Dodge Durango (DN). Manual — part 81

The higher engine speed and line pressure would

open the vent too far and reduce line pressure too
much. Throttle pressure, which increases with engine
speed (throttle opening), is used to oppose the move-
ment of the pressure valve to help control the meter-
ing passage at the vent. The throttle pressure is
combined with spring pressure to reduce the force of
the throttle pressure plug on the pressure valve. The
larger spring at the right closes the regulator valve
passage and maintains or increases line pressure.
The increased line pressure works against the reac-
tion area of the line pressure plug and the reaction
area left of land #3 simultaneously moves the regu-
lator valve train to the right and controls the meter-
ing passage.

The kickdown valve, along with the throttle valve,

serve to delay upshifts until the correct vehicle and
engine speed have been reached. It also controls
downshifts upon driver demand, or increased engine
load. If these valves were not in place, the shift
points would be at the same speed for all throttle
positions. The kickdown valve is actuated by a cam
connected to the throttle. This is accomplished
through either a linkage or a cable. The cam forces
the kickdown valve toward the throttle valve com-
pressing the spring between them and moving the
throttle valve. As the throttle valve land starts to
uncover its port, line pressure is “metered” out into
the circuits and viewed as throttle pressure. This
increased throttle pressure is metered out into the
circuits it is applied to: the 1–2 and 2–3 shift valves.

When the throttle pressure is high enough, a 3–2
downshift will occur. If the vehicle speed is low
enough, a 2–1 downshift will occur.

SWITCH VALVE

When the transmission is in Drive Second just

before the TCC application occurs (Fig. 41), the pres-
sure regulator valve is supplying torque converter
pressure to the switch valve. The switch valve directs
this pressure through the transmission input shaft,
into the converter, through the converter, back out
between the input shaft and the reaction shaft, and
back up to the switch valve. From the switch valve,
the fluid pressure is directed to the transmission
cooler, and lubrication pressure returns from the
cooler to lubricate different portions of the transmis-
sion.

Once the TCC control valve has moved to the left

(Fig. 42), line pressure is directed to the tip of the
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.

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DESCRIPTION AND OPERATION (Continued)

Fig. 41 Switch Valve-Torque Converter Unlocked

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DESCRIPTION AND OPERATION (Continued)

Fig. 42 Switch Valve-Torque Converter Locked

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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.

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 qual-
ity of the kickdown shift by restricting the rate of
fluid discharge from the front clutch and servo
release circuits. During a 3–2 kickdown, fluid dis-
charges through the shuttle by–pass circuit. When
the shuttle valve closes the by–pass circuit, fluid dis-
charge is restricted and controlled for the application
of the front band. During a 2–3 “lift foot” upshift, the
shuttle 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-

Fig. 43 Manual Valve

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