How the clutch works
The clutch operates when a driver depresses the pedal, selects a gear, and releases it while accelerating for smooth vehicle movement. The clutch, when operated, allows the engine power to be applied gradually when a vehicle is starting out, and interrupts power to prevent gear grinding during shifts. When engaged, the clutch transfers engine power to the transmission and drive wheels; when disengaged, it stops power transfer while keeping the engine running.
The parts of a clutch
The basic clutch components are the flywheel, clutch disc, pressure plate, throw-out bearing, and linkage. Hydraulic clutches include a slave and master cylinder.
Flywheel: Bolted to the engine's crankshaft with outer teeth for the starter motor. It balances the engine, dampens vibrations, and provides the friction surface for clutch contact.
Clutch disc: A steel plate covered in friction material positioned between the flywheel and pressure plate. Its hub fits over the transmission's splined input shaft, transmitting engine power when engaged.
Pressure plate: A spring-loaded clamp bolted to the flywheel with a metal cover, release springs, a pressure ring providing friction surface, and thrust ring for the release bearing.
Throw-out bearing: Central to clutch operation. When the clutch pedal is depressed, it moves toward the flywheel, pushing the pressure plate spring and interrupting power flow.
Hub and throw-out bearing: The bearing slides on a hollow shaft at the transmission's front. The clutch fork converts pedal movement to back-and-forth bearing movement.
Linkage: Mechanical or hydraulic systems operate the clutch. Mechanical linkage uses cable or shaft-and-lever styles with release levers, rods, and pedal assemblies. Hydraulic systems use a master cylinder attached to the pedal and a slave cylinder connected by tubing.
Signs of a failing clutch
Most modern clutch linkages self-adjust, but older vehicles show warning signs. Symptoms include:
- Clutch engages and disengages near the floorboard
- Transmission grinds when shifting
- Clutch pedal moves easily but transmission won't engage gears
- Clutch slipping without full engagement
- "Chatter" from overheated clutch caused by slipping on inclines or oil on the disc
- Fading pedal or unusual feel
A failing clutch, whether it is the hard parts, the linkage or the hydraulics, can cause you to break down while driving. Regular inspection and prompt repair of hydraulic leaks prevent breakdowns and ensure safe operation.