Clutch Operation

When the operator presses the clutch pedal, the clutch release mechanism pulls or pushes on the clutch release lever or fork (Figure 10-8). The fork moves the release bearing into the center of the pressure plate, causing the pressure plate to pull away from the clutch disc releasing the disc from the flywheel. The engine crankshaft can then turn without turning the clutch disc and transmission input shaft. When the operator releases the clutch pedal, spring pressure inside the pressure plate pushes forward on the clutch disc. This action locks the flywheel, the clutch disc, the pressure plate, and the transmission input shaft together. The engine again rotates the transmission input shaft, the transmission gears, the drive train, and the wheels of the vehicle.

Clutch Start Switch

Many of the newer vehicles incorporate a clutch start switch into the starting system. The clutch start switch is mounted on the clutch pedal assembly. The clutch start switch prevents the engine from cranking unless the clutch pedal is depressed fully. This serves as a safety device that keeps the engine from possibly starting while in gear. Unless the switch is closed (clutch pedal depressed), the switch prevents current from reaching the starter solenoid. With the transmission in neutral, the clutch start switch is bypassed so the engine will crank and start.

Clutch Adjustment

Clutch adjustments are made to compensate for wear of the clutch disc lining and linkage between the clutch pedal and the clutch release lever. This involves setting the correct amount of free play in the release mechanism. Too much free play causes the clutch to drag during clutch disengagement. Too little free play causes clutch slippage. It is important for you to know how to adjust the three types of clutch release mechanisms.

Clutch Linkage Adjustment

Mechanical clutch linkage is adjusted at the release rod going to the release fork (Figure 10-2). One end of the release rod is threaded. The effective length of the rod can be increased to raise the clutch pedal (decrease free travel). It can also be shortened to lower the clutch pedal (increase free travel). To change the clutch adjustment, loosen the release rod nuts. Turn the release rod nuts on the threaded rod until you have reached the desired free pedal travel.