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The regulated line pressure in REVERSEis held at much higher pressures than in the other gear positions: 145-280
psi. The higher pressure for REVERSE isachieved by the manual valve blocking the supply of line pressure to the
reaction area left of land #4. With this pressure blocked, there is less area for pressure to act on to balance the
force of the spring on the right. This allows line pressure to push the valvetrain to the right, reducing the amount
of fluid returned to the pump’s inlet, increasing line pressure.
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, throttle pressure will equal line pressure. With the kickdown valve 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 Valve - Wide Open Throttle
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KICKDOWN LIMIT VALVE
The purpose of the limit valve is to prevent a 3-2 downshift at higher speedswhen a part-throttle downshift is not
desirable. At these higher speeds only a full throttle 3-2 downshift will occur. At low road speeds the limit valve does
not come into play and does not affect the downshifts.
As the vehicle’s speed increases , the governor pressure 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
downshift plug becomes inoperative, because no pressure is acting on its reaction area.
Kickdown Limit Valve - Low Speeds
Kickdown Limit Valve - High Speeds
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1-2 SHIFT VALVE
The 1-2 shift valve assembly , or mechanism, 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 assem-
bly. With throttle pressure applied to the right side of the valve, there isnow both spring pressure and throttle pres-
sure acting on the valve, holding it against the governor plug. As the vehicle begins to move and build 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 combinedforce of the spring and throttle
pressureontheothersideofthevalve,thevalvewillbegintomoveovertothe right. As the valve moves to the
right, the middle land of the valve will close off the circuit supplying thethrottle pressure to the right side of the
valve. When the throttle pressure is closed off, the valve will move even farther to the right, allowing line pressure
to enter another circuit and energize the front servo, applying the front band.
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 combination of the line pressure and spring
pressure, the valve cannot move, preventing any upshift.
1-2 Shift Valve - Before Shift
1-2ShiftValve-AfterShift
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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 :
Aid in quality of the 1-2 upshift.
Aid in the quality and timing of the 3-2 kickdown ranges.
When the manual valve is set to the DRIVE position and the transmission is inthe 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 thekickdown servo apply pressure that is
needed to apply the kickdown and accumulator pistons. Thus, the 1-2 shift point is “cushioned” and the quality is
improved. During a WOT kickdown, kickdown pressure is applied between thekickdown valve and the 1-2 shift
control valve. This additional pressure is directed to the 1-2 shift control’s spring cavity, adding to the spring load on
the valve. The result of this increased “modulated” throttle pressure is afirmer WOT upshift.
1-2 Shift Control Valve
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2-3 SHIFT VALVE
The 2-3 shift valve mechanism 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 pressure 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 pres-
sure 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 over-
come the combined throttle and spring pressure on the right side of the valve. Since the throttle pressure end of the
2-3 Shift Valve - Before Shift
2-3ShiftValve-AfterShift
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2-3 shift valve is larger in diameter than the 1-2 shift valve, the 2-3 shiftwill always happen at a greater speed than
the 1-2 shift. 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 pres-
sure 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 , line pressure is directed 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, pre-
venting an upshift into direct drive. The theory for the blocking of the valve is the same as that of the 1-2 shift valve.
If the manual “2” or manual “1” gear position is selected from the drive position, the PCM will control the timing of
the downshift by targeting for a high governor pressure. When a safe vehicle speed is reached, the PCM will switch
to its normal control governor curve and the downshift will occur.
3-4 SHIFT VALVE
The PCM energizes the overdrive solenoid during the
3-4 upshift. 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.
3-4ShiftValveBeforeShift
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Line pressure on the 3-4 shift valve overcomes valve
spring pressure moving the valve to the upshift posi-
tion. 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.
3-4 Shift Valve After Shift
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3-4 TIMING VALVE
The 3-4 timing valve is moved by line pressure com-
ing through the 3-4 shift valve or the converter clutch
valve.
3-4 Shift Valve After Shift