Audi Center Diff FAILURE

[Mazur]

Last week at the Lincoln competition we had an interesting diff failure.

After the auto-x event we had the rear of the car on jackstands and one of the members noticed that we could move one of the wheels a large amount without affecting the differential or opposite wheel.

When we took the diff housing apart and removed the torsen unit we found a lot of metallic debris. What had happened was that most of the washers had failed and had been torn apart.

We currently are unsure of how this failure came about. Our housing was filled halfway with 75w-90 gear oil.

Besides possibly being a lubricity issue, does anyone have any other ideas as to what may have triggered this failure?

[Paul Achard]

Are you certain you timed it right?
Were the washers factory or homemade?
Is the diff casing factory or homemade?
Dodgy tolerances in the last two could be your culprit.
I've never experienced this failure, but one could expect all washers to fail once one of them does.

[Mazur]

The diff was all OEM and washers were installed in OEM orientation.

You ask about correct timing, but I am unsure of how the torsen we have can be timed in any specific way. There are NO markings on any of the planetary gears to suggest any specific orientation.

If in fact they can only be put together exactly the same way it came apart, then maybe unwanted preload in the assembly was the culprit.

[Paul Achard]

There are actually little indents on one end of the invex section of each planetary gear. I think it's possible to assemble it so it seems to turn freely, but there's actually periodic friction through one full rotation.

[Drew Price]

There are two version of the Torsens that Torsen Traction sold to FSAE teams, I am not sure if they are marked differently because I only ever used the old old version, the 012000.

This thread may help: http://fsae.com/eve/forums/a/t...607348/m/38110172041 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/38110172041)

However, whenever I had it together and it wasn't timed right it bound up tight. If it spun freely then it was probably timed fine.

Was all the oil still in it when you tore it down?

[Mazur]

Yes it still had oil.

And no, I did not find and indent marks on any of the gears. I cleaned them all out and not one element gear had any sort of marking. Either it had worn away or it was never there.

Oh well.

[Paul Achard]

I believe University of North Florida has an acrylic casing on their torsen, they should strap a gopro to it so we can see what the Gleason-Gnomes are actually doing in there.

[Owen Thomas]

You may want to look at how your differential carrier/casing is supported. If the differential casing becomes stressed in driving conditions from something like chassis flex, it may deform slightly and cause excessive gear wear (or maybe your problem?). I know, those hefty cast iron casings don't bend much, but steel is steel and 205 GPa is never as high as I wish it was. I mention this because our 2010 car eats differentials, and I suspect this to be the case (stressed rear box).



I believe University of Central Florida has an acrylic casing on their torsen, they should strap a gopro to it so we can see what the Gleason-Gnomes are actually doing in there.


I would sit down with popcorn and watch that at one frame per second for HOURS. Although I'm not certain mere mortals like myself were ever meant to comprehend the complicated witchcraft within one of these magnificent devices; I have tried, but ultimately failed to understand exactly how the Torsen works (and would love to be schooled).

[dmacke]

If you had driven with diff before I would bet it was timed correctly. If it is not the it is nearly impossible to move the gears. Our team had a similar failure but that was because we had a custom two piece housing on the bolts holding it together came loose causing it to eat the washers.

[Drew Price]

Originally posted by Mazur:

And no, I did not find and indent marks on any of the gears. I cleaned them all out and not one element gear had any sort of marking. Either it had worn away or it was never there.



I had to clean mine with solvent and Q-tips and bits of rag for a LONG time to find the marks, they are pretty shallow, but since they are in the roots of the spur teeth there's really no way for them to wear away.




Originally posted by dmacke:
If you had driven with diff before I would bet it was timed correctly. If it is not the it is nearly impossible to move the gears. .



^^^ This.

[KustomizingKid]

We blew up a torsen at comp, and have a few stored away that have some torn up internals... poor maintinence, inspection and instalation most likely to blame.

[Richard Pare]

Excessive wheelspin will destroy the washers fairly quickly by driving out the oil film between them, causing them to start galling onto each other. Saw this a lot back when I was the North America racing distributor.

[Paul Achard]

Interesting. Does this happen on Audis relatively frequently?

[Drew Price]

Originally posted by Paul Achard:
Interesting. Does this happen on Audis relatively frequently?

This is the center diff in the Audi application, my guess would be that it would probably not have as extreme a speed difference between the two outputs as in our application, but who's to say.

Almost the only failures I've heard of in the street cars is if all the oil comes out and the owner keeps running the car - they are pretty reliable.