MANUAL TRANSMISSION

The transmission is located at the rear of the engine between the clutch housing and the propeller shaft. The

Figure 2-3.-Cross section of a disc clutch.

Figure 2-4.-Disc clutch operation.

Figure 2-5.-Clutch linkage.

transmission transfers engine power from the clutch shaft to the propeller shaft and allows the operator to change the gear ratio between the engine and the rear wheels.

Dual-ratio, or two-speed rear axles are often used on trucks. They have two gear ratios that can be chosen by the operator, usually by a manual control lever. A dual-ratio rear axle works the same as the auxiliary transmission; it doubles the number of gear ratios for driving the vehicle under the various loads and on different roads.

The most common transmission type is the synchromesh transmission. The synchromesh transmission is basically a constant mesh, collar-shift transmission with an extra device, called a synchronizer, to equalize the speed of the mating parts before they engage. The synchronizer is used in all manual automotive transmissions and is common in other equipment where shifting while moving is required.

Part of the prestart operation is to check the fluid level in the manual transmission. The normal level of lubricant is usually at the bottom of the filler plug opening. When lubricant is needed, you should always check the operator's manual for the location and type of lubricant required for the transmission. When you keep the lubricant level correct, the gear teeth are protected, foam is reduced, and the transmission runs smoothly.

Some transmission troubles that you may encounter and must document are as follows:

l Hard shifting

l Slipping out of gear

l No power through the transmission

l Transmission noisy when in gear

l Gear clash in shifting

l Oil leaks

Manual Shift Operation

Skill in manual shifting is a requirement of professional driving. Poor manual shifting results in poor vehicle performance and can cause vehicle damage. Know the gearshift lever positions so well that you can shift to any gear without looking at the shift lever. The gearshift pattern is usually diagramed in the vehicle or in the operator's manual. Never move the gearshift lever from one position to another while the engine is running until you have fully depressed the

clutch pedal with your left foot. To shift gears smoothly and quietly, you must keep the pedal fully depressed until the shift has been completed.

You should understand that the clutch provides the means of applying engine power to the wheels smoothly and gradually. To be a professional operator, you must learn just where the clutch starts to engage, how far the pedal must move to become fully engaged how much free play there is in the pedal, and how fast you should engage the clutch.

Keep your foot off the clutch pedal except when actually starting, stopping, or shifting gears. Even the slight constant pressure on the clutch pedal causes excessive wear. For the same reason, when stopped on a hill, never slip your clutch to keep from rolling backward; instead, use the brakes. Depress the clutch pedal and shift the transmission shift lever into neutral while waiting for a long traffic light or when halted for other reasons. Release the clutch after shifting into neutral.

When slowing your vehicle to stop or make a turn, be sure to reduce the vehicle speed to 15 miles per hour or less before depressing the clutch pedal. Coasting a vehicle at a high rate of speed with the clutch pedal depressed is dangerous, because control becomes more difficult and damage to the clutch may occur. This kind of practice is abusive to the vehicle.