This sample chapter is for review purposes only. Copyright © The Goodheart-Willcox Co., Inc. All rights reserved.
Chapter
12
Driveline and
Wheel
Components
After
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studying this chapter, you will be able to:
Identify types of drive axles and drive shafts.
Explain the design and construction of constant velocity flexible joints.
Explain the design and construction of cross-and-roller flexible joints.
Explain the purpose of antifriction bearings.
Identify types of wheel bearings.
Match axle types to bearing types.
Identify types of hubs and axle flanges.
Identify types of wheel rims.
Explain rim size specifications.
Identify tire designs.
Explain tire ratings.
Identify wheel fastener designs.
Technical Terms
Independent drive axles
CV axles
Transfer shaft
Drive shaft
Yokes
Slip yoke
Constant velocity joints
Universal joint
Cross-and-roller joints
Antifriction bearings
Ball bearings
Straight roller bearings
Tapered roller bearings
Wheel hub
Axle flange
Wheel rims
Radial tires
Bias tires
Tire ratings
Section width
251
Aspect ratio
Load index
Speed rating
Uniform tire quality grading system
Temperature resistance rating
Traction rating
Tread wear rating
Wheel studs
Lug nuts
Tire pressure monitoring systems
252
Auto Suspension and Steering
Introduction
This chapter covers the components related to vehicle
drivelines and wheels. While some of these components
are not directly related to the suspension and steering
systems, they can cause vibration, noise, and other
problems. These problems are often blamed on the
suspension and steering components. Therefore, the suspension and steering technician must be familiar with the
design and operation of drivelines and wheels so the real
cause of problems can be determined.
Studying this chapter will illustrate how drivelines and
wheel components fit into the overall vehicle design, and
how they can affect vehicle operation. This chapter
will also discuss the design and materials used in the
construction of these parts.
Chapter 12
Driveline and Wheel Components
Drive Shafts
Drive plane
All rear-wheel drive vehicles use a drive shaft to
transfer engine power from the transmission to the rear
axle. Drive shafts are large hollow tubes that are carefully
balanced to reduce vibration. Flexible joints are installed at
each end through yokes, which are the mounting points for
the joints. Figure 12-5 is an illustration of a typical rearwheel-drive drive shaft. Four-wheel drive vehicles have a
front drive shaft that directs power from the four-wheel
drive transfer case to the front axle, Figure 12-6.
Cage
Inner race
253
Some drive shafts are two-piece types, Figure 12-7.
Two-piece drive shafts are usually used on large trucks,
where a single drive shaft would be overstressed and
break, and on some luxury cars, where any vibration
would be objectionable. When a two-piece drive shaft is
used, an extra flexible joint is necessary.
Slip Yoke
When the rear wheels move up and down, the
distance between the transmission and rear axle assembly
Figure 12-1. Typical front-wheel drive axle assembly.
C-clip lock
Brake backing plate
Intermediate
shaft
Seal
Rear axle housing
Driveline Components
Driveline components consist of the drive axles and
shafts, flexible joints, and related parts. Drive axles can be
roughly divided into solid and independent types. As a
general rule, solid axles are used on rear-wheel drive
vehicles and independent axles are used on front-wheel
drive vehicles. There are exceptions to this rule, especially
on sport-utility vehicles and sports cars. The application
and construction of both solid and independent drive axles
is discussed in the following section.
Several types of flexible joints are used on modern
vehicles. The type of flexible joints used depends on the
type of axle. Design and use of flexible joints is also
discussed below.
Independent Drive Axles
Independent drive axles are usually called CV axles
because they use a type of flexible joint called a CV joint.
All front-wheel drive vehicles, as well as a few rear-wheel
drive cars, use CV axles. CV axles are solid steel shafts that
connect the transaxle output shafts to the wheels. A few CV
axles are constructed of hollow tubes to reduce weight and
rotating mass. There are always two CV axles on a frontwheel drive vehicle. Figure 12-1 shows a typical CV axle
assembly. Note that there are four CV joints, two on each
axle.
On a few vehicles, a transfer shaft, or intermediate
shaft, is used between the transaxle and the CV shaft on
one side of the vehicle, Figure 12-2. Use of a transfer shaft
allows a support bearing to be placed midway between the
transaxle and the wheel. This reduces vibration and strain
on the CV axle components. Transfer shafts are used on
large cars and on cars with manual transaxles when there
is a large distance between the transaxle case and the
wheels.
CV
assembly
Support bearing
CV axle assembly
Figure 12-2. This front-wheel drive vehicle uses an
intermediate shaft assembly. Study the layout.
Bearing
retainer
Bearing
A few high-performance or sports cars use an
independent rear axle, with exposed drive shafts
containing CV joints. The construction of these shafts is the
same as those used on a front-wheel drive vehicle. Some
older independent rear axle shafts use U-joints instead of
CV joints.
Solid Drive Axles
On most rear-wheel drive cars and trucks, the drive
axles are solid steel shafts. The shafts extend from the
differential assembly gears to the wheel rims. Inside the
axle housing, external splines on the axle shafts mate with
internal splines on the differential gears. The shafts are
enclosed in the rear axle housing and are supported by
bearings.
Solid axle shafts are held in place by one of two
methods. One design locks the shaft in place with an
external retainer behind the brakes, while the other secures
the shaft with a C-lock located inside of the differential
assembly. Each design is shown in Figure 12-3.
Seals keep lubricant from leaking from the axle
housing. Remember from Chapter 7 that the rear axle may
be called a Hotchkiss axle or a Salisbury axle, depending
on the type of rear springs used.
A few four-wheel drive vehicles have a solid front axle
with solid shafts. To allow the vehicle to turn, the ends of
the shafts are attached to the wheel through flexible joints,
Figure 12-4.
Axle
shaft
Bearing
retainer nut
A
Side
gear
B
Axle
shaft
Ring gear
Figure 12-3. A—A bearing retainer is used to hold this axle shaft in the axle housing. B—A C-clip lock placed in a grooved slot on
the end of this axle shaft holds the shaft in the housing. (General Motors & Dodge)
Pitman arm
Steering stabilizer
Flexible joint
Steering
knuckle
Connecting rod
assembly
Tie rod
Tie rod jam nut
Figure 12-4. A four-wheel drive front axle assembly. (Chevrolet)
254
Auto Suspension and Steering
Flexible joint
Hollow tube
Slip yoke
Flexible joint
Chapter 12
Driveline and Wheel Components
255
Adjusting
nut
Mounting
flange
Dust boot
Intermediate shaft
Bearing
cap
Center support
bearing
Figure 12-5. This drive shaft uses flexible joints on each end and is used on rear-wheel drive vehicles. (Mazda)
Propeller shaft
Transfer case
Front drive shaft
Front
differential
Slip yoke
Retainer
Bolt
Bolt
Axle
Retainer
Figure 12-6. A front drive shaft used on a four-wheel drive
vehicle. (Chevrolet)
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.
Snap ring
Dust deflector
Mounting bolt
Nut
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.
Universal joint
Adjusting washer
Differential
Nut
Transmission
Propeller shaft assembly
Bolt
Figure 12-7. One type of two-piece drive shaft. Note the center support bearing. (Lexus)
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.
Transmission
Coil
spring
Slip yoke
A
Transmission
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.
Propeller shaft
Frame
Propeller shaft
Frame
Universal joints
Centrifugal force tends to throw lubricant out of a
CV joint. To keep grease from leaving the joint and protect
the joint from dirt and water, CV boots are installed over
the joint.
As the grease is thrown outward, it strikes the inner
cover of the boot. When the vehicle stops, the grease flows
back into the joint. The accordion pleats on the boot allow
the joint to move in and out as it compensates for changes
in axle length. CV boots are held in place by boot clamps.
Typical CV boots are shown in Figure 12-15.
Universal Joints
Bump
B
Figure 12-8. The drive shaft (propeller shaft) must compensate
for changes in drive shaft angle. A—Normal operating angle.
B—A bump forces the differential upward. The angle has
changed, and drive shaft is shorter. A slip yoke permits this
change in length.
The universal joint, or U-joint, is used on drive shafts.
Sometimes U-joints are used on the transfer shaft of a front
drive axle. U-joints are often called cross-and-roller joints
or Cardan joints. The basic U-joint consists of a central
four-pointed cross, or spider, with caps that contain needle
bearings. The caps are attached to yokes on the drive shaft
and corresponding parts. As the drive shaft turns through
an angle, the cross twists within the caps. The needle
bearings reduce friction and vibration. A typical U-joint is
shown in Figure 12-16.
256
Auto Suspension and Steering
Transmission
Chapter 12
Driveline and Wheel Components
Drive plane
Driven plane
Cage
Output
shaft
Boot
clamp
Outer race
Rear propeller
shaft
Strut
Wheel
Drive
shaft
Figure 12-12. The balls in a Rzeppa joint operate in a bisecting
plane between the angles of the axle shafts. As the joint
revolves, the position of the balls will change so they remain in
this bisecting plane. The position of the balls is controlled by
elongated openings in the cage. (AC Delco)
Needle rollers
Rear axle assembly
Grooves
Trunnion
Damper
Support
bearing
Constant velocity
joint
Ball joint
Ball bearing
Seal
Housing
Figure 12-10. Cutaway of both inboard and outboard CV joints.
(Honda)
In operation, the cross of the U-joint transmits power
between the two yokes. Since the cross cannot move back
and forth, the drive angle changes as the shaft rotates
through an angle. This causes the speed of the driven part
of the drive shaft to vary. See Figure 12-17. The greater the
angle, the more the vibration. For this reason, U-joints are
used only where the angle between the yokes is relatively
small.
Wheel Components
The following sections cover the components related
to a vehicle’s wheels. These components, which include
the wheel hubs, bearings, rims, tires, and fasteners, are
found on both driving and non-driving axles.
Retaining clip
Wheel Bearings
Housing
Figure 12-11. Exploded view of a Rzeppa (ball-type) constant
velocity joint. (AC Delco)
Due to their design, cross-and-roller U-joints do not
require a surrounding boot. Seals at the ends of the bearing
caps (where they enter the cross) keep lubricant in and
water and dirt out. Many U-joints are equipped with grease
fittings. Conventional front suspension lubricant can be
used to lubricate U-joints.
Bearing cap
Figure 12-13. Exploded view of a tripod constant velocity joint.
(AC Delco)
Spider plane
Differential
Drive shaft
yoke
Needle
bearing
Figure 12-16. A Cardan universal joint assembly. (Dodge)
Elongated
opening
Boot
Cross
C-clip
Shaft
(axle)
Cage
Needle bearing
Spider
Inner race
Intermediate
shaft
Seal
Balls
Balls (6)
Outer race
Hub
Wheel side
Bearing cap
Bisecting plane
Clamp
Figure 12-9. A two-piece drive shaft showing the slip yoke. (Chrysler)
Brake rotor
Drive shaft
Propeller shaft
Screw and
washer assembly
Constant velocity
joint
Boot clamp
Figure 12-15. A cutaway of a rear drive shaft showing the
CV boots and clamps. (Lexus)
Propeller
shaft
Slip
yoke
Boot
Differential side
Slip yoke
Bolt (2)
68 N•m
(50 ft. lbs.)
Clamp
Boot
Boot
clamp
Driven
Drive
Washer (2)
Clamp
Boot clamp
Inner race
Propeller
shaft and
center bearing
Boot
257
Driven
Drive
Spider
assembly
Figure 12-14. Tripod joint operation. The tripod joint uses three
balls on needle bearings to transmit torque between the spider
(splined to the axle shaft) and the housing. As the joint revolves,
the three balls will change their positions to stay in the same
plane as the spider. The balls can move in and out of the housing to allow for length changes as the suspension travels up and
down. (AC Delco)
The wheel bearings form a low-friction connection
between the rotating wheels and the stationary vehicle. All
wheel bearings are antifriction bearings. Antifriction
bearings consist of three basic parts: the inner race, the
rolling element, and the outer race. See Figure 12-18. The
rolling elements rotate between the two races, allowing the
races to move in relation to each other with a minimum of
friction. The rolling action also draws lubricant between
the moving parts. The rolling elements and races are made
of heat-treated steel for maximum durability.
The clearances between the parts of an antifriction
bearing must be tight enough to prevent unwanted movement and vibration. However, the clearances must be loose
enough to keep friction at a minimum, allow lubricant to
enter between the moving parts, and compensate for
expansion as bearing temperature increases.
Other parts of antifriction bearings include the
bearing cage, which keeps the individual rolling elements
separated as they turn, and seals or shields, which keep
lubricant in and dirt and water out.
258
Auto Suspension and Steering
30°
1200
Speeds of
driven shaft 1100
1000
for driving
shaft speed of 900
800
1000 RPM
90
Acceleration
Deceleration
180
Acceleration
Conventional universal joint
showing fluctuations
270
360
Deceleration
Constant velocity universal
joint, no fluctuations
Figure 12-17. Speed fluctuation chart. As a universal joint turns, the angle formed by the cross changes. It never divides the angle
equally between the two shafts, (except for one brief moment as the cross angle shifts from one extreme to the other). This causes
an acceleration-deceleration fluctuation that transmits torque in a jerky fashion. The dotted line illustrates the even speed that is
achieved when a constant velocity (later) universal joint is used. The undulating (waving) line represents the speed fluctuation present when a conventional universal joint is used. (General Motors)
Inner
race
Roller
Bearing Loads
Outer race
Cage
Spindle
Outer race
Seal
Cotter
pin
Hub
Inner
race
Grease
cap
Nut lock
Grease
Any load on the bearing tends to push the bearing
parts together. The resulting pressure increases friction and
heat. There are two types of loads placed on wheel
bearings: radial loads and axial loads. Radial loads are
caused by the weight of the vehicle passing through the
spindle or axle, through the bearing and hub, and to the
rim and tire. As the vehicle moves, bearing rotation causes
centrifugal force, which tends to make the bearing rollers
move outward. This combination of vehicle weight and
centrifugal force produces a radial load. Radial loading
occurs at a right angle to the bearing and shaft. This is
shown in Figure 12-19.
Hub
cavity
G
F
Figure 12-18. Cutaway of a roller bearing and front hub used on
a two-wheel drive truck. (Dodge)
Wheel bearings must be carefully selected to deal
with types of loads, maximum bearing speed, where the
bearing will be used on the vehicle, and what the vehicle
is used for. Overall bearing size, as well as the size of the
rolling elements, must be determined to give the longest
service without unnecessary weight and size.
Another factor that must be calculated carefully is
bearing preload. Preload is the amount of pressure placed
on the bearing before it is put into service. In other words,
preload is how tightly the rolling elements and races fit
together before other loads are placed on the bearing. Too
little preload will cause the rolling elements to rock and
vibrate, damaging the bearing. Insufficient preload also
intensifies the effect of shock loads. Too much preload will
press the rolling elements too tightly against the races, creating unnecessary friction and heat.
Ball bearing
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 are used on the front axles of some frontwheel 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.
Steering
knuckle
Lug
bolt
Axle
hub
Axle hub nut
Speed sensor rotor
Disc
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
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)
Housing
Shaft
J
LOAD
Thrust load
(axial)
K
C
B
Double-row
assembly
ball bearing
Ball Bearings
I
D
259
Wheel Bearing Types
H
E
Wheel Bearing Design
Driveline and Wheel Components
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.
One revolution of propeller shaft
0
Chapter 12
L
A
Thrust
load
Tapered Roller Bearings
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)
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.
Outer ring
retained
Figure 12-19. A radial-loaded ball bearing. Ball “A” is carrying
the greatest load, while balls E, F, G, H, and I are carrying the
smallest load. (Federal-Mogul)
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.
Inner ring
retained
Shaft
262
Auto Suspension and Steering
Chapter 12
Driveline and Wheel Components
263
Axle housing
Width
Axle housing
Outside
face
Inside face
Snap ring
Bearing retainer
Straight
roller
bearing
O-ring
Rear axle shaft
Outside face I.D.
Rear brake
assembly
Bore dia.
Free I.D.
Leaf spring
Oil
seal
Axle flange
Brake drum
Drum
retaining
screw
Figure 12-31. The brake drum mounts to the solid axle flange, which is forged as an integral part of the axle. (Toyota)
Mounting holes
Seal O.D.
Seal lip
Shaft dia.
Inside face I.D.
Axial
clearance
Lock
bolt
Brake drum
Tension spring
stationary vehicle. On most vehicles, the hub is also the
mounting surface for the brake drum or rotor. On nondriving axles, the hub often contains the bearing races.
Note the relationship between the hub, the tapered roller
bearings and the spindle in Figure 12-30. This design is
often used on front or rear non-driving wheels.
The front hubs used on many front-wheel drive
vehicles are pressed onto the axle. Splines on the hub and
the axle allow the axle to drive the hub. The hub may be
pressed into the bearings.
When solid axles are used, such as on the rear of rearwheel drive vehicles, the axle and drum are connected
through the use of an axle flange, Figure 12-31. The axle
flange is forged as part of the axle, or it is welded on later.
The flange forms a mounting surface for the wheel
assembly.
Wheel Rims
Wheel rims are the connection between the hub and
the tire. The tire is installed on the rim, and the
rim is bolted to the hub.
Wheel
cover
Axle shaft
Brake
backing plate
Figure 12-28. A cross-sectional view of one type of oil seal.
(General Motors)
Stamped bracket
Lug nut
Figure 12-29. An oil seal pressed into the axle housing bore.
Note that this axle uses straight roller bearings.
(General Motors)
Hub
Tapered roller
bearing
Tapered roller
bearing
Spindle
Seal
Figure 12-30. This cross section shows the relationship
between the hub, the tapered roller bearings, and the spindle.
(Hyundai)
Rim Construction
In many cases, rims are made of stamped steel,
Figure 12-32. Parts of the rim are stamped into shape and
then welded into a final form. The center section contains
Spider
(center section)
Rim
Drop center section
Figure 12-33. Cross-sectional view of a wheel and tire. When
the tire is inflated, the flanges hold the tire to the wheel. The
safety ridges help hold the tire on the wheel if the tire goes flat
while the vehicle is moving. (Chrysler)
Tire
bead
area
Figure 12-32. A steel drop-center wheel. The center section
may be welded or riveted to the rim. This particular wheel is
welded together. (Chrysler)
the wheel mounting holes. On some wheels, an extra
stamping is used to attach the wheel cover, Figure 12-33.
The flange holds the tire in place once it is installed and
inflated.
Steel rims are relatively light and reduce the amount
of unsprung weight. They are also durable and cheap to
manufacture. Some steel rims are chrome plated for
appearance, while others are painted and used with wheel
covers.
Modern vehicles are increasingly using rims made of
materials other than steel. These rims are usually called
custom rims. Common materials for custom rims are
aluminum, aluminum-magnesium alloys, and composites
of graphite and plastic. Figure 12-34 shows a typical
custom wheel.
Figure 12-34. This custom wheel is made of aluminum. (Nissan)
264
Auto Suspension and Steering
The rim design used today is called the drop-center
wheel. The center section of the rim is lowered (or
dropped), which allows the tire to be pulled to one side for
easier removal. Most rims have a small ridge behind the
tire bead to hold the tire in place if a blowout occurs.
These are called safety rims. See Figure 12-35.
Safety ridges
Tire
Drop center
Flange
Wheel
Driveline and Wheel Components
Tires
Figure 12-35. A safety rim holds the tire in place in the event of
a blowout. (Chrysler)
Center section
Flange height
Lug bolt
hole
Radial cord
body plies
Figure 12-37. Typical construction of a radial tire. Sidewall plies
are parallel with each other and at right angles to tread centerline. Belts are under tread area. (Firestone)
Tire Ratings
Modern tire ratings are designated by a system that
uses a series of numbers and letters. The ratings are
stamped into or molded into the tire’s sidewall. An
example of the rating that would be found on the sidewall
of a typical tire is given in Figure 12-38.
The letter P designates the tire as a passenger car tire,
Figure 12-39. Other letters used in this position are LT for
light truck, T for temporary (such as a space saver spare),
and C for commercial (large trucks and construction vehicles). On tires that are suitable for both cars and trucks, this
letter is not used.
The number 205 is the section width, which is
measured at the tire’s widest point. The section width is a
good indication of tread width, and is generally considered
to be the tire size. The section width ranges from about 175
on small tires to about 235 on large tires.
The number 70 is the aspect ratio, or the relationship
of the tire section width to its height, Figure 12-39. Low
numbers indicate a wide, low tire. The larger the number,
the taller the tire.
Diameter
Tire
sidewall
Bolt circle
Rim
Valve stem hole
Rim
width
Figure 12-36. The three most common rim measurements are diameter, rim width, and flange height. Another common
measurement is wheel offset. Wheel offset is measured from the flange edge to the back of the center (spider) section. (Isuzu)
Speed symbol
Section
width
(millimeters)
205
215
Etc.
Stabilizer
belts
Figure 12-38. Tire ratings are molded or stamped on the tire’s
sidewall. All-season tires are generally marked with “M+S,”
which means they are mud and snow rated. (Buick)
Rim
diameter
(inches)
14
15
16
Aspect
ratio
(Section height)
(Section width)
60
70
Section
width
95S
Load index
Tire type
P–Passenger
T–Temporary
LT–Light truck
Tire Construction
The external parts of the tire are the tread and the
sidewalls. Tread designs vary depending on the tire’s
application. The sidewalls form the support for the treads.
The tread and sidewalls are a blend of natural rubber and
a synthetic rubber called neoprene.
The internal parts of the tires are composed of plies
and belts. The plies are layers of tire cord that form the
general shape of the tire. Tire cords can be made of various
fabric materials, including nylon, rayon, polyester, aramid,
Kevlar, or fiberglass. The belts are installed directly under
the tread and can be made of the same materials as the
plies. Some belts are made of steel.
All modern tires are radial tires. In a radial tire, the
cords in the plies cross the centerline of the tire at a right
angle to the tread. Older tires were called bias tires. In a
bias tire, the cords cross the centerline on a bias, or a slant.
Almost all radial tires have one or two belts, which reduce
tread squirming, Figure 12-37.
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P 205 / 70 R 15
Tires perform two jobs: they cushion shocks and
provide traction. In their role as cushioning devices, they
can be considered part of the suspension system. As
traction devices, they transmit engine power, as well as
braking and turning efforts, to the road.
Rim Sizes
There are three measurements of rim sizes. The rim
diameter is most commonly used to describe rim size. Rim
width is the size of the rim between the flanges. The flange
height is how far the flange extends above the bead seat.
Figure 12-36 illustrates the three measurements of a rim.
These measurements apply to both steel and custom
wheels.
Chapter 12
Construction type
R–Radial
B–Bias–Belted
D–Diagonal (bias)
Section height
Figure 12-39. Tire sidewall markings and their meanings.
(Buick)
The letter R indicates a radial tire. Other letters that
could appear here are B and D for bias and belted tires.
The number 15 is the rim size in inches. The most
common rim sizes are 13, 14, and 15. A few vehicles have
12-, 16-, or 17-inch rims, but these are uncommon.
The number 95 is the load index. The load index is an
assigned number that corresponds to the amount of axle
weight the tire can carry. In this case, a 95 load index indicates the tire can support 1521 lb. (690 kg). Load indexes
usually range from 75–110.
The letter S is the speed rating. The speed rating
indicates the maximum speed at which the tire should be
operated. Speed rating letters range from B, with a maximum speed of 31 mph (50 km/h), to Z, with a maximum
speed of 149 mph (240 km/h). This number is also
eliminated on some tires.
Tire Quality Ratings
As standardized by the United States Department of
Transportation (DOT), tires are graded according to the
uniform tire quality grading system. The tire grades are
stamped on the sidewall of the tire. This grading system
establishes several quality grades, including the temperature resistance rating, the traction rating, and the tread
wear rating.
The temperature resistance rating rates the tire’s
resistance to heat generation. Note that this grade is the
resistance to generating heat, not its resistance to the heat
266
Auto Suspension and Steering
itself. The three grades are A, B, and C. A provides the
greatest resistance to heat; C provides the least.
The traction rating is also designated by the letters A,
B, and C. A tire with an A rating has the best traction on
wet surfaces, while a tire with a C rating has the least.
The tread wear rating is designated by a set of
numbers. These numbers range from 100 to 500. A tire
with a rating of 200 should last about twice as long as a tire
rated at 100.
Wheel Fasteners
An important factor in wheel and tire design is the
way the rim is mounted to the hub or axle flange. On
almost all cars and trucks, the hub or axle flange contains
the wheel studs, Figure 12-40. Most wheel studs are
threaded bolts or studs pressed into the hub or flange. A
knurled area on the rear section of the stud cuts into the
hub or axle metal to keep the stud from loosening. The
head of the stud resembles a bolt head and is wider than
the hole in the hub or flange. The head keeps the stud from
coming completely through the hole. To precisely center
the wheel, a central part of the hub or flange is slightly
raised and holds the center of the rim in position.
To install the wheel, the holes in the center section of
the rim are placed over the studs and lug nuts are threaded
onto the studs. The lug nuts can then be tightened in a
cross or star pattern. The tapered end of each lug nut
matches a tapered area in the wheel mounting hole. The
matching tapers help center the wheel. On most steel
wheels, the lug nuts can be tightened by hand or with an
impact wrench. Custom wheels have different metal
expansion rates than the steel and iron hubs, and the lug
nuts must be tightened to a specific torque.
A few imported vehicles use a somewhat different
design. Instead of studs, the hub or flange has threaded
holes. Tapered lug bolts, Figure 12-41, are installed
through the wheel and threaded into the holes. As with lug
nuts, tightening is very important.
Tire Pressure Monitoring
Every set of tires has an ideal pressure for best handling, braking and tire life. Even new tires lose some air
over time. For this reason, tire air pressure must be monitored and air added when necessary. The simplest way to
check tire pressure is with a mechanical pressure gauge.
Most drivers, however, rarely remember to check tire pressure. For this reason, many modern vehicles are equipped
with a tire pressure monitoring system. The tire pressure
monitoring system routinely checks pressure in each vehicle tire. If low pressure is detected, an instrument panel
Wheel studs
Chapter 12
Driveline and Wheel Components
Tapered head
lug bolt
Tire
Valve
stem
Locking lug
bolt
Locking lug
bolt key
Cap
Balance
weight
clip
Hub cap
Balance
weight
Steel wheel
Figure 12-41. This wheel is secured to the hub or flange (not
shown) with tapered lug bolts. (Audi)
warning light illuminates, informing the driver that one or
more tires are underinflated. The driver can then add air or
have the tire(s) serviced as necessary.
Pressure monitoring systems are either direct or indirect systems. The direct pressure monitoring system consists of a central control module and wireless pressure
transmitters at each wheel. The transmitters send a signal to
the module. If any transmitter signals low pressure, the
module illuminates an instrument panel warning light,
Figure 12-42.
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Indirect pressure monitoring systems do not have sensors at each tire. Instead, they use the vehicle’s anti-lock
brake system, or ABS, to monitor tire pressure. Modern
anti-lock brake systems have wheel speed sensors on each
wheel. The ABS control module compares relative wheel
speeds of all tires. When a tire loses air, the distance
between the tire tread and the center of the wheel
decreases. This smaller diameter causes a tire’s speed to
increase. The control module reads the higher speed and
compares it with the speed of the other tires. If tire speed
passes a set threshold, the module turns on an instrument
panel warning light.
Both systems have advantages and disadvantages. The
direct system is more accurate, but requires wheel sensors,
which must be handled carefully when the tire is removed
from the rim. A recalibration procedure must be performed
whenever tires are rotated. The indirect system does not
require any wheel hardware, and recalibration is usually
simpler. However it is less accurate and cannot detect
some common tire pressure problems, such as all four tires
gradually losing air.
Summary
Common driveline components are the drive axles
and shafts, flexible joints, and related parts. Generally,
solid axles are used on rear-wheel drive vehicles and
independent axles are used on front-wheel drive vehicles.
Dash
display
Pressure
sensors
Rear
hub
Brake disc
Lug nut
Flat screw
Center
cap
Aluminum wheel
Figure 12-40. This aluminum wheel is fastened to the rear hub with wheel studs and lug nuts. (Honda)
Warning
light
Pressure
sensor
Warning
chime
Sensor
signal
Receiver
Pressure
sensor
Figure 12-42. If a pressure sensor detects low tire pressure, it sends a radio signal to a receiver in the passenger compartment. This
signal triggers a warning light on the dash. (Toyota)
268
Independent drive axles are usually called CV axles.
CV axles are solid steel shafts or hollow tubes that connect
the transaxle output shafts to the wheels. There are always
two CV axles on a front-wheel drive vehicle. Some frontwheel drive vehicles have a transfer shaft on one side. A
few high-performance or sports cars use an independent
rear axle with CV joints. Some older independent rear
axles have U-joints.
On most cars and trucks with rear-wheel drive, the
drive axles are solid steel shafts that extend from the
differential assembly to the wheel hubs. Some four-wheel
drive vehicles have a solid front axle. All front-engine, rearwheel drive vehicles use a drive shaft between the
transmission and rear axle. Some drive shafts are two piece
types. Four-wheel drive vehicles also have a front
drive shaft.
Several types of flexible joints are used on modern
vehicles. The type of flexible joint used depends on the
type of axle being used. CV joints are used on all
front-wheel drive vehicles and a few rear-wheel drives.
They are able to transmit power through an angle without
causing variations in shaft speed. There are two kinds of
CV joints, the Rzeppa joint and the tripod joint.
The Rzeppa joint consists of a set of ball bearings
inside of two sets of races. The ball bearings can move
between the channels to compensate for changes in angle.
Tripod joints consist of a three point spider and trunnions
that rotate on roller bearings. The spider and trunnions are
placed in a housing. As the axle rotates, the trunnions and
spider are driven by the housing and tilt to compensate for
angle changes. CV joint boots keep lubricant in and dirt
and water out.
The U-joint, or Cardan joint, is used with drive shafts.
U-joints consist of a four-point cross and caps that turn on
needle bearings. The cross can twist as it rotates to
compensate for shaft angle changes. U-joints are used
when the angle change between rotating parts is
not too great.
Wheel bearings form a low-friction connection
between the wheels and the vehicle. All wheel bearings
are antifriction bearings consisting of three basic parts: the
inner race, the rolling element, and the outer race. There
are two kinds of bearing loads. Radial loads are caused by
the weight of the vehicle and by centrifugal force. Axial
loads are sideways loads that occur when the vehicle
is turned.
The three types of antifriction wheel bearings are the
ball bearing, the flat roller bearing, and the tapered roller
bearing. Ball bearings are found on the front axles of many
front-wheel drive vehicles. The balls and races are in a
single sealed unit. Straight roller bearings are often used on
the rear axles of rear-wheel drive vehicles. Tapered roller
bearings are used in front and rear axles and are always
installed in pairs to absorb sideways loads. Tapered roller
bearing preload is adjustable.
Most tapered wheel bearings are packed with wheel
bearing grease, which must be periodically renewed. Some
ball bearings and straight roller wheel bearings are greased
Auto Suspension and Steering
for life. Oil splash from the rotating gears is often used as a
lubrication method on solid rear axles.
The two main classes of wheel bearing lubricants are
wheel bearing greases and gear oils. Most wheel bearings
are lubricated by grease. Some solid rear axle wheel
bearings are lubricated with gear oil. The wheel bearings
on most modern vehicles call for EP lithium grease. Wheel
bearings used in solid rear axles are sometimes lubricated
with the gear oil used to lubricate other rear axle parts.
Bearing seals keep the oil or grease in, and water out.
The wheel hubs and axle flanges are the mounting
surface for the wheel rims and tires. The hub may contain
the bearing races. Front hubs used on front-wheel drive
vehicles are often pressed onto the axle.
Wheel rims are the connection between the hub and
the tire. The rim design used today is called the dropcenter wheel. Rims are made of stamped steel or various
alloys. Rim size determines what type of tire will be used,
and is composed of diameter, width and flange height.
Tires have the job of cushioning road shocks and providing traction. External parts of the tire are the tread and
the sidewalls. Internal parts are the plies and belts. Modern
tires are radial tires. Older tires were called bias tires. Tire
ratings and quality grades are stamped on or molded into
the side of the tire.
The wheel rim is mounted to the hub or axle flange
through wheel studs and lug nuts. A few vehicles use
tapered bolts instead of lug nuts and studs.
Review Questions—Chapter 12
1. Why are front-wheel drive independent axles called
CV axles?
2. While most CV axles are _____ steel shafts, a few are
_____ to reduce weight.
3. A four-wheel drive vehicle has two _____.
4. What is the purpose of a drive shaft slip yoke?
Matching
5.
6.
7.
8.
9.
10.
11.
12.
Match the drive axle with the type of flexible joint.
Independent front axle.
a. CV joint.
Independent rear axle.
b. U-joint.
Solid rear axle.
c. No flexible joint.
Rear-wheel drive shaft.
Front-wheel drive shaft, four-wheel drive.
A Rzeppa joint uses _____ between the races to
allow angle changes.
A tripod CV joint uses three _____, which are separated from the spider by needle bearings.
All wheel bearings are known as what kind of
bearings?
Chapter 12
Driveline and Wheel Components
13. All wheel bearings have a series of _____ elements
between inner and outer _____.
14. A tapered roller bearing always has a threaded nut,
which is used to adjust _____.
15. What lubricates the wheel bearings on a solid rear
axle?
16. Tires perform two jobs. What are they?
17. Nylon, rayon, polyester, and fiberglass are used to
make tire _____.
18. The letters LT at the front of a tire rating indicate that
the tire is intended for use on a(n) _____ _____.
19. The number 14 at the end of a tire rating indicates
the _____ size.
20. Wheel studs are usually _____ into the hub or axle
flange.
ASE-Type Questions—Chapter 12
1. Technician A says that front-wheel drive vehicles
always have four CV joints on the front axles.
Technician B says that front-wheel drive vehicles
always have transfer shafts. Who is right?
(A) A only.
(B) B only.
(C) Both A and B.
(D) Neither A nor B.
2. Why are some CV joints called plunging joints?
(A) They allow the axle shaft to move parallel to the
vehicles centerline.
(B) They allow the axle shaft to change length.
(C) They prevent grease loss.
(D) There is no reason.
3. Technician A says that CV boots keep CV joint
grease from flying out of the joint as it turns.
Technician B says that CV joints can be lubricated
with any kind of quality EP grease. Who is right?
(A) A only.
(B) B only.
(C) Both A and B.
(D) Neither A nor B.
4. Which of the following flexible joints is the most
likely to be equipped with grease fittings?
(A) Tripod CV joint.
(B) Rzeppa CV joint.
(C) Plunging CV joint.
(D) Cross-and-roller U-joint.
5. All of the following statements about bearing preload
are true except:
(A) preload is how tightly the rolling elements and
races fit together after all vehicle weight is placed
on the bearing.
269
(B) too little preload will damage the bearing
because of vibration.
(C) too little preload intensifies the effect of shock
loads.
(D) too much preload will create unnecessary friction and heat.
6. EP lubricant is a type of _____.
(A) hypoid oil
(B) gear oil
(C) lithium grease
(D) long fiber grease
7. Technician A says that the purpose of the garter
spring is to hold the lip of a seal to the shaft.
Technician B says that the purpose of the garter
spring is to create an oil film between the shaft and
lip. Who is right?
(A) A only.
(B) B only.
(C) Both A and B.
(D) Neither A nor B.
8. All of the following statements about tire construction are true except:
(A) the cords in radial tire plies cross the centerline
of the tire at a right angle to the tread.
(B) belts are installed directly under the tire tread.
(C) tire cords are made of a combination of natural
rubber and neoprene.
(D) some belts are made of steel.
9. Which of the following is NOT a common rim size?
(A) 12 inches.
(B) 13 Inches.
(C) 14 inches.
(D) 15 inches.
10. The tapered areas of the lug nut and wheel mounting
holes help to _____ the wheel rim and tire.
(A) balance
(B) center
(C) cool
(D) seal