CLUTCH SHIFTING.- After the prestart operation has been performed and you have acquainted yourself with the instruments and controls of the vehicle, warm the engine with the transmission in neutral. Start the vehicle moving with the transmission in low or first gear by following these steps:

1. Depress the clutch pedal and shift into low gear.

2. Check the mirrors, check blind spots, and give signals as required.

3. Let the clutch pedal up slowly, pausing at the friction point or when you feel it taking hold. Again, recheck the mirrors for traffic.

4. Release the parking brake and slowly release the clutch pedal, and at the same time, slightly depress the accelerator.

5. When the driving operation is under way, remove your left foot completely from the clutch pedal.

DOUBLE-CLUTCH SHIFTING.- Professional driving practice in trucks (1 1/2 ton or larger) often requires double clutching to permit proper engagement of the gears and to prevent loss of momentum. To shift to a lower gear by double clutching, follow these steps:

1. Release the pressure from the accelerator as you begin depressing the clutch pedal.

2. When the clutch pedal is fully depressed, move the gearshift lever to neutral position

3. Release the clutch pedal, and at the same time, depress the accelerator to speed up the engine.

4. Letup on the accelerator and depress the clutch pedal.

5. While the pedal is depressed move the gearshift lever to the next lower gear.

6. Release the clutch pedal, and at the same time, depress the accelerator to maintain engine speed as the load is again connected to the engine by the engagement of the clutch.

The procedure is the same for shifting to a higher gear speed, except that the engine is NOT accelerated while the transmission is in neutral.

CAUTION

When you are shifting gears in rough terrain and on hills, never let your vehicle slow down to a point where the engine begins to labor or jerk before shifting into a lower gear ratio. Always anticipate the need for extra power and shift gears accordingly. When descending a hill, with or without a heavy cargo load, always drive with your vehicle in gear and the clutch pedal out.

NOTE: You may encounter vehicles that may have more complicated transmissions, such as multigear ranges, dual-speed axles, or other special features. As an operator, read and understand the operator's manual pertaining to a particular vehicle before attempting to operate it.

AUTOMATIC TRANSMISSION

The automatic transmission, like the manual transmission, is designed to match the load requirements of the vehicle to the power and speed range of the engine. However, the automatic transmission (fig. 2-6) performs this automatically, depending on the throttle position, vehicle Speed, and position of the shift control lever. Automatic transmissions are manufactured in models that have two, three, four, or more forward 2-8speeds and some are equipped with overdrive. Operator control is limited to the selection of the gear range by moving a control lever.

Part of the prestart operation is to check the transmission fluid level when the engine is idling and at normal operating temperature, when the vehicle is level, and when the transmission control lever is in park. The transmission fluid is used as a combination power transmission medium, hydraulic control fluid, heat transfer medium, bearing surface lubricant, and gear lubricant. The manufacturer's recomendations must be followed when servicing and filling the transmission with fluid.

CAUTION

Do not overfill the transmission because overfilling causes foaming and shifting troubles.

Some transmission troubles you may encounter and must document are as follows: . No drive in any selected positions.

On standstill starts the engine speed accelerates but the vehicle movement lags.

Engine speed accelerates during upshifts.

Transmission will not upshift.

Upshift and downshift are harsh.

Vehicle creeps too much in drive.

Vehicle creeps in neutral.

Improper shift points.

Unusual transmission noise.

Oil leaks.

Fluid Couplings

In the past, fluid couplings were widely used with automatic transmissions. Fluid couplings act like an automatic clutch by slipping at idling speeds and by holding to increase power as the engine speed increases. There is no mechanical connection between the engine and transmission; power is transmitted by oil.

Figure 2-6.-Automatic transmission cross-sectional view.

The principle of fluid drive is shown in figure 2-7. As two fans face each other, the speed of rotation of one fan makes the other fan rotate. When the speed of one fan is changed from medium to low, power is lost at low speeds; but, if the fan speed increases from medium to high, the speed of the driven fan picks up.