Chevrolet 10 1971 Series Chassis Service Manual page 305

TURBO HYDRA-MATIC 400 TRAN SM ISSIO N
General D escription................................................................................ ...... 7-29
Maintenance and A djustm ents.............................................................. ...... 7-30
Transmission F lu i d ..................................................... , .......................... 7-30
Fluid Checking Procedure ................................................................ ...... 7-30
Fluid Level In d ic a t o r ......................................................................... ...... 7-31
Shift Control Linkage A d ju s tm e n t......................... ............. ................. 7-31
Detent Switch A d ju s tm e n t................................................................ ...... 7-32
Neutral Safety Switch A d ju s tm e n t......................................................... 7-32
Draining and Refilling Transmission................................................ ...... 7-32
Pressure Regulator Valve .................................................................. ...... 7-33
Control Valve B o d y ........................................................................... ...... 7-33
Governor .................................................................................................... 7-34
Modulator and M odulator V alve ....................................................... ...... 7-34
Parking L in k a g e ...................................................................................
The Turbo Hydra-Matic 400 transmission is a fully
automatic unit consisting primarily of a 3-element hy­
draulic 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
required 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. The compound planetary
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 counter-clockwise.
The torque converter housing is filled with oil and is
attached to the engine crankshaft by a flex plate and al­
ways 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
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 and turbine are being
driven at approximately the same speed - or at one-to-
one ratio.
A hydraulic system pressurized by a gear type pump
INDEX
Page
Rear Seal .................................................................................. ..
Other Service O perations................................ ...................... ...............
Transmission Replacement ..................................................................
Turbo Hydra-Matic
Sequence ................................................................ .............................
Oil Level and Condition C h e ck .................. ......................................
Manual Linkage ....................... ..........................................................
O il Leaks ................................................ , ...........................................
Case Porosity—R e p a ir......................... ...............................................
O il Pressure C h e c k ......................................................... ....................
Vacuum Modulator Assembly .........................................................
Pressure Switch C h e c k .......................................................................
Transmission Shift P o in ts .................................................. ...............
7-34
GENERAL DESCRIPTION
provides the working pressure required to operate the
friction elements and automatic controls.
External control connections to transmission are:
A vacuum modulator is used to automatically sense any
change in the torque input to the transmission. The vacu­
um modulator transmits this signal to the pressure
regulator for line pressure control, to the 1-2 accumu­
lator 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, LI.
P. - PARK position positively locks the output shaft to
R. - REVERSE enables the vehicle to be operated in a
N. - Neutral position enables the engine to be started
D. - DRIVE Range is used for all normal driving condi­
L2 - L2 Range has the same starting ratio as Drive
CLUTCHES AND TRANSMISSIONS 7-29
400 Diagnosis Procedure ..................................
Manual Linkage - To select the desired operating
range.
Engine Vacuum - To operate a vacuum modula­
tor unit.
12 Volt Electrical - To operate an electrical de­
tent solenoid.
the transmission case by means of a locking pawl
to prevent the vehicle from rolling in either direc­
tion. The engine may be started in Park position.
reverse direction.
and run without driving the vehicle.
tions and maximum economy. Drive Range has
three gear ratios, from the starting ratio to direct
drive. Detent downshifts are available by depress­
ing the accelerator to the floor.
Range, but prevents the transmission from shifting
above second speed to retain second speed accele­
ration when extra performance is desired. L2
Range can also be used for engine braking.
Page
7-34
7-34
7-34
7-35
7-35
7-35
7-35
7-35
7-36
7-36
7-36
7-37
7-38
L2
10-30 CHEVROLET TRUCK SERVICE MANUAL