MANUAL TRANSMISSION: Let's move on to a manual transmission. As its clearly seen in the diagram, the purpose of the manual transmission is to take the raw spinning power from the fly wheel and utilizing a series of gear reductions to transfer this power to the rear wheels. The clutch system on a manual transmission car serves to separate the spinning fly wheel from the spinning transmission so that the gears can be changed without clashing. During normal operation, the clutch disc is pressed tightly against the fly wheel so that the engine and transmission can operate as a unit. When the clutch pedal is depressed, the clutch release lever forces the throw out bearing to engage the pressure plate, which in turn reacts against the spinning fly wheel to disengage the clutch disc from the fly wheel so that the gears can be shifted. Working the gear shift lever allows the gears to slide in and out of mesh with each other and, therefore, depending on road speed, provide different gear ratios for efficient performance. Shifting successively into higher gears allows the vehicle to get higher road speed from slower engine rotation. Therefore, when top gear is reached, each revolution of the engine's crank shaft equals one revolution of the drive shaft. On transmissions with overdrive, it takes less than one revolution of the crank shaft to equal one revolution of the drive shaft, thus improving on fuel economy. The gears in the transmission are lubricated by the transmission oil. Once leaving the transmission, the power, which is now geared to the relevant speed, travels down the drive shaft to the differential. The differential, just as in an automatic transmission drive train, takes this power and reduces it to the proper gear ratio before turning it 90 degrees and sending it via the rear axle shaft to the rear wheels. Here we have an example of a manual transmission with clutch housing. The clutch is engaged or disengaged by the clutch actuating lever here and the gears are shifted, via mechanical linkages, here and here.
