Okay, this popped up when i was talking to my friend about an old thread about AWD and 4WD differences. We were talking and i explained the difference being the center differential absence in 4WD (i think i have that right. too many acronyms). his question to me was "what's the difference between an AWD's center diff and a 4WD's (such as a truck) transfer case?" Of course, I couldn't respond except to think that the center diff helps split torque to wheels with grip while the transfer case merely acts as a connecting point for a very long axle and helps elliminate any kind of sag in the axle line. Any clue as to the real difference?

 

you got me, i thought it was the same.

 

Some 4WD cars/trucks have no center diffs, so the front and rear differentials are just locked together. This means that the front wheels must spin at the same rate as the rear wheels (or more accurately, the sum of the two front wheels' speeds must equal the sum of the rear wheels' speeds).

This means that if you take a tight turn on a dry surface with 4WD engaged, bad things will happen because the front wheels want to describe a larger arc than the rear, so the wheels will be fighting.

A friend of mine has a Subaru Loyale 4WD--if you press the brake while driving in the snow with the 4WD engaged, the car wants to swap ends because it effectively has a 50/50 front-rear brake bias, which which is not desirable.

 

Sounds like a personal problem to me.