THERE SHOULD BE A CLIP THAT IS SPRING STEEL THAT CATCHES THE BOTTOM OF THE HUB ON MOTOR SHAFT THIS CLIP COULD HAVE LOST ITS TENSION OR BE BENT SO AS TONOT CATCH THE BOTTOM OF THE HUB TRY GENTLY TIPPING THE TAB TOWARDS THE CENTER OF HOLE ON WIPER ARM WHERE HUB GOES IN.THE TAB SHOULD HAVE TO BE PRESSED AGAINST HUB TO GET WIPER ARM ON.BECARFULL WHEN BENDING TAB TOMUCH PRESSURE COULD BRAKE THE TAB.