Dodge Durango (DN). Manual — part 39

KICKDOWN VALVE

When the throttle valve is as far over to the left as

it can go, the maximum line pressure possible will
enter the throttle pressure circuit. In this case, throt-
tle pressure will equal line pressure. With the kick-
down valve (Fig. 26) pushed into the bore as far as it
will go, fluid initially flows through the annular
groove of the 2–3 shift valve (which will be in the
direct drive position to the right).

After passing the annular groove, the fluid is

routed to the spring end of the 2–3 shift valve. Fluid
pressure reacting on the area of land #1 overcomes
governor pressure, downshifting the 2–3 shift valve
into the kickdown, or second gear stage of operation.
The valve is held in the kickdown position by throttle
pressure routed from a seated check ball (#2). Again,
if vehicle speed is low enough, throttle pressure will
also push the 1–2 shift valve left to seat its governor
plug, and downshift to drive breakaway.

KICKDOWN LIMIT VALVE

The purpose of the limit valve is to prevent a 3–2

downshift at higher speeds when a part–throttle
downshift is not desirable. At these higher speeds
only a full throttle 3–2 downshift will occur. At low
road speeds (Fig. 27) the limit valve does not come
into play and does not affect the downshifts. As the

vehicle’s speed increases (Fig. 28), the governor pres-
sure also increases. The increased governor pressure
acts on the reaction area of the bottom land of the
limit valve overcoming the spring force trying to push
the valve toward the bottom of its bore. This pushes
the valve upward against the spring and bottoms the
valve against the top of the housing. With the valve
bottomed against the housing, the throttle pressure
supplied to the valve will be closed off by the bottom
land of the limit valve. When the supply of throttle
pressure has been shut off, the 3–2 part throttle down-
shift plug becomes inoperative, because no pressure is
acting on its reaction area.

1–2 SHIFT VALVE

The 1–2 shift valve assembly (Fig. 29), or mecha-

nism, consists of: the 1–2 shift valve, governor plug,
and a spring on the end of the valve. After the manual
valve has been placed into a forward gear range, line
pressure is directed to the 1–2 shift valve. As the
throttle is depressed, throttle pressure is applied to
the right side of the 1–2 shift valve assembly. With
throttle pressure applied to the right side of the valve,
there is now both spring pressure and throttle pres-
sure acting on the valve, holding it against the gover-
nor plug. As the vehicle begins to move and build

Fig. 26 Kickdown Valve–Wide Open Throttle

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DESCRIPTION AND OPERATION (Continued)

speed, governor pressure is created and is applied to
the left of the valve at the governor plug.

When governor pressure builds to a point where it

can overcome the combined force of the spring and

throttle pressure on the other side of the valve, the
valve will begin to move over to the right. As the
valve moves to the right, the middle land of the valve
will close off the circuit supplying the throttle pres-

Fig. 27 Kickdown Limit Valve-Low Speeds

Fig. 28 Kickdown Limit Valve-High Speeds

Fig. 29 1–2 Shift Valve-Before Shift

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DESCRIPTION AND OPERATION (Continued)

sure to the right side of the valve. When the throttle
pressure is closed off, the valve will move even far-
ther to the right, allowing line pressure to enter
another circuit and energize the front servo, applying
the front band (Fig. 30).

The governor plug serves a dual purpose:
• It allows the shift valves to move either left or

right, allowing both upshifts and downshifts.

• When in a manual selection position, it will be

hydraulically “blocked” into position so no upshift can
occur.

The physical blocking of the upshift while in the

manual “1” position is accomplished by the directing
of line pressure between both lands of the governor
plug. The line pressure reacts against the larger land
of the plug, pushing the plug back against the end
plate overcoming governor pressure. With the combi-
nation of the line pressure and spring pressure, the
valve cannot move, preventing any upshift.

1–2 SHIFT CONTROL VALVE

It contains a valve with four lands and a spring. It

is used as both a “relay” and “balanced” valve.

The valve has two specific operations (Fig. 31):
• Aid in quality of the 1–2 upshift.

• Aid in the quality and timing of the 3–2 kick-

down ranges.

When the manual valve is set to the Drive position

and the transmission is in the first or second gear
range, 1–2 shift control or “modulated throttle pressure”
is supplied to the middle of the accumulator piston by
the 1–2 shift control valve. During the 1–2 upshift, this
pressure is used to control the kickdown servo apply
pressure that is needed to apply the kickdown and accu-
mulator pistons. Thus, the 1–2 shift point is “cushioned”
and the quality is improved. During a WOT kickdown,
kickdown pressure is applied between the kickdown
valve and the 1–2 shift control valve. This additional
pressure is directed to the 1–2 shift control’s spring cav-
ity, adding to the spring load on the valve. The result of

this increased “modulated” throttle pressure is a firmer
WOT upshift.

2–3 SHIFT VALVE

The 2–3 shift valve mechanism (Fig. 32) consists of

the 2–3 shift valve, governor plug and spring, and a
throttle plug. After the 1–2 shift valve has completed
its operation and applied the front band, line pres-
sure is directed to the 2–3 shift valve through the
connecting passages from the 1–2 shift valve. The
line pressure will then dead–end at land #2 until the
2–3 valve is ready to make its shift. Now that the
vehicle is in motion and under acceleration, there is
throttle pressure being applied to the spring side of
the valve and between lands #3 and #4.

As

vehicle

speed

increases,

governor

pressure

increases proportionately, until it becomes great enough
to overcome the combined throttle and spring pressure
on the right side of the valve. When this happens, the
governor plug is forced against the shift valve moving it
to the right. The shift valve causes land #4 to close the
passage supplying throttle pressure to the 2–3 shift
valve. Without throttle pressure present in the circuit
now, the governor plug will push the valve over far
enough to bottom the valve in its bore. This allows land
#2 to direct line pressure to the front clutch.

After the shift (Fig. 33), line pressure is directed to

the land between the shift valve and the governor
plug, and to the release side of the kickdown servo.
This releases the front band and applies the front
clutch, shifting into third gear or direct drive. The
rear clutch remains applied, as it has been in the
other gears. During a manual “1” or manual “2” gear
selection, line pressure is sent between the two lands
of the 2–3 governor plug. This line pressure at the
governor plug locks the shift valve into the second
gear position, preventing an upshift into direct drive.
The theory for the blocking of the valve is the same
as that of the 1–2 shift valve.

Fig. 30 1–2 Shift Valve-After Shift

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DESCRIPTION AND OPERATION (Continued)

3–4 SHIFT VALVE

The PCM energizes the overdrive solenoid during the

3-4 upshift (Fig. 34). This causes the solenoid check ball
to close the vent port allowing line pressure from the
2-3 shift valve to act directly on the 3-4 upshift valve.

Line pressure on the 3-4 shift valve overcomes valve
spring pressure moving the valve to the upshift position
(Fig. 35). This action exposes the feed passages to the
3-4 timing valve, 3-4 quick fill valve, 3-4 accumulator,
and ultimately to the overdrive piston.

Fig. 31 1–2 Shift Control Valve

Fig. 32 2–3 Shift Valve-Before Shift

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DESCRIPTION AND OPERATION (Continued)