Buick LeSabre 1965 Service Manual page 459

7 - 3 2 SERVICE PROCEDURES CHASSIS SUSPENSION
carefully engineered to provide
the best ride control over a wide
range of driving conditions. Sub-
stitution of other calibrations may
adversely affect car performance
and is not recommended by Buick
Motor Division.
7-18 FRONT WHEEL
ALIGNMENT
Wheel alignment is the mechanics
of properly adjusting all the fac-
tors affecting the position of front
wheels so as to cause the car to
steer with the least effort and to
reduce tire wear to a minimum.
Correct alignment of the frame is
essential to proper alignment of
front and rear wheels. Briefly,
the essentials are that the frame
must be square in plan view with-
in specified limits, that the top
and bottom surfaces of front
cross member must be parallel
fore and aft, and the bolt holes for
support upper arms and lower
control arm shafts must be of
correct size and location. Check-
ing frame alignment is covered
in Group 12.
It should also be understood that
wheel and tire balance has an
important effect on steering and
tire wear. If wheels and tires
are out of balance, ''shimmy*'
or "tramp" may develop or tires
may wear unevenly, and give the
erroneous impression that the
wheels are not in proper align-
ment. For this reason, the wheel
and tire assemblies should be
known to be in proper balance
before assuming that wheels are
out of alignment.
Close limits on caster, front
wheel camber, and theoretical
king pin inclination are beneficial
to car handling, but require only
reasonable accuracy to provide
normal tire life. With the type of
front suspension used, the toe-in
adjustment is much more impor-
tant than caster and camber in
so far as tire wear is concerned.
Caster and camber adjustments
need not be considered unless
visual inspection shows these set-
tings to be out, or unless the car
gives poor handling on the road.
In the majority of cases, services
consisting of inflating tires to
specified p r e s s u r e and inter-
changing tires at recommended
i n t e r v a l s (par. 7-8) adjusting
steering gear (par. 8-4 manual
and par. 8-13 power), and setting
toe-in correctly (subpar. e, fol-
lowing) will provide more im-
provement in car handling and
tire wear than will front end
alignment adjustments as usually
made on front end of alignment
equipment.
The correct use of accurate front
end alignment equipment is essen-
tial to determine whether front
suspension parts have been dam-
aged by shock or accident, and to
obtain correct alignment settings
after new parts have been
installed.
a. Design Considerations
Affecting Caster, Camber
and Toe Change
The caster angle of an independ-
ent front ball-joint suspension is
the angle made by a line passing
through the center of the upper
and lower ball joints, and a ver-
tical line through the centerline
of the spindle in relation to the
ground, when looking at the side
of a car. The angle is called
"positive" if the upper ball joint
is behind the lower, and "nega-
tive" if the upper ball is ahead of
the lower. See Figure 7-34.
Once the caster has been set, the
caster angle will change due to
one or both of the following:
1. A change in trim height of the
front suspension from the trim at
which the caster was set.
2. A change in trim height of the
rear suspension from the trim at
NEGATIVE
CASTER ANGLE
POSITIVE
CASTER ANGLE
Figure 7-34—Caster Angle
which the caster was set.
The front suspension is attached
to the front spring cross member
of the frame. The caster is deter-
mined by the angle of the line
through the upper and lower front
suspension ball j o i n t s to the
ground. Therefore, the angle of
the frame to the ground also con-
trols the caster angle.
Since the caster and camber are
in relation to the ground it is
necessary to have tires, spindles,
wheel bearings, and other related
parts correct before setting front-
end alignment.
STEERING AXIS
INCLINATION
-VERTICAL
Figure 7-35—Camber Angle and
Steering Axis Inclination