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7A4-2
1977 PONTIAC SERVICE MANUAL
Fig.
7A4-1 4 0 0
Transmission
-
Cross Section
GENERAL DESCRIPTION
The Turbo Hydra-Matic transmission is a fully
automatic unit consisting primarily of a 3-element hydraulic
torque converter and a compound planetary gear set (Fig.
7A4-1). Three multiple-disc clutches, two roller clutches and
two bands provide the friction elements required to obtain the
desired function of the compound planetary gear set.
The torque converter couples the engine to the planetary
gears
through
oil
and
provides
hydraulic
torque
multiplication when required. The compound planetary gear
set produces three forward speeds and reverse (Fig. 7A4-2).
The 3-element torque converter consists of a pump or
driving member, a turbine or driven member and a stator
assembly. The stator is mounted on a one-way roller clutch
which will allow the stator to turn clockwise but not counter-
clockwise when viewed from the front (Fig. 7A4-3).
The torque converter housing is filled with oil and is
attached to the engine crankshaft by a flex plate, thus always
rotates at engine speed. The converter pump is an integral
part of the converter housing, therefore the pump blades,
rotating at engine speed, set the oil within the converter into
motion and direct it to the turbine, causing the turbine to
rotate.
As the oil passes through the turbine, it is traveling in
such a direction that if it were not re-directed by the stator
it would hit the rear of the converter pump blades and impede
its pumping action. So, at low turbine speeds, the oil
I
INTERNAL GEAR
PLANET GEA
PLANET CARRIE
REACTION CARRIER
OUTPUT CARRtER
383
1
Fig.
7A4-2
Compound Planetary Gear Set
redirected by the stator to the converter pump in such a
manner that it actuallly assists the converter pump to deliver
power or multiply engine torque,
As turbine speed increases, the direction of the oil
leaving the turbine changes and flows against the rear side
of the stator vanes in a clockwise direction. Since the stator
is now impeding the smooth flow of oil, its roller clutch
releases and it revolves freely on its shaft. Once the stator
becomes inactive, there is no further multiplication of engine
torque within the converter. At this point, the converter is
merely acting as a fluid coupling as both the converter pump
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