Hi guys,

As I'm sure you're all aware, the viscous coupling inside of a transfer case can send maximum about 90Nm of torque to the rear shaft at operating temperature. That's factory settings.

Now, people at Dorfbrunen Garage can upgrade the viscous coupling (they say they upgrade the whole transfer box, but I'm not sure what else there is to upgrade anyway) so it can send 180Nm of torque to the rear shaft. I think cav16.co,uk does the same thing in the UK (cause he's a partner with Dorfbrunen).

Anybody here has the upgraded viscous coupling?
Any noticeable differences?

Anybody here tried to open the viscous coupling?

How do they upgrade it? Adding more inner and outer rings or placing a thicker silicone liquid... or both?

Seeing the graph here http://www.cav16.co.uk/vc.htm makes me think could it be possible to transfer more torque to the rear by simply implementing an oil cooling system?

What do you guys think?

Yup... I'm pretty sure I have every detail of Qrew's Calibra videos in my head by now

Do you have a rear LSD or std open diff? I'm currently chasing an LSD one from Omega (you guys in UK call it Carlton) and I'm curious what difference will it make on rear LSD. (I know I should probably look for Quaife front LSD first, but that's a bit expensive and will have to wait)

Now.. you mentioned upgraded case and internals... Upgraded how? Machined from scratch from a different material? What material?

I have opened my TXB now after 2 years (had the clutch plates and hydraulic piston replaced 2 yrs ago) and I didn't see the smallest piece of metal or any metal dust on the magnetic plug. I also inspected all the gears... not a single sign of wear. It has been 2 years of driving... 80% city, 15% highway and 5% track & drag.

That's why I'm curious to find out WHY exactly internals need to be upgraded and how?

to further answer your question, I only have standard diffs front and back.

What you have to consider is that with 4x4 then really you would want the front and rear diffs to be the same otherwise you have drive to the diagonal wheels (either front right with rear left or other way round) which would not be that great when cornering.  Therefore I would personally want a front and rear lsd or both open diffs.

So which would I prefer?

 I personally wouldn't want a front lsd, as the transfer box only transfers torque to the rear wheels when there is a difference in rotation between the front and rear wheels.  If you have a front lsd then you can push the car much further in grip before the front wheels start to slip and the transfer box starts to engage, therefore you are turning the car from a 4x4 car into more of a front wheel drive car.  Therefore I wouldn't want to run a front lsd as would rather have the 4x4 engage, and for reasons stated above therefore wouldnt want a rear lsd either.

I don't think anybody on this forum will be able to answer that question I am afraid mate.  I would suggest posting that question on vauxsport.com where Qrew sometimes visits (maxxtuning Sweden) who will be able to answer that.  Yes with a higher viscosity liquid you will be able to transfer more torque but do you know if the standard coupling casing can handle the increase in resultant pressure?

Most silicones are shear thinning liquids , some dont change under shear forces, what you need is a specially engineered one that shear thickens, i think those fluids wouldnt work ( we have filled many grades of silicone oils for use with model cars for companies in the model trade and they didnt seem to shear thicken at all as we filled them ( i never looked up the shear properties! ))

There is a to a supplier that sells bottles of the stuff used in the viscous coupling used on VW 4x4 camper vans ,I found it through a VW forum that were rebuilding couplings

http://www.dieselkontor.de/product_info.php?products_id=3022

Just vary the amount for different torque

If the fluid is the same ( quite likely ) weigh the full coupling and then wash it out and weigh it, then add new fluid till its back same weight and test it to see the torque transmitted   

Two questions for mic43:

1. What is this small bolt used for (it's 2 mm allen, and beneath it there is a small steel ball)


2. Once you have the tool (from the above picture), should you turn it clock or counter clock wise? (I made the similar one, but looks like I need a longer pipe)

Any feedback for the silicone fluid that you used?