Wheel Alignment Service

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Wheel Alignment Service

• Chapter 68

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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 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

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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

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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

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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

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