Chapter 12 Driveline and Wheel Components 259
Axial loads occur when the vehicle is turned. The
steering linkage turns the front wheels, but the body wants
to keep moving forward. In the rear, the tires tend to keep
moving in the same direction while the vehicle body is
turning. This places a sideways, or axial, load on the
bearings. See Figure 12-20. Axial loads are sometimes
called thrust loads. Axial loads are always parallel to
the shaft.
axial loads. Straight roller bearing assemblies are
self-contained units, and preload is not adjustable.
On a few older cars, the axle shaft serves as the inner race.
Tapered Roller Bearings
Tapered roller bearings are used in both front and rear
axles. They can be found on driving and non-driving
axles. Their tapered design allows them to handle any
combination of axial and radial loads. As with ball
bearings, tapered roller bearings are installed in pairs to
absorb sideways loads. See Figure 12-24. On most tapered
roller bearing designs, the inner race, rollers, and cage are
a single unit. The outer race is pressed into the hub.
Wheel Bearing Types
All modern wheel bearings are antifriction types.
Three types of antifriction bearings are used on late-model
vehicles: ball bearings, straight roller bearings, and tapered
roller bearings. The type of bearing used varies with
the weight placed on the bearing, whether it is used on a
steering or non-steering axle, and whether it is used on a
driving or non-driving axle.
Ball Bearings
Ball bearings are used on the front axles of some front-
wheel drive vehicles. Most of these applications use two
ball bearing assemblies. In some cases, two rows of
bearings are contained in a single housing. A dual ball
bearing assembly is shown in Figure 12-21. In addition to
splitting the weight, each bearing assembly can take axial
loads in one direction. Pairing the ball bearings handles
axial loads in both directions. Note in Figure 12-22 the
inner and outer races are designed to accept axial loads in
opposite directions. Modern ball bearings have the balls
and races in a single sealed unit. Preload is factory set and
cannot be adjusted.
Straight Roller Bearings
Straight roller bearings, Figure 12-23, are used on the
rear axles of many rear-wheel drive vehicles. Flat roller
bearings can absorb radial loads, but they cannot handle
Thrust
load
Housing
Shaft
Thrust load
(axial)
Inner ring
retained
Outer ring
retained
Shaft
Figure 12-20. Two roller bearing applications illustrating axial
(thrust) loading. Note that the thrust load is parallel to the shaft
or housing. (Federal-Mogul)
Steering
knuckle
Axle hub nut
Speed sensor rotor
Axle
hub
Lug
bolt
Double-row
assembly
ball bearing
Disc
Figure 12-21. A dual ball bearing assembly used on the front
axle hub. Note the speed sensor rotor, which is used by the
anti-lock brake system. Do not damage rotors when working
with bearings, hubs, etc. (Lexus)