Transfer case ? Rear diffs?
Since you have a 2wd, you do not have a Transfer case nor a front differential. You do have a rear differential that you can change the fluid in.
Transfer case - behind the transmission either send full power to rear wheels, or some form of splitting power to front axle and rear axle in a 4wd/awd vehicle.
Diff - Differential, allows for different speeds of tires (for turning), and changes the power of a driveshaft, to axle shafts to turn the tires. Inside the diffs are open/limited slip/locked carriers (allows for different %'s of split of power side to side).