What was found
DURING CLIMB THRU 16000 FT, ACFT JERKED ABRUPTLY LATERALLY DISPLACING ABOUT 10-20 DEGREES. ISSUE CONTINUED TO GET MORE VIOLENT AND VERY ABRUPT. DISCONNECTED THE YAW DAMPER AND ASSUMED MANUAL CONTROL. RUDDER TRIM SEEMED TO INITALLY WORK NORMAL BUT AS THE PROBLEM WORSENED, TRIMMING MADE THE BRICK DISPLAY MOVE IN THE OPPOSITE DIRECTION, DISCONNECTING THE YD DID NOT MAKE ANY DIFFERENCE. ACFT WAS FLYING UNCOORDINATED WITH CONSTANT UNCOMMANDED RUDDER INPUTS. MECHANICS REPLACED FCC 1 & 2 AND YAW DAMP ACTUATORS 1 AND 2.