Transfer case and differential fluid

[LTopher]

Either my search fu has left me or I'm going blind because I can't seem to find the answer to a very simple question: What fluid goes in the transfer case on a B8 A4 Quattro with 8 speed tiptronic?

I've seen reports of the older models using regular gear oil, but this seems wrong to me since I'm used to Jeep transfer cases requiring ATF. I plan on using 75w-90
gear oil (non-limited slip) in the front and rear diffs.

[LionKing]

75w-90 is what I've exchanged mine to.

Sent from my Pixel 2 XL using Tapatalk

[Spawne32]

transfer case? you have quattro, you dont have a transfer case

[19birel]

As Spawne32 said you don't have a transfer case. There is a center differential located in your transmission that connects to the prop shaft and sends power to the back. The front differential is also located in the transmission. Therefore you only need to change the transmission oil and rear diff oil.

[jfo]

As Spawne32 said you don't have a transfer case. There is a center differential located in your transmission that connects to the prop shaft and sends power to the back. The front differential is also located in the transmission. Therefore you only need to change the transmission oil and rear diff oil.

No, there is a front differential that uses 75W-90 like the rear diff. The centre diff also uses 75W-90 oil but has a friction modifier added called Sturaco. It's only available at a dealer and is quite expensive. There are threads here about changing diff oil.

[A4x]

As Spawne32 said you don't have a transfer case. There is a center differential located in your transmission that connects to the prop shaft and sends power to the back. The front differential is also located in the transmission. Therefore you only need to change the transmission oil and rear diff oil.

The front diff shares the same housing as the transmission but it uses its own oil which is sealed off from the transmission oil. It uses regular 75W90 GL5 gear oil.

https://www.audizine.com/forum/showt...2#post13055402

I've read that the center diff takes the same oil. The factory fill uses a Sturaco friction modifier in the center diff only, which may need to be replaced if you replace the fluid. There is also a theory that the froction modifier sticks to the steel components and does not need to be added during a fluid drain and re-fill.

[Spawne32]

No, there is a front differential that uses 75W-90 like the rear diff. The centre diff also uses 75W-90 oil but has a friction modifier added called Sturaco. It's only available at a dealer and is quite expensive. There are threads here about changing diff oil.

Didn't think the center diff was actually serviceable.

[jfo]

Didn't think the center diff was actually serviceable.

Yes... it has drain and fill plugs similar to the front. I did mine when I had the pan off the trans, since you need to drop the trans support to get at the diff drain plug. One poster got about 80% out of the fill opening with a hand suction pump. I would use that approach next time, if I ever need to do it again.

[LTopher]

transfer case? you have quattro, you dont have a transfer case

lols this explains why I couldn't find an answer!

After reading up on quattro, I still don't see the difference between a transfer case and center differential--both transfer power from the trans to the front and rear diffs.

No, there is a front differential that uses 75W-90 like the rear diff. The centre diff also uses 75W-90 oil but has a friction modifier added called Sturaco. It's only available at a dealer and is quite expensive. There are threads here about changing diff oil.

It's the same with certain transfer cases in Jeeps (again, failing to see the difference). Does anyone have a part number for this OEM liquid gold? I like to change my diff and transfer case fluid every 30k miles and my A4 is at 63k and I'm guessing has never had these fluids changed.

[jfo]

lols this explains why I couldn't find an answer!

After reading up on quattro, I still don't see the difference between a transfer case and center differential--both transfer power from the trans to the front and rear diffs.



It's the same with certain transfer cases in Jeeps (again, failing to see the difference). Does anyone have a part number for this OEM liquid gold? I like to change my diff and transfer case fluid every 30k miles and my A4 is at 63k and I'm guessing has never had these fluids changed.

Just different terminology for the same basic function. The oil is...G 055145 A2

[Spawne32]

lols this explains why I couldn't find an answer!

After reading up on quattro, I still don't see the difference between a transfer case and center differential--both transfer power from the trans to the front and rear diffs.



It's the same with certain transfer cases in Jeeps (again, failing to see the difference). Does anyone have a part number for this OEM liquid gold? I like to change my diff and transfer case fluid every 30k miles and my A4 is at 63k and I'm guessing has never had these fluids changed.

A transfer case is like a miniature transmission, in that it is a separate unit, usually chain driven, that has some sort of mechanism by which it transfers power between the front and rear axles. Quattro, and similar systems use a different principal of operation that is much more simplified and less costly usually.

[KFizz]

Is the transfer case the center diff? The oil for the center diff is expensive as hell and only available through the dealership as far as I'm aware. I got a quote a few months back and it was like $100CAD per liter, or something retarded like that.

Sent from my Pixel 2 XL using Tapatalk

[Spawne32]

Is the transfer case the center diff? The oil for the center diff is expensive as hell and only available through the dealership as far as I'm aware. I got a quote a few months back and it was like $100CAD per liter, or something retarded like that.

Sent from my Pixel 2 XL using Tapatalk

no its not a transfer case at all, its merely a differential, torsen in most cases, newer ones being a crown diff. i dont think it requires much more then 1 liter of fluid. its expensive because its proprietary and typically never serviced. im sure there are probably alternatives but who knows if it will be cranky afterwards. i know the zf transmissions can be even if the new fluid meets the specs.

[LionKing]

I change all of mine every 30k miles and I have 133k on the dash right now. In itself, it's hard for a diff to act up like a trans since they are all mechanical. The transmission has issues with valve bodies and small passages for fluid to pass through at a certain pressure, sometimes new fluid causes gunk build up to get dislodged and find it's way there to clog.. with a differential, there is none of that, just gearing... I want to drain and fill my transmission but it's hard to justify 45$ a qt when there are no issues.

Sent from my Pixel 2 XL using Tapatalk

[jfo]

I want to drain and fill my transmission but it's hard to justify 45$ a qt when there are no issues.

Sent from my Pixel 2 XL using Tapatalk

The point is to change it before issues start to become apparent....particularly with the trans. Why change a robust gear system like the rear diff every 30k but leave a complex expensive piece of equipment that uses that fluid to function?

edit: you can buy zf Lifeguard 8 forabout $25/L from non-dealer sources.

[LionKing]

The point is to change it before issues start to become apparent....particularly with the trans. Why change a robust gear system like the rear diff every 30k but leave a complex expensive piece of equipment that uses that fluid to function?

Understandably. But it's a hard bill to front, even though I'll be doing the work myself. I personally won't do a flush just because that would move too much, how many quarts do you think it would be for a drain and fill?

Sent from my Pixel 2 XL using Tapatalk

[LTopher]

A drain and refill for the ZF8 takes 5-6 quarts depending on if you drop the pan or not. I just did a drain and fill with filter change at 63k miles and the old fluid was nasty. I'll probably do just the fluid again soon to get more fresh fluid in.

HOLY !@#$ the OEM center diff fluid is expensive! Has anyone used any other fluid with success? Kind of surprised at the lack of issues since it seems most folks never service the center diff.

[LionKing]

A drain and refill for the ZF8 takes 5-6 quarts depending on if you drop the pan or not. I just did a drain and fill with filter change at 63k miles and the old fluid was nasty. I'll probably do just the fluid again soon to get more fresh fluid in.

HOLY !@#$ the OEM center diff fluid is expensive! Has anyone used any other fluid with success? Kind of surprised at the lack of issues since it seems most folks never service the center diff.

I have a zf6, mine is a 2010.. I'll do a drain and refill with filter and let that run for probably 5k miles, then do it again..

Sent from my Pixel 2 XL using Tapatalk

[jfo]

Understandably. But it's a hard bill to front, even though I'll be doing the work myself. I personally won't do a flush just because that would move too much, how many quarts do you think it would be for a drain and fill?

Sent from my Pixel 2 XL using Tapatalk

Most get 4L out with a drain only and about 5 with a filter change. This was my experience also. I would order 5 for a drain to be sure. Since you only get about 40% of the fluid out, a 2nd drain/fill is worthwhile, along with a filter change. It is an expensive change, but if you keep your car for the longer term...

[jfo]

HOLY !@#$ the OEM center diff fluid is expensive! Has anyone used any other fluid with success? Kind of surprised at the lack of issues since it seems most folks never service the center diff.

Yeah, it's a crazy price for a L of 75W-90 with 3% Sturaco friction modifier added. Since the centre diff is limited slip, it includes the friction modifier. After much research, I couldn't find any info on alternatives and you can't buy Sturaco in retail size. You can buy other gear oil brands that include friction modifiers but it's difficult to tell if there are any compatibility issues. Since I will probably only do this once in the life of the car, I bought the Audi fluid from an online dealer.

[A4x]

HOLY !@#$ the OEM center diff fluid is expensive! Has anyone used any other fluid with success? Kind of surprised at the lack of issues since it seems most folks never service the center diff.

Pretty sure you can use regular diff oil for the center diff. Some sources call for a Sturaco friction modifier, which makes the 1 L of fluid expensive. Other sources say this friction modifier is depositited on the metal components and won't come out with a simple fluid drain. So you should be good to refill with standard diff oil for $20 if you don't want to spend the $100.