i am curious if it still has the stock steering in it. i have heard of different ratio's per turn of the steering wheel. Usually if something is loose like a tie rod end it will wander and you are moving the steering wheel around a lot to keep it on the road,. I had replaced all the tie rods and had a alignment done in my old 75 fordup pickup . It still wandered and the mechanics suggested to tighten the screw that adjusts the gear mesh in the steering sector to tighten up the play that was comming from the sector itself. you usually go straight down the road so this is where the sector is the most wore out. Well it turned into what you are describing, instantly sending you into the ditch, and when you turned it seemed to be too tight and made the pump howl. I had to put a rebuilt steering sector in it and it is fine now.