The differential oil will go back just like any other oil system in your car. It should be changed at around 60,000 mile mark along with your transmission oil. You can wait longer, but why wait till it goes bad? Popular gear oil brands include Castrol, Mobil 1, and Red line gear oil can be purchased at less than $20 for the job.
In this article I will go over the simple steps to changing this oil and avoid the costly trip to the mechanic.
Audi recommends using 75w 90 gear oil. You will need about 1.5 Liters. I bought 2 bottles of mobil gear oil at autozone for $9 each. Buy amsoil if you prefer that brand. I don't think it matters but you want to be on the safe side as these cars are highly specific to their needs.
Jack up the car lifting all 4 wheels off the floor at a even level. This is required to accurately fill the fluid.
Now lets locate the rear differential drain plug(circle) and the fill plug (arrow, blocked not visible)
Open the Fill plug first! You do not want to drain the gear oil and not be able to fill it back up.
You will need a 10mm allen wrench for both plugs.
Once you have the fill plug opened. Its safe to open the drain plug.
Once its finished draining. Put the drain plug back in. And lets prepare to fill her up with new differential fluid. I used my pressure pump to push the fluid in. You can use any pump such as one from a shampoo bottle and attach a hose that will lead into the fill plug
A shot of hose going into the fill plug. It is done filling up once oil begins flowing out.
