Decouplers and Solid Shafts. Pros and Cons?

[keeno]

I will be fitting a de-coupler to the Doka shortly as most of my driving will be on the road. However, when I venture off road I like to go pretty full-on and find as much mud as possible, so was thinking of fitting a solid shaft instead of the VC. Presently, I have a knackered VC in my diff, so switching to solid may be a good answer. My questions are aimed towards the pros and cons of running a solid shaft instead of a VC. Will there be problems engaging the 4 WD on the road occasionally when there is snow and ice? Will the diffs get wound up? I have a lot of mechanical experience, but am relatively new to the whole 4 WD business, so am learning as I go. Any thoughts would be greatly appreciated. Ta

[Aidan]

Provided you keep the tyres rotated and even then occasional 4wd will not massively load the transmission but there will be slight wind up and scrub as there is even with a vc
I've seen some users of decouplers who basically run as 2wd and don't bother with rotation and buy tyres in 2s, but they do experience more wind up in 4wd on road, but don't use it thus hardly, it's amazing how far they can go in 2wd with just a bit of rear locker as required, depends what you are doing with it
I don't run a decoupler and keep it stock to have the shock absorbancy of the vc, but that was a new vw one 3 years ago which is still good, but I will have to buy new tyres this year, only 5 years out of them nearly 40k miles, some life left but won't do another winter, though if it's like this again then MTs for a few months

[syncropaddy]

From listening and looking I formed the opinion that the only real advantage of a decoupler is in sand. I also think that you are adding an extra thing to go wrong.
VW used them on the first few Syncros and then stopped with the exception of a few units to the Middle East. Why?

Fuel economy? No, you'd be a long time paying for a decoupler with the savings there! Tyres wear? Ditto.

Thats only my opinion though ...........

[SyncroSwede]

I run a decoupler with a tightish VC. I have found that it makes the van easier to drive in 2WD (which is 80-90% of the time) as I have no power steering and it saves tyre scrubbing (which I found to be quite noticeable having bought new tyres before the decoupler, I could almost see the wear every week!).

When it's a bit slippy like on a loose track or in the snow, I simply pull the knob and waft up the compressed icy snow in the lane to my house with barely a slip of a tyre. I have then decoupled as soon as I am on the properly cleared road.

The sand issue (if I understand it correctly) relates to those who take their Syncros to the desert/beach dunes who found the initial rear wheel slip prior to the VC engaging was sufficient to dig the rear tyres in requiring a dig out. The solution was to remove the VC and replace with a solid shaft which then required a decoupler to drive on a road etc.

I think the combination of VC/decoupler/solid shaft that each person chooses is reliant on the use to which the vehicle is put. I am probably only 10-20% off road and then only taking it a bit easy (I'm there for the views & solitude etc). So for me, it was worth the expense to buy a decoupler to save the drivetrain unnecessary strain and make the tyres last longer, not to mention the luxury of not needing a (nearly) matching set of four as regards to tread depth. I also had a tight but good VC which helped the decision. I think if I spent a lot more time off road in full on slippy conditions like mud or sand then I might consider the solid shaft but would expect my diffs to explode from time to time! I have found the VC in the snow to be sooo smooth as it seems to seek out the grip with the minimum of slipping. This to me is a good thing as I like smooth.

[syncrosimon]

agree with what Mal said.

The decoupler I believe was developed before the VC and the first syncro was a solid shaft one.

[The BCE]

Interesting thread this, how many people are running decouplers?

[Wolfsburg Willy]

I'm running a decoupler with tight VC on an '87 mTDi Hi-Top. The only check that I make on tyre wear is a monthly depth check to get an idea of rolling radius so that things don't get too far out of kilter. My thinking is that if I need 4WD then there will be sufficient traction slip at the wheels to avoid any wind-up due to slightly different tyre radii. I have toyed with the idea of a steel shaft to replace the VC but I can't see an immediate benefit (I am willing to stand corrected ). I use the van in 2WD 90% of the time (before my first Syncro I was a 'dyed in the wool' Landy driver for over 30 years, so switching 2WD/4WD doesn't seem odd) and the smooth engagement of the decoupler if I need 4WD is a delight. I also like the idea that I still retain the VC function in 4WD. Whether 'to do' or 'not to do' is your choice at the end of the day (I know that the purists amongst us will not agree with the 'hybrid' arrangement and I can see their point) but Syncro-use goes from the extreme off-road end of the spectrum to the 'don't get mud on my paintwork' end and all points in between; so if it suits you and it ain't gonna wreck your van or cost you a Banker's Bonus to do......I say do it!

[syncrosimon]

I love my de-coupler. Gives me confidence in doing long haul motorway work, and my tight VC is just perfect for this weather. Best of both worlds.

[syncropaddy]

This thread will go on for ages.... those who have de couplers love 'em and then there are those of us who cant see the advantage.

[The BCE]

I like threads that go on for ages

[SyncroSwede]

Looking back at your original question, Keeno, I see your VC is toast. Given that a lot of the off roading in the UK is loose stone and gravel with some muddy sections I would be happier with a good VC to let the Syncro work as designed. I would then get the decoupler as an addition to the good VC afterwards. I feel that there is too much risk of damaging the diffs by running a solid shaft and relying on yourself to decouple more frequently when traction is good. In the current snowy conditions I think the (working) VC is the best device to provide grip without winding up your diffs. My opinion but hope it helps.

[keeno]

Thanks guys for some interesting info. I do see the logic in running a decoupler with a good VC as I would then have the best of both worlds. On older Landrovers the 4WD was selectable and when engaged it was locked front to rear. I wonder if the landy guys have the same trouble with diffs 'winding up'...

I also like the sound of a more aggressive VC as it would engage quicker and would work in harmony with the decoupler. Does anyone have a tight VC for sale? I could part exchange my knackered VC which could be used as a core for a rebuild? just a thought...

As stated, the Doka is now my daily driver and I am keen to eek every last bit of economy out of it. I already have fitted a full TDI 1Z motor out of an Audi A4 and the mpg and power is much better than the old JX. Most of my driving will be to and from work, which also involves a nice and muddy green lane. So the 4WD will be used on a daily basis, but with the decoupler I can hopefully reduce some tranny drag on the road and therefore save on tyres and a little fuel. Also, perhaps some wear on the drive train.

The decoupler is on order with Jon at Syncrospares and will be fitted soon. If there is any interest, I could do a step-by-step pictorial of what's involved with the fitting of said item?

Regards, Matt

[Russel]

A tight VC is not a reliable answer as they can slip aswell or permanently open at any time. If you want to go that wrought you need to use a sports VC.
Russel

[KarlT]

I'd be interested in seeing a step by step pic guide.

[Yozza]

Step by step guide with lots of photos sounds good. Excuse my syncnorance, I understand the term 'tight' and 'open' VC, but what's a sports VC?
Cheerz