3.COMPARE SCAN TOOL GOVERNOR PRESSURE READING TO PRESSURE GAUGE READING
Turn the ignition off to the lock position.
Connect a 700 kPa (100 psi) Pressure Gauge to the Governor Pressure test port. (Refer to 21 - TRANSMISSION/
TRANSAXLE/AUTOMATIC - 48RE - DIAGNOSIS AND TESTING)
Start the engine and allow the engine to idle.
Warm the transmission to a normal operating temperature above 43° C (110° F).
With the scan tool, read the Governor Pressure and compare the scan tool Governor Pressure reading to the Pres-
sure Gauge reading.
Does the scan tool Governor Pressure reading match the Pressure Gauge reading within 6.9 kPa (1
psi)?
Ye s>>
Go To 4
No>>
Go To 7
4.TRANSMISSION - INTERNAL DAMAGE
Turn the ignition off to the lock position.
Remove the transmission oil pan per the Service Information. (Refer to 21 -TRANSMISSION/TRANSAXLE/AUTO-
MATIC - 48RE/FLUID - STANDARD PROCEDURE)
Inspect the transmission oil pan for burnt oil and/or excessive debris.
Does the transmission contain burnt oil and/or excessive debris?
Ye s>>
Repair internal transmission as necessary. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC -
48RE - REMOVAL)
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). (Refer to 21 - TRANSMISSION/
TRANSAXLE/AUTOMATIC - 48RE - STANDARD PROCEDURE)
No>>
Go To 5
5.CHECK INTERNAL TRANSMISSION FOR A FLUID LEAK
Inspect the transmission for internal fluid leakage in the Valve Body or the Governor Pressure Solenoid. (Refer to 21
- TRANSMISSION/TRANSAXLE/AUTOMATIC - 48RE/VALVE BODY - REMOVAL)
Were there any problems found?
Ye s>>
Repair the internal transmission as necessary per the Service Information. (Refer to 21 - TRANSMIS-
SION/TRANSAXLE/AUTOMATIC - 48RE/VALVE BODY - REMOVAL)
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). (Refer to 21 - TRANSMISSION/
TRANSAXLE/AUTOMATIC - 48RE - STANDARD PROCEDURE)
No>>
Go To 6
6.VERIFY OPERATION - TEST DRIVE
Remove the pressure gauge from the transmission.
Install the transmission oil pan and refill the transmission per the Service Information. (Refer to 21 - TRANSMIS-
SION/TRANSAXLE/AUTOMATIC - 48RE/FLUID - STANDARD PROCEDURE)
With the scan tool, erase Engine DTCs.
Test drive the vehicle.
Be sure to stop the vehicle and move the gear selector into the park positionfor a minimum of 5 seconds at least
three times during the drive cycle.
With the scan tool, read Engine DTCs.
Did the DTC reset?
Ye s>>
Using the schematics as a guide, check the Engine Control Module (ECM) pins, terminals, and connec-
tors for corrosion, damage, or terminal push out. Pay particular attentiontoallpowerandgroundcir-
cuits. If no problems are found, replace and program the ECM per the ServiceInformation. (Refer to 8
- ELECTRICAL/ELECTRONIC CONTROL MODULES/ENGINE CONTROL MODULE - REMOVAL)
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). (Refer to 21 - TRANSMISSION/
TRANSAXLE/AUTOMATIC - 48RE - STANDARD PROCEDURE)
No>>
Go To 10
7.CHECK THE 5 VOLT SUPPLY CIRCUIT FOR AN OPEN
Turn the ignition off to the lock position.
Disconnect the ECM C2 harness connector.
Disconnect the Transmission Solenoid Assembly harness connector.
NOTE: Check connectors - Clean/repair as necessary
Measure the resistance of the 5-volt Supply circuit between the Trans-
mission Solenoid Assembly harness connector and the ECM C2 har-
ness connector.
Is the resistance below 5.0 ohms?
Ye s>>
Go To 8
No>>
Repair 5-volt Supply circuit for an open.
Perform RE TRANSMISSION VERIFICATION TEST VER -
1 (DIESEL). (Refer to 21 - TRANSMISSION/TRANSAXLE/
AUTOMATIC - 48RE - STANDARD PROCEDURE)
8.CHECK THE 5 VOLT SUPPLY CIRCUIT FOR AN OPEN - INTERNAL
Reconnect the Transmission Solenoid Assembly harness connector.
Remove the Transmission Oil Pan perthe Service Information. (Refer to
21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 48RE/FLUID -
STANDARD PROCEDURE)
Disconnect the Governor Pressure Sensor harness connector internal to
the transmission.
NOTE: Check connectors - Clean/repair as necessary
Measure the resistance of the 5-volt Supply circuit between the ECM
C2 harness connector and the Governor Pressure Sensor connector
internal to the transmission.
Is the resistance below 5.0 ohms?
Ye s>>
Go To 9
No>>
Repair or replace the 5-volt Supply circuit for an open inter-
nal to the transmission.
Perform RE TRANSMISSION VERIFICATION TEST VER -
1 (DIESEL). (Refer to 21 - TRANSMISSION/TRANSAXLE/
AUTOMATIC - 48RE - STANDARD PROCEDURE)
page page
AUTOMATIC TRANSMISSION - 48RE - SERVICE
INFORMATION
DESCRIPTION ............................. 1268
OPERATION ............................... 1271
DIAGNOSIS AND TESTING
AUTOMATIC TRANSMISSION .............. 1277
PRELIMINARY ............................ 1277
ROAD TESTING .......................... 1277
HYDRAULIC PRESSURE TEST . ........... 1278
AIR TESTING TRANSMISSION CLUTCH
AND BAND OPERATION................... 1281
CONVERTER HOUSING FLUID LEAK ...... 1282
DIAGNOSIS CHARTS ..................... 1283
STANDARD PROCEDURE - ALUMINUM
THREAD REPAIR ......................... 1293
REMOVAL ................................. 1294
DISASSEMBLY ............................. 1298
CLEANING ................................. 1306
INSPECTION ............................... 1306
ASSEMBLY . ............................... 1307
INSTALLATION ............................. 1317
SCHEMATICS AND DIAGRAMS
HYDRAULIC SCHEMATICS ................ 1322
SPECIFICATIONS
TRANSMISSION .......................... 1336
SPECIAL TOOLS
RE TRANSMISSION ...................... 1339
ACCUMULATOR
DESCRIPTION ............................. 1341
OPERATION ............................... 1342
INSPECTION ............................... 1342
BANDS
DESCRIPTION ............................. 1343
OPERATION ............................... 1343
ADJUSTMENTS
ADJUSTMENT - BANDS ................... 1344
SYSTEM-BRAKE TRANSMISSION SHIFT
INTERLOCK
DESCRIPTION ............................. 1345
OPERATION ............................... 1345
DIAGNOSIS AND TESTING - BRAKE
TRANSMISSION SHIFT INTERLOCK ........ 1345
ADJUSTMENTS - BRAKE TRANSMISSION
SHIFT INTERLOCK ....................... 1345
GOVERNOR-ELECTRONIC
DESCRIPTION ............................. 1347
OPERATION ............................... 1348
REMOVAL ................................. 1349
INSTALLATION ............................. 1350SEAL-EXTENSION HOUSING
REMOVAL ................................. 1352
INSTALLATION ............................. 1352
FLUID AND FILTER
DIAGNOSIS AND TESTING
EFFECTS OF INCORRECT FLUID LEVEL . . . 1353
CAUSES OF BURNT FLUID ............... 1353
FLUID CONTAMINATION .................. 1353
STANDARD PROCEDURE
FLUID LEVEL CHECK ..................... 1353
FLUID AND FILTER REPLACEMENT ....... 1355
TRANSMISSION FILL ..................... 1357
CLUTCH-FRONT
DESCRIPTION ............................. 1358
OPERATION ............................... 1358
DISASSEMBLY . ............................ 1359
INSPECTION............................... 1360
ASSEMBLY................................ 1360
SERVO-FRONT
DESCRIPTION ............................. 1363
OPERATION ............................... 1363
DISASSEMBLY . ............................ 1364
CLEANING ................................. 1364
INSPECTION ............................... 1365
ASSEMBLY................................ 1365
CABLE-GEARSHIFT
DIAGNOSIS AND TESTING - GEARSHIFT
CABLE ................................... 1366
REMOVAL ................................. 1366
INSTALLATION ............................. 1367
ADJUSTMENTS - GEARSHIFT CABLE ........ 1368
PUMP-OIL
DESCRIPTION ............................. 1369
OPERATION ............................... 1369
DISASSEMBLY ............................. 1370
CLEANING ................................. 1371
INSPECTION ............................... 1371
ASSEMBLY................................ 1373
BEARING-OUTPUT SHAFT FRONT
REMOVAL ................................. 1375
INSTALLATION ............................. 1375
BEARING-OUTPUT SHAFT REAR
REMOVAL ................................. 1376
INSTALLATION ............................. 1376
CLUTCH-OVERDRIVE
DESCRIPTION ............................. 1377
OPERATION ............................... 1377
UNIT-OVERDRIVE
REMOVAL ................................. 1378
DISASSEMBLY ............................. 1379
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
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 nec-
essary.
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 DRBscan 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 roadtest.
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 differentialor 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.
ROAD TESTING
Before road testing, be sure the fluid level and control cable adjustmentshave been checked and adjusted if nec-
essary. 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 trans-
mission 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.
Clutch and Band Application Chart
SHIFT
LEVER
POSITIONTRANSMISSION CLUTCHES AND BANDS OVERDRIVE CLUTCHES
FRONT
CLUTCHFRONT
BANDREAR
CLUTCHREAR
BANDOVER-
RUNNING
CLUTCHOVER-
DRIVE
CLUTCHDIRECT
CLUTCHOVER-
RUNNING
CLUTCH
ReverseXXX
Drive -
FirstXXXX
Drive -
SecondXX X X
Drive -
ThirdXX XX
Drive -
FourthXX X
Manual
SecondXX X X
Manual
FirstXXX X X
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 rearclutch is slipping.
Applying the same method of analysis, note that the front and rear clutchesare 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.
Ifthetransmissionslipsinfourthgearbutnotinthirdgear,theoverdrive clutch is slipping. By selecting another gear
which does not use these clutches, the slipping unit can be determined. Forexample, if the transmission also slips
in Reverse, the front clutch is slipping. If the transmission does not slipin 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.
This process of elimination can be used to identify a slipping unit and check operation. Proper use of the Clutch and
Band Application Chart is the key.
Although road test analysis will help determine the 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.
Unless a malfunction is obvious, such as no drive in D range first gear, do not disassemble the transmission. Per-
form the hydraulic and air pressure tests to help determine the probable cause.
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. Oil Pressure Gauge C-3292 has a 100 psi range
and is used at the accumulator, governor, and front servo ports. Oil Pressure 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 transmis-
sion case.
Line pressure is checked at the accumulator port (3)
on the right side of the case. The front servo pressure
port (4) is at the right side of the case just behind the
filler tube opening.
The rear servo (1) and governor pressure (2) ports are
at the right rear of the transmission case. The over-
drive clutch pressure port (5) is at the left rear of the
case.
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 observedfrom driver seat if helper will be oper-
ating engine. Raise vehicle on hoist that will allow rear wheels to rotate freely.
2. Connect 100 psi Oil Pressure Gauge C-3292 to accumulator port. Then connect 300 psi Oil Pressure 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 asline 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 Oil Pressure Gauge C-3292 for
this test.
1. Leave vehicle in place on hoist and leave Oil Pressure 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 Oil Pressure Gauge C-3292 in place at accumulator port.
3. Move Oil Pressure 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 rear-
ward position:
Line pressure at accumulator in D range third gear, should be 54-60 psi (372-414 kPa) with throttle lever for-
ward and increase as lever is moved rearward.
Front servo pressure in D range third gear, should be within 3 psi (21 kPa) ofline pressure up to kickdown
point.
Test Four - Transmission In Reverse
This test checks pump output, pressure regulation and the front clutch andrear servo circuits. Use 300 psi Oil
Pressure Gauge C-3293-SP for this test.
1. Leave vehicle on hoist and leave Oil Pressure Gauge C-3292 in place at accumulator port.
2. Move 300 psi Oil Pressure Gauge C-3293-SP back to rear servo port.
3. Have helper start and run engine at 1600 rpm for test.
4. Move transmission shift lever four detents rearward from full forward position. This is Reverse range.
5. Move transmission throttle lever fully forward then fully rearward andnote 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 areincorrect 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 Oil Pressure 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 speedometerand pressure test gauge (do not
exceed 30 mph on speedometer). Governor pressure should increase in proportion to vehicle speed. Or approx-
imately 6.89 kPa (1 psi) for every 1 mph.
6. Governor pressure rise should be smooth and drop back to no more than 20.6kPa (3 psi), after engine returns
to curb idle and brakes are applied to prevent wheels from rotating.
7. Compare results of pressure test with analysis chart.
Test Six - Transmission In Overdrive Fourth Gear
This test checks line pressure at the overdrive clutch in fourth gear range. Use 300 psi Oil Pressure Gauge
C-3293-SP for this test. The test should be performed on the road or on a chassis dyno.
1. Remove tachometer; it is not needed for this test.
2. Move 300 psi Oil Pressure 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
1/2to3/4throttle.Notethatpressurecanincreasetoaround965kPa(140psi) 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 Pump and regulator valve OK
Line pressure OK in R but low in D, 2, 1 Leakage in rear clutch area (seal rings, clutch seals)
Pressure low in D Fourth Gear Range Overdrive clutch piston seal, or check ball problem
Pressure OK in 1, 2 but low in D3 and R Leakage in front clutch area
Pressure OK in 2 but low in R and 1 Leakage in rear servo
Front servo pressure in 2 Leakage in servo; broken servo ring or cracked servo
piston
Pressure low in all positions Clogged filter, stuck regulator valve, wornor faulty
pump, low oil level
Governor pressure too high at idle speed Governor pressure solenoid valvesystem fault. Refer
to diagnostic book.
Governor pressure low at all mph figures Faulty governor pressure solenoid, transmission
control module, or governor pressure sensor
Lubrication pressure low at all throttle positions Clogged fluid cooler or lines, seal rings leaking, worn
pump bushings, pump, clutch retainer, or clogged filter.
Line pressure high Output shaft plugged, sticky regulator valve
Line pressure low Sticky regulator valve, clogged filter, worn pump
AIR TESTING TRANSMISSION CLUTCH AND BAND OPERATION
Air-pressure testing can be used to check transmis-
sion front/rear clutch and band operation. The test can
be conducted with the transmission either in the vehi-
cle or on the work bench, as a final check, after over-
haul.
Air-pressure testing requires that the oil pan and valve
body be removed from the transmission. The servo
and clutch apply passages are shown.