have a 1990 F250 (460 4x4 if it matters) that doesnt have power steering to the right. power steering works great when turning to the left but turning right is darn near impossible. when it started about 2 months ago i went around a normal corner on a paved road at normal speeds and it was difficult that one time but didnt do it for the rest of the day. then eventually it slowly happend more and more and needed more force to turn it. eventually it got to the point where every right turn is armstrong steering. today i replaced the power steering pump and it didnt change anything. i dont go offroad in the rig and it doesnt look like anything is bent.

 

If it is only hard to turn in one direction then the steering gear is bad. Something in the control valve is broke or torn, just as easy to change the whole steering gear assembly. If the pump was bad it would have been hard to turn in both directions.