# Well, that DID go to plan - Rear Diff Oil Change



## Van Well (Apr 8, 2017)

There isn't really a rear differential oil change 'how to' in the Knowledge Base - maybe because it's pretty simple. So, I thought I would encourage the not-so-mechanically minded forum members, like myself, to have a go at it and save some coin....
After my Haldex oil change mishap the other day (New Haldex oil cartridge on order from the stealer), this is relatively simple, although you do need to make yourself a little 'hex' tool which will make the job easier and guarantee no stripping of the female fill plug  
The rear differential is separate from the Haldex drive unit; they don't share oil. The diff sump is just aft of the Haldex unit and the drain plug has easy access. The fill plug is a little trickier to access (although not hard like the Haldex filter) but where it is situated there is no way to get a socket ratchet up there. The photo below makes it look like there's more room than there actually is. Both the drain & fill plugs are female hex 17mm 'bolts'.

I borrowed this photo off the internet (forgot to take my own photo) - but the next photos are from my job









In this photo the person has placed a special 17mm hex socket up in the female fill plug with a ring spanner around it. I bought that socket but I cut it down to just a 'hex' block because that makes it much easier to put in place and much easier to re-position the spanner when tightening or loosening. I cut it down with a dremel.... Some people have used a 17mm bolt head with two nuts. I tried that but the bolt head wasn't a deep enough (or tight enough) fit in the female fill plug and it started to strip! Let me tell you, you do not want to strip or round the female fill plug - there is no access to drill it out. You would be in a world of trouble if that happened [smiley=bigcry.gif] All for the sake of an 8 pound socket that is built for the job and is deep enough to entirely fill the female hex fill plug. Buy a good quality one made of hardened steel!
Needless to say, do not try and remove the *drain* plug until you can access and loosen the *fill* plug!

Here is my cut down 'tool' - made the job super easy. Not the straightest of cuts but obviously insert the clean, machined end in the plugs! I did that cut at 11pm at night after I couldn't sleep..... :lol: 









You should have ideally driven your car to warm the oil, drive it up on ramps front on, then trolley jack the rear *carefully* and place axle stands in place underneath the jack point rubber donuts (or large blocks of wood under the rear wheels) to make the car as level as possible and easy to work under. Unlike the front end, the rear is easy to trolley jack up - place the trolley jack centrally under the U shaped piece of sub frame. It is easy to access and strong.










I actually used axle stands to level the rear, placed under the donuts. The above photo is afterwards, with the axle stands removed. I place some wood blocks under the wheels because it gives more height to position the trolley jack and then pull it out. I can then simply drive slowly backwards off the wheel ramps and wood blocks....

The car needs to be fairly level for this job because otherwise you won't drain all the old oil and it's hard to fill the diff to the correct level. It takes 1 litre of GL5 fully synthetic differential oil 75w90 - get good quality oil or buy the VW/Audi stuff if you prefer. However, the correct level of oil (as with most transmission/differential fill plugs on cars) is just below the lip of the fill plug. Mine took exactly 1 litre and just started to slightly drip out.
Once you have fully loosened the fill plug (but not yet removed it to avoid unnecessary drips of oil), go ahead and place a bucket under the drain plug and drop the oil. You can then fully remove the fill plug to allow air in to help the old oil to flow out. The drain plug is magnetic to pick up bits of metal swarth that may come out of the differential - mine was pretty clean with only a few little bits, which is a good sign. Clean the plug and after allowing the oil to drip out for a bit, reinsert it and tighten to 30Nm.

This is the easy way to fill the Diff. You can't see them, but the car is level with axle stands under the rear jacking donuts in this photo, ready to pour the oil...









Get some plastic hose (you can also use it to fill the front manual gearbox oil), a small funnel and lead the hose down like in the photo, through the right rear wheel maintaining a downward slope all the way to the fill plug. Check that it's not kinked and cut the hose to length - you should have about an inch of hose poking in the fill plug. I then stuffed a long rag in as well to lodge the hose in place during filling, but with a tail to soak up drips. Slowly pour in 500ml of oil then go check that the hose is still snug in the fill hole. Then go back and pour another 500ml. After that mine was just starting to drip slightly. I wiped away the oil and quickly reinserted the fill plug. Torque to 30Nm and job done.... 

In this photo if you look closely, you can see how I've lead the clear hose to the fill plug, always maintaining a 'downhill' run. Make sure you have reinserted the drain plug before filling with new oil! 









If you haven't had the rear diff oil changed for many a mile (or year), it's an easy job and let me tell you my old oil was pretty dark! No such thing as oil for life! For the sake of a few dollars or pounds, well worth it for the longevity of your Quattro drive.....


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## mitch65 (Mar 25, 2017)

Van Well said:


> There isn't really a rear differential oil change 'how to' in the Knowledge Base - maybe because it's pretty simple. So, I thought I would encourage the not-so-mechanically minded forum members, like myself, to have a go at it and save some coin....
> After my Haldex oil change mishap the other day (New Haldex oil cartridge on order from the stealer), this is relatively simple, although you do need to make yourself a little 'hex' tool which will make the job easier and guarantee no stripping of the female fill plug
> The rear differential is separate from the Haldex drive unit; they don't share oil. The diff sump is just aft of the Haldex unit and the drain plug has easy access. The fill plug is a little trickier to access (although not hard like the Haldex filter) but where it is situated there is no way to get a socket ratchet up there. The photo below makes it look like there's more room than there actually is. Both the drain & fill plugs are female hex 17mm 'bolts'.
> 
> ...


Wow, well done. I just don't have the room to do anything underneath the car so will be added this to the list of things for my mechanic to do. You've saved yourself a whole heap of cash though


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## Van Well (Apr 8, 2017)

mitch65 said:


> Wow, well done. I just don't have the room to do anything underneath the car so will be added this to the list of things for my mechanic to do. You've saved yourself a whole heap of cash though


Yes, and the manual gearbox is next..... as soon as my eBay 8 pound special M16 tamper proof torx arrives. I already have 3 litres of Redline MT90 waiting!


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## Gonzalo1495 (Oct 13, 2014)

Nice write up.

It seems like you went to a lot of extra work. I did mine recently as well, however I used almost the exact same socket as the first "borrowed" picture you posted. No need to cut it.

Also, I HIGHLY suggest investing in this cheap pump. I did my rear diff and transmission oil with it. 
https://www.amazon.com/gp/product/B000B ... UTF8&psc=1


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## Van Well (Apr 8, 2017)

Gonzalo1495 said:


> Nice write up.
> 
> It seems like you went to a lot of extra work. I did mine recently as well, however I used almost the exact same socket as the first "borrowed" picture you posted. No need to cut it.
> 
> ...


Thanks. Cutting the socket down to a small hex block just makes it light and small and therefore, quicker and easier to use. I was shown that trick by an engineer friend years ago when working on my motorbike (although he cut down a big allen key)..... Perhaps not necessary but easier. 
No extra work involved with a simple funnel and clear tube. The 'work' is done by gravity, there's no mess and you're standing comfortably next to your car instead of crammed under the car on your back. Putting it in place takes 1 minute.

The pump in your link looks like it would come in handy for lots of jobs and it's cheap, which is always a bonus  I just clicked on your build thread - Wow, amazing work! 8) I'm gonna take more time and read it from start to finish but right now it's Saturday morning and I have to fly....


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## watersbluebird (Oct 26, 2015)

Great write up. Bookmarked for future reference. :wink:


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## Van Well (Apr 8, 2017)

watersbluebird said:


> Great write up. Bookmarked for future reference. :wink:


Thank you. I've learned a lot from the knowledge base in the last 3 weeks since I joined and bought my TT, so I thought I'd give back a little


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## briancope (Jan 25, 2014)

Good write up Van Well.


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## Van Well (Apr 8, 2017)

briancope said:


> Good write up Van Well.


Thank you, Brian


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