Wheel Alignment Service

Transcription

1 CHAPTER 68 Wheel Alignment Service OBJECTIVES Upon completion of this chapter, you should be able to: Perform a prealignment inspection of the steering and suspension. Describe how to adjust caster, camber, and toe. Understand the different ways of adjusting wheel alignment angles. KEY TERMS bump steer crowned road four-wheel alignment eccentric cam geometric centerline radius plates slip plates spread steering pull thrust angle thrust line toe angle toe change torque steer INTRODUCTION Before wheel alignment can be checked or adjusted, the condition of the steering and suspension systems must be thoroughly inspected. Loose parts will prevent an accurate and lasting adjustment. Looseness between suspension or steering parts can result in steering wheel play, wheel shimmy, or an intermittent pull to one side or the other. The vehicle must also be riding at the correct height. A wheel alignment cannot be successful unless the suspension and steering components are in good working order. NOTE: Incorrect alignment settings can result in pull, instability, and tire wear. A vehicle with worn or loose parts cannot be aligned. Unusual tire wear and/or a problem with vehicle handling are often reasons that a driver will inquire about a wheel alignment. Front wheels experience more stress than rear wheels because they support powertrain weight and steer the vehicle. The rear axle is usually not the cause of a prob lem, but a technician needs to consider the entire frame and the steering and suspension systems in order to correctly align a vehicle. The first part of this chapter discusses suspension and steer ing system wear and inspection procedures. The latter part of the chapter deals with wheel alignment mea suring and adjusting procedures. PREALIGNMENT INSPECTION Before aligning a vehicle, inspect the suspension and steering systems. If parts are loose or worn, an alignment will not be successful. The following are some important considerations: The pressure in all four tires must be adjusted to specifications. The vehicle ride height must be correct. Bushings and pivot parts cannot be worn to the point where they allow movement of suspension and steering parts. Coupling points in the steering gear and linkage cannot have excessive clearance. The tires must be new or be worn evenly so the vehicle is level during the alignment measurements. TIRE WEAR INSPECTION Unusual tire wear can be caused by worn parts, incorrect inflation, hard cornering, or incorrect wheel alignment. Camber and toe are the two adjustable wheel alignment angles that often cause tire wear. Seeing the worn tires before a wheel alignment is an advantage to the alignment technician. If tires are worn evenly and 1257

2 1258 CHAPTER 68 the vehicle does not pull or wander, it is unlikely that caster and camber need to be adjusted. Tire Wear from Camber Tire wear from incorrect camber can be on either the outside or the inside of the tire tread (Figure 68.1). When there is camber, the inside and outside of the tire tread will have different diameters (see Figure 67.3). Positive camber causes wear on the outside of the tire tread. It is usually the result of an incorrect alignment setting or when a vehicle with high steering axis inclination is driven often through corners. NOTE: Camber wear results as springs on an aging vehicle sag, changing the height of suspension components. Tire Wear from Toe It is dangerous to drive a vehicle with excessive toe because its front tires are constantly sliding. A tire with incorrect toe will develop a feathered edge, which is a sawtooth pattern (Figure 68.2). When toe is severe, the feathered Figure 68.3 Be careful not to cut your hand on exposed steel belts. edge can be visible to the eye and can often be felt by hand. Tire wear from incorrect toe sometimes appears as wear to one side of the tire, similar to camber wear. SAFETY NOTE When inspecting for toe wear by hand, before you slide your hand across the tread surface, be sure the tire is not worn to the point where steel wire is exposed (Figure 68.3). Figure 68.1 Excess camber results in more wear on one side of the tire tread. To diagnose excessive toe wear on a tire: Move your hand across the tire s footprint area from the outside to the inside. If you feel a feathered edge, there is excessive toe-out (see Figure 68.2). If you feel a feathered edge when moving from the inside to the outside, there is excessive toe-in (Figure 68.4). Direction of travel Direction of travel Direction of tire slippage Toe-out wear Inside Figure 68.2 Toe wear results in a sawtooth pattern or feathered edge. The illustration depicts toe-out wear. Direction of tire slippage Figure 68.4 Toe-in wear. Toe-in wear Inside

3 Wheel Alignment Service 1259 SHOP TIP To remember the meaning of the direction of a feathered edge on tire tread some technicians think: smooth in, toe-in; smooth out, toe-out. Other Toe Wear Factors Radial tires on RWD vehicles with toe-in will both roll under, resulting in wear that looks like positive camber. The right front tire tends to toe in more than the left; its outside edge wears because the tire is rolling under at that edge. With toe-out, the inside edge of the left tire will roll under, resulting in wear on the inside edge of the left front tire. NOTE: On the rear of a vehicle, toe does not equalize between the two tires like it does on the front. If the tires are not regularly rotated, rear tires that are toed in or out will develop a diagonal wear pattern on the tread (Figure 68.5). RIDE HEIGHT CHECK Because springs are always supporting vehicle weight, they tend to sag as a vehicle gets older. Alignment specifica tions are based on the assumption that the ride height, or curb riding height, of the vehicle is correct. Although it is sometimes possible to adjust alignment when the springs have sagged beyond specifications, tire wear and unu sual handling are a likely result. Before you make any wheel alignment adjustments, measure the ride height and compare it to specifications (Figure 68.6). Figure 68.6 Measure and record ride height as shown prior to aligning wheels. Figure 68.7 Typical ride height measurement locations on an SLA suspension. NOTE: When vehicle ride height is either too high or too low, the camber setting will probably be outside of specified limits and the SAI will be off as well. A vehicle with a short-and-long arm (SLA) suspension with sagged springs will not function within its desired alignment range as the springs deflect. This can cause changes in the way the vehicle reacts to bumps. Figure 68.7 shows where typical ride height measurements would be checked on an SLA suspension. Figure 68.5 A common wear pattern resulting from incorrect toe on a rear wheel. TOE CHANGE The toe measurement can change as the suspension height changes (Figure 68.8). Suspension and steering systems are designed so that tie-rods remain parallel to the lower control arms when they pivot (Figure 68.9). When springs sag and the frame drops in relation to the control arms, toe change results. Toe change causes the tire to scrub against the road

4 1260 CHAPTER 68 Figure 68.8 Toe change resulting from changing ride height. Hunter Engineering Company NOTE: As caster changes, the height of the steering arm changes. Toe change can be caused by caster angles that are too different from side to side. TORQUE STEER Torque steer is when a vehicle turns abruptly to the side dur ing initial acceleration. This usually happens on front-wheel-drive (FWD) vehicles with axles of unequal lengths. Torque steer can also be caused by anything that causes the axles to be at different heights. This results in unequal constant velocity (CV) joint angles. A difference in height can be caused by a loose sub-frame or a problem with unequal spring height. Figure 68.9 The tie-rods are designed to remain parallel to the lower control arms when they pivot. Hunter Engineering Company HISTORY NOTE On RWD vehicles with small engines, torque steer was not a prob lem. When FWD became popular and horsepower increased, torque steer was more noticeable. Older FWD vehicles sometimes had front driving axles of different lengths. During acceleration, the long axle would twist, delaying power transfer to its front wheels; during quick deceleration, it would recoil. Some of the solutions attempted by auto makers were to use a thicker axle, change the scrub radius, or use an intermediate axle shaft so that drive axles would both be the same length. surface, wearing away tread. A correctly inflated tire can absorb a small amount of toe change when its sidewall deflects. Loose parts or incorrect wheel alignment can move the amount of allowable toe change out of normal limits. When toe change is confined to one side of a vehicle, bump steer, or orbital steer, can result. This happens when a wheel with tie-rods at unequal heights goes over a bump. Its toe changes and the vehicle momentarily steers off-center (Figure 68.10). Toe change measurement and correc tion is covered later in this chapter. SUSPENSION LOOSENESS A motto of one aftermarket suspension and steering part manufacturer is you can t align looseness. Steering and suspension components are designed to pivot, without allowing any change in the positions of parts. Perform a dry park check for steering and suspension looseness. With the tires on the ground, have a helper repeatedly turn the steering wheel back and forth (about 3" or so). Look under the vehicle for any signs of looseness between steering linkage parts. Travel arc of tie-rod and steering arm Tie-rod Bump steer Figure Bump steer. Steering arm

5 Wheel Alignment Service 1261 Linkages that are in good condition will allow pivoting only. During the dry park check, any slack between parts will become apparent due to the resistance of the tires as they try to turn against the ground. Always check the adjustment of the wheel bearings to see that they are not loose before attempting a wheel alignment. TEST DRIVE A test drive should be done before performing repairs, but only if the vehicle is safe to drive. Before driving the vehicle, check the following items: Suspension bushings, visually and with a prybar Steering linkage pivot connections firmly grasp each part and rock it to check for looseness Rubber grease boots on tie-rod ends and ball joints Shock absorbers Also check to see if there is any evidence of collision damage. TIRE CHECKS To perform a tire check, follow these steps: Adjust tire pressures to specifications. Check the condition of the valve stems and look for signs of impact damage that might have resulted in a bent wheel rim (Figure 68.11). A tire with a significant loss of air pressure is indicative of a slow leak. Carefully inspect the tread area for a nail, screw, or other foreign object. Look for unusual tread wear. Check for damage to the sidewalls or tread area (Figure 68.12). Be sure that tires of the correct size are used. Front tires should be of the same brand and tread pattern. Radials and bias tires should not be mixed. Figure Inspect wheels and tires for impact damage. Figure Distorted tread like this will affect a wheel alignment. Power Steering Checks To perform a power steering check, follow these steps: Check power steering fluid level. Look for fluid leaks. Check drive belt tension. Check the power assist to see that it works with equal ease in both directions. During the test drive, several conditions are checked: Hard steering can be caused by binding parts, incorrect alignment, low tires, or a failure in the power steering system. Be sure to note whether the vehicle is easier to steer at higher speeds. Do tires squeal on turns? This could be due to a bent steering arm or low tire pressures. Are there squeaks and clunks? This could be the result of bad bushings, which can also cause changes in camber, resulting in brake pull. Is there a shimmy or tramp (the steering wheel shakes from side to side)? This could indicate a bent or out-of-balance wheel, or excessive caster. A vehicle that wanders might have an incorrect caster angle setting. Does the steering wheel pull to one side? When the steering wheel wants to go to the side by itself, especially when you let go of the wheel, this is called steering pull. NOTE: Sometimes steering pull can be caused by the crown of the road. Be sure to perform the test on a flat surface. Does the vehicle pull to one side or the other? Does it always pull, or only during braking? This could be due either to alignment or brake problems. If the vehicle pulls, does the direction or amount of pull change if the tires are rotated? A defective or damaged tire can cause pull, usually to the side with the bad tire. Is it possible that a power steering problem could be causing the pull? Some vehicles have adjustable

6 1262 CHAPTER 68 spool valves. With others, the steering box might require service. With the wheels off the ground, start the engine and verify that the wheels do not self-steer in either direction. Does the owner complain of a rough ride? This could be due to tire pressures that are too high, or a bent or frozen shock absorber. Does the vehicle have body roll, where it leans excessively to one side or the other during fast turns? The shock absorbers could be worn out. Is there a noise during turns that changes in pitch as the vehicle weaves to the left and then to the right? The wheel bearings on the outside wheels spin faster during a turn. Due to this, and weight shift (which loads bearings), a bad bearing will make more noise when turning to one side than to the other. A wheel bearing noise will often be accompanied by looseness as well. Before attempting a wheel alignment, check for looseness in any related parts. With the vehicle raised, grasp the tires with your hands at the 6 o clock and 12 o clock positions and check for movement. If there is movement, readjust the wheel bearing. If there is still movement, locate its source in the suspension system. NOTE: A check for similar movement with your hands at the 3 o clock and 6 o clock positions verifies steering linkage condition. Test ball joints for looseness as described in Chapter 64. It is best to consult the appropriate service information because procedures vary. Some ball joints are designed to have a specified clearance. Several part manufacturers provide specification tables. INSPECTION CHECKLIST A checklist that can be used by technicians to make sure that no steps are accidentally forgotten during a suspension inspection and test drive is shown in Figure WHEEL ALIGNMENT PROCEDURES The front suspension is designed to keep the wheels in the best possible position when rolling. Wheels must roll freely with as little tire scuff (side-to-side wear) as Figure A prealignment inspection checklist.

7 Wheel Alignment Service 1263 Skid plate (rear wheels) Radius plate (front wheels) Leveling leg Turntable pocket spacer Figure A wheel alignment rack with ball bearing supported plates for the front and rear wheels. possible. Alignment settings can change accord ing to vehicle speed, road surface roughness, acceleration, braking, weight distribution, or corner ing. Specifications are developed by manufacturers so that alignment can be adjusted with the vehicle at rest on a level alignment rack (Figure 68.14). If tire wear is experienced when the settings are within specifications, the technician can make adjustments to compensate. Adjustments to original alignment settings might be needed because of wear on the inside of pivoting parts, bad road conditions, collision damage, spring sag, or unusual loads. A new vehicle might need an align ment because it came from the factory with adjust ments outside of the normal range of specifications. Design engineers list a range of adjustment limits for wheel alignment angles. If the adjustments fall within those limits and the vehicle tracks straight (goes straight on a level road), little tire wear should occur. Only three of the five alignment angles are possibly adjustable: Caster Camber Toe The other two angles are measured to check for damage to suspension and steering parts. Of the three adjustable angles, tire wear when traveling straight only results from incorrect camber and toe. Directional pull can be caused by unequal camber and caster. Snap-on Tools Company, Gauge Figure A radius plate. Turning radius plate Lock pins (see Figure 68.14). On four-wheel alignment racks, slip plates are under the rear tires and the front wheels are positioned on radius plates (Figure 68.15). Some radius plates have a gauge that measures in degrees how far a wheel is turned to the right or left. Pins hold the upper plate from moving on the bearings. After the vehicle is driven onto the plates, the pins are pulled out of the plates. Pushing down on the bumper lets the wheels creep into a relaxed position where they would be when rolling on the road. Air or hydraulic jacks raise the vehicle off the lift during alignment adjustments or to reposi tion the radius plates. Newer vehicles often have adjustable rear-wheel alignment. Four-wheel alignment inspection is done with a computer alignment machine (Figure 68.16). Mechanical measuring systems are covered in this chapter as well because it is important to understand what you are actually measuring when taking alignment readings. To get accurate measurements, the vehicle must be level. Toe is measured in inches, millimeters, or angle of toe. The remaining angles are measured in degrees of a circle. When adjustment is possible, caster and MEASURING ALIGNMENT Most alignment measurements are read in degrees and parts of degrees. Degrees represent part of a 360-degree circle in both the metric and inch systems. In the United States, remaining portions of degrees are either fractional or decimal. In the metric system, as in the world of science, portions of degrees are read in minutes (') and seconds ("). Like a clock, there are 60 minutes in a degree and 60 seconds in a minute. When taking alignment measurements, ball bearing supported plates are positioned beneath all four tires. These allow the tires to assume a relaxed position Figure A four-wheel alignment machine with sensors attached to each wheel. All four wheel heads send alignment position information to a computer. Hunter Engineering Company

8 1264 CHAPTER 68 camber are usually adjusted together because adjust ing caster affects the camber reading. Toe is adjusted last, after caster and camber, because when other alignment angles are changed or when parts are replaced, the toe setting changes. NOTE: If tires are to be replaced, the new tires should be installed before attempting an alignment. An alignment rack provides a level location for checking suspension angles. The heights of worn tires will affect alignment mea surements. VINTAGE WHEEL ALIGNMENT The tools used for measuring caster and camber in older and portable mechanical alignment measuring systems have bubble levels. These are used for making comparisons to an exact level position. To attach the gauges to the wheels, a wheel rim adapter clamp is used or a large magnet holds the gauge to the wheel hub (Vintage Figure 68.1). The tool is mounted against a machined area of the hub. The wheel bearing dust cap is removed so that a pilot can center the gauge on the center hole in the end of the spindle. Portable bubble alignment gauges mea sure both caster and camber. There are two levels on the gauge. One of the levels, used to measure caster, is adjustable using a thumbscrew. When a front wheel has been turned to 20 degrees on the radius plate, set the level to zero. Then turn the wheel 40 degrees until the wheel is 20 degrees in the opposite direction. The reading on the gauge at this point is the caster reading. Magnetic head Camber gauge MEASURING CAMBER Camber is simply a comparison measurement to true vertical, using a level. To measure camber, position the wheels straight ahead while reading the gauge. If the wheels are not straight ahead, the caster angle can cause an incorrect camber reading. The four-wheel alignment machine will direct you to move the tires until they are in the correct position. SHOP TIP If the toe adjustment is very far off, as it could be after parts are replaced, an inaccurate camber reading will result. When parts are replaced, make a preliminary toe adjustment first. Then read the camber setting. MEASURING CASTER Caster causes the camber angle of the wheel to change dur ing a turn. NOTE: The caster measurement is actually a reading of camber change while turning. To measure the caster setting, the wheel is first turned either inward or outward a specified amount. The amount and direction of the turn depend on the manufacturer. They are not all the same. NOTE: Alignment settings for caster and camber are usu ally within a range. However, adjusting alignment to within that range will not always ensure that the vehicle will go straight. ROAD CROWN AND PULL Roads are crowned (higher at the center than the outside) so that rain will run off (Figure 68.17). A vehicle aligned with equal settings from side to side will drift to the outer edge of a crowned road. Machined hub surface Caster gauge Adjustment knob Radius plate Level Vintage Figure 68.1 A portable alignment gauge attached to the hub with a magnet. Figure Roads are crowned so water can run off them.

9 Wheel Alignment Service 1265 To compensate for road crown, two methods can be used: Camber can be set slightly more positive on the driver s side. Caster can be set so that it is slightly more negative on the driver s side. Many alignment technicians like to correct for road crown using caster because camber that is too far positive will result in wear to the outer edge of the tire. NOTE: When correcting for road crown, caster creates less of a pull than camber. Caster must be within ½ degree of the caster setting on the other side of the vehicle. (a) Frame Adjusting Caster and Camber There are many methods of caster and camber adjustment. Alignment equipment manufacturers provide detailed charts and catalogs that describe specific adjustment methods. Four-wheel alignment equipment often includes instructions on the computer monitor. On SLA suspensions, the cam ber adjustment is made using shims, eccentrics, or movement in elongated slots. SLA Shim Adjustment Figure shows a common SLA adjustment in which shims are removed or installed to reposition the upper control arm. SHOP TIP Before making an alignment adjustment, decide if it would be helpful to unload the suspension components so the weight of the vehicle is not resting on the wheels. Understanding the suspension design can make removing and replacing shims or turning an adjustment eccen tric easier (see Figure 68.18). Before making an alignment adjustment, note the current camber angle while the vehicle is raised. Then make the required amount of change to the new camber reading. Plan Ahead When there are shims, caster and camber are changed together. Removing and replacing shims is sometimes a fair amount of work. Plan ahead! Think about the effect the shim will have. Look at the control arm inner shaft to see what the effect of adding or removing shims will be. Some vehicles (usually light trucks) have the pivot shaft located outboard of the frame. Shims have the opposite effect as the normal control arm with the pivot shaft inboard of the frame. Figure shows how to change camber on inboard and outboard pivot shaft locations. To change caster with shims requires removing or adding shims at either end of the control arm pivot Frame Add or remove equal number of shims on each side (b) Figure Changing camber with shims on inboard and outboard pivot shafts. (a) With this suspension design, it is easier to remove shims with the weight of the vehicle on the tire. (b) On this suspension, removing shims is easi est with the weight off the tire. shaft (Figure 68.19). This will change camber because it moves the control arm out or in on one side. Computer four-wheel alignment machines will calculate the necessary shim change and display individual shim location placement. To prevent camber from changing much during a caster adjust ment, the alignment machine might direct you to remove a shim from one side of the pivot shaft and install it at the other end. An example of the amount a shim would change a vehicle s alignment is as follows: 1 16" shim on one side only ½ degree caster change or Remove a 1 32" shim from one side and add it to the other for ½ degree caster change. Other Adjustment Methods Some vehicles use an eccentric cam adjust ment on the upper or lower control arm, or strut (Figure 68.20). Turning the adjustment repositions the camber and caster angle. Less common align ment adjustment methods include slotted holes in the upper control arm shaft and an eccentric bushing installed under a ball joint.

10 1266 CHAPTER 68 Tighten Frame Remove shim Remove shim Frame Tighten Figure Slots allow movement of the top of the strut to adjust alignment. Figure Changing caster. Removing shims from one side or adding them to the other moves the position of the upper ball joint toward the front or rear, depending on the position of the frame. Adjust camber Cams (a) Hunter Engineering Company Upper control arm Figure Camber can be adjusted at the bottom of this strut by turning the eccentric. Eccentric cam (b) Lower control arm Figure (a) An eccentric adjustment on an upper control arm. (b) An eccentric adjustment on a lower control arm. Some computer align ment machines have a feature that calculates the position of the bushing. When Macpherson struts are adjustable (not all of them are), there are slots in the upper bearing bracket for adjusting caster (Figure 68.21) or an eccentric between the shock tube and steering knuckle (Fig ure 68.22). When a vehicle has a narrow lower control arm, it has a strut rod connecting it to the frame for strength. There are threads on one end of the strut. Some struts have a shoulder that bottoms out in the frame to position the strut. Others use a nut on both sides of the frame. With these, repositioning the nuts on the threaded area moves the control arm in an arc (Figure 68.23). This causes caster to change. Moving the lower control arm toward the rear makes caster more negative.

11 Wheel Alignment Service 1267 Adjusting nut or spacer Strut bar Frame bent strut tower. When this happens, the camber angle will also change. If the included angle is correct but the camber angle is not, the spindle/steering knuckle is not bent, so replacing it will not correct the problem. If the included angle is not correct, parts must be replaced. When a front-wheel bearing wears out, check for a bent spindle. Front-wheel bearings on RWD vehicles do not wear out very often. However, bearing misalignment can be caused by a bent spindle; this increases the load on the bearing. Unless there is a symptom pointing to the possibility of incorrect SAI as a contributing cause, most technicians do not go through the extra procedures required to check SAI. Before checking SAI, camber must be set correctly. Comparing SAI from side to side is a good indicator of correct SAI angles. Lower arm Movement of lower ball joint center when strut bar length is changed Figure Adjusting the length of the strut bar changes the caster. MEASURING STEERING AXIS INCLINATION Steering axis inclination (SAI) does not change; it is not adjustable. Most manufacturers do not publish SAI specifications. If the side-to-side comparison is greater than 1.5 degrees, a problem is indicated. On FWD Macpherson strut vehicles, SAI is the primary direc tional control angle and the adjustable angles can be used to correct vehicle aim toward straight ahead. These vehicles have lighter suspensions that are more easily damaged than heav ier RWD vehicles. A change in SAI only occurs if the spindle has been bent or if there has been body damage resulting in a Cradle Shift If the cradle (the sub-frame) has shifted to one side, camber will change on both front wheels (Figure 68.24) but the included angle will remain the same. Some vehicles have an alignment hole that is used to verify correct cradle position in relation to the body. Measuring Included Angle The included angle is the amount of SAI minus camber. If camber is negative, subtract it from the SAI reading. If camber is positive, add it to the SAI reading. Included angle is usually within ½ degree from side to side. When camber cannot be adjusted, check the included angle. If the included angle is off, the spindle, strut, or steering knuckle is bent, which requires replacement of the part. MEASURING TOE Checking and adjusting toe after replacing a tie-rod end or other steering linkage component is an impor tant part of the job. When measuring toe, the distances between the fronts and the rears of the front tires are compared. Unibody 90 Cradle Figure When the cradle shifts to one side, camber will change but the included angle will remain the same.

12 1268 CHAPTER 68 VINTAGE WHEEL ALIGNMENT Before computer alignment machines, a measuring tape, trammel bar, or optical toe measuring gauge was used. When making a mechanical measurement with a trammel bar (also called a tram gauge), a technician would sight down the side of the front tire to the rear tire and make an adjustment so that each front wheel looked to be in line with the rear wheel on the same side of the vehicle. Measuring toe without an optical device requires an accurate line to be scribed on the tread s footprint. With the tire raised off the ground, the tire was spun while applying chalk to the center of its tread. Next, a narrow line was scribed in the middle of the chalked area using a special scribing tool or a board with a nail pounded through it. After the vehicle was lowered to the ground, the distances between the scribed lines on the tread surfaces at the front and rear of the tire were com pared (Vintage Figure 68.2). The trammel bar was adjusted to measure at the same height as the spindles at the centers of the wheel hubs, which resulted in toe being measured at the largest circumference of the tire tread. On earlier electronic wheel alignment equipment, an optical toe device projected an image to a gauge on the oppo site side of the vehicle. Scribe mark Pointer Trammel bar Vintage Figure 68.2 A trammel bar for measuring toe. Methods of Calculating Toe Toe has traditionally been measured as a distance in inches or millimeters, called total toe or toe distance. A more recent trend is to measure the toe angle, which is the angle between the two front tires. Toe angle is equal between the two front tires when they are rolling forward. The diameter of the tire does not Stock tire Difference Oversized tire distance Stock tire Oversized tire Figure Oversized tires will affect toe distance measurement but not toe angle. affect the toe angle reading as it does with traditional toe dis tance measurement (Figure 68.25). This is an advan tage, especially when oversized tires are used. When toe angle is measured in degrees: Toe-in is a positive ( ) angle. Toe-out is a negative ( ) angle. Zero toe is when the wheels are parallel. Figure lists conver sions of lengths and angles used in wheel alignment. Toe in FWD and RWD Vehicles FWD and RWD vehicles have different toe specifications because they react differently when their tires are in motion. The objective is to have zero toe when the vehicle is in motion. RWD vehicles are usually set slightly toed-in (about 1 16" on new vehicles). This is because the rolling resistance of the front tires tends to push them outward at the front. RWD toe-in also compensates for compliance (clearance or slack) within steering linkages and bushings (Figure 68.27). FWD vehicles are usually set with zero toe or a slight amount of toe-out. This is because the front tires tend to push inward at the front as they pull the vehicle forward on the road. The running toe setting can undergo even more change in response to scrub radius and to increased rolling resistance caused by low tire pressures or wider tires. Scrub radius is altered when wheels with more negative offset than original equipment are installed. ADJUSTING TOE Most vehicles have steering linkages with either two or four tie-rod ends. Shortening or lengthening the tie-rod changes the toe setting.

13 Wheel Alignment Service 1269 Length and Angle Conversions Used in Wheel Alignments Inch Inch Metric Degrees Degrees Degrees (Fractional) (Decimal) (mm) (Decimal) (Fractional) (Minutes) 1 / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / Figure Length and angle conversions used in wheel alignments. Wheel toe-in Front Standing still No toe Front Moving forward Figure On a rear-wheel-drive car, tires tend to toe out when rolling. Parallelogram Toe Adjustment On parallelogram steering, toe is adjusted by turning the threaded turnbuckle sleeves between the tie-rod ends (Figure 68.28). As the sleeve is turned, the tierod assembly either becomes longer or shorter because one of the tie-rod ends has a left-hand thread and the other has a right-hand thread. NOTE: The steering wheel is centered and held in place with a steering wheel clamp while making the adjustment (Figure 68.29). After the toe has been adjusted, the adjusting sleeve clamp must be correctly positioned before it is tightened. It must not be able to interfere with other parts as the wheels are turned from side to side. The opening in the clamp cannot be positioned over the split in the adjusting sleeve. Figure shows the right and wrong ways to install an adjusting sleeve clamp. If one tie-rod happens to be tilted one way and the other is tilted the other way, the tie-rod will not be able to pivot (Figure 68.31). The tie-rods are positioned so that they are not binding up. This is most easily done by turning both tie-rods in the same direction before tightening the clamp.

14 1270 CHAPTER 68 B Front of vehicle Tie-rod adjusting sleeves A Figure Turn the adjusting sleeves to adjust toe. SPX Service Solutions Counterclockwise rotation restricted Clockwise rotation restricted Steering arm Steering wheel holder Figure The steering wheel is centered and held in place with a steering wheel clamp while making a toe adjustment. Correct Incorrect Figure Position the clamp correctly. Tie-rod socket Correct Incorrect Figure Position the tie-rods so that they will not bind. Rack-and-Pinion Toe Adjustment Rack-and-pinion steering systems have a conven tional outer tie-rod and an inner tie-rod end with a jam nut on each side (Figure 68.32). Hold the tie-rod end with a wrench or pliers while loosening and tightening the jam nut (there is usually a provision on the tie-rod to accommodate a wrench). The inner end of the tie-rod is a ball socket that can be rotated to adjust toe. It will not bind if a tie-rod is turned off-center, like the parallelogram type shown previously in Figure NOTE: Loosen the clamp on the boot as needed to be sure the boot does not twist while you adjust toe.

15 Wheel Alignment Service 1271 Tie-rod end Jam nut Turn to adjust toe Figure Rack-and-pinion tie-rod end. Boot must not twist CENTERING A STEERING WHEEL Adjusting one of the tie-rods more than the other will tilt the steering wheel off-center. NOTE: In most vehicles it is important that the steering wheel be centered using the tie-rods, not by removing the steering wheel and putting it back on straight. If the steering wheel is not straight ahead when driving, the following procedure will allow turn signals to cancel during turns and minimize looseness in recircu lating ball and nut steering gears. Follow these steps to correctly straighten the steering wheel: Carefully count the number of turns of the steering wheel while turning it from lock to lock. The total can include fractions of a turn, so pay careful attention when counting. When you have determined the distance between the locks, position the steering wheel so it is halfway between them. It should be straight. If not, remove it and put it back in the correct position. Federal-Mogul Corporation Finishing the Toe Adjustment Use a steering wheel holder to keep the steering wheel centered while you finish the toe adjustment. When making a rough adjustment, turn each tie-rod an equal amount in opposite directions. This will approximately maintain the current toe setting. When you tighten the tie-rod clamps or jam nuts, a small amount of change in the toe setting can occur because of slack between the threads. SHOP TIP Correct adjustment often calls for the initial setting to be slightly off in anticipa tion of the change that will occur when the jam nut is completely tight. Knowing the correct amount will come with practice. SHOP TIP From the front of the vehicle you can get a rough estimate of the direction each tie-rod needs to be turned by sighting down the tires on each side of the vehicle to see if the front one aligns with the rear one. Correcting Toe after a Test Drive The computer wheel alignment equipment makes calculations that estimate the alignment settings so the vehicle will drive straight with the steering wheel on center. Sometimes a slight correction might be necessary, however. Test-drive the vehicle on a straight, level road. If the steering wheel is off-center, aimed to the left, adjust the tie-rods so the tires also point to the left (Figure 68.33). If the steering wheel is aimed Adjust each wheel to point left Steering wheel position Adjust each wheel to point right Adjusting sleeve Adjusting sleeve Figure Adjusting steering wheel center using the tie-rods. Adjust tie-rod sleeves equally in opposite directions.

16 1272 CHAPTER 68 to the right, adjust the tie-rods so the wheels face the opposite direction. NOTE: Customers occasionally have perceptions that might seem to you to be different from reality. For instance, a customer might say that the vehicle pulls because the steering wheel is off-center. The customer sees the wheel off-center and straightens it, causing the vehicle to steer to the side. Manufacturers specifications for maximum allowable steering wheel angle variation are typically ±3 degrees. CHECKING FOR TOE CHANGE The toe setting on a tire can change when the wheel goes into a pothole or over a bump. Sometimes toe only remains as set when the vehicle is at the correct ride height. This is something that should be checked during each wheel alignment. Raise the vehicle an equal amount on each side with the jack on the alignment rack (Figure 68.34). Toe should change equally on each wheel. If not, one end of the steering linkage is not at the correct height and needs to be corrected. The vehicle might have had an accident and require the services of a frame straightening shop. However, there are other possible causes of toe change. On some parallelogram steering systems, the idler arm bolts to slotted mount ing holes in the frame and its height is adjustable. NOTE: Aftermarket suspension parts sometimes relocate steering linkage connections, which can cause extreme toe change when the suspension moves. After installation of new parts, check for toe change. Rack-and-Pinion Level Adjustment When a rack-and-pinion steering gear has been mounted out of level, its tie-rods will be at unequal angles. Sometimes one or both of its holding brackets are loose or a bushing has become damaged. Measure and compare the height of the steering gear and linkage at several locations. A long straightedge can be helpful in spotting irregularities (Figure 68.35). Some vehicles use shims to adjust rack-and-pinion height to correct for toe change (Figure 68.36). Figure Raise the vehicle equally from side to side to check for toe change. 3" Figure Sometimes a long straightedge is helpful in spotting irregularities in steering linkage angle. Mounting bracket and bushing Shim Front cross member MEASURING TURNING RADIUS Rack-and-pinion steering gear Figure Some vehicles use shims to adjust rackand-pinion height to correct for toe change. When the radius plate has a pointer and degree strip, you can measure turning radius while making a caster measurement. As the wheels are turned from side to side, the outer wheel should make a turn that is 2 or 3 degrees less than the inside wheel. For example, when the outside wheel is turned 18 degrees, the inside wheel s radius plate gauge should read about 20 degrees (Figure 68.37). The reading should be within 1½ degrees of the specifica tions found in the service information. This measurement is done automatically on many alignment machines. The steering arms are angled to point to the center of the rear axle (Figure 68.38). This is the Ackerman angle (see Chapter 67). NOTE: Turning radius is not an adjustable angle, but if a steering arm becomes bent the turning radius is affected and the tires can squeal on turns.

17 Wheel Alignment Service 1273 Inside wheel turning radius 20 Front of vehicle Outside wheel turning radius 18 Figure The inner wheel turns at a sharper angle than the outer wheel. The driver s weight will usually cause camber to increase on the left front wheel and decrease on the right front wheel. When making a shim adjustment on an SLA suspension, changing camber will not affect caster, but changing caster can affect camber. Caster for both wheels should be set either positive or negative, not one positive and one negative. Caster spread between the front wheels should not be more than ½ degree. NOTE: Spread is the difference between alignment set tings from side to side. It is also called cross caster or cross camber. Camber is sometimes specified with more than a ½ degree of spread. Always follow the manufacturer s specifications. Make caster equal from side to side. Use camber to compensate for road crown. If caster is equal, set GENERAL WHEEL ALIGNMENT RULES Experienced wheel alignment technicians experiment with different vehicles to see what changes result from vari ous adjustments. Due to variations in suspension and steering design, the results of adjustments are not always consistent. The next section of this chapter covers general rules pro vided as a place to start Caster Camber Caster and camber are important adjustable wheel alignment angles. The following are some helpful rules: The vehicle will pull to the side with more negative caster. The vehicle will pull to the side with more positive camber (Figure 68.39). Adjusting to a more negative caster setting results in easier steering. A cambered wheel rolls like a cone Figure The vehicle will pull to the side with the most positive camber. Steering arm CL Geometric centerline Steering arm Figure The Ackerman angle has the steering arms point to the center of the rear axle.

18 1274 CHAPTER 68 the camber on the left side ¼ degree more positive than the right. Power steering vehicles can have caster as high as 10 degrees (e.g., Mercedes). Vehicles with manual steering are uncommon today, but on these vehicles caster is generally 0 to 1 degree negative. On a Macpherson strut vehicle, jounce the vehicle while measuring camber. If camber changes drastically on either front wheel, the strut is bent. Thrust line off center cl Thrust angle Toe The toe adjustment has the most impact on tire wear. The other angles are adjusted first. The following are some helpful rules to consider: Before driving on the alignment rack, be sure the pins are in the radius plates. Every ¼ turn of the adjusting sleeve results in about 1 16" of toe change. Changing caster and camber affects toe, so toe is adjusted last. Toe is measured in inches, millimeters, or degrees. FOUR-WHEEL ALIGNMENT Modern wheel alignment equipment measures the alignment of all four wheels. Rear-wheel toe and camber are often adjustable. When they are not, the front wheels are adjusted with reference to the settings in the rear. This concept is covered later. Geometric Centerline A vehicle s geometric centerline is a line drawn between the center of the front axle and the center of the rear axle. The geometric centerline is used when measuring individual toe at all four wheels. There are several measurement factors to consider regarding the geometric centerline. The direction in which the rear wheels point is called the thrust line (Figure 68.40). When the rear wheels are held in a fixed position, the thrust line defines the wheels true straight-ahead position. If the rear wheels are aimed to the right, the thrust line is to the right. The thrust angle is formed by the thrust line and the geometric centerline (Figure 68.41). A thrust angle is created when the rear wheels are not parallel Thrust line Centerline Figure Thrust line is the direction that the rear wheels are pointing. Offset Rear wheel toe correction Geometric centerline Figure Correct rear-wheel alignment adjusts the rear-wheel toe to specifications with the thrust angle near zero. to the vehicle centerline. This is caused by an accident or a severe impact that moves the axle position away from perpendicular to the centerline. The thrust angle is positive when off to the right and negative when off to the left. A comprehensive four-wheel alignment calls for adjusting rear-wheel toe to factory specifications with the thrust angle at or near zero. Independent rear suspensions usually have adjustable toe. Individual rear toe adjustment will compensate for incorrect thrust angle. NOTE: Individual toe is measured at each wheel and is in reference to the geometric centerline of the vehicle. To center the steering wheel, it will be necessary to adjust the individual toe at the front of each wheel. When the front and rear wheels are closer together on one side of the vehicle than the other, this is called wheelbase dif ference (Figure 68.42). Setback is the amount that a front wheel is behind the one on the other side of the vehicle (Figure 68.43). This is not adjustable, although it is mea sured by the computer during a four-wheel alignment. Incorrect setback can be caused by a collision. Symptoms include steering to one side or the other, or brake pull. Track width is when the distance between the front wheels is different than the distance between the rear wheels (Figure 68.44). On some vehicles, the front wheels have a narrower track width than the rear wheels. In winter weather, this is a problem because the rear tires will try to follow tracks made in snow or mud by the front tires.

19 Wheel Alignment Service 1275 Wheelbase difference cl Geometric centerline Figure The wheels on the right side are closer to each other than the wheels on the left side. This is called wheelbase difference. Figure Mount the wheel alignment head on the wheel. Setback Figure Setback is the amount that one front wheel is behind the one on the other side of the car. Figure Some newer alignment machines use a tar get on each wheel. Digital cameras monitor the location of each target. cl Figure The front wheels often have narrower track width than the rear wheels. SHOP TIP Sight across the sidewall bulges of the front tires while you look at the rear tires. If the rear wheels have a wider track width, you will be able to see a small amount of tread on each side. If you can observe an equal amount of tread on each side, the rear-wheel thrust line is straight and the steering wheel will be centered. PERFORMING A FOUR-WHEEL ALIGNMENT During a computer wheel alignment, sensors are installed on all four wheels (Figure 68.45). Some of the newest alignment machines use targets (Fig ure 68.46) rather than gauges on the wheels. Four digital cameras monitor the position of the targets. When all four wheels are checked at the same time, the computer calculates the thrust angle. If it is the same as the geometric centerline, the steering wheel will be correctly centered. COMPENSATING THE ALIGNMENT HEADS Alignment machines that use targets automatically compensate the alignment heads as the vehicle is rolled on the alignment rack (Figure 68.47). Older wheel alignment machines required repeated practice in order to adjust the wheel-mounted alignment

20 1276 CHAPTER 68 Four digital cameras in the opposite direction. When the wheels have been positioned correctly and the computer has the information needed to make the calculations, alignment readings are displayed on the monitor. Some computer align ment software include still photo and video tutorials on various procedures. If the vehicle has four-wheel steering, the special procedures are followed to lock the rear wheels in the straight-ahead position. Computer Targets ADJUSTING REAR-WHEEL ALIGNMENT Camber and toe adjustments can be made on some vehicles. A few vehicles allow rear caster adjustment; however, special equipment is required to measure this angle. Alignment rack Figure A modern alignment machine that auto matically compensates the wheels by simply rolling the vehicle on the alignment rack. heads. Alignment machines today are much quicker and easier to use. MEASURING CASTER AND CAMBER The amount of wheel sweep during a caster check is determined by the alignment program. The technician watches the moni tor while slowly turning the wheels a few degrees in one direction on the radius plates (Figure 68.48). This is followed by a turn Adjusting Rear Camber On a vehicle with a double wish bone rear suspension, camber is usually adjusted by turning an eccentric adjuster. On some rear strut suspensions, camber adjustment is accomplished by installing a tapered wedge between the top of the rear knuckle and the strut (Figure 68.49). Adjusting Rear Toe Rear-wheel toe can be adjusted in several ways, depending on the manufacturer. One method involves moving the lower control arm with an adjustable link age attached to the knuckle (Figure 68.50). Some manufacturers have a toe link with a slotted hole that allows the wheel to be moved to adjust toe when its holddown screw is loosened (Figure 68.51). One of the rear-wheel alignment adjustment methods uses a tapered shim like those used to adjust Camber adjustment wedge Strut Figure Using a computer alignment machine to make a caster reading. Knuckle Figure A rear strut suspension camber adjustment using a tapered wedge between the top of the rear knuckle and the strut.