After installing my dropped beam I had to deal with my bump steer problem. Choppin' the pitman are was the way to go. I have a 71' with power assist, so my arm has the bend. To keep the geometry aprox. the same minus the amount of throw, I built a jig to keep everything strait. I put a deep chamfer around everything and T.I.G. weld the crap outa it. Six passes around the whole thing, while letting completely cooling between passes. Strong as hell!. In the end I ended up moving the lower mounting hole up 1.750". Mounted up is just right. Drag link is now parallel to the ground. No more bump steer! Let the pictures do the talkin'.
I don't know the technical definition of "bump steer" but it is like driving with little control. the front wheels pull when brakes are applied or when ever the wheels are not strait. When you counter steer to keep it strait it pulls that way. Kinda fun but extremely dangerous.
Rick, the steering components tend to operate in arcs, while the suspension moves linearly. The steering geometry is set up so that when the components move, as much of the motion as possible is close to linear so that when you hit a bump, the wheels don't turn in a different direction due to the differences in motion. When you lower or raise the front suspension, you change the angles of components like the Pitman arm and the drag link so that their motion is in a slightly different direction when the suspension moves. It doesn't take much of a change - if the drag link isn't close to parallel to the ground or the Pitman arm isn't close to vertical, when you hit a bump, instead of the drag link just moving up and down, it will also move fore and aft a little, pulling the steering one way or another...or, if the tires stay straight, the wheel will jerk in your hands.
I lowered my 66, used original springs and had them re-arced at spring shop. White knuckle driving!! From bump steer. I moved my steering box to in front of axle, using original draglink. Also made a bracket and raised it so drag link was running horizontal. Then took to alignment shop and had toe set. Installed 22" tires. drives straight, no bump steer fun to drive now.