AUDI A4 B7 FrontTrak Differential (Front) Fluid Change

[Okedokey]

The automatic Audi A4 B7 has a front differential that is classed as a lifetime fill. I believe even Bentley doesn't have a fluid change procedure so I have decided to document my process for doing a fluid change on this critical part of the drivetrain.

Tools you'll need:

• 10mm hex socket
• 2 x 1/2-inch socket extensions
• 1 x 1/2-inch breaker bar
• Fluid extraction device (I used a large 80mL syringe style) - bigger would be better.
• 1L hand pump (1L / 1quart) with about 1m (3") of tubing
• Drain pan
• 4 x jack stands
• Hydraulic jack
• 17mm wheel lug socket
• Suitable torque wrench
• Drain pain
• 1L of suitable differential fluid. I used Castrol Syntrax Universal Plus 75W-90.

Recommended items:

• New fill / drain plug (I used this from ECS that has a magnet)
• 1 x large vice grips *explained below*
• Degreaser or brake fluid to clean up any spilt fluid from the differential casing etc.
• Tools to remove under tray (I don’t have one so you may or may not need to do this).

Step 1 - Accessing the drain / fill plug

1. Loosen the left hand front tyre lugs with a 17mm socket then raise car so that it is level on all four corners with sufficient space to get under the car.
   
   
   
   
   
2. Remove the left hand front tyre
   
   
   
3. Turn the wheels (with the steering wheel) hard left - to gain better access to the fill plug
   
   
   

Step 2 - Removing the fill / drain plug and old fluid

1. Place drain pan under the differential drain plug.
2. The drain plug is a 10mm hex. It is extremely soft so I recommend using a mallet or similar to drive in the hex socket into the plug. *I rounded mine off and had to use a pair of vice grips around the outer edge and using a cheater bar I finally loosened it*
   
   
   
3. Some fluid will probably come out, so prepare for that. It'll look pretty nasty. Mine is at 113,000 kms.
   
   
   
4. Using your fluid removal device (e.g. A large syringe) remove as much fluid as you can. I removed about 700mm. The front differential in the transmission receives approximately 1.3 litres of SAE75 W90 synthetic fluid and is filled through the check plug as seen below. You won’t get 1.3 litres in there so 1L purchased is plenty.

Step 3 – Filling the differential and clean-up

1. Pour your differential fluid into your hand pump.
2. Pump the fluid into the differential fill hole until it drains out.
   
   
   
3. Insert the new drain / fill plug and install it finger tight.
4. Start the car with the brakes on and select drive.
5. Carefully let the wheels spin a moderate speed for about 20 seconds.
6. Shutdown engine and remove the drain / plug again.
7. Continue to pump fluid in the differential until it overflows.
8. Install the differential drain / fill plug and torque to 20Nm (carefully its soft metal).
   
   
   
9. Spray degreaser or brake cleaner around the area of the plug and anywhere you spilt fluid during the fluid change. Wash off with water.

Step 4 - Finish and testing

1. Remove all items from beneath the car.
2. Mount the front left-hand wheel and partially tighten the lug nuts in a crisscross manner.
3. Lower the car on all four corners.
4. Tighten the left hand front wheel lug nuts to 120 Nm
5. Start car and check for no leaks.
6. Take for a short test drive ensuring you take some turns. Return to your garage and check for leaks.

You’re done.

[Dflogaus]

Do you have to reattach the wheel before spinning the diff, or did you have to take it off and on twice?