No matter how simple or complex a steering system happens to be, it's all just a series of right triangles. The one we're dealing with in reference to the drag link/Pitman arm/steering knuckle setup is no different. If the drag link is angled up or down, as the axle moves through its range of motion in jounce (spring compressed) and rebound (spring relaxed) the length of the long side of the triangle (hypotenuse) is going to change. If the drag link starts out level, the change is minimized through the full range of travel and the bump steer will be minimal. Once any measurement in the geometry of the triangle changes, something else must be done to compensate for the error. The simplest approach is to alter the height of the Pitman arm pivot by relocating the steering gear vertically, but it's also the most difficult to deal with because it will change the height of the steering column. Putting universal joints in the steering wheel shaft would be an obvious way to compensate for that if the resulting angles induced into the steering column aren't excessive.
Jerry
