WHAT IS A CLUTCH?
A clutch is the device that couples the engine to the drivetrain. It is designed so that it

can be positively disengaged by depressing the clutch pedal. This disconnects the engine and

drivetrain. Releasing the clutch pedal engages the clutch, connecting the engine and

drivetrain.

CLUTCH SYSTEMS
When the clutch couples the engine to the drivetrain, it is transmitting the power of the

engine to the drivetrain. In a street or a race application, the smoother the clutch applies

the power to the driveline, the better the vehicle will perform.

Think of your clutch system in terms of the braking system. If you lightly apply the brakes

in stopping, the vehicle will stop in a smooth manner. If you stab the brake pedal, the

brakes are likely to lock up and a skid will occur. The same principle applies to the

clutch. If the clutch is engaged with too much pressure, the tires are likely to spin. When

the pressure of the clutch is controlled, the clutch is able to apply the torque of the

engine smoothly to the drivetrain without excessive tire spin.

Just like your brake system, over time the friction components of the clutch system will

wear. The more you use the brakes, the faster they wear. The more the clutch is slipped to

provide smooth engagement, the faster it will wear.


COMPONENTS THAT MAKE UP A CLUTCH SYSTEM

PRESSURE PLATE
This is the pressure mechanism that clamps the disc to the flywheel to get the vehicle

moving. Pressing in the pedal relieves the pressure from the clutch disc to disengage the

engine from the drivetrain for shifting or stopping.

CLUTCH DISC
The clutch disc is a flat plate with friction materials on both sides. As the pressure plate

is engaged (pedal let out), the clutch disc is clamped to the flywheel. When the pressure

plate is disengaged, (pedal pushed in) the clutch disc is unclamped. The disc is connected

to the input shaft of the transmission by the splined hub, causing the input shaft to turn

when the clutch is engaged, thus causing the vehicle to move.

FLYWHEEL
The flywheel is an inertia device that is bolted to the engine crankshaft. It has several

functions including carrying the ring gear the starter uses to crank the engine, storing

energy to get the vehicle moving from a standing stop, and providing the friction surface

for the clutch disc to be clamped to.

RELEASE BEARING
The release bearing is the actuating device that engages and disengages the pressure plate.

When the clutch pedal is depressed, the release bearing applies pressure to the fingers of

the pressure plate to disengage the drivetrain. When the clutch pedal is released, the

release bearing retracts and allows the pressure plate to apply pressure to clamp the disc

against the flywheel.

RELEASE FORK
The release fork holds the release bearing, and pivots on a ball stud as the pedal is

pressed in or let out. Pushing in the pedal pivots the fork towards the pressure plate and

forces the release bearing against the clutch fingers, pressing them in to disengage the

clutch.

PILOT BUSHING
The pilot bushing or bearing installs in the end of the crankshaft. When the transmission is

installed, the input shaft tip inserts into the pilot bushing, which supports the input in

the back of the crankshaft.


TYPES OF PRESSURE PLATES
The pressure plate applies pressure to the clutch disc to clamp it against the flywheel and

engage the clutch. Pressure may be generated by spring (static) pressure or centrifugal

pressure. Static pressure is constant, meaning that whether the engine is turned off or

spinning 7000 RPM, the pressure never changes. Centrifugal pressure is not constant. It is a

function of engine RPM. Centrifugal pressure is generated by the clutch levers and increases

to the square of the engine RPM. It is less pronounced at lower engine speeds but very

effective in the higher RPM range.


DIAPHRAGM PRESSURE PLATES
The diaphragm pressure plate utilizes a Bellville or conical spring to apply pressure to the

pressure ring. This type of pressure plate has multiple fingers that the release bearing

presses against to disengage the clutch. Diaphragm clutches rely completely on static

pressure which is unaffected by engine RPM.

The Belleville spring allows the pressure plate to be released and engaged with a relatively

light pedal effort compared with coil spring clutches. This design is used almost

exclusively in late model vehicles that have hydraulic or cable release mechanisms, due to

the lighter effort required to engage and disengage the pressure plate.

The diaphragm clutch is excellent for use in street and heavy duty street applications where

drivability and pedal effort are a major concern for the user.


CENTRIFUGAL WEIGHTS IN DIAPHRAGM STREET/STRIP APPLICATIONS
Some aftermarket diaphragm pressure plates feature a centrifugal weighting system.

Centrifugal assist is useful in drag racing and other high RPM applications to apply

additional clamp load to the clutch disc. The drawback to centrifugal assist in highway

performance applications is that the centrifugal assist is low until the engine reaches high

RPM. The load on the clutch (the effort required to turn the driveshaft) is very high at low

RPM and decreases at higher RPM. In most highway applications centrifugal assist is not

effective in increasing holding power or performance because it fails to solve the high

torque load at low RPM problem.


BORG & BECK PRESSURE PLATES
The Borg & Beck pressure plate uses three levers to engage and disengage the clutch disc. It

is a coil spring design, where the pressure of the clutch is applied to the disc using coil

springs similar to a valve spring. By combining these springs at a specific installed

height, different pressures can be attained for the pressure plate. Borg & Beck clutches

rely completely on static pressure which is unaffected by engine RPM.

Borg & Beck pressure plates are found in GM, Chrysler, and AMC early model applications with

mechanical linkage. Borg & Beck clutches and can be identified by looking at the width of

the clutch fingers, which is about one inch. The coil spring design by nature will require

more pedal effort to engage and disengage the clutch.

Borg and Beck clutches are best suited to street and heavy street applications in older

muscle cars and trucks.


LONG STYLE CLUTCHES
In typical Long Style pressure plates weights are added to the clutch levers to increase the

plate pressure as RPM increases. Pressure plates are the Ford version of a three lever, coil

spring pressure plate. Long is the most popular type of pressure plate for drag racing

applications. Its design is the basis for today's professional drag racing clutches.

The inherent advantage of Long Style pressure plates is their ability to apply centrifugal

clamping pressure. As engine RPM increases, the levers in the plate pivot against the cover

and apply additional clamp load to the clutch disc. This is true in both counterweighted

lever and non-counterweighted designs. (Counterweighted levers have provision for

installation of weights to the backside of the levers to further increase the centrifugal

clamp effect.) Some Long Style clutches feature adjustable static pressure. By turning an

allen screw located on top of the spring, the pressure can be increased.

Long clutches were prevalent in early Ford muscle cars and trucks.


ADJUSTING STATIC PRESSURE ON LONG STYLE CLUTCHES
Increasing the static pressure of a Long Style pressure plate is achieved by turning the

Allen adjuster screw COUNTERCLOCKWISE to increase the static load. When the screw is turned,

it pushed against the cover and the adjuster base compresses the spring, increasing the

spring rate. Most pressure plates have a maximum of 7 turns adjustment. Turning the adjuster

screw further will cause it to come out of the adjuster base. When this occurs, the entire

plate must be disassembled for repair. Some racers mark the turns they have in the clutch on

the side of the bellhousing in order to keep track of where they are set.

As the adjuster screw is turned counterclockwise, the spring is compressed to increase clamp

pressure.




CLUTCH DISC CONSTRUCTION

There are two types of clutch disc construction - solid hub and spring dampened hub.

Solid hub discs have the splined hub riveted directly to the disc carrier plate (the

circular metal plate that carries the friction material). This construction is typical of

all out racing discs.

Sprung, or dampened hub discs, do not have the splined hub attached directly to the carrier

plate. The hub floats in a spring loaded assembly on the carrier. When the hub is loaded as

when the clutch is engaged, the springs help absorb the load rather than transfer it

directly to the carrier plate. This arrangement allows shock spikes from aggressive

engagement to be dampened out to avoid possible damage to the drivetrain. This type of

construction is used in factory replacement discs.

Performance discs feature stronger damper springs to absorb higher loads. Most RAM

performance discs are equipped with RAM poly-coil springs, which are encapsulated in

urethane providing a substantial increase in the spring rate over stock springs. The

stronger spring prevents over travel of the hub and subsequent damage to the disc.

Selecting the correct disc construction is simple. Stock applications use the dampened hub.

From there, as loads increase, the rigidity of the hub should increase right up to solid

hub.


COEFFICIENT OF FRICTION

Let's say we have a box sitting on a countertop. It takes 3 pounds of pressure to slide the

box across the countertop. Now we place the box on a rubber mat. It takes 8 pounds of

pressure to slide the box across the rubber mat. The rubber mat has more grip, or a higher

coefficient of friction than the smooth countertop, thus taking more effort to slide the

box.

In terms of the clutch disc material, a higher coefficient of friction means that it will

take more load on the clutch to cause it to slip.


FRICTION MATERIALS

As performance requirements increase, it is necessary to step up the friction

characteristics and durability of the clutch facing materials.

ORGANIC - Organic material is common to all stock clutch discs, and offers the best

drivability but has limitations as operating temperatures rise. Under high loads accompanied

by slippage, they fade because their coefficient of friction drops off. In addition, at high

RPM and high temperature they tend to fail structurally.

KEVLAR COMPOSITES - Kevlar material offers a higher coefficient of friction than organic

material, but with some loss in drivability. As the coefficient of friction goes up in the

disc material, so will the aggressiveness of the material on engagement. This means that

some chatter can be expected with this material in low gear and reverse. Kevlar is

compatibile with stock flywheels and pressure plates, making it a good upgrade choice for

later model vehicles. We do not recommend Kevlar for competition.

BRONZE METALLIC - Bronze metallic (paddle discs) is the most aggressive materials in terms

of engagement. It offers extended life using reduced static pressures, and a quick, clean

engagement. Bronze metallic is aggressive on the flywheel surface and should be used only

with steel or nodular iron friction surfaces. On the street, this material will cause

chatter on engagement.

SINTERED IRON - Sintered iron is well known for its ability to withstand some slippage and

not loose its coefficient of friction. It is the material choice for high horsepower clutch

applications for drag racing and truck pulling. A key feature of the competition sintered

iron material is that it is maintainable. If the clutch is slipped excessively, the disc can

be resurfaced and reused.


DRIVABILITY VERSUS PERFORMANCE

With disc choices ranging from organic to metallic to sintered iron, deciding which material

to use is ultimately up to the end user, based on the type of performance and drivability is

desirable. When deciding, one must think about what is most important for the vehicle. If

on-the-track performance is the most important, select a disc material that is fairly

aggressive. But realize that making this decision will effect how smoothly the vehicle will

operate under normal driving conditions. If smooth and drivable is most important, select

the disc based on this. Keep in mind though, that the life of the clutch disc under racing

conditions will likely be reduced.




FLYWHEELS
The flywheel is primarily an inertia device. As the flywheel spins it stores energy or

inertia that helps move the mass of the vehicle as you engage the clutch.

Factory flywheels are designed to apply the optimum amount of stored energy to provide good

drivability for the vehicle. Vehicles with smaller engines have relatively heavy flywheels

due to the extra inertia needed for a smooth transition to engagement. Reducing the weight

of the flywheel, while increasing performance, could reduce the drivability of the vehicle.

Under racing conditions, the flywheel weight can be used to control the inertia applied to

the drivetrain. For instance, if a vehicle tends to ‘bog' upon engagement of the clutch,

increasing the flywheel weight will increase the inertia needed to launch the vehicle

smoothly. Too much flywheel weight may cause excessive inertia to be applied, causing the

tires to spin. Reducing flywheel weight under this condition will reduce the inertia applied

to the vehicle and allow smoother acceleration.

Aluminum flywheels are used in drag racing high horsepower applications which require the

clutch to slip as the vehicle leaves the line. Steel flywheels are used primarily in street

driven vehicles.


GEARING AND FLYWHEEL WEIGHT
Other load factors can effect flywheel selection, such as rear gearing or transmission

gearing. With the abundance of gearing choices available today, it is possible to use almost

any flywheel if the proper selection of gears is made. This was not always the case in the

70's when the gearing choices were not available, racers had no choice but to use the

flywheel weight to control the vehicles on launch. It is more efficient to use a light

flywheel and proper gearing than to use tall gearing and a heavier flywheel.


FLYWHEELS AND DRIVABILITY
Selecting the proper flywheel helps you achieve the drivability you desire for your vehicle.

Heavy streetcars will benefit from a heavier flywheel to generate the inertia to get you

moving. An aluminum flywheel will not generate as much inertia to move the vehicle, and thus

it would be necessary to slip the clutch more on takeoff. Some street vehicles may benefit

from a lighter flywheel, but only if there is enough rear gear to help you transition the

clutch smoothly without excessive slippage.


HOW DO I SELECT THE PROPER FLYWHEEL?
When we are asked for a flywheel recommendation, several factors are considered to make a

proper recommendation:

- What is the primary use of the vehicle? For street driven vehicles, a steel flywheel will

provide easier engagement and longer clutch life.

- What is the rear end gearing? Lower (higher numerically) gears will make engaging the

clutch easier, while higher gearing requires the clutch to be slipped more on takeoff for a

smooth transition.

- What is the weight of the vehicle? If it is over 2800 pounds, we will generally recommend

steel.

Remember the flywheel's job is to get the car accelerating smoothly. If you have ever driven

a vehicle and tried to pull off in second gear, you know you had to slip the clutch

significantly more to get moving than if you started in low. This is the same effect you

would notice if the flywheel is too light.



RELEASE MECHANISMS
All clutch systems require a release mechanism to operate the clutch. There are several

types of systems that have been used over the years by the various manufacturers.

MECHANICAL LINKAGE
Mechanical linkage is most prevalent in vehicles produced pre-1980 and in race vehicles. It

usually consists of a bellcrank that pivots between the frame and the engine block. One side

of the bell crank attaches to the clutch pedal, and the opposite side attaches to the

adjustment rod for clutch release. The adjustment rod is inserted into the clutch fork and

lengthened or shortened to achieve the proper release and gap between the clutch fingers and

the bearing. Typically the ratio between the release mechanism and the pedal effort is

between three and four to one. Mechanical linkages provide the most flexibility in clutch

adjustment.

HYDRAULIC SYSTEMS
Hydraulic master/slave release systems are common in vehicles produced after 1980. This

system uses a master cylinder mounted on the firewall and a slave cylinder, usually mounted

on the bellhousing. A hydraulic line connects the two. The slave cylinder will usually have

a rod that fits into the clutch fork and either pulls or pushes the fork when the pedal is

depressed. Some hydraulic systems incorporate an adjustable slave cylinder, where you can

manually set the clutch release. Some later GM systems use non-adjustable slave cylinders

and are more difficult to deal with when installing non-stock clutches.

Often when changing clutches in vehicles with non-adjustable hydraulics, if the flywheel is

resurfaced more than .020 inch, a flywheel shim must be used between the crank flange and

the flywheel to shim the flywheel to its original position. Since the slave has no

adjustment, the only way to make these systems function properly is to have the pressure

plate mount so that the fingers are in the exact same position as stock in order for the

clutch to release properly.

CABLE RELEASE SYSTEMS
Cable release systems use a cable connected to the clutch pedal and the clutch fork to

actuate the release bearing. When the clutch pedal is depressed, the cable is pulled and in

turn pulls the clutch fork to disengage the clutch. Most cable systems are self adjusting,

using a ratchet mechanism mounted under the dashboard to keep the release bearing in

position for the clutch to release.

Aftermarket adjustable cables are available for many aftermarket clutch systems, the most

popular being the late model Ford Mustang.

INTERNAL HYDRAULIC RELEASE BEARINGS
Internal hydraulic release bearings are the newest release systems used in late model

vehicles. Typically, a slave cylinder that houses the release bearing mounts to the rear of

the bellhousing or on the front of the transmission. A hydraulic line connects the slave to

the master cylinder mounted on the firewall. When the clutch pedal is depressed, the slave

cylinder pushes the release bearing out and disengages the clutch. Most of these systems are

non adjustable and require the clutch to install so that the fingers are in the stock

location, or the clutch may not release. You may also hear these bearings referred to as

concentric release bearings.

Internal bearings are not new to the aftermarket. Several manufacturers have produced these

units for use in oval track racing, where space limitations preclude using a fork release

system. They are also very popular for kit car installations.


TYPES OF RELEASE BEARINGS
Two types of bearings are used for these release mechanisms. Standard release bearings have

the bearing and race pressed on the bearing collar. The bearing is static on a standard

bearing. SELF ALIGNING release bearings are assembled in the same manner, but have floating

design that allows the bearing to move about on the collar so it can find its exact center

once it comes in contact with the pressure plate fingers. Self aligning bearings are used in

most all late model applications.

pics?

someone found an old tech-school report????

ahh so mutch to read. cant you add pictures for people like me. who are to lazy.

nice work anyway

Just make sure you double clutch if you want to go faster. Granny shifting loses races!

So if i cant smoothly releases the clutch because of faster wear, other then dropping the clutch at every set of lights, what can i do to increase the life of my clutch.(i just replaced it 5 months ago and its 700 i dont wana have to spend anytimes soon )

Buy a heavy duty after-market clutch. Can come in at the same price as OEM but last longer, with better feel.

You'll find most oem parts (brake pads, oils, clutches) are for suckers. There's aftermarket parts that will do better for comparitive prices.

Practice heel-toe downshifting. Makes your downshifts smoother = less clutch slippage.

Try not to accelerate or brake too hard.
Try not to plant your foot while cornering.

All these, ironically, will give you better fuel consumption and slower brake wear. Its called driving sensibly, i believe. *shrugs*

now can we have one on torque convertors for us non left foot using drivers?

torque converter:
put foot down, car goes.

Wtf is double clutching? Hear it on movies all the time but it sounds lame.

Google is your friend.

ITs exactly what it sounds like. In gear > clutch in > neutral > Clutch out > rev a little > clutch in > gear.

Without double-clutching, i cant drop 1st in at any speed above 10kph. With double clutching, i can drop down into 1st at any speed up to about 50 kph.

It basically pre-spins up the gears/synchros so you can drop the next gear in easily.

I know a few prime-movers etc...you HAVE to double clutch, or your simply not getting into the next gear.

Initially its slow, takes a while to pick up, but once you do its second nature and EXTREMELY useful around town, let alone on the track.
Just like heel-and-toeing really.

double clutching is a requirement of shifting in a box without synchros. most boxes these days have all synchro, but older ones didn't have synchro on 1st or reverse, so as Liquidity said, he has to double clutch to 'manually synchronise' his box for 1st gear.

I dont HAVE to, but it makes it a lot easier and smoother. 1999 lancer CE.

yes, but you can change gears without a clutch too - the clutch and synchros make it smoother.

yeh is it tru that i can change gears without the clutch? like if u match the revs or something with the gear, then it will slip straight in?

eg. (for arguements sake) from first to 2nd, must be at 25000rpm, no clutch, 2nd will go straight in, with the correct timing, and revs? (this is just an example, so dont go trying it. )

can anyone shed any more light on this?

cheers
- mad89

yeah. Get in 2nd gear, and cruise along. start applying a bit of pressure to the gearstick...then...as you let off the throttle, push it into neutral. As the rev's drop, move it to third and apply light pressure. At the appropiate revs, it should just slot in. If it doesnt, you missed the revs, can can try blipping the throttle in neutral again and trying to slot it again.

DONT push it in HARD, you'll just grind things.

If your going DOWN gears...its just power-off > neutral > blip throttle up > slip into next gear.
A heel-and-toe guy does this while using the clutch and braking too.

It's amazing watching the V8 Supercar blokes heel and toe...

yeh, how awesome is that camera they have near their feet showing it.

amazing skill



- mad89

A few of them left-foot brake. Dont use the clutch at all.

yeah, looks awesome......

meh flat shifting is the way to go.

LOL thats my theory too Fudd mind you 3 gear box rebuilds in a VL-T and one eminent in the mazda some time soon im starting to think i enjoy driving autos now.

Google would also find an answer for almost every question asked on the forum. I choose to ask here, it was easier for me and now there is an explanation on CAA so its knowledgebase has expanded, win win situation?

I don't think that was mentioned in FF, or 2F2F so I think your way might be wrong