The shifter inside the passenger compartment of the vehicle is connected to the transaxle either directly, or through some sort of linkage, such as a cable. As it is shifted into its various positions, the transaxle changes from one gear to another.
Inside the transaxle are multiple sets of gears that reside on a main shaft, which goes all the way through the transaxle in most cases. As the shift lever is moved, the main shaft shifts forward or backward, allowing the selection of different gear sets. Some of the gears inside the transaxle have more teeth, and some have less. In this manner, different drive ratios are accomplished. It is the same idea of shifting from a smaller sprocket to a bigger sprocket on a 10-speed or mountain bike. The larger diameter and number of teeth on the second sprocket causes the bike to travel at different speeds.
In most pickup trucks and other rear-wheel drive vehicles, the transmission has a drive shaft that connects to the rear differential, which powers the axles. Inside the differential housing (sometimes called the pumpkin), the ring and pinion gears mesh together and send power to the wheels via the axles. In a transaxle, the ring and pinion gears are actually inside the transmission instead of being located externally. Because of this design, the axle shafts are located directly off of the transaxle, instead of a separate axle housing. Vehicles with transaxles do not employ drive shafts, because the power goes straight from the gears to the ring and pinion, and then on to the axles, all in one compact unit.
The axles are what give power to the drive wheels. As mentioned, the axles are connected inside the transaxle and spin via the ring and pinion gears. The axles will likely employ Constant Velocity (CV) joints so that they are able to continue spinning while the suspension cycles up and down. These joints are very reliable and rugged. As the axle spins with the gears, the wheels of the automobile also spin and result in the vehicle moving forward or backward.
