SRD

haha my bad...
yes the coupler is a seperate unit! Thats what I meant.
When I said viscous diff, I meant viscous type diff., not that they are one unit...
ahh you know what I mean.

mhj1r

I haven't read what everyone wrote so this may repeat what someone else said, but here goes:

A Viscous Coupling Differental (VCD) is a type of Limited Slip Differential (LSD) which uses a viscous coupling to limit the slip between the two output shafts.

A viscous coupling (VC) works using the principles of Drag.

Drag in a fluid is proportional to Viscosity
Drag is also proportional to Velocity^2

A simple VC has 2 plates, each connected to an output shaft, with a viscous fluid between them. As one plate begins to rotate faster relative to the other one, the fluid causes drag, which causes torque to be transferred to the slower plate. This also causes heat, which makes the fluid more viscous, causing more torque to be transferred.

If you want to make a simple VC at home, try this....
Take one bowl of cake batter, and another equally sized bowl of water.

Take a spoon and stir the bowl of water (without contacting the bowl)......nothing happens because water has a relatively low viscosity.

Take the spoon and stir the cake batter(without contacting the bowl).....you will see that if the batter is thick (viscous) enough and if you stir fast enough, the bowl will start spinning too.

I think howstuffworks.com probably explains this better than i did.

M