yes, both hubs need to engage for the front drive to work. if only one locks the frt drive is engaged but it is an open differential and spin the shaft with least resistance i.e. the hub that is not engaged. usually a good cleaning of the hub fixes this but the springs inside wear out and prevent locking. if you have a j/y close I would suggest getting a set of manual hubs. these are more reliable in my opinion, plus you know when it is locked or not.ive got a 5 MT
If the hubs dont engage, what does that mean? no power to the front wheels?