Transfer Case (VG), Function - GF28.10-D-0002HB
MODEL 906.131/133/135/153/155/233/231/235/253/255/631/633/635/637/653/655/657/731/733/735 with CODE (ZG3) Gear reduction for all-wheel drive
General
On vehicles with code (ZG3) Gear reduction for all-wheel drive, the slope climbing ability of the vehicle is increased by the engageable gear reduction (i = 1: 1.432). The gear reduction is achieved by using a planetary gear set.
The engageable all-wheel drive has an additional planetary gear set (in the transfer case) and 2 open differentials (in the rear axle and front axle).
With the all-wheel drive engaged, the distribution of torque between the front and rear axle is predetermined by the planetary gear set and is 33 % to the 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 engageable 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 all-wheel drive
The following requirements must be met:
- Circuit 15 ON
- Vehicle speed under 14 km/h; engagement must have been completed before the vehicle exceeds 14 km/h
- ON signal from all-wheel drive engagement button (S76/11)
- ESP not active
- Engine torque is below certain limit value
During engagement, the light emitting diode (LED) in the all-wheel drive engagement button flashes and the ESP indicator lamp (A1e14) lights up briefly.
If the all-wheel drive has been successfully engaged, the LED in the all-wheel drive engagement button remains lit.
On vehicles with code (JK3) High-end instrument cluster standard with speedometer in km, the message announcing that the all-wheel drive has been activated appears on the display (A1p1) of the instrument cluster (A1).
If it is not possible to engage the all-wheel drive, the LED in the all-wheel drive engagement button flashes three times.
Function requirements for successful engagement of gear reduction
The following requirements must be met:
- All-wheel drive engaged
- 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 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.
The acceleration slip regulation (ASR) and the ESP are unavailable while the all-wheel drive is being engaged. The antilock brake system (ABS) is available.
If Tml. 15 is OFF, the all-wheel drive is deactivated. If currently engaged, the gear reduction is also deactivated.
If due to the position of the gear wheels in the transfer case immediate engagement of the all-wheel drive or gear reduction is not possible, the respective 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 appropriate shift fork. This ensures that engagement of the all-wheel drive or gear reduction can occur with the next gear wheel rotation.
Possible faults in the all-wheel drive 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-0002-05HB |
| 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-1200HGB |
| Transfer case control unit, component description | GF28.19-D-3200HA |
| Transfer case actuator motor, component description | GF28.19-D-3202HA |
| All-wheel drive engagement button, component description | GF28.19-D-3150HA |
| All-wheel drive low range button, component description | GF28.19-D-3151HC |
| Turning angle sensor, component description | GF28.19-D-3204HA |