21 - 130 AUTOMATIC TRANSMISSION - 48RE DR
AUTOMATIC TRANSMISSION - 48RE
TABLE OF CONTENTS
page page
AUTOMATIC TRANSMISSION - 48RE
DESCRIPTION ........................132
OPERATION ..........................134
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTING - AUTOMATIC
TRANSMISSION .....................140
DIAGNOSIS AND TESTING - PRELIMINARY . 140
DIAGNOSIS AND TESTING - ROAD
TESTING ...........................140
DIAGNOSIS AND TESTING - HYDRAULIC
PRESSURE TEST ....................141
DIAGNOSIS AND TESTING - AIR TESTING
TRANSMISSION CLUTCH AND BAND
OPERATION ........................144
DIAGNOSIS AND TESTING - CONVERTER
HOUSING FLUID LEAK ................144
DIAGNOSIS AND TESTING - DIAGNOSIS
CHARTS ...........................145
STANDARD PROCEDURE - ALUMINUM
THREAD REPAIR .....................158
REMOVAL ............................158
DISASSEMBLY ........................160
CLEANING ...........................166
INSPECTION .........................166
ASSEMBLY ...........................166
INSTALLATION ........................174
SCHEMATICS AND DIAGRAMS
HYDRAULIC SCHEMATICS .............176
SPECIFICATIONS
TRANSMISSION .....................189
SPECIAL TOOLS
RE TRANSMISSION ..................191
ACCUMULATOR
DESCRIPTION ........................193
OPERATION ..........................193
INSPECTION .........................194
BANDS
DESCRIPTION ........................194
OPERATION ..........................194
ADJUSTMENTS
ADJUSTMENT - BANDS ...............195
BRAKE TRANSMISSION SHIFT INTERLOCK
SYSTEM
DESCRIPTION ........................196
OPERATION ..........................196
DIAGNOSIS AND TESTING - BRAKE
TRANSMISSION SHIFT INTERLOCK ......196
ADJUSTMENTS - BRAKE TRANSMISSION
SHIFT INTERLOCK ...................196
ELECTRONIC GOVERNOR
DESCRIPTION ........................197
OPERATION ..........................198
REMOVAL ............................199
INSTALLATION ........................200
EXTENSION HOUSING SEAL
REMOVAL ............................201
INSTALLATION ........................201
FLUID AND FILTER
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTING - EFFECTS OF
INCORRECT FLUID LEVEL .............201
DIAGNOSIS AND TESTING - CAUSES OF
BURNT FLUID .......................201
DIAGNOSIS AND TESTING - FLUID
CONTAMINATION ....................202
STANDARD PROCEDURE
STANDARD PROCEDURE - FLUID LEVEL
CHECK ............................202
STANDARD PROCEDURE - FLUID AND
FILTER REPLACEMENT ...............203
STANDARD PROCEDURE - TRANSMISSION
FILL ...............................204
FRONT CLUTCH
DESCRIPTION ........................205
OPERATION ..........................205
DISASSEMBLY ........................205
INSPECTION .........................206
ASSEMBLY ...........................207
FRONT SERVO
DESCRIPTION ........................208
OPERATION ..........................208
DISASSEMBLY ........................209
CLEANING ...........................209
INSPECTION .........................209
ASSEMBLY ...........................209
GEARSHIFT CABLE
DIAGNOSIS AND TESTING - GEARSHIFT
CABLE .............................210
REMOVAL ............................210
INSTALLATION ........................211
ADJUSTMENTS
GEARSHIFT CABLE ..................212
OIL PUMP
DESCRIPTION ........................213
OPERATION ..........................213
DISASSEMBLY ........................214
CLEANING ...........................214
INSPECTION .........................214
ASSEMBLY ...........................214
DR AUTOMATIC TRANSMISSION - 48RE 21 - 131
OUTPUT SHAFT FRONT BEARING
REMOVAL ............................216
INSTALLATION ........................216
OUTPUT SHAFT REAR BEARING
REMOVAL ............................216
INSTALLATION ........................217
OVERDRIVE CLUTCH
DESCRIPTION ........................217
OPERATION ..........................217
OVERDRIVE UNIT
REMOVAL ............................218
DISASSEMBLY ........................218
CLEANING ...........................225
INSPECTION .........................225
ASSEMBLY ...........................226
INSTALLATION ........................235
OVERRUNNING CLUTCH CAM/OVERDRIVE
PISTON RETAINER
DESCRIPTION ........................236
OPERATION ..........................236
DISASSEMBLY ........................236
CLEANING ...........................236
INSPECTION .........................237
ASSEMBLY ...........................237
PISTONS
DESCRIPTION ........................239
OPERATION ..........................239
PLANETARY GEARTRAIN/OUTPUT SHAFT
DESCRIPTION ........................241
OPERATION ..........................241
DISASSEMBLY ........................242
INSPECTION .........................243
ASSEMBLY ...........................244
REAR CLUTCH
DESCRIPTION ........................247
OPERATION ..........................248
DISASSEMBLY ........................248
CLEANING ...........................248
INSPECTION .........................248
ASSEMBLY ...........................249
REAR SERVO
DESCRIPTION ........................251
OPERATION ..........................251
DISASSEMBLY ........................251
CLEANING ...........................251
ASSEMBLY ...........................251
SHIFT MECHANISM
DESCRIPTION ........................252
OPERATION ..........................252
SOLENOID
DESCRIPTION ........................252
OPERATION ..........................252
SPEED SENSOR
DESCRIPTION ........................253
OPERATION ..........................253
THROTTLE VALVE CABLE
DESCRIPTION ........................253
ADJUSTMENTS - THROTTLE VALVE CABLE . 254
TORQUE CONVERTER
DESCRIPTION ........................255
OPERATION ..........................259
REMOVAL ............................260
INSTALLATION ........................260
TORQUE CONVERTER DRAINBACK VALVE
DESCRIPTION ........................261
OPERATION ..........................261
STANDARD PROCEDURE - TORQUE
CONVERTER DRAINBACK VALVE ........261
TOW/HAUL OVERDRIVE SWITCH
DESCRIPTION ........................261
OPERATION ..........................262
DIAGNOSIS AND TESTING - OVERDRIVE
ELECTRICAL CONTROLS ..............262
REMOVAL ............................262
INSTALLATION ........................262
TRANSMISSION RANGE SENSOR
DESCRIPTION ........................263
OPERATION ..........................263
DIAGNOSIS AND TESTING - TRANSMISSION
RANGE SENSOR (TRS) ................264
REMOVAL ............................265
INSTALLATION ........................266
TRANSMISSION TEMPERATURE SENSOR
DESCRIPTION ........................267
OPERATION ..........................267
VALVE BODY
DESCRIPTION ........................267
OPERATION ..........................272
REMOVAL ............................286
DISASSEMBLY ........................287
CLEANING ...........................298
INSPECTION .........................298
ASSEMBLY ...........................299
INSTALLATION ........................309
ADJUSTMENTS - VALVE BODY ...........310
21 - 132 AUTOMATIC TRANSMISSION - 48RE DR
AUTOMATIC TRANSMISSION 48RE
DESCRIPTION
The 48RE (Fig. 1) 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, overrunning 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 overdrive clutch, serve as the
holding components. The driving and holding components combine to select the necessary 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 regulation, 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.
DR AUTOMATIC TRANSMISSION - 48RE 21 - 133
AUTOMATIC TRANSMISSION - 48RE (Continued)
Fig. 1 48RE Transmission
21 - 134 AUTOMATIC TRANSMISSION - 48RE DR
AUTOMATIC TRANSMISSION - 48RE (Continued)
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
IDENTIFICATION
Transmission identification numbers are stamped
on the left side of the case just above the oil pan gasket surface (Fig. 2). Refer to this information when
ordering replacement parts.
Fig. 2 Transmission Part Number And Serial
Number Location
1 - PART NUMBER
2 - BUILD DATE
3 - SERIAL NUMBER
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 applying 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 conditions, 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 transmission 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 temperature.
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.
DR AUTOMATIC TRANSMISSION - 48RE 21 - 135
AUTOMATIC TRANSMISSION - 48RE (Continued)
PARK POWERFLOW
As the engine is running and the crankshaft is
rotating, 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 pressure. 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 associated parts are also
rotating, all being directly connected 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 (Fig. 3), which locks the parking gear on
the output shaft to the transmission case.
NEUTRAL POWERFLOW
With the gear selector in the NEUTRAL position
(Fig. 4), the power flow of the transmission is essentially the same as in the park position. The only
operational difference is that the parking sprag has
been disengaged, unlocking the output shaft from the
transmission case and allowing it to move freely.
Fig. 3 Park Powerflow
1 - PAWL ENGAGED FOR PARK
2 - PARK SPRAG
3 - OUTPUT SHAFT
Fig. 4 Neutral Powerflow
1 - PAWL DISENGAGED FOR NEUTRAL
2 - PARK SPRAG
3 - OUTPUT SHAFT
4 - CAM
5-PAWL
21 - 136 AUTOMATIC TRANSMISSION - 48RE DR
AUTOMATIC TRANSMISSION - 48RE (Continued)
REVERSE POWERFLOW
When the gear selector is moved into the
REVERSE position (Fig. 5), the front clutch and the
rear band are applied. With the application of the
front clutch, engine torque is applied to the sun gear,
turning it in a clockwise direction. The clockwise
rotation of the sun gear causes the rear planet pinions to rotate against engine rotation in a counterclockwise direction. The rear band is holding the low
reverse drum, which is splined to the rear carrier.
Since the rear carrier is being held, the torque from
the planet pinions is transferred to the rear annulus
gear, which is splined to the output shaft. The output
shaft in turn rotates with the annulus gear in a
counterclockwise direction giving a reverse gear output. The entire transmission of torque is applied to
the rear planetary gearset only. Although there is
torque input to the front gearset through the sun
gear, no other member of the gearset is being held.
During the entire reverse stage of operation, the
front planetary gears are in an idling condition.
1 - FRONT CLUTCH ENGAGED 5 - OUTPUT SHAFT
2 - OUTPUT SHAFT 6 - INPUT SHAFT
3 - LOW/REVERSE BAND APPLIED 7 - FRONT CLUTCH ENGAGED
4 - INPUT SHAFT 8 - LOW/REVERSE BAND APPLIED
Fig. 5 Reverse Powerflow
DR AUTOMATIC TRANSMISSION - 48RE 21 - 137
AUTOMATIC TRANSMISSION - 48RE (Continued)
FIRST GEAR POWERFLOW
When 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 or
NEUTRAL to DRIVE, the rear clutch applies, applying the rear clutch pack to the front annulus gear.
Engine torque is now applied to the front annulus
gear turning it in a clockwise direction. With the
front annulus gear turning in a clockwise direction, it
causes the front planets to turn in a clockwise direction. The rotation of the front planets cause the sun
to revolve in a counterclockwise direction. The sun
gear now transfers its counterclockwise rotation to
the rear planets which rotate back in a clockwise
direction. With the rear annulus gear stationary, the
rear planet rotation on the annulus gear causes the
rear planet carrier to revolve in a counterclockwise
direction. The rear planet carrier is splined into the
low-reverse drum, and the low reverse drum is
splined to the inner race of the over-running clutch.
With the over-running clutch locked, the planet carrier is held, and the resulting torque provided by the
planet pinions is transferred to the rear annulus
gear. The rear annulus gear is splined to the output
shaft and rotated along with it (clockwise) in an
underdrive gear reduction mode.
1 - OUTPUT SHAFT 5 - OVER-RUNNING CLUTCH HOLDING
2 - OVER-RUNNING CLUTCH HOLDING 6 - INPUT SHAFT
3 - REAR CLUTCH APPLIED 7 - REAR CLUTCH APPLIED
4 - OUTPUT SHAFT 8 - INPUT SHAFT
Fig. 6 First Gear Powerflow
21 - 138 AUTOMATIC TRANSMISSION - 48RE DR
AUTOMATIC TRANSMISSION - 48RE (Continued)
SECOND GEAR POWERFLOW
In DRIVE-SECOND (Fig. 7), the same elements
are applied as in MANUAL-SECOND. Therefore, the
power flow will be the same, and both gears will be
discussed as one in the same. In DRIVE-SECOND,
the transmission has proceeded from first gear to its
shift point, and is shifting from first gear to second.
The second gear shift is obtained by keeping the rear
clutch applied and applying the front (kickdown)
band. The front band holds the front clutch retainer
that is locked to the sun gear driving shell. With the
rear clutch still applied, the input is still on the front
annulus gear turning it clockwise at engine speed.
Now that the front band is holding the sun gear stationary, the annulus rotation causes the front planets
to rotate in a clockwise direction. The front carrier is
then also made to rotate in a clockwise direction but
at a reduced speed. This will transmit the torque to
the output shaft, which is directly connected to the
front planet carrier. The rear planetary annulus gear
will also be turning because it is directly splined to
the output shaft. All power flow has occurred in the
front planetary gear set during the drive-second
stage of operation, and now the over-running clutch,
in the rear of the transmission, is disengaged and
freewheeling on its hub.
1 - KICKDOWN BAND APPLIED 6 - INPUT SHAFT
2 - OUTPUT SHAFT 7 - REAR CLUTCH APPLIED
3 - REAR CLUTCH ENGAGED 8 - KICKDOWN BAND APPLIED
4 - OUTPUT SHAFT 9 - INPUT SHAFT
5 - OVER-RUNNING CLUTCH FREE-WHEELING
Fig. 7 Second Gear Powerflow
DR AUTOMATIC TRANSMISSION - 48RE 21 - 139
AUTOMATIC TRANSMISSION - 48RE (Continued)
DIRECT DRIVE POWERFLOW
The vehicle has accelerated and reached the shift
point for the 2-3 upshift into direct drive (Fig. 8).
When the shift takes place, the front band is
released, and the front clutch is applied. The rear
clutch stays applied as it has been in all the forward
gears. With the front clutch now applied, engine
torque is now on the front clutch retainer, which is
locked to the sun gear driving shell. This means that
the sun gear is now turning in engine rotation (clockwise) and at engine speed. The rear clutch is still
applied so engine torque is also still on the front
annulus gear. If two members of the same planetary
set are driven, direct drive results. Therefore, when
two members are rotating at the same speed and in
the same direction, it is the same as being locked up.
The rear planetary set is also locked up, given the
sun gear is still the input, and the rear annulus gear
must turn with the output shaft. Both gears are
turning in the same direction and at the same speed.
The front and rear planet pinions do not turn at all
in direct drive. The only rotation is the input from
the engine to the connected parts, which are acting
as one common unit, to the output shaft.
FOURTH GEAR POWERFLOW
Fourth gear overdrive range is electronically controlled 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 energized 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
Tow/Haul 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 overdrive 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
1 - FRONT CLUTCH APPLIED 6 - INPUT SHAFT
2 - OVER-RUNNING CLUTCH FREE-WHEELING 7 - OVER-RUNNING CLUTCH FREE-WHEELING
3 - OUTPUT SHAFT 8 - REAR CLUTCH APPLIED
4 - REAR CLUTCH APPLIED 9 - FRONT CLUTCH APPLIED
5 - OUTPUT SHAFT 10 - INPUT SHAFT
Fig. 8 Direct Drive Powerflow
21 - 140 AUTOMATIC TRANSMISSION - 48RE DR
AUTOMATIC TRANSMISSION - 48RE (Continued)
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 accelerating 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.
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTING - AUTOMATIC
TRANSMISSION
Automatic transmission problems can be a result of
poor engine performance, incorrect fluid level, incorrect linkage or cable adjustment, band or hydraulic
control pressure adjustments, hydraulic system malfunctions or electrical/mechanical component malfunctions. Begin diagnosis by checking the easily
accessible items such as: fluid level and condition,
linkage adjustments and electrical connections. A
road test will determine if further diagnosis is necessary.
DIAGNOSIS AND TESTING - PRELIMINARY
Two basic procedures are required. One procedure
for vehicles that are drivable and an alternate procedure for disabled vehicles (will not back up or move
forward).
VEHICLE IS DRIVEABLE
(1) Check for transmission fault codes using DRBt
scan tool.
(2) Check fluid level and condition.
(3) Adjust throttle and gearshift linkage if complaint was based on delayed, erratic, or harsh shifts.
(4) Road test and note how transmission upshifts,
downshifts, and engages.
(5) Perform hydraulic pressure test if shift problems were noted during road test.
(6) Perform air-pressure test to check clutch-band
operation.
VEHICLE IS DISABLED
(1) Check fluid level and condition.
(2) Check for broken or disconnected gearshift or
throttle linkage.
(3) Check for cracked, leaking cooler lines, or loose
or missing pressure-port plugs.
(4) Raise and support vehicle on safety stands,
start engine, shift transmission into gear, and note
following:
(a) If propeller shaft turns but wheels do not,
problem is with differential or axle shafts.
(b) If propeller shaft does not turn and transmission is noisy, stop engine. Remove oil pan, and
check for debris. If pan is clear, remove transmission and check for damaged drive plate, converter,
oil pump, or input shaft.
(c) If propeller shaft does not turn and transmission is not noisy, perform hydraulic-pressure test to
determine if problem is hydraulic or mechanical.
DIAGNOSIS AND TESTING - ROAD TESTING
Before road testing, be sure the fluid level and con-
trol cable adjustments have been checked and
adjusted if necessary. Verify that diagnostic trouble
codes have been resolved.
Observe engine performance during the road test.
A poorly tuned engine will not allow accurate analysis of transmission operation.
Operate the transmission in all gear ranges. Check
for shift variations and engine flare which indicates
slippage. Note if shifts are harsh, spongy, delayed,
early, or if part throttle downshifts are sensitive.
Slippage indicated by engine flare, usually means
clutch, band or overrunning clutch problems. If the
condition is advanced, an overhaul will be necessary
to restore normal operation.
A slipping clutch or band can often be determined
by comparing which internal units are applied in the
various gear ranges. The Clutch and Band Application chart provides a basis for analyzing road test
results.
DR AUTOMATIC TRANSMISSION - 48RE 21 - 141
AUTOMATIC TRANSMISSION - 48RE (Continued)
CLUTCH AND BAND APPLICATION CHART
SHIFT
LEVER
POSITION
Reverse X X X
Drive -
First
Drive -
Second
Drive -
Third
Drive Fourth
Manual
Second
Manual
First
Note that the rear clutch is applied in all forward
ranges (D, 2, 1). The transmission overrunning clutch
is applied in first gear (D, 2 and 1 ranges) only. The
rear band is applied in 1 and R range only.
Note that the overdrive clutch is applied only in
fourth gear and the overdrive direct clutch and overrunning clutch are applied in all ranges except fourth
gear.
For example: If slippage occurs in first gear in D
and 2 range but not in 1 range, the transmission
overrunning clutch is faulty. Similarly, if slippage
occurs in any two forward gears, the rear clutch is
slipping.
Applying the same method of analysis, note that
the front and rear clutches are applied simultaneously only in D range third and fourth gear. If the
transmission slips in third gear, either the front
clutch or the rear clutch is slipping.
If the transmission slips in fourth gear but not in
third gear, the overdrive clutch is slipping. By selecting another gear which does not use these clutches,
the slipping unit can be determined. For example, if
the transmission also slips in Reverse, the front
clutch is slipping. If the transmission does not slip in
Reverse, the rear clutch is slipping.
If slippage occurs during the 3-4 shift or only in
fourth gear, the overdrive clutch is slipping. Similarly, if the direct clutch were to fail, the transmission would lose both reverse gear and overrun
braking in 2 position (manual second gear).
If the transmission will not shift to fourth gear, the
control switch, overdrive solenoid or related wiring
may also be the problem cause.
FRONT
CLUTCH
TRANSMISSION CLUTCHES AND BANDS OVERDRIVE CLUTCHES
FRONT
BAND
XX XX
XX XX
XX X
XX XX
REAR
CLUTCH
XXXX
XXX XX
REAR
BAND
a slipping unit and check operation. Proper use of
the Clutch and Band Application Chart is the key.
slipping unit, the actual cause of a malfunction usually cannot be determined until hydraulic and air
pressure tests are performed. Practically any condition can be caused by leaking hydraulic circuits or
sticking valves.
in D range first gear, do not disassemble the transmission. Perform the hydraulic and air pressure tests
to help determine the probable cause.
OVER-
RUNNING
CLUTCH
This process of elimination can be used to identify
Although road test analysis will help determine the
Unless a malfunction is obvious, such as no drive
OVERDRIVE
CLUTCH
DIAGNOSIS AND TESTING - HYDRAULIC
PRESSURE TEST
Hydraulic test pressures range from a low of one
psi (6.895 kPa) governor pressure, to 300 psi (2068
kPa) at the rear servo pressure port in reverse.
An accurate tachometer and pressure test gauges
are required. Test Gauge C-3292 has a 100 psi range
and is used at the accumulator, governor, and front
servo ports. Test Gauge C-3293-SP has a 300 psi
range and is used at the rear servo and overdrive
ports where pressures exceed 100 psi.
Pressure Test Port Locations
Test ports are located at both sides of the transmission case (Fig. 9).
Line pressure is checked at the accumulator port
on the right side of the case. The front servo pressure
port is at the right side of the case just behind the
filler tube opening.
DIRECT
CLUTCH
OVER-
RUNNING
CLUTCH
21 - 142 AUTOMATIC TRANSMISSION - 48RE DR
AUTOMATIC TRANSMISSION - 48RE (Continued)
The rear servo and governor pressure ports are at
the right rear of the transmission case. The overdrive
clutch pressure port is at the left rear of the case.
Fig. 9 Pressure Test Port Locations
1 - REAR SERVO TEST PORT
2 - GOVERNOR TEST PORT
3 - ACCUMULATOR TEST PORT
4 - FRONT SERVO TEST PORT
5 - OVERDRIVE CLUTCH TEST PORT
Test One - Transmission In Manual Low
This test checks pump output, pressure regulation,
and condition of the rear clutch and servo circuit.
Both test gauges are required for this test.
(1) Connect tachometer to engine. Position tachometer so it can be observed from driver seat if helper
will be operating engine. Raise vehicle on hoist that
will allow rear wheels to rotate freely.
(2) Connect 100 psi Gauge C-3292 to accumulator
port. Then connect 300 psi Gauge C-3293-SP to rear
servo port.
(3) Disconnect throttle and gearshift cables from
levers on transmission valve body manual shaft.
(4) Have helper start and run engine at 1000 rpm.
(5) Move transmission shift lever fully forward
into 1 range.
(6) Gradually move transmission throttle lever
from full forward to full rearward position and note
pressures on both gauges:
• Line pressure at accumulator port should be
54-60 psi (372-414 kPa) with throttle lever forward
and gradually increase to 90-96 psi (621-662 kPa) as
throttle lever is moved rearward.
• Rear servo pressure should be same as line pressure within 3 psi (20.68 kPa).
Test Two - Transmission In 2 Range
This test checks pump output, line pressure and
pressure regulation. Use 100 psi Test Gauge C-3292
for this test.
(1) Leave vehicle in place on hoist and leave Test
Gauge C-3292 connected to accumulator port.
(2) Have helper start and run engine at 1000 rpm.
(3) Move transmission shift lever one detent rearward from full forward position. This is 2 range.
(4) Move transmission throttle lever from full forward to full rearward position and read pressure on
gauge.
(5) Line pressure should be 54-60 psi (372-414
kPa) with throttle lever forward and gradually
increase to 90-96 psi (621-662 kPa) as lever is moved
rearward.
Test Three - Transmission In D Range Third Gear
This test checks pressure regulation and condition
of the clutch circuits. Both test gauges are required
for this test.
(1) Turn OD switch off.
(2) Leave vehicle on hoist and leave Gauge C-3292
in place at accumulator port.
(3) Move Gauge C-3293-SP over to front servo port
for this test.
(4) Have helper start and run engine at 1600 rpm
for this test.
(5) Move transmission shift lever two detents rearward from full forward position. This is D range.
(6) Read pressures on both gauges as transmission
throttle lever is gradually moved from full forward to
full rearward position:
• Line pressure at accumulator in D range third
gear, should be 54-60 psi (372-414 kPa) with throttle
lever forward and increase as lever is moved rearward.
• Front servo pressure in D range third gear,
should be within 3 psi (21 kPa) of line pressure up to
kickdown point.
Test Four - Transmission In Reverse
This test checks pump output, pressure regulation
and the front clutch and rear servo circuits. Use 300
psi Test Gauge C-3293-SP for this test.
(1) Leave vehicle on hoist and leave gauge C-3292
in place at accumulator port.
(2) Move 300 psi Gauge C-3293-SP back to rear
servo port.
DR AUTOMATIC TRANSMISSION - 48RE 21 - 143
AUTOMATIC TRANSMISSION - 48RE (Continued)
(3) Have helper start and run engine at 1600 rpm
for test.
Move transmission shift lever four detents rear-
(4)
ward from full forward position. This is Reverse range.
(5) Move transmission throttle lever fully forward
then fully rearward and note reading at Gauge
C-3293-SP.
(6) Pressure should be 145 - 175 psi (1000-1207
kPa) with throttle lever forward and increase to 230 280 psi (1586-1931 kPa) as lever is gradually moved
rearward.
Test Five - Governor Pressure
This test checks governor operation by measuring
governor pressure response to changes in vehicle
speed. It is usually not necessary to check governor
operation unless shift speeds are incorrect or if the
transmission will not downshift. The test should be
performed on the road or on a hoist that will allow
the rear wheels to rotate freely.
(1) Move 100 psi Test Gauge C-3292 to governor
pressure port.
(2) Move transmission shift lever two detents rearward from full forward position. This is D range.
(3) Have helper start and run engine at curb idle
speed. Then firmly apply service brakes so wheels
will not rotate.
(4) Note governor pressure:
Governor pressure should be no more than 20.6
•
kPa (3 psi) at curb idle speed and wheels not rotating.
• If pressure exceeds 20.6 kPa (3 psi), a fault
exists in governor pressure control system.
(5) Release brakes, slowly increase engine speed,
and observe speedometer and pressure test gauge (do
not exceed 30 mph on speedometer). Governor pressure should increase in proportion to vehicle speed.
Or approximately 6.89 kPa (1 psi) for every 1 mph.
(6) Governor pressure rise should be smooth and
drop back to no more than 20.6 kPa (3 psi), after
engine returns to curb idle and brakes are applied to
prevent wheels from rotating.
Compare results of pressure test with analysis
(7)
chart.
Test Six - Transmission In Overdrive Fourth Gear
This test checks line pressure at the overdrive
clutch in fourth gear range. Use 300 psi Test Gauge
C-3293-SP for this test. The test should be performed
on the road or on a chassis dyno.
Remove tachometer; it is not needed for this test.
(1)
(2) Move 300 psi Gauge to overdrive clutch pressure test port. Then remove other gauge and reinstall
test port plug.
(3) Lower vehicle.
(4) Turn OD switch on.
(5) Secure test gauge so it can be viewed from
drivers seat.
(6) Start engine and shift into D range.
(7) Increase vehicle speed gradually until 3-4 shift
occurs and note gauge pressure.
(8) Pressure should be 524-565 kPa (76-82 psi)
with closed throttle and increase to 690-896 kPa
(100-130 psi) at 1/2 to 3/4 throttle. Note that pressure can increase to around 965 kPa (140 psi) at full
throttle.
(9) Return to shop or move vehicle off chassis
dyno.
PRESSURE TEST ANALYSIS CHART
TEST CONDITION INDICATION
Line pressure OK during
any one test
Line pressure OK in R
but low in D, 2, 1
Pressure low in D Fourth
Gear Range
Pressure OK in 1, 2 but
low in D3 and R
Pressure OK in 2 but low
in R and 1
Front servo pressure in 2 Leakage in servo; broken
Pressure low in all
positions
Governor pressure too
high at idle speed
Governor pressure low at
all mph figures
Lubrication pressure low
at all throttle positions
Line pressure high Output shaft plugged,
Line pressure low Sticky regulator valve,
Pump and regulator
valve OK
Leakage in rear clutch
area (seal rings, clutch
seals)
Overdrive clutch piston
seal, or check ball
problem
Leakage in front clutch
area
Leakage in rear servo
servo ring or cracked
servo piston
Clogged filter, stuck
regulator valve, worn or
faulty pump, low oil level
Governor pressure
solenoid valve system
fault. Refer to diagnostic
book.
Faulty governor pressure
solenoid, transmission
control module, or
governor pressure
sensor
Clogged fluid cooler or
lines, seal rings leaking,
worn pump bushings,
pump, clutch retainer, or
clogged filter.
sticky regulator valve
clogged filter, worn pump
21 - 144 AUTOMATIC TRANSMISSION - 48RE DR
AUTOMATIC TRANSMISSION - 48RE (Continued)
DIAGNOSIS AND TESTING - AIR TESTING
TRANSMISSION CLUTCH AND BAND
OPERATION
Air-pressure testing can be used to check transmission front/rear clutch and band operation. The test
can be conducted with the transmission either in the
vehicle or on the work bench, as a final check, after
overhaul.
Air-pressure testing requires that the oil pan and
valve body be removed from the transmission. The
servo and clutch apply passages are shown (Fig. 10).
Fig. 10 Air Pressure Test Passages
1 - LINE PRESSURE TO ACCUMULATOR
2 - REAR SERVO APPLY
3 - FRONT SERVO APPLY
4 - FRONT SERVO RELEASE
5 - PUMP SUCTION
6 - PUMP PRESSURE
7 - FRONT CLUTCH APPLY
8 - REAR CLUTCH APPLY
9 - TO TORQUE CONVERTOR
10 - TO COOLER
11 - FROM TORQUE CONVERTER
Front Clutch Air Test
Place one or two fingers on the clutch housing and
apply air pressure through front clutch apply passage. Piston movement can be felt and a soft thump
heard as the clutch applies.
Rear Clutch Air Test
Place one or two fingers on the clutch housing and
apply air pressure through rear clutch apply passage.
Piston movement can be felt and a soft thump heard
as the clutch applies.
Front Servo Air Test
Apply air pressure to the front servo apply passage. The servo rod should extend and cause the
band to tighten around the drum. Spring pressure
should release the servo when air pressure is
removed.
Rear Servo Air Test
Apply air pressure to the rear servo apply passage.
The servo rod should extend and cause the band to
tighten around the drum. Spring pressure should
release the servo when air pressure is removed.
DIAGNOSIS AND TESTING - CONVERTER
HOUSING FLUID LEAK
When diagnosing converter housing fluid leaks,
two items must be established before repair.
(1) Verify that a leak condition actually exists.
(2) Determined the true source of the leak.
Some suspected converter housing fluid leaks may
not be leaks at all. They may only be the result of
residual fluid in the converter housing, or excess
fluid spilled during factory fill or fill after repair.
Converter housing leaks have several potential
sources. Through careful observation, a leak source
can be identified before removing the transmission
for repair. Pump seal leaks tend to move along the
drive hub and onto the rear of the converter. Pump
body leaks follow the same path as a seal leak (Fig.
11). Pump vent or pump attaching bolt leaks are generally deposited on the inside of the converter housing and not on the converter itself (Fig. 11). Pump
o-ring or gasket leaks usually travel down the inside
of the converter housing. Front band lever pin plug
leaks are generally deposited on the housing and not
on the converter.
DR AUTOMATIC TRANSMISSION - 48RE 21 - 145
AUTOMATIC TRANSMISSION - 48RE (Continued)
(4) Inspect pump bushing and converter hub. If
bushing is scored, replace it. If converter hub is
scored, either polish it with crocus cloth or replace
converter.
(5) Install new pump seal, O-ring, and gasket.
Replace oil pump if cracked, porous or damaged in
any way. Be sure to loosen the front band before
installing the oil pump, damage to the oil pump seal
may occur if the band is still tightened to the front
clutch retainer.
(6) Loosen kickdown lever pin access plug three
turns. Apply Loctite™ 592, or Permatext No.2to
plug threads and tighten plug to 17 N·m (150 in. lbs.)
torque.
(7) Adjust front band.
(8) Lubricate pump seal and converter hub with
Fig. 11 Converter Housing Leak Paths
1 - PUMP SEAL
2 - PUMP VENT
3 - PUMP BOLT
4 - PUMP GASKET
5 - CONVERTER HOUSING
6 - CONVERTER
7 - REAR MAIN SEAL LEAK
transmission fluid or petroleum jelly and install converter.
(9) Install transmission and converter housing
dust shield.
(10) Lower vehicle.
DIAGNOSIS AND TESTING - DIAGNOSIS
CHARTS
TORQUE CONVERTER LEAK POINTS
Possible sources of converter leaks are:
• Leaks at the weld joint around the outside diam-
eter weld.
• Leaks at the converter hub weld.
CONVERTER HOUSING AREA LEAK CORRECTION
(1) Remove converter.
(2) Tighten front band adjusting screw until band
is tight around front clutch retainer. This prevents
front/rear clutches from coming out when oil pump is
removed.
(3) Remove oil pump and remove pump seal.
Inspect pump housing drainback and vent holes for
obstructions. Clear holes with solvent and wire.
The diagnosis charts provide additional reference
when diagnosing a transmission fault. The charts
provide general information on a variety of transmission, overdrive unit and converter clutch fault conditions.
The hydraulic flow charts in the Schematics and
Diagrams section of this group, outline fluid flow and
hydraulic circuitry. Circuit operation is provided for
PARK, NEUTRAL, FIRST, SECOND, THIRD,
FOURTH, MANUAL FIRST, MANUAL SECOND,
and REVERSE gear ranges. Normal working pressures are also supplied for each of the gear ranges.
21 - 146 AUTOMATIC TRANSMISSION - 48RE DR
AUTOMATIC TRANSMISSION - 48RE (Continued)
DIAGNOSIS CHARTS
CONDITION POSSIBLE CAUSES CORRECTION
HARSH ENGAGEMENT
(FROM NEUTRAL TO
DRIVE OR REVERSE)
1. Fluid Level Low. 1. Add Fluid
2. Throttle Linkage Mis-adjusted. 2. Adjust linkage - setting may be too long.
3. Mount and Driveline Bolts Loose. 3. Check engine mount, transmission
mount, propeller shaft, rear spring to body
bolts, rear control arms, crossmember and
axle bolt torque. Tighten loose bolts and
replace missing bolts.
4. U-Joint Worn/Broken. 4. Remove propeller shaft and replace
U-Joint.
5. Axle Backlash Incorrect. 5. Check per Service Manual. Correct as
needed.
6. Hydraulic Pressure Incorrect. 6. Check pressure. Remove, overhaul or
adjust valve body as needed.
7. Band Mis-adjusted. 7. Adjust rear band.
8. Valve Body Check Balls Missing. 8. Inspect valve body for proper check ball
installation.
9. Axle Pinion Flange Loose. 9. Replace nut and check pinion threads
before installing new nut. Replace pinion
gear if threads are damaged.
10. Clutch, band or planetary
component damaged.
11. Converter Clutch Faulty. 11. Replace converter and flush cooler and
10. Remove, disassemble and repair
transmission as necessary.
line before installing new converter.
DR AUTOMATIC TRANSMISSION - 48RE 21 - 147
AUTOMATIC TRANSMISSION - 48RE (Continued)
CONDITION POSSIBLE CAUSES CORRECTION
DELAYED ENGAGEMENT
(FROM NEUTRAL TO
DRIVE OR REVERSE)
NO DRIVE RANGE
(REVERSE OK)
1. Fluid Level Low. 1. Correct level and check for leaks.
2. Filter Clogged. 2. Change filter.
3. Gearshift Linkage Mis-adjusted. 3. Adjust linkage and repair linkage if worn
or damaged.
4. Torque Converter Drain Back (Oil
drains from torque converter into
transmission sump).
5. Rear Band Mis-adjusted. 5. Adjust band.
6. Valve Body Filter Plugged. 6. Replace fluid and filter. If oil pan and old
7. Oil Pump Gears Worn/Damaged. 7. Remove transmission and replace oil
8. Governor Circuit and Solenoid
Valve Electrical Fault.
9. Hydraulic Pressure Incorrect. 9. Perform pressure test, remove
10. Reaction Shaft Seal Rings
Worn/Broken.
11. Rear Clutch/Input Shaft, Rear
Clutch Seal Rings Damaged.
12. Regulator Valve Stuck. 12. Clean.
13. Cooler Plugged. 13. Transfer case failure can plug cooler.
1. Fluid Level Low. 1. Add fluid and check for leaks if drive is
2. Gearshift Linkage/Cable
Loose/Misadjusted.
3. Rear Clutch Burnt. 3. Remove and disassemble transmission
4. Valve Body Malfunction. 4. Remove and disassemble valve body.
5. Transmission Overrunning Clutch
Broken.
6. Input Shaft Seal Rings Worn/
Damaged.
7. Front Planetary Failed Broken. 7. Remove and repair.
4. If vehicle moves normally after 5
seconds after shifting into gear, no repair is
necessary. If longer, inspect pump bushing
for wear. Replace pump house.
fluid were full of clutch disc material and/or
metal particles, overhaul will be necessary.
pump.
8. Test with DRBT scan tool and repair as
required.
transmission and repair as needed.
10. Remove transmission, remove oil pump
and replace seal rings.
11. Remove and disassemble transmission
and repair as necessary.
restored.
2. Repair or replace linkage components.
and rear clutch and seals. Repair/replace
worn or damaged parts as needed.
Replace assembly if any valves or bores
are damaged.
5. Remove and disassemble transmission.
Replace overrunning clutch.
6. Remove and disassemble transmission.
Replace seal rings and any other worn or
damaged parts.
21 - 148 AUTOMATIC TRANSMISSION - 48RE DR
AUTOMATIC TRANSMISSION - 48RE (Continued)
CONDITION POSSIBLE CAUSES CORRECTION
NO DRIVE OR REVERSE
(VEHICLE WILL NOT
MOVE)
SHIFTS DELAYED OR
ERRATIC (SHIFTS ALSO
HARSH AT TIMES)
1. Fluid Level Low. 1. Add fluid and check for leaks if drive is
restored.
2. Gearshift Linkage/Cable
Loose/Misadjusted.
3. U-Joint/Axle/Transfer Case
Broken.
4. Filter Plugged. 4. Remove and disassemble transmission.
5. Oil Pump Damaged. 5. Perform pressure test to confirm low
6. Valve Body Malfunctioned. 6. Check and inspect valve body. Replace
7. Transmission Internal Component
Damaged.
8. Park Sprag not Releasing - Check
Stall Speed, Worn/Damaged/Stuck.
9. Torque Converter Damage. 9. Inspect and replace as required.
1. Fluid Level Low/High. 1. Correct fluid level and check for leaks if
2. Fluid Filter Clogged. 2. Replace filter. If filter and fluid contained
3. Throttle Linkage Mis-adjusted. 3. Adjust linkage as described in service
4. Throttle Linkage Binding. 4. Check cable for binding. Check for return
5. Gearshift Linkage/Cable
Mis-adjusted.
6. Clutch or Servo Failure. 6. Remove valve body and air test clutch,
7. Governor Circuit Electrical Fault. 7. Test using DRBT scan tool and repair as
8. Front Band Mis-adjusted. 8. Adjust band.
9. Pump Suction Passage Leak. 9. Check for excessive foam on dipstick
2. Inspect, adjust and reassemble linkage
as needed. Replace worn/damaged parts.
3. Perform preliminary inspection procedure
for vehicle that will not move. Refer to
procedure in diagnosis section.
Repair or replace failed components as
needed. Replace filter. If filter and fluid
contained clutch material or metal particles,
an overhaul may be necessary. Perform
lube flow test. Flush oil. Replace cooler as
necessary.
pressure. Replace pump body assembly if
necessary.
valve body (as assembly) if any valve or
bore is damaged. Clean and reassemble
correctly if all parts are in good condition.
7. Remove and disassemble transmission.
Repair or replace failed components as
needed.
8. Remove, disassemble, repair.
low.
clutch material or metal particles, an
overhaul may be necessary. Perform lube
flow test.
section.
to closed throttle at transmission.
5. Adjust linkage/cable as described in
service section.
and band servo operation. Disassemble
and repair transmission as needed.
required.
after normal driving. Check for loose pump
bolts, defective gasket. Replace pump
assembly if needed.
DR AUTOMATIC TRANSMISSION - 48RE 21 - 149
AUTOMATIC TRANSMISSION - 48RE (Continued)
CONDITION POSSIBLE CAUSES CORRECTION
NO REVERSE (D RANGES
OK)
HAS FIRST/REVERSE
ONLY (NO 1-2 OR 2-3
UPSHIFT)
MOVES IN 2ND OR 3RD
GEAR, ABRUPTLY
DOWNSHIFTS TO LOW
NO LOW GEAR (MOVES
IN 2ND OR 3RD GEAR
ONLY)
1. Gearshift Linkage/Cable
Mis-adjusted/Damaged.
2. Park Sprag Sticking. 2. Replace overdrive annulus gear.
3. Rear Band Mis-adjusted/Worn. 3. Adjust band; replace.
4. Valve Body Malfunction. 4. Remove and service valve body. Replace
5. Rear Servo Malfunction. 5. Remove and disassemble transmission.
6. Direct Clutch in Overdrive Worn. 6. Disassemble overdrive. Replace worn or
7. Front Clutch Burnt. 7. Remove and disassemble transmission.
1. Governor Circuit Electrical Fault. 1. Test using DRBT scan tool and repair as
2. Valve Body Malfunction. 2. Repair stuck 1-2 shift valve or governor
3. Front Servo/Kickdown Band
Damaged/Burned.
1. Valve Body Malfunction. 1. Remove, clean and inspect. Look for
1. Governor Circuit Electrical Fault. 1. Test with DRBT scan tool and repair as
2. Valve Body Malfunction. 2. Remove, clean and inspect. Look for
3. Front Servo Piston Cocked in
Bore.
4. Front Band Linkage Malfunction 4. Inspect linkage and look for bind in
1. Repair or replace linkage parts as
needed.
valve body if any valves or valve bores are
worn or damaged.
Replace worn/damaged servo parts as
necessary.
damaged parts.
Replace worn, damaged clutch parts as
required.
required.
plug.
3. Repair/replace.
stuck 1-2 valve or governor plug.
required.
sticking 1-2 shift valve, 2-3 shift valve,
governor plug or broken springs.
3. Inspect servo and repair as required.
linkage.
21 - 150 AUTOMATIC TRANSMISSION - 48RE DR
AUTOMATIC TRANSMISSION - 48RE (Continued)
CONDITION POSSIBLE CAUSES CORRECTION
NO KICKDOWN OR
NORMAL DOWNSHIFT
STUCK IN LOW GEAR
(WILL NOT UPSHIFT)
CREEPS IN NEUTRAL 1. Gearshift Linkage Mis-adjusted. 1. Adjust linkage.
1. Throttle Linkage Mis-adjusted. 1. Adjust linkage.
2. Accelerator Pedal Travel
Restricted.
3. Valve Body Hydraulic Pressures
Too High or Too Low Due to Valve
Body Malfunction or Incorrect
Hydraulic Control Pressure
Adjustments.
4. Governor Circuit Electrical Fault. 4. Test with DRBT scan tool and repair as
5. Valve Body Malfunction. 5. Perform hydraulic pressure tests to
6. TPS Malfunction. 6. Replace sensor, check with DRBT scan
7. PCM Malfunction. 7. Check with DRBT scan tool and replace
8. Valve Body Malfunction. 8. Repair sticking 1-2, 2-3 shift valves,
1. Throttle Linkage Mis-adjusted/
Stuck.
2. Gearshift Linkage Mis-adjusted. 2. Adjust linkage and repair linkage if worn
3. Governor Component Electrical
Fault.
4. Front Band Out of Adjustment. 4. Adjust Band.
5. Clutch or Servo Malfunction. 5. Air pressure check operation of clutches
2. Rear Clutch Dragging/Warped. 2. Disassemble and repair.
3. Valve Body Malfunction. 3. Perform hydraulic pressure test to
2. Verify floor mat is not under pedal, repair
worn accelerator cable or bent brackets.
3. Perform hydraulic pressure tests to
determine cause and repair as required.
Correct valve body pressure adjustments as
required.
required.
determine cause and repair as required.
Correct valve body pressure adjustments as
required.
tool.
if required.
governor plugs, 3-4 solenoid, 3-4 shift
valve, 3-4 timing valve.
1. Adjust linkage and repair linkage if worn
or damaged. Check for binding cable or
missing return spring.
or damaged.
3. Check operating pressures and test with
DRBT scan tool, repair faulty component.
and bands. Repair faulty component.
determine cause and repair as required.
DR AUTOMATIC TRANSMISSION - 48RE 21 - 151
AUTOMATIC TRANSMISSION - 48RE (Continued)
CONDITION POSSIBLE CAUSES CORRECTION
BUZZING NOISE 1. Fluid Level Low 1. Add fluid and check for leaks.
2. Shift Cable Mis-assembled. 2. Route cable away from engine and bell
housing.
3. Valve Body Mis-assembled. 3. Remove, disassemble, inspect valve
body. Reassemble correctly if necessary.
Replace assembly if valves or springs are
damaged. Check for loose bolts or screws.
4. Pump Passages Leaking. 4. Check pump for porous casting, scores
on mating surfaces and excess rotor
clearance. Repair as required. Loose pump
bolts.
5. Cooling System Cooler Plugged. 5. Flow check cooler circuit. Repair as
needed.
6. Overrunning Clutch Damaged. 6. Replace clutch.
SLIPS IN REVERSE ONLY 1. Fluid Level Low. 1. Add fluid and check for leaks.
2. Gearshift Linkage Mis-adjusted. 2. Adjust linkage.
3. Rear Band Mis-adjusted. 3. Adjust band.
4. Rear Band Worn. 4. Replace as required.
5. Overdrive Direct Clutch Worn. 5. Disassemble overdrive. Repair as
needed.
6. Hydraulic Pressure Too Low. 6. Perform hydraulic pressure tests to
determine cause.
7. Rear Servo Leaking. 7. Air pressure check clutch-servo operation
and repair as required.
8. Band Linkage Binding. 8. Inspect and repair as required.
SLIPS IN FORWARD
DRIVE RANGES
SLIPS IN LOW GEAR 9D9
ONLY, BUT NOT IN
MANUAL 1 POSITION
1. Fluid Level Low. 1. Add fluid and check for leaks.
2. Fluid Foaming. 2. Check for high oil level, bad pump
gasket or seals, dirt between pump halves
and loose pump bolts. Replace pump if
necessary.
3. Throttle Linkage Mis-adjusted. 3. Adjust linkage.
4. Gearshift Linkage Mis-adjusted. 4. Adjust linkage.
5. Rear Clutch Worn. 5. Inspect and replace as needed.
6. Low Hydraulic Pressure Due to
Worn Pump, Incorrect Control
Pressure Adjustments, Valve Body
Warpage or Malfunction, Sticking,
Leaking Seal Rings, Clutch Seals
Leaking, Servo Leaks, Clogged Filter
or Cooler Lines.
7. Rear Clutch Malfunction, Leaking
Seals or Worn Plates.
8. Overrunning Clutch Worn, Not
Holding (Slips in 1 Only).
Overrunning Clutch Faulty. Replace overrunning clutch.
6. Perform hydraulic and air pressure tests
to determine cause.
7. Air pressure check clutch-servo operation
and repair as required.
8. Replace Clutch.
21 - 152 AUTOMATIC TRANSMISSION - 48RE DR
AUTOMATIC TRANSMISSION - 48RE (Continued)
CONDITION POSSIBLE CAUSES CORRECTION
GROWLING, GRATING OR
SCRAPING NOISES
DRAGS OR LOCKS UP 1. Fluid Level Low. 1. Check and adjust level.
NO 4-3 DOWNSHIFT 1. Circuit Wiring and/or Connectors
1. Drive Plate Broken. 1. Replace.
2. Torque Converter Bolts Hitting
Dust Shield.
3. Planetary Gear Set Broken/
Seized.
4. Overrunning Clutch Worn/Broken. 4. Inspect and check for debris in oil pan.
5. Oil Pump Components Scored/
Binding.
6. Output Shaft Bearing or Bushing
Damaged.
7. Clutch Operation Faulty. 7. Perform air pressure check and repair as
8. Front and Rear Bands Mis-
adjusted.
2. Clutch Dragging/Failed 2. Air pressure check clutch operation and
3. Front or Rear Band Mis-adjusted. 3. Adjust bands.
4. Case Leaks Internally. 4. Check for leakage between passages in
5. Servo Band or Linkage
Malfunction.
6. Overrunning Clutch Worn. 6. Remove and inspect clutch. Repair as
7. Planetary Gears Broken. 7. Remove, inspect and repair as required
8. Converter Clutch Dragging. 8. Check for plugged cooler. Perform flow
Shorted.
2. PCM Malfunction. 2. Check PCM operation with DRBT scan
3. TPS Malfunction 3. Check TPS with DRBT scan tool at PCM.
4. Lockup Solenoid Not Venting. 4. Remove valve body and replace solenoid
5. Overdrive Solenoid Not Venting. 5. Remove valve body and replace solenoid
6. Valve Body Valve Sticking. 6. Repair stuck 3-4 shift valve or lockup
2. Dust shield bent. Replace or repair.
3. Check for debris in oil pan and repair as
required.
Repair as required.
5. Remove, inspect and repair as required.
6. Remove, inspect and repair as required.
required.
8. Adjust bands.
repair as required.
case.
5. Air pressure check servo operation and
repair as required.
required.
(look for debris in oil pan).
check. Inspect pump for excessive side
clearance. Replace pump as required.
1. Test wiring and connectors with test lamp
and volt/ohmmeter. Repair wiring as
necessary. Replace connectors and/or
harnesses as required.
tool. Replace PCM only if faulty.
assembly if plugged or shorted.
if plugged or shorted.
timing valve.
DR AUTOMATIC TRANSMISSION - 48RE 21 - 153
AUTOMATIC TRANSMISSION - 48RE (Continued)
CONDITION POSSIBLE CAUSES CORRECTION
NO 4-3 DOWNSHIFT
WHEN CONTROL SWITCH
IS TURNED OFF
CLUNK NOISE FROM
DRIVELINE ON CLOSED
THROTTLE 4-3
DOWNSHIFT
3-4 UPSHIFT OCCURS
IMMEDIATELY AFTER 2-3
SHIFT
WHINE/NOISE RELATED
TO ENGINE SPEED
1. Control Switch Open/Shorted. 1. Test and replace switch if faulty.
2. Overdrive Solenoid Connector
Shorted.
3. PCM Malfunction. 3. Test with DRBT scan tool. Replace PCM
4. Valve Body Stuck Valves. 4. Repair stuck 3-4, lockup or lockup timing
1. Transmission Fluid Low. 1. Add Fluid.
2. Throttle Cable Mis-adjusted. 2. Adjust cable.
3. Overdrive Clutch Select Spacer
Wrong Spacer.
1. Overdrive Solenoid Connector or
Wiring Shorted.
2. TPS Malfunction. 2. Test TPS and replace as necessary.
3. PCM Malfunction. 3. Test PCM with DRBT scan tool and
4. Overdrive Solenoid Malfunction. 4. Replace solenoid.
5. Valve Body Malfunction. 5. Remove, disassemble, clean and inspect
1. Fluid Level Low. 1. Add fluid and check for leaks.
2. Shift Cable Incorrect Routing. 2. Check shift cable for correct routing.
2. Test solenoids and replace if seized or
shorted.
if faulty.
valve.
3. Replace overdrive piston thrust plate
spacer.
1. Test connector and wiring for loose
connections, shorts or ground and repair as
needed.
Check with DRBT scan tool.
replace controller if faulty.
valve body components. Make sure all
valves and plugs slide freely in bores.
Polish valves with crocus cloth if needed.
Should not touch engine or bell housing.
21 - 154 AUTOMATIC TRANSMISSION - 48RE DR
AUTOMATIC TRANSMISSION - 48RE (Continued)
CONDITION POSSIBLE CAUSES CORRECTION
NO 3-4 UPSHIFT 1. O/D Switch In OFF Position. 1. Turn control switch to ON position.
2. Overdrive Circuit Fuse Blown. 2. Replace fuse. Determine why fuse failed
and repair as necessary (i.e., shorts or
grounds in circuit).
3. O/D Switch Wire Shorted/Open
Cut.
4. Distance or Coolant Sensor
Malfunction.
5. TPS Malfunction. 5. Check with DRBT scan tool and replace
6. Neutral Sense to PCM Wire
Shorted/Cut.
7. PCM Malfunction. 7. Check with DRBT scan tool and replace
8. Overdrive Solenoid Shorted/Open. 8. Replace solenoid if shorted or open and
9. Solenoid Feed Orifice in Valve
Body Blocked.
10. Overdrive Clutch Failed. 10. Disassemble overdrive and repair as
11. Hydraulic Pressure Low. 11. Pressure test transmission to determine
12. Valve Body Valve Stuck. 12. Repair stuck 3-4 shift valve, 3-4 timing
13. O/D Piston Incorrect Spacer. 13. Remove unit, check end play and install
14. Overdrive Piston Seal Failure. 14. Replace both seals.
15. O/D Check Valve/Orifice Failed. 15. Check for free movement and secure
3. Check wires/connections with 12V test
lamp and voltmeter. Repair damaged or
loose wire/connection as necessary.
4. Check with DRBT scan tool and repair or
replace as necessary.
if necessary.
6. Test switch/sensor as described in
service section and replace if necessary.
Engine no start.
if necessary.
repair loose or damaged wires (DRBT scan
tool).
9. Remove, disassemble, and clean valve
body thoroughly. Check feed orifice.
needed.
cause.
valve.
correct spacer.
assembly (in piston retainer). Check ball
bleed orifice.
DR AUTOMATIC TRANSMISSION - 48RE 21 - 155
AUTOMATIC TRANSMISSION - 48RE (Continued)
CONDITION POSSIBLE CAUSES CORRECTION
SLIPS IN OVERDRIVE
FOURTH GEAR
DELAYED 3-4 UPSHIFT
(SLOW TO ENGAGE)
TORQUE CONVERTER
LOCKS UP IN SECOND
AND/OR THIRD GEAR
HARSH 1-2, 2-3, 3-4 OR
3-2 SHIFTS
1. Fluid Level Low. 1. Add fluid and check for leaks.
2. Overdrive Clutch Pack Worn. 2. Remove overdrive unit and rebuild clutch
pack.
3. Overdrive Piston Retainer Bleed
Orifice Blown Out.
4. Overdrive Piston or Seal
Malfunction.
5. 3-4 Shift Valve, Timing Valve or
Accumulator Malfunction.
6. Overdrive Unit Thrust Bearing
Failure.
7. O/D Check Valve/Bleed Orifice
Failure.
1. Fluid Level Low. 1. Add fluid and check for leaks.
2. Throttle Valve Cable Mis-adjusted. 2. Adjust throttle valve cable.
3. Overdrive Clutch Pack Worn/
Burnt.
4. TPS Faulty. 4. Test with DRBT scan tool and replace as
5. Overdrive Clutch Bleed Orifice
Plugged.
6. Overdrive Solenoid or Wiring
Shorted/Open.
7. Overdrive Excess Clearance. 7. Remove unit. Measure end play and
8. O/D Check Valve Missing or
Stuck.
Lockup Solenoid, Relay or Wiring
Shorted/Open.
Lockup Solenoid Malfunction. Remove valve body and replace solenoid
3. Disassemble transmission, remove
retainer and replace orifice.
4. Remove overdrive unit. Replace seals if
worn. Replace piston if damaged. If piston
retainer is damaged, remove and
disassemble the transmission.
5. Remove and overhaul valve body.
Replace accumulator seals. Make sure all
valves operate freely in bores and do not
bind or stick. Make sure valve body screws
are correctly tightened and separator plates
are properly positioned.
6. Disassemble overdrive unit and replace
thrust bearing (NO. 1 thrust bearing is
between overdrive piston and clutch hub;
NO. 2 thrust bearing is between the
planetary gear and the direct clutch spring
plate; NO. 3 thrust bearing is between
overrunning clutch hub and output shaft).
7. Check for function/secure orifice insert in
O/D piston retainer.
3. Remove unit and rebuild clutch pack.
necessary
5. Disassemble transmission and replace
orifice.
6. Test solenoid and check wiring for
loose/corroded connections or shorts/
grounds. Replace solenoid if faulty and
repair wiring if necessary.
select proper spacer.
8. Check for presence of check valve.
Repair or replace as required.
Test solenoid, relay and wiring for
continuity, shorts or grounds. Replace
solenoid and relay if faulty. Repair wiring
and connectors as necessary.
assembly.
21 - 156 AUTOMATIC TRANSMISSION - 48RE DR
AUTOMATIC TRANSMISSION - 48RE (Continued)
CONDITION POSSIBLE CAUSES CORRECTION
NO START IN PARK OR
NEUTRAL
NO REVERSE (OR SLIPS
IN REVERSE)
1. Gearshift Linkage/Cable
Mis-adjusted.
2. Neutral Sense Wire Open/Cut. 2. Check continuity with test lamp. Repair
3. Park/Neutral Switch, or
Transmission Range Sensor Faulty.
4. Park/Neutral Switch, or
Transmission Range Sensor
Connection Faulty.
5. Valve Body Manual Lever
Assembly Bent/Worn/Broken.
1. Direct Clutch Pack (front clutch)
Worn.
2. Rear Band Mis-adjusted. 2. Adjust band.
3. Front Clutch Malfunctioned/
Burned.
4. Overdrive Thrust Bearing Failure. 4. Disassemble geartrain and replace
5. Direct Clutch Spring Collapsed/
Broken.
1. Adjust linkage/cable.
as required.
3. Refer to service section for test and
replacement procedure.
4. Connectors spread open. Repair.
5. Inspect lever assembly and replace if
damaged.
1. Disassemble unit and rebuild clutch
pack.
3. Air-pressure test clutch operation.
Remove and rebuild if necessary.
bearings.
5. Remove and disassemble unit. Check
clutch position and replace spring.
DR AUTOMATIC TRANSMISSION - 48RE 21 - 157
AUTOMATIC TRANSMISSION - 48RE (Continued)
CONDITION POSSIBLE CAUSES CORRECTION
OIL LEAKS. 1. Fluid Lines and Fittings Loose/
Leaks/Damaged.
2. Fill Tube (where tube enters case)
Leaks/Damaged.
3. Pressure Port Plug Loose
Loose/Damaged.
4. Pan Gasket Leaks. 4. Tighten pan screws (150 in. lbs.). If leaks
5. Valve Body Manual Lever Shaft
Seal Leaks/Worn.
6. Rear Bearing Access Plate Leaks. 6. Replace gasket. Tighten screws.
7. Gasket Damaged or Bolts are
Loose.
8. Adapter/Extension Gasket
Damaged Leaks/Damaged.
9. Park/Neutral Switch, or
Transmission Range Sensor
Leaks/Damaged.
10. Converter Housing Area Leaks. 10. Check for leaks at seal caused by worn
11. Pump Seal Leaks/Worn/
Damaged.
12. Torque Converter Weld
Leak/Cracked Hub.
13. Case Porosity Leaks. 13. Replace case.
NOISY OPERATION IN
FOURTH GEAR ONLY
1. Overdrive Clutch Discs, Plates or
Snap Rings Damaged.
2. Overdrive Piston or Planetary
Thrust Bearing Damaged.
3. Output Shaft Bearings Scored/
Damaged.
4. Planetary Gears Worn/Chipped. 4. Remove and overhaul overdrive unit.
5. Overdrive Unit Overrunning Clutch
Rollers Worn/Scored.
1. Tighten fittings. If leaks persist, replace
fittings and lines if necessary.
2. Replace tube seal. Inspect tube for
cracks in fill tube.
3. Tighten to correct torque. Replace plug
or reseal if leak persists.
persist, replace gasket.
5. Replace shaft seal.
7. Replace bolts or gasket or tighten both.
8. Replace gasket.
9. Replace switch and gasket.
seal or burr on converter hub (cutting seal),
worn bushing, missing oil return, oil in front
pump housing or hole plugged. Check for
leaks past O-ring seal on pump or past
pump-to-case bolts; pump housing porous,
oil coming out vent due to overfill or leak
past front band shaft access plug.
11. Replace seal.
12. Replace converter.
1. Remove unit and rebuild clutch pack.
2. Remove and disassemble unit. Replace
either thrust bearing if damaged.
3. Remove and disassemble unit. Replace
either bearing if damaged.
5. Remove and overhaul overdrive unit.
21 - 158 AUTOMATIC TRANSMISSION - 48RE DR
AUTOMATIC TRANSMISSION - 48RE (Continued)
STANDARD PROCEDURE - ALUMINUM
THREAD REPAIR
Damaged or worn threads in the aluminum transmission case and valve body can be repaired by the
use of Heli-Coils™, or equivalent. This repair consists of drilling out the worn-out damaged threads.
Then tap the hole with a special Heli-Coil™ tap, or
equivalent, and installing a Heli-Coil™ insert, or
equivalent, into the hole. This brings the hole back to
its original thread size.
Heli-Coil™, or equivalent, tools and inserts are
readily available from most automotive parts suppliers.
REMOVAL
NOTE: The overdrive unit can be removed and serviced separately. It is not necessary to remove the
entire transmission assembly to perform overdrive
unit repairs.
(1) Disconnect battery negative cable.
(2) Raise vehicle.
(3) Remove the transfer case skid plate (Fig. 12), if
equipped.
(4) Disconnect and lower or remove necessary
exhaust components.
(5) Remove engine-to-transmission struts.
(6) Remove starter motor. (Refer to 8 - ELECTRI-
CAL/STARTING/STARTER MOTOR - REMOVAL)
(7) Disconnect and remove the crankshaft position
sensor. (Refer to 14 - FUEL SYSTEM/FUEL INJECTION/CRANKSHAFT POSITION SENSOR REMOVAL) Retain the sensor attaching bolts.
(8) If transmission is being removed for overhaul,
remove transmission oil pan, drain fluid and reinstall
pan.
(9) Remove torque converter access cover.
(10) Rotate crankshaft in clockwise direction until
converter bolts are accessible. Then remove bolts one
at a time. Rotate crankshaft with socket wrench on
dampener bolt.
(11) Mark propeller shaft and axle yokes for
assembly alignment. Then disconnect and remove
propeller shaft. On4x4models, remove both propeller shafts. (Refer to 3 - DIFFERENTIAL & DRIVELINE/PROPELLER SHAFT/PROPELLER SHAFT REMOVAL)
(12) Disconnect wires from the transmission range
sensor and transmission solenoid connector.
(13) Disconnect gearshift cable (Fig. 13) from the
transmission.
Fig. 12 Transfer Case Skid Plate
1 - FRAME RAIL
2 - SKID PLATE
3 - BOLTS (6)
Fig. 13 Gearshift Cable At Transmission
1 - GEARSHIFT CABLE
2 - TRANSMISSION MANUAL LEVER
3 - CABLE SUPPORT BRACKET
DR AUTOMATIC TRANSMISSION - 48RE 21 - 159
AUTOMATIC TRANSMISSION - 48RE (Continued)
(14) Disconnect throttle valve cable from transmis-
sion bracket and throttle valve lever.
(15) On 4X4 models, disconnect shift rod from
transfer case shift lever.
(16) Support rear of engine with safety stand or
jack.
(17) Raise transmission slightly with service jack
to relieve load on crossmember and supports.
(18) Remove bolts securing rear support and cushion (Fig. 14) and (Fig. 15) to transmission and crossmember and remove rear support.
Fig. 15 Engine Rear Mount - 4X4 Automatic
Transmission
1 - TRANSMISSION
2 - ENGINE REAR MOUNT
3 - BOLT
Fig. 14 Engine Rear Mount - 4X2 Automatic
Transmission
1 - ENGINE REAR MOUNT
2 - BOLT
3 - NUT
4 - THROUGH BOLT NUT
5 - TRANSMISSION
(19) Remove bolts attaching crossmember to frame
and remove crossmember.
(20) On 4X4 models, remove transfer case with
transmission jack or aid of helper.
(21) Disconnect fluid cooler lines at transmission.
(22) Remove fill tube bracket bolts and pull tube
out of transmission. Retain fill tube seal. On 4X4
models, it will also be necessary to remove bolt
attaching transfer case vent tube to converter housing (Fig. 16).
(23) Remove all converter housing bolts.
(24) Carefully work transmission and torque converter assembly rearward off engine block dowels.
(25) Lower transmission and remove assembly
from under the vehicle.
(26) To remove torque converter, remove C-clamp
from edge of bell housing and carefully slide torque
converter out of the transmission.
Fig. 16 Fill Tube Attachment
1 - TRANSFER CASE VENT TUBE
2 - FILL TUBE (V8)
3 - TUBE SEAL
4 - FILL TUBE (V6)
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