I spent my Christmas productively, swapping in a 3.15 diff. I did the job on jack stands with the tilted torque tube method. The whole thing took 14 hours, 2 of which I spent adjusting the front flanges of the exhaust. Maybe I was tired or something but I just could not seem to get them line up properly. The first day I dropped the exhaust, removed the brakes and disconnected everything in 4 hours. The second day I worked for an hour to drop the rear cradle. The third day was another 4 hour session to drop the pumpkin, install a new one and jack up the cradle. The fourth day of Christmas I torqued everything together, installed the pipes, and updated the ECU.

I didn't expect to complete the job alone, but it was actually super easy with a low profile transmission jack. Since there are plenty of write ups, I'm not making my own, but I can answer any questions.

Why 3.15? Well, I got a low mileage 3.15 for $300, and I want to keep the car pretty much stock. The 3.15 feels like the car was designed for it, a perfect compromise for a 4 speed auto. Couldn't be happier with the choice.

 

Congrats on the upgrade. The 3.15 ratio should give you a bit more SOTP feel.

 

Nice job and title, now bring us some shrubbery!

 

why not 3.42 or 4.10? I had 4.10 in my fbody A4 and it was perfect.. HUUUGGE difference. 2.73 to 3.15 isn't worth the time IMO

 

"I got a low mileage 3.15 for $300, and I want to keep the car pretty much stock. The 3.15 feels like the car was designed for it, a perfect compromise for a 4 speed auto. Couldn't be happier with the choice."

 

Out of curiosity I must ask what update was needed on the ECU? I went the other way as my 3.15 took a giant dump and I picked up a low mileage 2.73 to get back on the road while I rebuilt the 3.15. No changes were necessary to the ECU. VSS sends the signal to the speedometer and everything works as well as before. Now the 3.15 sits ready for install.

 

It will throw an error code for excessive slippage as it sees the shorter ratio as a torque converter or tranny slip. It probably works the other way around if the software is not smart enough to monitor for "too little" slip.

The speedo is not affected either way.

 

Gotcha. Thanks.

One thing you may notice is that when using cruise control you will get a surge when going down a slight grade. Mine did it with the 3.15 but does not do it with the 2.73.

 

looks like an awesome use of time and a real cost savings

 

Congrats, great project!

 

Nice job. I am planning on doing the upgrade to the 3.15 too someday. Would like a little more SOTP feel. Mine has the 2.73's now and really don't care for it that much.

 

That switchover is very noticeable IMHO.
Fred

 

Christ,. I've got a '99 Z28 with the A4 2.73's that I DD. 4.10s would suuuuuck on gas.

 

The difference is that 2.73 feels like it's always on the wrong gear, whereas the 3.15 feels it's on the correct gear. No bogging at 1-2 shift anymore. With increased shift points and shift pressure it chirps the tires at WOT shift and kicks the tail easily.

 

2.73s are granny gears, you're gimping yourself.. sure, if you're on the highway 90% of the day doing 70mph then yeah you might want to go to a 3.73. but even then, I didn't notice a tremendous drop in fuel mileage. anyway, I was driving a low 12 sec car I didn't care about fuel.