Manual Transmission
 | |
| Illustration 1 | g01085091 |
A transmission provides forward and reverse drives, different speed ranges, and different pushing (or pulling) forces. A transmission controls the direction, speed, and force of machine movement.
Gear Train
 | |
| Illustration 2 | g01085093 |
A manual transmission uses gears and shafts (Illustration 2) to achieve various gear ratios. A gear train is a series of gears that are in mesh or engaged. The gear train transfers and adapts the engine power to the drive wheels or tracks of the machine.
The speed of the output shaft compared to the speed of the input shaft varies in each gear position. This allows the operator to change the amount of torque to the final drive. In lower gears, the torque is increased and the ground speed is reduced. In higher gears, the ground speed is increased and the torque is reduced.
Gear reduction and Overdrive
 | |
| Illustration 3 | g01085094 |
Gear reduction occurs when a small gear drives a larger gear in order to increase turning force or torque (Illustration 3, bottom diagram). Gear reduction is used in the lower transmission gears. An overdrive ratio exists when a larger gear drives a smaller gear. The speed of the output gear increases, but torque drops (Illustration 3, top diagram). Manual transmissions generally use spur gears or helical gears.
Bearings in a Transmission
 | |
| Illustration 4 | g01085095 |
The bearings, shafts, gears, and other moving parts in a manual transmission are lubricated by oil throw-off or splash lubrication. As the gears rotate, the gears sling oil around inside the transmission case.
Bearings are used to reduce the friction between the surfaces of rotating parts in the transmission (Illustration 4). Manual transmissions typically use three basic types of bearings:ball bearings, roller bearings and needle bearings. Bearings are lubricated by oil spray from the spinning transmission gears.
Manual Transmission Basic Components
 | |
| Illustration 5 | g01088312 |
Illustration 5 shows the major components of a manual transmission. The location and the function of these components are described below:
Transmission case (1) - Supports the bearings and shafts. Provides and contains the transmission gear oil.
Input shaft (2) - Transfers power from the flywheel clutch to the countershaft gears in the transmission.
Countershaft (3) - Transfers power from the input shaft to the output shaft.
Output shaft (4) - Transfers power from the countershaft to the final drive.
Shift lever (5) - Allows the operator to manually shift the gears.
Types of Manual Transmissions
- Sliding Gear Transmission
- Collar Shift Transmission
- Synchromesh Transmission
The sliding gear transmission has two or more shafts. These shafts are mounted in parallel or in line with sliding spur gears that are arranged to mesh with each other and provide a change in speed or direction.
The collar shift transmission contains parallel shafts with gears in constant mesh. Shifting is accomplished by locking free-running gears to their shafts using sliding collars.
The synchromesh transmission also has gears in constant mesh. The speeds of the mating gears are synchronized before the gears engage in order to eliminate noise.