Chevrolet 1977 light duty truck Service Manual page 337

The following caution applies to one or more steps in the assembly
procedure o f components in this portion o f the m anual as indicated at
appropriate locations by the terminology "See Caution on page l of this
Section".
C A U TIO N :
P A R T I N T H A T I T C O U L D A F F E C T T H E P E R F O R M A N C E OF
V IT A L C O M P O N E N T S A N D S Y S T E M S , A N D / O R CO U LD R E S U L T
IN M A J O R R E P A I R E X P E N S E . I T M U S T B E R E P L A C E D W I T H
O N E O F T H E S A M E P A R T N U M B E R OF W I T H A N E Q U I V A L E N T
P A R T I F R E P LA C E M E N T B E C O M E S N E C E S S A R Y. DO N O T U S E A
R E P L A C E M E N T P A R T OF L E S S E R Q U A L I T Y OR S U B S T I T U T E
D E S IG N .
D U R I N G R E A S S E M B L Y TO A S S U R E P R O P E R R E T E N T I O N OF
T H I S P A R T .
Universal Joints
The simple universal jo in t is basically two Y-shaped
yokes connected by a crossmember called a spider. The
spider is shaped like an X and arms that extend from it
are called trunnions. See figure 4A-1.
The spider allows the two yoke shafts to operate at
SECTION 4A
PROPSHAFT
T H I S F A S T E N E R I S A N I M P O R T A N T A T T A C H I N G
T O R Q U E V A L U E S M U S T B E
C O N T E N T S
G e n e ra l D e s c rip tio n ......................................................... 4A-1
Universal Jo in ts ............................................................... 4A-1
Propeller S h a ft................................................................. 4A-2
D ia g n o sis.............................................................................. 4A-3
O n C ar Service.................................................................. 4A-5
Specifications..................................................................... 4A-15
GENERAL DESCRIPTION
U S E D A S S P E C IF IE D
an angle to each other. W hen torque is transmitted at an
angle, through this type o f joint, the driving yoke rotates
at a constant speed while the driven yoke speeds up and
slows down twice per revolution. This changing of
velocity (acceleration) o f the driven yoke increases as the
angle between the two yoke shafts increases. This is the
prime reason why single universal joints are not used for
angles greater than three to four degrees. At four
degrees, for example the change o f velocity is .5%. At ten
degrees it is 3%. If the universal joint were set at 30
degrees and the driving yoke were turning at 1000 RPM
the velocity o f the driven yoke would change from 856
RPM to 1155 RPM in one q uarter o f a revolution. In the
rem aining quarter revolution the velocity would change
from 1155 RPM to 866 RPM.
On a one-piece drive shaft this problem can be
eliminated by arranging two simple universal joints so
that the two driving yokes are rotated 90 degrees to each
other. However the angle between the drive and driven
yokes must be very nearly the same on both joints for
this to work. Refer to figure 4A-2. This allows the
alternate acceleration and deceleration o f one jo in t to be
offset by the alternate deceleration and acceleration o f
the second joint. W hen the two joints do not run at
approximately the same angle, operation can be rough
and an objectionable vibration can be produced.
Universal joints are designed to consider the effects
I