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Why alignment?
1. To eliminate tire wear
2. To give vehicle proper handling– Eliminate pull, drift, wander, stiff steering
and poor steering return ability
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
Always check steering and suspension 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
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
If adjustments are possible, it will usually be at only one pivot point
Camber and caster are often adjusted together
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 camber
Shims
Found mostly on vehicles with SLA suspensions
Shims come in various thickness'
Can adjust both caster and camber
Cradle adjustment
Some vehicles allow cradle adjustment
Can affect both caster and camber
Should only be done if manufacture recommends
Toe adjustment
Always performed as last adjustment Adjusted by effectively lengthening or
shortening tie rods Some vehicles have only one
adjustable tie rod Sometimes toe is only adjustment
possible
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
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
Rear toe and camber
Can be adjusted using eccentrics, depending on their position, similar to front end