Transmission and Drivetrain: Description and Operation
Driveline SystemThe 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.
Idle rear driveshaft is connected to the output shaft of the transmission and to the rear axle. The front driveshaft is connected to the transaxle case and to the front axle. Universal 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 Tear 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.
- Two-piece rear driveshaft with three U-joints, a front coupling shaft, a center bearing and a rear driveshaft.
- 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.
Vehicle Certification (VC) Label Example
The Vehicle Certification (VC) label is located in the driver doorjamb. The first two digits of the axle code indicate the rear axle and the third digit refers to the front axle, if so equipped.
Front Axle Identification Tag
Rear Axle Identification Tag
Axle Identification Tag Denoting Interchangeability Connected Internally
CAUTION: The axle identification tog is the official service identifier. Do not damage the tag. Always reinstall the tag after removing it for axle inspection/repair.
The plant code denotes a particular axle design, a specific ratio, and if it is a conventional or limited slip traction-Lok) type. In addition, the plant code will not change as long as that particular axle assembly never undergoes an external design change. If, however, an internal design change takes place during the production life of the axle and that internal change affects parts interchangeability, a dash and numerical suffix is added to the plant code.
Note that the plant code in the front and rear axle identification tag illustrations is similar, but the illustration denoting interchangeability affected internally shows the addition of the suffix. This means that as an assembly both axles are interchangeable; however, internally they are different. Before each requires different internal parts at the time of repair.