If the drag link is lower at the steering gear end on a truck that has not had the axle modified, the springs are worn out. This allows the steering arm end of the drag link to sit higher than the end of the Pitman arm. When a bump is encountered, the front end of the drag link goes even higher and the increased angle pulls the steering arm away from the ""straight ahead" position of the wheels. Since both wheels are connected by the tie rod, the wheels swing side to side as the springs flex.
All vehicles will have a little bit of bump steer. The idea is to minimize its effect on the wheels by starting out with the drag link level. The further out of level the drag link is with the vehicle at rest, the more pronounced the steering input will be. The only way I can think of to minimize bump steer on a lowered vehicle would be to raise the steering gear on the frame the same amount the vehicle is lowered, causing the drag link to be level again.
Jerry
