purpose of the automatic transmission is the same as
standard transmissions-to match the load requirements
of a vehicle to the power and speed of the engine.
Changing the gear ratio automatically is controlled by
throttle position, shift control lever position, and vehicle
speed. It relieves the operator of the responsibility of
selecting the best possible gear ratio for each condition
and makes driving easier and safer.
Many different models of automatic transmissions
are manufactured today. Automotive applications
usually have three speeds forward and one reverse.
More recently the automotive industry has added a
lockup clutch to the torque converter, and on some
models, an overdrive gear. Automatic transmissions for
material handling and construction equipment will
normally have a lower gear ratio, be considerable y larger,
and may have over six speeds forward and more than
one reverse gear.
Whatever the case and regardless of design or
construction, all automatic transmissions have the
following six basic systems that enable them to
1. A torque converter or fluid coupling
2. A hydraulic system
3. A planetary gearset (usually more than one)
4. One or more spool valves used to direct fluid
5. Multidisk clutch packs or lockup bands
6. A control valve or a combination of control
In automatic transmissions, these systems all serve
the same purposes. For this reason, we will only discuss
one type of automatic transmission in this TRAMAN.
If you want information on a specific type, use the
manufacturers maintenance and repair manual for that
TURBO HYDRA-MATIC MODEL 400
The Model 400 Hydra-Matic transmission
(fig. 7-1 1) is a fully automatic unit consisting of a three
element torque converter and a compound planetary
Figure 7-11.Cutaway view of Model 400 Hydra-Matic transmission.