clutch literature

CLUTCH LITERATURE

Basics

The role of the clutch

Combustion engines have one problem: they deliver usable power only within a very specific engine speed range - completely unlike electric motors or steam engines. That means that engine speed, transferable engine power and transmission must be optimally reconciled in all sorts of driving conditions - and that's the role of the clutch. It works by connecting or disconnecting the engine drive train and the transmission. All drivers are familiar with this from everyday driving. When you depress the clutch pedal the drive train is disconnected and you can change gear. The clutch also enables smooth, gentle starting of cars, lorries and other commercial vehicles.

Highly demanding

The refinements in automotive design mean that today's clutches need to satisfy many requirements which have a significant effect on the comfort and handling of the vehicle. These relate to gentle starting, rapid gear-changing, vibration damping or noise suppressing. The vehicle designers have embraced these problems with enthusiasm A modern clutch is characterised by performance over a wide speed range, highly effective transmission, slim line dimensions, minimum recoil force and longevity.

The inner life of the clutch

The central components of the modern clutch include:

1) Flywheel and/or disc flywheel

2) Clutch disc

3) Clutch pressure plate

The flywheel

Engines never run completely true due to their essentially uneven combustion.

The flywheel, which is bolted to the engine crankshaft, functions here as an energy storage means and balances out the unevenness.

Note: the greater the mass of a flywheel, the more evenly the engine will run.

It is also designed so that the friction produced when the clutch engages is not only effortlessly absorbed but can also be dissipated in the best possible manner.

And because this component has a decisive influence on key factors such as start-up and wear-performance, selecting the right material for the flywheel is essential. Grey cast iron has proved the best choice.

There are two variants; the pot-style flywheel and the flat flywheel.

The clutch disc

As a friction partner we might call it the mediator between the disc flywheel and the clutch pressure plate or contact plate. It is instrumental in transferring the torque delivered by the engine to the clutch shaft.

It also enables gentle start-up and rapid gear shifting as well as isolating the drive train from engine torque fluctuations . We actually expect an awful lot of the clutch disc.

Firstly however it is enough to take a look at the key components. They are:

the friction linings

the lining resilience system

the torsion damper

the hub

The friction linings

The essential feature of an engaging/disengaging friction clutch is, as the name suggests, the transfer of forces via frictional engagement This frictional engagement is produced by the friction linings which are glued or riveted to the clutch disc.

(Photo to illustrate)

Friction linings are subject to extreme loads

Friction linings are subject, depending on use, to tensile, shearing and bending stresses. And they have to withstand even more than brake linings.

As they rotate at high speeds on the clutch disc they are subject to strong centrifugal force which causes considerable stresses within the lining.

An important criterion for the design and selection of clutch linings is therefore the bursting strength of the lining.

This bursting strength, also known as turning speed strength has to be greater by a factor of safety than the actual engine speed to which the clutch disc is subject under normal conditions.

Clutch linings need to be able to easily withstand peak temperatures in conjunction with over-revving due to gearshift errors.

Sintered bronze versus fatal burning

Today's linings are made predominantly of organic materials.

In extreme thermal load conditions however, inorganic clutch linings made of sintered materials prevail.

Depending on the main components, we distinguish here between sintered bronze and sintered iron alloys. Due to their heat resistance these sintered linings can easily withstand temperatures up to 600 degrees C.

The lining resilience system

Now we come to the lining resilience system, which makes a vital contribution to driving comfort and wear-resistance.

The clutch linings are given axial resilience by thin corrugated segmented plates.

These plates are made of sprung steel strips of 1 mm to 2 mm. This kind of lining resilience system delivers spring performance curves of 0.8 mm to 1.2 mm.

It offers two key benefits over a rigid design:

On the one hand, in expert terms it gives a better lining wear pattern. This is because the spring forces compensate for the thickness tolerances of the clutch linings and the expansion caused by heat. An even wear pattern also ensures an even heat distribution. That means that the danger of tension and heat fracture is significantly reduced.

It also allows a gentle start-up from cold. This is because the contact plate initially presses the clutch disc against the spring force of the lining resilience system onto the disc flywheel. As the pressure gradually increases the speed differential of the engine and the transmission gradually decreases - the result is gentle clutch engaging and a smooth start-up.

Constant friction diameter versus impact load

Clutches with large diameters, such as those used in commercial vehicles and elsewhere, a sudden impact load can cause distortion resulting in a significant reduction of the friction diameter. A suitable lining resilience system counteracts this problem and ensures the clutch transfer capacity.

Types of lining resilience systems

There are four different lining resilience systems in use, depending on requirements. We distinguish between:

single segment resilience systems

dual segment resilience systems

multi-plate resilience systems

inter-plate resilience systems

The torsion damper

Last but not least: we come now to the component that swallows up the vibrations before they ruin the journey for the passengers - the torsion damper.

As we know, unlike electric engines or turbines, combustion engines do not deliver constant torque.

They are characterised by a certain unevenness that cannot be wholly compensated for by the disc flywheel.

Crankshaft produces unwanted vibrations

This is because acceleration, deceleration, piston oscillations and constantly changing crankshaft speeds produce vibrations.

More precisely this relates to the so-called angular velocity about which we

need not go into more detail.

It suffices us to know that without countermeasures these vibrations will make their way through the drive train and magnify throughout the bodywork.

The torsion damper's job is to prevent this happening by isolating the vibrations. Important features of this kind of torsion damper are the distortion and friction mechanisms.

Distortion mechanism

The distortion mechanism comprises the drive plate, the meshing plate and a number of coil springs. These are inset into "windows" in the drive/clutch and meshing plates.

The springs enable the hub to twist circumferentially by up to +/-18 degrees. Further distortion is impeded by stop pins. The springs are constantly stressed and relaxed, thus damping the vibrations.

The use of a number of different springs enables multi-level, differentiated damping. (Illustrative photos or principle diagram)

Friction mechanism

The friction mechanism prevents the resonant rise of the torsion damper - an unwelcome effect of the vibrations.

This is achieved by axial bracing of the hub flange between the driver and the meshing plates through the insertion of friction rings made of plastic or organic material.

This guarantees the desired friction values and the corresponding wear-resistance. Small diaphragm springs press the friction mechanism together to enable a constant friction behaviour.

The clutch pressure plate

The main job of the clutch pressure plate is to connect and disconnect the drive train by applying the required compression force. It also releases the contact plate.

Its main components are as follows:

Contact plate

Diaphragm / coil spring

Contact plate

Let's take a closer look at the contact plate.

Along with the clutch disc it is one of the two friction-generating

components. As such it is subject to high thermal loads.. Depending on the conditions in which it is operating, average contact plate temperatures can easily reach 120 degrees C to 400 degrees C without detrimental effect.

However, it is smaller than the disc flywheel and it is also affected by heat passing through the clutch cover.

For this reason the service life of the clutch lining depends greatly on the right shape, dimensioning and material selection of the contact plate.

This is because its resistance to wear is greatly influenced by the effects of temperature. This is also the reason why the clutch lining wears considerably more on the contact plate side than on the flywheel side.

Contact plates require leaf springs

Each contact plate is connected by three stainless steel leaf springs which are riveted to the clutch cover. The main job of the leaf springs is to centre the contact plate within the clutch housing.The second requirement of the leaf springs is to transfer approx. 50% of the torque. This is related to the distribution of the power flow via the flywheel and the thrust plate.

he third requirement explains why springs are used at all. In fact they produce the release force for the contact plate.

Leaf springs are sensitive

It is important that the leaf springs, which are sometimes multi-layered stainless steel strips, are subject only to tensile strain.

Impact loads in the pushing direction which can be due to incorrect ignition setting or a dislodged shaft link can distort or even break leaf springs.

Plus, once they have suffered an impact, and this can easily happen during assembly and disassembly, clutch thrust plates may not be used any more.

Even being dropped from a small height can distort leaf springs. Precise checks must be carried out on a special test rig.

Coil spring and diaphragm spring

We are now getting close to the central element of the clutch: the coil spring or now usually known as the diaphragm spring.

To understand the operating principle of this kind of diaphragm spring better, we need to start with the design and the operation of the coil spring clutch.

Coil spring

OK, the clutch disc is fixed by the contact plate which presses against the clutch disc thanks to the force of the coil springs. They can be supported on the housing cover which is provided with spring cups for this purpose.

When the cover is pulled tight the coil springs press the components together. The clutch disc is then clamped, as explained earlier.

The contact plate is then withdrawn by a lever as shown on the following photos. The contact plate itself has a mechanism to which the lever is attached. The housing cover has a cam on which the lever rests.

When disengaging, the end of the lever is forced down from the release bearing thus freeing the disc.

Diaphragm spring

The whole clutch operates in principle similarly to the diaphragm spring- except that it is far more effective and has fewer mechanical requirements. No wonder that the coil spring clutch has largely taken over in recent times and is currently making inroads into the commercial vehicle sector.

A clutch assembly with diaphragm spring comprises the following: disc flywheel, clutch disc, contact plate, diaphragm spring and the housing cover to which the diaphragm spring is riveted.

If the cover is then screwed tight the spring is strained and, exactly like the coil spring clutch, it compresses the clutch disc between the flywheel and the contact plate.

However, the clutch is still missing the lever mechanism for disengaging the clutch.

This is the ingenious advantage of the diaphragm spring: it is both tension spring and release lever in one.

If the release bearing presses onto the spring finger ends it pivots, thereby releasing the contact plate as well as the clutch disc. The next drawing shows this clearly.

Special features of the diaphragm spring

Pivot ring or support ring

The diaphragm spring can pivot on its edge. Two pivot rings or support rings are therefore attached at this point.

These rings form the bearing for the lever simultaneously formed by the springs, which enable the pivot action in the first place.

They are around 4 mm in cross section. There are other versions with just one pivot ring. These nevertheless require extra design measures. For instance, a cover groove on the pressure plate.

It's always possible to make a mistake

Externally mounted pivot rings are occasionally mistaken as transport fasteners If they are removed the diaphragm springs cannot pivot and the clutch is useless.

Take care when installing

Extra attention is needed when installing. The ends of the fingers of the diaphragm springs can be straight or spherical.

You must note the shape of the fingers therefore when choosing the

release bearing.

Note: straight tongues must be combined with a spherical release bearing contact surface. Spherical tongue ends require a straight contact surface.

Photos: diaphragm springs with spherical and central contact surfaces

Release bearing

The release bearing forms the link between the clutch pressure plate that is rotating at the engine speed and the fixed release mechanism.

It is therefore involved in transferring the release force when engaging and releasing the clutch pedal and the clutch pressure plate.

Note: the release bearing features "fixed-rotating" force transfer.

More accurately it travels over the contact plane between the contact surface of the release bearing and tips of the so-called diaphragm spring fingers about which we shall hear more later.

Developments in automotive design eventually led to self-centring release bearings.

There was good reason for this. They balance the slight central displacement that is caused by production tolerances between the engine and the transmission or the release bearing and the clutch. They permit up to 2.5 mm radial adjustment

History

The clutch has undergone enormous technical development throughout the history of the automobile.

Electric and steam drive systems had no need for a clutch due to their practically ideal torque transfer.

Things changed with the arrival of the combustion engine. As this delivered power only when the engine was turning it consequently needed a means of disconnecting the engine and the transmission.

The first clutches used flat belts

The first clutches for motor cars used leather belts.

Tensioned over a pulley it transferred the drive power from the engine sprocket to the drive wheels. When slackened, the belt slipped and the drive was disengaged.

Since this wore the belts down rapidly, however, the designers sought better solutions.

Friction clutch

Various types of clutch were developed based on the principle of the friction clutch. The clutch engaged as a disc seated at the end of the crankshaft approached a second fixed disc bolted to the crankshaft.

When they made contact they generated friction and the non-fixed disc began to rotate, driven by the other disc. As the compression force rose the driving disc carried the non-fixed disc with it, with the result that both discs rotated at the same speed.

The basic form of this design principle was used as early as 1889 in Daimler's Steel Wheel Car.

This vehicle was fitted with a cone friction clutch. In this clutch a non-fixed friction cone engaged in the fixed conical flywheel.

This was fixed to the clutch shaft by the clutch housing. A spring forced the cone into the counterpart flywheel. Pressure on the footbrake pulled the cone back over the free-moving release coupling therefore interrupting the power transference.

Multi-plate or multiple disc clutch

Some cars used the so-called multi-plate or multiple disc clutch.

In this type of clutch a drum-shaped housing was connected to the disc flywheel. This had grooves on the inside into which located discs which bore corresponding notches on their outer edges. These rotated with the crankshaft or the flywheel but could also move lengthways.

An identical number of discs was correspondingly centered with internal notches on a hub connected to the clutch shaft. They could move lengthways along the clutch shaft.

During assembly alternate inner and outer clutch discs were combined to form a multiple disc assembly. The result was that a driving disc was always followed by a driven disc and vice versa.

These disc pairs were compressed together by thrust washers for each clutch spring. All clutch disc assemblies therefore engaged one after another.

This gradual increase in friction force meant that multiple disc clutches engaged very gently. As the spring force was released the discs disengaged once more.

Single plate dry clutch overtakes cone and multiple disc clutches

In the twenties the single plate dry clutch quickly overlook the cone- and multiple disc clutches.

The benefits were obvious: the small size of the meshing plate meant that it stopped rotating faster after the clutch was released. This made changing gear far easier.

The first design for the single plate clutch was relatively costly. However, the coil spring clutch eventually became a success. In this clutch the thrust force was generated by coil springs. Initial experiments were carried out with a central spring.

However, the first mass production was of a design in which several small springs were placed around the outer edge of the clutch housing.

The coil springs were forced together by levers which operated a release coupling which could move freely on the clutch shaft. This relieved the thrust plate, thus disengaging the clutch.

Varying spring configurations allowed a variable compression force. It had the distinct disadvantage however that centrifugal force pressed the coil springs ever harder against the spring cups as the engine speed increased. This made the clutch increasingly unresponsive.

In addition the release lever bearing tended to wear and the spring cups wore through quickly, especially when shifting gear at high revs.

The diaphragm spring clutch makes its triumphal entrance

The seventies saw the diaphragm spring clutch start on its triumphant way to the top. The replacement of the entire coil spring and lever system by a diaphragm spring which could perform both tasks brought many advantages.

The simple mechanical construction, the minimal space requirement and the constant thrust force were all factors which resulted in its almost universal use in the motor cars of today.

The diaphragm spring clutch is also being increasingly used in commercial vehicles.

The clutch disc has been optimised alongside this development. It is now equipped with a torsion damper and a lining resilience system which

prevent the engine vibrations from being transferred to the transmission via the crankshaft and clutch.

Clutch slips

Diaphragm-spring fingers worn

Cause:

Incorrect preload

Friction material worn to rivet head

Causes:

Excessive friction material wear. Vehicle was still being driven, even though the clutch was slipping

Clutch slipped for long periods?

Improper use?

Defective release system

Grease/oil on linings

Cause:

Too much grease used on hub - Excess grease on the hub splines was not removed and grease ran

Leaking engine or transmission shaft seal out onto the linings

Incorrect fitment

Causes:

Clutch disc installed backwards

Incorrect clutch disc installed

Flywheel modifications not made

Lining surfaces glazed

Causes:

Oil on linings - - Leaking shaft seal(s)

Lining coefficient of friction decreased due to allowing the clutch to slip for too long (overheated linings).

Linings worn down to the rivet heads

Causes:

Excessive lining wear - Vehicle was still being driven, even though the clutch was slipping.

Driver error - Allowing the clutch to slip for too long

Improper use of the clutch


Severe scoring and glazing on the pressure plate

Cause:

Overheating

Lining worn beyond

permissible limits

Worn clutch levers

Causes:

Incorrectly adjusted release bearing

Faulty release mechanism

Specific Circumstance

Cause Action Needed

Slipping and Impossible to Change Gear

Overheating due to excessive clutch

slippage

Install new clutch kit. Check all components of the release system, particularly self-adjusting release

systems and guide tubes. Check for leaking oil seals.

Slipping and Chattering

Driver resting foot on the clutch pedal or

incorrect clutch adjustment

Do not use the clutch pedal as a footrest. Inspect for correct clutch

adjustment.

SlippingThe self-adjusting mechanism has become jammed

Replace or repair the self-adjusting mechanism or in the case of

semiautomatic adjusters - reset.

Slipping Clutch facing material is oil contaminated

Replace leaking oil seals. Clean off excess oil and install new clutch.

Clutch judders

Faulty clutch mechanism

Cause:

Worn cable.

- Inner cable worn and unable to move freely.

- Old cables whilst they may look sound are worn.

Heavy chatter marks on the pressure plate

Causes:

Oil or grease on the facing

Stiff clutch linkage

Worn engine mountings

Worn transmission linkages

Engine badly tuned

Release fork worn

Cause:

Worn release fork mountings - Worn guide sleeve

Release shaft binding

Cause:

Worn release shaft and/or bearings

Release-fork bearing surface worn

Causes:

Incorrect installation - The transmission input shaft has been forced into the driven plate splines (the driven plate was not aligned when the pressure plate was installed).

Incorrect driven plate fitted

Tangential leaf spring bent

Causes:

Excessive clearance in the drive train

Driver error - Poor gear-shifting habits

Improper storage - Clutch fell or was dropped during installation

Clutch fails to disengage

Broken clutch levers

Causes:



Release bearing failure

Broken pivot pin

Causes:


Worn out torsion damper on the crankshaft

Incorrect setting of injectors

Casing and bearing damaged

Causes:

Overheating of the release bearing due to incorrect clearance causing loss of grease and break up of the bearing

Clutch disc distorted 1

Causes:

Improper installation - The clutch disc carrier was damaged by the transmission/PTO input shaft due to misalignment when the transmission

Clutch disc distorted 2

Causes:

Improper installation - The clutch disc carrier was damaged by the transmission/PTO input shaft due to misalignment when the transmission was reinstalled on the engine

Facing stiction

Cause:

Vehicle has been left standing for a long time

Fouling marks on the hub

Causes:

Fitting fault - Driven plate fitted wrong way around

Incorrect driven plate

Gearbox snout worn

Causes:

Incorrect adjustment of the release fork

Offset wear by the release fork

Hub splines chewed out on one side, tapered wear on splines

Causes:

Spigot (pilot) bearing worn

Angular misalignment of engine and transmission

Hub splines damaged

Causes:

Clutch incorrectly installed

Captive disc shaft incorrectly aligned

PTO hub shaft incorrectly aligned

Pressure plate not aligned to flywheel step

Pressure plate not torqued down correctly

Wrong drive plate installed

Linings torn off 1

Causes:

The rotational speed of the driven plate has exceeded the burst speed of the lining material, this condition occurs when the vehicle is allowed to coast with the clutch pedal depressed and the vehicle speed exceeds the maximum speed of the gear selected. This sort of damage is independent of engine rpm. The determining factor is transmission input-shaft rpm.

Linings torn off 2

Causes:

Worn flywheel face not machined flat.

Pivot ring removed

Causes:

Fitting fault - Pivot ring removed following fitting

Pivot ring is not an aid to fitment

Pressure plate broken

Causes:

Pressure-plate overheating due to slipping the clutch for excessively long periods

Clutch was slipping due to worn friction

Binding in the release system

Defective slave cylinder

Oil on linings due to a leaking shaft seal

Release bearing claering

Causes:

Insufficient bearing preload (specification 80-100 N)


Retractor plate clamping ring worn

Cause:

Defective release system - Insufficient preload

Rust on the hub

Cause:

Hub splines were not lubricated.

Sintered friction material destroyed

Causes:

Sintered friction material not bedded in. Tractor was put under heavy load immediately following fitting.

Excessive slip due to fitment of clutch disc against worn and grooved flywheel

Tangential leaf spring broken

Causes:

Play in the drive train

Driver error - Poor gear-shifting habits

Worn clutch levers

Causes:



Release bearing failure

Worn spring fingers

Causes:

Release bearing seized



Clutch makes a noise

A torsion spring has broken out

Causes:

Oil on clutch linings

Improperly tuned engine


Wrong driven plate installed

Driver error

Juddering damages the torsonalvibration damper.

Diaphragm-spring fingers worn

Causes:

Insufficient preload

Release bearing seized

Fouling marks on the hub

Causes:

Fitting fault - Driven plate fitted wrong way around

Incorrect driven plate

Gear box snout worn

Causes:

Offset wear by the release fork


Release bearing worn

Causes:

Insufficient bearing preload (Specification 80-100 N)

Incorrect adjustment of the release

Signs of wear on torsional vibration damper

Causes:

Clutch disc installed backwards

Incorrect clutch disc installed

Flywheel modifications not made

Worn splines

Causes:

Badly tuned engine - Faulty or incorrectly set injectors

Induced torsional vibration in tractor PTO

Specific Circumstance Cause Action Needed

Noisy ClutchBroken location lug due to worn release fork and or

no lubrication

Replace any worn components and install

new clutch. Apply a liberal amount of high

temp grease to the fork contact pads.

Chattering After Changing the Clutch Flywheel surface worn

Replace or resurface flywheel and install new

clutch.

Grating Noise when No lubrication on the Clean and lubricate using

Pulling Away clutch fork contact areas the grease supplied with the Valeo Clutch Kit.

Noise when in Neutral

Oil or grease has contaminated the disc pre-

damper making it ineffective

Install new clutch and sparingly use the spline grease supplied in the

Valeo Clutch Kit.

Noise During Release Worn pilot bearing or bushing

Replace pilot bearing or bushing

Noise

Installation is missing the transmission to engine dowel sleeves or pilot

bushing/bearing. This has created a concentric misalignment of the

engine to the transmission. The torsion

damper is destroyed, damper springs are

broken, stop pins show contact from the hub

flange and the hub pilot is worn.

Carefully inspect for missing dowel sleeves and worn dowel sleeve

holes in the bell housing. Replace pilot

bushing/bearing and inspect the transmission

to engine alignment.

Clatter on EngagementExcessive amount or

incorrect type of grease applied to input shaft

Install new clutch and use the spline grease supplied

in the Valeo Clutch Kit.

Difficulty Changing Gears

Cause Action Needed

The transmission was forced into position

damaging the splines of the disc hub.

Install new clutch and carefully control the position and alignment of the transmission during installation. Use a

transmission jack and possibly install temporary guide pins to assist in aligning the transmission to the engine.

The cover assembly has been dropped.

Install new clutch. Always inspect the drive straps for damage before installation.

The cover has not been located on the flywheel

Install new clutch and ensure all flywheel dowel pins are in position and in good condition. Do not use air tools to

dowel pins correctly. tighten the bolts.

The self-adjusting mechanism fails to lock

due to worn ratchet and pawl.

Repair self-adjusting release system. Replace ratchet and pawl.

Release bearing travel is insufficient.

Inspect release mechanism for full travel or lost motion due to worn parts. A stamped steel release arm can wear and

break. Always remove and check arm and external pivots. Install new fork bushings and lubricate as required with

high melting point grease.

Loss of Drive

Cause Action Needed

Transmission has been hung on the shaft

during installation. Angular misalignment of the transmission to

engine.

Install new clutch and support transmission during installation. Do not allow the transmission to hang on the

clutch disc during installation. Check for missing bell housing dowel sleeves, worn pilot bushing/bearing or

foreign matter between transmission and engine including wires, cables or brackets. The above problems will cause

cracking in the segments, leading to separation of the damper and facing segments.

Driver resting foot on the clutch pedal

resulting in release system sticking.

Install new clutch. Check all components of the release system, particularly self-adjusting release systems, and

guide tubes. Check for leaking oil seals.

The clutch has been disengaged at speeds

in excess of the maximum for the gear

selected or the incorrect gear has been

selected. This has caused the facings to

burst.

Install new clutch and educate the driver.

Clutch Pedal

Specific Circumstance

Cause Action Needed

Vibration Through the Clutch Pedal

The transmission shaft has struck and bent the

diaphragm spring fingers during

installation

Install new clutch and carefully align and control the position of

the transmission during installation.

Noise While Depressing Clutch

Pedal

Seized release bearing due to excessive heat caused by incorrect

bearing pre-load or loss of grease

Install new clutch and check all components and adjustments of the release system i.e. cables, linkages, fork, ball studs, fork

bushings and self-adjusting release systems.

Clutch Pedal Binding

The release bearing guide tube is worn or

the release arm/fork is bent or worn

Install new clutch and guide tube. Inspect all release system

components and repair or replace as needed.

Grating Noise and Stiff Pedal

Insufficient lubrication of the clutch fork,

particularly at the pivot point

Clean and lubricate all components using a high temp grease. If

excessively worn, replace the fork and ball stud.

High Pedal EffortThe release bearing

does not freely slide on the guide tube

Clean and lubricate the guide tube to bearing contact area with high temp grease. If the guide tube is worn or scored, replace the guide

tube.

Metallic Noise at Bottom of Pedal Travel, Difficult

Shifting

The release travel is excessive causing the diaphragm spring to

contact the clutch disc

Install new clutch and ensure correct clutch adjustment.

Metallic Noise at Bottom of Pedal

Travel

The release travel is excessive causing the diaphragm spring to contact the bearing

carrier

Install new clutch and ensure correct clutch adjustment.

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