Parts Of The Gear box and Transfer Case in Gear Mechanism – Automobile Study material

Parts of the gear box

Gear box housing

The Box like arrangement where
the bearings (which support the shafts) are mounted, filler plug with air vent hole,oil drain plug are present is called as the gear box housing. This box is generally made of cast iron as shown in Figure

Gear box input or clutch shaft

It is connected with the clutch plate
at one end supported by the flywheel and a gear fitted at the other end. The view of input shaft can be seen in Figure

Lay shaft

It is mounted at the bottom of
the gear box casing. Different gears are mounted on the lay shaft depending on the speed of the gear box. The picture of lay shaft can be seen in Figure

Gear box output shaft or main shaft

It is located at the top of the gear box
casing at straight line with the input shaft.Slots are present in this shaft. Through this shaft the power is transmitted to the propeller shaft.

Reverse gear shaft

The smallest shaft in the gear box
is the reverse gear shaft which has only one gear called as the idler gear. It is fitted on the gear box casing. This shaft is used for transmitting the power from the lay shaft to the main shaft.

Speedometer drive

Skew gear is connected with the
main shaft. With the skew gear a cable with a small gear is connected at one end and the other end of the cable is fitted at the dashboard of the driver. This drive is used for knowing the speed of the vehicle.

Gear selector mechanism

On the top of the gear box, an
arrangement with a lever with a gear
knob, selector rod and shifting fork are connected. This arrangement is called as the gear (shifting) selecting mechanism.Gear selector mechanism is used for selecting the required gear for the required speed of the vehicle. The picture of a gear selector mechanism can be seen in Figure

Types of gear shift mechanisms

1. Floor gear shifting Mechanism
2. Steering Gear Shifting Mechanism

Floor gear shifting mechanism

If the gear shifting mechanism is located at the top of the gearbox, then it is called as the floor gear shifting mechanism

Steering gear shifting mechanism

If the gear shifting mechanism is located at the sideway of the steering column, then it is called as the steering gear shifting

Gear box lubrication

1. In the gear box, lubricating oil of SAE
90 has to be filled.
2. The lubricating oil must be filled until the lay shaft is (dipped) covered by the oil. The lubricating oil must be highly viscous.
3. When the gears are rotating, the
lubricating oils is sprayed on all the
parts of the gear box and lubricated.
4. After 1000 kilo meters of the vehicles run lubricating oil top up must be done.
5. After 10000 kilometers of the vehicle the lubricating oil must be completely replaced by the new lubricant.
6. To pour the oil filler cap is provide on the top of the gear box. An air vent is also provide to allow the atmospheric air to enter.
7. A drain plug is provided at the bottom of the gear box to drain the lubricating oil.

Transfer case

The arrangement used for transmitting the engine’s power to all the four wheels is called as the transfer case The transfer case is fitted on thevehicles with four wheel drive. This arrangement is generally used in military vehicles and jeeps.


In the main shaft of the gear box
two gears are present. Between the two gears a sliding gear is present. The gear in the main shaft is in mesh with the idler gear. With this front axle drive gear and rear axle drive gear aru connected. A clutch is fitted with the front axle drive gear.


With the help of the gear shift
mechanism when the sliding gear in the main shaft is shifted to right or left, through the idler gear the power is transmitted to the front or rear wheels with low or high speeds. In addition to this, when there is no need for drive power to the front wheels, with the help of the clutch
arrangement the drive power can be
disengaged. If necessary the four wheel drive can be also obtained.

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