Description - GMC 1986 P-Truck Service Manual

4A-2 PROPELLER SHAFT
PROPELLER SHAFT
Torque is transmitted from the transmission to the
rear axle through one or more propeller shafts and
universal joint assemblies. The number of propeller
shafts and universal joint assemblies vary with the
v e h ic le w heel base, and the c o m b in a tio n of
transmission, transfer case (front drive) and rear axle
equipment.
All propeller shafts are the balanced tubular type
(figure 1). A splined slip joint is provided in some
drivelines and others use a companion flange at the
transmission end of the driveline. If two or more
propeller shafts are used on a vehicle the slip joint is
usually at the forward end of the rear propeller shaft.
Phasing
The propeller shaft is designed and built with the
yoke lugs (ears) in line with each other (figure 1). This
design produces the smoothest running shaft possible,
and is called phasing.
Vibration can be caused by an out of phase propeller
shaft. The propeller shaft will absorb vibrations from
speeding up and slowing down each time the universal
joint goes around. This vibration would be the same as
a person snapping a rope and watching the " wave"
reaction flow to the end. A propeller shaft working in
phase would be similar to two persons snapping a rope
at the same time, and watching the " waves" meet and
cancel each other out. In comparison this would be the
same as the universal joints on a propeller shaft. A
total cancellation of vibration produces a smooth flow
of power in the driveline. It is very important to
reference mark the propeller shaft before removal, to
assure phased installation alignment. Some propeller

DESCRIPTION

Figure 1— P ro peller Shaft A ssem bly Phased
shafts have alignment marks or arrows stamped on the
shaft at the time of production.
CENTER BEARING
Center bearings support the driveline when two or
more propeller shafts are used. The center bearing is a
ball type bearing mounted in a rubber cushion that is
attached to a frame crossmember. The bearing is
pre-lubricated and sealed by the manufacturer (figure
2).
UNIVERSAL JOINT
A universal joint is two Y-shaped yokes connected by
a crossmember called a spider. The spider is shaped
like a cross having arms of equal length called trun­
nions (figure 3).
Universal joints are designed to handle the effects of
various loadings and rear axle w indup d uring
acceleration. Within the designed angle variations the
universal joint will operate efficiently and safely. When
the design angle is changed or exceeded the
operational life of the joint may decrease.
The trunnion bearings used in universal joints are
the needle roller type. The needle rollers are held in
place on the trunnions by round bearing cups. The
bearing cups are held in the yokes by e ith e r
(depending on the manufacturer) snap rings or injected
plastic.
When a driveline has a large or deep angle a
constant velocity joint is used. Essentially, the constant
velocity joint is made of two universal joints coupled by
a yoke and phased for constant velocity. A centering