# 4MOTION torsen drive train problem



## Dangerrous (Sep 14, 2014)

I thought I was going to give the car a surgery rest but no!

This has always been a niggle when driving the car. If you pull away on full lock ie. out of a turning, there's a shudder/ripping sensation from the rear drivetrain. Unfortunately this phenomenon plagues all torsen 4 wheel drive systems, the planet gears in the torsen mid diff engage too quickly locking up the front and rear drive. The early landrover transfer box was a constant 50/50 unit and would give the same result, but in it's very nature this was never a real problem. Four wheel drive in a luxury sedan whether it's an Audi A6/8 or an inline Passat or a Phaeton, is a PITA. There are several remedies depending on the severity of the lockup.
1) new box, which has the torsen diff as part of the unit- several cases of Audi's being done under warranty
2) new torsen planetary diff replacement- I didn't read of any cases
3) oil check/change on all diffs - some notes on the Passat and Audi forum, positive results were given

I read with interest the changing point of view regarding the diff oil type, THE CORRECT VW SYNTHETIC OIL MUST BE USED, a representative and VW owner swears by AMSOIL, whilst others hint that although amosil say their oil meet the vw specs, VW don't endorse it, other widely used manufacturers are redline and royal purple, I'm sure these are good oils, but I'd like to know who makes VW stuff and if I can purchase it.

I've yet to track down a vw equivalent specified oil, but at a retail price of around £40litre you can understand why I'm looking, 
ZF instructions note that there are 4 gear oil fill points, they being front diff, rear diff centre transfer, and torsen diff. The front and rear diff have their own synthetic grade, whilst the centre transfer and torsen diff have a different type, again with reference to the slip properties of the designated oil




Transfer case total filling (separate) 0.528 liter SAF - AG4 1016
0.022 liter STURACO FM 1992
Transfer case in combined transmission 0.528 liter SAF - AG4
0.022 liter STURACO FM 1992
WARNING:
The "STURACO FM 1992" additive is only needed after renewal (exchange) of the Torsen differential.
After assembly, pour the additive directly (axially) into the Torsen differential with the transfer case in a vertical
position.


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## cbh123 (Aug 25, 2013)

I wrote to ZF on this subject.. 
here is their reply

for further processing of your request, we kindly ask for the following information:

Oil in Differential

The oil in the differentials are not shared with the transmission. It is a separate type of oil that goes into the differentials. 

If you have a VW Phaeton the same oil is used for a 5speed or a 6speed transmission

-Filling front axle differential with transmission oil Castrol SAF-AG4 -Filling rear axle differential with transmission oil Castrol SAF-AG4 Q (SAF-AG4 + 4% FM Additive)

does not mention centre diff.. however I am pretty sure that SAF-AG4 is redline equivalent - except it need the "Q" friction modifier - redline also sells the friction modifier in the diff oil section 

http://www.redlineoil.com/product.aspx?pid=46&pcid=7


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## Gabs08PHTN (Jan 6, 2011)

cbh123 said:


> Filling rear axle differential with transmission oil Castrol SAF-AG4 Q (SAF-AG4 + 4% FM Additive)


I think that what ZF refers as "rear differential" is the actual torsen diff, as it is an integral part of the transmission. Also, in the ZF TE-ML 11 German edition, the torsen differential is referred as "Hinterachsmittendifferenzial", which means something like rear axle center differential.
The Sturaco friction modifier can be obtained from Mercedes Benz as part Nº A0009898203, and also from ZF as part Nº ZF S671_600_020.
I hope it helps.

Gabriel


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## Dangerrous (Sep 14, 2014)

Thankfully I'm not thinking of changing the torsen yet, I'll have a look for the correct oil today. Sorry I didn't clarify that the zf rear diff is the torsen and not vw's rear drive diff
Darren


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## n968412L (Apr 23, 2009)

Dangerrous said:


> the planet gears in the torsen mid diff engage too quickly locking up the front and rear drive.


Hi Darren - could you elaborate on this - do you mean there's something about the behaviour of the diff that, I assume, is putting too much torque to the back wheels? I didn't imagine there was any engagement involved in the sense that the gears in the diff are all permanently engaged with each other... but I think their relative ease of motion/friction is what determines the transmitted torque.... which does sound like a factor where the oil will be very significant.

Just trying to refine my mental picture of all this....

Regards

M


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## Dangerrous (Sep 14, 2014)

As far as I'm aware from technical explanations, the torsen diff has a measured tolerance on slip which is mechanically and oil slip specific, once the slip differential exceeds the mechanical tolerance the torsen drive locks, if any of the exacting tolerances on normal operation are not met the torsen control starts to lock up prematurely, this in turn puts the front and rear drive into the same wheel speed ratio 50/50. If you turn from standstill the difference of the front speed to the back speed is enough for the torsen drive to act, if you increase the torque delivery the torsen will lock the ratio delivering the same speed to the front and back drive, something has to give, this will be the rear inside wheel which is fighting for grip, but being forced to go round faster by the 4 wheel drive system, hence the shudder. The oil acts as a buffer reducing the effectiveness of the torsen drive, this allows (as long as the torsen is mechanically sound) it to negotiate comers without locking up the rear. 
I suspect the oil is past it's best and although still lubricates the torsen it's allowing it to lock up too soon, hence my shudder.
Going through all the various forums regarding the torsen drive I have not come across any failures, this has lead me to believe that the oil is suspect, just as my ATF proved to be. Remember this P has had minimal 'lifetime' fluids changes if any. Again I would like to think that such a complicated piece of machinery may have a schedule attached, there's plenty of info on how to change the oil.

NB
By saying 'lock' I mean reducing slip and sending biase torque to the front or rear.

This is how the torsen works in my head, and the possible solutions may help with my problem. I'm quite surprised how many people complain about the shudder and just except it as part of the 4 wheel drive system.
Darren


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## n968412L (Apr 23, 2009)

Dangerrous said:


> As far as I'm aware from technical explanations, the torsen diff has a measured tolerance on slip which is mechanically and oil slip specific, once the slip differential exceeds the mechanical tolerance the torsen drive locks, if any of the exacting tolerances on normal operation are not met the torsen control starts to lock up prematurely, this in turn puts the front and rear drive into the same wheel speed ratio 50/50. If you turn from standstill the difference of the front speed to the back speed is enough for the torsen drive to act, if you increase the torque delivery the torsen will lock the ratio delivering the same speed to the front and back drive, something has to give, this will be the rear inside wheel which is fighting for grip, but being forced to go round faster by the 4 wheel drive system, hence the shudder. The oil acts as a buffer reducing the effectiveness of the torsen drive, this allows (as long as the torsen is mechanically sound) it to negotiate comers without locking up the rear.
> I suspect the oil is past it's best and although still lubricates the torsen it's allowing it to lock up too soon, hence my shudder.
> Going through all the various forums regarding the torsen drive I have not come across any failures, this has lead me to believe that the oil is suspect, just as my ATF proved to be. Remember this P has had minimal 'lifetime' fluids changes if any. Again I would like to think that such a complicated piece of machinery may have a schedule attached, there's plenty of info on how to change the oil.
> 
> ...


Thanks Darren - all perfectly clear - and accords with my mental model of the torsen diff. I'm probably the least best person to detect this - I could barely tell when I'd got four wheel drive selected in my Landrovers... and these were Series IIs - with just a solid lock up between front and rear prop shafts.... The only time I noticed any handling oddities with those was on a couple of occasions when I snapped a rear half shaft. Fortunately the design allowed (by pressing the yellow knob!) me to drive home using the front axle... but a front wheel drive Landrover without constant velocity joints definitely didn't feel like the normal rear wheel drive verson!

But I'll be practising some starts on full lock now to see if I can detect anything...


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## Dangerrous (Sep 14, 2014)

Finally got round to having the torsen drive fluid changed. I had looked into the genuine oil from VAG £125 per litre! Alternative sources desired. Redline and Royal purple have a good reputation, I emailed redline, as their products are readily available in the UK and they came back to me with the correct oil with the friction modifier already added.
I can only go by the advice of the technical team of Redline but they pointed me toward RED LINE Synthetic Gear Oil 75W-90 GL5 about £20/ltr

Due to the complexities of this oil change I trusted this job to a mechanic I know, he changed the oil (removed gearbox mount etc.. for access) I've now done the recommended 100mile bedding in.

The shudder has gone, I thought it was still there but it was just a rough road with loose stones, well pleased 

I think my bucket list on this car is finally at a point where I can drive it without something niggling me in the background. V happy
D


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## snapdragon (Aug 8, 2006)

New oil cured mine too - I used this one on all 3 diffs...
http://www.opieoils.co.uk/p-982-fuchs-titan-sintopoid-fe-sae-75w-85-fully-synthetic-gear-oil.aspx


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