I currently have 2:73's on my O2 Z28 A4 and want a little more off the line power. I do a lot of highway driving so I figure 3:42 is the best choice. I do not plan on using drag tires. Ok, here are my questions.
1)Do I need to replace the stock steel driveshaft with a aluminum one?
2)Other than just the gears, what do I need. I want strength, but don't want to replace the whole rear end. I have about $1,200 to spend.

 

i'd say just get the 3.42s and have a good guy install them (maybe from the dealer and get a warranty)... you dont need to change anything but the gears and little parts (maybe just gears, i dunno) but i do know you dont need to spend more then $300 for the gears and i dunno how much to install

 

You will need to change your carrier bearings from a series 2 to a series 3, and I would change the driveshaft to the aluminum unit, or you will experience increased vibration at higher RPM's. A "T/A girdle, and stud kit" is optional (I have it), it will keep pressure on the carrier bearings and keep them from "floating" under hard acceleration.

You could probably buy an entire rearend from someone off the boards that has had a six speed, and upgraded to a 12 bolt rear(If you want to go the 3.42 route).

I personally have 3.73's in my 2001 A4, and do alot of freeway driving, I am currently getting 265 miles per tank of gas, not a bad trade off for more fun behind the wheel.

No matter what gear change you do, you will need to recalibrate the speedometer, via a HPP3 programmer, or a speedometer recalibrater unit (as I did), if not your car will not shift correctly.

There is more to the gear change than "SwingDriverZ28" is saying.

Good luck.

SteveC