1973 OPEL 1900 Service Manual

7C- 561973 OPEL SERVICE MANUALMODULATORFigure
7C-42 Low Speed Downshift Timing Valve
During a “coast” condition, the vacuum is high and
the modulator pressure is zero. The spring holds the
timing valve in a bottomed position and the servo
release pressure is exhausted through a restricting
orifice, thus delaying the apply of the servo.
During a “power on” 3-2 downshift at lower car
speeds, the servo must be applied rapidly. During
such a shift, the vacuum will be somewhat lower and
the resulting modulator pressure will force the valve
over against the spring. This provides an unrestricted
passage for servo release, thus permitting rapid apply
of the servo.
High Speed Downshift Timing Valve
When a 3-2 downshift is “forced” at high car speeds,
the application of the band must be delayed. Servo
apply pressure is directed through the high speed
downshift timing valve. See Figure
7C-43.The timing valve is held in a bottomed position by
the spring at lower car speeds. This permits an unre-
stricted
flow for servo apply. At higher car speeds,
approximately 25 to 35 MPH, (depending on axle
ratio and engine), governor pressure forces the valve
over against the spring. This closes off the direct feed
to servo apply and the feed is controlled by a fixed
orifice.While it may outwardly appear that the functions of
the two downshift timing valves are contradictory,
whether or not the application of the band is delayed
during a 3-2 downshift is a combined function of car
speed and throttle position.
--Figure
7C-43 High Speed Downshift Timing Valve
Second Clutch Orifice Valve
For reasons of shift timing, it is necessary to have
different restricting orifice sizes for the feed and ex-
haust of the second clutch. This is accomplished by
introducing a “one way” ball check in the second
clutch circuit. See Figure
7C-44.2ND CLUTCH
I?C-44
Figure
7C-44 Second Clutch Orifice Valve
When the second clutch is being applied, the apply
pressure seats the ball and the feed is directed
through a single orifice. During the release of the
clutch, the ball is unseated and the clutch can ex-
haust at a faster rate through the two orifices.

AUTOMATIC TRANSMISSION7c-57
ACCUMULATORFigure
7C-46 1-2 Accumulator
l-2 AccumulatorIn order to obtain a smooth 1-2 upshift, it is neces-
sary to control the rate of pressure build-up in the
second clutch. This is accomplished by introducing
a hydraulic modulator in the clutch circuit. Prior to
the second clutch being applied, the spring holds the
accumulator piston in an upward position. When
line pressure is introduced to the second clutch cir-
cuit by way of the 1-2 shift valve, the pressure in the
second clutch will be permitted to build up rapidly
until the clutch pressure acting on the accumulator
piston is sufficient to overcome the accumulator
spring. As the clutch pressure increases on the top
side of the accumulator piston, the piston will start
to move against the spring force until the piston is
forced all the way down. This provides a time delay
for the apply of the second clutch before the pressure
reaches its maximum value. When upshifts are made
at heavier throttle, it is necessary to increase the
pressure at which this time delay occurs. This is
accomplished by introducing a vacuum sensitive
pressure from the 1-2 accumulator valve to the bot-
tom side of the accumulator piston. This pressure
assists the spring and the clutch pressure will have to
build up to a higher value before the accumulator
piston will move. See Figure
7C-46.
SERVO7c-47
Figure 7C-47 Low Servo
Low ServoThe low servo provides a dual function. See Figure
7C-47. It is the means by which the band is applied
and it provides an accumulator action for the third
clutch during a 2-3 upshift.
In first and second gear, servo apply pressure acting
on the bottom side of the low servo piston moves the
piston against the spring force and applies the band.
During a 2-3 upshift, third clutch pressure is intro-
duced to the top side of the servo piston. When third
clutch pressure, acting on the top side of the piston
and assisted by the servo release spring, is sufficient
to overcome the servo apply force, the servo will
move downward. This removes the apply force from
the band and the band will release while the clutch
is being applied. During the downward movement of
the piston, a time interval occurs which cushions the
apply of the third clutch in the same manner that the
1-2 accumulator cushions the apply of the second
clutch. It is because of this accumulator action that
the band adjustment is so critical. The main function
of the band adjustment is to control the servo release
spring load rather than to control band clearance.

7c. 581973 OPEL SERVICE MANUAL
a. NEUTRAL & PARK
- ENGINE RUNNING
Neutral
- Engine Running
Reverse Clutch. Released
Second Clutch. Released
Sprag
- LockedThird Clutch
- Released
Low Band .
.ReleasedIn neutral, the low band and all clutches are released. With this condition, no member of the planetary gear set is
held and there is no reaction member. All gears are free to rotate around their own axis and no torque is trans-
mitted to the planet carrier assembly and output shaft.
Park
- Engine Running
The same power flow conditions in the neutral position are in effect in the park position. Additionally, mechan-
ical linkage actuates a parking pawl which engages with the
splines in the periphery of the governor assembly.
Since the governor assembly is splinad to the output shaft, the parking pawl holds the output shaft locked to the
extension, preventing the vehicle from rolling.7ci48
Figure 7C-48 Neutral and Park Engine Running

AUTOMATIC TRANSMISSION7c- 59
b. DRIVE RANGE . FIRST GEAROrive Range . First Gear
Reverse Clutch Released
Second Clutch. Released
Sprag Locked
In Drive Range. First Gear, the low band is applied and all clutches are released.
Figure 7C-49 Drive Range First GearThird Clutch. Released
Low Band. Applied
The low band holds the reaction sun gear and drum stationary, which serves as the reaction member of the planet-
ary gear set in first gear. The input shaft drives the third clutch drum in a clockwise direction, which turns the
sprag race and retainer assembly clockwise. The sprags wedge and drive the input
sun gear.
The power is then transmitted through the gear set to the output shaft as outlined in “Principles of Operation”.
The ratio in first gear is 2.4O:l.
Low RangeIn Low Range, the third clutch is applied together with the low band. The input power flow is exactly the
Same as
drive range first gear except that the third clutch is engaged and prevents the sprag from overrunning, thus pro-
viding engine braking when coasting in Low Range.
7c49

7C- 601973 OPEL SERVICE MANUAL
c. DRIVE RANGE. SECONO GEAROrive Range . Second Gear
Reverse Clutch - Released
Second Clutch -Applied
Sprag
- Overrunning
In Drive Range. Second Gear, the low band and second clutch are applied.Third Clutch
- Released
Low Band -Applied
The input shaft drives the third clutch drum and the second clutch composition plates. When the second clutch
piston is applied, the rotating second clutch composition plates are locked
w the second clutch steel plates. Since
the second clutch drum is now rotating in a clockwise direction, the ring gear is driven clockwise. As described in
“Principles of Operation”, the carrier is driven in a clockwise direction. The long planet pinions also drive the
short planet pinions, which drive the input sun gear clockwise, causing the sprag assembly to overrun. The ratio
is 1.48:1.
second Range
In Second Range, the Power flow is exactly the seme as drive range - second gear.7c50
Figure
7C-50 Drive Range - Second Gear

AUTOMATIC TRANSMISSION 7C- 61
d. DRIVE RANGE - THIRD GEAR
Drive Range
- Third Gear
Reverse Clutch
- Released
Second Clutch. Applied
Sprag . LockedThird Clutch -Applied
Low Band
- Released
In Drive Range
- Third Gear, the low band is released and both the second and third clutches are applied.
In this condition, the ring gear is locked o the input sun gear. With two planetary members connected
inthismanner, the entire planetary system will rotate as a solid unit and provide a direct drive with a ratio of 1 to 1. The
input is split between the ring gear end input sun, and the rarrier is the output member.
Figure 7C-5 1 Drive Range Third Gear

Third Clutch -Applied
Low Band. Released

AUTOMATIC TRANSMISSION ?C- 63