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.

There are several different types of clutches depending on the application or use of the vehicle.

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

1. 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.

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.