254 Auto Suspension and Steering
changes, Figure 12-8. To allow the drive shaft to
compensate for this change in length, a slip yoke is
installed somewhere on the drive shaft. The slip yoke
consists of an internally splined yoke that slides into the
external splines of a matching part, usually the output shaft
of the transmission. A typical slip yoke is shown in
Figure 12-9.
Flexible Joints
The purpose of all flexible joints is the same: to allow
the drive axle or drive shaft to rotate through an angle.
Since the transmission or transaxle is attached to the
vehicle’s body and the drive wheels move with the road
surfaces, the angle between each end of the drive axle
changes constantly. To do this, the joint must be able to
move through an angle. Several flexible joint designs are
used, including constant velocity joints and universal
joints.
Constant Velocity Joints
Constant velocity joints, or CV joints, are used on all
front-wheel drive vehicles and a few rear-wheel drive
vehicles. The advantage of a CV joint is that it can transfer
rotation through various angles with no variations in drive
shaft speed. The design of a typical CV joint allows the
center of rotation to change without any change in speed
between the two sides of the joint. See Figure 12-10. The
CV joint can also compensate for changes in drive axle
length as the wheels move in relation to the transaxle. For
this reason, CV joints are sometimes called plunging joints.
There are two kinds of CV joints: the Rzeppa joint and
the tripod joint. Placement of the two joints varies, but as
a general rule the Rzeppa joint is the joint nearest the
wheel, and the tripod joint, when used, is the joint nearest
the transaxle. Both types are discussed below.
Rzeppa Joints
The Rzeppa joint consists of a series of ball bearings
installed between two sets of channels, or races. A sheet
metal cage holds the balls in place. For this reason the
Rzeppa joint is sometimes called a ball-and-cage joint.
A typical Rzeppa joint is shown in Figure 12-11. One race
is external; the other race is internal. The internal and
external races are connected to opposite sides of the drive
axle. Power flows through one race, through the balls, and
into the other race. Figure 12-12 shows the relationship
between the internal parts and the drive axle of a typical
Rzeppa joint. The ball bearings can turn to compensate as
the angle between the inner and outer races changes.
Tripod Joints
Tripod joints are also constant velocity joints. They
consist of a three-pointed assembly called a spider.
Trunnions on the spider allow the spider to move along
internal channels in a housing. A typical tripod joint is
shown in Figure 12-13. Note that the spider is splined to
the axle shaft. Thin roller bearings called needle bearings
are installed between the spider points and the trunnions.
As the axle rotates, the spider is driven by the housing
and drives the shaft. If the angle between the two sides of
the joint changes, the tripod can tilt to compensate. See
Figure 12-14. The spider can also move back and forth
inside of the housing to compensate for changes in axle
length as the wheels move up and down over road
irregularities.
CV Joint Lubrication
Special grease is used to lubricate CV joints. This
grease resists water and forms a film that retards corrosion
on the CV joint parts. It is supplied in plastic packets that
are packaged with replacement CV joints and boots.
Ordinary front-end greases should never be used to
lubricate a CV joint.
Slip yoke
Flexible joint
Hollow tube
Flexible joint
Mounting
flange
Bearing
cap
Figure 12-5. This drive shaft uses flexible joints on each end and is used on rear-wheel drive vehicles. (Mazda)
Front
differential
Slip yoke
Front drive shaft
Transfer case
Retainer
Bolt
Bolt
Retainer
Axle
Figure 12-6. A front drive shaft used on a four-wheel drive
vehicle. (Chevrolet)