Four Wheel drive vehicles require a transfer case to harness power from the transmission and move it in a non linear fashion. Usually from the rear of the transmission to the front drive axle. In some cars it is from the front drive axle to the rear wheels.
BMW OEM ZF USED 5HP 24 Automatic TRANSMISSION M62B44 V8 E31 840CI E38 740i 740IL E39 540i E53 X5 4.4i 4.6i RANGE ROVER
BMW OEM 24007511019 USED 24001423926 A5 390R X E46 330XI M54 6 CYL Automatic TRANSMISSION & TRANSFERCASE 1999 2005