CHAPTER 15 Drive Axle Shafts and CV Joints

Describe how CV joints work. OBJECTIVES After studying Chapter 15, the reader will be able to: Prepare for ASE Suspension and Steering (A4) certification test content area “C” (Related Suspension and Steering Service). Name driveshaft and U-joint parts, and describe their function and operation. Describe how CV joints work. Explain how the working angles of the U-joints are determined. List the various types of CV joints and their applications.

KEY TERMS Cardan joints Center support bearing CV joint boot CV joints Double-Cardan joints Drive axle shaft Driveshaft Fixed joint Half shaft Plunge joint Propeller shaft Rzeppa joint Spider Trunnions Universal joints

INTRODUCTION A drive axle shaft transmits engine torque from the transmission or transaxle (if front wheel drive) to the rear axle assembly or drive wheels. Driveshaft is the term used by the Society of Automotive Engineers (SAE) to describe the shaft between the transmission and the rear axle assembly on a rear-wheel-drive vehicle. General Motors and some other manufacturers use the term propeller shaft or prop shaft to describe this same part.

INTRODUCTION FIGURE 15–1 Typical rear-wheel-drive powertrain arrangement. The engine is mounted longitudinal (lengthwise).

INTRODUCTION FIGURE 15–2 Typical front-wheel-drive powertrain arrangement. The engine is usually mounted transversely (sideways).

INTRODUCTION FIGURE 15–3 Typical driveshaft (also called a propeller shaft). The drivershaft transfers engine power from the transmission to the differential.

DRIVESHAFT DESIGN Most driveshafts are constructed of hollow steel tubing. The forces are transmitted through the surface of the driveshaft tubing. The surface is therefore in tension, and cracks can develop on the outside surface of the driveshaft due to metal fatigue. Driveshaft tubing can bend and, if dented, can collapse. A dented driveshaft should be replaced and no attempt should be made to repair the dent.

DRIVESHAFT DESIGN FIGURE 15–4 This driveshaft failed because it had a slight dent caused by a rock. When engine torque was applied, the driveshaft collapsed, twisted, and then broke.

DRIVESHAFT DESIGN FIGURE 15–5 A center support bearing is used on many vehicles with long driveshafts.

DRIVESHAFT DESIGN FIGURE 15–6 Some driveshafts use rubber between an inner and outer housing to absorb vibrations and shocks to the driveline.

Driveshaft balance should be within 0.5% of the driveshaft weight. All driveshafts are balanced. Generally, any driveshaft whose rotational speed is greater than 1000 RPM must be balanced. Driveshaft balance should be within 0.5% of the driveshaft weight. (This is one of the biggest reasons why aluminum or composite driveshafts can be longer because of their light weight.)

DRIVESHAFT BALANCE Driveshafts are often not available by make, model, and year of the vehicle. There are too many variations at the factory, such as transmission type, differential, or U-joint type. To get a replacement driveshaft, it is usually necessary to know the series of U-joints (type or style of U-joint) and the center-tocenter distance between the U-joints.

U-JOINT DESIGN AND OPERATION Universal joints (U-joints) are used at both ends of a driveshaft. U-joints allow the wheels and the rear axle to move up and down, remain flexible, and still transfer torque to the drive wheels. A simple universal joint can be made from two Y-shaped yokes connected by a crossmember called a cross or spider. The four arms of the cross are called trunnions.

U-JOINT DESIGN AND OPERATION FIGURE 15–7 A simple universal joint (U-joint).

U-JOINT DESIGN AND OPERATION FIGURE 15–8 How the speed difference on the output of a typical U-joint varies with the speed and the angle of the U-joint. At the bottom of the chart, the input speed is a constant 1000 RPM, while the output speed varies from 900 RPM to 1100 RPM when the angle difference in the joint is only 10°. At the top part of the chart, the input speed is a constant 1000 RPM, yet the output speed varies from 700 to 1200 RPM when the angle difference in the joint is changed to 30°. (Courtesy of Dana Corporation)

U-JOINT DESIGN AND OPERATION FIGURE 15–9 The joint angle is the difference between the angles of the joint. (Courtesy of Dana Corporation)

U-JOINT DESIGN AND OPERATION ACCEPTABLE WORKING ANGLES Universal joints used in a typical driveshaft should have a working angle of 1/2 to 3 degrees. FIGURE 15–10 The angle of this rear Cardan U-joint is noticeable.

CONSTANT VELOCITY JOINTS Constant velocity joints, commonly called CV joints, are designed to rotate without changing speed. Regular U-joints are usually designed to work up to 12 degrees of angularity. If two Cardan-style U-joints are joined together, the angle at which this double-Cardan joint can function is about 18 to 20 degrees. FIGURE 15–11 A double-Cardan U-joint.

CONSTANT VELOCITY JOINTS FIGURE 15–12 A constant velocity (CV) joint can operate at high angles without a change in velocity (speed) because the joint design results in equal angles between input and output.

What Is a 1350-Series U-Joint? Most universal joints are available in sizes to best match the torque that they transmit. The larger the U-joint, the higher the amount of torque. Most U-joints are sized and rated by series numbers. See the accompanying chart for series numbers and sizes.

What Is a 1350-Series U-Joint?

CONSTANT VELOCITY JOINTS OUTER CV JOINTS The Rzeppa-type CV joint is most commonly used as an outer joint on most front-wheel-drive vehicles. The outer joint must do the following: Allow up to 40 degrees or more of movement to allow the front wheels to turn Allow the front wheels to move up and down through normal suspension travel in order to provide a smooth ride over rough surfaces Be able to transmit engine torque to drive the front wheels

CONSTANT VELOCITY JOINTS OUTER CV JOINTS FIGURE 15–13 A Rzeppa fixed joint. This type of CV joint is commonly used at the wheel side of the drive axle shaft. This joint can operate at high angles to compensate for suspension travel and steering angle changes. (Courtesy of Dana Corporation)

CONSTANT VELOCITY JOINTS OUTER CV JOINTS FIGURE 15–14 The protective CV joint boot has been torn away on this vehicle and all of the grease has been thrown outward onto the brake and suspension parts. The driver of this vehicle noticed a “clicking” noise, especially when turning.

CONSTANT VELOCITY JOINTS OUTER CV JOINTS FIGURE 15–15 A tripod fixed joint. This type of joint is found on some Japanese vehicles. If the joint wears out, it is to be replaced with an entire drive axle shaft assembly.

CONSTANT VELOCITY JOINTS INNER CV JOINTS Inner CV joints attach the output of the transaxle to the drive axle shaft. Inner CV joints are therefore inboard, or toward the center of the vehicle. Inner CV joints have to be able to perform two very important movements: Allow the drive axle shaft to move up and down as the wheels travel over bumps. Allow the drive axle shaft to change length as required during vehicle suspension travel movements. CV joints are also called plunge joints.

CONSTANT VELOCITY JOINTS INNER CV JOINTS FIGURE 15–16 The fixed outer joint is required to move in all directions because the wheels must turn for steering as well as move up and down during suspension movement. The inner joint has to be able to not only move up and down but also plunge in and out as the suspension moves up and down. (Courtesy of Dana Corporation)

CONSTANT VELOCITY JOINTS DRIVE AXLE SHAFTS Unequal-length drive axle shafts (also called half shafts) result in unequal drive axle shaft angles to the front drive wheels.

CONSTANT VELOCITY JOINTS DRIVE AXLE SHAFTS FIGURE 15–17 Unequal-length driveshafts result in unequal drive axle shaft angles to the front drive wheels. This unequal angle side-to-side often results in a steering of the vehicle during acceleration called torque steer. By using an intermediate shaft, both drive axles are the same angle and the torque steer effect is reduced. (Courtesy of Dana Corporation)

What Is That Weight for on the Drive Axle Shaft? Some drive axle shafts are equipped with what looks like a balance weight. It is actually a dampener weight used to dampen out certain drive line vibrations. The weight is not used on all vehicles and may or may not appear on the same vehicle depending on engine, transmission, and other options. The service technician should always try to replace a defective or worn drive axle shaft with the exact replacement. When replacing an entire drive axle shaft, the technician should always follow the manufacturer’s instructions regarding either transferring or not transferring the weight to the new shaft.

What Is That Weight for on the Drive Axle Shaft? FIGURE 15–18 A typical drive axle shaft with dampener weight.

CONSTANT VELOCITY JOINTS DRIVE AXLE SHAFTS Typical types of inner CV joints that are designed to move axially, or plunge, include the following: Tripod Cross groove Double offset CV joints are also used in rear-wheel-drive vehicles and in many four-wheel-drive vehicles.

CONSTANT VELOCITY JOINTS DRIVE AXLE SHAFTS FIGURE 15–19 A tripod joint is also called a tripot, tripode, or tulip design. (Courtesy of Dana Corporation)

CONSTANT VELOCITY JOINTS DRIVE AXLE SHAFTS FIGURE 15–20 A cross-groove plunge joint is used on many German front-wheel-drive vehicles and as both inner and outer joints on the rear of vehicles that use an independent-type rear suspension. (Courtesy of Dana Corporation)

CONSTANT VELOCITY JOINTS DRIVE AXLE SHAFTS FIGURE 15–21 Double-offset ball-type plunge joint. (Courtesy of Dana Corporation)

CONSTANT VELOCITY JOINTS CV JOINT BOOT MATERIALS The pliable boot surrounding the CV joint, or CV joint boot, must be able to remain flexible under all weather conditions and still be strong enough to avoid being punctured by road debris. There are four basic types of boot materials used over CV joints: Natural rubber (black) Silicone rubber (gray) Hard thermoplastic (black) Urethane (usually blue)

CONSTANT VELOCITY JOINTS CV JOINT BOOT MATERIALS FIGURE 15–22 Getting the correct boot kit or parts from the parts store is more difficult on many Chrysler front-wheel-drive vehicles because Chrysler has used four different manufacturers for its axle shaft assemblies. (Courtesy of Dana Corporation)

CONSTANT VELOCITY JOINTS CV JOINT GREASE CV joints require special greases. Grease is an oil with thickening agents. Greases are named for the thickening agents used. Most CV joint grease is molybdenum-disulfide-type grease, commonly referred to as moly grease.

SUMMARY The driveshaft of a rear-wheel-drive vehicle transmits engine torque from the transmission to the differential. Driveshaft length is usually limited to about 65 inches due to balancing considerations unless a two-piece or a composite material shaft is used. Universal joints (U-joints) allow the driveshaft to transmit engine torque while the suspension and the rear axle assembly are moving up and down during normal driving conditions.

SUMMARY Acceptable working angles for a Cardan-type U-joint fall within 1/2 to 3 degrees. Some angle is necessary to cause the roller bearings to rotate; a working angle of greater than 3 degrees can lead to driveline vibrations. Constant velocity (CV) joints are used on all front-wheeldrive vehicles and many four-wheel-drive vehicles to provide a smooth transmission of torque to the drive wheels regardless of angularity of the wheel or joint. Outer or fixed CV joints commonly use a Rzeppa design, while inner CV joints are the plunging or tripod type.

REVIEW QUESTIONS Explain why Cardan-type U-joints on a driveshaft must be within 1/2-degree working angles. What makes a constant velocity joint able to transmit engine torque through an angle at a constant velocity? What type of grease must be used in CV joints?

CHAPTER QUIZ 1. The name most often used to describe the universal joints on a conventional rear-wheel-drive vehicle driveshaft is ________. Trunnion Cardan CV Spider

CHAPTER QUIZ 2. A rear-wheel-drive vehicle shudders or vibrates when first accelerating from a stop. The vibration is less noticeable at higher speeds. The most likely cause is ________. Driveshaft unbalance Excessive U-joint working angles Unequal U-joint working angles Brinelling of the U-joint

3. All driveshafts are balanced. CHAPTER QUIZ 3. All driveshafts are balanced. True False

CHAPTER QUIZ 4. The maximum difference between the front and rear working angle of a driveshaft is ________. 1/4 degree 1/2 degree 1 degree 3 degrees

5. Which series U-joint has the greatest torque capacity? CHAPTER QUIZ 5. Which series U-joint has the greatest torque capacity? 1260 1310 1350 1480

CHAPTER QUIZ 6. Two technicians are discussing torque steer on a front-wheel-drive vehicle. Technician A says that equal length drive axle shafts help reduce torque steer. Technician B says that equal drive axle shaft angles help reduce torque steer. Which technician is correct? Technician A only Technician B only Both Technicians A and B Neither Technician A nor B

CHAPTER QUIZ 7. The outer CV joints used on front-wheel-drive vehicles are ________. Fixed type Plunge type

8. The proper grease to use with a CV joint is ________. CHAPTER QUIZ 8. The proper grease to use with a CV joint is ________. Black chassis grease Dark blue EP grease Red moly grease The grease that is supplied with the boot kit

9. Drive axle shafts are also called ________. CHAPTER QUIZ 9. Drive axle shafts are also called ________. Double-Cardan shafts Half shafts Driveshafts Propeller shafts

CHAPTER QUIZ 10. Two technicians are discussing a dented driveshaft. Technician A says that it should be repaired. Technician B says it should be replaced. Which technician is correct? Technician A only Technician B only Both Technicians A and B Neither Technician A nor B