Here is a short video of differential gears working.
It is an example of how the gears allow for cornering without sliding one wheel.
The main central feature is the wheels rotating, you can see the left one slow down as if it is taking a corner at different speeds.
At the top right, you can see how the actual gears work in principal, allowing for one gear to still be driven by the shaft, while the other is slowed because of the resistance on the wheel. This is not how it finally looks in the car, though it was really fun to rig and is a good example of the principal.
There is a slight twitch on the wheel, for some reason I messed up the easiest part, the wheel is not in exact centre of it’s rotation somehow 
Though I did not realise until after I rendered so have not re-rendered.
Here is the original FANTASTIC ‘documentary’ from 1937-
This is how I learnt to make this. I was thinking about recreating the whole video using the original audio with every scene.