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.
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.
CHAPTER XXXVI
STEERING GEARS, TYPE, CONSTRUCTION
Operation and Care
The steering mechanism used in automobile construction is arranged to operate independent of the axle, or in other words the wheels turn on a pivot, or knuckle, held between the yoked ends of the axle. A spindle or axle extends outward from each steering knuckle to accommodate the wheels. A set of short arms extend to rear of the steering knuckles; an adjustable spacer bar, commonly called a tie or spread rod, serves as the connection between the arms. The arms incline slightly toward each other; which causes the inside wheel to turn on a shorter angle than the outside wheel when turning a corner. Another steering arm carrying a ball at the outer end, describes a half circle over the axle, and is attached to either the spread rod arm or the steering knuckle. An adjustable rod, or drag-link, carrying a ball socket at each end serves as the connection between the steering arm extending from steering gear and the half circle arm of the knuckle. To adjust wheels see chapter on “[Wheels and Axle Alignment].”