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7-102
GROUP 7-AUTOMA TIC TRANSMISSION
2-3 shift valve to the bottom of the
1-2 shift valve, where it tends to force
a downshift into low
gear.
3-2 DOWNSHIFT
CONTROL VALVE
The 3-2 downshift control valve
operates in the front servo release
pressure passage between the 2-3
valve and the front servo
.
A check
valve is installed parallel with the
downshift valve in the same passage
so that release pressure flow to the
servo by-passes it.
The downshift valve controls the
rate of front servo release pressure
exhaust (flow from the servo), and
thereby the rate of front band applica-
tion.
The 3-2 downshift control
valve:
eliminates the possibility of a
run-·
away condition in the transmission
during a 3-2 kickdown at low car
speed (about 25 mph). It also elimi-
nates the possibility of a tie-up during
the same shift at higher speeds (50
mph and more)
.
2-1 SCHEDULING VALVE
Four ports intersect the 2-1 schedul-
ing valve bore. From left to right, the
first port is vented to exhaust, the sec-
ond is connected to the spring end of
the inhibitor valve through the inhibi-
tor shuttle ball check valve, the third
is connected to the 1-R-P passage of
the manual valve and the right-hand
port is vented to exhaust.
When the selector lever is moved
to I to force a downshift from high
or intermediate gear to low, 1-R-P
fluid pressure is directed to the third
port of the 2-1 scheduling valve. The
force due to line pressure acting on
the differential area moves the valve
to the left, compressing the spring.
As the valve moves to the left it seals
off the line pressure port and uncovers
the exhaust passage at the left end of
the
valve,
allowing some of the fluid
in the differential pocket to escape to
exhaust. The loss of pressure in the
differential pocket allows the spring
to force the valve back to the right,
where it is again charged with line
pressure. The pressure resulting from
the regulating cycle is routed to the
spring end of the inhibitor valve, where
it assists the inhibitor valve spring in
tending to force the valve upward
against the force due to governor pres-
sure acting on top of the valve.
If vehicle speed and resulting gov-
ernor pressure on the upper end of the
inhibitor valve is low enough the
downward force on the valve will be
less than the upward effort resulting
from spring force plus 2-1 scheduling
pressure on the bottom of the valve
and the inhibitor valve will move up
in its bore, opening the necessary
passages to permit a downshift into
low gear.
2-3 SHIIT ORIFICE BY-
PASS BALL CHECK VALVE
Line pressure from the D passage of
the manual valve is directed through
the 2-3 shift orifice to the 2-3 shift
valve. When the 2-3 shift valve moves
downward in its bore, directing D
fluid from the 2-3 shift orifice into the
direct and reverse clutch apply circuit,
the 2-3 shift orifice check ball seats on
the bypass hole, causing the clutch
apply pressure to be orificed. However
when the transmission selector lever
is moved to 2 to force a downshift to
second gear, the check ball unseats
from the bypass hole, allowing direct
and reverse clutch apply pressure to
exhaust at the manual valve without
further obstruction.
1-2 SHIIT VALVE SHUTTLE
BALL CHECK VALVE
Fluid is directed from the D and
1-R-P passages of the manual valve
to the lower valley of the 1-2 shift
valve. When the D passage is pressur-
ized the 1-R-P passage is open to ex-
haust at the manual valve, and vice
versa. Therefore a shuttle ball check
valve is provided in the line connect-
ing to the lower valley of the 1-2 shift
v.elve. When the transmission is opera-
aung in D range the shuttle ball seals
off the 1-R-P passage, preventing D
pressure from exhausting at the man-
ual
valve.
Similarly, when the trans-
mission is in I, 2 or P ranges the
shuttle ball seals off the D passage,
preventing the loss of 1-R-P fluid at
the manual valve.
INHIBITOR VALVE
SHUTTLE BALL CHECK
VALVE
The spring end of the inhibitor
valve is pressurized at various times
by the following
pressures:
I.
D fluid and 1-R-P fluid from
1-2 shift circuit shuttle ball check
.
2. 2-1 scheduling pressure from 2-1
scheduling valve.
A shuttle ball check valve is pro-
vided in the passage connecting to the
spring end of the inhibitor valve. When
pressure from the 1-2 shift valve shut-
tle ball check is directed to the inhibi·
tor valve, the inhibitor valve shuttle
ball check seals off the passage to the
2-1 scheduling valve, preventing loss
of pressure through the 2-1 scheduling
valve.
Similarly when 2-1 scheduling
pressure is present, the shuttle ball
seals off the passage connecting to
the 1-2 shift valve shuttle ball check
.
HYDRAULIC CONTROL
SYSTEM-NEUTRAL
The manual valve at N selector
'lever position blocks the fluid flow
to both clutches and both bands
(Fig.
24).
With no fluid pressure in the
clutches or servos, the clutches and
bands are released by spring pressure,
preventing power being transmitted
to the transmission output shaft.
Neutral operation of the transmis-
sion keeps control pressure up to its
proper value, maintains a full torque
converter, lubricates the transmission,
and maintains a flow of fluid through
the cooling system.
HYDRAULIC CONTROL
SYSTEM-D, FIRST GEAR
When the selector lever is moved
from N to D, the manual valve opens
three passages to control
pressure.
From left to right, the first passage
admits control pressure to supply the
2-3 valve and close the rear servo lock-
out valve
.
The second passage admits
control pressure to apply the front
clutch and supply the governor and
transition valve. The third passage ad-
mits control pressure to flow through
the 1-2 and inhibitor valves and close
the transition valve.
With the front clutch applied, .the
primary sun gear tries to drive the
pinion carrier in a counterclockwise
direction
.
Counterclockwise rotation
at the pinion carrier is prevented by
the one-way clutch
.
With the front
clutch applied and the pinion carrier
held, the transmission is in first gear.
HYDRAULIC CONTROL
SYSTEM-D, SECOND GEAR
The 1-2 shift occurs when gover-
nor pressure force on the 1-2 shift
valve overcomes shift plug pressure
and spring forces
.
The 1-2 valve moves
inward, exhausting the fluid which
holds the transition valve closed. The
transition valve opens and admits con-
trol pressure to apply the front band
.
The front clutch remains on, and
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