Figure 5-1.Drive line assembly.
The drive shaft, also called a propeller shaft, is
commonly a hollow steel tube with yoke(s) welded on
the end. The tubular design makes the drive shaft
strong and light. Most vehicles use a single, one-piece
drive shaft. However, many trucks have a two-piece
drive shaft. This cuts the length of each shaft to avoid
drive line vibration.
Since a drive shaft spins at full engine t-pm in high
gear, it must be straight and perfectly balanced (weight
evenly distributed around center line of shaft). If NOT
balanced, the shaft can vibrate violently. To prevent
this vibration, drive shaft balancing weights are
welded to the shaft at the factory. Small metal weights
are attached to the light side to counteract the heavy
side for smooth operation.
The drive shaft can be either open or enclosed,
depending on the type of drive used. The HOTCHKISS
drive has an open drive shaft that operates a rear axle
assembly mounted on springs (fig. 5-2). The
HOTCHKISS drive requires that the springs be rigid
enough to withstand the twisting action (torque) of the
rear axle and the driving and braking forces that the
springs transmit to the frame. This type of drive is
common to the equipment you will encounter in the
Another type of drive is a torque tube. Torque
tubes differ from the Hotchkiss design in that a solid
drive shaft is enclosed in a hollow torque tube and
rotates within a support bearing to prevent whipping.
One universal joint is used at the front of the drive
Figure 5-2.Hotchkiss drive.
shaft, and the rear of the drive shaft is attached to the
axle drive pinion through a flexible coupler.
A universal joint, also called a U-joint, is a flexible
coupling between two shafts that permits one shaft to
drive another at an angle to it. The universal joint is
flexible in a sense that it will permit power to be
transmitted while the angle of the other shaft is
A simple universal joint is composed of three
fundamental units consisting of a journal (cross) and