What kind of posi unit is this?

[69TowRig]

Gov-Lock, it's an Eaton unit. The Power Lok is a Precision Gear unit and the Powr-Lok is a Dana unit.

It has a centrifugal weight system that engages a ratcheting dog-clutch that locks the axle shafts to the carrier when a significant amount of wheelspin occurs (one wheel relative to the other). Over a certain carrier RPM the unit will disengage, or when the applied torque is removed (take your foot out of it).

Visit http://traction.eaton.com/prod2.htm and click the link halfway down to see an animation.

The Gov-Lock is a mechanical locking differential that is OEM on a ton of GM vehicles. For a street rig it's fine but not a limited-slip, so the operation is not seamless, it's either locked or it's not, and it takes some wheelspin to make it lock. The others mentioned above are clutch-type limited-slip differentials.

Personally I wouldn't run one in a street rig with a decent engine nor in an offroad rig. Normal locking differentials handle big input torque by keeping the shafts locked to the carrier under normal drive conditions, and only unlock when a wheel overspeeds the carrier like in a turn. Detroits are like this. The Gov-Loc works backwards, only locking when the torque is applied heavily, which lends itself to more breakage and the nickname "Gov-Bomb". For a street rig I'd run an Eaton Posi, for an offroad rig I'd run a Detroit or a drop-in locker.