Transmission and Drivetrain: Description and Operation

The source of the drivetrain's power is generated by the engine and delivered to the transmission. The driveline transfers the engine torque through the driveshaft to the axle.
- On 2-wheel drive vehicles, power is transmitted through the transmission to the driveshaft and then to the rear axle.
- On 4-wheel drive vehicles, power is transmitted through the transmission and the transfer case. The transfer case directs the power to the rear driveshaft and then to the rear axle. When engaged, it also transmits power through the front driveshaft to the front axle.
- On all wheel drive vehicles, power is transmitted through the transmission and continuously proportioned to the front and rear axles through the transfer case.

The rear driveshaft is connected to the output shaft of the transmission and to the rear axle. The front driveshaft is connected to the transfer case and to the front axle. Universal joints and CV joints are used at both ends of the driveshaft to allow for angular motions. Slip yokes are used to allow for any changes to the length of the driveshaft. The engine torque enters the axle through the drive pinion, which rotates the ring gear. The ring gear is mounted to the differential case, which contains the gears that transmit power to the rear axle shafts or front halfshafts. These shafts rotate the drive wheels.
Vehicles have the following types of driveshafts:
- One-piece rear driveshaft with two U joints and a front slip yoke.
- One-piece front driveshaft with one front U joint, a slip yoke and a rear CV joint.
The engine angle is built into the engine mounts. If the engine angle is out of specification, the engine mounts must be inspected for damage.