A differential allows for the driving wheels to spin at different rotations per minute therefore allowing a car to turn corners. This is because the inside wheel in a turn has less distance to cover than the oudside wheel on the vehicle in the same turn. Think plastic coffe cup on it's... The locking differential limits the two wheels on an axle to rotate at the same speed. In essence, it locks them together as a unified shaft. Both wheels then turn together, regardless of whatever traction is available. With a locked differential, each wheel can apply as much spinning force as the traction will allow. A rear locking differential is often supplied to make up for this compromise – if a wheel is lifted off the ground, the locking differential can be brought into play, driving the wheel that remains on the ground. DIY Locking Differential for Offroad . ... How to Upgrade a Posi Rear End ... touch up paint imperfections, airbrush custom graphics and more in the Body & Paint ... 2210 differential lock My New Holland manual says to reduce shock loads don't engage the diff lock at speeds higher than 5 MPH or in turns. I prefer to use it only after I'm stuck or lost all traction as it is nearly impossible to detect if one rear wheel is slipping especially having 4 wheel drive.