The front wheels shake like crazy when the wheel is turned, with weight on the front or off the ground. It seems to change with RPM, is this the pump going bad?
What do you mean by shake? Turning in and out fast? How far do the move? Give us more info...
It shakes back and forth, the tip of the tire moves about 2 inches. As if I were jerking the steering wheel back and forth rapidly, like 2 to 3 Hz.
My truck did that, it was a bad ball joint that had seized dry.
I don't think there is any chance this is a pump problem. Something is causing the control valve on top of the steering cylinder above the front axle to recycle rapidly. Maybe slack in just the wrong place in the linkage? Keep in mind, that linkage has to have slack in the right places to activate the power steering. The first thing I'd do is recenter it, while looking that whole area over carefully. What's frustrating is I remember fixing this problem on a 4500 at least once, though I'm sure it was at least 20 years ago. I don't think it was a big deal. Don't worry, I'm better at fixing tractors I can touch, rather than those I can only read about.