wheel alignment service

© 2012 Delmar, Cengage Learning

Wheel Alignment Service

Chapter 68


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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

wheel alignment service

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