Drive shaft for cars

A drive shaft, driveshaft, driving shaft, tailshaft (Australian English), propeller shaft (prop shaft), or Cardan shaft (after Girolamo Cardano) is a component for transmitting mechanical power and torque and rotation, usually used to connect other components of a drivetrain that cannot be connected directly because of distance or the need to allow for relative movement between them. As torque carriers, drive shafts are subject to torsion and shear stress, equivalent to the difference between the input torque and the load. They must therefore be strong enough to bear the stress, while avoiding too much additional weight as that would in turn increase their inertia.

start

• 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.

After studying Chapter 96, the reader should be

able to:

OBJECTIVES:

• Explain how the working angles of the

U-joints are determined.

• List the various types of CV joints and their

applications.

After studying Chapter 96, the reader should be

able to:

OBJECTIVES:

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

KEY TERMS:

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.

The SAE term will be used throughout this textbook.

A drive axle shaft transmits engine torque from the transmission or

transaxle (front wheel drive) to the rear axle assembly or

drive wheels

Figure 96–1 Typical rear-wheel-drive power train arrangement The engine is mounted longitudinal (lengthwise)

Figure 96–2 Typical front-wheel-drive power train arrangement The engine is usually mounted

transversely (sideways)

Continued

Figure 96–3 Typical driveshaft (also called a

propeller shaft) The drivershaft transfers

engine power from the transmission to the

differential.

A typical driveshaft is a hollow steel tube

A splined end yoke is welded onto one end that slips over the splines of the output shaft

of the transmission An end yoke is welded onto the other end of the driveshaft Some driveshafts use a center support bearing.

DRIVESHAFT DESIGN

Most driveshafts are constructed of hollow steel tubing The forces

are transmitted through the surface of the driveshaft tubing The

surface is 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

Continued

Figure 96–4 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

Most rear-wheel-drive cars and light trucks use a one- or two-piece driveshaft A steel tube driveshaft has a

maximum length

of about 65 in (165 cm) Beyond this length, a center support bearing, called a steady bearing or hanger

bearing, must be used.

Some vehicle manufacturers use aluminum driveshafts; these can be as long as 90 in (230 cm) with no

problem Many extended-cab pickup trucks and certain vans use aluminum driveshafts to eliminate the need

(and expense) of a center support bearing.

Composite-material driveshafts are also used in some vehicles These carbon-fiber-plastic driveshafts are very

strong yet lightweight, and canbe made in extended lengths without the need for a center support bearing.

See Figure 96–5.

Figure 96–5 A center support bearing is used on many vehicles with long driveshafts.

Figure 96–6 Some driveshafts use rubber between an inner and outer housing to absorb

vibrations and shocks to the driveline.

To dampen driveshaft noise, it is common to line the inside of the hollow driveshaft with cardboard This helps eliminate the tinny

sound whenever shifting between drive and reverse in a vehicle

equipped with an automatic transmission

DRIVESHAFT BALANCE

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 reason why aluminum or composite

driveshafts can be longer because of their light weight.)

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-to-center distance between the U-joints.

Continued

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 A similar design

is the common U-joint used with a

socket wrench set.

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.

Figure 96–7 A simple universal joint (U-joint).

Most U-joints are called cross-yoke joints or Cardan joints, named for a sixteenth-century

Italian mathematician who worked with objects that moved freely in any direction.

Torque from the engine is transferred through the U-joint The engine drives the U-joint at

a constant speed, but the output speed of the U-joint changes because of the angle of the

joint The speed changes twice per revolution.

See Figure 96–8.

Continued

The greater the angle, the greater the change in speed (velocity).

Figure 96–8 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°

If one U-joint were used in a driveline, change in speed of the

driven side (output end) would generate vibrations in the driveline.

To help reduce vibration, another U-joint is used at the other end of the driveshaft If the angles of both joints are nearly equal, the

acceleration and deceleration of one joint is offset by the alternate deceleration and acceleration of the second joint

It is very important that both U-joints operate at about the same angle to prevent excessive driveline vibration

Figure 96–9 The joint angle

is the difference between

the angles of the joint

(Courtesy of Dana

Corporation)

Acceptable Working Angles Universal joints used in a typical driveshaft should have a working

angle of 1/2 to 3 degrees The working angle is the angle between the driving and driven end

of the joint.

If the driveshaft is perfectly straight (0-degree working angle), then the needle bearings inside the

bearing cap are not revolving because there is no force (no difference in angles) to cause the rotation

of the needle bearings.

If the needle bearings do not rotate, they can exert a constant pressure in one place and damage the

bearing journal

See Figure 96–10

Figure 96–10 The angle of

this rear U-joint is

noticeable.

If a two-piece driveshaft is used, one U-joint (usually the front)

runs at a small working angle of about 1/2 degree, just enough to

keep the needle bearings rotating The other two U-joints (from the center support bearing and rear U-joint at the differential) operate

at typical working angles of a single-piece driveshaft.

Continued

If the U-joint working angles differ by more than 1/2 degree, a vibration is usually

produced that is torque sensitive As the vehicle is first accelerated from a stop, engine

torque can create unequal driveshaft angles by causing the differential to rotate on its

suspension support arms.

This vibration is most noticeable when the vehicle is heavily loaded and being accelerated

at lower speeds The vibration usually diminishes at higher speeds due to decrease in the

torque being transmitted.

If the driveshaft angles are excessive (over 3 degrees), a vibration is usually produced that increases as the speed of the vehicle (and driveshaft) increases.

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

Continued

Figure 96–11 A double-Cardan U-joint

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.

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

Double-Cardan U-joints were first used on large rear-wheel-drive vehicles to help reduce

drive-line-induced vibrations, especially when the rear of the vehicle was fully loaded and driveshaft

angles were at their greatest.

As long as a U-joint (either single or double Cardan) operates in a straight line, the driven shaft

will rotate at the same constant speed (velocity) as the driving shaft As the angle increases, the

driven shaft speed or velocity varies during each revolution.

This produces pulsations and a noticeable vibration or surge.

The higher the shaft speed and the greater the angle of the joint,

the greater the pulsations.

Continued

NOTE: Many four-wheel-drive light trucks use standard Cardan-style joints in the front drive axles If the front wheels are turned sharply and

U-then accelerated, the entire truck often shakes due to the pulsations created

by the speed variations through the U-joints This vibration is normal and cannot be corrected It is characteristic of this type of

design and is usually not noticeable in normal driving.

NOTE: Many four-wheel-drive light trucks use standard Cardan-style joints in the front drive axles If the front wheels are turned sharply and

U-then accelerated, the entire truck often shakes due to the pulsations created

by the speed variations through the U-joints This vibration is normal and cannot be corrected It is characteristic of this type of

design and is usually not noticeable in normal driving.

The first constant velocity joint was designed by AlfredH Rzeppa (pronounced shep’pa) in the mid-1920s

The Rzeppa joint transfers torque through six round balls that are held in position midway between the

two shafts This design causes the angle between the shafts to be equally split regardless of the angle

Because the angle is always split equally, torque is transferred equally without the change in speed

(velocity) that occurs in Cardan-style U-joints.

This style of joint results in a constant velocity between driving and driven shafts It can also function at

angles greater than

simple U-joints can, up to 40 degrees.

See Figure 96–12

Continued

Figure 96–12 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

NOTE: CV joints are also called LOBRÖ joints, the brand name of an

original equipment manufacturer.

NOTE: CV joints are also called LOBRÖ joints, the brand name of an

original equipment manufacturer.

Outer CV Joints The Rzeppa-type CV joint is most commonly

used as an outer joint on most front-wheel-drive vehicles See

Figure 96–13

Continued

The outer joint must do the following:

1 Allow up to 40 degrees or more of movement to allow the

front wheels to turn

2 Allow the front wheels to move up and down through normal

suspension travel in order to provide a smooth ride over rough surfaces

3 Be able to transmit engine torque to drive the front wheels

See Figure 96–13

Figure 96–13 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)

Outer CV joints are called fixed joints The outer joints are also

attached to the front wheels They are more likely to suffer from

road hazards that often can cut through the protective outer

flexible boot.

See Figure 96–14.

Once this boot has been split open, the special high-quality grease

is thrown out and contaminants such as dirt and water can enter

Some joints cannot be replaced individually if worn.

See Figure 96–15.

Continued

Figure 96–14 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.

Figure 96–15 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

Figure 96–16 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)

axle shaft Inner CV joints are inboard, or toward the center of

the vehicle.

Continued

NOTE: Research has shown that in as few as eight hours of driving time,

a CV joint can be destroyed by dirt, moisture, and a lack of lubrication if

the boot is torn The tech should warn the owner as to the cost involved in replacing the CV joint itself whenever a torn CV boot is found.

NOTE: Research has shown that in as few as eight hours of driving time,

a CV joint can be destroyed by dirt, moisture, and a lack of lubrication if

the boot is torn The tech should warn the owner as to the cost involved in replacing the CV joint itself whenever a torn CV boot is found.

Inner CV joints have to be able to perform two very important movements:

1 Allow the drive axle shaft to move up and down as the

wheels travel over bumps.

2 Allow the drive axle shaft to change length as required

during vehicle suspension travel movements (lengthening

and shortening as the vehicle moves up and down; same as

the slip yoke on a conventional RWD driveshaft) CV joints

are also called plunge 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 This unequal angle often results in a pull on the

steering wheel during acceleration.

This pulling to one side during acceleration due to unequal engine torque being applied to the

front drive wheels is called torque steer.

To help reduce the effect of torque steer, some vehicles are manufactured with an intermediate

shaft that results in equal drive axle shaft angles Both designs use fixed outer CV joints with

plunge-type inner joints.

See Figure 96–17.

Continued

Figure 96–17 Unequal-length driveshafts result in unequal drive axle shaft ngles 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)