Can anyone please explain to me in simple terms what one of these does and what advantages it has? Did a Google search but much technical blurb was being thrown about  LL.B (Hons) - University of Derby
LOT (Lord of Time) - University of Gallifrey

In normal use the diff is the same as any other but when one wheel breaks traction it allows a small amount of slip and then locks up giving traction to both driven wheels (simplified version).

I see, thanks. I ask because it is mentioned as a feature on the rear wheels of the Subaru Outback which is one of the many cars I have been considering for purchase in the spring.

So if in snow or mud for example and the rear left wheel had no traction, instead of spinning aimlessly, it would apply the power to the rear right wheel that does have traction. Is that right? LL.B (Hons) - University of Derby
LOT (Lord of Time) - University of Gallifrey

Hi
yes basically thats how it works, if you have 5 mins look at this....

Thanks, I'll take a look  LL.B (Hons) - University of Derby
LOT (Lord of Time) - University of Gallifrey

Basically, a diff is needed to allow slight differences between the wheel speeds, to enable good on-road handling etc. but the a conventional "open" diff will allow all torque to be lost through one wheel if there's no grip.

(If equations are your thing, an open diff is represented by A=B+C, A being the input. Indeed, many moons ago they were used as a mathematical instrument. )

A limited slip one, basically does what it says on the tin. Only a limited difference in wheel speed is permitted - enough to provide suitable handling on roads, but also to provide grip in reduced traction (not just off-road, but on performance vehicles on road too).

Then you get a locking diff, allowing the diff to be locked so all torque is transmitted equally through both wheels. The most complex type is an "Electronic Torque Managed" diff (commonly referred to as an "E-diff" or "active diff"). This allows a variable degree of slippage (usually from 0 to 100%) usually controlled automatically by the vehicle - the Haldex coupling the the FL2 is a form of this.

Traction Control systems are commonly used to do the same job, but a locking diff (of some form) has the advantage of reaction before slippage occurs.

 Freelander 2 2007 TD4 Manual HSE Tambora Flame
Discovery 3 2006 TDV6 Auto HSE Zambezi Silver
Previously: Freelander 2 2007 TD4 Manual SE Santorini Black

One modern equivalent is for the system to apply the brakes to the wheel thats slipping so the power then all goes the opposing wheel to get grip.