Chevrolet 30 Series 1967 Service Manual page 431

TURBO HYDRA-MATIC TRANSMISSION
General Description......................................................... .....7-45
Maintenance and Adjustments
Transmission F l u i d ................................................... .....7-46
Fluid Level Indicator ................................................ .....7-46
Shift Control Linkage A dju stm en t.............................. .....7-46
Neutral Safety Switch A dju stm en t.............................. .....7-48
Draining and Refilling T r a n s m is s io n ........................ .....7-48
Pressure Regulator V a l v e .......................................... .....7-48
Control Valve Body...................................................... .....7-48
G o v e rn o r..................................................................... .....7-48
Modulator and Modulator V a l v e ................................. .....7-48
Parking L in k a g e ......................................................... .....7-48
The Turbo Hydra-Matic transmission is a fully auto­
matic unit consisting primarily of a 3 - element hydraulic
torque converter and a compound planetary gear set.
Three multiple-disc clutches, one sprag unit, one roller
clutch, and two bands provide the friction elements re­
quired to obtain the desired function of the compound
planetary gear set.
The torque converter couples the engine to the plane­
tary gears through oil and provides hydraulic torque
multiplication when required.
gear set produces three forward speeds and reverse.
The 3 -element torque converter consists of a pump or
driving member, a turbine or driven member, and a sta­
tor assembly. The stator is mounted on a one-way roller
clutch which will allow the stator to turn clockwise but
not counterclockwise.
The torque converter housing is filled with oil and is
attached to the engine crankshaft by a flex plate and
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 is re-directed by the stator to the converter pump
in such a manner that it actually 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 rol­
ler 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 coup­
ling as both the converter pump and turbine are being
driven at approximately the same speed - or at a one-to-
one ratio.
A hydraulic system pressurized by a gear type pump
provides the working pressure required to operate the
friction elements and automatic controls.
External control connections to transmission are:
Page
....................................... .....7-46
GENERAL DESCRIPTION
The compound planetary
NDEX
Rear S e a l ......................................................................... 7-48
Other Service O p e ra t io n s ................................................ .... 7-49
Transmission R ep lacem en t............................................. .... 7-49
Turbo Hydra-Matic Diagnosis P ro c e d u re ........................ .... 7-49
Sequence ..................................................................... .... 7-49
Oil Level and Condition C h e c k .................................... .... 7-49
Manual Linkage ......................................................... .... 7-49
Oil L e a k s ..................................................................... .... 7-49
Case Porosity - Repair
Oil Pressure C heck...................................................... .... 7-50
Transmission Shift P o i n t s .......................................... .... 7-51
Manual Linkage
Engine Vacuum
12 Volt Electrical - To operate an electrical
Signal
A vacuum modulator is used to automatically sense
any change in the torque input to the transmission.
vacuum modulator transmits this signal to the pressure
regulator for line pressure control, to the
tor valve, and to the shift valves so that all torque re­
quirements of the transmission are met and smooth
shifts are obtained at all throttle openings.
The detent solenoid is activated by an electric switch
on the carburetor. When the throttle is fully opened, the
switch on the carburetor is closed, activating the detent
solenoid and causing the transmission to downshift for
passing speeds.
The selector quadrant has six selector positions: P,
R, N, D,L2, L I.
P. - Park position positively locks the output shaft to
the transmission case by means of a locking pawl
to prevent the vehicle from rolling in either di­
rection. The engine may be started in Park
position.
R. - Reverse enables the vehicle to be operated in a
reverse direction.
N. - Neutral position enables the engine to be started
and run without driving the vehicle.
D. - Drive Range is used for all normal driving condi­
tions and maximum economy. Drive Range has
three gear ratios, from the starting ratio to direct
drive. Detent downshifts are available by de­
pressing the accelerator to the floor.
L2. - L2 Range has the same starting ratio as Drive
Range, but prevents the transmission from shifting
above second speed to retain second speed accel­
eration when extra performance is desired.
Range can also be used for engine braking.
Range can be selected at any vehicle speed, and
the transmission will shift to second gear and re­
main in second until the vehicle speed or the
throttle are changed to obtain first gear operation
in the same manner as in D Range.
CLUTCHES AND TRANSMISSIONS 7-45
............................................. .... 7-50
- To select the desired op­
erating range.
- To operate a vacuum mod­
ulator unit.
detent solenoid.
accumula­
1 - 2
CHEVROLET TRUCK SERVICE M ANUAL
Page
The
L2
L2