AUTOMATIC TRANSMISSION - 48RE

1 AUTOMATIC TRANSMISSION - 48 RETABLE OF CONTENTS pagepageAUTOMATIC TRANSMISSION - AND TESTINGDIAGNOSIS AND TESTING - AND TESTING - PRELIMINARY . 140 DIAGNOSIS AND TESTING - AND TESTING - HYDRAULICPRESSURE AND TESTING - AIR TESTINGTRANSMISSION CLUTCH AND AND TESTING - CONVERTERHOUSING FLUID AND TESTING - PROCEDURE - ALUMINUMTHREAD AND DIAGRAMSHYDRAULIC TOOLSRE - TRANSMISSION SHIFT AND TESTING - BRAKETRANSMISSION SHIFT - BRAKE TRANSMISSIONSHIFT HOUSING AND FILTERDIAGNOSIS AND TESTINGDIAGNOSIS AND TESTING - EFFECTS OFINCORRECT FLUID AND TESTING - CAUSES OFBURNT AND TESTING - PROCEDURESTANDARD PROCEDURE - FLUID PROCEDURE - FLUID ANDFILTER PROCEDURE - CABLEDIAGNOSIS AND TESTING - - 130 AUTOMATIC TRANSMISSION - 48 REDROUTPUT SHAFT FRONT SHAFT REAR CLUTCH CAM/OVERDRIVEPISTON GEARTRAIN/OUTPUT VALVE - THROTTLE VALVE CABLE.

2 254 TORQUE CONVERTER DRAINBACK PROCEDURE - TORQUECONVERTER DRAINBACK OVERDRIVE AND TESTING - OVERDRIVEELECTRICAL RANGE AND TESTING - TRANSMISSIONRANGE SENSOR (TRS).. TEMPERATURE - VALVE TRANSMISSION - 48RE21 - 131 AUTOMATIC TRANSMISSION -48 REDESCRIPTIONThe 48re (Fig. 1) is a four speed fully automatictransmissions with an electronic governor. The 48 REis equipped with a lock-up clutch in the torque con-verter. First through third gear ranges are providedby the clutches, bands, overrunning clutch, and plan-etary gear sets in the TRANSMISSION . Fourth gearrange is provided by the overdrive unit that containsan overdrive clutch, direct clutch, planetary gear set,and overrunning TRANSMISSION contains a front, rear, and directclutch which function as the input driving compo-nents.

3 It also contains the kickdown (front) and thelow/reverse (rear) bands which, along with the over-running clutch and overdrive clutch, serve as theholding components. The driving and holding compo-nents combine to select the necessary planetary gearcomponents, in the front, rear, or overdrive planetarygear set, transfer the engine power from the inputshaft through to the output valve body is mounted to the lower side of thetransmission and contains the valves to control pres-sure regulation, fluid flow control, and clutch/bandapplication. The oil pump is mounted at the front ofthe TRANSMISSION and is driven by the torque con-verter hub. The pump supplies the oil pressure nec-essary for clutch/band actuation and - 132 AUTOMATIC TRANSMISSION - 48 REDRFig. 1 48re TransmissionDRAUTOMATIC TRANSMISSION - 48RE21 - 133 AUTOMATIC TRANSMISSION - 48re (Continued)IDENTIFICATIONT ransmission identification numbers are stampedon the left side of the case just above the oil pan gas-ket surface (Fig.)

4 2). Refer to this information whenordering replacement RATIOSThe 48re gear ratios :1 OPERATIONThe application of each driving or holding compo-nent is controlled by the valve body based upon themanual lever position, throttle pressure, and gover-nor pressure. The governor pressure is a variablepressure input to the valve body and is one of thesignals that a shift is necessary. First through fourthgear are obtained by selectively applying and releas-ing the different clutches and bands. Engine power isthereby routed to the various planetary gear assem-blies which combine with the overrunning clutchassemblies to generate the different gear ratios. Thetorque converter clutch is hydraulically applied andis released when fluid is vented from the hydrauliccircuit by the torque converter control (TCC) solenoidon the valve body.

5 The torque converter clutch is con-trolled by the Powertrain Control Module (PCM). Thetorque converter clutch engages in fourth gear, andin third gear under various conditions, such as whenthe O/D switch is OFF, when the vehicle is cruisingon a level surface after the vehicle has warmed torque converter clutch can also be engaged inthe MANUAL SECOND gear position if high trans-mission temperatures are sensed by the PCM. Thetorque converter clutch will disengage momentarilywhen an increase in engine load is sensed by thePCM, such as when the vehicle begins to go uphill orthe throttle pressure is increased. The torque con-verter clutch feature increases fuel economy andreduces the TRANSMISSION fluid the overdrive clutch is applied in fourth gearonly and the direct clutch is applied in all rangesexcept fourth gear, the TRANSMISSION operation forpark, neutral, and first through third gear will bedescribed first.

6 Once these powerflows are described,the third to fourth shift sequence will be - TORQUE CONVERTER10 - OVERDRIVE CLUTCH2 - INPUT SHAFT11 - DIRECT CLUTCH3 - OIL PUMP12 - PLANETARY GEAR4 - FRONT BAND13 - INTERMEDIATE SHAFT5 - FRONT CLUTCH14 - OVERDRIVE OVERRUNNING CLUTCH6 - REAR CLUTCH15 - DIRECT CLUTCH SPRING7 - PLANETARIES16 - OVERDRIVE PISTON RETAINER8 - REAR BAND17 - OIL PAN9 - OVERRUNNING CLUTCH18 - VALVE BODYFig. 2 TRANSMISSION Part Number And SerialNumber Location1 - PART NUMBER2 - BUILD DATE3 - SERIAL NUMBER21 - 134 AUTOMATIC TRANSMISSION - 48 REDRAUTOMATIC TRANSMISSION - 48re (Continued)PARK POWERFLOWAs the engine is running and the crankshaft isrotating, the flexplate and torque converter, whichare also bolted to it, are all rotating in a clockwisedirection as viewed from the front of the engine. Thenotched hub of the torque converter is connected tothe oil pump s internal gear, supplying the transmis-sion with oil pressure.

7 As the converter turns, itturns the input shaft in a clockwise direction. As theinput shaft is rotating, the front clutch hub-rearclutch retainer and all their associated parts are alsorotating, all being directly connected to the inputshaft. The power flow from the engine through thefront clutch hub and rear clutch retainer stops at therear clutch retainer. Therefore, no power flow to theoutput shaft occurs because no clutches are only mechanism in use at this time is the park-ing sprag (Fig. 3), which locks the parking gear onthe output shaft to the TRANSMISSION POWERFLOWWith the gear selector in the NEUTRAL position(Fig. 4), the power flow of the TRANSMISSION is essen-tially the same as in the park position. The onlyoperational difference is that the parking sprag hasbeen disengaged, unlocking the output shaft from thetransmission case and allowing it to move 3 Park Powerflow1 - PAWL ENGAGED FOR PARK2 - PARK SPRAG3 - OUTPUT SHAFTFig.

8 4 Neutral Powerflow1 - PAWL DISENGAGED FOR NEUTRAL2 - PARK SPRAG3 - OUTPUT SHAFT4 - CAM5-PAWLDRAUTOMATIC TRANSMISSION - 48RE21 - 135 AUTOMATIC TRANSMISSION - 48re (Continued)REVERSE POWERFLOWWhen the gear selector is moved into theREVERSE position (Fig. 5), the front clutch and therear band are applied. With the application of thefront clutch, engine torque is applied to the sun gear,turning it in a clockwise direction. The clockwiserotation of the sun gear causes the rear planet pin-ions to rotate against engine rotation in a counter-clockwise direction. The rear band is holding the lowreverse drum, which is splined to the rear the rear carrier is being held, the torque fromthe planet pinions is transferred to the rear annulusgear, which is splined to the output shaft.

9 The outputshaft in turn rotates with the annulus gear in acounterclockwise direction giving a reverse gear out-put. The entire TRANSMISSION of torque is applied tothe rear planetary gearset only. Although there istorque input to the front gearset through the sungear, no other member of the gearset is being the entire reverse stage of operation, thefront planetary gears are in an idling 5 Reverse Powerflow1 - FRONT CLUTCH ENGAGED5 - OUTPUT SHAFT2 - OUTPUT SHAFT6 - INPUT SHAFT3 - LOW/REVERSE BAND APPLIED7 - FRONT CLUTCH ENGAGED4 - INPUT SHAFT8 - LOW/REVERSE BAND APPLIED21 - 136 AUTOMATIC TRANSMISSION - 48 REDRAUTOMATIC TRANSMISSION - 48re (Continued)FIRST GEAR POWERFLOWWhen the gearshift lever is moved into the DRIVE position the TRANSMISSION goes into first gear (Fig. 6).As soon as the TRANSMISSION is shifted from PARK orNEUTRAL to DRIVE, the rear clutch applies, apply-ing the rear clutch pack to the front annulus torque is now applied to the front annulusgear turning it in a clockwise direction.

10 With thefront annulus gear turning in a clockwise direction, itcauses the front planets to turn in a clockwise direc-tion. The rotation of the front planets cause the sunto revolve in a counterclockwise direction. The sungear now transfers its counterclockwise rotation tothe rear planets which rotate back in a clockwisedirection. With the rear annulus gear stationary, therear planet rotation on the annulus gear causes therear planet carrier to revolve in a counterclockwisedirection. The rear planet carrier is splined into thelow-reverse drum, and the low reverse drum issplined to the inner race of the over-running the over-running clutch locked, the planet car-rier is held, and the resulting torque provided by theplanet pinions is transferred to the rear annulusgear.