A viscous coupling installed instead of a center differential, with freewheel mechanism to disconnect the driven axle when braking. Open rear differential. Open front differential.
In normal conditions, this is a front wheel drive vehicle. In normal driving conditions 95% of torque transferred to front axle. Because viscous coupling is considered to be "slow" (some time is needed for silicone fluid to warm-up and solidify), 5% of torque is transferred to rear axle at all times to "pre-tension" the viscous coupling and reduce activation time. The coupling locks when slipping occurs and up to near 100% of torque is automatically transferred to rear axle. In on-road conditions the car will not move if one front wheel and one rear wheel lose traction.
The freewheel segment, installed inside the rear differential, lets rear wheels rotate faster than front wheels without locking the viscous coupling and preventing ABS from applying brakes to each wheel independently. Because of the freewheel, torque can be transferred to rear axle only when vehicle is moving forward. For all wheel drive to work when reversing, a vacuum-actuated "throttle control element" is installed on the differential case. This device locks the freewheel mechanism when in reverse gear. The freewheel mechanism unlocks when the gear shift lever is pushed to the right pass the 3rd gear. The freewheel is not unlocked immideately after leaving reverse gear on purpose - this is to prevent the freewheel from cycling from locked to unlocked if the car is stuck and driver is trying to rock the car by changing from 1st to reverse and back.
Disadvantages of this all wheel drive system are related to actuation time of the viscous coupling. 1: When cornering under acceleration on a slippery surface, rear axle is engaged with delay causing sudden change in the car's behaviour (from understeer to oversteer). 2: When starting on a sandy surface, front wheels can dig into the sand before all wheel drive is engaged.
Figure: Volkswagen Golf MkII Syncro (87KB)
Figure: Volkswagen Golf MkII Syncro power transfer to the rear axle (99KB)
Figure: Volkswagen Golf MkII Syncro rear axle gear unit with visco-clutch, free-wheel unit, and bevel gear differential. (119KB)
Full-time all wheel drive. 50/50 torque split under normal conditions. Multiplate clutch lockable center differential. Optional rear lockable differential. Front open differential. Low gear. Differential locks are engaged by ECU, but also can be engaged manually by the driver. The car is also equipped with Hill Descent Control, Hill Start Assist.
Figure: volkswagen touareg 4motion (35KB)
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There is a small lever on the floor between the driver's and passenger's seat located next to the passenger's seat that shifts between 4wd and 2wd. This switching is purely mechanical. When you put the Iltis into 2wd it goes into rear-wheel-drive. Engaging the 4wd lever will engage the front wheels.
Between the driver's and passenger's seat located next to the driver's seat is another small lever which switches the differential lock in and out. The diff lock is on the rear wheels. This switching is purely mechanical. Diff lock is normally left in the out position.
The super low first, which is labelled "G" on the shifter, is only available 4wd.
Do you own Volkswagen Schwimmwagen Type 166? Can you please make a photo of the car's 4x4 transmission, switches, dashboard lights, etc. and send it to ?
Last changed: 2021/01/01 00:00
There are 4 comments
May 17, 2016 - 19:07
How do I get a print of this great illustration.
Reply to Rob Barnes
May 17, 2016 - 21:13
February 13, 2015 - 07:25
Touareg II has two different AWD system:
4motion, the same with Q7, Torsen center differential
4Xmotion, Multiplate clutch lockable center differential updated from the first generation, which has more powerful off-road capacity
October 12, 2014 - 09:04
I'm Alessandro I've a vwT4 syncro '98 when I insert manually the 4wd system does not turn on the marker lights!
What can be the causes?
Thank you much