Chevrolet LIGHT DUTY TRUCK (SERIES 10-35) Service Manual page 348

procedure of components in this portion of the manual as indicated at
appropriate locations by the terminology "See Caution on page 1 of this
Section".
could affect the performance of vital components and systems, and/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...................................................................... .4A-1
Diagnosis....................................................................................... .4A-3
On Car Service................................................................................. 4A-5
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 4A-1.
The spider allows the two yoke shafts to operate at an
angle to each other. When 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
SECTION 4A
PROPELLER SH A F T
The following caution applies to one or more steps in the assembly
This fastener is an important attaching part in that it
CAUTION:
CONTENTS
Universal Joints........................................................................... .4A-1
Propeller Shaft............. ............................................................... .4A-2
GENERAL DESCRIPTION
PROPELLER SHAFT
(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 not used for 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 RPM the velocity of the
driven yoke would change from 856 RPM to 1155 RPM in
one quarter of a revolution. In the remaining 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 of one joint to be offset by the alternate
deceleration and acceleration of the second joint. When 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
operate safely and efficiently. However, when the design
angles are exceeded the operational life of the joints may
decrease.
The bearings used in universal joints are the needle
roller type. The needle rollers are held in place on the
trunnion by round bearing cups. The bearing cups are held
4A-1
LIGHT TR U CK S ER V IC E MANUAL