Wheel Alignment Service Chapter 68 2012 Delmar, Cengage Learning 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 2012 Delmar, Cengage Learning
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
2012 Delmar, Cengage Learning 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 2012 Delmar, Cengage Learning 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 2012 Delmar, Cengage Learning 2012 Delmar, Cengage Learning 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 2012 Delmar, Cengage Learning 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 2012 Delmar, Cengage Learning 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 2012 Delmar, Cengage Learning 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 2012 Delmar, Cengage Learning 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 2012 Delmar, Cengage Learning 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 2012 Delmar, Cengage Learning 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 2012 Delmar, Cengage Learning 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 2012 Delmar, Cengage Learning 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 2012 Delmar, Cengage Learning Road Crown and Pull (contd.) 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 2012 Delmar, Cengage Learning 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 2012 Delmar, Cengage Learning 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 2012 Delmar, Cengage Learning 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 2012 Delmar, Cengage Learning 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 2012 Delmar, Cengage Learning 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 nonlevel position Tie rod will be at unequal angles Some vehicles use shims to adjust rack-andpinion height to correct for toe change 2012 Delmar, Cengage Learning 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 2012 Delmar, Cengage Learning 2012 Delmar, Cengage Learning General Wheel Alignment Rules Caster/camber Vehicle pulls to side: negative caster and positive
camber Adjusting for negative caster yields easier steering Drivers 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 2012 Delmar, Cengage Learning General Wheel Alignment Rules
(contd.) Caster for both wheels should be set either positive or negative Caster spread between front wheel settings should not be more than 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 2012 Delmar, Cengage Learning
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 2012 Delmar, Cengage Learning 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 2012 Delmar, Cengage Learning 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 its normally driven 2012 Delmar, Cengage Learning 2012 Delmar, Cengage Learning
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