DRIVE LINES, DIFFERENTIALS, DRIVE AXLES, AND
POWER TRAIN ACCESSORIES
Learning Objective: Identify the components and
explain the functions and the maintenance procedures
for a drive line assembly, differentials, drive axles, a
transfer case, and a power takeoff unit. Describe the
different types of universal and constant velocity joints.
Explain the adjustments and measurements of the ring
and pinion gears. Describe the procedures for removing
and replacing axle bearings and seals.
One important function of the power train is to
transmit the power of the engine to the wheels. In a
simple situation, a set of gears or a chain could perform
this task, but automotive vehicles usually are not
designed for such simple operating conditions. They
are designed to have great pulling power, move at
different speeds, operate forward and reverse, and
travel on rough as well as smooth surfaces. To meet
these widely varying conditions, a number of units
have been added. In this chapter we will discuss drive
lines, differentials, drive axles (rear and front drive),
and power train accessories (transfer cases and power
DRIVE LINE ASSEMBLY
Learning Objective: Identify the parts and the
functions of different types of drive lines. Describe the
different types of universal joints.
The drive line assembly has several important
functions. It must perform the following:
Send turning power from the transmission to the
rear axle assembly.
Flex and allow up-and-down movement of the
rear axle assembly.
Provide a sliding action to adjust for changes in
drive line length.
Provide a smooth power transfer.
The assembly provides a path through which
power is transmitted from the transmission to the drive
axle assemblies or auxiliary equipment. Vehicles,
having a long wheelbase, are equipped with a drive
shaft that extends from the transmission or transfer
case to a center support bearing and a drive shaft that
extends from the center support bearing to the rear
The drive line assembly (fig. 5-1) consists of the
SLIP YOKEconnects the transmission output
shaft to the front universal joint.
FRONT UNIVERSAL JOINTthe swivel
connection that fastens the slip yoke to the drive
DRIVE SHAFTa hollow metal tube that
transfers turning power from the front universal
joint to the rear universal joint.
REAR UNIVERSAL JOINTa flex joint that
connects the drive shaft to the differential yoke.
REAR YOKEholds the rear universal joint
and transfers torque to the gears in the rear axle
SLIP YOKE (JOINT)
The type of transmission (manual or automatic)
determines how the slip joint is connected to the drive
shaft. On a manual transmission, the slip yoke is
splined to the drive shaft with the yoke for the universal
joint directly behind the transmission or transfer case,
whereas, with the automatic transmission, the slip
yoke is splined to the output shaft. Either way they
serve the same purposeto provide the necessary
telescopic action for the drive shaft. As the axle
housing moves forward and backward, the slip joint
gives freedom of movement in a horizontal direction
and yet is capable of transmitting rotary motion.
The slip yoke used with an automatic transmission
has the outer diameter machined smooth. This smooth
surface provides a bearing surface for the bushing and
rear oil seal in the transmission. The transmission rear
oil seal rides on the slip yoke and prevents fluid
leakage out of the rear of the transmission. The seal
also keeps dirt out of the transmission and off the slip