a hydraulic control system. However, they used a manual
clutch in place of a fluid coupling. The clutch was used to
engage the transmission when the vehicle was first started,
after which the hydraulic system made all the shifts.
Figure 1-5 shows this early design. In 1939 (1940 models),
Oldsmobile introduced an updated version of this transmission,
replacing the clutch with a fluid coupling. Cadillac began
using this transmission in 1940. This was the first fully
automatic hydraulic transmission. See Figure 1-6.
The first transmission to use a torque converter
instead of a fluid coupling was the 1948 Buick Dynaflow,
Figure 1-7. This transmission relied entirely on a complex
torque converter with multiple stators and turbines for
torque multiplication. Although the torque converter pro-
vided a much more efficient transfer of power than a fluid
coupling, the Dynaflow had no gear changes, and the
planetary gears were always in direct drive. The planetary
gears were also used for manual low and reverse. The
Dynaflow was smooth but extremely inefficient.
The first transmission that resembled modern trans-
missions was designed by Ford and Borg-Warner and
offered in 1950. It used a torque converter and a hydraulic
control system that automatically changed gears. The first
models were two-speed types, while later designs had
three speeds. A similar Borg-Warner transmission appeared
on Studebakers. The Studebaker transmission, as well as
one offered by Packard, contained the first version of the
lockup torque converter, which eliminated slippage in certain
gears. See Figure 1-8. The Studebaker automatic was the
first to use a one-way clutch to obtain different gear ratios.
At first, all automatic transmissions had cast iron
cases. Aluminum bell housings and tailshaft housings
were used on some Ford and Chrysler transmissions during
the 1950s. The first transmission to use an all-aluminum
case was the Chevrolet Turboglide installed in the 1958
models, Figure 1-9. The Chrysler Torqueflite followed in
1960. All automatics were being designed with aluminum
cases by 1965. Around this time, simplified gear trains
were introduced, some with only two forward gears. A
late-1960s transmission might have fewer than half the
parts of a comparable model produced ten years earlier.
The Chrysler Corporation reintroduced the lockup
torque converter in 1977. It was controlled by hydraulic
pressure, and the lockup clutch applied only in third gear.
Later lockup torque converters were operated electrically
or electronically. Lockup clutches were applied in all gears
but first and reverse.
In the early 1960s, a few vehicles, such as the Corvair,
Volkswagen, and Porsche, used rear engines and were
equipped with transaxles. A few imported front-wheel
drive cars had transaxles. However, the front-wheel drive
automatic transaxle was unknown in the United States
until the introduction of the 1966 Oldsmobile Toronado.
The Toronado’s engine was mounted longitudinally (facing
forward), and its transaxle used a conventional cast iron
differential bolted to the transmission case. In 1976,
14 Automatic Transmissions and Transaxles
Front of
vehicle
Engine
Torque
converter
Transmission
Drive shaft
Rear drive axles
Differential
assembly
A
Front of
vehicle
Torque
converter
Engine
Front drive axles
Transaxle
Rear dead axle
B
Engine
Front
differential
Front of
vehicle
Drive shaft
Drive shaft
Transfer case
Rear differential
Rear drive axles
Transmission
Torque
converter
Front drive axles
C
Figure 1-4. Various automotive drive trains. A—Rear-wheel
drive vehicle with a longitudinal engine and a transmission.
B—Front-wheel drive vehicle with a transverse engine and a
transaxle. C—Four-wheel drive vehicle with a transmission and
a transfer case.