Dodge Ram Truck 1500-2500-3500. Manual — part 1759

48RE

T

ransmission

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AUTOMATIC TRANSMISSION - 48RE - SERVICE INFORMATION

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The 48RE is a four speed fully automatic transmissions with an electronic governor. The 48RE is equipped with a
lock-up clutch in the torque converter. First through third gear ranges are provided by the clutches, bands, over-
running clutch, and planetary gear sets in the transmission. Fourth gear range is provided by the overdrive unit that
contains an overdrive clutch, direct clutch, planetary gear set, and overrunning clutch.

The transmission contains a front, rear, and direct clutch which function as the input driving components. It also
contains the kickdown (front) and the low/reverse (rear) bands which, along with the overrunning clutch and over-
drive clutch, serve as the holding components. The driving and holding components combine to select the neces-
sary planetary gear components, in the front, rear, or overdrive planetary gear set, transfer the engine power from
the input shaft through to the output shaft.

The valve body is mounted to the lower side of the transmission and contains the valves to control pressure reg-
ulation, fluid flow control, and clutch/band application. The oil pump is mounted at the front of the transmission and
is driven by the torque converter hub. The pump supplies the oil pressure necessary for clutch/band actuation and
transmission lubrication.

IDENTIFICATION

Transmission identification numbers (1) are stamped
on the left side of the case just above the oil pan gas-
ket surface. Refer to this information when ordering
replacement parts.

1 - TORQUE CONVERTER

10 - OVERDRIVE CLUTCH

2 - INPUT SHAFT

11 - DIRECT CLUTCH

3 - OIL PUMP

12 - PLANETARY GEAR

4 - FRONT BAND

13 - INTERMEDIATE SHAFT

5 - FRONT CLUTCH

14 - OVERDRIVE OVERRUNNING CLUTCH

6 - REAR CLUTCH

15 - DIRECT CLUTCH SPRING

7 - PLANETARIES

16 - OVERDRIVE PISTON RETAINER

8 - REAR BAND

17 - OIL PAN

9 - OVERRUNNING CLUTCH

18 - VALVE BODY

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GEAR RATIOS

The 48RE gear ratios are:

1st

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.45:1

2nd

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.45:1

3rd

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.00:1

4th

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.69:1

Rev.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.20:1

OPERATION

The application of each driving or holding component is controlled by the valve body based upon the manual lever
position, throttle pressure, and governor pressure. The governor pressure is a variable pressure input to the valve
body and is one of the signals that a shift is necessary. First through fourth gear are obtained by selectively apply-
ing and releasing the different clutches and bands. Engine power is thereby routed to the various planetary gear
assemblies which combine with the overrunning clutch assemblies to generate the different gear ratios. The torque
converter clutch is hydraulically applied and is released when fluid is vented from the hydraulic circuit by the torque
converter control (TCC) solenoid on the valve body. The torque converter clutch is controlled by the Powertrain
Control Module (PCM). The torque converter clutch engages in fourth gear, and in third gear under various condi-
tions, such as when the O/D switch is OFF, when the vehicle is cruising on a level surface after the vehicle has
warmed up. The torque converter clutch can also be engaged in the MANUAL SECOND gear position if high trans-
mission temperatures are sensed by the PCM. The torque converter clutch will disengage momentarily when an
increase in engine load is sensed by the PCM, such as when the vehicle begins to go uphill or the throttle pressure
is increased. The torque converter clutch feature increases fuel economy and reduces the transmission fluid tem-
perature.

Since the overdrive clutch is applied in fourth gear only and the direct clutch is applied in all ranges except fourth
gear, the transmission operation for park, neutral, and first through third gear will be described first. Once these
powerflows are described, the third to fourth shift sequence will be described.

PARK POWERFLOW

As the engine is running and the crankshaft is rotat-
ing, the flexplate and torque converter, which are also
bolted to it, are all rotating in a clockwise direction as
viewed from the front of the engine. The notched hub
of the torque converter is connected to the oil pump’s
internal gear, supplying the transmission with oil pres-
sure. As the converter turns, it turns the input shaft in
a clockwise direction. As the input shaft is rotating, the
front clutch hub-rear clutch retainer and all their asso-
ciated parts are also rotating, all being directly con-
nected to the input shaft. The power flow from the
engine through the front clutch hub and rear clutch
retainer stops at the rear clutch retainer. Therefore, no
power flow to the output shaft occurs because no
clutches are applied. The only mechanism in use at
this time is the parking sprag (1), which locks the
parking gear (2) on the output shaft (3) to the trans-
mission case.

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NEUTRAL POWERFLOW

With the gear selector in the NEUTRAL position, the
power flow of the transmission is essentially the same
as in the park position. The only operational difference
is that the parking sprag (1) has been disengaged,
unlocking the output shaft (3) from the transmission
case and allowing it to move freely.

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