Sometimes I learn things the hard way...DE-COUPLER KABOOM

[tencentlife]

If you want to really check the pinion bearing radial play, here's an idea: up on stands, handbrake on, nose cone off, trans in 4th gear. Have a helper put a wrench on the crankshaft pulley bolt (30mm) with a long lever and try to turn it back and forth while you are below looking for movement. They'll have to work it pretty hard, remember there is over 100ft.lb. going down that shaft normally. This will simulate the sideforces inside the gearbox that wallow out the shaft bearings, by putting hard torsion directly into the 4th gear pair; that's the pair that beats the forward bearings as the torque makes the gears try to push apart from one another. You might turn up play this way that you wouldn't be able to simulate by hand; remember there is another pinion bearing just a couple inches behind the forward one on a Syncro trans, which may thwart your efforts to establish play by hand. Doing what I describe generates forces inside the gearbox that you will not be able to simulate from outside.

I would try it in 4th gear first, then also engage G and reverse since those gears are in between the two forward pinion shaft bearings.

Curious to see what you find out, but my opinion is that no amount of imbalance or misalignment of propellor shaft or CV axles that you could stand to drive down the road with could result in the trouble you've described. And just because it works well with the standard nose cone back on isn't conclusive, that would be comparing an apple to a pomegranate.
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[gears]

[Classicvibe]

[tencentlife]

I'm just saying that between the front end of the pinion shaft and the output flange stub, you have a different assembly, that connects to the pinion shaft in a slightly different way, and is able to rotate independently of the output flange when disengaged. I'm not saying that what you observe by putting the stock nose cone back on means nothing, just that it isn't conclusive of anything. You need more data to make any meaningful determination. It's a basic logical distinction, there are other variables that that doesn't account for. You're not swapping one component for another of the same, therefore apple to pomegranate (because a pomegranate is a "Granada Apple", which is closer to an apple, namewise at least, than an orange is. But I digress...).

There is the possibility that if the locating pins were omitted, the nose cone could shift a bit and that would cause a tight and true-running pinion shaft to wallow out the decoupler spline or guide bushing if it ends up being off-center. But there are so many bolts holding the cover on that I think it would stay where it was bolted even under heavy lateral loading, but without the locating pins how would you know it was installed on-center in the first place? Once again, though, the omission of guide pins would be an installer error, sorry to say. And so far as I know, yours were where they were supposed to be anyway.

If you did have loose front and center pinion shaft bearings, I would think you would have some whine in the top gears, 3 and 4, but the gears would probably still engage smoothly. When I sent my Syncro trans off to Daryl, with about 170k miles on the OEM build, the main gearcase had to be replaced because the shaft bearing housings had wallowed out. He says that is very common. But I don't know for sure whether it was the main or secondary bearing housing that had gotten beaten out, or both. I'm presuming it was the forward bearings because the spreading force is greatest between the taller gears as I understand it. But I'm not a trans guy so consider what I say with the appropriate skepticism, like the kind I have when dweebs go off about engines.
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Please don't PM here, I will not reply.

Experience is kryptonite to doctrine.

[JED THE SPREAD]

Why do you lot love decouplers so much? it takes the syncro out of the syncro as far as most of us think in the UK. You buy a vehicle that has this amazing early 80's technology way ahead of its time to take away the forward thinking of off road driving, complimented with diff locks then fit a product to take all that away and complane when you fit a Japanese engine in a german van that is not ment to be in that messes your van up?

I dont get it

Ok i know VW popped the odd decoupler in here and there for a specialized market, And I also know of the sports or solid VC. I can understand why you would want a decoupler under these conditions but why for road trip use etc...

What is the point in spending x amount of $ on something that makes your van for those who actually go off road less capable

jed
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[gears]

I really think Simon's insight is spot on. (Of course only the OP knows if the sleeves were omitted). The forward pinion needle roller bearings don't really "fail" in the same dramatic fashion as say, a mainshaft ball bearing will. There would have had to have been missing rollers to contribute to this failure.

I feel that this should serve as a lesson for the supplier, too (of course it isn't a "lesson" for them unless they suck it up for the replacement bits). The locating sleeves are typically removed when the output housing ("nosecone") is located on a mill for machining. Sometimes they are damaged in the process of removal. At any rate, the supplier should be making certain that any housing returned has two installed locating sleeves, even if the core was received without them. For the cost of this kit, what's another couple bucks?

... and I think you're paying too much for the decoupler kit. You're definitely being bent over for the replacement parts. JMHO

[BushChicken]

[syncrosimon]

[JED THE SPREAD]

[JED THE SPREAD]

[syncrosimon]

[gears]

Well, let me tag along next time you go to the horse races ;>)

Think about it ... Would you install the intermediate housing without the dowel pins? Without the locating pins (or sleeves), your chances of the two housings aligning perfectly and staying there are low. "How Low" is anyone's guess.

[Classicvibe]

Tencent and Gears and others, thanks for the brainstorming. Let me respond to narrow the scope being considered here:

[gears]

Gee, I almost would have put money on those locating sleeves being absent. Oh well ...

Since the supplier and seller haven't ever seen anything like this, and since the seller's "bearing theory" doesn't really hold water, it sounds to me as though you're getting shafted (because of the high price you're being charged for replacement components).

Unless, of course, there was insufficient lubrication (low oil level), or the 1-way check valve was omitted.

[syncrosimon]

Just another idea, if you installed the de-coupler and to do so loosened the front diff mounts to allow the prop to drop, then forgot to re-tighten the three 17mm bolts and went for a drive, if you hit the brakes real hard would not the weight of that front diff pull on the decoupler, fracturing it? This would also cause the wear that the group refer to, as the de-coupler would be jarred to one side (it is not symmetrical). This would also explain why your old cone would work fine.

Just a thought. Perhaps a sliding yoke prop would eliminate this? It's more spendy though, but you got this far.

Simon.
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[syncrosimon]

[syncrodoka]

[syncrosimon]

Plus you can jack up a wheel and spin it, like for setting the hand brake, or for doing up those CV bolts and prop shaft bolts.

You can feel how much less stress there is in the system in 2wd. You just dont need 4wd on a dry freeway.

You can get towed by a regular tow-truck.

You can park so much easier, especially if you dont have power steering.

At the vehicle testers you can put the brakes on the rollers for the regular 2wd test.

The third knob on the dash looks cool.

It's about as expensive as a VC, and will make a good VC last many years longer.

Most modern vehicles will have some form of automatic de-coupler in the gearbox, as it is best to do it this way, and you dont need 4x4 to park your car at the Mall.

It does not matter what tyres you use, and can pick up a spare which would heat a VC on the motorway, if you have a puncture or two.

For high miler's de-couplers are essential.
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1991 16" 2.1 DJ Syncro factory hightop ex Finnish Army Ambulance, now sold.
Thinking about Thing or 181 (182) ownership.

[Classicvibe]

Hello all,

It seems that a group of us have come to a "most likely" scenario. To simplify what has happened:

1) Drove for a while on stock nose cone
2) Replaced stock with new decoupler
3) Did not couple because VC was shot
4) Driveline comes off, then on (removing for various reasons not related)
5) Within weeks, decoupler cracks around interior of bolts
6) Install stock cone and continue cruising without issue (with driveline attached) for weeks/months
7) Removed driveshaft for balancing
Driveshaft was indeed out of balance (January, 2011)

So from this scenario (which has been duplicated by a few others), we gathered that the difference between the two set ups is indeed the obvious...one was coupled and the other, not. It sounds like those who have reported the same incident noticed vibration or increased vibration when de-coupled.

I could ramble on about what I think is happening, but I just got an email from someone much more eloquent, saying the same thing (I removed his name because I didn't ask to copy his comments here. He will chime in I am sure if things get weird):

"As for decouplers breaking with bad drivelines..I have only seen 1 stock nose break and heard of several (like 5 guys) non-stock powered vans that have broken multiple decoupler housings. My theory is if coupled, they will not break them but if un-coupled there is the potential for the pinion and decup shaft to vibrate more with a driveline issue. Coupled, they have the slider internally keeping the 2 shafts in sync and de-coupled they are separate entities even though there is a sleeve of bearing to theoretically keep them lined up. No absolute proof, but seen too many recently to believe otherwise."

This fits the scenario well, and became my number one choice once I verified my drive line was whacky. There is still a chance I have another issue, but there is no doubt the driveline had a wobble to it. I should mention the U-joints felt fine. I did have one replaced, but in the end, the wobble was 99% due to a balance issue caused by inconsistencies in the metal skin.

Anyway, the "how things work" about metal shrinkage and expansion on your driveline may be good conversation for a different thread. All you need to know is, listen for a wobble and have your driveline checked periodically regardless (they don't all make noise!). This is a must for installing a de-coupler for the first time, and as for driving de-coupled, well, it seems your chances of failure may be greater than coupled driving. Cracks in your decoupler are not the end of the world because they can be welded fairly easily. The whole process just blows however, so keep your wobble to a min. Let me be clear, this is just a theory, but the physics of it all are there, and I cannot think of another (better) theory. There are smarter folks giving credence to this as well, so for now, I like it.

The worlds most expensive 2wd is about to get locked and loaded YO! I have actually never had a functioning AWD or 4wd on this thing (it took me a while to figure out my VC was jacked). I will install the straight shaft once I get my repaired decoupler back and then try my hand at rebuilding the VC (posting the experience here of course).
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