CLUTCH
PURPOSE AND FUNCTION OF A CLUTCH
1. To disconnect the engine from the transmission/transaxle to permit the engine to remain running when the
vehicle is stopped and to permit the transmission/transaxle to be shifted
2. To connect and transmit engine torque to the transmission/ transaxle
3. To dampen and absorb engine impulses and drive train vibration
4. To provide a smooth engagement and disengagement between the engine and the transmission/transaxle
PURPOSE AND FUNCTION OF A CLUTCH
• Transmission refers to rear-wheel-drive vehicles
• Transaxle refers to front-wheel-drive vehicles that have a differential built into the unit.
• A separate differential is used with a transmission.
COMPONENT PARTS AND OPERATION OF A
CLUTCH ASSEMBLY
COMPONENT PARTS AND OF A CLUTCH
CLUTCH PEDAL LINKAGE
1. Levers and rods. Through a series of levers and rods, the release fork is forced against the throwout bearing.
2. Cable operation. A cable is used similar to a brake cable used on a bicycle. Mechanical operation usually takes
place through a Bowden-cable. The cable consists of a steel cable and a steel cable sheath. The sheath absorbs
the force of the clutch operation.
COMPONENT PARTS OF A CLUTCH
CLUTCH PEDAL LINKAGE
3. Hydraulic.
COMPONENT PARTS OF A CLUTCH
CLUTCH PEDAL LINKAGE
1. Pushing the pedal results in a hydraulic pressure in the system. This leads to an increase of the piston at the slave cylinder, which
pushes the clutch fork.
2. Advantages of this system are:
3. • Hardly any friction. The efficiency is about 90%.
4. • This system is relatively maintenance-free.
COMPONENT PARTS OF A CLUTCH
CLUTCH PEDAL LINKAGE
1. This system is easily made self-adjusting. A spring in the slave cylinder
compensates for the wear in the clutch plate.
2. There are also hydraulic thrust bearings; this renders the clutch fork redundant.
The pedal force is applied directly to the thrust bearing.
COMPONENT PARTS OF A CLUTCH
Clutch plate
The clutch plate can move along the spline on the input shaft so that it can engage and disengage drive on application. The clutch plate
rotates on the splined gearbox input shaft.
A clutch is a 'wear-component'; wear quicker than the flywheel and clutch release assembly.
COMPONENT PARTS OF A CLUTCH
Clutch plate (Clutch lining)
The clutch lining used to contain asbestos. Organic material is now used.
A clutch plate has to meet these demands:
• excellent mechanical strength
• resistant to high temperatures
• high coefficient of friction
• excellent heat dissipation
• silent operation
• long life
• low weight
COMPONENT PARTS OF A CLUTCH
Clutch plate (Clutch lining)
Metal particles are embedded in the lining, to improve the thermal conductivity.
The plate lining is grooved to dissipate heat and dirt.
The lining is riveted to the lining carrier, using hollow rivets. These rivets are
made of steel, copper or brass. The clutch plate has extra holes in it to prevent it
from "sticking" to the flywheel.
COMPONENT PARTS OF A CLUTCH
Clutch plate (Axial springing)
Axial springing is applied to enable engagement without snatching and juddering.
The lining carrier is divided into segments; & slightly bent. These gradually engage the clutch plate to the flywheel.
This axial springing is also known as plate springing.
The marcel spring also helps to absorb & smooth the initial shock of engagement and of the clutch.
COMPONENT PARTS OF A CLUTCH
Clutch plate (Axial springing)
Before being fully engaged, these segments are compressed gradually.
COMPONENT PARTS OF A CLUTCH
FLYWHEELS
1. Smoothes out or dampens engine power pulses.
2. Absorbs some of the heat created by clutch operation.
3. Provides the connection point for the starter motor to crank the engine.
4. Provides the application surface for the clutch friction disc.
COMPONENT PARTS OF A CLUTCH
DUAL-MASS FLYWHEELS.
By allowing a very slight amount of movement between the two flywheels, the damper absorbs engine torque peaks
and normal vibration to provide smoother drive train operation.
The damper assembly is completely sealed, which also helps absorb vibration and transmit torque. Typically, the two
flywheels twist out of phase with each other by up to about 60 degrees to absorb torsional oscillations.
COMPONENT PARTS OF A CLUTCH
Clutch plate (Torsional damping springs)
A combustion engine delivers a uneven motion. This unevenness is
partially counteracted by the flywheel.
Torsional damping springs in the clutch counteract these negative
qualities in a combustion engine even further.
To minimise vibration, springs with different characteristics are used.
COMPONENT PARTS OF A CLUTCH
STOCK CLUTCH DISC
Around the center hub of the clutch disc are torsional dampers that absorb the initial shock of engagement and help
dampen engine-firing in pulses being transmitted into and through the transmission/transaxle.
The torsional dampers are either coil springs or are made of rubber. In the space between the friction surfaces is a wavy
spring steel material called a cushioning spring or marcel spring.
COMPONENT PARTS OF A CLUTCH
HIGH-PERFORMANCE CLUTCH
DISC with friction material is a ceramic and metallic mixture.
This creates a hard, long-lasting lining, but is more expensive and does not cushion clutch engagement as much as a softer lining.
Instead of a full circle of softer friction material, the disc may have only a few segments or buttons of this ceramic-metallic material.
Clutches that use these discs, which are sometimes called “ button clutches,” are found in racing applications where strength and
durability are a greater concern than smooth engagement.
COMPONENT PARTS OF A CLUTCH
Clutch release assembly
The object of a clutch release assembly is to transfer clutch pedal force into movement.
The pressure plate can move axially (= along the gearbox input shaft spline). This way, the clutch plate is 'sandwiched
between flywheel and clutch release.
COMPONENT PARTS OF A CLUTCH
Clutch release assembly
There are two kinds of clutch release assemblies:
1. with a diaphragm spring
2. with coil springs
COMPONENT PARTS OF A CLUTCH
Clutch Release Assembly With Coil Springs
• It is used in trucks and motorbikes.
• The pedal force in this assembly increases linearly.
COMPONENT PARTS OF A CLUTCH
Clutch release assembly with diaphragm
• The special shape of the diaphragm spring ensures a better force distribution.
• The straps transfer the torque to the pressure plate, ensure that the pressure
plate remains centred and that the pressure plate springs back when
disengaging the clutch.
• The wire rings provide the pivot point for the diaphragm spring.
COMPONENT PARTS OF A CLUTCH
Clutch release assembly with diaphragm & Coil Spring
• An advantage of the diaphragm clutch is the rapid decrease of pedal force.
Also, the construction of this clutch is:
• lighter
• simpler
• cheaper
• more compact
❖ A disadvantage of the coil spring clutch is the force applied to the thrust
bearing is relatively high.
❖ One advantage of the coil spring clutch is that the force distribution is linear;
this makes it possible to operate the clutch with more feel. This is particularly
useful with motorbikes.
COMPONENT PARTS OF A CLUTCH
COMPONENT PARTS OF A CLUTCH
CLUTCH PROBLEM DIAGNOSIS
CLUTCH SLIPS Possible causes:
1. Clutch is worn or out-of-adjustment.
2. Clutch disc has oil on the surface.
3. Flywheel height is out-of-specifications.
If the clutch is slipping, it cannot transfer engine torque to the transmission or drive wheels. A common
method used to check for a slipping clutch is the following:
1. Drive the vehicle to a safe location where it can be accelerated safely.
2. Rapidly accelerate the vehicle in first or second gear and rapidly shift the transmission into a higher
gear.
The engine speed should drop as the clutch is released after selecting a higher gear. If the clutch is
slipping, the engine speed will either rise or not drop after the clutch pedal is released (clutch is engaged).
CLUTCH SYMPTOM GUIDE
• Clutch is that it sometimes will not fully disengage. Symptoms will occur if there is a fault in the clutch
or in the linkage or hydraulic system that could prevent the clutch from being fully disengaged:
1. The transmission will be difficult (or impossible) to shift into reverse.
2. The transmission will be difficult (or impossible) to shift between forward gears.
CLUTCH GRABS Possible causes:
1. Clutch disc has oil on the surface.
2. Clutch linkage is binding.
CLUTCH SYMPTOM GUIDE
CLUTCH NOISES
1. Sometimes transmission noise can be mistaken for clutch noise. When the noise only happens when the pedal is moved, try
moving the pedal while the engine is off.
2. A noise when the clutch is first engaged (pedal let out and disc being wedged against the flywheel and pressure plate) is due to a
problem with the friction lining.
3. Release bearing (without self-adjusting clutch) free travel is not designed to contact the clutch release levers except when the
pedal is applied. If the noise only happens when your foot is resting lightly on the pedal, the release bearing is probably at fault.
4. Pilot bearing. Shift the transmission into gear, depress the clutch pedal, and start the engine. The crankshaft will spin the pilot
bearing against the bearing surface at the front of the input shaft, which is being held still because the transmission is in gear.
CLUTCH NOISES Possible causes:
1. Pilot bearing is defective or worn.
2. Release bearing is defective or worn.
CLUTCH SYMPTOM GUIDE
TRANSMISSION NOISE
1. Sometimes noise occurs only when the engine is idling in neutral with the clutch engaged (pedal up).
This causes the transmission input shaft to turn with the clutch disc. The front transmission bearing
on the input shaft and the mainshaft pilot bearing at the back of the input shaft are the only bearings
that are rotating. Therefore, one of these bearings is probably the source of the noise.
CLUTCH NOISES Possible causes:
1. Pilot bearing is defective or worn.
2. Release bearing is defective or worn.
CLUTCH SYMPTOM GUIDE
CLUTCH SLIPS Possible causes:
1. Clutch is worn or out-of-adjustment.
2. Clutch disc has oil on the surface.
3. Flywheel height is out-of-specifications.
CLUTCH GRABS Possible causes:
1. Clutch disc has oil on the surface.
2. Clutch linkage is binding.
CLUTCH NOISES Possible causes:
1. Pilot bearing is defective or worn.
2. Release bearing is defective or worn.
