We already published a first status report on the T4 Viscous Coupling in June 2019. Now we want to share the findings of the past year with you:

By measurements of VCs from test vehicles before and after, we were able to find the following:

• In hard terrain, the VC (original setup) runs a large part in the (wear-intensive) hump mode. This high load causes the silicone oil to age prematurely. As a result the hump temperature increases steadily and the viscous coupling loses its effectiveness quickly.

• If you increase the basic torque by 25% from 400 to 500 Nm, the VC is able to master difficult offroad situations without hump-mode. In addition, the VC engages much faster and the front wheels produce significantly less slip. Without hump-mode the VC works practically wear-free because in the viscose-mode the torque is transmitted just via fluid friction.

• Up to 550 Nm basic torque, additional tension in the drive train is practically barely noticeable. From 600 Nm, one will notice significant tension in the drive train, especially with the long wheelbase. The negative effects show particularly  in increased tire wear.

• In tough off-road situations, a basic torque of 600 Nm is not a major advantage compared to 500 Nm. When used exclusively off-road, however, the high basic torque has a positive influence on the service life of the VC, since the hump mode isn’t been needed anymore.

• The high basic torque reduces the load on all components of the drive train in off-road use, as the hump- mode part is greatly reduced. Because the hump sets in suddenly and leads to an abrupt load peak (catapult start), while the viscous friction has a soft engagement behavior.

Here are some examples from before and after measurements of different test VCs:

VC4008 Mixed driving; Mostly driving long distances

425 Nm – Standard VC after 150tkm / 2.5 years +2°C hump-temperature (without practical relevance)

503 Nm – Sport VC after 15tkm / 2 years No increase measurable (within the tolerance range)

VC4017 Just driving Off-Road on a daily basis (forestry-working)

600 Nm – Super Sport VC after 5tkm / 0.5 years No increase measurable (within the tolerance range)

We think we have now finally reached our goal we are aiming at since late 2016:

• Develop a robust and durable VC for the T4 Syncro
• Make the T4 Syncro a real all-wheel drive vehicle

We are now satisfied with the test results for the first time. We would never have expected such a great outcome! Now we are convinced that we can offer the professional overhaul of the T4 VC by mid-October 2020.