Here is what Frank told me to do and it worked:
Nope. Stop right now and I can save you some work. I will lay odds that it is a step in the face of the cam on the end of the actuator sleeve. Look back in the archives for some of my previous repsonses on that, and you'll likely find some of the illustrations I ginned up in MS Paint.
If you remove the actuator sleeve, you'll find two short, 1/4" dowel pins. They ride on a form cam face and on a parallel form on the end of the actuator sleeve. When you turn the wheel and meet a resistance, the spring loaded pins ride up, or down depending on a LH or RH turn, and displace the actuator sleeve in a fore or aft direction. When this movement takes place, the lever hooked to the actuator sleeve pushes or pulls a spool valve which directs fluid to one side or the other of the rotary cylinder of the lower pedestal, and this assists your turn. Now over time, the pins get worn with flats, the cam faces get worn with flats right in the center of travel (straight ahead), so in combination, when you go to turn, the pins will not easily slide up the cam face, instead hanging up on the step until you give it a harder nudge, then it jumps right now, you get instant assist, but you feel it in the wheel as a "crunch" or jerk. Stoning the cam faces back to smooth and parallel and replacing the pins generally cures everything, provided you don't have any other leaking going on. Let me know when you mean to go through it. Be happy to tag along via e-mail.