4 wheel lockup

My 91 PF doesn't lock up all four tires in when in snow in 4low. I was told that PF's had true 4 wheel lockup. Is ther a prob with my PF or my source of info. She is a stock 4x4.

A 91 Pathfinder, just like the Xterra, is at best a 2WD vehicle when the going gets dicey, and the two wheels that are "driven" will be spinning uselessly. An open or limited-slip diff at both ends means that when one of the wheels on the axle (front or rear) has more traction than the other, the power ends up going to the path of least resistance and will start the other tire spinning once the available grip is exceeded. There is no center differential, so the wheel that start spinning at the front and the wheel that starts spinning at the rear are locked together and all your power will be sent out through them leaving the other two tires that have some grip left sitting idle.

A locking differential (locker) locks the left and right wheels together on the axle it is installed on, either automatically when a wheel starts to spin, or at the flip of a switch. This means that even if a tire is in the air, the tire on the other side gets half the power and will still be able to work for you.

Brent