Wheel Alignment Service

1. Wheel Alignment Service Chapter 68

2. Objectives • 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

3. Introduction • Steering and suspension • Inspect before aligning wheels • Loose parts prevent accurate and lasting adjustment • Wheel alignment • Requested because of unusual tire wear and/or handling problems • Front axles experience more stress

4. Prealignment Inspection • Parts are loose or worn • Alignment will not be successful • Important considerations • Tire pressure must be adjusted • Vehicle ride height must be correct • Worn bushings must not allow movement of suspension and steering parts • Steering gear and linkage coupling points must not have excessive clearance • Tires must be new or worn evenly

5. Tire Wear Inspection and Ride Height Check • Tire wear inspection • Wear from incorrect camber shows on outside or inside of tire tread • Driving a vehicle with excessive toe is dangerous because front tires slide • RWD cars with radial tires toe-in will roll under • Ride height check • Specifications assume ride height is correct • Check ride height prior to wheel alignment

7. Toe Change • Suspension height changes: toe measurement changes • Example: springs sag • Toe change causes tire scrub on road surface • Wears away tread • Toe change confined to one side of vehicle • Bump steer can result

8. Torque Steer • Vehicle turns abruptly to side during initial acceleration • Found on front-wheel-drive cars with axles of unequal lengths • Results in unequal CV joint angles • Could be due to loose sub-frame or problem with unequal spring height

9. Suspension Looseness • “You can't align looseness” • Perform a dry park check for steering and suspension looseness • Linkages in good condition will allow pivoting only • Any slack between parts will become apparent due to the resistance of the tires • Always check adjustment of wheel bearings

10. Test Drive • Test drive before performing repairs • Unless vehicle is unsafe • Perform visual inspection before driving • Suspension bushings • Steering linkage pivot connections • Rubber grease boots on tie-rod ends and ball joints • Shock absorbers

11. Tire Checks and Inspection Checklist • Perform a tire check and power steering check • Sometimes pull results from the crown of the road surface • Before attempting wheel alignment: check for looseness in any related parts • Test ball joints for looseness • Inspection checklist • Used by technicians to make sure no steps are accidentally forgotten

12. Wheel Alignment Procedures • Front suspension: designed to keep wheels in best possible position when rolling • Alignment settings change • Vehicle speed • Roughness of road surface • Acceleration and braking • Weight distribution and cornering • Adjustments to original settings may be needed • Adjustable angles: caster, camber, and toe

13. Measuring Alignment • Alignment measurements • Read in degrees and parts of degrees • Important considerations • Slip plates are under the rear tires • Front wheels are positioned on radius plates • Computerized alignment machines do four-wheel alignment inspection • Vehicle must be level to get accurate measurements • Toe is adjusted last

14. Measuring Camber and Measuring Caster • Camber • Comparison measurement to true vertical, using a level • Position wheels straight ahead while reading gauge • Caster • Causes camber angle to change during a turn • Wheel is turned either inward or outward a specified amount

15. Road Crown and Pull • Roads are crowned so rain with run off • Methods to compensate for road crown • Camber set slightly more positive on driver's side • Caster set slightly more negative on driver's side • SLA suspensions • Camber adjustment is done with shims, eccentrics, or movement in elongated slots

16. Road Crown and Pull (cont’d.) • When there are shims, caster and camber are changed together • Shims have the opposite effect as the normal control arm • Other adjustment methods • Some vehicles use an electric cam adjustment on the upper or lower control arm, or strut • Several other less common adjustments

17. Measuring Steering Axis Inclination • SAI does not change • Not adjustable • Change in SAI occurs if: • The spindle has been bent • There is body damage resulting in a bent strut tower • Cradle has shifted to one side • Camber will change on both front wheels • Included angle • Amount of SAI minus camber

18. Measuring Toe • Check and adjust toe after replacing steering linkage component • Distances between fronts and rears of front tires are compared • Traditionally measured as a distance in inches or millimeters • Recent trend is to measure the toe angle • FWD and RWD vehicles • Different toe specifications

19. Adjusting Toe • Steering linkages on most vehicles • Have either two or four tie-rod ends • Shortening or lengthening changes toe setting • Major steps • Center the steering wheel and hold it in place • Make adjustments • Position clamp properly and tighten • Rack-and-pinion steering systems • Have an outer tie-rod and inner tie-rod end with a jam nut on each side

20. Centering a Steering Wheel • Steps to straighten wheel • Count the number of turns of the steering wheel while turning it from lock to lock • Position steering wheel so that it is half-way between the locks • Use a steering wheel holder to keep the steering wheel centered while adjusting • Correct toe after a test drive

21. Checking for Toe Change • Sometimes toe only remains as set when the vehicle is at the correct ride height • Should be checked during wheel alignment • Rack-and-pinion steering gear mounted in non-level position • Tie rod will be at unequal angles • Some vehicles use shims to adjust rack-and-pinion height to correct for toe change

22. Measuring Turning Radius • Observe the pointer on the radius plate while making a caster measurement • Ackerman Angle • Steering arms are angled to point to the center of the rear axle • Turning radius is not an adjustable angle

24. General Wheel Alignment Rules • Caster/camber • Vehicle pulls to side: negative caster and positive camber • Adjusting for negative caster yields easier steering • Driver’s weight will cause camber to increase on left front wheel and decrease on right front wheel • Shim adjustment on SLA suspension • Changing camber will not affect caster • Changing caster will affect camber

25. General Wheel Alignment Rules (cont’d.) • Caster for both wheels should be set either positive or negative • Caster spread between front wheel settings should not be more than ½ degree • Make caster equal from side to side • Power steering vehicles can have caster as high as ten degrees • Macpherson strut vehicle: jounce while measuring camber • Toe adjustment has the most impact on tire wear

26. Four Wheel Alignment and Performing Four-Wheel Alignment • Important considerations • Geometric centerline: line drawn between center of front axle and center of rear axle • Thrustline: direction rear wheels point • Thrust angle: formed by thrustline and geometric centerline • During computer wheel alignment: sensors are installed on all four wheels • Thrust angle is same as geometric centerline: steering wheel will be correctly centered

27. Compensating the Alignment Heads and Measuring Caster and Camber • Machines with targets automatically compensate the alignment heads • Many older machines require higher level of skill • Machines today are quicker and easier • Amount of wheel sweep during a caster check is determined by the alignment program • Wheels have been positioned correctly: alignment readings are displayed

28. Adjusting Rear-Wheel Alignment • Camber and toe adjustments • Possible on some vehicles • Camber adjustment on double wishbone rear suspension: done by turning eccentric adjuster • Rear-wheel toe • Can be adjusted in several ways • Wheel alignment rules • No heavy loads in vehicle • Fuel tank should be full • Vehicle is aligned in condition it’s normally driven