Chevrolet 1977 light duty truck, Service Manual

Page: 693 / 861

SECTION 7 A
AUTOMATIC TRANSMISSION
C O N T E N T S OF T H IS SEC TIO N
CBC 350 T ra n sm issio n .................................................................. 7A-1
THM 400 T ran sm issio n ................................................................. 7A-21
S p e c ificatio n s...................................................................................... 7A-37
Special T o o ls...................................................................................... 7A-38
CBC 3 5 0 TRANSMISSION
INDEX
G e n e ra l D e s c rip tio n ...........................................................7A-1
M ain ten an ce and A d ju stm e n t...................................... ..7A-4
T ransm ission F lu id ...........................................................7A-4
C hecking T ran sm issio n M o u n t.................................. ..7A-5
S h ift C o n tro ls......................................................................7A-5
D eten t D o w nshift C a b le .............................................. ..7A-7
N e u tral S tart S w itc h ........................................................7A-7
D ia g n o sis .............................................................................. ..7A-9
Sequence for D ia g n o sis................................................ ..7A-9
Fluid C hecking P ro ced u res............................................7A-9
Fluid Leak D ia g n o s is ................................................... ..7A-9
Oil Pressure C h e c k ...........................................................7A-10
Case Porosity R e p a ir .......................................................7A-10
V acuum M odulator D ia g n o sis ................................... .7A-10
C lutch Plate D ia g n o s is ................................................. ..7A-11
C auses of Burned Clutch P la te s .................................7A-11
G o v e rn o r Pressure C h e c k ............................................ .7A-12
M anual L in k a g e .............................................................. ..7A-12
Road T est.............................................................................7A-12
T rouble D ia g n o sis............................................................. .7A-13
D iagnosis C h a rt............................................................... .7A-14
Service O p e ra tio n s ..............................................................7A-18
T ransm ission R eplacem ent (Except K M odels)... 7A-18
T ransm ission R eplacem ent (K M o d e ls)................. ..7A-18
Extension H ousing Oil S e a l.........................................7A-18
Speedom eter D riven G e a r ............................................7A-19
Speedom eter D rive G e a r ..............................................7A-19
M anual Shaft, R ange Selector In n er Lever and
P arking L in k a g e ...........................................................7A-19
G o v e r n o r............................................................................ .7A-19
Vacuum M odulator and M o d u lato r V a lv e .............7A-19
Valve Body A sse m b ly ................................................... .7A-20
l -2 A c c u m u la to r.............................................................. .7A-20
Oil Cooler P ipes.............................................................. .7A-20
GENERAL DESCRIPTION
T he CBC 350 transm ission is a fully autom atic u nit
consisting p rim a rily o f a 3-elem ent hydraulic torque
co n v erter and two p la n e ta ry g ear sets. F our m ultiple-disc
clutches, two roller clutches, and an in term ed iate overrun
b an d provide the friction elem ents req u ired to o b tain the
d esired function o f the two p la n etary gear sets.
T he 3-elem ent torque converter consists o f a pum p,
tu rb in e and a stato r assem bly. T h e stato r is m ounted on
a one w ay roller clutch which will allow the stato r to turn
clockwise, but not counterclockw ise. R eferences to
clockwise a n d counterclockw ise are d eterm ined by
looking tow ard re a r o f vehicle.
T he torque converter is o f w elded construction and
is serviced as a com plete assem bly. The u n it is filled w ith
oil a n d is attach ed to the engine cra n k sh a ft by a
flywheel, thus always rotates at engine speed. T he
co n v erter p u m p is an integral p art o f the converter
housing, there fo re, the p um p blades, ro ta tin g at engine
speed, set the oil w ithin the converter into m otion and
direct it to the tu rb in e, causing the turbine to rotate.
As the oil passes thro u g h o u t the tu rb in e it is
traveling in such a directio n th at if it were not redirected
by the stator it would hit the re a r o f the converter pum p
blades and im pede its pum p in g action. So at low tu rb in e
speeds, oil is red irected by the stator to the converter
pum p in such a m a n n e r that it actually assists the
converter p um p to deliver power, or m ultiply engine
torque.
As tu rb in e speed increases, the direction o f oil
leaving the tu rb in e changes and flows against the re a r
side o f the stato r vanes in a clockwise direction. Since
the stato r is now im p ed in g the sm ooth flow o f oil, its
roller clutch releases and it revolves freely on its shaft.
Once the stato r becom es inactive, there is no fu rth er
m ultiplication o f engine torque w ithin the converter.
At this point, the converter is m erely acting as a
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