Transfer Case - Servicing Chevrolet Chevy Express H2500

APPLICATION

Note. For additional information on transfer case, refer to REMOVAL & INSTALLATION - T/C and DIAGNOSIS - T/C .

TRANSFER CASE APPLICATION

General Description

The Borg Warner (BW) model 4473 RPO NP3 transfer case is a one-speed, full time AWD, transfer case. The BW 4473 provides one operating mode, 4HI full-time AWD. The transfer case has a planetary differential gear set, which provides a 35 percent/65 percent torque split, front/rear, full time.

Both axles are constantly being driven for maximum traction, and the best balance of vehicle handling characteristics under all operating conditions is provided.

The BW 4473 case halves are high-pressure die-cast aluminum. The transfer case requires DEXRON®III ATF Fluid GM P/N 12346143 (Canadian P/N 10952622), which is red in color.

Scheme 1

The power flows from the transmission to the transfer case input shaft (1). The input shaft (1) delivers the power to the planetary center differential (4), which splits the torque 35 percent through the differential pinion gears (8) to the front sun gear (7), through the sprocket drive (2), via the chain (10) to the front output shaft (9) and to the front propeller shaft. 65 percent of the torque is delivered to the rear output, which goes through the differential ring gear (6), which is connected to the rear output shaft (5), and to the rear propeller shaft.

The viscous coupling (3), torque biasing device, has a series of opposing discs which are attached to the front and rear output shafts. One set turns with the front axle and the one set turns with the rear axle. The viscous coupling has a sealed housing, which is filled with high viscosity silicone fluid. When there is a speed difference between front and rear axles, the inner and outer plates of the coupling turn relative to each other. The silicone fluid provides resistance to the speed difference, and torque is transferred to the axles to equalize the speed difference. The tuning of the coupling is such that binding is not felt in tight turns, on dry surfaces, while being high enough to bias torque quickly to the wheels that have traction in a vehicle slip event. If the speed difference between the axles is high, the viscous coupling can go into "hump" mode. This occurs when the heat generated by the high speed difference expands the viscous fluid in the coupling, which results in pressure between the plates, forcing them in to contact each other, similar to a clutch pack. In the "hump" mode, the coupling can bias torque 100 percent to one axle. To prevent damage to the viscous coupling, the following should be avoided in the vehicle

1. Do not tow with only two wheels on the ground.
2. Do not drive with one propeller shaft removed.
3. Do not drive with a mini spare tire for any extended period of time.

Customers may have concern that the transfer case is not operating properly, because one set of tires spun for a brief period. It is normal for one set of tires to spin until the viscous coupling engages. Turning off the traction control switch, if equipped, enhances the function of the viscous coupling. The viscous coupling, as described above, engages by heat. Allowing one set of tires to spin or slip for a very brief period, generates heat in the viscous coupling. The engine speed should be kept at a constant speed during the brief spin of the tires. Feathering the engine speed, or hard acceleration, will not allow the viscous coupling to operate properly.

Scheme 2

During normal operation, 100 percent engine torque is delivered to the input shaft (1) from the transmission. The torque is split 65 percent to the rear output shaft (5), and 35 percent to the front output shaft (9), by the planetary differential (4). Because there is not a loss in traction, or slip in the front or rear wheels, the viscous coupling (3) is locked in place and there is no "shear" mode or "hump" mode involved.

Scheme 3

When traction is lost at the front wheels, the viscous coupling (3) works in conjunction with the planetary differential (4) to bias the torque more to the rear wheels. The rear torque goes higher than 65 percent, up to 100 percent torque to the rear output shaft (5). The torque at the front output shaft (9) is lowered from 35 percent, to as low as 0 percent torque.

SERVICE INTERVALS

Every 12 months, or at engine oil change intervals, check front axle and transfer case and add lubricant when necessary. A fluid loss could indicate a problem. Check and have it repaired, if needed. Check vent hose at transfer case for kinks and proper installation.

CHECKING FLUID LEVELS

1. Raise and support vehicle. Remove filler plug located on rear of transfer case.
2. Ensure fluid is level with bottom edge of filler plug hole.
3. Fill transfer case through oil filler plug hole to specified capacity using recommended fluid. See «RECOMMENDED FLUIDS»(/chevrolet/chevy-express-h2500/2003-2003/remont/transfer-case/#transfer-case-servicing__recommended-fluids) .
4. Install the fill plug. Apply pipe sealant (P/N-12346004) to the threads on the fill plug. Tighten to specification. See «TORQUE SPECIFICATIONS»(/chevrolet/chevy-express-h2500/2003-2003/remont/transfer-case/#transfer-case-servicing__torque-specifications) .

RECOMMENDED FLUIDS

TRANSFER CASE FLUID TYPE

FLUID CAPACITIES

TRANSFER CASE FLUID CAPACITIES (1)

DRAINING & REFILLING

Note. When performing the following service procedures, use only hand tools to remove and install the fill or drain plugs.

Scheme 4

1. Raise and support vehicle.
2. Remove filler plug located on rear of transfer case. NOTE: When draining transfer case, make sure that an approved drain pan is used.
3. Remove drain plug from bottom of transfer case. Allow fluid to drain. (Scheme 4)
4. Replace drain plug, apply pipe sealant (P/N-12346004) to the threads on the drain plug. (Scheme 4) Tighten drain plug to specification. See «TORQUE SPECIFICATIONS»(/chevrolet/chevy-express-h2500/2003-2003/remont/transfer-case/#transfer-case-servicing__torque-specifications).
5. Fill transfer case through oil filler plug hole to specified capacity using recommended fluid. See «RECOMMENDED FLUIDS»(/chevrolet/chevy-express-h2500/2003-2003/remont/transfer-case/#transfer-case-servicing__recommended-fluids). Ensure fluid is level with bottom edge of filler plug hole.
6. Install the fill plug. Apply pipe sealant (P/N-12346004) to the threads on the fill plug. Tighten to specification. See «TORQUE SPECIFICATIONS»(/chevrolet/chevy-express-h2500/2003-2003/remont/transfer-case/#transfer-case-servicing__torque-specifications).
7. Disconnect the electrical connector from the speed sensor.
8. Remove the speed sensor and the O-ring from the transfer case.
9. Add 1.0 Liter (1.06 quarts) of DEXRON®VI fluid, P/N 88861003 (in Canada, P/N 88861004) through the threaded speed sensor opening.
10. Install the speed sensor into the transfer case with the new O-ring seal. See «TORQUE SPECIFICATIONS»(/chevrolet/chevy-express-h2500/2003-2003/remont/transfer-case/#transfer-case-servicing__torque-specifications).
11. Connect the electrical connector to the speed sensor.
12. Lower the vehicle.

REMOVAL & INSTALLATION

Scheme 5

1. Raise the vehicle.
2. Remove the transfer case from the vehicle. Refer to «TRANSFER CASE»(/chevrolet/chevy-express-h2500/2003-2003/remont/transfer-case/#transfer-case-removal-installation).
3. Remove the mounting bolts from the adapter to the transmission. (Scheme 5)
4. Remove the adapter from the transmission.
5. Remove the seal between the transfer case and the adapter.
6. Remove the transfer case to the adapter gasket.

Installation Procedure

Note. Always use a new gasket and seal for the adapter. Do not use any type of sealant or adhesive in place of or with the gasket or the seal.

1. Install the new seal on the adapter. (Scheme 5) NOTE: The transfer case adapter must be installed so that the adapter is evenly seated to the transmission before installing the retaining nuts.
2. Install the adapter to the transmission. CAUTION: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
3. Install the adapter mounting bolts to the transmission. Tighten Tighten the mounting bolts to 50 N.m (37 lb ft). NOTE: The locating tab on the gasket should always be pointing up
4. Install the new gasket to the adapter.
5. Install the transfer case to the adapter. Refer to «TRANSFER CASE»(/chevrolet/chevy-express-h2500/2003-2003/remont/transfer-case/#transfer-case-removal-installation).
6. Install the transmission support member. Refer to TRANSMISSION SUPPORT REPLACEMENT in FRAME AND UNDERBODY.
7. Remove the transmission jack from the transmission.
8. Check the fluid level of the transfer case. Refer to «DRAINING & REFILLING»(/chevrolet/chevy-express-h2500/2003-2003/remont/transfer-case/#transfer-case-servicing__draining-refilling).
9. Lower the vehicle.

INPUT SHAFT SEAL

Tools Required

1. J 45758 Seal Installer
2. J 36825 Output Shaft Oil Seal Remover
3. J 23907 Slide Hammer

Removal Procedure

Scheme 6

1. Raise the vehicle.
2. Remove the transfer case from the adapter. Refer to «TRANSFER CASE»(/chevrolet/chevy-express-h2500/2003-2003/remont/transfer-case/#transfer-case-removal-installation).
3. Using the J 36825 (2) and J 23907 (1) remove the input shaft seal. (Scheme 6) Poke a hole in the seal using a very small punch. Thread the tool J 36825 (2) into the hole.

Procedure

Note. When installing the input shaft seal, make sure that the part numbers on the seal are facing outward toward the technician.

Scheme 7

1. Position the seal on the input shaft.
2. Using the J 45758, install the input shaft seal in the transfer case. (Scheme 7)
3. Install the transfer case to the adapter. Refer to «TRANSFER CASE»(/chevrolet/chevy-express-h2500/2003-2003/remont/transfer-case/#transfer-case-removal-installation).
4. Lower the vehicle.

OUTPUT SHAFT SEAL (FRONT)

Tools Required

1. J 8092 Universal Handle
2. J 43484 Front Output Shaft Seal Installer

Note. The front output shaft seal is a two piece internal seal. The inner seal is force fit on the front output shaft.

Removal

1. Raise the vehicle.
2. Remove the front propeller shaft from the vehicle. See «PROPELLER SHAFT REPLACEMENT - FRONT»(/chevrolet/chevy-express-h2500/2003-2003/remont/driveshaft-universal-joints/#propeller-shaft-and-universal-joints).
3. Insert a flat-tipped screw driver in the inner race. (Scheme 8) Pry the inner race forward.
4. Insert a small pry bar in the inner race. Pry the inner part of the seal from the outer seal body. Remove the inner part of the seal. (Scheme 9)
5. Insert a flat-tipped screw driver or small pry bar in the space between the outer race of the seal and the transfer case. Pry the outer race out of the transfer case. Remove the outer part of the seal. (Scheme 10)

Scheme 8

Scheme 9

Scheme 10

Installation

1. Using the front output shaft seal installer (2) and the universal handle (1), install the transfer case output seal. (Scheme 11)
2. Install the front propeller shaft. See «PROPELLER SHAFT REPLACEMENT - FRONT»(/chevrolet/chevy-express-h2500/2003-2003/remont/driveshaft-universal-joints/#propeller-shaft-and-universal-joints).
3. Check the transfer case fluid level. See «DRAINING & REFILLING»(/chevrolet/chevy-express-h2500/2003-2003/remont/transfer-case/#transfer-case-servicing__draining-refilling).
4. Lower the vehicle.

Scheme 11

OUTPUT SHAFT SEAL (REAR)

Tools Required

1. J 45756 Rear Output Shaft Seal Installer

1. Raise and suitably support the vehicle.
2. Remove the rear propeller shaft. See «PROPELLER SHAFT REPLACEMENT - ONE PIECE»(/chevrolet/chevy-express-h2500/2003-2003/remont/driveshaft-universal-joints/#propeller-shaft-and-universal-joints).
3. Remove the rear output shaft seal by prying it out with a flat tipped screwdriver. (Scheme 12)
4. To install, use rear output shaft seal installer and install a NEW rear output shaft seal. (Scheme 13)
5. Install the rear propeller shaft. See «PROPELLER SHAFT REPLACEMENT - ONE PIECE»(/chevrolet/chevy-express-h2500/2003-2003/remont/driveshaft-universal-joints/#propeller-shaft-and-universal-joints).
6. Check the fluid level. See «CHECKING FLUID LEVELS»(/chevrolet/chevy-express-h2500/2003-2003/remont/transfer-case/#transfer-case-servicing__checking-fluid-levels). Add fluid, if necessary.
7. Lower the vehicle.

Scheme 12

Scheme 13

1. Raise the vehicle.
2. Remove the electrical connector from the speed sensor. (Scheme 14)
3. Remove the speed sensor and the "O" ring from the transfer case. (Scheme 15)
4. Install the NEW speed sensor into the transfer case with a NEW "O" ring seal. (Scheme 15) Tighten the right rear speed sensor to specification. See «TORQUE SPECIFICATIONS»(/chevrolet/chevy-express-h2500/2003-2003/remont/transfer-case/#transfer-case-servicing__torque-specifications).
5. Install the electrical connector to the speed sensor. (Scheme 14)
6. Lower the vehicle.

Scheme 14

Scheme 15

TORQUE SPECIFICATIONS

Torque Specifications

Scheme 16

Scheme 17

Scheme 18

See also:
• REMOVAL & INSTALLATION - T/C
• DIAGNOSIS - T/C
• PROPELLER SHAFT REPLACEMENT - FRONT
• RECOMMENDED FLUIDS
• TORQUE SPECIFICATIONS
• DRAINING & REFILLING
• CHECKING FLUID LEVELS