GMC 1982 Light Duty Truck Service Manual page 404

4 A -2 PROPELLER SHAFT
operate safely and efficiently. H ow ever, when the design
angles are ex ceeded the operational life o f 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
in the yoke by either (depending on the manufacturer) snap
rings or plastic injection. These joints usually are lubricated
for life and cannot be lubricated while on the vehicle.
Constant Velocity Joint-Double Cardan Joint
As mentioned previously, the simple universal joint will
operate efficiently through small angles only. Also, two
simple universal joints phased properly and operating
through the same angle will transm it constant velocity.
W hen a large angle is encountered in a driveline, a simple
universal joint will introduce two vibrations in each
revolution. It is in this situation that a constant velocity joint
is used.
Essentially, the constant velocity joint is two simple
universal joints closely coupled by a coupling yoke, phased
properly for constant velocity.
A centering ball socket between the joints maintains
the relative position of the two units. This centering device
causes each of the two units to operate through one-half of
the complete angle between the drive shaft and differential
carrier. See figure 4A-3.
The ball/socket on this Constant Velocity joint requires
periodic lubrication. A lubrication fitting is provided for this
purpose, and is illustrated later in this section.
Propeller Shafts
The propeller shaft is a steel tube which is used to
transmit power from the transmission output shaft to the
differential. To accommodate various model, wheelbase and
transmission combinations, drive shafts differ in length,
diameter and the type of splined yoke. Each shaft is installed
in the same manner. A universal joint and splined slip yoke
are located at the transmission end of the shaft, where they
are held in alignment by a bushing in the transmission rear
extension. The slip yoke permits fore and aft movement of
the drive shaft as the differential assembly moves up and
down. The spline is lubricated internally by transmission
lubricant or grease. An oil seal at the transmission prevents
leakage and protects the slip yoke from dust, dirt and other
harmful material.
Since the drive shaft is a balanced unit, it should be
kept completely free of undercoating and other foreign
material which would upset shaft balance.
Both one piece and two piece propeller shafts are used
depending on the model. All are tubular and use needle
bearing type universal joints.
On models that use a two piece shaft, the shaft is
supported near its splined end in a rubber cushioned ball
bearing which is mounted in a bracket attached to a frame
crossmember. The ball bearing is permanently lubricated
and sealed.
Four wheel drive models use a front propeller shaft
incorporating a constant velocity joint.