Driveline and Wheel Components

Transcription

1 This sample chapter is for review purposes only. Copyright The Goodheart-Willcox Co., Inc. All rights reserved. Chapter 12 Driveline and Wheel Components After studying this chapter, you will be able to: Identify types of drive axles and drive s. 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 s. Identify types of wheel s. Match axle types to 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 Drive Yokes Constant velocity joints Universal joint Cross-and-roller joints Antifriction s Ball s Straight roller s Tapered roller s Wheel hub Axle flange Wheel rims Radial tires Bias tires Tire ratings Section width 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 251

2 252 Auto Suspension and Steering Chapter 12 Driveline and Wheel Components 253 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. Drive plane Cage Inner race Figure Typical front-wheel drive axle. Intermediate Drive Shafts All rear-wheel drive vehicles use a drive to transfer engine power from the transmission to the rear axle. Drive s 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. Four-wheel drive vehicles have a front drive that directs power from the four-wheel drive transfer case to the front axle, Figure Brake backing plate Rear axle housing Some drive s are two-piece types, Figure Two-piece drive s are usually used on large trucks, where a single drive would be overstressed and break, and on some luxury cars, where any vibration would be objectionable. When a two-piece drive 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 C-clip lock Driveline Components Driveline components consist of the drive axles and s, 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 s that connect the transaxle output s 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. Note that there are four CV joints, two on each axle. On a few vehicles, a transfer, or intermediate, is used between the transaxle and the CV on one side of the vehicle, Figure Use of a transfer allows a support to be placed midway between the transaxle and the wheel. This reduces vibration and strain on the CV axle components. Transfer s 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 A few high-performance or sports cars use an independent rear axle, with exposed drive s containing CV joints. The construction of these s is the same as those used on a front-wheel drive vehicle. Some older independent rear axle s use U-joints instead of CV joints. Solid Drive Axles Support CV axle Figure This front-wheel drive vehicle uses an intermediate. Study the layout. On most rear-wheel drive cars and trucks, the drive axles are solid steel s. The s extend from the differential gears to the wheel rims. Inside the axle housing, external splines on the axle s mate with internal splines on the differential gears. The s are enclosed in the rear axle housing and are supported by s. Solid axle s are held in place by one of two methods. One design locks the in place with an external retainer behind the brakes, while the other secures the with a C-lock located inside of the differential. Each design is shown in Figure s 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 s. To allow the vehicle to turn, the ends of the s are attached to the wheel through flexible joints, Figure Bearing retainer A Bearing Bearing retainer nut Axle B Ring gear Figure A A retainer is used to hold this axle in the axle housing. B A C-clip lock placed in a grooved slot on the end of this axle holds the in the housing. (General Motors & Dodge) Steering knuckle Tie rod Flexible joint Tie rod jam nut Figure A four-wheel drive front axle. (Chevrolet) Pitman arm Side gear Axle Steering stabilizer Connecting rod

3 254 Auto Suspension and Steering Chapter 12 Driveline and Wheel Components 255 Flexible joint Hollow tube Flexible joint Mounting flange Intermediate Adjusting nut Dust boot Bearing cap Figure This drive uses flexible joints on each end and is used on rear-wheel drive vehicles. (Mazda) Center support Propeller Front differential Transfer case changes, Figure To allow the drive to compensate for this change in length, a slip yoke is installed somewhere on the drive. The slip yoke consists of an internally splined yoke that slides into the external splines of a matching part, usually the output of the transmission. A typical slip yoke is shown in Figure Flexible Joints Front drive Axle The purpose of all flexible joints is the same: to allow the drive axle or drive 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 Bolt Retainer Retainer Bolt Figure A front drive used on a four-wheel drive vehicle. (Chevrolet) 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 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 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 s 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 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 shows the relationship between the internal parts and the drive axle of a typical Rzeppa joint. The ball s 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 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 Note that the spider is splined to the axle. Thin roller s called needle s are installed between the spider points and the trunnions. As the axle rotates, the spider is driven by the housing and drives the. If the angle between the two sides of the joint changes, the tripod can tilt to compensate. See Figure 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. Transmission Snap ring Dust deflector Nut Adjusting washer Universal joint Figure One type of two-piece drive. Note the center support. (Lexus) A B Transmission Transmission Universal joints Propeller Frame Propeller Frame Bolt Coil spring Bump Figure The drive (propeller ) must compensate for changes in drive angle. A Normal operating angle. B A bump forces the differential upward. The angle has changed, and drive is shorter. A slip yoke permits this change in length. Nut 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 Universal Joints Propeller Mounting bolt Differential The universal joint, or U-joint, is used on drive s. Sometimes U-joints are used on the transfer 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 s. The caps are attached to yokes on the drive and corresponding parts. As the drive turns through an angle, the cross twists within the caps. The needle s reduce friction and vibration. A typical U-joint is shown in Figure

4 256 Auto Suspension and Steering Chapter 12 Driveline and Wheel Components 257 Transmission Output Drive plane Cage Inner race Driven plane Outer race Boot clamp Boot clamp Boot Boot Boot clamp Boot clamp Clamp Boot Clamp Washer (2) Bolt (2) 68 N m (50 ft. lbs.) Propeller and center Clamp Propeller Drive Bisecting plane Driven Differential side Drive Wheel side Figure A cutaway of a rear drive showing the CV boots and clamps. (Lexus) Bearing cap Slip yoke Propeller Screw and washer Figure The balls in a Rzeppa joint operate in a bisecting plane between the angles of the axle s. 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 Cross Rear propeller Figure A two-piece drive showing the slip yoke. (Chrysler) Rear axle Grooves Needle rollers Trunnion Balls Spider C-clip Needle Brake rotor Wheel Strut Drive Constant velocity joint Intermediate Balls (6) Inner race Cage Outer race Housing Shaft (axle) Figure Exploded view of a tripod constant velocity joint. (AC Delco) Drive yoke Bearing cap Retaining clip Figure A Cardan universal joint. (Dodge) Hub Constant velocity joint Ball joint Ball Boot Damper Support Differential Figure 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 rotates through an angle. This causes the speed of the driven part of the drive to vary. See Figure 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. Elongated opening Figure 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. s at the ends of the 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. Wheel Components The following sections cover the components related to a vehicle s wheels. These components, which include the wheel hubs, s, rims, tires, and fasteners, are found on both driving and non-driving axles. Drive Housing Spider plane Spider Driven Figure Tripod joint operation. The tripod joint uses three balls on needle s to transmit torque between the spider (splined to the axle ) 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) Wheel Bearings The wheel s form a low-friction connection between the rotating wheels and the stationary vehicle. All wheel s are antifriction s. Antifriction s consist of three basic parts: the inner race, the rolling element, and the outer race. See Figure 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 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 temperature increases. Other parts of antifriction s include the cage, which keeps the individual rolling elements separated as they turn, and seals or shields, which keep lubricant in and dirt and water out.

5 258 Auto Suspension and Steering Chapter 12 Driveline and Wheel Components Speeds of driven for driving speed of 1000 RPM Wheel Bearing Design Wheel s must be carefully selected to deal with types of loads, maximum speed, where the will be used on the vehicle, and what the vehicle is used for. Overall 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 preload. Preload is the amount of pressure placed on the 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. Too little preload will cause the rolling elements to rock and vibrate, damaging the. 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. One revolution of propeller Acceleration 90 Deceleration 180 Acceleration 270 Deceleration 360 Conventional universal joint showing fluctuations Bearing Loads Constant velocity universal joint, no fluctuations Figure Speed fluctuation chart. As a universal joint turns, the angle formed by the cross changes. It never divides the angle equally between the two s, (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) Grease cap Inner race Cotter pin Nut lock Cage Roller Grease Outer race Hub Hub cavity Spindle Outer race Inner race Figure Cutaway of a roller and front hub used on a two-wheel drive truck. (Dodge) Any load on the tends to push the parts together. The resulting pressure increases friction and heat. There are two types of loads placed on wheel s: radial loads and axial loads. Radial loads are caused by the weight of the vehicle passing through the spindle or axle, through the and hub, and to the rim and tire. As the vehicle moves, rotation causes centrifugal force, which tends to make the rollers move outward. This combination of vehicle weight and centrifugal force produces a radial load. Radial loading occurs at a right angle to the and. This is shown in Figure D E C F B G LOAD A H L I K Ball Figure A radial-loaded ball. Ball A is carrying the greatest load, while balls E, F, G, H, and I are carrying the smallest load. (Federal-Mogul) J 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 s. See Figure Axial loads are sometimes called thrust loads. Axial loads are always parallel to the. Wheel Bearing Types All modern wheel s are antifriction types. Three types of antifriction s are used on late-model vehicles: ball s, straight roller s, and tapered roller s. The type of used varies with the weight placed on the, 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 s are used on the front axles of some frontwheel drive vehicles. Most of these applications use two ball assemblies. In some cases, two rows of s are contained in a single housing. A dual ball is shown in Figure In addition to splitting the weight, each can take axial loads in one direction. Pairing the ball s handles axial loads in both directions. Note in Figure the inner and outer races are designed to accept axial loads in opposite directions. Modern ball s have the balls and races in a single sealed unit. Preload is factory set and cannot be adjusted. Straight Roller Bearings Straight roller s, Figure 12-23, are used on the rear axles of many rear-wheel drive vehicles. Flat roller s can absorb radial loads, but they cannot handle Thrust load Housing Outer ring retained Shaft Inner ring retained Thrust load (axial) Shaft Figure Two roller applications illustrating axial (thrust) loading. Note that the thrust load is parallel to the or housing. (Federal-Mogul) Steering knuckle Axle hub nut Speed sensor rotor axial loads. Straight roller assemblies are self-contained units, and preload is not adjustable. On a few older cars, the axle serves as the inner race. Tapered Roller Bearings Double-row ball Disc Lug bolt Axle hub Figure A dual ball 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 s, hubs, etc. (Lexus) Tapered roller s 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 s, tapered roller s are installed in pairs to absorb sideways loads. See Figure On most tapered roller designs, the inner race, rollers, and cage are a single unit. The outer race is pressed into the hub.

6 262 Auto Suspension and Steering Chapter 12 Driveline and Wheel Components 263 Width Axle housing Axle housing Inside face Outside face Snap ring Axial clearance lip Inside face I.D. Free I.D. Shaft dia. Outside face I.D. Bore dia. O.D. Straight roller Oil seal Axle Leaf spring O-ring Rear brake Bearing retainer Axle flange Rear axle Brake drum Figure The brake drum mounts to the solid axle flange, which is forged as an integral part of the axle. (Toyota) Mounting holes Stamped bracket Lug nut Drum retaining screw Wheel cover Brake backing plate Lock bolt Tension spring Figure A cross-sectional view of one type of oil seal. (General Motors) 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 races. Note the relationship between the hub, the tapered roller s and the spindle in Figure 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 s. 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 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. 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. Brake drum Figure An oil seal pressed into the axle housing bore. Note that this axle uses straight roller s. (General Motors) Tapered roller Rim Construction Hub Tapered roller Spindle Figure This cross section shows the relationship between the hub, the tapered roller s, and the spindle. (Hyundai) In many cases, rims are made of stamped steel, Figure Parts of the rim are stamped into shape and then welded into a final form. The center section contains Spider (center section) Drop center section Rim Tire bead area Figure 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 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 shows a typical custom wheel. Figure 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) Figure This custom wheel is made of aluminum. (Nissan)

7 264 Auto Suspension and Steering Chapter 12 Driveline and Wheel Components 265 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 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 illustrates the three measurements of a rim. These measurements apply to both steel and custom wheels. Wheel Diameter Safety ridges Drop center Tire Flange Figure A safety rim holds the tire in place in the event of a blowout. (Chrysler) Flange height Tires 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. 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 Center section Lug bolt hole Tire Ratings Stabilizer belts Radial cord body plies Figure 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) 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 The letter P designates the tire as a passenger car tire, Figure 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 Low numbers indicate a wide, low tire. The larger the number, the taller the tire. P 205 / 70 R 15 95S Tire type P Passenger T Temporary LT Light truck Section width (millimeters) Etc. Aspect ratio (Section height) (Section width) Section width Section height Load index Speed symbol Rim diameter (inches) Construction type R Radial B Bias Belted D Diagonal (bias) Figure 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 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. Rim width Bolt circle Rim Valve stem hole Figure 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) Tire sidewall Figure 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) 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

8 266 Auto Suspension and Steering Chapter 12 Driveline and Wheel Components 267 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 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 Wheel studs 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 Balance weight clip Balance weight Tire Valve stem Steel wheel Tapered head lug bolt Locking lug bolt Locking lug bolt key Cap Hub cap Figure 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 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 s, 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 Flat screw Lug nut Center cap Aluminum wheel Figure 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 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)

9 268 Auto Suspension and Steering Chapter 12 Driveline and Wheel Components 269 Independent drive axles are usually called CV axles. CV axles are solid steel s or hollow tubes that connect the transaxle output s to the wheels. There are always two CV axles on a front-wheel drive vehicle. Some frontwheel drive vehicles have a transfer 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 s that extend from the differential to the wheel hubs. Some four-wheel drive vehicles have a solid front axle. All front-engine, rearwheel drive vehicles use a drive between the transmission and rear axle. Some drive s are two piece types. Four-wheel drive vehicles also have a front drive. 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 speed. There are two kinds of CV joints, the Rzeppa joint and the tripod joint. The Rzeppa joint consists of a set of ball s inside of two sets of races. The ball s 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 s. 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 s. U-joints consist of a four-point cross and caps that turn on needle s. The cross can twist as it rotates to compensate for angle changes. U-joints are used when the angle change between rotating parts is not too great. Wheel s form a low-friction connection between the wheels and the vehicle. All wheel s are antifriction s consisting of three basic parts: the inner race, the rolling element, and the outer race. There are two kinds of 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 s are the ball, the flat roller, and the tapered roller. Ball s are found on the front axles of many front-wheel drive vehicles. The balls and races are in a single sealed unit. Straight roller s are often used on the rear axles of rear-wheel drive vehicles. Tapered roller s are used in front and rear axles and are always installed in pairs to absorb sideways loads. Tapered roller preload is adjustable. Most tapered wheel s are packed with wheel grease, which must be periodically renewed. Some ball s and straight roller wheel s are greased 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 lubricants are wheel greases and gear oils. Most wheel s are lubricated by grease. Some solid rear axle wheel s are lubricated with gear oil. The wheel s on most modern vehicles call for EP lithium grease. Wheel s 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 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 Why are front-wheel drive independent axles called CV axles? 2. While most CV axles are steel s, a few are to reduce weight. 3. A four-wheel drive vehicle has two. 4. What is the purpose of a drive slip yoke? Matching Match the drive axle with the type of flexible joint. 5. Independent front axle. a. CV joint. 6. Independent rear axle. b. U-joint. 7. Solid rear axle. c. No flexible joint. 8. Rear-wheel drive. 9. Front-wheel drive, four-wheel drive. 10. A Rzeppa joint uses between the races to allow angle changes. 11. A tripod CV joint uses three, which are separated from the spider by needle s. 12. All wheel s are known as what kind of s? 13. All wheel s have a series of elements between inner and outer. 14. A tapered roller always has a threaded nut, which is used to adjust. 15. What lubricates the wheel s 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 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 s. 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 to move parallel to the vehicles centerline. (B) They allow the axle 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 preload are true except: (A) preload is how tightly the rolling elements and races fit together after all vehicle weight is placed on the. (B) too little preload will damage the 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. Technician B says that the purpose of the garter spring is to create an oil film between the 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