Detent Valve; Vacuum Modulator Valve - Buick LeSabre 1965 Service Manual

5 - 1 0 2 DESCRIPTION & OPERATION
SUPER TURBINE "400"
or detent 3-2 downshift is possi-
ble by depressing the accelerator
fully. This engages an electri-
cally operated switch at the car-
buretor and actuates the detent
s o l e n o i d . The detent solenoid
opens an orifice that allows line
oil at the detent valve to be ex-
hausted, thus permitting the de-
tent regulator valve to operate.
Line oil acting on the detent valve
and solenoid is supplied by a
s m a l l e r orifice. See Figure
5-246.
Drive oil on the detent regulator
valve is then regulated to a pres-
sure of approximately 70 psi and
called detent oil. Detent oil is
then routed to the;
1. Modulator Passage
2. 1-2 Regulator Valve
3. 2-3 Modulator Valve
4. 3-2 Valve
5. 1-2 P r i m a r y Accumulator
Valve
6. Vacuum Modulator Valve
Detent oil in the modulator pass-
age and at the 2-3 modulator
valve will close the 2-3 shift
valve below approximately 70
MPH, shifting the transmission
to second gear.
A detent 2-1 downshift can also
be accomplished below approxi-
mately 20 MPH because detent
oil is directed to the 1-2 regula-
tor valve, regulating or exhaust
port. This allows detent oil to
act on the 1-2 regulator and 1-2
detent valve to close the 1-2 shift
valve, shifting the transmission
to first gear.
To insure clutch durability during
1-2 upshifts under detent condi-
tions, detent oil is directed to the
1-2 accumulator primary valve
to increase 1-2 accumulator oil
pressure acting on the rear servo
accumulator piston.
Detent oil is also directed to the
modulator valve to prevent modu-
lator pressure from regulating
70 psi at high speeds or at high
altitudes.
f. L
2
Range—Valves in
Second Speed Position
A 3-2 downshift can be accom-
plished by moving the selector
lever from Drive to L
2
Range.
When the selector lever is in the
L
2
position, L
2
oil from the man-
ual valve is directed to the: (See
Figure 5-247).
1. Pressure Boost Valve
2. 2-3 Shift Valve
L
2
oil at the boost valve will in-
crease line pressure to 150 psi.
This increased intermediate oil
pressure at the 2-3 shift valve
will close the 2-3 shift valve,
regardless of car speed.
For engine braking the front band
is applied by exhausting servo oil
at the manual valve in L
2
Range.
This allows intermediate clutch
oil, acting on the servo piston,
to move the piston and apply the
front band. Once the transmission
is in second speed - L
2
Range,
it cannot upshift to third gear
regardless of vehicle speed.
SUMMARY
The f o r w a i d and intermediate
clutches and front band are ap-
plied. The transmission is in
second gear - L
2
Range.
L
1
Range—First S p e e d -
Valves in First Speed
Position
Maximum downhill braking can be
attained at speeds below 40 MPH
with the selector lever in Lo
position as this directs Lo oil
from the manual valve to the:
(See Figure 5-248).
1. Rear Servo
2. 1-2 Accumulator Valve
3. Detent Regulator Valve
Basic Control
Lo oil flows past a ball check to
the apply side of the rear servo
piston and to the 1-2 accumulator
valve to raise the 1-2 accumula-
tor oil to line pressure for a
smooth band apply.
Lo oil acts on the detent regulator
valve. Combined with the detent
spring, Lo oil holds the detent
valve against line oil acting on
the detent valve, causing drive oil
to flow through the detent regula-
tor v a l v e into the d e t e n t and
modulator p a s s a g e s . Modula-
tor and detent oil at line pressure
acting on the 1-2 regulator and
1-2 detent valve overcomes gov-
ernor oil on the 1-2 shift valve
at any vehicle speed below ap-
proximately 40 MPH and the
transmission will shift to first
gear.
With the transmission in first
speed - L
1
Range, the transmis-
sion c a n n o t upshift to second
speed regardless of vehicle or
engine speed. The forward clutch
and rear band are applied. The
transmission is in first speed -
L
1
Range.