3A-2 Front End Alignment; Description; Definition Of Terms - GMC G Service Manual

3A-2 FRONT END ALIGNMENT

"Front End Alignment" refers to the angular relationship
between the front wheels, the front suspension attaching
parts and the ground.
Proper front end alignment must be maintained in order
to insure efficient steering, good directional stability and to
prevent abnormal tire wear.
The most important factors of front end alignment are
wheel toe-in, wheel camber, and axle caster (Figure 1).

DEFINITION OF TERMS

CAMBER
Camber is the inward or outward tilting of the front
wheels from the vertical. When the wheels tilt outward at
the top, the camber is positive ( + ). When the wheels tilt
inward at the top, the camber is negative ( - ) . The amount
of tilt measured in degrees from the vertical is called the
camber angle. Camber is designed into the front axle
assembly of all four-wheel drive vehicles and is non-adjust-
able.
If camber is extreme or unequal between the wheels,
improper steering and excessive tire wear will result. Nega­
tive camber causes wear on the inside tire, while positive
camber causes wear to the outside.
A minus B .. .Camber (Inches)
C . .Camber (Degrees Positive)
D .. .Caster (Degrees Positive)
E minus F ........ Toe-In (Inches)

DESCRIPTION

Front View
Figure 1 — Caster-Camber-Toe-ln
CASTER (Figure 1)
Caster is the tilting of the wheel axis either forward or
backward from the vertical (when viewed from the side of
the vehicle). A backward tilt is positive (+ ) and a forward tilt
is negative ( - ) .
On the short and long arm type suspension you cannot
see a caster angle without a special instrument, but if you
look straight down from the top of the upper control arm to
the ground, the ball joints do not line up (fore and aft) when
a caster angle other than 0 degree is present. With a posi­
tive angle, the lower ball joint would be slightly ahead
(toward the front of the vehicle) of the upper ball joint center
line. Caster is designed into the front axle assembly on all
four-wheel drive vehicles, and is non-adjustable.
TOE-IN
Toe-in is the turning of the front wheels. The actual
amount of toe-in is normally a fraction of a degree. Toe-in is
measured from the center of the tire treads or from the
inside of the tires. The purpose of toe-in is to insure parallel
rolling of the front wheels and to offset any small deflections
of the wheel support system which occurs when the vehicle
is rolling forward. Incorrect toe-in results in excessive toe-in
and unstable steering. Toe-in is the last alignment to be set
in the front end alignment procedure.
Side View