FOURTH GEAR POWERFLOW
Fourth gear overdrive range is electronically con-
trolled and hydraulically activated. Various sensor
inputs are supplied to the powertrain control module
to operate the overdrive solenoid on the valve body.
The solenoid contains a check ball that opens and
closes a vent port in the 3-4 shift valve feed passage.
The overdrive solenoid (and check ball) are not ener-
gized in first, second, third, or reverse gear. The vent
port remains open, diverting line pressure from the
2-3 shift valve away from the 3-4 shift valve. The
overdrive control switch must be in the ON position
to transmit overdrive status to the PCM. A 3-4
upshift occurs only when the overdrive solenoid is
energized by the PCM. The PCM energizes the over-
drive 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. Line pressure on the 3-4
shift valve overcomes valve spring pressure moving
the valve to the upshift position. 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. Line pressure through the timing
valve moves the overdrive piston into contact with
the overdrive clutch. The direct clutch is disengaged
before the overdrive clutch is engaged. The boost
valve provides increased fluid apply pressure to the
overdrive clutch during 3-4 upshifts, and when accel-
erating in fourth gear. The 3-4 accumulator cushions
overdrive clutch engagement to smooth 3-4 upshifts.
The accumulator is charged at the same time as
apply pressure acts against the overdrive piston.
RECOMMENDED FLUID
NOTE: Refer to the Service Procedures section of
this Group for fluid level checking procedures.
FLUID TYPE
Mopar
t ATF Plus 3, Type 7176 automatic trans-
mission fluid is the recommended fluid for Chrysler
automatic transmissions.
Dexron II fluid IS NOT recommended. Clutch
chatter can result from the use of improper
fluid.
FLUID ADDITIVES
Fluid additives other than Mopar
t approved fluo-
rescent leak detection dyes are not to be used in this
transmission.
FLUID
NOTE: Refer
to
the
maintenance
schedules
in
Group 0, Lubrication and Maintenance for the rec-
ommended maintenance (fluid/filter change) inter-
vals for this transmission.
NOTE: Refer to Service Procedures in this group
for fluid level checking procedures.
DESCRIPTION
Mopar
t ATF Plus 3, Type 7176, automatic trans-
mission fluid is the recommended fluid for Daimler-
Chrysler automatic transmissions.
Dexron II fluid IS NOT recommended. Clutch
chatter can result from the use of improper
fluid.
Mopar
t ATF Plus 3, Type 7176, automatic trans-
mission fluid when new is red in color. The ATF is
dyed red so it can be identified from other fluids used
in the vehicle such as engine oil or antifreeze. The
red color is not permanent and is not an indicator of
fluid condition. As the vehicle is driven, the ATF will
begin to look darker in color and may eventually
become brown. This is normal. A dark brown/black
fluid accompanied with a burnt odor and/or deterio-
ration in shift quality may indicate fluid deteriora-
tion or transmission component failure.
FLUID ADDITIVES
DaimlerChrysler strongly recommends against the
addition of any fluids to the transmission, other than
those automatic transmission fluids listed above.
Exceptions to this policy are the use of special dyes
to aid in detecting fluid leaks.
Various “special” additives and supplements exist
that claim to improve shift feel and/or quality. These
additives and others also claim to improve converter
clutch operation and inhibit overheating, oxidation,
varnish, and sludge. These claims have not been sup-
ported to the satisfaction of DaimlerChrysler and
these additives must not be used. The use of trans-
mission “sealers” should also be avoided, since they
may adversely affect the integrity of transmission
seals.
OPERATION
The automatic transmission fluid is selected based
upon several qualities. The fluid must provide a high
level of protection for the internal components by
providing a lubricating film between adjacent metal
components. The fluid must also be thermally stable
so that it can maintain a consistent viscosity through
a large temperature range. If the viscosity stays con-
stant through the temperature range of operation,
transmission operation and shift feel will remain con-
sistent. Transmission fluid must also be a good con-
ductor of heat. The fluid must absorb heat from the
internal transmission components and transfer that
heat to the transmission case.
21 - 10
42RE AUTOMATIC TRANSMISSION
WJ
DESCRIPTION AND OPERATION (Continued)