Rear Drive Axle Description and Operation
The rear drive axle assembly in this vehicle consists of an aluminum housing which contains an electric clutch which is located in the driveline torque tube (for vehicles equipped with all wheel drive AWD only) and separate from the rear drive. The differential fluid is only contained in the rear drive axle portion of the rear differential assembly.
The clutch assembly for AWD vehicles is serviced separately from the driveline torque tube assembly. The clutch control module (CCM) is located on the torque tube housing and is also serviced separately.
The clutch assembly contains automatic transmission fluid (ATF). There is a seal that protects the driveline torque tube from the ATF contained inside the clutch assembly. Another seal protects the clutch assembly from gear oil.
The fluid level range for proper rear drive axle assembly operation is 0.8 to 1.0 liter depending on the housing design (location of the fill/inspection pug). New service replacement units will be shipped dry (without fluid). Fill new units with 0.8 liter of GL Synthetic fluid. More importantly, the minimum fluid level should be even with the bottom of the fill hole.
The driveline torque tube houses the third section of the propeller shaft for packaging purposes only. There is one bearing at each end of the torque tube assembly.
The rear drive axle system operates as follows:
- System distributes torque evenly between the 2 rear wheels.
- The system distributes torque to the rear wheels to enhance traction and improve vehicle handling performance.
- The rear differential clutch control assembly contains a main clutch, pilot clutch, electromagnetic coil, rear wheel shaft, main cam, pilot cam, and temperature sensor.
- The clutch control module operates by utilizing a clutch pack for transferring torque. The engagement mechanism consists of an electromagnetic coil and armature which modulates torque through a pilot clutch and thrust amplification device.
- The rear differential has a micro computer which receives information from the clutch control module (CCM).
- The CCM reads an internal temperature sensor, which will maintain consistent and continuous temperature compensation for torque transfer from -40°C to +120°C. When the temperature of the rear differential is determined to be beyond its limits, the CCM will temporarily disable the rear drive system and turn on the AWD Disabled message. When the temperature of the rear differential is back within the limits, the CCM will enable the rear drive system. The temperature sensor and coil are internal to the rear differential, and is replaced as an assembly.
- If the vehicle is being driven very aggressively, and or an unexpected tire size has been used, the AWD disabled message will be turned on. This should not result in the replacement of CCM module.
- The AWD disable message will be turned on if the mini-spare tire or a very small sized tire has been installed. This should not result in the replacement of CCM module.
- The clutch coil receives current from the CCM which is used to modulate torque through the use of the engagement mechanism. The greater the current the greater the torque. The safe current range is between 0.1-3.0-amps. If the current range is not within those values we have DTCs that set and the Service AWD message will appear. The temperature sensor is internal to the differential, and is serviced as part of the assembly.
- The module uses vehicle speed, steering angle, wheel slip, thermal compensation, and chassis control intervention to determine current. These are messages on GMLAN from other modules.
- Replace the CCM, the CCM needs to be configured for the clutch control calibrations. The connector on the clutch (that plugs into the CCM) will have a 2 digit value. Use that 2 digit value to program the CCM using the Tech 2.
- Voltage for our module is between 5-24 volts. We set a low voltage code but not a high voltage code as we can withstand a voltage up to 24 volts.
- Displays 2 messages in DIC or IP. Amber AWD Disabled (All Wheel Drive Off) - DIC Service All Wheel Drive.