1.Some types of power train layouts use a “transaxle”, which is simply a combination of the transmission and the differential. These are usually found on front wheel drive cars, but are also used on rear-engine cars. 2.If you have an automatic transmission, the mechanism changes without any help from you. This is accomplished through a system that works by oil pressure. Each shift of the gears is controlled by a shift valve; and the gear changes depend on speed, the road, and load conditions.