How Does a Clutch Work

How does a clutch work? Knowing the answer can help you troubleshoot transmission problems. Knowing what the inner workings do may also convince you to avoid driving practices that can damage the parts inside your clutch.

Why Have a Clutch?
A clutch is needed because a vehicle's engine continues to turn when the vehicle is stopped. If there was no clutch, when coming to a stop, the engine would stall. Even an automatic vehicle has a clutch. The clutch allows the spinning engine to engage or disengage the transmission. When the transmission is disengaged, the engine keeps spinning, but the transmission stops, so the engine stops turning the drive shafts and the wheels.

Clutch Operation
Friction is created between the clutch plate and the flywheel. The flywheel is attached to the engine, and the clutch is attached to the transmission. When the clutch pedal is up, the springs in the clutch push the pressure plate against the clutch disc. The clutch disc then presses against the flywheel, locking the spinning engine to the input shaft of the transmission. This lets the transmission and the engine spin at the same speed.

When you press the clutch pedal to the floor, a hydraulic piston, or a cable on a manual clutch, pushes on a fork, releasing it. The release of the fork puts pressure on a throw-out bearing, which pushes the middle of a diaphragm spring. The diaphragm spring then causes the pins near the outside of the spring to pull the pressure plate away from the disc. The clutch is now released from the spinning engine.

In an automatic vehicle, the transmission has many clutches. The clutches engage and disengage planetary gears, and move using hydraulic fluid. When hydraulic pressure falls, the springs allow the clutch to release. As pressure rises, the clutch engages.

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