Dodge RAM TRUCK 1500 1995 Service Manual page 1387

21 - 104 42RH/46RH/47RH AUTOMATIC TRANSMISSION CONTROLS AND OPERATION — — B R
by throttle pressure which is dependent on the de­
gree of throttle opening. The regulator valve Is lo­
cated In the valve body.
The throttle valve determines line pressure and
shift speed. The throttle valve controls upshift and
downshift speeds by regulating pressure according to
throttle position.
SHIFT WALWE FLOW CONTROL
The manual valve is operated by the gearshift link­
age and provides the operating range selected by the
driver.
The 1-2 shift valve provides 1-2 or 2-1 shifts and
the 2-3 shift valve provides 2-3 or 3-2 shifts.
The kickdown valve provides forced 3-2 or 3-1
downshifts depending on vehicle speed. Downshifts
occur when the throttle is opened beyond downshift
detent position. Detent is reached just before wide
open throttle position.
The 2-3 valve throttle pressure plug provides 3-2
downshifts at varying throttle openings depending on
vehicle speed.
The 1-2 shift control valve transmits 1-2 shift pres­
sure to the accumulator piston. This controls kick-
down band capacity on 1-2 upshifts and 3-2
downshifts.
The 3-4 shift valve, timing valve and accumulator
are only actuated when the overdrive solenoid is en­
ergized.
The solenoid check ball controls a vent port to the
3-4 valve. The check ball either diverts line pressure
away from or directly to, the 3-4 shift valve. Energiz­
ing the solenoid causes the check ball to close the
vent port allowing line pressure to act upon the 3-4
upshift valve.
The valve body is equipped with a limit valve. The
valve determines maximum speed at which a 3-2
part throttle kickdown can be made. On transmis­
sions without a limit valve, maximum speed for a 3-2
kickdown is at detent position.
The 2-3 shuttle valve has two functions. First is
fast front band release and smooth engagement dur­
ing lift-foot 2-3 upshifts. The second is to regulate
front clutch and band application during 3-2 down­
shifts.
The 3-4 timing valve is moved by line pressure
coming through the 3-4 shift valve. The timing valve
holds the 2-3 shift valve in an upshift position. The
purpose is to prevent the 2-3 valve from up or down­
shifting before the 3-4 valve.
The 3-4 accumulator is mounted on the overdrive
housing. It performs the same function as the 2-3 ac­
cumulator. It is used to smooth engagement during
the 3-4 shift.
CONWERTER DRAINBACK WALWE
The drainback valve is located in the transmission
cooler outlet (pressure) line. The valve prevents fluid
from draining from the converter into the cooler and
lines when the vehicle is shut down for lengthy peri­
ods.
Production valves have a hose nipple at one end,
while the opposite end is threaded for a flare fitting.
Some early valves have hose nipples at both ends.
The valves have an arrow mark (or similar mark) to
indicate direction of flow through the valve.
•300ST WALWE OPERATION
The boost valve provides increased fluid apply pres­
sure for converter clutch and overdrive clutch en­
gagement.
The boost valve is connected to the overdrive clutch
circuit via a tube connected between the valve body
upper and lower housings. The valve is connected to
the converter clutch circuit via the regulator valve,
switch valve and 3-4 shift and timing valves.
Hydraulic circuitry for the boost valve is shown in
the hydraulic flow diagrams. The diagrams are lo­
cated at the end of the transmission diagnosis and
test section.
During converter clutch engagement in fourth gear,
the valve supplies full line pressure directly to the
clutch. The increased pressure available at the clutch
provides smooth shifting and positive engagement.
A 3-4 upshift causes the boost valve to increase line
pressure to the overdrive clutch. Pressure also in­
creases with throttle opening. This ensures positive
clutch engagement during periods of high throttle
opening acceleration.
QUICK FILL WALWE OPERATION
The 3-4 shuttle valve is replaced by a 3-4 quick fill
valve in the valve body. The purpose of the valve is
faster engagement of the overdrive clutch during up­
shifts.
In operation, the valve temporarily bypasses the
clutch piston feed orifice at the start of a 3-4 upshift.
This exposes a larger passage into the piston retainer
resulting in a much faster clutch fill and apply se­
quence.
The valve does not bypass the regular clutch feed
orifice throughout the 3-4 upshift. Instead, once a
predetermined pressure develops within the clutch,
the valve closes the bypass. Clutch fill is then com­
pleted through the regular feed orifice.
CONVERTER CLUTCH CONTROL
The converter clutch valve applies the converter
clutch when supplied with line pressure through the
converter clutch solenoid. The solenoid is mounted on
the valve body and energized by an electrical signal
from the powertrain control module. Electronic con-