Tractor Construction

A diesel engine is generally used as prime mover and mounted on the tractor frame and delivers the power through a clutch to the main power shaft.
The power is transmitted from the engine to the final drive through engine clutch, torque convertor, change speed gear box transmission to rear differential and then finally to the rear drive axle.
The drive is also transmitted through front differential to the front axle.

Engine clutch is provided to disconnect the engine from the rest of the transmission system so that gears can be changed to change the speed of the tractor.
Care should be taken while changing the gears that the engagement of the clutch should be gradual to avoid undue strain on the surfaces of the clutch plates. The clutch control in small and medium sized tractors is through pedal like that of a truck, but in large tractors it is through lever operated by hand.

Transmission system provides speed reduction and multipication of torque of engine shaft, since final drive needs a high torque at low speed. Reduction on the speed is done by the gear box. Now a days a torque convertor is also used for speed reduction.
Using a bevel gears in the drives also reduces the speed by some extents
The differential also facilitates in steering.
As tractor changes its direction, one of rear wheels must travel faster then others, and this is achieved by differentials.
In the wheeled tractor the steering is done by through the front wheel.
The outer ends of two half shafts carry pinions which mesh with larger gears of the final drive, resulting variation in the speeds when tractor is taking a turn.

The power from drive axle is transmitted through wheels or crawler chains in wheeled tractors and crawler tractors respectively.
Wheeled tractors generally have two large wheels in the rear and two smaller wheels in the front. For better traction under adverse load and ground conditions two wheels are fitted on each of the rear hubs.
To make rear heavy for better stability of the tractor rear tyres are filled with water.
The tread of the tyre should be selected carefully as it greatly affects Its tractive efforts on a particular type of soil where it operates.

Following main factors should be considered while selecting a tractor dozer:

Size of the dozer for a given job.
The type of work expected from the tractor dozer e.g: bulldozer, ripping, land clearing, pulling a scraper etc.
The type and condition of haul road
Gradient of the haul road.
Distance to be moved.
Type of work expected to be taken from the equipment after the present job is completed.