Even if your vehicle doesn’t have a manual (sometimes called standard) transmission, you should understand how a manual transmission works. The principles involved are fairly simple, and automatic transmissions do basically the same things, just without a manual clutch and with less manual shifting.
his section takes a closer look at each major part of a manual transmission. You encounter most of them in the drive train section earlier in this chapter, but this section puts them into closer perspective. Figure 18-1 shows you where each part is located on the drive train of a manual transmission. shows a five-speed manual transmission
You use the gearshift to select and change gears. It’s usually found on the floor in front of or between the front seats. Older cars used to have shifts with three forward speeds located on the steering column. Then sportier models with four forward speeds emerged.
The gearshift in those vehicles was located on the floor, which gave rise to the phrase “four on the floor.” Today, vehicles with manual transmissions have as many as seven forward speeds! Gearshifts also have positions for Reverse and Neutral (so the vehicle.
You use the clutch when you start, stop, and shift gears. In each case, you step on the clutch pedal with your left foot to disengage the clutch disk from the engine flywheel so that the engine’s crankshaft can turn independently of the transmission input shaft (the turning shaft that carries the power from the engine into the transmission).
If you attempt to shift gears without using the clutch, the gears in the transmission will rotate at different speeds and could clash and injure the transmission. The clutch consists of the following major parts.
The transmission contains the gears and responds to messages from the gearshift and the clutch. On manual transmissions, the gears are metal wheels with notches on the rims that allow them to mesh with one another.
Originally, the gears in most manual transmissions were moved into and out of mesh with each other by the gearshift lever. In modern vehicles, the gears are always in mesh and only the synchronizers move, causing a change in power flow.
The number of gear wheels in the transmission depends on the number of forward speeds the vehicle has. An additional gear reverses the direction of power so that your car can move backward. Because you must bring a vehicle to a stop before you back up and because you rarely want to hit high speeds in Reverse, this gear works in conjunction with the lowest gear because it can provide the power to overcome inertia and get the car moving backwards.
How a manual transmission works
Generally speaking, the faster your engine runs, the more power it puts out. If you need extra power to get up a hill — or to overcome inertia and just get that heavy monster moving in the first place — your engine must run faster than it runs when it’s just maintaining a steady speed. Low gears supply that power by making your wheels turn at a slower rate than your engine does.
On the other hand, if you drive faster than the range of speed provided by a gear, your vehicle will “red line” — go beyond the maximum number of rpm (revolutions per minute) your engine is capable of — and damage the engine. That’s why you have to shift up to the next higher gear as your speed increases. The ratio between how fast your engine turns and how fast your wheels turn is called the gear ratio.