Some of you might want to know what the Haldex system is and how you change the fluid.
The Haldex system is installed on both the A3 and TT quattro models.
Its located on the rear axle and has the control module connected to it, now a haldex equipped car is a full time front wheel drive car until any wheel slip is detected by the brake electronics, then the haldex unit pulses the rear wheels hundreds of times a second making it four wheel drive. This unit MUST get the fluid changed every 20K miles.
Its a very easy procedure to carry out yourself, the special tools you will need is a filter removal tool (dealer) and a caulking gun. Pull the little allen drain plug out and let it drain, once its drained you can go ahead and use your special tool for removing the filter, the filter however doesn't need to be changed every 20k they can go up to 60k without getting fouled up.
Now to fill the unit can be a little tricky, this is where the caulking gun comes into place. Place the tube of haldex oil (dealer part) into the caulking gun and pump it into the drain hole until its empty, now make sure you have the drain plug handy cause you need to take out the gun and put the plug back in really fast so you don't lose the fluid you just filled.
Now your good for another 20k.

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2001 Audi S4 2.7T Biturbo (sold)
2000 Audi A4 1.8T