This mod takes a differential that could only send 2 times the torque of the other end of the car that is slipping up to 4 times the torque of the other end of the car that is slipping. It will allow you to send upwards of 80% of the torque to the end that is slipping. This is useful in situations like an auto-x where you are attempting to make it around a turn faster and normally once you loose traction, you will continue to go straight whereas with this mod, you will be able to induce over steer and correct. The nice thing about this mod is that for daily driving where you are not in a situation where you are trying to hammer through turns, the car will drive and behave just like stock utilizing the static 50/50 bias. It makes the car more predictable and agile. The torsen bias will mimic that of the Audi RS4 which comes from the factory with this bias.


No warranties expressed or implied. This information is for educational purposes only. I am not liable or responsible for anything you do. By reading this article, you are in agreement with the aforementioned terms.


This article is specifically written for the facelift style (99.5 to 01.5) Audi A4 1.8T Quattro with a manual transmission. All photos are from a 2001 Audi A4 1.8T Quattro with a manual transmission. Granted these instructions can be used for other models as well because the idea is very similar but keep in mind that it is directed specifically at the A4.


Replication of any portion of this site including (but not limited to) it's HTML, Images, etc. is strictly forbidden without the expressed, written consent of its author.


2 Hours (air tools are recommended and were used in this write-up)


Supplies Needed

Tools Needed

Information Sources


Step 1 - Jack up the car

Make sure you are on a level surface and begin setting up by jacking up the car at all 4 corners. It's important to be on a level surface to make sure that you can drain the transmission and once you are done, refill it with 3.5 quarts of gear oil.

Make sure you are using jack stands:

Step 2 - Check to make sure you can open the fill port

Checking to make sure you can open the fill port is important because once you open the drain port; you are not in a good spot if you cannot open the fill hole.

Fill port:
Drain port:

Step 3 - Remove driveshaft

Driveshaft heat shield bolts:
10mm socket:
Driveshaft heat shield bolts:
Driveshaft to center differential bolts:
8mm allen socket:
Driveshaft (disconnected from center differential):

Step 4 - Remove center differential

Center differential:
Center differential (front):
Center differential (bottom):

Step 5 - Separate the torsen from housing


Step 6 - Remove Spirol pins

Be careful with these. I'm not sure where you would get replacements.

Inserting 6-32 bolts:
Pulling the Spirol pins:
Spirol pins removed:

Step 7 - Disassemble differential

Torsen diagram:
Replace washers 1 & 4:
Swapped washers:
Torsen gears:
Torsen marked:
Torsen marked:
Inner gears removed:
Torsen with inner gears removed:
Old washers:

Step 8 - Reassemble differential

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Good luck!

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