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© 2012 Delmar, Cengage Learning
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 (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
© 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 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
© 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– 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
© 2012 Delmar, Cengage Learning
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
© 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 it’s normally driven
© 2012 Delmar, Cengage Learning