The very basics of clutch operation is that the driver depresses the clutch pedal, selects
a gear and releases the clutch pedal, while accelerating for a smooth transition into moving the vehicle. The clutch when operated allows the engine power to be applied gradually when a vehicle is starting out and it interrupts the power to avoid grinding gears when shifting.
Engaging the clutch allow the engines power to transfer to the transmission and drive wheels. Disengaging the clutch stops the power transfer and allows the engine to keep turning without force to the drive wheels. The basic components of a clutch are the flywheel, clutch disc, pressure plate, throw-out bearing and linkage. A hydraulic clutch uses some additional components like a clutch slave and master cylinder.
The flywheel is bolted to the crankshaft of the engine, it has teeth around the outer edge and is used in conjunction with the starter motor to turn the engine over at initial start up. The flywheel also acts as the balancer for the engine, it dampens vibrations caused from the engine firing, and it provides a smooth machined friction surface that the clutch can contact.
The clutch disc is a steel plate that is covered in friction material (similar to brake friction material) that goes between the flywheel and the pressure plate. In the center of the disc is a hub that fits over the splined input shaft of the transmission. When the clutch is engaged, the disc is “squeezed” between the flywheel and the pressure plate, and the power from the engine is transmitted through the hub onto the input shaft of transmission.
The pressure plate is like a spring loaded clamp that bolts to the flywheel. It has a metal cover, heavy release springs, a pressure ring that provides a friction surface for the clutch disc, and a thrust ring or fingers for the release bearing and levers.
The throw-out bearing is at the center of the clutch operation. When the clutch pedal is depressed the throw-out bearing moves toward the flywheel, pushing the pressure plate spring force. This action causes the pressure plate to move away from the clutch disc, interrupting the power flow from the engine to the transmission.
The hub and the throw-out bearing slides on a hollow shaft at the front of the transmission housing. The clutch fork and connecting linkage convert the movement of the clutch pedal to the back and forth movement of the clutch throw-out bearing. To disengage the clutch, the release bearing is moved toward the flywheel by the clutch fork. As the bearing contacts the pressure plate’s release fingers, it begins to rotate with the pressure plate assembly. The release bearing continues to move forward and pressure on the release levers or fingers causes the force of the pressure plate’s spring to move away from the clutch disc. To engage the clutch, the clutch pedal is released and the release bearing moves away from the pressure plate. This action allows the pressure plate’s springs to force against the clutch disc, engaging the clutch to the flywheel. Once the clutch is fully engaged, the release bearing is normally stationary and does not rotate with the pressure plate.
A mechanical or hydraulic linkage usually operates the clutch in a manual transmission. If your vehicle has a mechanical linkage, it is usually either a cable or shaft and lever style. The shaft and lever linkage has many parts and various pivot points, including a release lever and rod, an equalizer or cross shaft, a pedal to equalizer rod, an “over-center” spring (to return the clutch pedal to the rest position), and the pedal assembly that transfers the movement of the clutch pedal to the throw-out bearing.
A master cylinder is attached to the clutch pedal by an actuator rod, and the slave cylinder is connected to the master cylinder by high-pressure tubing. The slave cylinder is normally attached to a bracket next to the bell housing, so that it can move the clutch release fork directly.
How do I know what the warning signs are that a clutch needs adjustment or replacement? Most newer car clutch linkages are self-adjusting, and cannot be manually adjusted, but if you have an older vehicle, here are some symptoms: if the clutch engages and disengages close to the floorboard or the transmission “grinds” when shifting, your clutch may need attention. If your clutch pedal move easily, but the transmission will not go into gear, we recommend having it checked out. If the clutch slips where it does not fully engage the linkage could be grossly out of adjustment, or the clutch disk could be worn to the point of replacement. Clutch “chatter” is often caused by an overheated clutch which can be caused by “slipping” the clutch when starting on an incline or from oil on the clutch disc. If you clutch pedal is fading and feels funny in anyway, again the vehicle should be checked out.
A failing clutch, whether it is the hard parts, the linkage or the hydraulics can cause you to breakdown while driving. Having the operation of your clutch regularly inspected and any leaks of the hydraulic system repaired upon realization will help to keep you and your vehicle motoring down the road safely.
Steve and Karen Johnston are owners of All About Automotive in Historic Downtown Gresham. If you have questions or comments, call them at 503-465-2926 or email them at firstname.lastname@example.org. Steve and Karen Johnston are owners of All About Automotive, providing auto repair and auto maintenance in Historic Downtown Gresham. If you have questions or comments, call them at 503-465-2926 or email them at email@example.com, you can also visit our website at www.allaboutautomotive.com.