DRIVING AXLES 

Thee third axle, part of a bogie drive, is joined to the rearmost axle by a trunnion axle, as shown in figure 2-17. The trunnion axle is attached rigidly to the frame.

Figure 2-17.-Bogie drive.

Figure 2-18.-Four-wheel drive transmission.

Its purpose is to help in distributing the load on the rear of the vehicle to the two live axles that it connects.

The three types of live axles that are used in automotive and construction equipment are as follows: semifloating, three-quarter floating, and full floating.

DRIVING WHEELS

Wheels attached to live axles are the driving wheels. Wheels attached to the outside of the driving wheels make up dual wheels. Dual wheels give more traction

to the driving wheels and distribute the weight of the vehicle over more surface. Consider dual wheels as single wheels in describing vehicles.

The number of wheels is sometimes used to identify equipment; for example, a 4 by 2 could be a passenger car or a truck with four wheels, two of them driving. On a 4 by 4 (fig. 2-18), power is delivered to the transfer case where it is divided between the front and rear axle, allowing all four wheels to drive. A 6 by 4 truck with dual wheels in the rear is identified by six wheels, four of which drive. When a live axle is in front, the truck becomes a 6 by 6 (fig. 2-19), in which all six wheels drive.

Figure 2-19.-Six-wheeled drive transmission.