jack should be slowly released until the weight of the vehicle is on the stands.
Like floor jacks, safety stands also have a capacity rating. Always use a jack stand of the correct size and weight rating.
Never put yourself under a vehicle when only a hydraulic jack supports it. Rest the vehicle on the safety stands before moving around the vehicle.
The recommended reason for removing the hydraulic floor jack after it is safely supported on the stands is that this will eliminate a hazard, such as a jack handle sticking out into a walkway.
A hydraulic floor jack handle that is bumped or kicked can cause a tripping accident or the vehicle to fall.
Raising a heavy-duty truck on a lift requires special care. Adapters and hoist plates must be positioned correctly on twin-post and rail-type lifts to prevent damage to the underbody of the vehicle. There are specific lift points to use where the weight of the vehicle is evenly supported by adapters or hoist plates. The correct lift points can be found in the vehicle's service manual. Before operating any lift or alignment machine, carefully read the manufacturer's literature and understand all the operating and maintenance instructions.
Heavy subcomponents, such as engines and transmissions, should be removed using a chain hoist or jacks. To prevent serious injury, chain hoists or the jacks must be properly attached to the parts being lifted. Use equipment of sufficient strength rating for the object being lifted or lowered.
The following are some general rules for using jacks, lifts, frame machines, and hoists:
To hold a 2,500- to 5,000- pound vehicle above the ground, the suspension must be very powerful. The weight of the vehicle puts the spring under a great deal of tension. This tension, known as spring tension, can injure you if it is not properly released. If you remove the bolts that secure parts under spring tension without properly releasing the spring tension, the parts could fly apart with great force. This force is great enough to break ribs or crush hands and feet. Always determine whether a part is under spring tension before removing its fasteners. If necessary, compress the spring to release the tension. If the fasteners seem to be under tension as the first few threads are loosened, stop immediately and determine why the part is still under spring tension. Never assume that the parts are not under tension.
Alignment machines. Using an alignment machine is the most convenient and reliable way to align a vehicle. The alignment machine takes the place of all the individual alignment units. It has alignment units, usually called heads, that attach to the wheels of the vehicle. The heads are used in combination with a special rack, front and rear turning plates, and other components to check all alignment angles in one operation.
You may have once used an older alignment machine that used light beams to display readings on a screen mounted in front of the vehicle. Heads installed on the front wheels generated the light beams, which were directed on the screen. Markings on the screen allowed the mechanic to translate the position of the light beams into alignment angles.
Electronic align machines are now commonly used. These machines have four heads, one for each wheel. When all four heads are installed on the wheels, they transmit a laser beam or infrared light to each other. The system's computer receives readings from each of the heads and computes the front and rear wheel alignment. The alignment readings are displayed on a computer screen.
Alignment machines use flat panels that contain target dots. The panels attach to the vehicle's wheels. The alignment machine's computer calculates the position of the target dots and displays the vehicle alignment on the computer screen. This system is simpler to set up than older systems.
Alignment wrenches. Various specially designed wrenches are needed to perform alignments. Alignment wrenches are specially shaped wrenches. These wrenches are often thinner than normal so they can fit in tight spots. Some alignment wrenches are self-contained; others are designed to be used with a ratchet.
Ball joint and tie-rod end removal tools. Many ball joint and tie-rod end removal tools are screw-type pullers with two or more arms that fit around the part. Tightening the central screw on the tool forces the tie-rod stud from the associated part. A variation of this tool expands between the stud and an adjacent component to remove the stud from the associated part.
A fork-shaped tool with two pointed tines is often used to remove a ball joint stud from a part. This tool is usually called a pickle fork. The fork section is inserted between the ball socket fitting and the linkage part. Hammering on the end of the tool forces the fork between the parts, breaking them loose.
Coil spring compressor. A coil spring compressor must often be used to compress coil springs during removal and installation. If the springs are not compressed before the fasteners are removed, the suspension parts will fly apart with great force. On most vehicles, an uncompressed coil spring cannot be reinstalled. Two types of coil spring compressors are required to service coil springs: the MacPherson strut spring compressor and the conventional spring compressor.
Bushing installers. Bushing installers are used to install and remove bushings in control arm, strut rods, and stabilizer bars. Some installers are round drivers. Drivers are used with a hammer to drive bushings in control arms, strut rods, or stabilizer bars.
Another type of bushing installer resembles a large C-clamp with adapters. The bushing is placed in the installer and the screw is tightened to force the bushing into the part.
Hammers. Hammers are used to loosen parts and to drive bushings and seals into place. Typical hammers used are ball peen, soft face, or rubber mallet. It is important to use the proper hammer for the job. Select a hammer that is large enough for the job. Never use claw hammers or other woodworking hammers for automotive service.
Inner tie-rod tools. The inner tie rods of most rack-and-pinion gears are threaded directly into the rack. To remove the tie rods, an inner tie-rod tool is used. This tool is a tube with a slotted opening on one end and a ½-inch drive fitting on the other end. After removing the outer tie rod, bellows, and any locking pins at the rack, place the inner tie- rod tool over the inner tie rod. Turn the tool with a ½-inch wrench to remove the tie rod. Most inner tie-rod tools can also be used to install a new inner tie rod.
Lever-type adjusting tool. To move the control arms on various vehicles, a lever-type adjusting tool is needed. The tool is typically attached to the control arm and the frame.
With the control arm fasteners loosened, the tool's handle can be moved in either direction to move the control arm.
Mechanical alignment testers. Many shops have various alignment devices that operate mechanically. Using these devices requires more time and attention than using the alignment machines. However, if used carefully, mechanical devices do an excellent job of aligning front suspensions. These devices cannot be used to check rear suspensions.
Metal cutting tools. Suspension components or frame metal must be cut to allow for part removal and vehicle alignment. In other cases, suspension and steering parts are tightly installed and are almost impossible to remove with hand tools. In these cases, metal cutting tools must often be used. Typical cutting tools are the following:
Rotary cutters can also be used for other jobs. Rotary cutters can be used with an air or electric drill.
Pitman arm puller. A pitman arm puller is used to remove the pitman arm from the gearbox of a conventional steering system. After removing the nut from the sector gear shaft, place the arms of the puller over the pitman arm. Then, tighten the central screw against the shaft to remove the pitman arm.
Pry bars. Pry bars are often used to free sticking or corroded parts. They are also used to move control arms during alignment procedures.
Punches and drifts. Punches and drifts are often needed to drive pins out of parts. Tapered punches are useful for aligning bolt holes in parts.
Tie-rod adjusters. On most conventional and some rack-and-pinion steering systems, the adjuster sleeves can be moved with a tie-rod tool. This tool has a hooked area that fits in the split in the sleeve. When the tool is turned, the hook tends to open the sleeve, allowing it to turn more easily. There are many variations of these tools. Some of them are self-contained units and others are used with a ½-inch drive ratchet.
Threaded adjusting tools. Threaded adjusting tools are used to move various parts of the suspension for alignment. These tools use a multiplying action of screw threads.
The tool typically consists of two rods with a central, threaded nut. The tool is installed with the rods in matching holes. There is one hole in the suspension part and the other is in the frame. With the fasteners loose, turning the nut causes the rods to move the suspension part in relation to the frame. A variation of this tool is used to adjust caster and camber.
Torque Wrenches. Torque wrenches are sometimes needed to adjust the tightness of wheel bearings, lug nuts, power steering gears, and other components. There are three basic types of torque wrenches.
Torque wrenches are designed to measure torque in Newton-meters, inch-pounds, or foot-pounds.
- To Table of Contents -
Correct wheel alignment is vital to vehicle operation. Incorrect alignment can cause handling problems, steering difficulties, pulling, poor tracking, and rapid tire wear.
Talk to operator. If possible, talk to the vehicle's operator if available and find out why he or she thinks the vehicle needs an alignment. Ask about the specific problems and how the vehicle is reacting when operated. On occasion, the problem may be something that an alignment will not fix. Worn parts or unbalanced tires may cause what the operator perceives as a wheel alignment problem. This is particularly true of vibration complaints. For future reference, explain to the operator that misalignment rarely causes vibration.
Road Test. If possible, road test the vehicle before beginning the alignment. Pick a quiet, level street for the road test. The road test can be brief, but it should be complete. Make a series of stops and turns. Drive several blocks in a straight line. Listen, look, and feel for road wander, unusual noises, pulling, hard steering effort, excessive road shocks, and other handling problems. The results of the road test will give you a basis for making other pre-alignment checks and for determining what alignment adjustments will be necessary.
To the shop. After the road test is complete and you have determined it is an alignment problem, drive the vehicle onto the alignment rack. Make sure that the front tires are centered on the turning plates.
Before beginning the alignment procedures, always check ride height, the tire and rims, and the vehicle's underbody.
Height. Check the riding height. If incorrect, adjust the height if the suspension uses torsion bars, or replace parts, as needed.
Before deciding that ride height is incorrect, check the backseat, trunk, or bed for excess weight. Remove excess weight before proceeding with the height check.
Worn parts. Once the vehicle is properly positioned on the rack, raise the front and rear wheels to check for worn parts. Do not skip this step. It is impossible to align a vehicle with worn or damaged parts.
If the vehicle is equipped with an electronic suspension system, open the trunk and turn the suspension switch off before raising the vehicle.
Raise the suspension so the ball joints are unloaded. On a suspension with the spring on the lower control arm, place the jack under the control arm. On suspensions with the spring on the upper control arm or around the MacPherson strut, place the jack on the frame. On solid axles, place the jack under the axle.
With the vehicle properly raised, perform a shake test. Grasp the wheel at the front and back and shake it. If the vehicle has an offset strut assembly, it may be necessary to grasp the wheel at about 45° counterclockwise from the top and bottom and then shake it. If the wheel moves excessively in any direction or makes knocking or clunking noises, look for worn or loose parts.
As a general rule, looseness when the wheel is shaken from the top and bottom indicates worn ball joints or very worn control arm or strut rod bushings. Worn tie rods or other steering system parts will cause looseness when the wheel is shaken from front and back. Loose or worn out wheel bearings usually cause looseness in all directions. If looseness is detected, have an assistant shake the wheel while you look for worn parts. Sometimes it is necessary to pry on parts using a pry bar. On some vehicles, the tie rods will be looser when the wheels are on the ground. Check your service manual for recommendations.
Once the shaker test is complete, visually inspect the suspension for wear, damaged seals, improper adjustment, or loose fasteners. Check the lower ball joints, upper ball joint (when used), control arm bushings, stabilizer bar bushings, and strut rod bushings. Check the steering gear, pitman arm and idler arm (when used), relay rod, and all tie- rod ends. Check the shock absorbers and struts for leaks. Check the operation of the power steering system and
ensure that the power steering reservoir is full. If the vehicle has any kind of electronic suspension system, make sure the warning light is out and no other problems are evident. Check the drive shaft or CV axles, as applicable. Look for looseness, torn boots, or obvious dents or bends. Shake or twist all flexible joints to uncover any looseness.
Tires and wheels. Inspect the vehicle's tires and wheels for damage, as shown in Figure 15. Carefully note tire conditions that might indicate an alignment problem. Figure 16 shows some common tire defects and their possible causes. If the tires were recently rotated, rear tire condition will be a sign of front- end problems, and front tire condition will indicate rear problems. Check the tire size and air pressure. You cannot align a vehicle when the tires are at different air pressures, are different sizes, or when one tire on an axle is worn and the other has ample tread. Add air or replace tires as needed. Spin the wheel to check for badly bent rims, dragging brakes, and loose wheel lugs.
Figure 15 - Tire condition can indicate alignment problems.
Figure 16 - Tread wear.
Underbody damage. Check all suspension and steering parts for bends, scrapes, and other signs of underbody damage. Carefully check the vehicle's frame at the front and rear for kinked areas or bends. Check for obvious severe setback on the front wheels, especially when collision damage is evident. The simplest way to check for setback is to measure the distance from the rear of each tire to the fender opening. If the setback varies by more than 1 inch between sides, a suspension part is bent. Make all necessary repairs before continuing with the alignment.
The following are procedures for setting up electronic or light alignment equipment.
Installing the Alignment Head. The alignment head consists of the electronic or light assembly and the head frame assembly. The electronic assembly is free to turn in relation to the head frame assembly, which is attached to the rim. A lock is used to tighten the electronic assembly to the wheel or frame when necessary. Most alignment heads are attached by clamping them on the inside of the rim. After the head is clamped to the rim, safety straps are attached to the rim to keep the head from falling on the floor and being damaged if the clamps slip. On some machines, alignment wires, called strings, must be installed between the front and rear heads.
Compensating the Alignment. All rims have some runout; therefore, there is no way to install the alignment head without slight misalignment between the rim and head. This runout must be removed to prevent inaccurate readings. The procedure to remove runout may vary from one equipment manufacturer to another. With most types of equipment, the procedure is to spin the wheel and rim ½ turn again and repeat the procedure.
Most computerized alignment machines use lights on the head or readouts on the screen to tell you when the head is properly compensated. Repeat the procedure for all wheels. When all four wheels are compensated, the screen will give a set of alignment readings. Since the wheels are off the ground, disregard the readings at this time.
Never allow the rim and head assembly to turn after it has been compensated. Any movement from the vertical (straight up and down) position will affect readings.
Lowering the Vehicle. Before lowering the vehicle, make sure the turning plates are centered under the wheels and remove the turntable locking pins. Apply the parking brake firmly and then lower the vehicle. When the vehicle is resting on the turning plates, bounce it at the front and rear bumpers. This will take any tension out of the suspension parts and allow the vehicle to settle to its normal resting position.
Centering the Steering Wheel. If the vehicle has power steering, start the engine and allow it to idle. Then turn the steering wheel from side to side several times to equalize play in the steering linkage. Then, center the steering wheel. Turn the engine off, if necessary. It is not necessary to install the wheel-holding tool. However, you will need this tool later during the alignment procedure.
Locking Brakes. Lock the brakes with a brake pedal depressor. This prevents excessive wheel movement while checking caster. At this time, you should firmly apply the parking brake. If the vehicle has an automatic transmission, shift it into park.
After all preliminary steps have been completed, the alignment can be measured. This should be done in the order given in the following:
Checking Camber and Toe. If the alignment machine has a display screen, front and rear camber and toe will be shown on the screen. On most machines, this is an automatic process once the heads have been compensated. On older alignment machines using lighted heads, the front camber and toe will be shown by the position and slant of the light lines on the display boards. If necessary, record the camber and toe readings.
Checking Caster. To check caster, be sure the brake pedal compressor is applied. Most alignment equipment manufacturers specify that the heads be locked into position (unable to pivot on the mounting frame) for the caster check. Turn the wheels to the left and right, according to the alignment machine manufacturer's instructions. This can be done by turning the wheels themselves or by turning the steering wheel. When using the steering wheel to turn the wheel, do not sit in or lean on the vehicle. This will change suspension height and affect the readings. On some systems, you must turn the steering wheel until the screen indicates that the readings have been obtained. On other systems, the turntables must be turned an exact amount, usually 20°. Record the caster reading if the alignment machine does not automatically do this.
Checking Steering Axis Inclination. Steering axis inclination (SAI) is usually checked as part of the caster checking process. SAI should be checked whenever there is evidence of collision damage or the vehicle has a handling or tire wear problem that cannot be accounted for by another cause. The brakes should be locked for the SAI check. Some equipment manufacturers specify that the heads be free to pivot on the head frame when both caster and SAI are checked in one position.
Checking Toe on Turns. Toe-out on turns is seldom incorrect, but it should be checked whenever you suspect steering arm damage or when the tires squeal excessively on turns. To check toe-out on turns, the brake pedal depressor should be in place. To make this check, turn one of the front wheels inward until the turntable indicator reads 20°. After this is done, move to the other side of the vehicle and read the indicator on that turntable. The reading should be slightly more than 20°. Record this reading; then turn the wheel inward to the 20° indicator on the turntable. Read the indicator on the other turntable. This reading should also be slightly more than 20°. Compare the readings with specifications. If the readings are incorrect, the steering arms should be replaced.
Adjusting Toe with Trammel Bars. When a vehicle needs only toe adjustment, a trammel bar can be used. To use a trammel bar, rise both wheels off the ground and scribe a mark completely around the tire. Hold a punch or other pointed tool against the outside of each tire tread as another mechanic spins the tire. Then place the vehicle on the ground and drive it back and forth a few times to settle the suspension. Use the trammel bar to measure the distance between the scribed lines at the front of the tire.
Then measure the distance between the lines at the rear of the tires. The measurement can also be done with a steel tape if you have an assistant to hold one end of the tape. No matter what type of measurement device is used, the measuring point should be at the same height at the front and rear of the tire. The difference in the front and rear distances is the toe. If the measurement is greater at the rear, the vehicle is toed. If the measurement is greater at the front, the vehicle is toed out. The trammel bar method will give an acceptable toe measurement, but it cannot be used to center the steering wheel.
Many trucks use a solid or twin I-beam front axle, and there are no provisions for adjusting caster and camber. The only way to adjust caster and camber on these trucks is to replace the upper ball joint bushing with a special eccentric bushing, or sleeve.
Before installing one of these bushings, calculate the amount of caster and camber change needed. Then consult the correct chart to select the needed bushing. A typical bushing application chart is shown in Figure 17.
Figure 17 - A sample chart listing camber and/or caster alignment sleeves.
To install the eccentric bushing, remove the alignment head and wheel. Then remove the upper ball joint nut from the ball joint. Pry up the old bushing to remove it. Install the eccentric bushing over the ball joint. Before reinstalling the nut, make sure the eccentric bushing is turned in the right direction. Then reinstall the ball joint nut and a new cotter pin. Reinstall the wheel and the alignment head, and recheck caster and camber.
On some trucks, the bushing can be turned after installation. If you are not sure about the exact placement of the bushing, install the nut loosely so it can be turned after the wheel and alignment head are reinstalled. Turn the new bushing as necessary, then tighten and install a new cotter pin.
- To Table of Contents -
Recommended caster settings. Vehicle manufacturers specify varying caster settings, depending on the vehicle model, what type of load it is carrying, whether it is tandem or single drive axle, and whether it is manual or power steering. The objective is to provide just enough positive caster to ensure wheel stability and good wheel recovery. The following settings are some examples used for vehicles with a manual steering gear:
Caster specifications are based on vehicle design load (no load), which will usually result in a level frame. If the frame is not level when alignment checks are made, this must be factored in the caster measurement. With the vehicle on a smooth, level surface, measure the frame angle with a protractor or inclinometer placed on the frame rail. Positive frame angle is defined as forward tilt (front end down) and negative angle as tilt to rear (front end high).
The frame tilt angle should be added or subtracted, as required, from the caster specification in the service manual, noting the following:
For instance, if the specified caster setting is a positive 1 degree and you measure the vehicle frame angle to be positive 1 degree, the measured caster is 0 ± ½ degree. This calculates to the desired 1 degree ± ½ degree caster angle when the chassis settles to level the frame under load.
Caster should be measured with the vehicle on a level floor. If the vehicle is equipped with a manually controlled air-lift axle, adjust it so that the frame is as normal operating height. Replacement of worn suspension, frame, and axle components should be done before caster is measured.
Measuring caster. Caster can be measured in a number of ways. One way is to use a protractor. Another is to use a radius gauge Modern computerized alignment equipment is the fastest, most accurate method measuring caster (and other equipment angles) and these are increasingly being used.
Protractor. A protractor measures the angle between its base and true horizontal, as determined by a bubble cylinder on one side of the dial.
To measure caster angle:
Figure 18 - Placement of a protractor to measure caster.
There are digital protractors or inclinometers (Figure 19) available that will do the same as the bubble protractor. The angle is displayed on a LCD screen and indicates whether negative or positive.
Figure 19 - Digital protractor.
Camber/Caster Gauges. Figure 20 shows a camber/caster gauge. The following steps must be performed before making both camber and caster measurements. Wheel runout should be checked using a tram bar or dial indicator to make an accurate camber/caster reading.
Figure 20 - Camber/caster gauge.
Figure 21 - Basic wheel alignment equipment.
Figure 22 - The camber/caster gauge attached to the wheel clamp.
Some camber/caster gauges have a runout compensation adjustment. Follow the OEM procedure when using this equipment.
Measure caster. To measure caster using radius gauges, use the following procedure:
If the caster difference from side to side exceeds ½ degree, the axle is probably twisted. Also, remember that the right side should not have less positive caster than the left. If the right side has less, it will tend to lead the vehicle to the right, particularly on crowned roads.
Caster shims. Caster angle is changed by using caster shims, which are angled metal wedges inserted between the spring seat and axle pad. Shims are typically manufactured in half-degree increments, from ½ degree to about 4 degrees, and in a choice of 3-, 3½-, or 4-inch widths to accommodate typical spring pack widths.
When inserting caster shims under spring seats, you should observe the following:
Changing caster. After determining the caster desired for each side of the axle, use the following procedure to install the caster shims:
When changing caster, be sure to block the wheels so that the vehicle will not roll. Also, use safety stands to support the springs when changing the caster shims.
Measuring camber. The preparatory procedure that has to be performed before measuring camber is further detailed in the section on caster. Perform those steps first. Then stabilize the front end. Next, visually align the center of the bubble with the left- or right-hand camber graduation to read the camber from the camber scale. Camber is positive if the bubble gravitates toward the positive sign and negative if it gravitates toward the negative sign. It should be emphasized that the camber should be checked but seldom has to be adjusted in truck front ends.
Toe-in is the most important alignment setting for tire life. Incorrect toe can also cause poor handling. An extreme toe-in or toe-out condition is the only alignment problem that can cause vibration, although this rarely happens. The toe must be set correctly, or adjusting the other alignment settings is a waste of time.
To set the toe, turn the ignition switch to the ON position. If the vehicle has power steering, start the engine. Then turn the steering wheel and install the steering wheel holder. Turn the ignition switch to the locked position.
Carefully position the steering wheel before installing the steering wheel holder. If the steering wheel is not centered correctly, it will be crooked when the vehicle is driven.
Next, observe the toe readings on each side and decide what must be done to correct it. If centering the steering wheel causes the wheels to be severely toed to one side, the steering wheel may be improperly installed.
Never attempt to adjust the toe to compensate for an incorrectly installed steering wheel. If the tie-rod adjusters are moved excessively, they can cause the tie-rod ends to bind. The lock bolts used on sleeve-type adjusters may contact the body and cause the steering to jam. If the tie rods are turned too far out, there may not be enough threads left to allow the tie-rod locknuts or bolts to be properly tightened. The steering linkage may come apart when the vehicle is driven, causing an accident.
If the steering wheel is off by more than about ½ of a turn (45°), check the steering linkage to ensure that there are no bent parts. Ensure that the toe was not previously misadjusted or that the steering component has not been improperly installed. If there are no serious problems, it can usually be assumed that the steering wheel was improperly installed in the past. In this situation, it is generally easier and safer to reposition the steering wheel than to change the alignment.
Loosen the tie-rod adjusting sleeve clamp bolts, as shown in Figure 23, or the tie-rod lockouts, as shown in Figure 24.If the vehicle has a metal bar preventing sleeve movement, loosen its clamp or bend it out of the way. This bar is used during vehicle assembly and does not have to be reinstalled.
Figure 23 - Tie-rod adjusting sleeve.
Figure 24 - Tie-rod locknut on a rack- and-pinion steering assembly.
Adjust toe by turning the sleeves or rods to obtain exactly half the needed toe on each wheel. If the toe is not divided exactly, the steering wheel will not be straight. Some vehicles have an adjustment on only one side of the linkage. If there is only one sleeve, the steering wheel cannot be centered without removing the wheel.
Some vehicles have two sleeves, one for adjusting toe, and one for centering the steering wheel. When adjusting this type of vehicle, always set the toe first, and then the center wheel.
It is typical practice to center the steering wheel again once toe has been set. This is especially useful when the toe has been changed a great deal. If the toe is now different on each side, reset it as necessary. If the toe is still equal on both sides, tighten the sleeve bolts or locknuts as applicable.
It is advisable to torque the fasteners to manufacturer's specifications. Some vehicles with conventional steering have
a specific location for the tie-rod adjusting sleeve clamp bolts. If the bolts are not placed in this position, they could contact other underbody parts. On any vehicle, make sure the bolts cannot contact any part of the underbody.
After the toe has been set, you may find that the steering wheel is slightly off center when the vehicle is driven in a straight line. To straighten the steering wheel without affecting toe, first drive the vehicle back onto the alignment rack. Make sure the turn plates are not locked and place the steering wheel in the centered position. Install the steering wheel lock.
Raise the vehicle to a comfortable working height and loosen the toe adjuster locknuts or lock bolts at the tie rods. Be sure not to move the adjusters themselves. Then sight down the front and rear of the outside sidewall of one front tire. Then sight down the outside of the other tire. One tire will appear to be toed in and the other will appear to be toed out. Turn each adjuster the same amount until both tires are straight ahead. For example, if the right adjuster is turned out ¼ turn, the left adjuster should b e moved ¼ turn.
Tire position can be determined by sighting down the outside sidewall of each front tire. The front tires are straight when sighting down the front and rear sidewall allows you to see the outer sidewall of the rear tire. Once the tires appear to be pointed straight ahead, remove the steering wheel lock and turn the wheel from side to side several times. Then center the steering wheel and sight down the tire sidewalls again. Readjust the tire position if necessary. Once both tires are straight, retighten the adjuster locknuts. Lower the vehicle and road test to determine whether the steering wheel is straight. If the steering wheel is still not centered, repeat the centering procedure as needed.
- To Table of Contents -
When a vehicle turns a corner, the inner wheel must turn on a smaller circle than the outer wheel. The inner wheel is said to turn in a shorter radius. On the rear axle, the wheels are not connected by linkage, and the difference in turning radius does not affect vehicle operation. In the front, however, the linkage holds the wheels parallel and one tire has to break loose from the pavement every time the vehicle makes a turn. To prevent this, the front wheels must automatically toe out on turns to allow the inner wheel to turn in a shorter radius. The steering arms are designed to angle slightly toward the center of the vehicle. When the wheels are turned, the inside steering arm swivels at a greater angle. This causes the inner wheel to turn more sharply than the outer, increasing toe out. The bend in the steering arm does not affect toe when the vehicle is traveling straight ahead.
Like caster, steering axis inclination is a line formed by the relative positions of the top ball joint or strut mounting in relation to the bottom ball joint. While caster is formed by the back- and-forth positions of the upper and lower ball joints (for the lower ball joint and the strut mounting), steering axis inclination is formed by the in- and-out positions of these parts in relation to the centerline of the vehicle. SAI is always slanted inward at the top (Figure 25).
Figure 25 - Steering axis inclination shown on a front-wheel drive, independent suspension.
The imaginary lines formed by SAI, camber, and true vertical always contact the road very closely to each other. This causes road shocks to be absorbed by the steering knuckle instead of being transmitted to the steering linkage. The sideways angle of the SAI centerline also causes the force of the road shocks to enter the frame at a sideways angle, compensating somewhat for the upward shock of the wheel assembly. The SAI angle also keeps the vehicle weight on the inner wheel bearing, eliminating the need for excessive camber, which would wear the tire.
SAI uses the weight of the vehicle to improve tracking. Tracking improvements result from the fact that whenever the wheels are turned from the straight position, the vehicle caster setting raises the body on one side. When the turn is completed, the weight of the vehicle through the SAI centerline forces the spindles to swivel back to their original position. This returns the wheels to the straight-ahead position.
Included Angle. Included angle is the total of the SAI and the camber. A typical included angle is shown in Figure 26. The included angle is usually not needed, but may be used to calculate the points at which the SAI and camber centerline contact the road. SAI cannot be changed without replacing parts, but the included angle will change when the camber is changed.
Figure 26 - Illustration depicting the included angle in relationship with steering axis inclination.
Setback. When one wheel spindle is positioned behind the other spindle on a single axle, the condition is called setback. Slight setback will be found on all vehicles due to manufacturing tolerances. Severe setback, however, is mostly caused by collision damage. Setback usually affects the caster reading and may cause the vehicle to pull toward the side with the wheel that is farthest back.
- To Table of Contents -
Many vehicle defects can affect the included angle in relationship with steering axis inclination.alignment of the suspension and steering. Some defects are directly related to the suspension and steering system, while others are less obvious. However, they can have an effect on the handling and tire life of the vehicle.
Worn or otherwise damaged parts are the most common cause of alignment complaints, as well as of suspension and steering problems in general. Striking road debris, pot holes, or curbs can bend steering or suspension parts. Often, the driver is not aware that damage has occurred. Moving parts can wear out, again without the driver actually realizing it. The power steering can fail for many reasons. Electronic suspension and steering systems can develop defects. Remember that an alignment is useless unless all steering and suspension defects are corrected first.
Power steering systems can develop seal or valve problems that result in unequal pressures in the right and left power chambers. This will cause pulling that could be misdiagnosed as an alignment problem. Electronically controlled steering systems can fail and provide too much or too little power assist. This can cause hard steering at low speeds or road wander at cruising speeds. This could be mistaken for incorrect caster or camber. Electronically controlled suspension can develop problems that cause one side (or one corner) of the vehicle to be below normal ride height. A height problem will affect camber. The mechanic who is not aware that there is a suspension defect may try to adjust camber when the real problem is in the electronic suspension.
Even the smallest vehicles have frames and body structures that will keep their shape under normal operating conditions. However, a collision can bend the frame of the most rugged vehicle. Bent frames are relatively uncommon, but they should be checked for, especially when other body damage is evident, when wheel setback is excessive, or when the adjusting device is at its limit of travel without reaching the correct alignment.
A related problem occurs when the body mounting bushings are worn or damaged. These bushings are used where the frame or subframe contacts the body. Bolts can loosen or the bushing can be damaged. This may not affect the suspension directly, but it may cause incorrect ride height or noises. A common sign of damaged body mounting bushings is the inability to center the steering wheel.
Tires are a common and often overlooked cause of problems. Other than obvious tread wear, the most common tire problem is tread separation. Tread separation is a common cause of pulling and vibration. Using tires that are too wide can cause hard steering.
Using tires that are too wide for the rim can distort and stress the sidewalls, resulting in tire failure. Tires that are too narrow can result in noise and poor traction. Tires that are too small for the vehicle weight will also wear out quickly. Other factors, such as improper alignment, cause the tires to wear. The worn tires, in turn, can cause other handling problems or noises.
Road crown is the tendency of most roads to slope away from the center. Roads are designed in this manner to assist in water runoff. Since road crown causes the road to slope toward the right, the vehicle alignment can be set to cause the vehicle to drift slightly to the left. This compensates for the slope caused by the road crown and reduces the tendency of the vehicle to pull to the right.
Mechanics try to set the caster and camber to compensate for road crown. Camber should be slightly more positive on the left side than the right side; caster should be slightly more negative on the left than the right. This is called caster or camber split. Very little split is needed to compensate for road crown. In most cases, ½ ° is sufficient. Too much compensation could cause the vehicle to pull left on roads with no road crown.
As the vehicle is driven, it inevitably travels over bumps, potholes, and other variations in the road surface. These variations cause the wheels to move up and down, changing camber. Depending on the suspension design, camber changes caused by suspension movement may also change caster a small amount.
General roughness of the road surface is caused by various paving materials, wear, and built-in, anti-skid grooves. Surface roughness varies greatly between roads and even along stretches of the same road. The rougher the road surface, the more noise and tire wear. There are no alignment adjustments to compensate for rough road surfaces.
Suspensions are designed so that normal loading will not change alignment excessively. However, vehicles are often overloaded, usually in the rear. Overloading causes the vehicle to be lower (called squat or sit down) in the rear, with corresponding rise in the front suspension. Raising the front suspension changes the camber, caster, and toe. If the rear suspension is an independent type, its alignment will change also. Vehicle handling will be greatly affected as long as the overload is present. If the vehicle is driven a long distance with an overload, tire wear will be greatly affected as long as the overload is present. If the vehicle is driven a long distance with an overload, tire wear will be severe.
Acceleration and braking forces cause the suspension height to change. Acceleration causes the vehicle front end to rise, with a corresponding lowering of the rear. Braking causes the opposite effect. This raising and lowering of the vehicle causes changes to the suspension, altering the alignment. Vehicles are designed to compensate for acceleration and braking forces, but some alignment changes do occur.
Turning forces occur whenever the vehicle turns in either direction. When the vehicle makes a turn, the tires are in contact with the road and try to turn the vehicle in the exact direction the wheels are aimed. The turning force created by the tires is called cornering force. Cornering force is opposed by inertia, which is the tendency of the vehicle to continue moving straight ahead. The actual path the wheels take is a combination of cornering force and inertia. The difference in the intended path and the actual path is called the slip angle. Slip angle is more pronounced at higher speeds. The higher the vehicle speed, the greater the slip angle, and large slip angles increase tire wear. There is no adjustment for slip angle, and the only way to reduce tire wear is to corner at reasonable speeds.
- To Table of Contents -
The chain section of the track is made up of track links, pins, and bushings. A considerable number of these interconnect with each other to form the track. The complete track and undercarriage system is made up of more than just the chain section. There are actually a number of components that form the complete track system. The drive sprocket, front idler, track rollers, tension mechanism, roller guards, and the frame are all required to make up a track and undercarriage system.
The final drive on a crawler tractor drives a complete track and undercarriage system on each side of the equipment. Each link of the track is held together with a press-fit pin and bushing to keep each link section in proper alignment with each other link section during operation. This combination of parts is called a link assembly. Pressed together, each section acts like a hinge, which allows the chain flexibility when rotating on the undercarriage. The track links also provide a means for attaching the track shoes that are bolted to the links. The parts of each link assembly are induction hardened to provide good wear characteristics. Pins and bushings are machined to provide a smooth bearing between them, which also increases durability. A master link or master pin completes the track assembly.
The master link, as shown in Figure 27, is slightly different from the rest of the links. The bushing used in the master link assembly is slightly shorter than the rest of the bushings, and the master pin, as shown in Figure 28, has a smaller diameter to facilitate easy installation and removal. Some manufacturer's master pins can be identified by a mark or drill hole on the end of the outside face of the pin; yet other manufacturers use a two-piece master link that bolts together. The master link uses the same pins and bushings as the rest of the track, making splitting the track easier because no special tools are required to disassemble the track. Before attempting any maintenance or repairs to a track and undercarriage system, always refer to the manufacturer's technical documentation or service manual.
Figure 27 - Master link.
Figure 28 - Master pin.
Track systems also come in what is commonly called a sealed system, where the pin and bushing are lubricated on assembly and are sealed from dirt entering between them. This design eliminates internal wear.
Track shoes are bolted to the link assembly to provide a means of supporting the equipment and better traction and flotation during operation. They are generally constructed from a hardened metal plate and come in many different configurations. Refer to Figure 29 for design features of a track shoe. The operating ground conditions will determine the type of shoes to be used. Operation on highly abrasive soil demands a high quality, hardened surface that will resist wear. The number of ridges (called grousers) on the track shoe designates the terrain on which the shoe will operate. The hardness of the surface material on the grousers determines whether they are standard or extreme-service track shoes.
Figure 29 - Track shoe.
Track Links, Pins, and Bushings. Each track section is made up of two track links (Figure 30), a hardened pin, and bushing. These individual track sections are interconnected to the link assembly. The two track links used in a section have provisions for attaching a track shoe and also provide a rail for the track rollers to maintain accurate track alignment. Sealed tracks have a solid pin. Sealed and lubricated tracks have a hollow pin, which provides a path for lubricating the pin and bushing of the next track section (Figure 31). When installing a center-drilled pin, the cross drill hole must be installed toward the rail of the link, which keeps the pin in compression to resist the possibility of crushing. The pins and bushings are press-fit into the links. Be sure to follow the correct orientation; there are both right-hand and left- hand hand links. Clearance between the pins and bushings is minimal, providing only enough clearance for lubrication. In the case of a sealed track, the seal fits over the pin against the track link before installing another link.
Figure 30 - Track link.
Figure 31 - Lubricated track.
Drive Sprockets. The sprocket, as shown in Figure 32, is not mounted to the track frame but is attached to the final drive. Its job is to transfer drive torque to the track. The teeth on the outside of the sprocket act as gear teeth. They engage the track links and propel the equipment on the continuous track loop. Older track equipment often has a one-piece sprocket assembly; the use of individual bolts on segments showed up more recently. On the older models, the old sprocket had to be cut off and a new one welded in its place. Often, the welded version was replaced with a welded-on adapter, which allowed for the bolted, segmented type of sprocket, saving considerable time for future changes.
Figure 32 - Drive sprocket.
Changing sprocket segments is quick and easy. Position the track so the segment that requires changing is on the inside (away from the track links), unbolt the old segment, and bolt in and torque the new one. Rotate the track a few feet and repeat the procedure until all segments are replaced.
By design, the sprocket has an odd number of teeth to provide a change in tooth-to-sprocket contact every revolution of the sprocket. This is commonly called "tooth hunting." This design allows for the even distribution of wear among the sprocket teeth.
Elevated Sprockets. Improvement in track equipment design has led to the inception of the elevated track design, which offers a few major advantages over a conventional track sprocket arrangement. The major benefit of this design is that it isolates the final drive from excessive shock loads. The position of the final drive also creates a better balance arrangement that also provides better traction, as shown in Figure 33. This design requires the use of two idlers and a separate roller frame for the front and rear.
Figure 33 - Mechanics working on a bulldozer with an elevated sprocket.
There is always a down side to any design, and this one is no exception. Compared to a conventional undercarriage design, which has one travel loaded flex point, the elevated sprocket undercarriage has three flex points where loading takes place during operation. Therefore, in the long run, the conventional undercarriage with only one load point during forward travel will likely last longer.
The two rear track frames are connected together with a pivot shaft that allows the shock loads to be absorbed by the main frame. The front roller frames fit inside the rear roller frames and are connected to each other with an equalizer bar that is pinned in the center with limited movement from side to side. A recoil spring provides track tension.
Track Rollers and Carrier Rollers. Current track design utilizes two different types of track rollers to maintain track alignment. The bottom rollers are called track rollers. They support the weight of the equipment and ensure that the weight of the equipment is distributed evenly over the bottom of the track. The track rollers are spaced closely together, and there are generally a large number of them mounted to the bottom side of the track frame. The track rollers maintain track alignment as well as distribute the weight of the equipment evenly over the length of the track.
There are two types of track roller designs: single flange and double flange. Single flange rollers are used closest to the sprockets. Double flange rollers maximize track stability and alignment. The surface of the track rollers is hardened to the same Rockwell scale as the track links. Lubrication and cooling are provided by oil sealed in the housing. Because of the twin flanges, double flange track rollers are used to maximize track alignment.
There are several different design configurations of track rollers. Always refer to the specific shop manual of the equipment on which you are working for detailed instructions. Figure 34 shows the parts breakdown of a typical track roller.
Figure 34 - Track roller.
Carrier rollers are located above the frame rail. Their purpose is to support the weight of the top section of track as it rolls between the idler and the sprocket. These rollers generally have a single flange that aids in controlling track sag and whipping during operation. A secondary function of the carrier rollers is to maintain alignment on the upper portion of the track between the idler and sprocket. These rollers also have a hardened surface that is equal in hardness to the track link surfaces. This hardness can have a slight negative effect on the life of the track links. Some manufacturers cantilever mount the carrier rollers to minimize material buildup.
Figure 35 shows an exploded view of a typical carrier roller. The retaining ring on a roller fastens the end collar to the roller shell and is held in position on the support shaft by a groove. The bearings are held in place in the carrier shell by the end collar and seals, which also prevent oil from leaking out of and dirt getting into the bearings. The two roller bearing assemblies allow the carrier roller to roll freely on the shaft. The shaft has mounting points to secure the carrier roller to the track frame. A plug and O-ring seal the lubrication opening in the shaft. The retainer plate, which mounts to the shaft, holds the tapered roller bearings inside the carrier housing. A roller cover provides a seal on one end and is fastened with bolts to the end of the carrier shell.
Figure 35 - Carrier roller.
Seals. Tracks operate in extremely abrasive conditions and quickly wear out the pins and bushings if they are not protected with seals. Seals keep lubrication in and dirt out, providing a much longer service life. Not only do seals keep dirt out, but they also carry a certain amount of side load, preventing unnecessary wear of the track links' counterbore. Conventional track seals use Bellville washers that are capable of maintaining sealing pressure as they wear, which helps keep dirt out.
Some manufacturers use rigid seals, which consist of two individual parts similar to those used on lubricated tracks. These parts are made up of a lip seal and stiff wear- resistant material on the inside, called the "can." The seal shape integrity is maintained by an extremely durable urethane material. The seal holds the bushings by a load ring. These seals are capable of withstanding operating temperatures as high as 170°. The seal is protected from thrust loads by a steel thrust ring, which limits seal compression.
This type of seal system is considerably more costly than conventional Bellville washer design, but the result is a much longer pin and bushing life. Over the long haul, this type of seal system will yield lower operating costs. Wear is generally not an issue with this type of seal system, and operation is quieter due to the lubricated pins and bushings. Frictional losses are reduced more with a lubricated track than with a conventional track, resulting in lower operating fuel costs.
Track Guards. To keep the tracks from getting packed with dirt, roller guards are often used to keep the rocks and foreign debris from getting between the track rollers and track links. The track guard also helps guide the track. Good practice requires that the area around the track guard be cleaned regularly, especially after operating in muddy conditions. Operating equipment with packed debris in the track mechanism results in a track condition that is too tight, which greatly accelerates wear. Track tension should be checked periodically during and after operations in mud, clay, fractures or quarry rock, and heavy vegetation or roots. All of these objects have the potential to enter the track assembly.
Frame. The frame is the backbone of the tack assembly. It holds the front idler in place, and the track rollers and guards are bolted to its underside. The recoil assembly and the track carrier roller(s) are all mounted to the frame. Generally, the frame causes very few problems when compared to the rest of the track components.
Equalizer Bar. The track frames on each side of the equipment are connected together through an equalizer bar near the front of the machine and are mounted to the sprocket that is part of the final drive at the rear of the machine. All the weight of the equipment is carried by the track rollers and frame. With this type of mounting, each side can move independently on uneven terrain to maintain contact with the ground. Diagonal braces are used to maintain track alignment when on uneven terrain. One end of each brace is welded to the track frame, while the other end is mounted to the sprocket shaft and swivels on a bearing. These bearings must be lubricated at regular intervals.
Older track loading equipment does not have a pivoting equalizer bar; therefore, independent track movement is not possible. Instead, this older type of equipment has a rigid frame, and as a result, is unable to operate on uneven terrain effectively. Typically, older track loading equipment is best suited to operate on flat, hard surfaces, such as quarries and pits.
Some manufacturers have added an oscillating undercarriage, as shown in Figure 36, as an alternative to independent track movement. This design has the added benefit of being able to pivot from the front to rear, which can increase stability when the equipment is operating on uneven ground. The track frames have an equalizer bar mounted between to allow each track frame to pivot independently on a pivot shaft. With this design, an idler swing link is used to permit the idler to move horizontally to absorb any shock loads it may encounter during operation. This ensures that the correct amount of track tension is always maintained. Pins are used to prevent the equalizer bar from having excessive oscillating travel. Rubber pads are used to dampen vibration between the equalizer bar and the main frame.
Figure 36 - Oscillating undercarriage for a track loader.
For the following example, refer to Figure 37:
Figure 37 - Aligning track roller frame with sprocket.
Depending on the track design, the equipment could have one or two idlers per track section. If the equipment has an elevated sprocket system, there will be two idlers: a front idler and a back idler. Equipment that has a conventional oval track requires only one idler (Figure 38). The purpose of an idler is to help guide the track through the track rollers and to help support part of the weight of the equipment. Besides providing alignment, the idler's job is to maintain the correct tension and slack on the track. The tension on the track is adjusted by moving the idler back and forth on the track frame. This is accomplished with the use of hydraulic pressure to compress a high- tension spring mechanism to tighten the track.
Figure 38 - Front idler.
Equipment with oval tracks can have a two- position idler, with one position that is used when drawbar work is required. This position minimizes the amount of track that is in contact with the ground, resulting in less track wear. When equipment must operate with heavy implements attached to the front, the use of the lower mount for the idler places more track on the ground, making the equipment more stable but causing more track wear. Too much track tension is a contributing factor to accelerated wear because of increased loading on the track components.
Figure 39 shows an exploded view of a typical idler assembly. The bearing used between the idler shaft and shell is a plain bimetallic bearing with excellent load and wear characteristics. A retainer ring holds the end collar to the idler shell. The end collar holds the seals and the other parts inside the assembly. The outer circumference of the idler, as with all track components, is the same as the track links.
Figure 39 - Exploded view of an idler.
The tensioning mechanism connects to the idler to maintain the correct track tension. On older equipment, the tensioning mechanism uses a coil spring with a mechanically adjusted rod to adjust track tension (Figure 40). On newer equipment, you will find the use of hydraulic pressure to balance spring equipment.
Figure 40 - Idler with coil spring and adjustable tension rod.
The most important controllable factor in undercarriage wear is correct track-chain adjustment. Correct track sag for all conventional crawlers is two inches (± 1/4 inch). Tight tracks can increase wear up to 50 percent. For example, a crawler in the 80- horsepower range with 1/2-inch track-chain sag results in approximately 5,600 pounds of chain tension when measured at the track adjuster. The same machine with the suggested 2-inch track chain sag results in approximately 800 pounds of chain tension when measured at the track adjuster. A tight track magnifies the load, which results in more wear on the track bushings to sprocket teeth contact areas and the track-link-to- idler roller contact areas. Increased wear also occurs at the track-link-to-idler contact point and track-link-to-roller contact points. More load means more wear on the entire undercarriage system. Also, a tight track requires more horsepower and more fuel to do the job. Follow this method to adjust track-chain tension:
Figure 41 demonstrates the proper procedure for track adjustment and sag. Always adjust track sag in the actual underfoot working condition and check sag often. To adjust track-chain tension, move the machine forward slowly and let the machine roll to a stop, centering the track pin over the carrier roller, as shown in Figure 41, View A. Put a straight edge over the track, as shown in Figure 41, View B, and measure the sag at the lowest point, as shown in Figure 41, View C.
Figure 41 -Track sag.
Figure 42 provides a quick reference for troubleshooting track problems.
Figure 42 - Troubleshooting track problems.
- To Table of Contents -
Wheel alignment is the process of repositioning the suspension and steering parts to compensate for normal wear and the effects of replacing parts to compensate for normal wear. Correct wheel alignment should be checked after parts replacement and periodically during the life of the vehicle.
Wheel alignment is a series of angles that position the tires in relation of the vehicle's body, road, and the other tires. The angles for a particular wheel are interrelated, and the angles are related between each of the vehicle's wheels. Camber is the inward or outward tilt of the top of the wheels when viewed from the front of the vehicle. Caster is the tendency of the tire to follow behind the center of movement formed by the steering axis. Kingpin inclination is the amount in degrees that the top of the kingpin inclines away from the vertical, viewed from the front of the vehicle. Toe is the relative position of the tires on the axle. When the front of the tires is closer together than the rear, the tires are toed in. When the front of the tires is farther apart than the rear, the tires are toed out. Turning radius or angle is the degree of movement from a straight-ahead position of the front wheels to either an extreme right or left position. Ackerman geometry is the means used to steer a vehicle so that the tires track freely during a turn. During a turn, the inboard wheel on a steer axle has to track a tighter circle than the outer wheel.
All vehicles are built around a geometric centerline that runs through the center of the chassis from the back to the front. The thrust line is the direction the rear axle travels if unaffected by the front wheels. This condition is called tracking. An ideal alignment has all wheels running parallel to the centerline, making the thrust line parallel to the centerline. Not only is this true with vehicles, but it also is true with trailers.
The most common cause of accidents is carelessness. Many mechanics become rushed and forget to do the job safely. An accident may result in personal injury, long- term bodily harm, or damage to equipment or property. Accidents are also caused when personnel fail to correct hazardous conditions and take shortcuts instead of following proper procedures. Many suspension parts are under spring tension. The mechanic must be sure that all spring tension is removed from any part before trying to remove it.
There are a number of specialty tools required for frontend alignment, and using the proper tools is vital to doing the job properly and safely. Mechanical alignment testers include caster-camber testers, toe gauges, and turning plates. Alignment machines have alignment heads that are attached to the wheels of the vehicle. Electronic alignment machines use infrared or laser beams to send signals to a computer that displays the alignment on a screen.
Conduct pre-alignment checks, to include talking to the operator; road testing; checking height, tire, and wheel damage; and checking for worn parts and underbody damage.
To set up the vehicle for wheel alignment, the wheels must be free to turn. The vehicle must be at its correct curb weight. After obtaining alignment specifications, install the alignment heads to the rim and compensate it.
After all pre-alignment procedures have been accomplished, check camber, caster, and toe. Also check SAI and toe out on turns, if required.
Adjustable suspension angles are caster, camber, and toe. Follow the prescribed specifications and procedures for measuring caster and camber. Nonadjustable wheel alignment angles are turning radius, steering axis inclination, or SAI. The included angle is the combination of SAI and camber.
Many vehicle defects can affect the alignment of the suspension and steering. These include defective parts, bent frames, defective tires, road crown and irregularities, vehicle load, acceleration and braking, and turning forces.
The chain section of the track is made up of track links, pins, and bushing. Several components together form a track system, to include the drive sprocket, front idler, track rollers, tension mechanism, roller guards, and frame.
Improvement in track design has led to the inception of the elevated track design, which has a few advantages over the conventional track sprocket arrangement. The major benefit of this design is that it isolates the final drive from excessive shock loads. The elevated track design requires the use of two idlers.
Tracks utilize two different types of track rollers to maintain track alignment. The bottom rollers support the weight of the equipment and ensure that the weight of the equipment is distributed evenly over the bottom of the track.
Carrier rollers are located above the frame rail. The purpose is to support the weight of the top section of the track as it rolls between the idler and the sprocket.
The purpose of the idler is to help guide the tack through the track rollers and to support the weight of the equipment. Besides providing alignment, the idler's job is to maintain the correct tension and slack on the track. A tension mechanism connects to the idler to maintain the correct track tension. The track tensioning mechanism uses either a recoil spring with a mechanically adjusted rod or a hydraulically tensioning cylinder to adjust track tension.
Correct track adjustment is necessary to maintain long track life. Nothing shortens the life of the tack faster than incorrect adjustments. If the track is adjusted too tightly, excessive loads are placed on the mating components, which accelerate track component wear. If the track is adjusted too loosely, it will cause the track whip at higher speeds and lead to excessive wear of undercarriage components.
- To Table of Contents -
1. Abnormal wear on the side of the tire tread is caused by what?
2. When the lower ball joint is ahead of the top ball joint or strut mounting, to which angle are you referring?
3. One of the advantages of positive caster is that it makes it easy to turn the wheels from the straight-ahead position when entering a turn.
4. What is the name of the angle that, when in conjunction with camber angles, places the approximate center of the tire tread footprint in contact with the road?
5. What should you do to the suspension prior to measuring toe angle?
6. Within the steps for adjust turning radius, what is adjusted to make proper contact with the axle stop?
7. What allows the inner and outer wheel to turn at different angles so that both wheels can negotiate the turn without scrubbing?
8. The length and angle of the steering control arms and length of the cross tube determine the actual toe-out during what maneuver?
9. When all the axles are following in line with each other and perpendicular to the to the vehicle centerline, this is known as what?
10. In trailer tracking, what is it called when the drive axles are not parallel?
11. What will you plug into when working with electrical tools in wet conditions?
12. To ensure your safety, what should you do with a jack stand when working outside, repairing a vehicle that is parked on asphalt?
13. Spring tension is no concern because once you raise the vehicle, all tension is removed.
14. What is the purpose of the tool that sometimes is referred to as a pickle fork?
15. Which of the following hammers should never be used when working on vehicles?
16. Which tool arm that typically attaches to the control arm and frame would be used to move the control?
17. Of the different methods to remove a spot weld, which one is the most expedient?
18. What type of torque wrench is considered the most accurate?
19. After conducting the road test, check before beginning alignment procedures.
20. When you inspect the tires, all tires should be ?
21. All rims have some runout, so when installing the alignment head, what might you have to do for this situation?
22. What is your next step after installing the alignment heads and lowering the vehicle?
23. What is the other procedure that is conducted along with the caster checking process?
24. Which angle(s) cannot be checked on trucks with solid front axles?
25. At what position should caster be measured?
26. When measuring caster angle with a protractor and it tilts toward the rear, it is what?
27. When measuring caster using a radius gauge, how many degrees do you turn the front wheel?
28. How many shims can you use on each side when changing the caster angle?
29. Which is the most important setting regarding tire life?
30. When you are adjusting toe and the steering wheel, and the vehicle has two sleeves, what adjustment is made first?
31. Steering axis inclination is a nonadjustable angle.
32. What does steering axis inclination use to improve tracking?
33. Which of the following components is not part of the track system?
34. What is the type of track system that has the pin and bushing already lubricated on assembly and is designed to eliminate internal wear?
35. What is the purpose of the drive sprocket?
36. What component has seen Improvement in design on some bulldozers?
37. Along with distributing the weight of the equipment, what else do track rollers accomplish?
38. On a typical carrier roller, the bearings are held in place in the carrier shell by which component(s)?
39. What do conventional seals use that maintains sealing pressure as they wear and helps keep dirt out?
40. Rigid seals, although more costly than Bellville washers are able to withstand temperatures up to degrees.
41. Which component allows the track frame to pivot independently on a pivot shaft?
42. Which component of tracked equipment adjusts the track tension and guides the track through the track rollers?
43. A tight track is essential to distribute the load evenly over the rollers and to prevent throwing the track.
- To Table of Contents -
Copyright © David L.
All Rights Reserved