GMC 1982 Light Duty Truck Service Manual page 403

procedure of components in this portion of the manual as indicated at
appropriate locations by the terminology "See Notice on page 1 of this
Section".
affect the performance of vital components and systems, a nd/or could result
in major repair expense. It must be replaced with one of the same part
number or with an equivalent part if replacement becomes necessary. Do not
use a replacement part of lesser quality or substitute design. Torque values
must be used as specified during reassembly to assure proper retention of this
part.
General Description
Universal J o in ts.....
Propeller S h a f t ......
Diagnosis....................
On-Vehicle Service..
Specifications..........
Fig. 4A-1--Simple Universal Joint
GENERAL DESCRIPTION
Universal Joints
The simple universal joint 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 4 A -1.
The spider allows the two yoke shafts to operate at an
angle to each other. W hen torque is transmitted at an angle,
through this type of 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) of the driven yoke increases as the angle
between the two yoke shafts increases. This is the prime
reason why single universal joints are generally not used for
SECTION 4A
PROPELLER SHAFT
The following notice applies to one or more steps in the assembly
N O T IC E : This fastener is an important attaching part in that it could
CONTENTS
angles greater than three to four degrees. At four degrees,
for example the change of 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 R P M the velocity of the
driven yoke would change from 856 R P M to 1155 R P M in
one q u a rte r of a revolution. In the rem aining q u arte r
revolution the velocity would change from 1155 R P M to 866
R PM .
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 of one joint to be offset by the a ltern a te
deceleration and acceleration of 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 of
various loadings and rear axle windup, during acceleration.
Within the design angle variations the universal joints will
PROPELLER SHAFT 4 A -1
4A-1
4A-1
4A-2
4A-2
4A-5
4 A -11