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Discussion Starter #1 (Edited)
There have been a number of excellent posts on other forums regarding the workings and potential service of a viscous coupling but it seems that so far no one has touched one from a T4. The only option appears to be either, sending to Walter in Germany (makes an interesting telephone conversation!!) at Dorfbrunnen garage for £1K, buy a new viscous coupling £2.5k (yeah right) or remove the syncro capability (what’s the point in that). However, after much research it appears to me that the T4 coupling is just like any other and has the potential to be refilled and seals replaced. The question is, how do you remove the top? And to this end the mystery is now solved. I managed to acquire a split viscous coupling (long story!) that I have dissected with the view to being able to service the viscous coupling on my van. Below is the process I have come up with and used successfully to disassemble my unit.
On the cast iron side of the viscous coupling, remove the filler cap and most importantly bleed nipple. You will notice the bleed nipple is long and this provides a locking mechanism for the cap. The viscous coupling should not be under pressure but due to various reasons when the silicon has gone bad the pressure increases. So expect a bit of a mess.
Place viscous coupling in freezer. Aluminium contracts more than cast iron.
Unscrew the cast part of the coupling from the aluminium part. Now I have made a tool to unscrew the coupling as it is exceedingly tight because the seal for the coupling is on the other side of the thread and thus I think silicon must enter the thread and hinder the process of opening.


Hey Presto! The viscous coupling is open. Now with a bit of silicone and a few seals you can be back on the 4x4 road ASAP.
I can supply all parts to service your VC yourself or I can do it for you, so send me a PM.
Option
1. Supply DIY service kit includes seals, laser cut tool to open, silicone £130
2. Send me your VC to open and I will post back with a service kit for £160
3. I undertake the full service for you £350

I can also supply the correct grade silicone for £30 per 500gm
The wear sleeve from the outside for £45 (this is not available from VW and is a bespoke precision made item.

I also have a good spare VC that I may consider selling in exchange for one that needs servicing. this is a video of the general procedure
http://youtu.be/VqDiAS6l8mE

I am now recommending you add an anti wear additive to the silicone. This will provide a much more stable unit. If you read the entire post you will see it is likely that vw added anti wear agents to the VC originally, which is why they last 120k miles. After this mileage the silicone does degrade quickly. Without an anti wear agent I would change the silicone annually or after 20kmiles

I can supply the anti wear agent for £35
 

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Discussion Starter #3
A quick update
I have found a place that can make quad seals to my specification, so they are on order. I have started to clean off and inspect the plates and all is looking very good. It took an hour to do about 15 plates so I have a few hours ahead of me yet. The plates alternate one with fingers/one without. There is not really much to these viscous couplings!

Stack of plates


This shows where the filler nipple locates in the housing to lock the cap.


Stack of cleaned plates.... good god it is sticky stuff to get off (wife is not happy about me using all her kitchen roll!! why are they so possessive about kitchen roll?)


Don't panic, the top plate was from the broken VC that I disected and you can see that it is worn and has bent fingers. Now that we know it is possible to crack these suckers open, it is vital that the fluid is changed every 80k as the silicone goes bad and both wears the plates and increases the pressure until it goes pop. Presumably changing the fluid will extend the life of the coupling considerably.
 

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Really?!!

It's just a bleed nipple acting as the lock? Slap me with a side of lamb...I hope that's the case for me. I'm going to have to climb under the DOKA now just to have a squiz as I'm approaching 200,000 kilometres on the clock...

Happily source a seal kit from you if you get it set up someday and would send it to Australia...it'd be my way of thanking ye for having a crack!
 

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Discussion Starter #5
Really?!!

It's just a bleed nipple acting as the lock? Slap me with a side of lamb...I hope that's the case for me. I'm going to have to climb under the DOKA now just to have a squiz as I'm approaching 200,000 kilometres on the clock...

Happily source a seal kit from you if you get it set up someday and would send it to Australia...it'd be my way of thanking ye for having a crack!
Yes the bleed nipple acts as the lock. But the silicone enters the threads and we already know it has amazing shear properties as that is how the VC works and so the cap is incredibly tight, i needed a 5ft bar to give me the leverage to open it. and remember, if you undo the nipple, silicone will start oozing out, as at that mileage it will have degraded and will be under pressure. So don't take the nipple out until you are ready to service.
 

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I'm in the same boat as Seano. This is ringing a bell with something I read about haldex (I have an Audi quattro) There is a company (or person) in canada that sells a different nipple that effectively makes the haldex 50/50. so sounds like your nipple theory is similar.
 

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Discussion Starter #7
I'm in the same boat as Seano. This is ringing a bell with something I read about haldex (I have an Audi quattro) There is a company (or person) in canada that sells a different nipple that effectively makes the haldex 50/50. so sounds like your nipple theory is similar.
The bleed/ filler nipple is simply the retaining pin for the cast iron cap. Without taking out first you can't undo the cast iron cover. It serves no other purpose except for factory filling.
 

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Ian that is top result!T: No one had worked out how to open these vcs. There's a thread on vwvortex of a guy machining the alloy end cap on a Passat vc to open it - I thought this might be the same on a T4 Syncro! It's a good thread http://forums.vwvortex.com/showthread.php?5958346-Viscous-Coupler-SAE-Technical-Documentation-and-Rebuild-Info/page2

Had you thought how to calculate the volume of silicon fluid to refill the vc? I know T25 syncro vcs have to have a volume of air so they aren't 100% filled, as space is needed for the fluid to expand as it heats up. I have a spare vc and can (hopefully) borrow a set of those super accurate scientific scales - I've used them in school to weigh the air in a balloon. That way you can weigh the complete vc then weigh the empty, stripped down vc and calculate the difference. In the vwvortex Passat rebuild they also calculated the volume from the weight and fluid viscosity! I'm only about an hour from you so happy to come over and help out if needed.

However if you have an alternative method let us know. Have you sourced the fluid too?
 

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Discussion Starter #12
Yes I had seen the thread on vwvortex, it was that info that convinced me to have a go. The quoted air gsp amount is 7%, Although there was a conflicting volume on the syncro site saying an 86% fill. However, i think this is too low. I'm expecting the volume of the VC to be around the 300ml mark and I'm just goin to fill the top and bottom with fluid and measure the volume. The silicon is so thick that the volume of the VC less the 7% air gap will be converted to weight using the mass density of 0.97 which is quoted on the side of the silicone Bottle I have. I would be interested to know what your VC weighs to compare to another one I have and to the empty one. The more info on this the more likely we are to get it right. If the amount is wrong I can always open up again, now I know how to do it.

I will let you know if I need any help. If you want to come round I can open your VC for you and you can start cleaning the internals.
 

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Discussion Starter #13
The new wear sleeves are ready. This is the bit that is on the outside and runs in the diff oil seal. It makes sense to replace this as mine had a definite groove.
 

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Cheers Ian I may well take you up on helping to open up my spare vc at some point. I'll get it weighed and pass on the measurements - yes the more info we have the better.

The spare vc is of unknown condition (I got it with a rear diff as a spare from a breakers a while back). I have welded up some metal work so I could turn it using using a bar to workout if it was seized or failed open, etc. It turns with a some force from a bar so it isn't seized. I got the idea from German 'syncro 16' wiki - I'm sure you've seen that rebuild. Next I want to adapt it so I can put a torque wrench on it.

Will follow your progress with interest.T:
 

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brilliant thread and has come at a right time. I am in the process of stripping a syncro with a view to add it to my 2wd van. So since the VC will be off, after a 160k, it would be right to service it, given I know the diff has been previously serviced.

So I like to tinker, dont exactly have a workshop with a vice etc at my house but I manage. Similarly if you need access to my VC to measure weight/fluid just to add more data to the spreadsheet, then I will happily obligue and come round for a brew A: Not sure what help I will be but will do my best T:
 

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The new wear sleeves are ready. This is the bit that is on the outside and runs in the diff oil seal. It makes sense to replace this as mine had a definite groove.
Hello and greetings from Norway.

First of all A: and thumbs up for a job well done! Have you considered to offer reconditioning service for us forum members? If so, that would bee of great! I would like to have this done. My car is getting on with age and the VC have never been touched.
 

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Discussion Starter #17 (Edited)
Hello and greetings from Norway.

First of all A: and thumbs up for a job well done! Have you considered to offer reconditioning service for us forum members? If so, that would bee of great! I would like to have this done. My car is getting on with age and the VC have never been touched.
Well that's a possibility (provided the process works and its early days yet) but I don't have a lot of time and it has taken me 3 hours to just clean all the old silicone off! The actual process is very straight forward. So I am toying with the idea of putting together a kit of parts with instructions so that folks can do it themselves.
See first post for kit options

With all the parts you should be able to do the job in a weekend but I must stress you need to be able to hold the aluminium part very securely.
I am happy to open your VC up and then let you do the cleaning and rebuild for the local chaps. Will post some more pics later.
 

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If this all comes to fruition it will be fantastic and will be great to put an end to that nagging feeling (when my vc goes its gonna cost a load to put right kinda thing)that crops up in my noggin every so often.Again nice one fella keep up the good workA:
 

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Ian you are a brave and resourceful man. We took off our Syncro parts with intention of refilling the coupling but it still lies under the bench.... If you need a 5' bar to move the top how did you hold the aluminium casing without damage to it? Any tips please.

What solvent works for cleaning everything? It looks a very messy business. Put us on the list for one of your kits please. We shalln't be doing it until the winter. Cheers, Andy
 

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Discussion Starter #20
A bit of progress, finished cleaning the disks and whilst her indoors went outdoors to do some shopping, loaded them all into the dishwasher for a final clean :)
Silicone is weird stuff, you can get it all over your hands and yet it just wipes off and a bit of soap and its all gone. I just wiped all the disks with kitchen roll(used 2 rolls) and sprayed some contractors solvent every now and again. I have taken the aluminium casing for a vapour clean so will be sparkly when it returns. I held the casing in my lathe and locked the chuck. An average person may get away with a shorter bar but as I weigh less than 9 stone, I was jumping on the b*gg*r. There are some marks where I tightened the jaws but nowt too bad. It may be possible in a big vice with some wood blocks.


I picked up the quad seals today and o rings, I am assured they are the right ones but they seem big to me. I will have to do some checking on that.



As soon as I get the case back I will need to measure the interior volume. I think I will do this in a variety of ways with the top and bottom separate and then together and compare.
 
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