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.
S BMW ZF 5HP-24 AUTOMATIC TRANSMISSION M62B44 V8 E31 840CI E38 740i 740IL E39 540i E53 X5 4.4i 4.6is RANGE ROVER
S BMW 24007511019 24001423926 A5S 390R-XC E46 330XI M54 6 CYL AUTOMATIC TRANSMISSION & TRANSFERCASE 1999-2005