The lack of alignment of front wheels gives as much trouble as anything else in the front unit. This lack not only makes steering difficult, inaccurate, and uncertain, but it also influences tire wear to a tremendous extent. As Fig. 92 indicates, even if the rear axle should be true with the frame, at right angles to the driving shaft, and correctly placed crosswise - that is, correct in every particular with the shafts both straight so that the wheels must run true - the fronts may be out with the frame, out of track with the rears, or out with respect to one another.
Fig. 92. Diagram Showing Front Axle and Wheels Out of True.
Fig. 93. Simple Measuring Rods for Truing-Up Wheels.
Now in order to know about the front wheels, they should be measured, and while this sounds simple, it is anything but that. In the first place there is little to measure from, or with. A good starting place is the tires, and a simple measuring instrument is the one shown in Fig. 93. This consists of a rod about ¼ inch in diameter and about three feet long, fitted into a piece of pipe about two feet long, with a square outer end on each and a set screw to hold the measurements as obtained. By placing this between the opposite sides of the front tires, it can be ascertained whether these are parallel, and whether they converge or diverge toward the front. But knowing this, the driver or repair man is little better off than before, because this may or may not be the practice of the makers of the car, and it may or may not cause the trouble.
Fig. 94. Accurate Measuring Rod for Truing-Up Wheels. Better Design than Fig. 93.
In short, a more accurate and more thorough measuring instrument is needed, Fig. 94. Such a one can be bought, but a similar outfit can be made from 3/8-inch bar stock, using thumb nuts where the two uprights join the base part, and also at the two points, or scribers, on these uprights. Having the floor to work from, the heights can be measured, and thus the distance between tires may be taken on equal levels. Thus, a bent steering knuckle can be detected with this apparatus. Similarly, the center line and frame lines of the car can be projected to the floor, and by means of the instrument, it can be determined whether the axle is at a perfect right angle with these, and whether the wheels are perfectly parallel. Given the frame line, too, it can be determined whether the wheels track with one another.
Fig. 95. Template for Showing if Axle Is Bent.
When an axle is bent, as in a collision, a template is useful in straightening it. This can be cut from a thin sheet of metal, light board, or heavy cardboard. It is an approximation at best and should be used with great care. Fig. 95 shows such a template applied to an axle which needs straightening.
When the axle is bent back to its original position, a pair of straight edges laid on top of the spring pads will be of great assistance in getting the springs parallel, as the worker can look across the straight edges with considerable accuracy. This is indicated in the first part of Fig. 96 which shows the general scheme. It shows also how the axle ends are aligned, using a large square on top of a parallel bar, but of course this cannot be done until the last thing, at least not until the spring pads are made parallel.