Viscous Coupling
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[edit] Testing the Viscous Coupling
Volkswagen's original (German) repair manual doesn't say much about how to test the viscous coupling. They only recommend placing the rear wheels in a brake testing stand. If you then switch to the G-gear (creeping gear), the front wheels should move the van out of the test stand as soon as the engine is revving slightly above idle. If the front wheels fail to do so the viscous coupling is to be replaced, Volkswagen says. Volkswagen adds another tiny sentence to this, saying that only when the engine is revving at idle and when the transmission is in G-gear the viscous coupling is able to absorb all the torque to the front wheels and keep them from moving.
To me this last and rather ill-formulated (in the German manual) sentence is the key to testing the viscous coupling. For in most cases we are not dealing with viscous couplings doing less than their share, but rather with hard-going viscous couplings which don't have a problem at all in moving the van out of the test stand with the engine just idling.
Thus the really important thing here is not the van successfully leaving the test stand. On the contrary, the important thing here is the van not moving and staying put in the test stand with the G-gear switched in and the engine just idling. If your Syncro doesn't pass this test your viscous coupling is probably worn out and ready for a replacement. Or put the other way round: as long as your van's viscous coupling is working properly you will not notice your van has got one.
As soon as you are encountering problems with your Syncro when cornering, in particular after a long and fast drive, or as soon as -- despite of power steering -- steering becomes a bit difficult when turning and the Syncro slows down considerably when going round a corner ... as soon as one or more of these things are happening, your viscous coupling is most probably due for replacement. When the tires start whining while cornering it might well be too late already ...
I once had all of these symptoms and it was immediately clear to me that the viscous coupling was the culprit. But it took some time for me to react, and it took some more time for the new viscous coupling to arrive at my door. Should you ever encounter similar problems I would urge you to immediately get under your van and remove the driveshaft between gearbox and front differential. If you fail to do this and wait too long, severe damage to the gearbox and/or front differential is the probable result.
[edit] Life Expectancy of a Viscous Coupling
When I was shopping for a new viscous coupling (according to all reliable sources I contacted repairing them is not economically feasible) I asked several knowledgable people how long a viscous coupling is expected to last. Apart from "it depends" (an employee at Steyr-Daimler-Puch in Austria, the firm which was producing the Syncros and in particular the viscous couplings for Volkswagen) the answers ranged from "some 60,000 km" to "between 170,000 and 200,000 km". Mine was replaced after 150,000 km but I bought the Syncro with 80,000 km on the clock and don't know for sure whether or not this was still the first viscous coupling. But I'm assuming it was.
As for the reason why the silicone in the viscous coupling gets too stiff and starts causing trouble, the people I asked unanimously answered: too much strain. However, this is not referring to relentless off-road driving in groundless mud, but rather to small but permanent differences in rotational speed between front and rear axle while doing normal on road driving. These differences in rotational speed can be caused by such things as unequal tire wear. Tire diameters should be the same within a 2 to 4 mm tolerance. Or, in other words, if you're measuring the tread depths of your tires, the differences should not exceed 1 to 2 mm.
In contrast to tread depth, different tire pressure in different tires does not cause a problem (at least not for the viscous coupling), because tire pressure has almost no influence on a tire's rolling circumference, which is, roughly speaking, determined by the amount of rubber, rather than by the amount of air.
Thus people not caring tire wear, people having mounted different tire brands on the front and rear axles, as well as people never routinely using their spare tire so it gets worn roughly the same way as the other tires are most probably ruining their viscous coupling pretty fast.
[edit] Removing the Driveshaft as an Emergency Measure
If you have to, and provided you're slim enough, you can remove the driveshaft on the bare ground (at least if it's a Syncro 16"), just with a little help of the factory jack. In case your driveshaft was balanced in its current position, it may be a good idea to mark the alignment points of the flanges before removal. Then you'll have to use a pair of 13 mm wrenches (due to space constraints only open wrenches are usable) to remove four bolts and nuts at either end of the driveshaft (sometimes the nuts are only 12 mm). If you want to do it properly you'll also have to loosen (only loosen, don't remove!) the three nuts and bolts (17 mm) which hold the front differential in place via rubber stops, so the front differential can move out of the way a bit for the driveshaft to be removable. However, when lying on the bare ground just below the van this might be hard to do. If your driveshaft has got this rubber element in it you may try to simply use a screw driver and a hammer to cautiously separate the two flanges at one end of the driveshaft. Knocking gently at the flanges at the other end will then take the driveshaft down. As to the rubber element: in diesel and gasoline engined vans the rubber element was facing opposite sides. Thus you'd better take some notes as to whether the rubber element is at the gearbox end or at the front differential end.
[edit] Removing Front Differential to Replace the Viscous Coupling - "The European Method"
To replace the viscous coupling you'll have to pull the front differential first. I don't think it's feasible to replace the viscous coupling right under the van with the front differential in place. In particular, reassembly would thus be much more difficult and would cause plenty of cursing. And you'd have to drain the oil first. By and large, there is no witchcraft involved in pulling the front differential, but you should do it with the van on a lifting platform or above a grease-pit. And it takes two people as well as a floor jack.
First of all losen but don't yet remove the three 17 mm nuts already mentioned which hold the front differential in place. Then remove the speedometer cable as well as the six bolts in each of the inner constant velocity joints. For this bolts you'll need either a 6 mm hexagonal or an 8 mm multipoint socket. If you haven't done it yet you should now remove the driveshaft as described above (however, it's sufficuent to only disconnect the driveshaft at its front end and to secure it using a coat hanger). If you have a front differential lock (never officially exported to the US) unplug it electrically as well as pneumatically (tag the hoses so you can't confuse them later). Now remove the bolt holding the banjo fitting of the vent hose for the differential and then remove the three 17 mm nuts and bolts holding the front differential. Get the floor jack in place and remove the front and rear mounting brackets. Then together with a second person cautiously move the differential forward along the skid plate and out. Look out for the differential lock if there is one.
Place the front differential on your workbench in such a way that the flange for the driveshaft is facing upwards. You can now easily remove the ten 13 mm bolts with which the housing of the viscous coupling is attached to the front differential without risking any oil leaking. Lift the housing which is containing the input shaft. You will now see the viscous coupling itself and a little spacing collar sitting on top of it. Take this spacing collar, grease the top rim of it and again place it on the input shaft in the housing and slightly press it with its greased rim against the bearing so it will stay there. This will greatly ease reassembling the differential later. Now remove the old viscous coupling and put in the new one. Then apply silicone sealing compound to the contact flange of the housing and, inserting the input shaft into the viscous coupling, put the housing back in place. Finally, gently tighten the ten 13 mm bolts crosswise, applying 20 Nm (15 ft lb.), and your front differential is ready to be reinstalled.
Perhaps you should use the opportunity while the differential is still sitting on your workbench to check what has been caught by the magnet at the oil drain plug.
To re-install the front differential in the van simply reverse the steps laid out above. At the very last fasten the bolts of the front and rear mounting brackets as well as the three 17 mm bolts through the rubber stops (apply 45 Nm (33 ft lb.) to these), thereby making sure that the output flange of the transmission and the input flange of the front differential are strictly parallel. The driveshaft is not required to be straight from end to end, but if it is not, it must be "Z-shaped". A "U-shaped" driveshaft may cause resonance vibrations at various speeds.
[edit] Tools and torques needed
Front differential mounting brackets: 17 mm socket and ratchet, perhaps with extension. Use 17 mm wrench to counter at the other side, 45 Nm (33 ft lb.)
Viscous coupling housing: 13 mm socket with extension and ratchet, 20 Nm (15 ft lb.)
Constant velocity joints: either 6 mm hexagonal or 8 mm multipoint socket with extension and ratchet, 35 Nm (26 ft lb.)
Driveshaft: two open 13 mm wrenches (sometimes only 12 mm for the nuts), 35 Nm (26 ft lb.)
[edit] Acknowledgements
Special thanks go to Wolfgang Carolsfeld in Canada <wolfgang@island.net> who not only proofread this text, helped me with some technical English terms I failed to find in my dictionary, and did the math involved in converting the torques from Nm to ft lb, but who also successfully applied the underlying German version of this text to his Syncro to make sure it works :-)
[edit] Addendum #1 (Rebuilding Viscous Couplings)
It was again Wolfgang who pointed me to a firm in California which does in fact repair viscous couplings (as of July 1998):
Weddle Engineering
Performance Transaxle Products
P.O. Box 15466
Long Beach, California USA 90815
Free catalog (562) 598 2731
Syncro transmission rebuilt US$ 1995.00, 2 year warranty at their shop, your transport costs. US$ 600 for core.
Front differential rebuild US$ 1195.00,
Viscous coupling rebuild US$ 595.00, US$ 300 for core.
[edit] Addendum #2 Replacing VC Without Removing Front Differential - "The American Method"
[edit]
For the "American method" you have to drain the oil from the front differential, remove the central driveshaft at least at its front end, and then remove the housing of the viscous coupling. However, before draining the oil make sure you're able to remove the oil fill plug. And be aware that -- due to construction -- you can't drain all the oil. So be prepared to catch the rest of the oil when you remove the housing of the viscous coupling. The beauty of the American method is that you do not have to remove the front axles, or use a jack to lower the front diff from the vehicle, and carry it over to your workbench, and back.
A complete set of instructions follow, with additional comments by world renowned syncronistas in parallel:
No special tools or automotive experience are needed for this job, and because it is so simple, it should not be farmed out to a transmission shop. The best thing I could say, going from memory, is to....
1. Drive van up on 4 ramps
2. Put jackstands under van in case ramps fail
3. Record and mark the alignment of the driveshaft to the front differential so that you can put the same bolt through the same holes of each unit upon reassembly. This will reduce the chances of your ending up with an out of balance driveshaft on reassembly.
3. Unbolt the four forward bolts holding the driveshaft on with either a 1/2 inch or 13mm open end wrench and some liquid wrench. If the 13mm wrench doesn't work that great, try the 1/2 inch open end wrench.
4. Loosen the four 17mm bolts holding the front differential so that differential may be shifted around.
5. Shift the front diff forward so that the driveshaft will fall away from the front diff. Shift that driveshaft out of the way.
6. Remove the oil from the front diff through the oil drain hole. Throw that oil away by bringing it to your nearest auto repair shop for disposal.
Ranier Adds This Comment:
"There's one very important point missing here, if you're replacing the viscous coupling with the diff installed: before you remove the oil
drain plug by all means make sure you can remove the oil fill plug first (the same holds -- of course -- for changing gearbox oil)! If, for some reason or other, you can't remove the oil fill plug, forget about replacing the viscous coupling right under the van."
7. Remove the 13 ish? mm bolts holding the back half of the front differential onto the vehicle and then pop the rear third of the differential off backwards. Do not loosen the big bolt at the rearmost point in the front differential
8. Have something on the ground to catch the residual oil that will spill out.
9. Pull the VC out and replace, being careful to reinstall the little metal washer that is wedged in there. No special tools or measurements of any kind are needed.
Steve Schwenk (sxs@concentric.net) adds this comment here:
"At steps 7-9 it might be noted that it is a little tricky removing the casing to get to the VC. It can hang up on the Diff. mount bar, the one in a "U" shape, and I had to remove that bar to get it off and out of the way."
10. Bolt everything back together, but bolt the front differential down last after shifting it around to properly seat it in relation to the rear transmission. Make sure everything front to back are arranged in a perfect strait line front to back. This is very important, as there are (unconfirmed) arguments that not doing so can lead to excess stress on your VC. When bolting the driveshaft back on, either replace the 4 driveshaft nuts with factory new ones the way VW says to do it (proper way), or just use Red Loctite the way about half the people on the list do it (universal list method) or reuse the original nuts with no loctitie the way the other half does it (pogo stick method; see below).
11. Refill the front differential with GL-5 Transmission oil using the factory specified viscocity. Mobil 1 makes a good GL-5 for the front diff. (Make sure not to use GL-5 in the rear transmission, however, as that takes only GL-4--eveybody wisely uses Redline GL-4 synthetic for the rear.) You can also use the Redline GL-5 or GL-4 for your front differential.
Rainer adds this comment here:
Lately -- at least here in Germany -- VW seems to have issued a new order of the day with respect to gearbox oil. They're now recommending a single new synthetic oil for ALL of their gearboxes (not only Vanagons). It is said to eliminate cold shifting problems, and it is also said to only marginally keep even small metallic particles in suspension.
The new specification is "G50", the weight is SAE 75W-90, and the VW part number is G 005 000 05 for the half litre plastic bottle, and, I
think, G 005 000 for the one litre tin can.
Derek's comment on Rainer's comment:
If you want to try this new oil and try to order at the VW dealer, it is a reasonable thing to do. Nevertheless, I think most experts in America would still go with a synthetic GL-5 in the front and Redline GL-4 in the back, at least pending evidence that the G50 oil Rainer writes of is indeed somehow superior. There is a possibility that the G50 is both much more expensive, harder to get, and no better. There is also the possibility it is much better. At this time, we simply do not know.
12. The entire job should take you about 1 hour. But for some reason --I cannot predict in advance why -- it will actually take you 5 hours :-). Some members have reported broken bolts holding the diff in place, or broken rubber mounts, so be prepared to hunt these parts down if you decide you need to replace them.
13. Some people decide to remove the diff entirely to do this job, commonly known as "The European Method. You can do that, but that means you have to disconnect the front CV joints and haul the front diff out from under the vanagon, all of which is a pain. Still, those front CV joints probably need their grease to be renewed anyway. And as long as you are regreasing the inner front cv joints, you might as well do the outers too, and inspect the boots, and then why not the rears and HEY lets not loose focus here...
[edit] Addendum #3 (Floor Jack Test)
Since all German cars have to undergo a biannual technical inspection which includes measurement of the effectiveness of the brakes, brake test stands are rather common over here. Basically in such a test stand each wheel of one axle is sitting on (or rather halfway between) two drums which can be rotated with large electric motors. When the drums rotate and the tranny is in neutral they will simply rotate the wheels (on a non-Syncro). You can then apply the brakes which will slow down the rotation of the drums and this is measured on either side individually.
If you sit on this test stand with your rear wheels and you've got a rear wheel driven vehicle like a non-Syncro Vanagon and the test stand drums were not locked, you wouldn't have a chance to get out. But a Syncro should get out even with freely rotating drums, provided you're revving the engine at least a little bit.
Since brake test stands seem rare and far between in the United States, some ingenious Americans have invented a variation of this test which includes using a floor jack to lift up both rear wheels barely off the ground and at the same time blocking the front wheels with a 2 by 4. Idling in G-gear the Syncro should stay put with rear wheels rotating in the air, but she should start climbing over the 2 by 4 and drag along the floor jack as soon as you're revving her a bit.
Mind, however, that this floor jack test is by far more risky than the original brake test stand test! Dragging along the floor jack could damage a lot of things on your Syncro!
(The first draft of this article was posted to the Vanagon List somewhen in 1998)
addendum: I belive the article was written by Derek Drew (A. Bell)
