The clutch is a physical disconnect between the engine and the wheels of the car. More specifically, it disconnects the flywheel which is connected to the engine,  from the gearbox which is connected to the wheels. This allows the engine to spin independently of the wheels, which is necessary for starting and stopping.

For More Read: Death of the Gearshift In more detail...the engine spins the flywheel, which is basically a plate at the rear of the engine (transverse engine mounting aside). This spinning plate presses against the clutch, which is essentially another spinning plate, but connected to the gearbox. When you press the clutch pedal in, the clutch plate moves backward, coming out of contact with the flywheel. When you let the clutch pedal out, the clutch plate is pressed forward by a spring, applying pressure to the flywheel and eventually spinning up/down to the same rpm via friction. When your car is coming to a stop, putting in the clutch pedal allows your wheels, gearbox, and clutch plate to stop spinning while your engine and flywheel keep spinning.  Putting the car into neutral is essentially putting a gap in the sequence where the gearbox is, so you can let the clutch pedal out. Now, your engine, flywheel, and clutch plate are in contact and spinning, there is no gear selected in the gearbox, and the wheels are free to spin.
There are several classifications for of clutches.

On the basis of presence of lubricant, 1.Dry clutch : In this type of clutches, lubricant is not applied and hence the torque transmitting of these clutches is better.

2.Wet clutch : In this type of clutches, lubricant is applied to dissipate the heat from the frictional surfaces in contact. The torque transmitting capacity is slightly reduced due to decreased co-efficient of friction between the contact surfaces due to the presence of lubricant.

On the basis of number of plates, 1. Single plate clutch : These cluthes are having a single frictional surface to transmit the power between two shafts. These clutches are larger in size when compared to multi plate clutches of the same transmission capacity.

2. Multi plate clutches : These clutches are used in the applications where you dont have enough space to install large single plate clutches. They provide better co efficient of friction, as the surface area is increased due to the presence of multiple plates.

There are different types of clutches depending on the method of operation,

Dog Clutches : These clutches don't have frictional plates but they have teethes, which are mounted on both the shafts which are to be coupled.At a certain combination of teethes, power is transmitted between the shafts.

Centrifugal clutches : As the name itself suggests, works on the principle of centrifugal force and transmits the power between the shafts when a certain speed is attained by the shafts.

Pneumatic and Hydraulic clutches : When the engagement and disengagement forces are large enough to be operated manually then, hydaulic or pneumatic actuators are installed , to get that extra amount of force.

Electromagnetic clutches : Instead of frictional surfaces, these clutches have electromagnets which are excited manually to engage or disengage the shafts.

Read More: DIVIDER THAT CAPTURES CARBON EMITTED BY THE PASSING VEHICLES The clutch is under gradually increasing strain, caused by greater power, torque and weight. Experts recommend investigating seemingly minor issues, to avoid more serious damage and offer these tips to avoid consequent clutch damage.

  1. Cleanliness is crucial. Touching the clutch with oily hands can cause damage to the clutch.
  1. The clutch hub must be appropriately lubed. If an excessive amount of oil is used, the centrifugal powers extend the lubricants onto the clutch facings bringing about glitches.
  2. The clutch disk should be checked for axial run out prior to installation.
  3. The clutch  disk should be checked for central run out preceding installation.
  4. To avoid subsequent damage to the clutch and most importantly to the hub spine, don't use any sort of power to combine the clutch disk and the transmission input shaft hubs.
  5. Fix clasping screws and stiffen them according to the requirements utilizing the star design and applying the predetermined torque.Our experts suggest investigating the discharge system and, if appropriate, changing worn parts. And if the related vehicle has a CSC (concentric slave cylinder), it usually must be changed.

The adjoining parts should also be investigated during a clutch substitution. If any adjoining parts are worn or flawed, these should be changed also doing as such will save money on costly follow-up repairs.