2017 Audi A6 3.0T - Diff & Transfer Case Oil Change

[Touareggg]

I have decided to change differential oil and I was wondering which part (rear diff or transfer case) shares the same oil as the transmission? I only know that that’s the case of 6MT, but not for 8AT (ZF8HP).

I bought the LiquiMoly 75w-90 gl4/5 (1qt) for the rear diff, but which oil do the front diff and case use? Is it the same one?

Thanks for future help.

[Valpo A7]

Any GL5 synthetic will work. On my 3.0 I went with Valvoline

[Touareggg]

I bought LiquidMoly 75w90 GL5 Only, not the GL4+ (GL4/GL5) and the shop told me to get GL4+ because that’s what popped up in their system as OEM equivalent. Shall I return these and get GL4+?

[MyDimeIsUp]

Never heard of GL4+ and doesn't look like it has SAE designation (https://bobistheoilguy.com/forums/th...6/#post-729255)

I've done GL4/GL5 75W-90 in my front, center, and rear. ZF, who makes the center diff/transfer case, says the $100/L Audi gear oil w/ Sturaco (G-055-145-A2) isn't necessary unless you install a brand-new center diff. If I can find the ZF published PDF I read before about this I'll link it here. Basically, just get 3L of 75W-90 and you're good.

[will.k.315]

So how do you replace the center diff fluid? I bought erwin for a day and trying to find the procedure for doing the center diff / transfer case

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[cuerna]

I bought Ravenol awd-torsen for center diferrential ($75) and redline 75W-90 for rear and front.

[cuerna]

So how do you replace the center diff fluid? I bought erwin for a day and trying to find the procedure for doing the center diff / transfer case

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20231030_171612.jpg

[will.k.315]

20231030_171612.jpg

Is that under maintenance or repair procedures?

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[Valpo A7]

This video is for the center diff (transfer case) on a 2012 A8 4.2 but its basically the same.

https://www.youtube.com/watch?v=oz3gftOh9mA

ALWAYS make sure to loosen the fill plug first. You want to know you can refill it BEFORE you drain it.

[elcA6]

https://www.audizine.com/forum/showt...ZF8-automatic)

[will.k.315]

https://www.audizine.com/forum/showt...ZF8-automatic)

That's just the front diff though isn't it? Where is the center diff?

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[Valpo A7]

That's just the front diff though isn't it? Where is the center diff?

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See my video. Ass end of the transmission.

[will.k.315]

See my video. Ass end of the transmission.

Oh I thought that was the fill and drain for the transmission itself

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[elcA6]

Sorry, there are a number of links in that thread that are helpful. This should be really helpful:

New DIY Videos!!
1. Rear Differential Gear Oil video:https://youtu.be/RLyTP5qIRQk

2. Front Differential Gear Oil video:https://youtu.be/xwD-gGGTyfE

3. Transmission fluid and Center Transfer Case oil video:https://youtu.be/IY_VRHlfJuQ

[Valpo A7]

Oh I thought that was the fill and drain for the transmission itself

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No, the transmission fluid change is much more involved than 2 plugs. To do the trans right you have to drop the whole pan and change the filter as well. When you refill it then you need a way to monitor the transmission fluid temp and be in a certain window to fill it up to the correct level.

[DanTheC7Man]

Never heard of GL4+ and doesn't look like it has SAE designation (https://bobistheoilguy.com/forums/th...6/#post-729255)

I've done GL4/GL5 75W-90 in my front, center, and rear. ZF, who makes the center diff/transfer case, says the $100/L Audi gear oil w/ Sturaco (G-055-145-A2) isn't necessary unless you install a brand-new center diff. If I can find the ZF published PDF I read before about this I'll link it here. Basically, just get 3L of 75W-90 and you're good.

Did you find that PDF by chance? I've been looking into the transfer case oil and can't seem to find anything official saying putting regular 75W-90 is okay (for refills). What I found so far is a picture from what seems to be an Audi service manual that says to use the gear oil w/ 4% Sturaco (G055145A2) on both initial fill and refill (see image below).

I also found a ZF PDF about which transmission fluids to use: https://aftermarket.zf.com/remotemed...e-ml-11-en.pdf

If you go to page 4 of the PDF and look beside the 8HP55A, there's a little "(2)" footnote. If you go find it on page 6 it also says to use G055145A2 oil for what they call the transmission's rear diff (car center diff). Granted it does only say "filling" and not re-filling on that one.

I really want to be able to put regular GL-4/GL-5 oil in my transfer case since the cost is like 5x less and I have it on hand but at the same time, I don't want to risk damaging it. If you or anyone can find something from ZF stating regular GL-4/GL-5 is fine for refills, I'd greatly appreciate it!

In the meantime, I'll keep researching and update if I find anything. Thanks!

--Update--

I found another thread where user djn876 claims having emailed ZF and they responded saying that the oil with friction modifier is recommended.
Direct link to thread comment (#36): https://www.audizine.com/forum/showt...1#post14437261

Just to be safe, I'll probably go with the Ravenol AWD-TOR since it has the special additives and tested to be better than OEM at a lower price (still comes out to about $85 w/ tax & shipping ). I guess the silver lining is I'll be able to get 2 changes out of the 1L bottle...

[will.k.315]

No, the transmission fluid change is much more involved than 2 plugs. To do the trans right you have to drop the whole pan and change the filter as well. When you refill it then you need a way to monitor the transmission fluid temp and be in a certain window to fill it up to the correct level.

I plan on doing all of these. I’m hearing a whirring/whining noise under acceleration starting at around 30mph, hoping it’s not one of my diffs. Guess I’ll find out when I drain them. Might also check the driveshaft carrier, saw something on another thread where a similar sound turned out to be that. So any gl4/gl5 75w90 can be used for the diffs and I should use the special one for the center diff/transfer case?

[Valpo A7]

I put regular gl5 in my center and had no issues. Had close to 30,000 miles on the fluid when I traded the car in with no issues