Transmission and Drivetrain
A drivetrain may be the least understood part of a vehicle. This is due to several factors, including the fact that the term “drivetrain” is often used interchangeably with powertrain and driveline.
The drivetrain includes the transmission, the driveshaft, the axles, and the wheels. Simply put, it works in conjunction with the engine to move the wheels. The drivetrain system is an essential component of a vehicle and the transmission is an integral part of the drivetrain.
The drivetrain and the transmission are actually two very different concepts. The main function of the transmission is similar to the chain on a bicycle: it keeps the engine turning in time with the wheels, regardless of what gear the vehicle is in. The drivetrain represents everything that is behind the transmission involved in propelling the vehicle. The main function of the drivetrain is basically to convey power from the vehicle’s engine, through the transmission to the drive wheels on the vehicle to control the amount of torque.
The drivetrain is comprised of a collection of components in a vehicle that transfer power from the transmission to the wheels/ drive it forward. These components include the driveshaft, CV joints, the differential, the axle shafts and the U-joints.
A driveshaft is a long tube of steel that is linked to a car's transmission at one end and the wheels at the other. It transfers the mechanical power from the transmission to the other components of the vehicle.
A U-joint, or universal joint, is a flexible pivot point that transmits power allowing for varying angles of the driveshaft.
CV joints, or constant-velocity joints, are part of the driveshaft. These joints are designed to be able to bend in any direction while continuing to turn the drive wheels at a constant velocity.
The differential is where the power makes its last stop before spinning the wheels (see ‘How Differentials Work’).
Axle shafts are a single rotating shaft, on either side of the differential, which delivers power from the final drive assembly to the drive wheels.
Driveline, Drivetrain, Powertrain
Technicians sometimes refer to driveline, drivetrain and powertrain interchangeably when referring to the drivetrain system of an automobile. This can cause confusion, but in essence, all of these terms describe the same system within the vehicle.
The powertrain in a vehicle is composed of everything that makes the vehicle move. This includes everything from the engine to the transmission to all the parts that allow the power from the engine to get to the wheels. A vehicle’s driveline consists of all of the powertrain’s components except for the engine.
The drivetrain is the part of a motorized vehicle which connects the engine and transmission to the wheel axles.
The driveline includes everything in the chain from the engine to the drive wheels, but the drivetrain consists of everything after the transmission — all driveshafts, axles, joints, differentials and wheels.