AND AUTOMATIC TRANSMISSIONS
This chapter provides information about the clutch
and the automatic transmission to enable you to
understand the operation of these units, to diagnose
problems, and to prescribe corrective action. To obtain
more detailed information on the operation and repair
of specific units, refer to the specific manufacturers
maintenance and repair manual.
To make practical use of engine power, a coupling
device, or clutch, is needed to connect and disconnect
the engine from the drive line, as necessary. The clutch
or torque converter provides for complete separation of
power or at least slippage at an idle. The automatic
transmission, like manual transmissions, matches load
requirements of the vehicle to the power and speed of
It is important to briefly review the purpose of the
clutch and also the various types of clutches. The clutch
permits the operator to couple and uncouple the engine
and transmission. When the clutch is in the coupling (or
normal running) position, power flows through it from
the engine to the transmission. If the transmission is in
gear, power flows through to the vehicle wheels, so the
vehicle moves. Essentially, the clutch enables the
operator to uncouple the engine temporarily, so the gears
can be shifted from one forward gear position to another
or into reverse or neutral. The flow of power must be
interrupted before the gears are shifted; otherwise, gear
shifting is extremely difficult if not impossible.
The clutch assembly (fig. 7-1) contains a friction
disk (fig. 7-2), or driven plate about a foot in diameter.
Figure 7-1.Typical clutch assembly.