What was found
AIRCRAFT WAS GROUNDED: CAPTAIN'S YOKE HAS ABNORMAL TRAVEL WHEN HAND FLYING. WITH AUTO PILOT OFF, SMOOTH NON TURBULENT AIR, AND NO CONTROL INPUTS, THE YOKE CAN BE ROCKED FORWARD AND BACKWARD, ABOUT THE VERTICAL CONTROL COLUMN. THE BASE OF THE YOKE IS NOT FULLY CONNECTED TO THE CONTROL COLUMN AND IS EVIDENT WHEN HAND FLYING. TRAVEL CAN ALSO BE OBSERVED FROM THE FIRST OFFICER'S POSITION. FIRST OFFICER YOKE IS NORMAL. DECESION MADE TO RETURN TO ORD EMERGENCY DECLARED AND AIRCRAFT LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED CAPTAIN'S AILERON CONTROL WHEEL SHAFT BEARING IAW SOPM 20-50-03 AND AMM 27-11-41.