A locking differential having a collar member (35) fixed to rotate with the gear case (11), but free to move axially, and cooperating with a first sidegear (19) to define interdigitated lock members (41,43) operable, when the collar member is locked (FIG. 1), to prevent rotation of the first sidegear relative to the gear case (11). A spring (61) is disposed between the collar member and the gear case, to bias the collar member toward unlocked (FIG. 3). A plurality of actuation members (47) is provided, each having a first end (49) in engagement with the collar member, and a second end (51) in engagement with a ramp plate (53). When the actuating means is in the actuated condition, the ramp plate rotates relative to the gear case, and the actuation members ramp-up on the ramp plate and move the collar member from unlocked to locked.