Replaced the power steering ram cylinder, filled the reservoir, bled the system. When I started her up, just the slightest turn of the steering wheel, things went south. The steering wheel began this rapid left-right turning on its own. What in the world went wrong?

 

Welcome to the forum.

You're lucky it didn't break your arm. You need to adjust the centering valve per the factory service manual. Check here w/ Willcox.