Exploder replied:

F’ed if I know, what information does it have stamped on it, might give you a starting point, or maybe it is missing the air or vacuum pump.

I don’t think there would be enough pressure build up in the diff to activate it and even if there was it would take so long to engage, it would be almost pointless, don’t you think?

GaryInOz (Vic) replied:

It is not a locker.

What it is, is a disconnect for the front driveshaft when the vehicle is in 2WD.

The Vitaras don't have unlockable wheel hubs like most part time 4WD's. What Suzuki did was to disconnect one side of the diff from the other when the from within the diff center casing (via the vacuum actuator mechanism you found). It's just another way of achieving the same outcome as lockable hubs.

The way it works is when you put the vehicle in 4WD, a vacuum solenoid is actuated by a switch on the transfer case, that actuates the mechanical bit in the differential to connect both sides to the (open) diff. The tcase is now able to feed power into the front driveshaft, and with both sides of the halfshafts connected to the diff, transfer power to the wheels.

The reason they need this system is so that the vehicle does not have to push an otherwise disconnected front axle assembly when the vehicle is in 2WD. Disconnecting it the way they have allows the diff hat and therfore ring to remain stationary, along with the pinion and front driveshaft. The only minor prob is that the side gears and spider gears in the diff are still turning.

Mainly done to improve fuel economy and reduce unnecessary wear-and-tear to the front diff.

Hope you can understand my explanation