Make sure the steering linkage is tight! The linkage is known as a "parallelogram" type system. If the relay rod is not "parallel" to the ground (you can eye-ball whether it's level with the oil pan). If this is not level, you will get what's called "bump steer". A dangerous situation going over bumps just like you describe. Like was mentioned, ck the bolts on the gear box, looseness at the idler or the non-parallel situation. Try raising the front of the car off the ground, then start the car. If the steering wheel cranks to one side or the other, the gear box pressure valve needs adjusted. Again, make sure ALL bushings, ball joints, etc are in good, safe working order. Hope this helps!! Jeff