Buick LeSabre 1965 Service Manual page 235

SUPER TURBINE " 3 0 0 '
HYDRAULIC CONTROLS 5 - 2 1
L. FEED
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y
1 1 IsOLENOlB
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s JVALVE
v — / ~ \ I ~ - / — \ nJTOLENOID
DETENT VALVE DE-ENERGIZED
Figure 5-28—Solenoid Valve
De-Energized
at main line pressure then oc-
cupies the center of the valve and
bears against the fifth land of the
valve as well as the first land.
The detent v a l v e spring then
moves the valve to the position
shown in Figure 5-28, shutting off
the modulator, detent and limited
modulator ports.
h. High Speed Down Shift
Timing Valve
The high speed downshift timing
valve is a spring loaded valve
located in the main valve body.
Its function is to control the rate
of low servo application at high
road speeds.
At sufficiently high road speeds
governor pressure against the
first land of the valve overcomes
spring pressure to move the valve
to the position shown in Figure
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Figure 5-29—High Speed Downshift
Timing Valve
5-29. With the valve in this po-
sition oil for low servo applica-
tion must pass two orifices as
shown. At lower car speeds, gov-
ernor valve pressure is not suf-
ficient to overcome the spring
pressure and low servo applica-
tion is made through passages
containing one orifice as shown
in Figure 5-30.
i. Coast Down Shift
Tinning Valve
As the car is decelerating with
closed t h r o t t l e or very l i g h t
throttle (such as when approach-
ing a stop) governor valve pres-
sure diminishes to a point where
spring pressure moves the shift
valve to the down shift position.
When this occurs, oil is exhausted
from the band release chamber of
the low servo through the coast
down shift timing valve
A rush of oil through the valve
moves the ball retainer and ball
against light spring pressure off
its seat, oil may then escape
around t h e ball retainer and
spring. This action cushions the
initial engagement of the low
band. See Figure 5-31.
j. Operation of Hydraulic
Controls in Drive Range
(Part Throttle Upshifted)
During operation in Drive range
the manual shift control valve is
positioned as shown in Figure
5-32. During part throttle accel-
eration main line oil is directed
to the modulator valve and manual
shift control valve. Main line oil
entering the manual shift control
valve is routed into the drive oil
passage and then directed to the
governor valve, shift valve, de-
tent valve, high speed down shift
timing valve and low servo.
Main line oil being directed to the
modulator valve enters between
the first and second lands. At low
Figure 5-30—High Speed Downshift
Timing Valve Regulated
engine vacuum the vacuum modu-
lator tends to keep the valve
toward the bottom of its bore.
In this position oil is delivered
through a drilled passage in the
valve to the space between the
first land of the valve and the
valve body. Oil under pressure
in this area plus governor pres-
sure on the second land of the
second modulator valve tends to
move the valve against the force
of its spring to regulator modu-
lator oil pressure leaving the
valve. Modulator oil leaves the
modulator valve and is routed to
the boost valve, detent valve,
modulator limit valve, and to the
second land of the shift control
Figure 5-31—Coast Downshift
Timing Valve