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AUTOMATIC TRANSMISSION—42RE 21 - 1
AUTOMATIC TRANSMISSION—42RE
CONTENTS
page
page
42RE TRANSMISSION DIAGNOSIS ..........
GENERAL INFORMATION ..................
IN-VEHICLE SERVICE—42RE ..............
OVERDRIVE UNIT OVERHAUL-42RE .......
SPECIFICATIONS .....................
TRANSMISSION OVERHAUL—42RE ........
TRANSMISSION/OVERDRIVE REMOVAL
AND INSTALLATION—42RE .............
GENERAL INFORMATION
INDEX
page
page
Converter Clutch Engagement ...............
Electronic Governor Components ..............
Front Band Adjustment .....................
Gear Ratios .............................
Governor Pressure Curves ..................
Overdrive Off Switch ......................
Quick Fill Valve ..........................
Recommended Fluid ......................
Service Manual Updates ....................
Torque Converter .........................
Transmission Description ....................
Transmission Identification ...................
Transmission Shifting ......................
TRANSMISSION DESCRIPTION
The Chrysler 42RE is a 4-speed automatic transmis-
sion. Mechanical and hydraulic components in the
42RE are similar to those in Chrysler 42RH transmis-
sions. The major difference between them involves the
method of producing governor pressure for shift speed
control. The 42RE uses electronic components to de-
velop governor pressure. A mechanical governor is used
to generate governor pressure in the 42RH.
First through third gear ranges in the 42RE are
provided by the clutches, bands, overrunning clutch
and planetary gear sets in the transmission unit.
Fourth gear range is provided by the overdrive unit
which contains an overdrive clutch, direct clutch, plan-
etary gear set and overrunning clutch.
The overdrive clutch is applied in fourth gear only.
The direct clutch is applied in all ranges except fourth
gear.
The 42RE valve body transfer plate is completely
new. It is redesigned to accept a new governor body and
different hydraulic circuitry. The governor pressure
solenoid valve and sensor are mounted in this body.
The new transfer plate channels line pressure to the
solenoid valve through the governor body. It also chan-
nels governor pressure from the solenoid valve to the
governor circuit. It is the solenoid valve that develops
necessary governor pressure.
The 42RE overdrive unit is quite different from
previous overdrive units. It is shorter in length as a
result of eliminating the mechanical governor mecha-
nism, governor tubes and governor support.
Fig. 1 42RE Automatic Transmission (4 x 2 Model)
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AUTOMATIC TRANSMISSION—42RE 21 - 3
TORQUE CONVERTER
A three element torque converter is used for all
applications (Fig. 1). Converter elements consist of the
turbine, stator and impeller. The converter also con-
tains an overrunning clutch and a converter clutch
mechanism.
The converter clutch is an electronically controlled
mechanism. The clutch provides reduced engine speed
and greater fuel economy when engaged. Clutch en-
gagement also provides reduced transmission fluid
temperatures.
The converter clutch is engaged in fourth gear and in
third gear when the overdrive control switch is in the
OFF position.
The overrunning clutch is mounted in the stator hub.
This one-way clutch prevents the stator from rotating
in a direction opposite to engine rotation. This retains
the torque multiplication feature of the converter.
The torque converter is not a serviceable component.
It should be replaced as an assembly when: diagnosis
indicates a malfunction has occurred, or when a major
malfunction allows debris to enter the converter.
Fig. 2 Transmission Identification Number And
Code Location
ELECTRONIC GOVERNOR COMPONENTS
Governor pressure is developed and controlled elec-
tronically in the 42RE transmission. Components used
for development and control of governor pressure in-
clude:
²
GEAR RATIOS
Forward Gear ratios for the 42RE transmission are:
governor body
²
new design valve body transfer plate
²
First gear = 2.74:1
²
governor pressure solenoid valve
²
Second gear = 1.54:1
²
governor pressure sensor
²
Third gear = 1.00:1
²
fluid temperature thermister
²
Fourth gear = 0.69:1.
²
transmission speed sensor
²
throttle position sensor
RECOMMENDED FLUID
The only fluid recommended for the 42RE transmis-
sion is Mopar ATF Plus, type 7176. Do not use Dexron
II except in an emergency or if ATF Plus is not
available.
²
transmission control module (TCM)
Governor Pressure Solenoid Valve
The solenoid valve generates the governor pressure
needed for upshifts and downshifts. It is an electro-
hydraulic device and is located in the governor body on
the valve body transfer plate (Fig. 3).
The inlet side of the solenoid valve is exposed to
normal transmission line pressure. The outlet side of
the valve leads to the valve body governor circuit.
The solenoid valve regulates line pressure to produce
governor pressure. The average current supplied to the
solenoid controls governor pressure. One amp current
produces zero kPa/psi governor pressure. Zero amps
sets the maximum governor pressure.
The transmission control module (TCM) supplies
electrical power to the solenoid valve. Operating volt-
age is 12 volts (DC) and is provided through the battery
terminal on the module.
The solenoid is polarity sensitive. The TCM ener-
gizes the solenoid by grounding it through the power
ground terminal on the transmission control module.
TRANSMISSION IDENTIFICATION
The transmission part/identification numbers and
codes are stamped on the left side of the case just above
the oil pan gasket surface (Fig. 2).
The first letter/number group is the assembly part
number. The next number group the transmission
build date. The last number group is the transmission
serial number. Refer to this information when ordering
replacement parts.
FRONT BAND ADJUSTMENT
The front band adjustment for 42RE transmissions is
considerably different from prior 4-speed models.
On 42RE transmissions, the front band is
backed
off 3-5/8 turns
after tightening the adjusting screw to
specified torque.
Refer to the front band adjustment procedure in the
In-vehicle Service section when band adjustment is
necessary.
Governor Pressure Sensor
The governor pressure sensor measures output pres-
sure of the governor pressure solenoid valve (Fig. 4).
21 - 4 AUTOMATIC TRANSMISSION—42RE
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Fig. 3 Governor Pressure Solenoid Valve
the converter clutch, and governor pressure. Normal
resistance value for the thermister at room tempera-
ture is approximately 1000 ohms.
The transmission control module (TCM) prevents
engagement of the converter clutch and overdrive
clutch, when fluid temperature is below approximately
1°C (30°F).
If fluid temperature exceeds 126°C (260°F), the
transmission control module will cause a 4-3 downshift
and engage the converter clutch. Engagement is ac-
cording to the third gear converter clutch engagement
schedule.
The overdrive OFF lamp in the instrument panel,
also illuminates when the shift back to third occurs.
The transmission will not allow fourth gear operation
until fluid temperature decreases to approximately
110°C (230°F).
The thermistor is mounted on the underside of the
converter clutch solenoid (Fig. 6). It is immersed in
transmission fluid at all times.
The sensor output signal provides the necessary
feedback to the transmission control module. This
feedback is needed to adequately control governor
pressure.
Fig. 4 Governor Pressure Sensor
Governor Body And Transfer Plate
A new transfer plate is used with the 42RE valve
body. The transfer plate is designed to: (a) supply
transmission line pressure to the governor pressure
solenoid valve and (b) to return governor pressure.
The governor pressure solenoid valve is mounted in
the governor body. The body is bolted to the lower side
of the transfer plate (Fig. 5).
Fig. 6 Converter Clutch Solenoid And Thermistor
Location
Transmission Speed Sensor
The speed sensor (Fig. 7), is located in the overdrive
gear case. The sensor is positioned over the park gear
and monitors transmission output shaft rotating
speed. The sensor used with the 42RE transmission is
the same as is used in Chrysler 41TE and 42LE
front drive automatic transmissions.
Speed sensor signals are triggered by the park gear
lugs as they rotate past the sensor pickup face. Input
signals from the sensor are sent to the transmission
control module for processing.
The vehicle speed sensor also serves as backup to the
transmission speed sensor. Signals from this sensor are
shared with the powertrain control module.
Fig. 5 Governor Body
Throttle Position Sensor (TPS)
The TPS provides throttle position input signals to
both the transmission control module and powertrain
controller. This input signal is used to determine
overdrive and converter clutch shift schedule and to
select the proper governor curve.
Transmission Fluid Temperature Thermister
Transmission fluid temperature readings are sup-
plied to the transmission control module by the ther-
mister (Fig. 6). The temperature readings are used to
control engagement of the fourth gear overdrive clutch,
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AUTOMATIC TRANSMISSION—42RE 21 - 5
The conditions under which a shift to fourth will not
occur, also remain the same. These being:
²
shift to third not yet completed
²
overdrive switch is in OFF position
²
throttle is at 3/4 to wide open position
²
vehicle speed too low for 3-4 shift to occur
transmission fluid temperature is below 1°C (30°F)
or above 121°C (250°F).
Fig. 7 Transmission Speed Sensor
CONVERTER CLUTCH ENGAGEMENT
The torque converter clutch is engaged by the clutch
solenoid on the valve body. The clutch can be engaged
in third and fourth gear ranges depending on overdrive
control switch position.
If the overdrive control switch is in the normal ON
position, the clutch will engage after the shift to fourth
gear, and above approximately 72 km/h (45 mph).
If the control switch is in the OFF position, the clutch
will engage after the shift to third gear, at approxi-
mately 56 km/h (35 mph) at light throttle.
Transmission Control Module (TCM)
The TCM controls operation of the converter clutch,
overdrive clutch, and governor pressure solenoid.
The control module determines transmission shift
points based on input signals from the transmission
thermistor, transmission output shaft speed sensor,
crankshaft position sensor, vehicle speed sensor and
throttle position sensor.
Operating voltage is supplied through the battery
terminal on the control module. The ignition voltage
signal is supplied through a terminal on the ABS
control module.
The DRB II scan tool can be used to check operation
of the control module and transmission electrical com-
ponents. The diagnostic connector (for the scan tool) is
located under the driver side of the instrument panel.
The connector has a 6-way terminal and is blue in
color.
OVERDRIVE OFF SWITCH
The overdrive Off switch is located in the instrument
panel. The switch is a momentary contact device that
signals the TCM to toggle current status of the over-
drive function. At key-on, overdrive operation is al-
lowed.
Pressing the switch once causes the overdrive Off
mode to be entered and the overdrive Off switch lamp
to be illuminated. Pressing the switch a second time
causes normal overdrive operation to be restored and
the overdrive lamp to be turned off.
The normal position for the control switch is the ON
position. The switch must be in this position to ener-
gize the solenoid and allow a fourth gear upshift.
The control switch has an indicator light. The light
illuminates when the overdrive switch is turned to the
OFF position, or when illuminated by the transmission
control module.
The control switch indicator light is also used to
signal fault flash codes for diagnostic purposes.
GOVERNOR PRESSURE CURVES
There are four governor pressure curves pro-
grammed into the transmission control module. The
different curves allow the control module to adjust
governor pressure for varying conditions.
One curve is used for operation when fluid tempera-
ture is at, or below 1°C (30°F).
A second curve is used when fluid temperature is at,
or above -0.5°C (31°F) during normal city, or highway
driving.
A third curve is used during wide open throttle
operation. The fourth curve is used when driving with
the transfer case in low range.
QUICK FILL VALVE
The 3-4 shuttle valve is replaced by a 3-4 quick fill
valve in the 42RE valve body. The valve maintains a
prefill pressure of approximately 5 psi in the overdrive
clutch. Prefill pressure is maintained in all drive (D)
ranges. The purpose of the valve is faster engagement
of the overdrive clutch during 3-4 upshifts.
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.
TRANSMISSION SHIFTING
Shift valve operation in 42RE transmissions with the
electronic governor mechanism is basically unchanged.
The 1-2 and 2-3 upshift sequence occurs exactly the
same as in non-electronic governor transmission.
The valve body shift valves are still moved by a
combination of throttle and governor pressure. The
only real difference is that governor pressure is gener-
ated by electrical components instead of a mechanical
valve and weight assembly.
²
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