Transmission vs Transaxle

Transmission vs Transaxle

Last Updated August 26, 2020 | Alison Smith

Both transaxles and transmissions are drivetrain components that deliver power to the wheels. Although they serve the same purpose, they function differently. A transaxle is a transmission, axle, and differential housed in one integrated unit. It combines the gear-changing function of a transmission with an axle and differential. A transmission only handles changing the gears, sending power to the differential through the driveshaft.

Image of a transmission with white background

What Is a Transmission?

A transmission is a series of gears that transmits power from the engine to the wheels. Most RWD vehicles with a longitudinal engine will have a transmission. Longitudinal engines mount down the center of the vehicle so the crankshaft faces front to back. This creates a straight line from the crankshaft to the transmission, driveshaft, and rear differential.

There are a few different types of transmissions available. They can either be manual, automatic, continuously variable (CVT), or semi-automatic.

How Does a Transmission Work?

Transmissions connect to the engine crankshaft through a flywheel and clutch, torque converter, or system of pulleys. Transmissions usually have one output shaft. The output shaft connects to the rear axle via the driveshaft.

Each type of transmission works differently, but they all control the speed and torque available at the drive wheels. Most transmissions, whether automatic or manual, do this through the use of gears. Continuously variable transmissions use pulleys or rollers rather than gears.

Diagram showing transmission in a longitudinal engine layout

Shifting Gears

The easiest way to understand how a transmission works is to look at a manual transmission. The transmission is connected to the engine by an input shaft and to the drive wheels via an output shaft. Gears on the input shaft slide back and forth to meet the gears on the output shaft. Gears are engaged through the use of a clutch pedal and a shifter.

When the clutch is pressed, the engine and input shaft are disconnected. When changing gears, the gears on the shaft move and disconnect the power between the engine and transmission. The gear is then selected and the clutch is released, sending the engine power toward the input shaft. Automatic transmissions use a torque converter instead of a clutch to shift gears.

Gear Ratios

The transmission balances torque and speed through gear ratios. Lower gear ratios provide more torque at lower RPMs, which is used to get the car moving from a stop. A higher gear ratio is used when driving at faster speeds to keep the vehicle moving and RPMs low. So in first gear, you have more wheel torque but a lower top speed. At fifth or sixth gear, you’ll have lower wheel torque but a higher top speed.

This also pertains to different driving conditions. When you’re driving up a hill, the transmission reduces the speed for higher torque output while maintaining the same power input. If the torque demand is lower, the transmission speed can be higher.

Gears within a transmission

What Is a Transaxle?

A transaxle is a single unit that combines the transmission, axle, and differential. It’s a smaller version of a transmission, found primarily in FWD vehicles with automatic transmissions. Most vehicles with a transaxle have a transverse engine layout. This means the engine is mounted with the crankshaft running left to right. Transaxles usually contain automatic transmissions, though they can be manual or continuously variable.

Transaxles have the axle integrated into its assembly for a much smaller package. Instead of having the differential in the rear of the vehicle, it’s located in the transaxle housing that’s mounted parallel to the transmission. This simplifies the vehicle's driveline as the driveshaft doesn’t have to connect to a differential before power is sent to the wheels. Cars with transaxles often weigh less as they have fewer drivetrain components.

Transaxles are usually found on vehicles with a front engine and FWD or a rear engine and RWD. But the transaxle can also be integrated into the rear axle on cars with a front engine and rear-wheel drive. The transaxle is in the rear where the differential would be rather than beside the engine.

Front engine RWD cars aren’t as common, but some performance cars use this setup for better weight balance and handling. Porsche, Corvette, and Mercedes have all used transaxles in a few of their vehicles.

Diagram showing transaxle in a transverse engine layout

How Does a Transaxle Work?

The transmission part of a transaxle operates the same as any other transmission. However, rather than connecting to the rear axle via the driveshaft, a transaxle contains both the transmission and the differential. When power is applied, the transmission’s output shaft rotates a pinion gear that connects to the ring gear on the differential. Power is transferred to the wheels through two axle shafts, or half shafts, connecting the transaxle and the wheels.

Transaxles use a torque-splitting differential so the axle shafts can operate at different speeds. This allows the car to corner effectively.

Differentials inside a transaxle often use four or more gears, with one gear attached to each axle and two more connected to the differential pinion shaft.

Transmission, differential, and axle inside a transaxle

Differences Between Transaxles and Transmissions

Whether a vehicle has a transmission or transaxle largely depends on the engine setup. Many of the key differences between a transaxle and a transmission overlap with the differences between transverse and longitudinally mounted engines.

Transmission & Transaxle Differences
Transmission Transaxle
Longitudinal engine layout Transverse engine layout
Usually found on RWD vehicles Usually found on FWD vehicles
Connects to the rear axle through the driveshaft Has two output shafts that connect to the drive wheels through a pair of half shafts
Allows for larger engine displacements Has a smaller, more compact design
Can be automatic, manual, CVT, or semi-automatic Usually automatic, but can be manual or CVT
Separate rear differential allows for upgrades

Some vehicle designs aren’t suited for a transaxle. For one, the added weight in the engine bay can disrupt the performance of a RWD vehicle. The less weight there is on the driven wheels, the less traction the car can have. When a transmission is mounted behind the engine, it brings more of the vehicle’s weight towards the rear.

There are also more ways to bolster the strength of a transmission than a transaxle. While some transaxles can handle powerful engines, the compact design poses engineering challenges. Transmissions have more room for larger displacement engines and modifications. Additionally, the separate rear differential means it can be easily upgraded.

Transaxles generally don’t come with a manual transmission. A transaxle will almost always be an automatic, with the CVT becoming a more popular option. If you want a performance car with a manual transmission, it’d likely be RWD with a transmission anyway.

Source: CARiD, Popular Mechanics, Pearson, Sun Auto Service, How Stuff Works, Automotive Basics, MotorBiscuit, Car Throttle, Engineering Explained

Transmission vs Transaxle

Transmissions and transaxles both transmit power from your engine to your wheels. Transmissions are usually found in RWD vehicles, while transaxles are used in FWD cars. A transaxle is a combination of a transmission, axle, and differential.