A header drivetrain coupling system (20;120) comprises a harvester driveline (38; 138) mounted to a harvesting vehicle (10) and a header driveshaft (40) mounted to a detachable header (18). The harvester driveline (38; 138) is supported for rotation at an inboard end on a feederhouse (16) and at an outboard end on a header tilt frame (24) even when the header is detached therefrom. The harvester driveline comprises a telescopic portion (48; 148) which permits a coupling member (97; 197) on the outboard end to be moved into and out of engagement with a coupling member (99) on the header driveshaft (40). A sliding support assembly (64; 164) is provided to support a bearing housing (56; 156) which holds the outboard end of the harvester driveline on the tilt frame (24). An actuator (84) is configured to move the bearing housing (56; 156) with respect to the tilt frame (24) to selectively engage and disengage the coupling members (97,99;197,199).
