The other day I could examine another tiny part about the “oil-sucking” issue. My understanding is, that it’s a design failure, where the extrem high thermal expansion of the silicon oil causes the problem at low temperatures during winter. Therefore this problem would remain, also at new overhauled VC. And such a piece of evidence came across, but let’s begin in 2015…
Anybody who already opened an old VC knows what I mean – the offensive smell of the deep black silicone fluid. But why does it stink so badly?
After having tested a so called baking oven VC months ago, I decided to test another one due to verification resasons.
I got the baking oven VC from a german guy who cooked it at 120°C with a 60K silicon fluid.
After the first minutes of the testrun I was absolutely sure, that the VC is missing a lot of fluid, because the chart was much to low for a high 60K viscosity. During the testrun, the air in the VC is mixing with the silion oil as tinny bubbles – which looks like super sparkling mineral water. These tinny bubbles in the fluid reduce the shear force of the silcone oil:
more air = more bubbles = lower effektive viscosity
At a temperature of 135°C the teststand stops automatically for safety resasons. After a short cooling break, we did another testrun at a higher temperature of 155°C – that’s the maximum temperature that should not do any harm to the X-ring sealings. But there was not any signs for a Hump.
I refilled the baking oven VC with 12,5K silicon oil to find out the amount of missing fluid. All in all 20,3g (!) fluid was necessary to get the VC in the correct range of tolerance. Two gram silicon oil increases the hump-temperature in 8°C. This means, that the baking oven VC would have had a theoretical hump-temperature of 200°C. But that’s just theortical, because practical the X-rings would have been damaged at these high temperatures.
It’s not always that simple, even if it seems so. Some thoughts why the baking temperature can’t be identical with the hump temperature can be found in the last section of the first baking oven test we did months ago.
In the last weeks I got a few inquiries regarding due to the activation-time of a viscous-coupling.
Typical questions looked like these:
- How fast activates a working VC?
- My VC activates after 20sec / 5 wheel turns – is that ok?
Altough the overall impression of the Visco Werkstatt (regarding the homepage) has been quite silence the last weeks – the opposite is true. Since a few days the Visco-Werkstatt has moved in a completely new home.
After a bunch of inquiries on how to remove a VC, we decided to document the process of replacing a broken VC.
The background for this approach is the official “VW Vanagon Factory Repair Manual”.
After improving the Viscous-Coupling of the T3-Synro with a special valve and solving the oil-sucking-problem I was thinking about how to make our VC even better.
In order to test the accuracy of the baking oven method for overhauling viscous couplings, I ran an extensive test session on one of these units on the test rig. This posting documents the results of the session and also gives you an insight on the technical backgrounds.
In order to prepare my Syncros for longer rides, I decided to install a convertible roof – the Westfalia Mosaik retrofitting convertible roof. This posting shows how I prepared essential components that were missing (roof frame) in order to install the roof.