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4A-4
1977 PONTIAC SERVICE MANUAL
MAINTENANCE AND ADJUSTMENTS
CHECKING REAR UNIVERSAL
JOINT ANGLE
When torque is transmitted through any ordinary
universal joint, the driven yoke fluctuates slightly in speed.
In other words, although the driving yoke rotates at a
constant speed, the driven yoke speeds up and slows down
twice per revolution. This fluctuation of the driven yoke is
in direct proportion to the angle through which the universal
joint is operating; the greater the angle, the greater the
fluctuation.
Whenever two universal joints are used, this fluctuation
effect can be eliminated by staggering the joints so that the
two driving yokes are 90 degrees apart provided the two joints
are transmitting torque through the same angle.
Therefore, when two universal joints are used, the angles
through which they operate must be very nearly the same.
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 is rough and an
objectionable vibration is produced.
The actual optimum angles desired must also consider
the effects of various passenger loadings and rear axle windup
during acceleration so that it is unlikely that the front and
rear joints will be found to be the same in actual practice.
In addition, universal joints are designed to operate
safely and efficiently within certain angles. If the designed
angle is exceeded, the joint may be broken or otherwise
damaged.
The front universal joint angle is actually the angle
between the engine-transmission centerline and the propeller
shaft. This angle is determined by the design of the frame
assembly and may be altered by adding or removing shims
between the transmission rear bearing retainer and the
transmission mount.
Because sensitivity to pinion angle adjustment has been
reduced, non-adjustable rear upper control arms are installed
at the best pinion angle during factory installation.
Minor rear joint angle corrections can be made by
shimming between the spring plates on
X
Series cars or by
loosening all of the rear suspension control arm bolts on all
other cars and repositioning the pinion nose up or down. This
takes advantage of all the bolt hole tolerances in the brackets.
All complaints of propeller vibration should be
accompanied by rear trim height measurements at curb
weight. An incorrect trim height may cause some vibration.
If vibration is severe enough, removal or installation of spring
shims may be required. If any irregular roughness or
vibration is detectable in the drive line, the rear universal joint
angle should be checked. Also, if a car is involved in a severe
rear end collision or if the rear axle housing is replaced, the
rear universal joint angle should be checked and arms
replaced if necessary.
INCLINOMETER METHOD
This method can be used with the car over a pit or on
a drive-on platform hoist as long as the car is at curb weight
with a full tank of gasoline. Jounce car up and down to assure
curb height.
Readings should be taken at the following locations in
the following manner:
Angle A t Rear Universal Joint
1. Place inclinometer (J 23498) on rear propeller shaft
bearing cup (Fig. 4A-3). Center bubble in sight glass and
record measurement. Bearing cup must be straight up and
down and free of dirt or other foreign material to obtain an
accurate measurement.
2. Rotate propeller shaft 90 degrees and place
inclinometer on companion flange yoke bearing cup (Fig. 4A-
4). Center bume in sight glass and record measurement.
Fig. 4A-3 Measuring Angle at Rear Propeller Shaft
Bearing Cup
3. Subtract both figures to obtain existing rear joint
angle.
4. For installation of shims to correct angle on the
X
and
F
Series, use the following procedure:
a. With rear wheels or axle housing supported, place
floor stands forward of the front leaf spring attaching points.
b. Loosen, but d o not remove, the
"U" bolt attaching
nuts.
"U" bolt nuts should be loosened 3 or 4 threads beyond
the bottom of the
"U" bolts. Perform operation on one side
at a time.
c. Install proper degree shim between the upper spring
plate cushion and the spring. T o decrease the angle, install
shim with the thick end toward the front of the car. If it is
necessary to increase the angle, install shim with thick end
toward the rear of car.
d. Install the spacers between the upper and lower spring
plates with the thick end in the same direction as the thick
end of shim.
e. Torque
"U" bolt nuts to 45 1b.ft.
f. Recheck angle for proper correction.
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