Couple of thoughts. Have you tried getting both front wheels off the ground and turning the wheel lock to lock with the engine off? It should turn fairly freely. If its hard to turn with no load and no boost, you should be able to tell what is binding.
A different ratio box will increase or decrease bump steer depending on which way the change went.
Also, the box has a spool valve in it which is centered by a spring. When you start to turn the wheel, the output arm tries to move. When it cannot because of normal load on the steering, the load moves the spool valve by compressing the spring. When the spool valve moves, it sends fluid pressure to assist the turn. When the arm moves to the point that the load is relieved, the valve recenters via the spring and the boost stops.
Of course, normally you continue to turn the wheel, and the valve "chases" the turn.
The amount of load you feel in the wheel, is mostly determined by that spring tension.
Many years ago, there was an outfit that would sell a rebuilt steering box with what ever spring tension you wanted. I got interested in that when a truck in our fleet apparently suffered a spring breakage in the steering box. It drove great, no slop, but had absolutely no load on the steering wheel other than the input bearings. It was like driving a video game. It was all the more strange because there was a big rack that stuck out over the hood. When you drove it, you really felt like it was a game. You just turned the wheel and the world moved back and forth in front of you.
We were going to replace the box, but the guy whose truck it was begged us not to. Said it was the coolest driving thing he had ever driven.
It stayed that way until we sold the whole truck and got a new one a few years later.
If your box is setup with a heaver spring, then it will be harder to turn, and would allow more feedback before the valve moved to counteract it.
However, a stiffer spring would be constant, and yours sounds like it changes with conditions.
Try it with wheels up and engine off, I suspect you will see what is binding.
J.
A different ratio box will increase or decrease bump steer depending on which way the change went.
Also, the box has a spool valve in it which is centered by a spring. When you start to turn the wheel, the output arm tries to move. When it cannot because of normal load on the steering, the load moves the spool valve by compressing the spring. When the spool valve moves, it sends fluid pressure to assist the turn. When the arm moves to the point that the load is relieved, the valve recenters via the spring and the boost stops.
Of course, normally you continue to turn the wheel, and the valve "chases" the turn.
The amount of load you feel in the wheel, is mostly determined by that spring tension.
Many years ago, there was an outfit that would sell a rebuilt steering box with what ever spring tension you wanted. I got interested in that when a truck in our fleet apparently suffered a spring breakage in the steering box. It drove great, no slop, but had absolutely no load on the steering wheel other than the input bearings. It was like driving a video game. It was all the more strange because there was a big rack that stuck out over the hood. When you drove it, you really felt like it was a game. You just turned the wheel and the world moved back and forth in front of you.
We were going to replace the box, but the guy whose truck it was begged us not to. Said it was the coolest driving thing he had ever driven.
It stayed that way until we sold the whole truck and got a new one a few years later.
If your box is setup with a heaver spring, then it will be harder to turn, and would allow more feedback before the valve moved to counteract it.
However, a stiffer spring would be constant, and yours sounds like it changes with conditions.
Try it with wheels up and engine off, I suspect you will see what is binding.
J.
