Transfer Case (VG), Function - GF28.10-D-0002HC
MODEL 906.131/133/135/153/155/231/233/235/253/255/631/633/635/637/653/655/657/731/733/735 with CODE (ZG4) Permanent all-wheel drive with gear reduction
General
On vehicles with code (ZG4) Permanent all-wheel drive with gear reduction, the slope climbing ability of the vehicle is increased by the engageable gear reduction (i = 1: 1.432). The gear reduction is achieved by means of a planetary gear set. The permanent all-wheel drive has an additional planetary gear set (in the transfer case) and 2 open differentials (in the rear axle and front axle). The distribution of torque between the front and rear axle is predetermined by the planetary gear set in the transfer case and is 33 % to front axle and 67 % to the rear axle.
The special feature is dispensing with the mechanical inter-axle and inter-wheel locks.
Instead, the all-wheel drive operates together with the electronic stability program (ESP) which is specially adapted to the all-wheel drive.
The ESP switches on automatically if one or more wheels begin to spin on slippery ground.
In these cases it selectively brakes the spinning wheel or spinning wheels or influences the engine torque.
As a result the drive torque increases simultaneously at the wheels which still have adequate road surface adhesion.
Automatic intervention by the brake system by means of ESP can simulate the effect of up to 3 differential locks.
The permanent all-wheel drive increases the number of driven wheels, thus improving tire-to-road adhesion.
As a result, slip is reduced and the driving power is distributed to all of the wheels.
The distributed driving power means that a higher traction and higher lateral stability results at the wheels.
Function requirements for successful engagement of gear reduction
The following requirements must be met:
- Vehicle stationary
- ON signal from all-wheel drive low range button (S76/12)
- Selector lever at position "P" or "N", on vehicles with transmission 722.6
- Service brakes operated
- Change in status (actuated, not actuated) of clutch pedal switch (S40/3), on vehicles with transmission 711.6
- Manual transmission in neutral position, indicated by transmission neutral position switch (S164), on vehicles with transmission 711.6
The LOW RANGE indicator lamp (A1e37) in the instrument cluster (A1) flashes while the gear reduction is being engaged.
If the gear reduction has been successfully engaged, the LOW RANGE indicator lamp remains lit. If engagement of the gear reduction is not possible, the LOW RANGE indicator lamp flashes three times.
If Tml. 15 is OFF, the engaged gear reduction is deactivated.
If due to the position of the gear wheels in the transfer case immediate engagement of the gear reduction is not possible, the shift collar is pretensioned by the torsion spring in the worm gear of the all-wheel drive actuator motor (M88), by the selector drum and by the shift fork. This ensures that engagement of the gear reduction can occur with the next gear wheel rotation.
Possible faults in the permanent all-wheel drive with gear reduction system are stored in the ESP control unit (N30/4) and can be read out there using STAR DIAGNOSIS.
| Transfer case (VG), power flow | GF28.10-D-0002-05HC |
| Front axle differential, component description | GF33.30-D-1000H |
| Rear axle differential, component description | GF35.30-D-1000H |
| Planetary gear set component description | GF28.50-D-1200HGC |
| Transfer case control unit, component description | GF28.19-D-3200HA |
| Transfer case actuator motor, component description | GF28.19-D-3202HA |
| All-wheel drive low range button, component description | GF28.19-D-3151HC |
| Turning angle sensor, component description | GF28.19-D-3204HA |