A transaxle is a single mechanical device which combines the functions of an automobile's transmission, axle, and differential into one integrated assembly. It can be produced in both manual and automatic versions.
Transaxles are nearly universal in all automobile configurations that have the engine placed at the same end of the car as the driven wheels: the front-engine/front-wheel drive; rear-engine/rear-wheel drive; and mid-engine/rear-wheel drive arrangements.
Many mid- and rear-engined vehicles use a transverse engine and transaxle, similar to a front-wheel drive unit. Others use a longitudinal engine and transaxle like Ferrari's 1989 Mondial t which used a "T" arrangement with a longitudinal engine connected to a transverse transaxle. Front-wheel drive versions of modern Audis, from the A4 upwards, along with their related marques from the Volkswagen Group (which share the same automobile layout) also use a similar layout, but with the transaxle also mounted longitudinally.
The front-wheel drive Renault 16 had a longitudinal engine and transaxle, with the engine behind the transaxle. The transaxle case was designed to allow the final-drive ring gear to be on either side of the pinion; this allowed the engine-transaxle assembly to be used in the rear-wheel drive Lotus Europa, which had the engine in front of the transaxle (i.e., mid-engined).
Front-engine, rear-wheel drive vehicles tend to have the transmission up front just after the engine, but sometimes a front engine drives a rear-mounted transaxle. This is generally done for reasons of weight distribution, and is therefore common on sports cars. Another advantage is that as the driveshaft spins at engine speed it only has to endure the torque of the engine, instead of that torque multiplied by the 1st gear ratio. This design was pioneered in the 1934 Škoda Popular, and then in the 1950 Lancia Aurelia, designed by Vittorio Jano.
Since this placement of the gearbox is unsuitable for a live axle (due to excessive unsprung mass), the rear suspension is either independent, or uses a de Dion tube (notably in Alfa Romeos). Rare exceptions to this rule were the Bugatti T46 and T50 which had a three speed gearbox on a live axle.
The Nissan GT-R and Ferrari FF (and its successors) are unusual in being all-wheel-drive cars with front-engined layouts and rear-mounted transaxles. In the Nissan, one driveshaft sends power to the transaxle (which also contains the 'center' differential) and another driveshaft sends power back along the car to the front wheels. In the Ferrari, the rear transaxle works in the conventional manner, whilst the drive to the front wheels comes from a separate gearbox at the front of the engine.
Notable Front-engine, rear-wheel drive layout vehicles with a transaxle design include:
All Audi cars with longitudinal engines and their 'trademark' quattro four-wheel drive (4WD) system, along with their related marques from the Volkswagen Group which share the same layout, utilise a transaxle. This is mounted immediately behind the front-mounted engine (again, longitudinally) and contains the 'gearbox' (manual, automatic, DSG, or CVT), along with both the centre differential, and the front differential and final drive unit.
Other 4WD applications include: