Major components include the transmission (RWD or 4WD) or transaxle (FWD or AWD), clutch (pressure plate and disc), release bearing, pilot bearing (if used), clutch linkage (hydraulic or cable) and shift linkage.
Manual gearboxes are limited mostly to sports and performance cars, and are usually 5- or 6-speed gearboxes, with the 5th and 6th gears being overdrive ratios for better fuel economy. If the synchronizers (which match the speeds of the rotating gears when shifting) inside the transmission are worn or damaged, the gears may grind when shifting. A low lubrication level (or wrong lubrication) inside the transmission also can increase noise and lead to premature failure. Follow the vehicle manufacturer’s lubricant recommendations.
The clutch couples the engine to the transmission, and transmits torque from the flywheel to the transmission input shaft. The clutch cover is bolted to the flywheel and uses a spring-loaded (diaphragm or multiple coil springs) “pressure plate” to hold the clutch disc against the flywheel when the clutch is engaged. When the clutch pedal is depressed, a release bearing pushes against the clutch to release the pressure on the clutch disc. A worn release bearing may make noise when the clutch pedal is depressed.
The clutch disc has friction linings on both sides. If the disc is contaminated with engine oil or transmission oil as a result of seal or gasket leaks, the clutch may slip. A new clutch should not be installed until the leak has been fixed. High-mileage clutches should be replaced as a complete set (new clutch cover, disc and release bearing). Clutch kits also eliminate the risk of mismatched parts, which can sometimes happen when different clutch components are sourced from different suppliers. Upgrading to a stiffer, stronger performance clutch may also be recommended for hard-use applications.
Most newer vehicles have a hydraulic clutch linkage with a master cylinder attached to the clutch pedal and a slave cylinder to actuate the clutch. Fluid leaks and seal wear may prevent the clutch from disengaging. The slave cylinder often fails first because it is the lowest point in the system.
Some diesel pickup trucks and performance cars have a “dual mass” flywheel, which is like two flywheels in one. If a dual mass flywheel is cracked, damaged or the internal springs have failed, it must be replaced. Resurfacing dual mass flywheels is not recommended.
Required to pass this section of the P2 test:
1. Identify major manual transmission & clutch components.
2. Identify component function and common reasons for replacement.
3. Identify basic related items, including lubricants and service tools.
4. Provide basic use, maintenance, installation, and warranty information.