Hi.
I just help a BMW out with towing him out from som bushes. It has snowed a bit lately. At one moment my 2003 was spinning only at The front tires. And then later only at The rear tires. To me it it seems that The center diff lock is not working. What is controlling The center diff lock, and how does it work? Anyone.
Thx R. -03V td6
-72 Cadillac Coupe DeVille 7,7liter.

The NV225 transfer box fitted to your TD6 uses a Torsen T-2/Type B centre differential. This is a self-contained mechanical unit with no capability of external control.

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Sow i guess its broken or else i would have minimum 35% tracktion on The rear/front wheels? -03V td6
-72 Cadillac Coupe DeVille 7,7liter.

As neither of the final drive differentials have limited-slip/diff. locks this means that if one wheel spins then none of the other wheels will receive any torque. The Torsen differential can’t prevent this. The traction control system therefore relies on controlling the application of the wheel brakes to provide enough torque reaction to cause drive to be sent to the non-slipping wheels.

The later models (’06MY petrol and ‘07MY diesel onwards) fitted with the DD295 transfer box do have an electronically-controlled centre differential which can be locked.

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thx rrphil -03V td6
-72 Cadillac Coupe DeVille 7,7liter.

Yes it's bust, I have all four spinning regularly........ Pete

__________________________________________________
2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Parchment over Navy Interior. Sold
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand, Jet Interior. Sold
2002 L322 Vogue 4.4 V8 Epson Green, Ivory over Aspen Interior (Fatty Offroader) Sold
-Click for Project Fatty off roader-

If you maintained forward momentum I would suggest its working fine.
The torque split can apply either more to the front or the rear, spinning both wheels on one axle is good. Spinning diagonal wheels, cross axle is bad......makes you stop.
Drop the oil take a look see whats going on, if anything at all.

It's highly unlikely the diff is broken, if it was, you would almost definitely hear it!
It is a purely mechanical geared diff, if it's broken then you have metal grinding metal somewhere.

It sounds like it was working correctly but the Traction Control wasn't kicking in properly or helping.

As RRPhil says the centre diff on the earlier cars is a Torsen T2 diff (Torsen = Torque Sensing). It will only transfer torque if there is no slip. If there is slip then it acts just like an open diff and no torque will be transferred.
To get around this you have traction control which will brake any wheel it detects as spinning (spinning means a wheel is moving at a different rate to another wheel, if all four wheels are spinning at the same rate TC won't kick in). If a spinning wheel or wheels are braked then it acts like a wheel is not slipping and the Torsen diff can transfer the resultant torque.
For the TC to kick in you do need to be slightly more aggressive on the throttle than you would compared to any vehicle with locking diffs as it needs to detect a speed difference before it works plus when it does kick in you need to overcome the power loss from a braked wheel (or you could stall the engine, modern systems probably take that into account).

This demonstrates traction control probably the best, although it's a P38 it works same:
https://youtu.be/bE6zvcEf_CY?t=25s
Hopefully you can see it initially got in a cross axle situation where the front right and left rear had no grip and were spinning. It wasn't until he used a bit more throttle that the TC braked the spinning wheels and transferred the resulting torque to the wheels with grip and it moved forward. The same applied at the top of the slope it was just cross axled in the other direction. The trick is to apply just enough throttle so it can move forward without stalling and not so much that it damages the ground and your tyres from a lead foot! Ideally as RRP38 says above you need to make sure you have just enough momentum to clear any obstacle so you don't get in a situation where you get stuck in the first place.

It's also worth mentioning that even a locked centre diff would make no difference in this situation, all you would be locking together would be the two spinning wheels.
This guy hasn't got a clue according to his video title as even a single locked diff would make no difference in this situation, you would need two:

In fact as he has TC all he has to do is accelerate until the TC kicks in and transfer the torque to another wheel with grip and away you go, exactly as per the previous P38 video.

I've always thought of locking diffs this way on a 4x4 in a low grip situation (slightly over simplified but it works): If you have one locking diff then you can only keep moving if three wheels or more have grip. Two locking diffs and you can only keep moving if two wheels or more have grip. Three locking diffs and you can keep moving if only one wheel or more has grip....if no wheels have grip you are going no where no matter what you have

Getting back to the Ops problem, if there is an issue then it's more likely the TC is at fault than the centre diff.
Being in snow did you turn off the TC? That might be your problem, I'm not sure how clever the TC is as some systems the TC is never fully off even if you switch it off.
Bear in mind nothing is perfect, if there is no grip you won't go anywhere no matter what you have (that's why we have winches).

Thats an excellent example of cross axle stall.
So, do we have 4wds?
Poor driving skills will stop even the best equiped 4wd off road and see you passed by even a 2wd well driven.

If he has "just" the front or "just" the rear spinning then there is something wrong... no way it can send power just one way if it's working correctly....

Having said that, if you left the DSC button on then it could have not allowed enough power through to spin the other wheels...

If you are on a slippy surface, it's best to disengage the DSC, this leaves the TC working but doesn't limit power by winding back the engine...

This is on the early cars without terrain response.... Pete

__________________________________________________
2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Parchment over Navy Interior. Sold
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand, Jet Interior. Sold
2002 L322 Vogue 4.4 V8 Epson Green, Ivory over Aspen Interior (Fatty Offroader) Sold
-Click for Project Fatty off roader-

The front or rear can just spin if they have no grip, I've seen before on rollers with an L322, however the TC should eventually sort it out. If it's not sorting it out, perhaps because it's not spinning fast enough to do it as per the video above, then it will sit and just spin, that's the way a Torsen diff works.
If one output side of the centre Torsen diff is just spinning then it will act as an open diff and you will get no torque transfer to the opposite output side. All the torque is spun away on the free spinning side.
It's shown on the Torsen website via a graph:

With one output side on a high traction surface (co-efficient of friction = 1.0µ) and the other output side on a surface as shown on the graph then you can see with no grip (0µ) the Total Tractive Effort is also 0, in other words you're going no where which is exactly the same as an open diff.
It's one of the few disadvantages of a Torsen diff. As RRPhil mentions above they are great for use on tarmac all the while they have grip but as soon as they slip they act as an open diff.

I would have thought it's pretty rare to find a surface with co-efficient of friction of 0µ under both wheels which is why it's rarely seen however I suspect that's what might have happened in Norways case if it was sitting in snow and ice.
What should happen though is the TC should kick in and brake the spinning wheels and allow torque transfer to the wheels with more grip. I'm not sure why that was not happening in Norways case unless the revs weren't high enough for the TC to kick in.