ALIGNMENT
Attention should be given quite frequently to wheel alignment, as the
life and service of tires depends almost entirely upon wheel alignment.
When either of the front wheels become out of line, through a bent
spindle, worn spindle pin, loose or worn bearing the tire on this wheel
is subject to cross traction. That is, when the car moves forward, the
tire on the out of line wheel is forced to move forward by the other
three points of traction, and as it is not in line with the forward
movement the tire must push or drag crosswise at the traction point.
This results in the tread being worn or filed off in a very short time,
exposing the layers of fabric to dampness and wear which results in a
“blow-out” and ruined tire, which would probably have given several
thousand miles of service had proper attention been given to wheel
alignment.
=Alignment Test.=--To test the alignment, first look at the lower
side of the springs where they rest on the axle seats. If one of the
springs has slipped on the seat through a loose clamp, the direction
and distance of the slip may be noted by the rust mark left by the
movement. Drive the axle back, leave the clamp loose, measure the
distance between the centers of the front and rear hub caps on the
unaffected side with a tape or string, move the tape to the affected
side and make the center distances the same, tighten the nuts on all
clamps using new spring or lock washers.
=Lengthwise Wheel Alignment.=--Before lining up the wheels lengthwise,
jack each wheel separately and shake it to detect a loose bearing or
worn spindle pin which is usually the seat of the trouble. After the
defective part has been readjusted or replaced, test the alignment
as follows: Using a string or straight edge, which should be placed
or drawn across the front and rear tire, making four contacts as near
center as possible without interference from the hubs. The string or
straight edge is then moved to the other side of the car and three
contacts are made, one on the rear center of the front tire, and two
across the center of the rear tire. The spread rod should then be
adjusted to allow the front contact point to converge or lean from the
line toward the other front wheel.
[Illustration: Fig. 134. Wheel-Alignment Diagram]
=Mechanical Alignment.=--When a motor vehicle turns the inside wheel
has to describe a curve of smaller radius than the outside wheel. A
line drawn lengthwise through the steering arms, extending from the
spindles or knuckles, should meet at a point in the center of the rear
axle to determine the correct wheel base, otherwise the car will turn
in two angles, which causes the tire on the outside to slide crosswise
at the traction point. Fig. 134 shows the position of the wheels and
the direction they travel in describing two distinct curves in turning
to the left. The correct mechanical alignment and wheel base will be
seen in the diagram, A B. The front wheels have been turned to a 45 per
cent angle, e-e1 lines drawn through the spindles will meet at E, a
line drawn through the rear axle. E1 in this diagram shows the effect
on the steering of lengthening the wheel base of the car. In this case
the wheel base has been lengthened 10″ and the lines e and e1 meet at
different angles at a point on E1. The car tries to turn about two
distinct centers, as this is an impossibility, sliding of the tire
occurs.