Propeller shafts may be solid or tubular type and
require little or no maintenance.
Solid shafts are
normally used where high shaft speeds are unnecessary.
They are used extensively to power auxiliary
equipment, such as winches and hydraulic pumps. The
hollow shaft is used almost exclusively to transmit
power to the axles on automotive vehicles. The hollow
shaft, because it rotates at high speed, must be balanced
to prevent vibration and premature bearing failure in the
transmission and differential assemblies.
A slip joint at one end of the propeller shaft takes
care of end play.
The driving axle, attached to the
springs, is free to move up and down, while the
transmission is attached to the frame and cannot move.
Any upward or downward movements of the axle causes
the suspension springs to flex. This action shortens or
lengthens the distance between the axle assembly and
the transmission. The slip joint makes up for this
changing vertical distance.
The type of slip joint normally used consists of a
splined stub shaft, welded to the propeller shaft, that fits
into a splined sleeve in the universal joint, as shown in
A universal joint acts as a flexible coupling
between two shafts and permits one shaft to drive
another shaft that is at an angle to it. The universal
joint is flexible in the sense that it permits power to
be transmitted, while the angle of the shaft is being
A conventional universal joint assembly is
composed of three fundamental units: a journal (cross)
and two yokes, as shown in figure 2-12. The two yokes
are set at right angles to each other and are joined by the
journal. This design permits each yoke to pivot on the
journal, allowing the transmission of rotary motion from
one yoke to the other. As a result, the universal joint can
transmit power from the engine through the shaft to the
drive axle, even when the engine is mounted in the frame
at a higher level than the drive axle, as shown in figure
Universal joints need little, if any, maintenance
other than lubrication.
Some universal joints have
grease fittings and should be lubricated according to the
CENTER SUPPORT BEARINGS
When two or more propeller shafts are connected
together in tandem, their alignment is maintained by a
rubber-bushed center support bearing, secured to a cross
member of the frame. A typical center support bearing
assembly is shown in figure 2-14. The standard bearing
is prelubricated and sealed and requires no further
lubrication; however, some support bearings on
heavy-duty vehicles have lubrication fittings. The first
indication of support bearing failure is excessive chassis
vibration at low speed caused by the bearing turning
with the shaft in the rubber support.
A final drive transmits the power delivered from
the propeller shaft to the drive wheels or to sprockets
equipped on tracklaying equipment. Because it is
located in the rear axle housing, the final drive is
usually identified as a part of the rear axle assembly.
The final drive consists of two gears, called the ring
gear and pinion. These are beveled gears, and they
may be worm, spiral, spur, or hypoid, as shown in
The function of the final drive is to change by 90
degrees the direction of the power transmitted through
the propeller shaft to the driving axles. It also provides
a fixed reduction between the speed of the propeller
shaft and the axles driving the wheels. In passenger
Figure 2-14.Center support bearing.