Want to know what the inside of your viscous coupling unit (VCU) on your Freelander 1 looks like? Here is a diagram:
1. Cylinder
2. Slotted disc
3. Input shaft
4. Roller bearing
5. Ball bearing
6. Torsional damper flange
7. Output shaft

In normal conditions your rear wheels only have 0.8% drive, so your Freelander is effectively front wheel drive. When you get a significant speed differential between the front and rear propeller shafts, such as when the front wheels lose traction, the viscosity and resistance to rotation of the silicon jelly increases to a level that slows or stops relative rotation of the slotted discs. With the front and rear propeller shafts locked together, drive is thus transferred from the IRD to the rear wheels, and you have full 4×4.

Remember the issue with the VCU is the age of the viscous fluid inside it. After about 70,000 miles this becomes past its usable life and the VCU needs replacing. If it is replaced with a reconditioned VCU it is imperative that the correct grade of viscous fluid is used in the unit, as the wrong grade can cause the VCU never to lock the front and rear propeller shafts and hence never transfer drive to the rear wheels – in this case you have wasted your money and you might as well just have just left the VCU off!