9781284145267 Auto Drivetrain & Transmissions, Chapters 6 and 7

MASTER AUTOMOTIVE TECHNICIAN SERIES

SAMPLE CHAPTERS 6 and 7

Automotive Drivetrain & Manual Transmissions

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Education Foundation

Keith Santini Kirk VanGelder

CDX MASTER AUTOMOTIVE TECHNICIAN SERIES NEW

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CONTENTS

Chapter 1

Strategy-Based Diagnostics

Chapter 2

Vehicle, Customer, and Service Information

Chapter 3

Manual Transmission and Driveline Fundamentals

Chapter 4

Bearings, Seals, Gaskets and Lubricants

Chapter 5

Drive shafts and Half-shafts

Go to

Chapter 6

Clutch Theory and Operation

Go to

Chapter 7

Clutch System Service

Chapter 8

Axles and Open Differentials

Chapter 9

Mechanical Limited Slip Differentials

Chapter 10

Driveline Sensors and Testing

Chapter 11

Electronic Limited Slip Systems

Chapter 12

Manual Transmission Theory and Operation

Chapter 13

Manual Transmission Repair

Chapter 14

Manual Transaxle Repair

Chapter 15

Dual Clutch Transmissions

Chapter 16

4wd Theory and Operation

Chapter 17

Transfer Cases

Chapter 18

4wd Maintenance and Repair

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CHAPTER 6

Clutch Theory and Operation Learning Objectives after reading this chapter, you will be able to: ■ ■

6-01 Explain the purpose and function of a clutch.

6-02 Identify the basic components in a clutch system.

■

6-03 Identify the various types of clutch operating mechanisms.

You Are the Automotive Technician a customer brings in their Subaru that is used for racing. the vehicle needs a new clutch, and the customer wants your recommendation about what to do to help prevent another clutch failure. Before you can give your recommendation, you will need to do some research about the availability of certain aftermarket parts.

1.

2.

3.

4.

are there any factory clutch versions that are heavier duty than the one that came in this vehicle?

Is there an aftermarket dual clutch setup available for this vehicle? are there clutches available with a different coefficient of friction? are there pressure plates with greater holding power available for this vehicle?

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Chapter 6 Clutch Theory and Operation

▶▶ Introduction

Bell Housing Engine

Crankshaft

Clutch Assembly

Transmission

Transmission Input Shaft Flywheel

The clutch is a mechanical device located in the bell housing, which sits between the engine and the transmission. The clutch allows the driver to engage, and disengage, the engine from the transmission while operating the vehicle. The driver controls the operation of the clutch with their foot through the clutch pedal. The clutch has a series of components that help to make driving an interactive experience, allowing the driver to control the shifting of gears in the vehicle. An automatic transmission does not use a manual clutch, so the driver’s control over transmission operation is limited to putting the vehicle into or out of drive (FIGURE 6-1).

▶▶ Clutch

Principles

The purpose of the clutch is to allow the driver to disconnect, and progressively connect, the engine to the transmission by progressively transmitting torque FIGURE 6-1 An illustration of a basic clutch, located between the engine and transmission. from the engine to the transmission. The clutch also allows the driver to disconnect the transmission from the engine to shift between gears while accelerating or decelerating the vehicle. The clutch is typically operated using a foot pedal 6-01 Explain the purpose and function of a clutch. located next to the brake pedal (FIGURE 6-2).

Most clutches on automotive manual transmissions are dry clutches—unlike those on automatic transmissions, which are mostly wet clutches that run in a lubricating fluid. Dry clutches use the friction between the clutch surfaces to transmit torque from the engine to the transmission. The amount of torque a clutch can transmit depends on the amount of friction between the clutch disc and the mating surfaces of the flywheel and p ­ ressure plate.

This friction depends on four variables: the coefficient of friction of the clutch disc facings, the diameter of the clutch, the number of clutch discs in the clutch assembly, and the total spring force clamping the parts together. Coefficient of friction is a measurement of how much drag a particular material imparts as it moves across a surface (FIGURE 6-3).

Increasing the friction of the clutch disc increases its torque-carrying ability, but it also makes the clutch grab, which increases the difficulty of starting from a stop. IncreasFIGURE 6-2 A clutch pedal that is used to operate a traditional clutch. ing the diameter of the clutch gives it more leverage, which increases its torque capacity but also takes up more area.

Increasing the number of clutch discs increases torque capacity, but it is also a more complicated system, due to the extra parts. Increasing the spring force clamping the

A

B

FIGURE 6-3 Types of clutches. A. Dry clutch from a manual transmission. B. Wet clutch from an automatic transmission.

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Clutch Principles

153

parts together increases torque capacity, but it also requires more foot pressure in order to operate the clutch pedal. Manufacturers balance all of these factors when designing a clutch for a particular application. These considerations also come into play when the engine is modified to develop more horsepower. The clutch may need to be upgraded as well.

Input and Output Shaft Speed Because vehicles depend on shifting between various gears in order to be able to drive down the road at a variety of speeds, it is important to understand how the transmission input and output shaft speeds play a critical role in shifting. First, be aware that output shaft torque and speed can each be increased, but not at the same time. In low gear, the input shaft speed is relatively high, while the output shaft speed is relatively low. This results in an increase of torque from the output shaft. However, the speed of the output shaft (and the speed of the vehicle) is relatively low. This setup makes for good acceleration from a stop or while driving at slow speeds. As higher transmission gears are selected, the output shaft speed increases with each higher gear. However, the torque of the output shaft is also lessened with each higher gear, allowing the vehicle to travel at higher speeds without over-revving the engine, but with less torque.

The second role of the input and output shaft speeds can be observed during the actual shift. When transitioning from one gear to another, the relative speeds of the shafts must change to allow the gears to shift from one set to another. In order for a gear to be selected, at least one of the shafts must be able to turn freely in order to accommodate the required change in speed. The input shaft is able to connect to, and disconnect from, the engine’s flywheel through the operation of the clutch, thus allowing the input shaft’s speed to change during a shifting of the gears. Since the output shaft is connected directly to the wheels through the drivetrain components, it cannot be disconnected during a shift. This means that any time the vehicle is moving, the output shaft is turning. The faster the vehicle speed, the faster the rotation of the output shaft. This has an impact on shifting because the speeds of both shafts must be such that the individual gears can be selected. The clutch plays the role of engaging and disengaging the input shaft, so the input shaft speed can be changed as needed (FIGURE 6-4).

Transmission Output Shaft

Drive Shaft Final Drive FIGURE 6-4 The transmission output shaft turns with the wheels because they are directly connected.

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Chapter 6 Clutch Theory and Operation

▶▶ Clutch

Components

The main components of a clutch assembly are the flywheel, clutch disc, pressure plate, throw-out bearing clutch fork, and pilot bearing. The flywheel bolts onto the rear of the crankshaft, and the pressure plate bolts onto the flywheel. Most light-duty Clutch Cover Flywheel Pressure vehicles use a single-plate clutch disc with two friction facings attached to a Pressure Plate Plate central hub and splined to engage the transmission input shaft. The friction Assembly Friction Diaphragm Facings facings on the clutch disc are clamped between the flat surfaces of the engine Clutch Cable Spring Clutch Disc flywheel and the spring-loaded pressure plate. With engine rotation, the flyClutch wheel and pressure plate rotate together with the clutch disc. The flywheel and Clutch Fork Central Hub Pedal pressure plate are the drive unit, and the clutch disc is the driven unit. Engine torque is transferred from the flywheel and pressure plate through the friction facings of the driven clutch disc to the splines of the input shaft and into the Crankshaft transmission (FIGURE 6-5).

Throw-out Bearing Pushing the clutch pedal operates the release mechanism, which conPilot Transmission Input Shaft Bearing trols the flow of torque between the engine and the transmission. The release Splines mechanism acts by retracting the pressure plate against the force of its springs, Bolt thereby freeing the friction disc from its clamping action (FIGURE 6-6).

FIGURE 6-5 The components that make up the clutch Releasing the clutch pedal reapplies the clamping force and reconnects system for a light-duty vehicle. the engine and transmission, by firmly clamping the clutch disc between the pressure plate and the flywheel, allowing them to rotate as a unit.

Some vehicles will use a multidisc clutch. There are two different types of multidisc clutches. The first type uses several clutch discs to increase the holdRetracted Pressure Plate ing power of the clutch. These are often found in high-performance and racing Freed Clutch vehicles. The second type is a dual clutch transmission, which will be covered in (friction) detail in Chapter 15.

Disc 6-02 Identify the basic components in a clutch system.

Clutch Fork

Flywheel

Disengaged Depressed Transmission Clutch Input Shaft Pedal Throw-out Bearing FIGURE 6-6 Depressing the clutch pedal retracts

the pressure plate against the force of its springs and frees the friction disc.

Driven Unit Disengaged

Flywheel Drive Unit

Pressure The main purpose of the flywheel is to smooth out the power pulses from Plate the pistons during the power strokes. It also provides a friction surface for the clutch disc and a mounting surface for the pressure plate. The flywheel is quite heavy. It is usually made of cast iron so that it can store energy from each Clutch Pedal power pulse from the engine; it then uses that energy to keepDepressed the crankshaft turning through the intake, compression, and exhaust strokes. However, a heavy flywheel also has the effect of slowing the engine’s acceleration. A lighter flywheel does not smooth out the power pulses as effectively, but it works well Transmission Driven Unit Shaft on a drag-racing car, for example, because itInput allows the engine to accelerate (disengaged) faster (FIGURE 6-7).

Clutch Disc

Flywheel Pressure Plate

Driven Unit Disengaged

Driven Unit Engaged Drive Unit

Clutch Pedal Depressed

Transmission Input Shaft Clutch Disc

Driven Unit (disengaged)

A

Clutch Pedal Released B

Driven Unit Engaged FIGURE 6-7 Releasing the clutch pedal reapplies the clamping force and reconnects the engine and transmission, firmly clamping

them together and allowing them to rotate as a unit.

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Clutch Components

155

FIGURE 6-8 A flywheel

bolted to the rear of the crankshaft.

The flywheel is bolted to the rear of the crankshaft and allows the crankshaft to mate with the transmission via the clutch system. It also incorporates the flywheel ring gear, which enables the starter motor drive gear to crank the engine over. In most cases, the ring gear is made of hardened steel and is press fit onto the outer edge of the flywheel (FIGURE 6-8).

Types of Flywheels There are two main types of flywheels: the single, one-piece flywheel and the dual mass flywheel. The single, one-piece flywheel is by far the most common on light-duty vehicles, and it is what most people think of when they think of a flywheel. Its one-piece construction makes it simple, inexpensive, and reliable. It usually has a starter ring gear pressed onto its outer edge and a machined mating surface for the clutch disc. The center of the flywheel has machined holes for bolts to mount it firmly to the flywheel. In FIGURE 6-9 The bolt holes for a flywheel may be offset to prevent the flywheel from being installed incorrectly. some cases, the bolt pattern is designed so that it can be mounted in any position. In other cases, where the flywheel is used as the primary method of balancing the engine, it may have offset bolt holes so that it can be mounted in only one position on the crankshaft. Flywheels are generally not interchangeable even if they look similar (FIGURE 6-9).

Some flywheels are of the stepped style. In this design, the friction surface of the flywheel is recessed, whereas the outer diameter, against which the pressure plate is bolted, is raised. The purpose of this flywheel design is to reduce the overall weight of the vehicle. By making the outer edge of the flywheel thicker, the mass of the flywheel is moved farther out, resulting in greater centrifugal force. With a stepped flywheel, the manufacturer can obtain the same balancing result with a lighter flywheel, resulting in better fuel economy and performance (FIGURE 6-10).

The depth of the step is critical for the proper operation of the clutch assembly. If it is too deep, the clutch will slip or not engage. If it is too shallow, the clutch will be stiff and may not dis- FIGURE 6-10 A stepped flywheel for a Honda automobile. engage. Both stepped and flat flywheels can be resurfaced if the wear or defects are minor. Stepped flywheels are, however, more difficult to machine when resurfacing (FIGURE 6-11).

The dual mass flywheel improves the engine’s fuel economy by smoothing out the power pulses and focusing them in the direction of engine rotation. Its inner workings

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Chapter 6 Clutch Theory and Operation

FIGURE 6-12 A dual mass

flywheel removed from a BMW Z3.

FIGURE 6-11 Checking the depth of

the step after machining a flywheel.

Torsion Springs

Ring Gear

A

Cushion

help absorb engine vibrations, thus minimizing gear rattle and putting less strain on the drivetrain components. This also makes for smoother shifting. There are two basic types of dual mass flywheels (FIGURE 6-12). The first is composed of a primary and a secondary flywheel with a series of torsion springs and cushions. The second uses a planetary gear and torsion springs (FIGURE 6-13).

In the first type of dual mass flywheel, a friction ring is located between the inner and the outer flywheel, whose purpose is to allow the inner and the outer flywheel to slip. This feature is designed to alleviate any damage to the transmission when torque loads exceed the vehicle rating of the transmission. The friction ring is the weak spot in the system and can wear out if excessive engine torque loads are applied. This type of dual mass flywheel also has a center support bearing that carries the load between the inner and the outer flywheel and is fitted with damper springs to absorb shocks.

The second type of dual mass flywheel incorporates planetary gearing along with torsion springs. It is designed for engines with stronger vibrations at lower engine speeds.

Some manufacturers use this style for their high-performance vehicles to gain greater driving and shifting comfort. Because of the increased dampening effect at lower engine speeds, the engine can be idled at fewer revolutions per minute (rpm), which reduces fuel consumption slightly.

Primary Flywheel Torsion Springs

Secondary Flywheel

B

Planetary Gear

Ring Gear

Cushion

Primary Flywheel

Secondary Flywheel

FIGURE 6-13 There are two types of dual mass flywheels. A. The first is composed of a primary and secondary flywheel with a series

of torsion springs and cushions. B. The second uses a planetary gear and torsion springs.

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Clutch Components

Dual mass flywheels are most often fitted to light-duty diesel trucks with manual transmissions and to higher performance luxury vehicles. However, dual mass flywheels are now being used in economy-type vehicles to dampen vibrations in the drivetrain.

The function of the dual mass flywheel is to absorb torsional crankshaft vibrations, which are twisting forces created in opposite directions. A twisting force happens in one direction when a piston is on the compression stroke, and the opposite direction on the power stroke. This vibration is magnified in diesel engines, which have higher compression ratios than gasoline engines. By minimizing the torsional vibration, the dual mass flywheel eliminates any potential damage to the transmission gear teeth. If the dual mass flywheel was not used, the torsional vibration could cause increased wear or even cause the transmission gears to get chipped.

The dual mass flywheel construction relocates the light-duty torsional damper. In a one-piece flywheel, the damper is located on the clutch disc, and in the dual mass flywheel style, it is located on the engine flywheel. This repositioning and heavy-duty torsional damper dampens engine torsional vibrations much more effectively than is possible with standard clutch disc dampening technology. Light-duty torsional dampers will be covered later, in the Clutch Discs section.

157

▶▶TECHNICIAN TIP The author once had a customer bring her Corvette into the shop with a complaint about a knocking engine. When the author called the customer to provide an estimate to repair the vehicle, she was expecting to hear that the vehicle needed an engine. Rather, she was given an estimate for a new clutch and dual mass flywheel. The flywheel had failed and was knocking, much like an engine knock.

Pressure Plates The pressure plate provides the force to clamp the clutch disc between the pressure plate and the flywheel so that torque can be transmitted between those parts. The clamping force is generated by one or more very strong springs. When the driver pushes on the clutch pedal, the clutch pedal in turn pushes on the spring(s) in the pressure plate. Pushing the clutch pedal compresses the spring(s) and removes the clamping force from the clutch disc. Releasing the clutch pedal allows the spring(s) to apply their clamping force to the clutch disc again. Most automotive pressure plates are of the diaphragm spring style.

Diaphragm Pressure Plate In light-duty vehicles, the pressure plate is normally a diaphragm type and is serviced as an assembly, which means it is not designed to be disassembled and repaired. A diaphragm pressure plate consists of a pressed steel cover, a pressure plate with a machined flat surface, several spring steel drive straps, and the diaphragm spring. This diaphragm spring is inside the clutch cover on two fulcrum rings and held in place by rivets passing through the diaphragm. The pressure plate is connected to the cover by the spring steel drive straps, which are riveted to the cover at one end and to two or more projecting lugs on the plate at the other. Retraction clips hold the pressure plate in contact with the outer edge of the diaphragm. During clutch operation, the throw-out bearing pushes on the diaphragm levers. The diaphragm pivots on the fulcrum rings and pulls the outer edge of the diaphragm away from the flywheel. The retraction clips pull the pressure plate away from the clutch disc. Diaphragm clutches are known for their lighter feel when the clutch pedal is fully down, making them more comfortable to drive (FIGURE 6-14).

Coil Spring Pressure Plate The coil spring pressure plate uses coil springs to create the clamping pressure and uses release levers to release the clutch disc. Typically, three or four release levers are used, depending on whether the clutch is in a car or a truck. The release levers control the movement of the friction portion of the pressure plate. They pivot on the pedestals that are part of the pressure plate housing. When the release bearing pushes the levers toward the flywheel, they pivot and pull the friction portion

FIGURE 6-14 A light-duty diaphragm pressure plate that has been cut

away to show the internal components.

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Chapter 6 Clutch Theory and Operation

Flywheel

Clutch Plate

Pressure Plate

Friction facings

Release Lever

Coil Spring

FIGURE 6-15 The coil spring pressure plate uses coil springs to create

of the pressure plate back toward the driver, which then relinquishes its clamping pressure on the clutch disc. When the clutch pedal is released, the levers return to their rest position, the clamping force is restored to the clutch disc, torque is transmitted, and the vehicle moves forward (FIGURE 6-15).

An advantage of the coil spring pressure plate is that the more coil springs there are, the tighter the clamping force and torque capacity. The coil spring pressure plate can also be rebuilt.

One disadvantage is that if the clutch disc overheats, the springs can become weak, and then the clamping force will be compromised, causing the clutch to slip. This slippage causes more heat, which weakens the coil springs even further. Once a clutch starts slipping, it likely will need to be replaced very soon. Additional disadvantages are that the spring pressure is less evenly spaced on many coil spring pressure plates and that there are fewer release levers, which can cause uneven wear on the friction surface over time.

Semi-Centrifugal Pressure Plate

Additional clutch holding power can always be added by increasing the spring tension in the pressure plate. However, this also leads to a higher clutch pedal effort that results in driver fatigue.

Some aftermarket companies have created semi-centrifugal pressure plates.

These pressure plates have small weights located on the release levers or on the fingers of the diaphragm spring. The spring pressure holds the clutch at low speeds, and as the engine speed increases, the weights fly out due to centrifugal force. The force of these weights flying out creates additional holding power on the clutch disc. The advantage of this system is that the clutch pedal effort is not increased at all (FIGURE 6-16).

clamping pressure and uses release levers to release the clutch disc.

Clutch Disc The clutch disc is also called a driven center plate or a friction disc. The clutch disc provides the friction material needed to transmit engine torque from the flywheel and pressure plate to the input shaft of the transmission. On the clutch disc, the friction facings are riveted to waved spring steel segments, which are themselves riveted to a steel disc. The central alloy steel–splined hub is separate FIGURE 6-16 A semi-centrifugal pressure plate. from the steel disc. Drive is transmitted from the steel disc to the hub through heavy torsion coil springs or rubber blocks. This arrangement dampens torsional ▶▶TECHNICIAN TIP vibrations from the engine and absorbs shock loads imposed on the driveline by sudden Students often ask about the difference or violent clutch engagement. A molded friction washer between the hub and the spring between a Stage 1, Stage 2, and Stage 3 retaining plate also acts as a damper (FIGURE 6-17). clutch. The main differences are between Waved spring steel segments, sometimes called cushion springs, are located between the friction material and the tension on the friction facings. The cushion springs cause the facings to spread apart slightly when the springs. Students then all want to purthe clutch is disengaged and compress them as it is engaged. These waved springs allow a chase a Stage 3 clutch kit, and the author progressive application of the pressure plate clamping force as the waved springs are being warns them that the amount of pedal effort might increase dramatically. Several students have not observed the warning and a few months later are replacing the clutch a second time in the car they drive every day in Chicagoland stop-and-go traffic. A factory clutch is perfectly fine for a stock vehicle (if the driver knows how to drive a manual transmission correctly).

A Stage 3 clutch is designed for a heavily modified vehicle that is producing very large amounts of horsepower (kilowatts) and will not be driven on the street.

Friction Facing

Waved Springs

Friction Facing

Central Plate Hub

Hub Cover

FIGURE 6-17 An Torsional Springs

illustration of clutch disc components.

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Clutch Components

compressed when the pedal is being released. This results in smoother clutch engagement when starting from a stop. These cushion springs also help to push the clutch disc away from the pressure plate and the flywheel when the clutch is disengaged.

When the vehicle is parked, the cushion springs are compressed.

If a vehicle is stored for a long period of time, or is rarely driven, these cushion springs will begin to lose their shape. This results in a clutch pedal that has very little “feel” to it. The clutch will not engage smoothly, resulting in a harsher ride. The author has a Trans Am that has very few miles (kilometers) on it. This vehicle currently has an issue in which the cushion springs have flattened out, resulting in a clutch that is very difficult to feel when it starts to grab. Trying to teach a person to drive on a vehicle that has a clutch like this is almost impossible as the author found out while attempting to teach his wife how to drive manual transmission on this vehicle (FIGURE 6-18).

Clutch Throw-Out Bearing and Clutch Fork

159

Waved Spring

Friction Facings

Pressure Plate Rivet Flywheel

The clutch throw-out bearing and clutch fork work together FIGURE 6-18 Waved springs, called cushion springs, allow progressive application of the clutch. (along with the clutch linkage) to compress the pressure plate springs when the clutch pedal is pressed. The throw-out bearing is also sometimes called the clutch release bearing. Since the pressure plate rotates with the engine flywheel when the engine is running, the throw-out bearing must be able to rotate with the pressure plate while the Clutch Release Bearing Fork clutch fork remains stationary. Thus, the throw-out bearing must include a thrust bearing as part of its assembly. Throw-out bearings are usually thrust-type angular-contact ball bearings that are pressed onto a carrier. The carrier slides on the sleeve of the front bearing retainer that extends from the front of the transmission. This is considered a Throw-out Bearing push-type clutch design because the throw-out bearing pushes on the levers of the pressure plate. However, there are pull-type designs used on heavy-duty truck applications. The bearing carrier is located on the clutch release bearing fork (FIGURE 6-19).

Moving the clutch release fork (clutch fork) brings the bearing thrust face into contact with the pressure plate levers. This causes the bearing thrust face to rotate against the linear motion of the clutch fork and absorb the rotary motion of the levers. The thrust-type angular-contact ball bearing is FIGURE 6-19 An illustration of a clutch release bearing fork. packed with lubricant during manufacture and requires no periodic maintenance during its service life as long as it is not abused and the clutch free play is maintained. They will, however, fail very rapidly if a customer rests a foot on the clutch pedal while driving. Some older throw-out bearings did have a grease fitting that needed to be greased at regular maintenance intervals (FIGURE 6-20).

The clutch fork is usually made of stamped steel or cast iron.

It pivots either in the center or inside the bell housing at the end.

The pivot is generally screwed into the bell housing and is usually replaceable. The pivot should be inspected for wear and lubricated whenever the clutch is replaced. The release bearing engages in tabs in the clutch fork and is usually held in place by clips.

Not all release bearings are operated by a clutch fork. Some are operated directly by collar-style slave cylinders. These are sometimes called central, or concentric, slave cylinders because they are donut shaped and fit around the input shaft. This style uses hydraulic pressure to directly push the release bearing against the pressure plate fingers without the use of a clutch FIGURE 6-20 A heavy-duty pull-type pressure plate and release bearing. fork (FIGURE 6-21).

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Chapter 6 Clutch Theory and Operation

Pilot Bearing

FIGURE 6-21 A collar-style clutch cylinder operates the throw-out

bearing directly without a clutch fork.

A

The pilot bearing is essentially an alignment support bearing for the snout of the input shaft to ride on (FIGURE 6-22). It takes two bearings to support a rotating shaft: the pilot bearing is the front bearing for the input shaft, and the transmission input bearing is the input shaft on the other end. The pilot bearing can be a brass or bronze bushing, a needle-type bearing, or a roller-type bearing (FIGURE 6-23). Larger vehicles, such as trucks, may use a ball bearing type. Some of these bearings are installed in the cavity on the end of the crankshaft, or they may be placed or pressed into the center of the flywheel. To access the pilot bearing, should it fail in any way, the transmission and clutch assembly must be removed. Because of the construction of the input shaft, some vehicles do not require a pilot bearing. On this type of shaft, the input shaft is made long enough (typically front-wheel drive) so that it is supported on the front and back of the transaxle case by support bearings (FIGURE 6-24).

B

FIGURE 6-22 A. Pilot bearing installed in the flywheel. B. Pilot bearing removed from a crankshaft next to the input shaft.

A

C

B

FIGURE 6-23 A. Brass or bronze bushing B. Needle-type

bearing C. Roller-type bearing.

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Clutch Operating Mechanisms

161

Rear Support Bearing Input Shaft

Front Support Bearing

FIGURE 6-24 A vehicle that

doesn’t use a pilot bearing, because its two bearings are located in the transmission.

▶▶ Clutch

Operating Mechanisms

Movement of the clutch pedal is transferred through an operating mechanism to the clutch assembly on the rear of the flywheel. This mechanism may be one of three traditional methods or one of two more methods that manufacturers have recently added. The original three methods are cable operated, mechanical linkage, or a hydraulic system that is similar to a brake system. In addition to the three traditional methods, there are two newer ones: electric motors or computer-controlled hydraulic pistons.

6-03 Identify the various types of clutch operating mechanisms.

Cable Mechanisms Cable-operated clutch control systems are easily installed in the vehicle during manufacture and take up less overall engine compartment room. The outer cable housing is fixed to the pedal support inside the vehicle and to the transmission bell housing in the engine compartment. The inner cable connects between the upper end of the clutch pedal and an external lever on the end of the clutch fork. This lever is part of the clutch fork, which operates the throw-out bearing. Depressing the clutch pedal transfers the movement through the cable, and the throw-out bearing thrusts against the levers on the pressure plate, pushing the clutch pressure plate into the released position (FIGURE 6-25).

The clutch cable can be adjusted to provide the proper amount of free play between the throw-out bearing and the pressure plate levers. Free play is the distance that the throw-out bearing can move before it contacts the pressure plate. Free play prevents constant contact between the bearing and the pressure plate levers.

Since the bearing rotates when in contact with the pressure plate levers, free play prevents premature wear as well as excessive bearing noise. Some cable-operated clutches are adjusted manually by turning a threaded nut or collar. Other vehicles use a quadrant ratchet, which automatically adjusts the clutch pedal free play as needed when the driver’s foot pulls back on the pedal.

Cable-operated clutches have a disadvantage, though: the cable stretches over time, resulting in the need to adjust the free play, so very few late-model vehicles use a cable-operated clutch.

Master Cylinder

Clutch Cable

Quadrant Gear Pawl

Pedal Support

Firewall

Clutch Cable

Brake Pedal

Dust Cover

Clutch Pedal

FIGURE 6-25 A cable-operated clutch.

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Chapter 6 Clutch Theory and Operation

Hydraulic Clutch Mechanisms

Reservoir Master Cylinder

Clutch Pedal Metal Line

Clutch Housing

Return Spring

Clutch Fork

Rubber Hose Slave Cylinder

FIGURE 6-26 An illustration of a hydraulic clutch system.

Reservoir Pressure Out Return Spring Piston

Center Valve

Secondary Seal Primary Seal

FIGURE 6-27 Cutaway view of a clutch master cylinder.

In hydraulic clutch release mechanisms, the clutch pedal acts on a master cylinder, connected by a hydraulic tube and flexible hose to a clutch cylinder, mounted on an external type or in an internal type transmission bell housing. The clutch cylinder operates the clutch fork (external type) or acts directly on the throw-out bearing (internal type) on some vehicles. With the clutch pedal in the released position, the center valve in the master cylinder is clear of the inlet port, and fluid is free to flow to or from the reservoir into the cylinder. This allows the fluid to expand or contract as it heats and cools (FIGURE 6-26).

When the clutch pedal is initially depressed, the master cylinder piston moves forward, along with the valve assembly. The center valve closes off the inlet port from the reservoir, trapping fluid in the cylinder bore. Further piston movement displaces fluid through the outlet port and into the connecting lines to act on the clutch cylinder piston. The movement of the clutch cylinder piston is commonly transferred through a pushrod to the clutch release fork to operate the clutch. In other configurations, the clutch cylinder is located directly behind the throw-out bearing and pushes directly on it (collar style). When the clutch pedal is released, displaced fluid returns to the master cylinder and the center valve returns to being slightly clear of the inlet port, allowing excess fluid to return to the reservoir. Most hydraulic clutches are self-adjusting since the clutch fork causes the clutch cylinder piston to return as far as necessary, venting any excess hydraulic fluid to the master cylinder reservoir. This system automatically compensates for any clutch disc wear, which prevents the clutch from needing to be adjusted in most cases (FIGURE 6-27).

When an internal clutch cylinder needs to be replaced, the transmission must be removed to provide the necessary access.

Therefore, the author recommends that the internal clutch cylinder be replaced at the same time as the clutch disc. External clutch cylinders can be replaced more easily, without pulling the transmission, so they should be replaced only when needed (FIGURE 6-28).

Most modern hydraulic clutch systems use DOT 3 or DOT 4 brake fluid (where “DOT” is short for the US Department of Transportation) for their hydraulic fluid. Some older import vehicles used mineral oil as hydraulic fluid. These two fluids cannot be mixed. If brake fluid is installed in a vehicle that requires mineral oil, the seals in the master cylinder and clutch cylinder will fail

A

B

FIGURE 6-28 A. An internal clutch cylinder. B. An external clutch cylinder.

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Clutch Operating Mechanisms

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▶▶TECHNICIAN TIP

FIGURE 6-29 A clutch

master cylinder reservoir that specifies DOT 3 fluid only.

rapidly (FIGURE 6-29). If mineral oil is installed in a system that requires brake fluid, the seals will swell up. In severe cases, the clutch pedal will not even be able to be depressed.

Most vehicles identify on the master cylinder cap what type of fluid is required.

On some vehicles, the clutch master cylinder and brake master cylinder share the same fluid reservoir. On most vehicles, however, the clutch will have its own reservoir.

The author used to have a group of customers that had 1960s Jaguar vehicles.

These vehicles originally used mineral oil for their clutch systems. Typically, when either the clutch cylinder or master cylinder needed to be replaced, both would have to be replaced, and then the vehicle would have to be switched over to using brake fluid. Clutch cylinders and master cylinders that were designed for mineral oil were not available through the local suppliers. When working on older cars like these, make sure that both components are set up for the same fluid.

Linkage-Operated Systems Older technology systems used a series of links and levers, with an equalizing mechanism called a bell crank (equalizer bar) that rotated and was attached to the engine and the vehicle frame. The bell crank pivoted in plastic or nylon bushings that wore out over time. Adjustments were made at the end of the link connected to the clutch fork by using a threaded rod and lock nuts. As the clutch plate wore, adjustments were necessary to maintain proper clutch pedal free play so that the clutch would operate correctly. This linkage also required lubrication at every oil change. Some of the linkClutch Push Rod age points, such as the bell crank, had grease fittings, whereas others Firewall required that grease be applied with a brush (FIGURE 6-30).

Seal Manufacturers stopped using linkage systems for a few reasons. The first was the fact that the linkage and clutch would wear, Bell requiring frequent adjustments. The second reason was that in the Crank event of an engine mount failure, the clutch might not be able to be released, because the bell crank attachment was between the Return Clutch frame and the engine block. Further, linkage systems required the Spring Housing clutch to be located near the clutch pedal so that the linkage could easily operate the clutch. This did not work well on front-wheelClutch Fork drive (FWD) vehicles. The final reason that linkage systems fell Release Rod (threaded out of favor was the fact that the linkage system was exposed to rod with lock nuts) the elements. Snow and ice could pack up into the linkage system, FIGURE 6-30 An illustration of a linkage-operated system. limiting movement (FIGURE 6-31).

A

Clutch Pedal

B

FIGURE 6-31 A. A bell crank installed between the engine and frame. B. Linkage connection to the clutch fork.

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Chapter 6 Clutch Theory and Operation

FIGURE 6-32 High speed AC motors mounted on the outside of the

FIGURE 6-33 Clutch actuation mechanism that has been removed

bell housing.

from the bell housing.

Electrically Controlled Clutch On some newer vehicles, such as the Ford Focus, clutch operation is controlled by electric motors that are commanded by the transmission control module (TCM). These electric motors are high speed, alternating current (AC) motors that move a clutch fork in and out (FIGURE 6-32). The motors are located on the outside of the bell housing and can be replaced without removing the transmission. The fork is installed onto a wedge that moves in and out when the electric motor spins. As the motor spins the wedge inward, the clutch is released. As it spins outward, the clutch is engaged. The TCM will automatically learn the slippage of the clutch and maintain the correct amount of free play (FIGURE 6-33).

Computer-Controlled Hydraulic Clutch

FIGURE 6-34 A wet clutch assembly.

On some dual clutch transmissions, the clutches that engage the transmission to the engine are operated through hydraulic pistons. A TCM controls a hydraulic solenoid that controls the flow of hydraulic oil to a large-diameter piston. The piston is located inside a cylinder. The cylinder is typically bolted or splined to the flywheel. Whenever the engine is spinning, the cylinder is spinning. The cylinder has multiple clutches, called frictions, splined to the inside of the cylinder. There is a steel between each friction. The steels are splined to the input shaft of the transmission. The piston is forced out by the hydraulic pressure, and it squeezes the clutch discs and steels together, causing them to lock the input shaft of the transmission to the cylinder, which is spinning at engine speed. These clutches are called wet clutches because they are constantly soaked with hydraulic oil or may even be submerged in oil, depending on the design. A wet clutch tends to run much cooler and can allow a more gradual clutch application (FIGURE 6-34).

▶▶Wrap-Up Ready for Review ▶▶ ▶▶

▶▶

The clutch is designed to engage and disengage the engine from the vehicle’s transmission.

The driver controls the shifting of gears via the clutch while the vehicle is in operation.

▶▶

Dry and wet (automotive) clutches rely on friction to transmit torque from the engine to the transmission.

There are four variables affecting the clutch torque transmission: amount of friction between the clutch disc and mating surfaces of the flywheel and pressure plate;

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▶▶ ▶▶ ▶▶ ▶▶

▶▶

▶▶

▶▶

▶▶

▶▶ ▶▶

▶▶ ▶▶

▶▶ ▶▶

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Wrap-Up

diameter of the clutch; number of clutch discs in the clutch assembly; and total spring force clamping the parts together.

Speed and output shaft torque have an inverse relationship: when one is increased, the other is decreased.

The clutch disengages the input shaft from the engine flywheel in order to switch gears.

The output shaft cannot be disengaged, because it is ­directly connected to the wheels.

The clutch assembly is composed of the flywheel, clutch disc, pressure plate, throw-out bearing, clutch fork, and pilot bearing.

Flywheels are designed to provide a friction surface for the clutch disc and dampen the power pulses from pistons during power stroke.

Types of flywheels include the single, one-piece flywheel (light-duty vehicles) and the dual mass flywheel (diesel trucks and luxury vehicles).

A dual mass flywheel can be made of a primary and ­secondary flywheel, with a series of torsion springs and cushions, or it can use a planetary gear and torsion springs.

The pressure plate uses springs to clamp the clutch disc between the pressure plate and flywheel, allowing it to transmit torque.

Pressure plates use diaphragm spring pressure (light-duty vehicles) or coil spring pressure (heavy-duty vehicles).

A clutch disc (also known as a driven center plate or friction disc) allows engine torque to transmit from the flywheel and pressure plate to the transmission input shaft by providing the necessary friction material.

The clutch throw-out bearing and clutch fork compress the pressure plate springs.

Pilot bearings can be brass or bronze bushing, needle type, or roller type, and they provide alignment support for the input shaft.

Clutch operating mechanism styles can be linkage, cable, hydraulic, electric, or wet clutch hydraulic.

Cable-operated clutch control systems must be adjusted to ensure adequate free play between the throw-out bearing and pressure plate levers.

Hydraulic clutch control systems rely on a clutch cylinder to operate the clutch fork.

Clutches can be single-plate (light-duty vehicles) or multiplate (heavy-duty vehicles).

Clutch vibrations may be torsional or driveline.

Key Terms carrier The part of the throw-out bearing assembly that holds the bearing. clutch cylinder The component in a hydraulically operated clutch that converts hydraulic pressure to mechanical movement at the clutch fork. clutch disc The center component of the clutch assembly, with friction material riveted on each side. Also called a clutch plate or friction disc.

165

clutch fork The part of the clutch linkage that operates the throw-out bearing. coefficient of friction The amount of resistance to movement between any two surfaces that are in contact with each other. coil spring pressure plate A type of pressure plate that uses coil springs to provide the clamping force. diaphragm pressure plate A slightly conical, spring steel plate used to provide the clamping force for the clutch assembly. driven center plate The friction disc that is held firmly against the flywheel by a pressure plate and transfers power from the flywheel to the transmission input shaft. flywheel ring gear A large, round, externally toothed gear that is usually press fit to the outer diameter of the flywheel, and used along with the starter, to crank the engine over. flywheel A heavy metal disc bolted to the crankshaft that is used to smooth out the engine’s power pulses and keep the engine moving through the non-power strokes. Also provides the mating surface for the clutch disc and pressure plate. free play The amount of clearance in the clutch release mechanism, as measured at the clutch pedal. The proper amount of free play is critical to clutch operation and longevity. friction facing The material riveted to each side of the clutch disc that mates to the flywheel and pressure plate. It is used to provide friction and a wear surface for the clutch assembly. front bearing retainer The housing that bolts the input shaft bearing in place on the front of the transmission. fulcrum ring A steel ring that is used as a pivot point for the diaphragm spring in the pressure plate. multi-plate clutch A clutch assembly that is comprised of two or more clutch plates and used to increase the torque-carrying capacity of the clutch. pilot bearing The bearing or bushing that supports the front of the transmission input shaft. pressure plate The assembly that applies and removes the clamping force on the clutch disc. push-type clutch A typical clutch system used in modern vehicles where the clutch fork pushes the release bearing forward to release the friction facing from the pressure plate. quadrant ratchet The device used in some cable-operated clutches to provide self-adjustment as the clutch disc wears.

Some quadrant ratchets adjust if lifted up on the clutch pedal. release mechanisms Components that operate the clutch.

Usually included are the throw-out bearing and the clutch fork.

Some manufacturers include the operating system. single-plate clutch A clutch assembly that uses only one plate to transfer torque from the engine to the transmission. This is the most common type of light vehicle clutch. slippage A condition in which two surfaces in firm contact with each other slide. splined torsional dampening center hub The center portion of a clutch disc that splines to the input shaft. It also incorporates a spring-loaded damper that absorbs engine pulsations for a smoother ride.

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Chapter 6 Clutch Theory and Operation

throw-out bearing The part of the clutch release mechanism that imparts clutch pedal force to the rotating pressure plate levers. thrust-type angular-contact ball bearing A type of bearing that uses a deep groove in the bearing races where the ball bearings ride; this design is for thrust conditions. torsional vibrations The speeding up and slowing down of a shaft, which happen at a relatively high frequency. Crankshafts have torsional vibrations due to the power pulses of the pistons. transmission input shaft The shaft that brings engine torque into the transmission.

Review Questions 1. Identify the function of a clutch. a. To allow the driver to disconnect, and progressively connect, the engine to the transmission. b. To reduce the difficulty of starting a vehicle from a stop. c. To allow the different wheels to rotate at different speeds. d. To maintain tractive contact with the road surface according to driver inputs.

2. Which of the following statements is true? a. Increasing the diameter of the clutch reduces its leverage. b. Increasing the friction of a clutch disc increases its torque-carrying ability. c. Decreasing the number of clutch discs increases torque capacity. d. Decreasing the spring force clamping the parts together requires more foot pressure.

3. Why does the clutch engage and disengage the transmission input shaft? a. To increase the input shaft torque and speed at the same time. b. To allow the output shaft to be disconnected during a shift. c. To change the input shaft speed as needed. d. To avoid over-revving of the engine at lower engine speeds.

4. In a clutch assembly, the flywheel bolts onto the rear of the ________. a. crankshaft b. output shaft c. central hub d. synchronizer assembly 5. The ________ on a clutch disc are clamped between the flat surfaces of the engine flywheel and the spring-loaded pressure plate. a. fulcrum rings b. clutch forks c. coil springs d. friction facings 6. Identify the component that is the drive unit of a clutch system. a. Flywheel b. Pressure plate c. Clutch disc d. Both A and B

7. _______ is the driven unit of a clutch system. a. Flywheel b. Clutch disc c. Pressure plate d. Clutch fork 8. Which of the following components enables the starter motor drive gear to crank the engine over? a. Clutch cylinder b. Diaphragm pressure plate c. Flywheel ring gear d. Fulcrum ring 9. ________ is the distance that the throw-out bearing can move before it contacts the pressure plate. a. Slippage b. Bearing push c. Free play d. Driveline angularity 10. ________ automatically adjusts the clutch pedal free play as needed when the driver’s foot pulls back on the pedal. a. Quadrant ratchet b. Diaphragm pressure plate c. Clutch cylinder d. Fulcrum ring

ASE Technician A/Technician B Style Questions 1. Technician A says that the pressure plate friction surface rides on the flywheel friction surface to transmit torque.

Technician B says that the flywheel can be either flat or stepped. Who is correct? a. Technician A b. Technician B c. Both A and B d. Neither A nor B 2. Technician A says that insufficient clutch pedal clearance (free play) can cause gear clashing when shifting. Technician B says that when the engine is idling and the clutch pedal is released, the friction disc should stop rotating.

Who is correct? a. Technician A b. Technician B c. Both A and B d. Neither A nor B 3. Technician A says that hot spots on the flywheel are a result of excessive heat. Technician B says that a pulsation in a clutch pedal could be due to uneven clutch pressure plate levers. Who is correct? a. Technician A b. Technician B c. Both A and B d. Neither A nor B 4. Technician A says that a leaking rear main seal can cause clutch damage. Technician B says that the throw-out bearing rides directly on the clutch disc. Who is correct? a. Technician A b. Technician B

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Wrap-Up

c. Both A and B d. Neither A nor B 5. Technician A says that the flywheel runout can be checked with a dial indicator. Technician B says that when checking flywheel runout, it is good practice to also check crankshaft end play. Who is correct? a. Technician A b. Technician B c. Both A and B d. Neither A nor B 6. Technician A says that clutch slippage can be a result of excessively strong pressure plate spring(s). Technician B says that when replacing the friction disc, it is good practice to also replace the pressure plate. Who is correct? a. Technician A b. Technician B c. Both A and B d. Neither A nor B 7. Technician A says that the pilot bearing can be a n ­ eedle-style bearing. Technician B says that the pilot bearing can be a brass or bronze bushing style. Who is correct? a. Technician A b. Technician B c. Both A and B d. Neither A nor B

167

8. Technician A says that a bad pilot bearing can cause a whirring noise when the clutch pedal is released. Technician B says that many ring gears are press fit onto the flywheel.

Who is correct? a. Technician A b. Technician B c. Both A and B d. Neither A nor B 9. Technician A says that having waved springs between the clutch facings results in a smoother engagement of the clutch when starting from a stop. Technician B says that the heavy torsion coil springs in the clutch disc clamp the clutch disc between the flywheel and pressure plate. Who is correct? a. Technician A b. Technician B c. Both A and B d. Neither A nor B 10. Two technicians are discussing clutch operating systems.

Technician A says that most hydraulic clutches need to be adjusted periodically. Technician B says that cable-operated clutches use a clutch cylinder to operate the clutch fork.

Who is correct? a. Technician A b. Technician B c. Both A and B d. Neither A nor BABC

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CHAPTER 7

Clutch System Service Learning Objectives After reading this chapter, you will be able to: ■ ■ ■

7-01 Maintain various types of clutch systems.

7-02 Checking, adjusting, and bleeding a hydraulic clutch system.

7-03 Diagnose clutch system concerns.

■ ■ ■

7-04 remove a transmission/transaxle and clutch.

7-05 Inspect the clutch system and related components.

7-06 Install a clutch and related components.

You Are the Automotive Technician A customer brings their 2008 Ford Mustang into the shop for a clutch inspection. They have noticed the clutch slipping when they are in fourth gear, driving on the highway. You inform the customer that it would be beneficial to perform a road test to properly diagnose this problem.They agree, and you verify that the clutch slips when applying throttle while going up a hill.You drive back to the shop and inform the customer that you need to perform some additional diagnostic procedures in the shop and will let them know what you find.

1.

2.

3.

4.

What things should be done to confirm the clutch is worn out before removing the transmission?

Why is a test drive important to help diagnose clutch system issues?

What are the main components in the clutch assembly?

What are the different clutch operating systems?

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Chapter 7 Clutch System Service

▶▶ Introduction At some time, every clutch will require maintenance and or repair. Repairs are often directly related to the driver’s ability. If a clutch is maintained and has a qualified driver, it is ­possible for a clutch to last over 200,000 miles (322,000 km). Every technician should be able to perform system maintenance and diagnose clutch issues. Unlike automatic transmission problems, many shops will perform clutch repairs without sending the vehicle out to a specialty shop.

▶▶ Maintenance 7-01 Maintain various types of clutch systems.

SAFETY TIP Never use compressed air to blow off clutch parts such as the flywheel, ­pressure plate, clutch plate, transmission, or engine bell housings. Although it is possible that the dust does not contain asbestos, even dust that does not ­ contain asbestos is ­hazardous and can damage lungs. Blowing the dust off of parts puts the dust into the air, where it can be inhaled. OSHAapproved methods use a soap-and-water solution brushed onto the component to loosen and remove the dust, then it is rinsed off and collected in a container to be properly disposed of according to regulations.

Above all, work in a clean and orderly manner whenever servicing a clutch. Keeping things clean will help ­prevent grease and dirt stains and will also help ensure nothing is forgotten during reassembly.

of Clutch Systems

Clutch maintenance and repair can be hazardous if the proper safety precautions are not taken.

Wear appropriate clothing and eye protection while servicing all clutch components. Gaining access to work on clutches generally requires a lift or jack stands. Always make sure the vehicle is properly secured on jack stands or lifts before performing any type of service. Since transmissions are heavy and awkward to remove and install, use an approved transmission jack, along with the appropriate tie-down adapters. In many cases, it is best to get the assistance of another technician when removing or installing a transmission, to aid in preventing an injury.

Always be mindful of spills and clean the area as necessary to avoid any slips or falls.

Asbestos is a carcinogen. In fine particles, it can be breathed into the lungs, making it a health hazard. It was commonly present in older clutch disc linings. Modern technology has generally replaced asbestos by using organic compound resins with imbedded copper filings and some ceramic materials. Depending on the country of origin, there may be a greater chance of a clutch still containing asbestos. Use equipment approved by the O ­ ccupational Safety and Health Administration (OSHA) to remove all clutch dust and debris, and follow all regulations for particulate disposal (FIGURE 7-1).

Tools The following are the main tools used to maintain and repair the clutch system: ■■

■■ ■■

■■

■■ ■■

Transmission jack—a tool used to support a transmission during removal and installation (FIGURE 7-2).

Dial indicator—a tool used to measure runout or end play in clutch service (FIGURE 7-3).

Clutch alignment tool—a tool used to center the clutch plate between the flywheel and the pressure plate when installing the pressure plate (FIGURE 7-4) and (FIGURE 7-5).

Flywheel wrench—a lever-type tool that grabs onto the ring gear teeth and holds the flywheel while the flywheel bolts are being torqued (FIGURE 7-6).

Pilot bearing puller—a tool used to remove pressed-in pilot bearings (FIGURE 7-7).

Torque wrench—a tool used to correctly install bolts (FIGURE 7-8).

FIGURE 7-1 A washing system for clutches and brakes, used to help

FIGURE 7-2 A transmission jack.

prevent asbestos exposure.

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Maintenance of Clutch Systems

FIGURE 7-3 A dial indicator.

FIGURE 7-4 A universal clutch alignment tool.

FIGURE 7-5 A vehicle-specific clutch alignment tool.

FIGURE 7-6 A flywheel wrench.

FIGURE 7-7 A pilot bearing puller.

FIGURE 7-8 A digital torque wrench.

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Preventive Maintenance Regular preventive maintenance should be performed on the clutch at ­manufacturer-specified intervals. Clutch pedal free play should be checked and compared to specifications. ­Maintaining the specified clutch pedal free play is critical to

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Chapter 7 Clutch System Service

FIGURE 7-9 Free play is critical for proper clutch operation.

▶▶TECHNICIAN TIP When checking hydraulic clutch fluid, test strips can be used, except on vehicles that use plastic lines. The test strips identify the presence of copper in the fluid, which shows up only if the vehicle has galvanized steel lines. Plastic lines do not react in the same manner, so a brake fluid safety meter is the only way to test the fluid on these vehicles.

FIGURE 7-10 A clutch cylinder should be checked for leakage behind

the dust boot.

maintaining clutch life. Pedal free play is the amount of distance the clutch pedal can travel before the throw-out or release bearing touches the pressure plate. If the free play is too small, the throw-out ­bearing will wear out rapidly. If the free play is too great, the clutch may not release completely, and the vehicle could have gear clash while shifting, or the vehicle may creep forward when stopped. Clutch pedal free play can be checked and maintained by following the specified adjustment procedures for the clutch system being maintained (FIGURE 7-9).

The operation of the clutch pedal and return springs should be checked for binding and excessive movement. If a clutch switch is used on the clutch pedal, check that it is ­functional by verifying that it prevents the engine from cranking over while the clutch pedal is released. Mechanical linkage should be inspected for damage and lubricated with ­specified lubricants at all pivot points.

Hydraulic clutches should be checked for moisture-contaminated fluid in a m ­ anner similar to checking brake fluid. Clutch fluid is often more neglected than brake fluid, so there is a good chance that the clutch fluid needs to be flushed if the vehicle is more than a few years old. Hydraulic clutch lines should be checked for leaks at the master ­c ylinder and the clutch cylinder. If accessible, pull the boot back on the clutch ­c ylinder and inspect it for signs of leakage. Check that all hydraulic lines are not kinked or leaking at their c­ onnections. Make sure all hydraulic components are secure in their mountings (FIGURE 7-10).

Checking and Adjusting a Mechanical Clutch

FIGURE 7-11 A mechanical clutch linkage on a vintage Corvette.

As the clutch wears, the friction disc becomes thinner. This results in the pressure plate release levers moving closer to the release bearing and the clutch linkage losing its ­ operational clearance. Some clutches self-compensate for wear, whereas ­ others require checking and adjusting. Refer to the manufacturer’s shop i­nformation to find out exactly where any adjustment should be made. Modern vehicles will not typically use a mechanical clutch, so this type of maintenance is generally performed only on a ­vintage vehicle (FIGURE 7-11).

It is important to periodically check the clutch linkage ­mechanism for proper ­operation and correct the adjustment (free play). It is common to do so during every routine ­maintenance service. If the clutch pedal has too little free play, the throw-out bearing could remain in contact with the pressure plate levers and

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Maintenance of Clutch Systems

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prevent the pressure plate springs from applying full pressure. This would result in the disc not being completely clamped, leading to premature wear or failure of the clutch assembly and it needing to be replaced. Also, the pedal has to be released a long way before the clutch starts to engage. If the adjustment has too much free play, the clutch pedal may not have enough travel to fully release the pressure plate when the pedal is pushed down, causing the gears to clash (grind) when shifting and resulting in heavy synchronizer wear. With this condition, the clutch will start to engage immediately from the floor when releasing the pedal.

To check and adjust a linkage-style clutch, follow the steps in SKILL DRILL 7-1.

SKILL DRILL 7-1 Checking and Adjusting a Linkage-Style Clutch 1. Following the specified procedure, measure the amount of clutch pedal free play. If the free play is incorrect, it will need to be adjusted after a thorough inspection.

2. Inspect the clutch linkage parts for damaged, worn, bent, or missing components. Look for signs of binding, looseness, and excessive wear. Observe the operation of the components while an assistant operates the clutch pedal.

3. Inspect the clutch pivot and linkage that is located under the dash of the vehicle.

Continued

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Chapter 7 Clutch System Service

4. Check the clutch linkage components under the hood for the same signs of wear or damage as the components under the dash.

5. Measure the clutch pedal height. Compare the reading to specifications, and determine any necessary actions to correct any fault.

6. Measure the clutch pedal free play. Perform any adjustments as necessary, following the manufacturer’s procedure.

7. Inspect engine and transmission mounts for breakage or wear because these can affect clutch operation.

Continued

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Maintenance of Clutch Systems

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8. Lubricate the pivot points with the type of grease recommended by the manufacturer.

9. Lubricate the threads of the clutch adjustment rods to prevent them from becoming corroded.

10. Start the vehicle and depress the clutch. The clutch should engage at the proper height and have the proper free play. Make a gear selection to ensure the gears do not clash when going into mesh.

Cable-Operated Clutch Inspection and Adjustment Some vehicles use a cable-operated clutch mechanism to release the clutch. On these ­vehicles, clutch adjustment is required at regular intervals, due to not only the normal wear to the clutch and components listed above but also the fact that cables tend to stretch.

As these cables stretch, the clutch may not release completely, resulting in damage to the ­transmission or t­ ransaxle. On some vehicles, the cable has an automatic adjustment s­ ystem; on others, a threaded rod on the end of the cable is used. This adjustable threaded rod

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Chapter 7 Clutch System Service

SKILL DRILL 7-2 Inspecting and Adjusting a Cable-Operated Clutch 1. Operate the clutch pedal several times to check the feel of the pedal, and make sure it operates smoothly.

2. Inspect the quadrant gear (typically located under the dashboard) for signs of wear or damage (if equipped). Rust can be common on vehicles that have been stored incorrectly for an extended amount of time.

3. Inspect the tension spring and pawl on the self-adjuster mechanism (if equipped). Make sure that the pawl will move freely.

4. Inspect the entire cable for signs of fraying, chaffing, kinks, or rust.

5. Inspect the clutch fork end of the cable. On manually adjusted cables, the adjustment screw may be located here, and it will need to be inspected.

6. Inspect the clutch fork for signs of wear.

7. Inspect all rubber boots on the system to check for tears that will allow water and contaminants in.

8. Measure the clutch free play and adjust it as needed.

9. Lightly lubricate the cable with an approved lubricant.

10. Test-drive the vehicle to check the operation of the clutch.

can be located on either the clutch pedal side of the cable or the clutch fork side of the cable. Any of the ­components in this system can have wear, resulting in improper operation.

The author has even found a vehicle in which the clutch fork had completely worn through where the cable was attached. To inspect and adjust a cable-operated clutch, follow the steps in SKILL DRILL 7-2. ▶▶TECHNICIAN TIP The author once had a customer vehicle towed in with a failed transaxle. The vehicle was a 1988 Pontiac Fiero GT in which the clutch and shift cables had stretched over time, resulting in an internal transaxle failure. 1988 Fieros are a one-year-only vehicle with very limited parts availability because only about 6,000 GTs were made, and even fewer had manual transmissions. Most parts have to come from the few companies around the United States that purchase used vehicles and parts to resell or that manufacture replacement parts. After several weeks of searching for a transmission, or enough parts to rebuild the one in the car, a used transmission was found in Alabama for $1,500. (The Internet was not yet the online shopping mall that it is today.) $1,500 was a large amount of money for a used transmission in 1995, not to mention the $1200 core charge the company required, plus $200 to ship the transmission to Illinois. All of this expense could have been saved if the $12 clutch cable had been adjusted or replaced when the problem was first detected.

▶▶ Checking, Adjusting, and

Bleeding a Hydraulic Clutch System

7-02 Checking, Adjusting, and Bleeding a Hydraulic Clutch System.

Most vehicles in production today use a hydraulic clutch system, due to its many b ­ enefits.

One of those benefits is that the system reduces periodic maintenance; however, some ­maintenance is still required. It is important to check the clutch hydraulic s­ystem and ­components for proper operation and correct adjustment. It is common to do so during ­routine maintenance service. If the hydraulic clutch system is improperly ­maintained, clutch operation could be compromised in a similar manner as the operation of a ­mechanical linkage clutch, ­resulting in pressure plate, friction disc, and transmission ­synchronizer failure. The author has his s­ tudents inspect the clutch system during every oil change on vehicles equipped with a clutch.

Also, improper or old fluid in the hydraulic system can cause master cylinder and clutch cylinder damage and leaks. Most modern vehicles use brake fluid in the ­hydraulic clutch system. Brake fluid is hygroscopic, meaning it will absorb moisture. As brake fluid absorbs water, the boiling point of the fluid goes down, and the fluid becomes more ­corrosive. On a traditional brake system, the brake fluid can be tested by using a safety meter or fluid test strips. These fluid test strips detect the amount of copper in the fluid. The copper in the fluid comes from the inside of the brake lines. Many vehicles with hydraulic clutches use either plastic lines or stainless steel lines that do not have any copper. Thus, it is ­recommended to test clutch fluid only by using a safety meter and/or replace it every three years.

To check and adjust a hydraulic clutch, follow the steps in SKILL DRILL 7-3.

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SKILL DRILL 7-3 Checking and Adjusting a Hydraulic Clutch 1. Inspect the clutch master cylinder for correct fluid level.

2. Use a brake fluid safety meter to check the boiling point of the fluid. Test strips do not always work on clutch fluid.

3. Inspect all line connections to the master cylinder and remote reservoir, if equipped.

4. Check that all hydraulic lines are not kinked or leaking at their connections. This will require that the system be repaired and bled of any air. Check all rubber hoses for dry rot, bulges, or leaks. Make sure all hydraulic components are secure in their mountings.

Continued

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5. Check the boot on the clutch cylinder for seepage (if possible), which may indicate a leaking clutch cylinder piston seal. If possible, pull the boot back and check for fluid behind the boot.

6. Check clutch pedal height. Measure clutch pedal free play by using a tape measure. If the free play is not correct, the components on a hydraulic clutch will typically need to be replaced. Compare the readings to the specifications, and determine any necessary actions to take to correct any fault.

Bleeding a Hydraulic Clutch System In the case of a hydraulic clutch system failure, it may be necessary to bleed the air from the system. Bleeding is also needed whenever any hydraulic component is replaced or if the hydraulic fluid becomes unfit for use due to age or contamination. Not all systems are fitted with a bleeder screw; whether a system has one depends on the construction of the system. Also, it may be necessary to bleed the system from the line entering the clutch cylinder. A clutch master cylinder must not be overfilled. As the clutch heats up, the fluid will also heat up and thus expand. The expanding fluid has no room to expand, other than by ­expanding the clutch cylinder and applying pressure on the throw-out bearing. This will result in s­ lipping clutches, worn-out throw-out bearings, and other damage (FIGURE 7-12).

Research the procedure and specifications for bleeding the hydraulic clutch system. There are three types of bleeding: gravity bleeding, manual bleeding, and pressure/vacuum bleeding.

Determine the proper method of bleeding to use by consulting the manufacturer’s specifications.

Gravity bleeding uses the weight of the brake fluid to push old fluid and air from the master cylinder and lines through the clutch cylinder bleeder screw. In most vehicles, the clutch master cylinder is quite a bit higher than the clutch cylinder. The weight of the fluid can therefore be used to supply the pressure to push fluid and air out of the system. Using gravity bleeding is very helpful for a technician because the vehicle can be bleeding while the technician is working on another component.

FIGURE 7-12 A clutch cylinder from a vehicle in which the customer To bleed/flush a hydraulic clutch system by using the gravity overfilled the master cylinder, resulting in clutch slippage and in the clutch cylinder severely overheating (and melting). method, follow the steps in SKILL DRILL 7-4.

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SKILL DRILL 7-4 Bleeding/Flushing a Hydraulic Clutch System by Using the Gravity Method 1. If the fluid needs to be flushed, use a suction gun or old antifreeze tester to remove the fluid from the clutch master cylinder reservoir.

2. Fill the reservoir with the specified fluid, from a freshly opened bottle.

3. Install a hose onto the end of the bleeder screw to prevent making a mess while bleeding the clutch. Place the other end into an empty bottle.

4. Open the bleeder screw on the clutch cylinder.

Continued

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5. Allow air and fluid to drain from the system into a container.

6. Keep the master cylinder filled. Once all air and old fluid have been removed, close the bleeder screw and operate the clutch pedal to check for normal operation.

7. After bleeding the clutch hydraulic system, fill the master cylinder to the correct level with the specified type of fluid. Do not overfill.

The manual bleeding method uses the clutch master cylinder to push fluid and air out of the system. The procedure usually requires an assistant to hold the clutch pedal down while the other person opens the bleeder valve on the clutch cylinder. This forces air and old fluid out of the system. The technician and their assistant need to coordinate actions.

The assistant will need to hold the pedal down until the technician has closed the bleeder screw. The assistant should also allow the pedal to rise slowly to allow fluid to be drawn from the reservoir into the clutch master cylinder bore. Allowing the pedal to rise too fast can create a vacuum that draws air into the cylinder past the rubber seals. The assistant should avoid pumping the pedal because it can cause a single air bubble to break up into smaller bubbles and become distributed throughout the system. If this occurs, more time will be required to bleed the system completely. Be careful not to allow the master cylinder to run dry. A clutch master cylinder does not hold as much fluid as a brake master cylinder.

To bleed/flush a hydraulic clutch system by using the manual method, follow the steps in SKILL DRILL 7-5.

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SKILL DRILL 7-5 Bleeding/Flushing a Hydraulic Clutch System by Using the Manual Method 1. Remove all old fluid from the reservoir by using an old antifreeze tester or vacuum bleeder.

2. Fill the master cylinder with the specified fluid.

3. Install a hose onto the bleeder screw and place the other end into a container to prevent making a mess.

4. Open the bleeder valve on the clutch cylinder.

Continued

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5. Have an assistant depress the clutch pedal slowly.

6. Allow the fluid to flow into the container. When the fluid stops flowing, close the bleeder valve and slowly release the pedal. Repeat this process until all air and old fluid are removed from the system.

7. After bleeding the clutch hydraulic system, check for correct pedal feel, and fill the master cylinder to the correct level with the specified type of brake fluid.

▶▶TECHNICIAN TIP Technicians must be careful of the pressure of the fluid that comes out of the clutch cylinder because the fluid may splash or spray into their eyes. Also, brake fluid will dissolve paint, so when handling brake fluid, cover fenders and clean up any spilled fluid with generous amounts of water.

The pressure method and the vacuum bleeding method are the most common m ­ ethods of bleeding a hydraulic clutch in a shop. These methods use either pressure or ­vacuum to push or pull fluid and air out of the system. These methods work well for ­systems that tend to trap air in the hydraulic system that cannot be bled m ­ anually, since it keeps the fluid moving continuously through the system. It does require s­pecial bleeding tools or ­equipment to create the pressure or vacuum. On some vehicles, there may not be an adapter to bleed the clutch by using the pressure bleeder; if not, a s­ pecialty adapter will need to be purchased. These specialty adapters may not be worth purchasing unless the model of vehicle is one that typically appears in a technician’s shop. A newer tool that can be used is a

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▶▶TECHNICIAN TIP

FIGURE 7-13 A reverse

bleeding tool being used to bleed a clutch system.

reverse bleeding tool (FIGURE 7-13). This bleeder will force fluid up through the bleeder to the master cylinder. Air has the tendency to rise in brake fluid. By forcing new fluid in from the bottom of the system, it can help to push the air out at the top of the system.

To bleed a hydraulic clutch system by using the pressure/vacuum method, follow the steps in SKILL DRILL 7-6.

The author once had a vehicle in the shop that had a clutch cylinder that was a concentric style, meaning it was mounted around the input shaft of the transmission. This vehicle was a modified vehicle, and after the clutch had been replaced, the air could not be removed from the clutch cylinder. Gravity, manual, vacuum, and pressure bleeding were all tried, but due to the design of the clutch cylinder and the angle of the transmission, air remained trapped in the cylinder. Reverse bleeding systems were not common at this time. However, the air was able to be removed by raising the rear wheels higher than the front wheels and using a pry bar to push back on the clutch cylinder, forcing the air out of the bleeder.

SKILL DRILL 7-6 Bleeding a Hydraulic Clutch System by Using the Pressure/Vacuum Method 1. Remove all old fluid from the reservoir. Fill it with the specified fluid.

2. Hook up the pressure or vacuum bleeding tool to the vehicle with the correct adapters.

Continued

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3. Apply pressure or vacuum to the system.

4. Install a hose onto the end of the bleeder screw, if using a pressure bleeder. Place the other end of the hose into a container.

5. Open the bleeder screw, and allow the fluid and air to be purged from the system. Repeat this process as necessary.

6. After bleeding, check for correct pedal feel, and fill the clutch master cylinder to the correct level with the specified type of brake fluid.

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▶▶ Clutch

Clutch System Diagnosis

185

System Diagnosis

Clutch diagnosis is performed usually only when the driver makes a complaint about abnormal operation, sounds, or chatter that could be related to the clutch. Clutch d ­ iagnosis generally starts with getting as much information from the customer as possible. That is ­typically followed by a test drive to verify the concern and gather information about the fault. Depending on the condition present, the cause of the condition may be determined based on the test drive alone. In some cases, further inspection is needed to pinpoint the cause. This could be as simple as inspecting the linkage, or it could be more complex, requiring that the transmission be removed to further inspect the clutch components.

Often, when a customer has a clutch-related complaint, the vehicle is towed to the shop, so a test drive is not possible. If the vehicle cannot be driven, verify the symptoms as best as possible, and then perform a visual inspection. For example, if the customer’s complaint is that the clutch pedal is spongy and that they can’t put the vehicle in gear when the engine is running, consider checking the level of fluid in the hydraulic clutch master cylinder. If it is low, that will likely need to be repaired before test-driving the vehicle and checking out the operation of the clutch, to determine whether there are any other faults in the clutch assembly.

Once the symptoms have been verified and understood, research them in the ­appropriate service information to determine the possible causes and steps to diagnose the concern. Be sure to identify the root cause of the concern. For example, if the clutch disc is badly worn, it could be caused by weak pressure plate springs or misadjusted clutch free play. Just replacing the clutch disc will result in the clutch disc quickly wearing out again.

Common Issues Clutches typically have several relatively common faults that occur when there is an issue. The more familiar a technician is with clutch fundamentals and the ­manufacturer’s ­diagnostic procedures, the more likely they are to successfully diagnose the cause of the customer complaint. Some common clutch-related complaints include noises, pedal ­pulsations, slippage, clutch binding or drag, clutch vibration, and clutch chatter. These issues will be explored individually in the forthcoming sections .

Noises Clutch-related noises come from three general places: the pilot bearing, the release ­bearing, and the transmission input shaft bearing. A worn pilot bearing can make a howling or squeaking sound. The noise generally can be heard by fully depressing the clutch pedal with the engine idling and the transmission in first gear. This causes the pilot bearing to rotate on the input shaft, which will cause noise if the bearing is faulty (FIGURE 7-14).

A typical throw-out bearing noise may be more pronounced when the clutch pedal is partially or fully depressed and may disappear when the clutch pedal is released. A growling

7-03 Diagnose clutch system concerns.

▶▶TECHNICIAN TIP The author once sent out an email to the school staff looking for vehicles that needed driveline work. He specifically asked for vehicles that needed to have their clutch replaced and that needed half shaft, U-joint, and driveline fluid services, for the students. One staff member responded that her Camaro was very difficult to shift, and she was told by a shop that it probably needed a new clutch, the cost for which would run around $1,000.

She then continued to explain that she had to put a pot holder over the shift knob and used a hammer to shift the vehicle in and out of gear.The author was shocked that someone could drive a car this way. The vehicle was scheduled for the next day, parts were ordered, and the students were assigned to the vehicle.

When the vehicle showed up, the students went outside to pull the vehicle in to replace the clutch and came back in very confused because the vehicle was an automatic. Always get all of the information and confirm the customer complaint before giving an estimate. A broken shift interlock solenoid was all that was required to get the vehicle back on the road—without the hammer to push the button down!

FIGURE 7-14 A worn throw-out bearing that was making noise when the clutch pedal was depressed.

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▶▶TECHNICIAN TIP It can be very bad customer service to ask a customer if they drive a vehicle abusively. Some customers may not think of their driving habit as abusive. The author at one time noticed that the Tire Rack website listed a driving style on their review sheets as “spirited.” Since he saw this, he has tended to use this term when asking people how they tend to drive a vehicle. Most of the customers who are asked this find it amusing and then agree that they would call their ­driving “­ spirited,” and often they state that maybe they should tone it down a bit.

▶▶TECHNICIAN TIP Core plugs seal the holes in the block as part of the casting process and are located around the outside of the cylinder block and head(s), including behind the flywheel. Core plugs can rust from either side. They may look good on the outside, but they may be almost rusted through from the inside. A variety of core plugs are available to choose from when they need to be replaced. Be aware of hot coolant that may be leaking from the core plugs if the engine has recently been running.

noise or whirring noise is prevalent when the throw-out bearing is going bad. Thus, f­ orcing the throw-out bearing into the pressure plate levers by slightly depressing the clutch pedal will reveal the difference between a worn pilot bearing and a worn throw-out bearing. A worn throw-out bearing, generally, will make noise starting with contact of the throw-out bearing with the pressure plate levers, whereas a pilot bearing will not start making noise until the clutch disengages. Noise that occurs when the engine is idling in neutral and the clutch pedal is in the released position may indicate a worn transmission input shaft ­bearing, misalignment of the transmission, low transmission fluid level, or abuse by the operator. On some vehicles, a bad throw-out bearing can also be felt in the clutch pedal.

Pedal Pulsations Pedal pulsations are continual, up-and-down pulsations caused by release bearing ­contact, either from diaphragm lever misalignment or coil spring pressure plates that have lever ­misalignment. Pedal pulsations may also be due to abuse of the clutch, such as heavy ­slippage while trying to pull a heavy boat and trailer up a steep boat ramp. As a result of clutch abuse, the flywheel and/or pressure plate may overheat and acquire hot spots.

Hot spots are places where the metal has overheated. The metal will be harder than the ­surrounding metal, making machining the flywheel difficult.

Excessive slippage from a misadjusted clutch can contribute to overheating the clutch components and pedal pulsations. To check for this, lightly push down on the clutch pedal.

Usually, the pedal pulsations can be felt as soon as the release bearing starts to contact the pressure plate levers. Further diagnosis will require removing the clutch assembly and replacing worn and damaged parts (FIGURE 7-15).

Slippage A slippage condition can usually be identified while driving the vehicle in a gear that is direct drive, typically fourth gear, while accelerating. Observe both the engine speed and the vehicle speed. They should both increase proportionally. If there is slippage, the engine rpm will increase much faster than the vehicle speed. In this case, the clutch is unable to transmit full engine torque, so it slips, which is indicated by the increased engine speed (FIGURE 7-16).

As the clutch disc starts to wear, it becomes thinner, resulting in less clamping pressure from the pressure plate and less clutch pedal free play. This will then result in an engine rpm increase as slippage starts to occur, which will decrease the amount of torque being transferred to the transmission. To properly diagnose this problem, a road test is required.

The slippage may also be palpable as each gear is being shifted and the throttle is being depressed.

FIGURE 7-15 A pressure plate that shows hot spots that resulted in

FIGURE 7-16 A clutch that was slipping and has burned the friction

pedal pulsations.

material.

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Another method to diagnose this condition requires the vehicle to be at rest. Engage the parking brake, and shift the transmission into fourth gear. Slowly let the clutch pedal release.

If the clutch disc and pressure plate are still working p ­ roperly, the engine should stall. If the engine continues to run, check the clutch adjustment, and then repeat the same ­procedure.

If it fails to stall and continues to run, the a­ ssembly must be replaced and the flywheel should be checked for w ­ arpage and hot spots. This condition may require replacing or resurfacing the flywheel (FIGURE 7-17).

Clutch Binding Clutch binding occurs when the clutch does not quite ­disengage when the clutch pedal is depressed, causing a dragging of the clutch assembly. Clutch binding causes a grinding noise when FIGURE 7-17 A transmission front bearing hub that has severe wear shifting into and between gears. Trying to shift into a gear while that caused the clutch to bind. the gears are being powered by the binding clutch is very d ­ ifficult.

It also can make it difficult to put the transmission into neutral.

If clutch binding is present, it will be evident when trying to engage a gear with the engine running. If the transmission shifts easily when the engine is off but is difficult to shift with the engine running, suspect a binding clutch condition. Clutch binding may result from a damaged clutch disc, a warped clutch disc, or rusted input shaft splines and clutch hub. A bad input shaft bearing or pilot bearing may also cause clutch dragging. Loose transmission bolts cause input shaft misalignment, and clutch dragging will occur. A twisted input shaft will affect the engagement and disengagement of the clutch disc. This condition may result from driver abuse or possibly from the driver’s foot slipping off the clutch pedal due to rain, snow, or ice. Other possible causes of clutch binding include a clutch linkage that is bent or binding due to excessive wear or a damaged or rusted firewall that flexes and does not allow the clutch to be released fully. If this occurs, the firewall can sometimes be reinforced by bolting a metal plate to it.

Clutch Vibration Clutch vibration can be very annoying to a driver, so technicians need to be familiar with its diagnosis. First, isolate the type of vibration that is present. Torsional ­vibrations may be the result of engine parts that are starting to go bad. A vibration damper or flywheel that is out of balance can cause torsional vibrations. If this is the case, the vibration will be felt throughout the rpm ranges of the engine. If it is a clutch disc that is out of balance (usually due to clutch lining that has broken off), the vibration will be worse when the clutch pedal is released and the transmission is in neutral. Driveline vibrations may come from worn U-joints or CV joints, along with motor mounts that are worn and are allowing the engine to contact the frame or cross member. Thoroughly inspect and diagnose all of these ­conditions before removing the clutch assembly parts for inspection.

Clutch Chatter Clutch chatter should not be taken lightly, because it can result in failure of the clutch.

Clutch chatter is a shuddering feeling as the clutch pedal is being released. If there is uneven wear of the friction disc, or friction surfaces, of the pressure plate and flywheel, chatter may become palpable as the pressure plate starts to contact the friction disc. Oil on the friction disc, from either a leaking rear main seal or front transmission seal, can also contribute to this condition.

Too much crankshaft end play from a severely worn crankshaft thrust bearing may also create clutch chatter. As the engine is running, the crankshaft can move back and forth, and if so, a shuddering may be felt. Verifying this condition may require removing the engine oil pan to inspect the thrust bearing. Clutch chatter can also be caused by a binding clutch linkage, worn or broken motor mounts, misalignment of the bell housing, a bent or warped friction disc, the friction disc hub binding on the input shaft, or loose

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FIGURE 7-18 A cushion spring that has flattened out from the vehicle being

stored for a long period of time. In this case, the vehicle had sat for over 30 years without running.

friction disc facings. A thorough inspection of each component is required to determine the cause of the chatter.

Clutch Grabbing When a clutch is grabbing, it is very difficult to drive because it is hard to determine when the clutch begins to make contact. A good clutch will allow the clutch pedal to be slowly released and engine power to be increased in a smooth transition. A grabbing clutch does not transfer power smoothly. As the driver slowly lets up on the clutch pedal, there is no transfer of power, and then there is full transfer of power. This sudden transfer of power can cause the engine to stall. The author has generally found that there are two reasons for a clutch to act in this manner. The first is that a clutch cylinder has leaked brake fluid onto the friction disc. The second is that the cushion springs between the friction discs are worn out. The cushion springs can wear out on vehicles that have been parked for many years or on older vehicles that aren’t driven frequently (FIGURE 7-18).

▶▶ Removing

a Transmission/Transaxle and Clutch

7-04 Remove a transmission/transaxle and clutch.

▶▶TECHNICIAN TIP In some applications, such as fourwheel-drive (4WD) and all-wheel-drive (AWD) vehicles, it may be faster to remove the engine than it is to remove the transmission in order to gain access to the clutch assembly. Look up the flat rate time for removing the engine and compare that time to the transmission removal time.

Removing the transmission is required usually only when the clutch is not operating correctly; the flywheel ring gear is damaged; there is a major concern with the transmission; or access to the rear of the engine is needed for leaks involving core plugs, oil gallery plugs, or the crankshaft rear main seal. This job can be time-consuming and requires the ability to remember how components and parts go back together again. Depending on the vehicle, it can be difficult to gain access to the fasteners and other components necessary to remove and reinstall the transmission. Since the transmission is heavy and awkward, use a transmission jack with a solid support system during removal and installation. Also, many of the parts related to the transmission, clutch, and flywheel have very sharp edges, so wear leather or nylon gloves and be careful when grabbing onto parts.

To remove and a transmission/transaxle, follow the steps in SKILL DRILL 7-7.

Clutch and Pilot Bearing Removal When the transmission or transaxle has been removed from the vehicle, that is a good time to replace the clutch (or maybe clutch replacement is why the transmission was pulled in the first place). The author recommends that the pilot bearing be replaced every time the clutch is replaced as long as the bearing is available. To remove the clutch, pilot bearing, and related components, follow the steps in SKILL DRILL 7-8.

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SKILL DRILL 7-7 Removing a Transmission/Transaxle 1. Research the procedures and specifications according to the service information provided by the manufacturer. Ensure that bolts, clips, and fasteners are kept in containers. Make sure the vehicle is secure on the lift. If necessary, drain the transmission fluid to avoid spills.

2. Disconnect the shifter from the inside of the vehicle. This may require removing the shifter boot.

3. Disconnect the drive shaft, or axles, and secure them from hanging. Tape any U-joints to prevent the caps from falling off.

4. Disconnect all wires, tubes, and hoses, and inspect for damage.

Continued

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Chapter 7  Clutch System Service

5. Disconnect the clutch and shifter linkage, if required. Inspect for wear or damage.

6. Support the engine, using an engine support tool on an engine lifting hook.

7. Secure the transmission with a transmission jack. Raise the transmission up slightly, and remove any transmission mounts.

8. Loosen and remove the bolts holding the transmission to the bell housing, or if the transmission and bell housing are integrated, remove the bell housing bolts from the engine.

Continued

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9. Pull the transmission straight back from the engine so that the input shaft can slide out of the clutch disc.

10. Once the input shaft is clear of the clutch disc, lower the transmission down.

11. Transfer the transmission to the floor or to a work bench so that it does not fall off of the jack.

SKILL DRILL 7-8 Removing the Clutch, Pilot Bearing, and Related Components 1. Use an approved washing system to remove all of the dust from the clutch, pressure plate, and bell housing area.

Continued

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2. If the pressure plate is going to be reused, mark its location to the flywheel using a paint marker.

3. Loosen the pressure plate bolts one-quarter turn at a time, working in a star pattern. This will slowly release the tension of the pressure plate.

4. Remove the pressure plate from the flywheel and the clutch disc.

5. Mark the flywheel-to-crankshaft location by using a paint marker.

Continued

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6. Loosen and remove the bolts holding the flywheel to the crankshaft. Using an impact gun makes this job easier.

7. Locate the correct pilot bearing puller for the type and style of pilot bearing used in the vehicle.

8. Insert the jaws of the puller into the center of the pilot bearing.

9. Turn the adjustment nut to force the jaws out to grab the pilot bearing. The jaws should grab behind the pilot bearing. This pilot bearing has been removed to show how the pilot bearing removal tool works.

Continued

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10. Slowly turn the forcing screw to pull the pilot bearing out of the crankshaft.

11. Remove the throw-out bearing from the clutch fork or clutch cylinder.

▶▶ Clutch 7-05 Inspect the clutch system and related components.

System Component Inspection

Before installing a new clutch and reinstalling the transmission and transaxle, it will be necessary to inspect all of the components to prevent costly comebacks. A leaking rear main engine seal could cause the new clutch to fail rapidly. A worn-out flywheel ring gear is easily replaced while the transmission is out of the vehicle. If the ring gear fails a few months after the clutch job, the customer is not going to be happy to pay the labor to pull the transmission again.

Any time the author pulls a transmission, he will purchase a complete clutch kit if it is available. A clutch kit will contain a new pressure plate, a new friction disc, a new pilot bearing, a new throw-out bearing, and a clutch alignment tool. If a clutch kit is available, it will not be necessary to inspect these components, except as necessary to help determine why the clutch failed (FIGURE 7-19).

Inspecting the Flywheel and Ring Gear

FIGURE 7-19 A complete clutch kit.

Any time the clutch assembly has been removed, it is a good idea to conduct a thorough visual inspection of the flywheel and ring gear. The flywheel should be checked for bluing, hot spots, and cracks. These conditions can result from possible driver abuse or clutch maladjustment, causing the clutch disc to overheat.

Also inspect the flywheel friction surface for cupping by using a straightedge and feeler blades. Cupping can happen because the pressure plate exerts a pulling force on the outside diameter of the flywheel, which can cause the outer edge to bend over time.

In addition, the outer edge of the friction surface wears more quickly than the inner edge. A straightedge can help identify this situation quickly.

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Some flywheels are designed with a step, meaning that the friction surface is lower than the outer surface against which the pressure plate is bolted. The depth of the step is critical to the operation of the pressure plate. If it is too deep, the pressure plate will not develop enough clamping force to keep the clutch from slipping. If it is not deep enough, the clutch might not be able to be released. In any case, the depth of the step must be within the ­manufacturer’s specifications. This becomes more important to check if the flywheel has been resurfaced. The machinist should have made sure the depth is correct, but a technician still needs to double-check it.

With respect to resurfacing flywheels, most vehicle manufacturers, as well as clutch suppliers, suggest that the flywheel be resurfaced whenever the clutch is replaced. Resurfacing gives a new, flat, and consistent friction surface that helps prevent clutch chatter. It is a good practice to check flywheel runout once a resurfaced flywheel has been reinstalled on the crankshaft so that any machining errors can be identified.

Ring gears must be inspected for missing teeth as well as for excessive wear on the teeth. If any of these conditions are present, the ring gear should be replaced. Many ring gears are press fit onto the flywheel; others are a permanent part of the flywheel. If a ring gear is press fit onto the flywheel, it can be removed by heating it up carefully with an acetylene torch to ~300°F (~150°C) and then using a hammer and punch to quickly drive it off of the flywheel. To reinstall it, a good method is to cool the flywheel in a freezer for 30 minutes and to place the ring gear in an oven at about 300°F (150°C). Then, using welding gloves, quickly take them out, set the flywheel on a solid surface, and slide the ring gear over the flywheel. Use a hammer and flat punch to seat the ring gear against the flange on the flywheel.

To inspect the flywheel and ring gear (with the transmission removed), follow the steps in SKILL DRILL 7-9.

SKILL DRILL 7-9 Inspecting the Flywheel and Ring Gear 1. Clean up any clutch dust and debris, using an approved method for disposing of hazardous dust if it was not already cleaned.

2. Inspect the flywheel for wear, hot spots, bluing, and cracks.

Continued

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3. Use a straightedge to check the flatness of the flywheel.

4. Inspect the ring gear for wear, chipped teeth, and cracks. If teeth are worn in one area, the starter drive may also need to be replaced.

5. Check that the ring gear is secure on the flywheel.

6. Inspect the starter drive because it may have been damaged from a faulty ring gear.

Continued

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7. Inspect the mounting holes on the flywheel for damaged threads.

Measuring the Flywheel Runout and Crankshaft End Play The flywheel must rotate true. This means that the surface of the flywheel must not wobble, which would indicate excessive runout. It is always a good idea to check and measure the flywheel runout in the case of catastrophic clutch failure, or routine clutch replacement, any time the transmission is removed. Flywheel runout can be measured with a dial indicator, which is held in position against the flywheel friction surface. When the flywheel is rotated, the runout should be within specifications, near zero. If the runout is excessive, use the dial indicator to measure the crankshaft runout to determine whether the crankshaft is causing the excess flywheel runout.

Crankshaft end play is the amount of forward and rearward movement of the ­crankshaft, and it must be within the specifications for the vehicle being worked on. ­Crankshaft end play must be checked if any irregular clutch noises have been detected.

Too much crankshaft end play could be caused by an engine’s crankshaft thrust bearing ­becoming worn past its specified tolerance. Crankshaft end play can also result in clutch chatter when the clutch pedal is being released.

Use a dial indicator to measure crankshaft end play. If the engine oil pan has been removed, the thrust bearing clearance can also be measured with a feeler gauge. Also, check runout of the pilot bearing cavity because this could indicate that the pilot bearing may not be held in position, as is required for proper operation. If so, damage to the clutch assembly may result.

To measure flywheel runout and crankshaft end play, follow the steps in SKILL DRILL 7-10.

SKILL DRILL 7-10 Measuring Flywheel Runout and Crankshaft End Play 1. Following the manufacture’s specified procedure, measure flywheel runout. Mount the dial indicator base on the engine block.

Continued

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2. Place the plunger of the dial indicator on the flywheel friction surface.

3. Rotate the crankshaft by using a flywheel wrench or a socket and breaker bar. Find the high spot on the flywheel, and zero the dial indicator. Continue rotating the crankshaft until the dial indicator reads the greatest amount of runout. Record the reading and compare it to specifications.

4. If flywheel runout is excessive, remove the flywheel and measure the runout on the crankshaft flange by using a dial indicator. To get an accurate reading, make sure to keep the crankshaft pushed forward against the thrust bearing while rotating it.

5. Crankshaft end play should also be checked with a dial indicator to make sure it is not excessive; if it is, it should be addressed before replacing the clutch. Mount the dial indicator on the engine block surface, and set the dial on the rear face of the crankshaft flange.

Continued

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6. Carefully move the crankshaft back and forth, using a pry bar to pry on a bolt threaded into one of the crankshaft bolt holes. Record the reading and compare it to manufacturer specifications.

Inspecting the Engine Block While the flywheel is removed, it is a good practice to inspect the rear of the engine block for any damage to the mating surfaces and alignment dowels. This should include inspecting the threads of all bolt holes to make sure they are not stripped. Also, check for leaking coolant and/or engine oil, and check the integrity of the soft plugs. Now is the time to address any issues in this area because having to go back in later to fix something requires substantial disassembly time.

Many newer engines use a full-circle rear main seal around the crankshaft flange at the rear of the block. This can be replaced only by removing the transmission and flywheel.

If the clutch and flywheel have been removed, now would be an ideal time to inspect and change the full-circle rear main seal.

To inspect the engine block, follow the steps in SKILL DRILL 7-11.

SKILL DRILL 7-11 Inspecting the Engine Block 1. Mark the flywheel-to-crankshaft position. Remove the flywheel to access the rear of the engine.

2. Inspect the engine block for obvious defects.

Continued

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Chapter 7  Clutch System Service

3. Inspect the core plugs. Test their integrity by tapping on them lightly with a punch. Replace the core plugs if they are leaking or show signs of deterioration.

4. Check the rear crankshaft oil seal for seepage, since this could leak onto the clutch assembly.

5. Inspect the clutch (bell) housing for elongated holes or broken ears that could result from loose bolts.

6. Inspect the transmission/transaxle case mating surfaces for flatness. Inspect the alignment dowels for proper fit, sizing, and wear.

Check the engine block for stripped bolt holes.

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Inspecting the Clutch and Related Components Inspecting the clutch disc itself can help diagnose problems with the system and help ­prevent future problems. First, inspect the friction surfaces of the clutch. A discolored ­friction surface is typically one that has burned from slipping. This slipping can also be due to a rear main seal leaking on the clutch (FIGURE 7-20).

The friction material should be securely fastened to the assembly. If the friction can move back and forth on the rivets, it should be replaced. If it is not replaced, the friction material may break off while the vehicle is operating. Inspect the rivets to ensure that all are tight and none is missing (FIGURE 7-21).

Inspect the hub of the clutch disc for damage to the splines. A high mileage clutch may have wear on the splines from moving back and forth on the input shaft. Inspect the ­torsion damper springs, or rubber blocks, for looseness or wear. If the springs show wear, it is often from clutch abuse. Examples of such abuse are harsh shifting and/or shifting ­without depressing the clutch pedal, in severe cases. This information is important to know in the event of a warranty claim (FIGURE 7-22). (Even though most clutches do not have any warranty, some companies will offer a limited warranty.)

Inspect the pressure plate fingers for wear on the tips. This wear can be the result of a bad throw-out bearing or a customer that rests their foot on the clutch pedal while driving.

The throw-out bearing will also, typically, have wear on the edge of the bearing where it touches the pressure plate. Either of these conditions will require that both parts be replaced (FIGURE 7-23). Inspect the pressure plate for broken or bent fingers. Also inspect it for warpage, discoloration, and cracks.

▶▶TECHNICIAN TIP Refinishing the flywheel moves the pressure plate toward the engine and away from the throw-out bearing, i­ncreasing free play. If too much material is removed from the flywheel surface, some release mechanisms will not be able to compensate for the loss, and then the clutch will not fully release. Also, as more material is machined from the flywheel, the clutch center hub may contact the flywheel bolts. So, even though most ­ manufacturers do not list a minimum thickness for the flywheel, know that it can cause problems if it becomes too thin.

FIGURE 7-20 A clutch that was slipping due to a failed rear main seal.

FIGURE 7-21 A clutch disc in which the friction material broke off.

FIGURE 7-22 A clutch disc that has worn damper springs.

FIGURE 7-23 A pressure plate and throw-out bearing that are worn

out and should be replaced.

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FIGURE 7-24 Inspecting

the clutch fork for signs of wear.

Inspect the clutch fork for cracks and wear. The end of the fork where the clutch c­ ylinder operates can wear, along with the pivot point. Inspect the pivot ball for wear. The pivot ball should have a spherical shape; if it does not, it needs to be replaced. The clutch fork holds the throw-out bearing in some manner, often using small metal clips. Make sure these clips are neither broken nor bent (FIGURE 7-24).

7-06 Install a clutch and related components.

▶▶TECHNICIAN TIP Although it is understandable to assume that when a clutch plate wears over time, the clutch free play increases. But in fact, it decreases. As the lining wears, the pressure plate levers move backward toward the throw-out bearing, reducing clutch pedal free play. If the clutch disc wears enough, all free play can be lost, meaning that even with the driver’s foot off of the clutch pedal, the linkage is holding some pressure on the lining. This reduces the pressure plate clamping force and, if bad enough, can cause the clutch to slip, leading to a burned clutch that needs to be replaced.

▶▶ Installing

a Clutch Assembly

Whether a clutch is being replaced because of a failure or the clutch is being removed and ­reinstalled after replacing an engine, all components must be thoroughly inspected to ensure that the clutch will operate properly and last a long time. Installing the clutch assembly requires a few precautions. First, the clutch disc is directional, meaning that it must be installed with the correct face toward the flywheel. New clutch discs are usually marked with a sticker or paint indicating the “flywheel side” or “engine side.” This marking cannot usually be read on used discs, so always mark the clutch disc when removing it if it may be reinstalled. Second, the clutch disc must be aligned before bolting down the pressure plate so that the input shaft can align with the clutch disc hub and pilot bearing without binding. Using a pilot shaft or clutch alignment tool will help ensure proper clutch disc alignment. With the clutch disc inserted, under no circumstances the pilot shaft be removed until after the clutch pressure plate has been installed and torqued to specification. If it is removed prematurely, clutch disc misalignment will occur, and installing the transmission will be extremely difficult or impossible.

Upon installation of the pressure plate, insert bolts and tighten them about a turn at a time in a multistep, crisscross pattern, which will allow the pressure plate cover to be seated slowly and without distortion. Double-check all torque values to ensure proper installation.

To install a clutch assembly, follow the steps in SKILL DRILL 7-12.

SKILL DRILL 7-12 Installing a Clutch Assembly 1. Research the procedure and any specifications for inspecting the clutch assembly.

Continued

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2. Install the new pilot bearing using the correct installation tool.

3. Lubricate the pilot bushing with the correct lubricant, if required.

4. Line up the marks on the flywheel and crankshaft, and place the freshly machined flywheel onto the crankshaft.

5. Install the correct thread lock compound onto the threads of the flywheel bolts.

Continued

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6. Install the flywheel bolts, and torque to specification, following a star pattern.

7. Spray off the flywheel with brake clean or another suitable solvent.

8. Place the clutch disc up onto the flywheel in the correct direction.

9. Install a clutch alignment tool through the clutch disc and into the pilot bearing.

Continued

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10. Spray off the pressure plate with brake clean or other suitable solvent.

11. Install the pressure plate onto the flywheel, and begin installing the retaining bolts.

12. Tighten the pressure plate bolts down just until they contact the pressure plate. Then tighten each bolt one-quarter turn, following a star pattern.

13. Continue tightening the bolts one-quarter turn at a time until all the bolts are torqued to the manufacturer’s specification.

Continued

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14. The clutch alignment tool can now be removed. It should slide out of the clutch with minimal effort.

15. Install the throw-out bearing into the clutch fork in the correct direction.

16. Lubricate the clutch fork pivot ball with the correct, specified lubricant.

17. Install the clutch fork into the bell housing and onto the pivot ball.

Continued

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18. Lubricate the input shaft splines on the transmission.

19. Install the bell housing onto the engine, and torque the bolts to the manufacturer’s specification if the vehicle is equipped with a separate bell housing.

20. With the transmission on a suitable transmission jack, raise the transmission up until the input shaft lines up with the clutch disc.

21. Push the transmission input shaft into the clutch disc until the transmission seats against the bell housing. Wiggle and shake the transmission to get the input shaft to line up with the splines in the clutch disc.

Continued

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22. Install the bolts that hold the transmission to the bell housing.

Do not use the bolts to pull the transmission into the bell housing, because doing so will damage the clutch disc. Torque the bolts to the manufacturer’s specifications.

23. Install the transmission mount, and lower the transmission jack.

24. Install the clutch linkage or clutch cylinder.

25. Install all wires, hoses, and cables onto the transmission.

Continued

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26. Install the driveshaft or half shafts.

27. Check the fluid level in the transmission.

28. Install the shifter and any shift linkage into the vehicle.

29. Completely fill the master cylinder, and bleed the system if applicable.

Continued

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30. Adjust the clutch free play, if applicable.

31. Test-drive the vehicle to confirm that the clutch is operating properly.

▶▶Wrap-Up Ready for Review ▶▶

▶▶

▶▶ ▶▶ ▶▶

▶▶

▶▶ ▶▶

▶▶

Cable-operated clutch control systems must be adjusted to ensure adequate free play between the throw-out bearing and pressure plate levers.

Common clutch-related problems include noises, ­pedal pulsations, slippage, clutch binding or drag, clutch ­vibration, and clutch chatter.

Clutch vibrations may be torsional or driveline.

Proper clutch diagnosis will likely require performing a test drive.

Follow proper safety precautions during clutch ­maintenance and repair; older clutch disc linings may contain asbestos.

Tools needed to maintain and repair a clutch ­system ­include a transmission jack, dial indicator, clutch ­alignment tool, flywheel wrench, and clutch wash station.

Perform regular preventive clutch maintenance, per the manufacturer’s guidelines.

Check and adjust the clutch linkage mechanism (­mechanical or hydraulic) during routine maintenance service.

▶▶ ▶▶ ▶▶ ▶▶ ▶▶

Hydraulic clutch systems may need to be bled if the system fails, when a component is replaced, or if the hydraulic fluid becomes unfit for use.

Hydraulic clutch systems may be bled via gravity, ­manually, or via the pressure/vacuum method.

Removing a transmission and transaxle is difficult; ­remember how components go back together again.

Inspect the flywheel, ring gear, and engine block whenever the clutch assembly has been removed.

Measure the flywheel runout and crankshaft end play any time the transmission is removed.

Be sure to properly align the clutch disc when installing a clutch assembly.

Key Terms clutch binding A condition in which the clutch disc is d ­ ragging, leading to grinding gears during gear shifts, and possibly clutch chatter. clutch chatter A condition in which the clutch shudders when the clutch pedal is released, and the vehicle starts to move forward.

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Wrap-Up

clutch disc The center component of the clutch assembly, with friction material riveted on each side; it is also called a clutch plate or friction disc. clutch fork The part of the clutch linkage that operates the throw-out bearing. crankshaft end play The amount of forward and rearward movement of the crankshaft in the main bearings. Crankshaft end play is controlled by the engine main bearing thrust bearing. driveline vibrations Rotational fluctuations caused by o ­ ut-of-balance, misaligned, worn, or bent driveline components. free play The amount of clearance in the clutch release mechanism, as measured at the clutch pedal. The proper ­ amount of free play is critical to clutch operation and longevity. pilot bearing The bearing or bushing that supports the front of the transmission input shaft. pressure plate The assembly that applies and removes the clamping force on the clutch disc. release mechanisms Components that operate the clutch. ­Usually included are the throw-out bearing and the clutch fork.

Some manufacturers include the operating system. clutch cylinder The component in a hydraulically-operated clutch that converts hydraulic pressure to mechanical m ­ ovement at the clutch fork. throw-out bearing The part of the clutch release mechanism that imparts clutch pedal force to the rotating pressure plate levers. torsional vibrations The speeding up and slowing down of a shaft, which happens at a relatively high frequency. Crankshafts have torsional vibrations due to the power pulses of the pistons.

Review Questions 1. Which of the following is true with regard to clutch system maintenance? a. Compressed air should be used to blow off clutch parts. b. A soap-and-water solution should be brushed onto clutch components to loosen and remove the dust. c. A clutch needs to be replaced every 5,000 miles. d. Asbestos clutch disc linings do not pose a health hazard.

2. Identify the tool used to measure runout or end play in clutch service. a. Clutch alignment tool b. Pilot bearing puller c. Dial indicator d. Torque wrench 3. A ________ is used to center the clutch plate between the flywheel and the pressure plate when installing the pressure plate. a. dial indicator b. torque wrench c. flywheel wrench d. clutch alignment tool 4. A ________ should be used to check the boiling point of a clutch fluid. a. valve tester kit b. safety meter

211

c. UV detector kit d. grit suit 5. Which of the following is used to flush clutch fluid using the gravity method? a. Suction gun b. Drain plug c. Bleeder screw d. Vacuum pump 6. Which of the following statements is true? a. Manual bleeding uses the weight of the brake fluid to push old fluid and air from the master cylinder. b. The master cylinder of a clutch hydraulic system needs to be overfilled to compensate for small leaks. c. When bleeding a clutch system, the master cylinder should be allowed to run dry. d. A clutch master cylinder does not hold as much fluid as a brake master cylinder.

7. Identify the type of noise that is present when the throwout bearing of a clutch is going bad. a. Clattering b. Growling noise c. Squeaking noise d. Single thud 8. Noise that occurs when the engine is idling in neutral and the clutch pedal is in the released position may indicate a worn ________. a. release bearing b. transmission input shaft bearing c. throw-out bearing d. pilot bearing 9. A vibration damper or flywheel that is out of balance can cause ________. a. driveline vibrations b. clutch chatter c. clutch grab d. torsional vibrations 10. When removing the clutch, the pressure plate bolts should be loosened in ________ to slowly release the tension. a. star pattern b. clockwise direction c. random pattern d. anticlockwise direction

ASE Technician A/Technician B Style Questions 1. Technician A says that most shops will send a vehicle out to a transmission shop to replace a clutch. Technician B says that many shops will not rebuild a transmission, but will replace a clutch disc. Who is correct? a. Technician A b. Technician B c. Both A and B d. Neither A nor B 2. Technician A says that insufficient clutch pedal ­clearance (free play) can cause gear clashing when shifting. T ­ echnician

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Chapter 7 Clutch System Service

B says that when the engine is idling and the clutch pedal is released, the friction disc should stop rotating. Who is correct? a. Technician A b. Technician B c. Both A and B d. Neither A nor B 3. Technician A says that hot spots on the flywheel are a result of excessive heat. Technician B says that a pulsation in a clutch pedal could be caused by uneven clutch pressure plate levers. Who is correct? a. Technician A b. Technician B c. Both A and B d. Neither A nor B 4. Technician A says that a leaking rear main seal can cause clutch damage. Technician B says that the throw-out ­bearing rides directly on the clutch disc. Who is correct? a. Technician A b. Technician B c. Both A and B d. Neither A nor B 5. Technician A says that the flywheel runout can be checked with a dial indicator. Technician B says that when checking flywheel runout, it is also good practice to check crankshaft end play. Who is correct? a. Technician A b. Technician B c. Both A and B d. Neither A nor B 6. Technician A says that clutch slippage can be a result of excessively strong pressure plate spring(s). Technician B says that when replacing the friction disc, it is also good practice to replace the pressure plate. Who is correct?

a. Technician A b. Technician B c. Both A and B d. Neither A nor B 7. Technician A says that the hydraulic clutch cylinder should be replaced when replacing the clutch. Technician B says the hydraulic clutch cylinder should be replaced if it is ­leaking. Who is correct? a. Technician A b. Technician B c. Both A and B d. Neither A nor B 8. Technician A says that a bad pilot bearing can cause a ­whirring noise when the clutch pedal is released. T ­ echnician B says that many ring gears are press fit onto the flywheel.

Who is correct? a. Technician A b. Technician B c. Both A and B d. Neither A nor B 9. Technician A says that clutch life depends on the skill of the driver. Technician B says that most clutches last around 25,000 miles (40,000 km). Who is correct? a. Technician A b. Technician B c. Both A and B d. Neither A nor B 10. Technician A says that the flywheel should be cleaned up with a die grinder before installing the new clutch. ­Technician B says that the flywheel should be sent out for machining before installing a new clutch. Who is correct? a. Technician A b. Technician B c. Both A and B d. Neither A nor BAB

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MASTER AUTOMOTIVE TECHNICIAN SERIES

SAMPLE CHAPTERS 6 and 7

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