TRUCK SERVICE MANUAL
PROPELLER SHAFT
General
Fig. 4. Universal Joint Speed Fluctuations
UNIVERSAL JOINT CANCELLATION
If two joints are placed in the drive line, one at each
end of the propeller shaft, having equal working angles,
A single universal joint operating between two shafts
the rear joint will provide the inverse condition of the
at a given angle will not turn at an even and constant
forward joint. In other words, the rear joint will slow down
speed; that is to say that, although the speed of the
by the same amount that the forward joint speeds up,
driving shaft is constant, the driven shaft speed is going
resulting in joint cancellation. The driving and driven
to fluctuate up and down.
shafts will turn at constant and identical speeds.
During the first 90 degrees of rotation, the forward
PROPELLER SHAFT PHASING
universal joint speed will increase, Fig. 4. From 90
degrees to 180 degrees the speed will decrease to again
match the driving shaft speed. This sequence is again
one yoke or flange with another on the same shaft within
repeated respectively from 180 degrees to 270 degrees
a 360 degree revolution.
and from 270 degrees to 360 degrees. This speed
fluctuation is known as torsional excitation (winding up
Correct phasing is equally important when compared
and unwinding) of the propeller shaft.
with other factors governing proper drive line operation.
Fig. 5. Propeller Shaft in Phase
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