Figure 13-6.-Power flow through a four-speed transmission.
The double-disk clutch (fig. 13-4) is basically the
same as the single-plate disk clutch except that another
driven disk and intermediate driving plate are added.
A multiple-disk clutch is one having more than three
plates or disks. Some have as many as 11 driving plates
and 10 driven disks. Because the multiple-disk clutch
has a greater frictional area than a plate clutch, it is
suitable as a steering clutch on crawler types of tractors.
The multiple-disk clutch is sometimes used on heavy
trucks. Its operation is very much like that of the plate
clutch and has the same release mechanism. The facings,
however, are usually attached to the driving plates rather
than to the driven disks. That reduces the weight of the
driven disks and keeps them from spinning after the
clutch is released.
You may run into other types of friction clutches
such as the lubricated plate clutch and the cone clutch.
These types are seldom used on automatic equipment.
However, fluid drives are largely replacing the friction
clutches in automobiles, light trucks, and some tractors.
For information on fluid drives (automatic trans-
missions), refer to Construction Mechanic 3 & 2,
NAVPERS 10644G-1, chapter 11.
The transmission is part of the power train. It
consists of a metal case filled with gears (fig. 13-5). It
is usually located in the rear of the engine between the
clutch housing and the propeller shaft, as shown in
figure 13-1. The transmission transfers engine power
from the clutch shaft to the propeller shaft. It allows the
driver or operator to control the power and speed of the
vehicle. The transmission shown in figure 13-5 and 13-6
is a sliding gear transmission. Many late model trucks
have either a constant mesh or synchromesh trans-
mission (explained later). However, both transmissions
have the same principles of operation and the same gear
A review of chapter 6 of this book will help you to
understand the transmissions and power transfer
mechanisms described in this chapter.