Taken from another site.
If you have a manual transmission, a manual transfer case and manual lockout hubs, you can tow your four-wheel-drive vehicle with all four wheels down and sustain no damage. Of course, you'll have to refer to the owner's manual to learn how to properly unlock, or disengage, all of these features to ensure that none of the components will be damaged during the actual towing. If your four-wheel-drive vehicle does not have a manual transfer case and manual lockout hubs, then you'll need to install a drive shaft coupling device on the rear drive shaft [source: Remco Towing].
A drive shaft coupling is useful when you're towing a four-wheel-drive vehicle that does not have a manual transfer case. Instead of manually disconnecting and removing the drive shaft from your car or truck, a drive shaft coupling allows you to quickly switch between driving (drive shaft engaged) and towing (drive shaft disengaged) modes right from the driver's seat [source: Remco Towing].
Probably the best bit of advice that anyone can offer you for towing a four-wheel-drive vehicle is to suggest that you review your owner's manual for towing instructions and precautions. The manufacturer sets guidelines that are specific to the year, make and model of each of its vehicles. Ignoring this information could be an expensive mistake.
If you dont have the all manual it suggests using a 4 wheel dolly or a flatbed to avoid damage to transmission.