Solenoid update, plus a find worth writing down.
@ikarus , ran your test. Unplugged the solenoid and drove it. Steering got much heavier at low speed, close to no power steering at all, which matches what you described. Took it out on the road and the effort stayed heavy but the character didn't change. Same stickiness, same sawing. So the valve isn't what's creating the problem, all unplugging does is remove assist.
Here's the interesting part. On top of the solenoid there's a post and nut that adjusts, same idea as the box adjuster. Mine was cranked all the way in. I backed it out a little and the steering loosened up a lot and now feels like normal power steering. Spring is intact, so the unit is complete, somebody had just run that adjuster all the way to the stop. Given the spring was missing when I bought the truck, I'd guess the same person was in there.
Anyone know what that adjuster is actually supposed to be set to? All the way in is clearly wrong but "a bit out" is my guess, not a spec. I'll ask Redhead too.
So counting it up, I've now removed two friction sources. The stabilizer and this adjuster. Both made the truck feel less like it's fighting me. Neither changed the crown-follow or the failure to self-center.
Which lines up with what I'm starting to think is going on. Friction was making it feel sticky. Something else is making it follow the road. My money is on two things:
Scrub radius. My wheels are 17x9 at -38, roughly 3.0" backspacing against a stock 4.5. A crowned road puts constant lateral force through the tire, and at that offset the force acts through a much longer lever than Toyota designed for. That's leverage, not friction, so it wouldn't change no matter how free the steering chain is. Which is exactly what I'm seeing.
Bump steer. Explains the speed bump shake and the sawing over uneven pavement.
Measuring bump steer this weekend. Jack a corner 2-3", watch toe change, both sides. Will post numbers.
