1) the haldex and the diff oil are 2 different things.
Yes... Haldex is a hydraulicly operated clutch that engages the rotation of the prop shaft to the roation of the rear diff... much like the clutch up front does between the engine and gearbox
2) when changing the HALDEX oil, you should also replace the filter and you need a special tool to remove this. The service kit and tool are sold on ebay but maybe cheaper from GSF or similar. HALDEX oil should be serviced at the same intervals as the car.
Audi suggests Haldex oil every 20k and Haldex filter every 40k... for the effort and peace of mind it gives then I do both every 20k... If you know you are going to keep the car long enough to rack up the mileage then its worth the extra IMO...
3) changing the DIFF oil should be a little easier than the haldex oil, there is no filter involved and you can pretty much use the same syringe/mastic gun setup to put in new oil although there are no service intervals.
The drain and filler plugs can become encrusted and could be a ****** to remove... I bought new ones from Audi to replace mine... magnetic one at the bottom (drian) and a replacement for the filler one... clean them round with a small wire brush and apply penatrating fluid allowing it to soak for a while... uses a 17mm allen headed removal tool that I fashioned from a short 17mm headed bolt and nuts to lock it together... I then used a spanner to undo but any 17mm allen type sump tool should do the same thing.
I used a 1ltr squeeze bottle (as this is what it normally comes in) to fill with and had an additional 4ltr of gearbox oil that I used to fill the squeeze bottle up with as it ran out until the diff was full. Its full when the level is just below (although I think I let it run out tbh) the filler hole... I used a bit of welding rod bent round to act as a 'dipstick'
4) Gearbox oil is different again to the haldex and diff oil. Not sure about service intervals.
Yes, very different... Haldex oil is hydraulic fluid, diff oil is gearbox oil...
Audi don't specify a service interval for the diff or the gearbox for that matter but its 20k for Haldex oil and 40k for Haldex filter... as said before, I do both at the same time...
And can somebody (preferably someone who's done the oil changes) confirm the amount AND type of oil required for each change?
The Haldex oil comes in tube to be used in a caulking gun, I used a bit of silicon tube and cut the nozzle in half joining it with the silicon... this is because you have to fill the Haldex from underneath!!??!! and if you are doing this on axle stands or ramps then you won't get the caulking gun at the right angle to do it....
For the diff use 75W90 semi synthetic gear oil... I bought a 1ltr squeeze bottle and a 4ltr container of the stuff so I could do both the gearbox and the diff... I can't remember exactly how much each used if I was honest but I do have a bit left in my 4ltr bottle and thast was filling both gearbox and rear diff of course.
You are welcome
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