Sorry, forgot to answer this question as well.
And what exactly does a locker do?
In a stock differential, the differential is what's called an "open diff." When making a right-hand turn, the outside-track-wheels are the driver-side wheels. When making a left-hand turn, the outside-track-wheels are the passenger-side wheels. What happens when you drive on the street and turn a corner? The wheels on the outside track will travel a longer distance than the inside-track. To counteract this, preventing dragging a tire, and maintaining better control under power through a turn, the "open diff" will (in effect) send power to the wheel with the least resistance - in the case of a turn, the outside-track-wheel - until the power sent produces a load on the axle of the outside-track-wheel which equals the load on the axle of the inside-track-wheel. The torque on each axle-side will always seek to be the same.
See
Open Differentials on Howstuffworks.comThe problem this creates for four-wheeling is evident once you get a wheel into the air. Since there is
no resistance on the airborne wheel (therefore no torque on its axle) and (usually) full resistance to the grounded wheel at the other end of that axle assembly, all the power gets sent to the airborne wheel resulting in
no torque being produced to either wheel. You're stuck. Better hope your other pair of wheels can pull you through. If you have one wheel of each axle assembly in the air, forget it. Your only option is to take a fast run at it if you can do it safely.
Now the answer to your question: a locker will (on command) lock the two output pinion gears (within the differential) together preventing differential movement of the left and right axle-halves, and
effectively (in a sense) turn your two independent axle-halves into one solid axle, sending power equally to each wheel, regardless of torque on either axle-side. This is what dreams are made of on the trail, because even if one wheel is in the air (doing nothing to assist your movement), the other, grounded wheel will still give full assist rather than just take a nap.
Hope this helps.
