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alignment

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									Alignment
            Why alignment?
1. To eliminate tire wear
2. To give vehicle proper handling
  – Eliminate pull, drift, wander, stiff steering
    and poor steering returnability
    Three types of alignments
 Geometric    centerline (2 wheel) (POOR)
  – Aligns front wheels to center of vehicle
 Thrust   angle (2 wheel)            (GOOD)
  – Aligns front wheels to thrust angle
 Total   alignment (4 wheel)         (BEST)
  – Aligns all 4 wheels to geometric centerline
  – Not possible on all vehicles
            Before alignment
       check steering and suspension
 Always
 components for wear
  – Including wheel bearings
 Always    check tire pressure
  – A low tire may cause pull
 Always    check tire condition
  – Tire wear will indicate possible problems
 Try   to duplicate the complaint if possible
                  Camber
 Inward   or outward tilt of the top of the
  tire
 Outward tip is positive / Inward tip is
  negative
 If excessive (about 1 1/4 degree off)
  positive or negative, camber will cause
  tire wear
 May cause pull to most positive side
 Maximum cross camber usually .5deg
                  Caster
 Forward   or rearward tilt of the steering
  axis
 Forward is negative \ rearward is
  positive
 Positive gives steering stability and
  returnability
 Negative decreases turning effort
 May cause pull to most negative side
 Maximum cross caster usually .5deg
Camber roll
                    Toe
 Difference   between the front and rear of
  the tires
 Toe in or positive toe means the front of
  the tires are closer than the rear of the
  tires
 Toe out or negative toe means the rear
  of the tires are closer than the front of
  the tires
                   Toe
 Excessive   toe in (positive) will cause
  wear on the outer tire edges
 Excessive toe out (negative) will cause
  wear on the inner tire edges
 Incorrect toe is THE most common
  cause of tire wear
 Different toe side to side will cause
  steering wheel to be off center but will
  not cause pull
  Camber and caster adjustments
 Ifadjustments are possible, it will
  usually be at only one pivot point
 Camber and caster are often adjusted
  together
             Slotted holes
 Common on
  MacPherson strut
  with 2 bolts at
  knuckle
 Common at top of
  strut mount
                Eccentrics
 SLA may have 2
  eccentrics on upper
  control arm bolts
 MacPherson strut
  may have eccentric
  at knuckle attaching
  bolts
 Depending on
  design, may be
  used to adjust both
  angles or just
                     Shims
 Found mostly
  on vehicles with
  SLA suspensions
 Shims come
  in various
  thickness'
 Can adjust
  both caster
  and camber
                   Strut rod
   Lengthening or
    shorting strut rod
    attached to lower
    control will change
    caster
          Cradle adjustment
 Some vehicles allow
  cradle adjustment
 Can affect both
  caster and camber
 Should only be done
  if manufacture
  recommends
Shim practice
           Toe adjustment
 Always  performed as last adjustment
 Adjusted by effectively lengthing or
  shortening tie rods
 Some vehicles have only one adjustable
  tie rod
 Sometimes toe is only adjustment
  possible
Steering axis inclination
     Included angle
     Diagnostic angles
              Definitions
 SAI  a line drawn through the steering
  axis, as viewed from the front
 SAI allows smaller camber angles but
  keeps load on inboard of spindle
 SAI moves spindle in arc like caster
 Included angle is the total of SAI +
  camber
              SAI and IA
 Both angles are used for diagnostics
  when bent or loose components are
  suspect
 Many vehicles do not give specs
 Side to side differences most important
 1.5 deg diff side to side or off of specs
  maximum allowed
 Should be checked whenever camber is
  found to be way off
             Cradle adjusting
   If SAI off opposite
    amounts side to side
    suspect cradle
    alignment
Rear Wheel Alignment
             Rear wheels
 Usually only front wheel drive vehicles
 Purpose is to realign thrust angle and
  geometric centerline
 Camber and toe only angles
 Rear toe or camber problems can cause
  lead, pull, dog tracking, tire wear
       Adjusting rear wheels
 Camber  adjusted first if available
 Toe adjustment more common than
  camber
Common adjustments
                   Rear toe
   Can be adjusted by
    tie rods similar to
    front
          Rear toe and camber
   Can be adjusted using eccentrics, depending
    on their position, similar to front end
            Afftermarket shims
   Full contact shims can adjust both angles
Shim example
The End

								
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