Dodge Durango (DN). Manual — part 41

switch valve, forcing the valve to the right. The
switch valve now vents oil from the front of the pis-
ton in the torque converter, and supplies line pres-
sure to the (rear) apply side of the torque converter
piston. This pressure differential causes the piston to
apply against the friction material, cutting off any
further flow of line pressure oil. After the switch
valve is shuttled right allowing line pressure to
engage

the

TCC,

torque

converter

pressure

is

directed past the switch valve into the transmission
cooler and lubrication circuits.

MANUAL VALVE

The manual valve (Fig. 43) is a relay valve. The

purpose of the manual valve is to direct fluid to the
correct circuit needed for a specific gear or driving
range. The manual valve, as the name implies, is
manually operated by the driver with a lever located
on the side of the valve body. The valve is connected
mechanically by either a cable or linkage to the gear-
shift mechanism. The valve is held in each of its
positions by a spring–loaded roller or ball that
engages the “roostercomb” of the manual valve.

Fig. 42 Switch Valve-Torque Converter Locked

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DESCRIPTION AND OPERATION (Continued)

CONVERTER CLUTCH LOCK-UP VALVE

The torque converter clutch (TCC) lock-up valve

controls the back (ON) side of the torque converter
clutch. When the PCM energizes the TCC solenoid to
engage the converter clutch piston, pressure is
applied to the TCC lock-up valve which moves to the
right and applies pressure to the torque converter
clutch.

CONVERTER CLUTCH LOCK-UP TIMING VALVE

The torque converter clutch (TCC) lock-up timing

valve is there to block any 4–3 downshift until the
TCC is completely unlocked and the clutch is disen-
gaged.

SHUTTLE VALVE

The assembly is contained in a bore in the valve

body above the shift valves. When the manual valve
is positioned in the Drive range, throttle pressure
acts on the throttle plug of the shuttle valve (Fig. 31)
to move it against a spring, increasing the spring
force on the shuttle valve. During a part or full throt-
tle 1–2 upshift, the throttle plug is bottomed by
throttle pressure, holding the shuttle valve to the
right against governor pressure, and opening a
by–pass circuit. The shuttle valve controls the quality
of the kickdown shift by restricting the rate of fluid
discharge from the front clutch and servo release cir-
cuits. During a 3–2 kickdown, fluid discharges
through the shuttle by–pass circuit. When the shuttle

valve closes the by–pass circuit, fluid discharge is
restricted and controlled for the application of the
front band. During a 2–3 “lift foot” upshift, the shut-
tle valve by–passes the restriction to allow full fluid
flow through the by-pass groove for a faster release
of the band.

BOOST VALVE

The boost valve (Fig. 44) provides increased fluid

apply pressure to the overdrive clutch during 3-4
upshifts (Fig. 45), and when accelerating in fourth
gear.

ACCUMULATOR

DESCRIPTION

The accumulator (Fig. 46) is a hydraulic device

that has the sole purpose of cushioning the applica-
tion of a band or clutch. The accumulator consists of
a dual–land piston and a spring located in a bore in
the transmission case. The 3–4 accumulator is
located in a housing attached to the side of the valve
body (Fig. 47).

OPERATION

Both the accumulator and the 3–4 accumulator

function the same. Line pressure is directed between
the lands of the piston (Fig. 48), bottoming it against
the accumulator plate. The accumulator stays in this
position after the transmission is placed into a Drive

Fig. 43 Manual Valve

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DESCRIPTION AND OPERATION (Continued)

position. When the 1–2 upshift occurs (Fig. 49), line
pressure is directed to the large end of the piston and
then to the kickdown servo. As the line pressure
reaches the accumulator, the combination of spring
pressure and line pressure forces the piston away
from the accumulator plate. This causes a balanced
pressure situation, which results in a cushioned band
application. After the kickdown servo has become
immovable, line pressure will finish pushing the
accumulator up into its bore. When the large end of

the accumulator piston is seated in its bore, the band
or clutch is fully applied.

NOTE: The accumulator is shown in the inverted
position for illustrative purposes.

PISTONS

DESCRIPTION

There are several sizes and types of pistons used in

an automatic transmission. Some pistons are used to
apply clutches, while others are used to apply bands.

Fig. 44 Boost Valve Before Lock-up

Fig. 45 Boost Valve After Lock-up

Fig. 46 Accumulator

1 – ACCUMULATOR PISTON
2 – PISTON SPRING

Fig. 47 3–4 Accumulator and Housing

1 – ACCUMULATOR PISTON
2 – 3–4 ACCUMULATOR HOUSING
3 – TEFLON SEALS
4 – PISTON SPRING
5 – COVER PLATE AND SCREWS

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DESCRIPTION AND OPERATION (Continued)

They all have in common the fact that they are
round or circular in shape, located within a smooth
walled cylinder, which is closed at one end and con-
verts fluid pressure into mechanical movement. The
fluid pressure exerted on the piston is contained
within the system through the use of piston rings or
seals.

OPERATION

The principal which makes this operation possible

is known as Pascal’s Law. Pascal’s Law can be stated
as: “Pressure on a confined fluid is transmitted
equally in all directions and acts with equal force on
equal areas.”

PRESSURE

Pressure (Fig. 50) is nothing more than force (lbs.)

divided by area (in or ft.), or force per unit area.
Given a 100 lb. block and an area of 100 sq. in. on
the floor, the pressure exerted by the block is: 100
lbs. 100 in or 1 pound per square inch, or PSI as it is
commonly referred to.

PRESSURE ON A CONFINED FLUID

Pressure is exerted on a confined fluid (Fig. 51) by

applying a force to some given area in contact with
the fluid. A good example of this is a cylinder filled
with fluid and equipped with a piston that is closely
fitted to the cylinder wall. If a force is applied to the
piston, pressure will be developed in the fluid. Of
course, no pressure will be created if the fluid is not
confined. It will simply “leak” past the piston. There
must be a resistance to flow in order to create pres-
sure.

Piston

sealing

is

extremely

important

in

hydraulic operation. Several kinds of seals are used
to accomplish this within a transmission. These
include but are not limited to O–rings, D–rings, lip
seals, sealing rings, or extremely close tolerances
between the piston and the cylinder wall. The force
exerted is downward (gravity), however, the principle
remains the same no matter which direction is taken.

Fig. 48 Accumulator in Neutral and Drive Positions

Fig. 49 Accumulator in Second Gear Position

1 – BOTTOM IN BORE
2 – SHUTTLE VALVE

Fig. 50 Force and Pressure Relationship

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DESCRIPTION AND OPERATION (Continued)