01E swap FTL (TDI) transmission swap rear differential question

[Fastguy]

So, I was initially told (or maybe I just assumed) that the rear dif of the stock RS6 would work fine with the 01E swap. I'm now assuming this is true of the standard 01E 6 speed U.S cars that have a final drive of 4.11:1. From what I have been able to gather, the FTL coded trans (which I think came from a 00-04 euro 2.5l a6 tdi) has a final drive of 3.89:1.

Now I have a small dilemma. First, I've been driving the car this way. I hope I did not damage the trans (not a big deal with the rear dif as it will need swapped). Second; I don't really want to wait four weeks for a dif from U.K. and pay huge shipping cost (doesn't matter if I have no other option). But it seems there may be the same dif used in the U.S only with other models of Audi/Volkswagen. When I search for replacements, no one lists (or even has knowledge of) the final drive of the rear dif. The part number I have been able to find from a UK sourced rear dif that will work lists the part number as 01R525053

Does anyone have any knowledge of a U.S sourced rear dif that will fit and uses the correct final drive?

[P1054]

Well without consulting ETKA I don't know the answer to your question, but I do have one of my own. Where did you get the transmission from? I purchased a TDI trans from Advanced Automotion for my swap and it was a DQT coded one, from a Euro TDI, with a 4.11:1 final drive. That said, I think a 3.89:1 final drive would be much better, but I didn't think any of the TDI transmissions came with it and wasn't about to start swapping out both the front and rear diffs. Edit: now that I think about it, I want to say that Advanced Automotion did offer the option of a 3.89:1 final drive on the TDI transmission..

One other item of note is that I believe the RS6 is the only C5 that has cooling fins on the rear diff cover for extra cooling. If you do need to switch your rear diff, might it be possible to swap the gears in the case rather than the whole diff?

[Fastguy]

I had no idea either (and it sounds like everyone else I talked to assumed 4.11:1 as well). It must be that ftl coding on the trans. I found multiple places list it as 3.89. I contacted Scott at advanced automotion and it sounds like he's going to get me the correct dif.

I know this trans was from a 2.5l tdi 4b as they listed it and it came from Germany. Not even sure of the model year it came from.

How important are those cooling fins?

[SteveKen]

I hope you're wrong about this and that your issue is something simple. However, if they are different, you're taxing your center differential and might need to refurb or replace it.

Here's where I make some guesses.

From what I recall, final drive and the differential ratio are different.

For example, the model guide states that the final drive for the RS6 is 3.197 and we all know that the rear diff has a 4.11:1 EUU ring and pinion.

I always thought that the allroad from the 01E was the only transmission that had a non-compatible front diff ratio from the rear.

[SteveKen]

As for the fins, I'm guessing it does lower the fluid temps, but I don't run it.

Since other cars don't' have them, it's most likely not detrimental to not have that added cooling.

[Fastguy]

As for the fins, I'm guessing it does lower the fluid temps, but I don't run it.

Since other cars don't' have them, it's most likely not detrimental to not have that added cooling.

Hopefully Scott is correct then. I have already detached the driveshaft and rear axles. 3 mount bolts out and it'll be in the ground. Oh, and for some weird reason I don't think mine has the fins on it anyway. If they are mounted to the bottom, it looks like something had previously been removed.
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[P1054]

Odd, they do appear to be missing. Mine definitely has fins there where yours doesn't. Well I guess that's one less thing to worry about then!

[LaserSVT]

I hope you're wrong about this and that your issue is something simple. However, if they are different, you're taxing your center differential and might need to refurb or replace it.

Here's where I make some guesses.

From what I recall, final drive and the differential ratio are different.

For example, the model guide states that the final drive for the RS6 is 3.197 and we all know that the rear diff has a 4.11:1 EUU ring and pinion.

I always thought that the allroad from the 01E was the only transmission that had a non-compatible front diff ratio from the rear.

Pardon my ignorance but I dont understand that statement. How is final drive 3.197 and 4.11? In my little world final drive is usually talking about the rear end gear ratio.

[Fastguy]

Correct rear dif on the way. But now what to do about center dif? Run it and hope for best or drop the whole trans again and pull it? What a mess

[SteveKen]

Wha????

Did you get a car with the wrong rear diff? Someone swap it out?

If you see the code EUU on it, then it's the 4.11:1 ratio.

[hahnmgh63]

By changing out the rear diff to a 3.89 your going to have even longer legs on that FTL coded tranny. Might help a little with the low first gear but it's going to make that .56 6th gear even taller, although not by a lot.

[Fastguy]

Wha????

Did you get a car with the wrong rear diff? Someone swap it out?

If you see the code EUU on it, then it's the 4.11:1 ratio.

I think there is some confusion about this. I do have the stock rear dif with the 4.11:1 ratio. The problem is that the ftl coded 01e transmission I source from Europe IS NOT 4.11:1. It is 3.89:1. So I need to match the rear dif to the transmission which would require me to remove and replace the rear with the proper 3.89:1 rear dif. ....or... I change the center dif in the ftl to 4.11:1. I already have the correct 3.89:1 rear dif ordered and on the way and the stock rs6 (4.11:1) dif removed. Time to wait.

[Fastguy]

I don't mind if that's the case. An even taller 6th is fine. It's basically an overdrive. It will be fine cruising at 70-80. I didn't even shift into 6th until about 70 anyway. Besides, anything to make that first gear a little longer would be worth it. That first gear, I call the "tractor gear". The car could climb a mountain with it. It's like if you have a pickup and stick it in 4 low.

[nubcake]

[...] So I need to match the rear dif to the transmission which would require me to remove and replace the rear with the proper 3.89:1 rear dif. ....or... I change the center dif in the ftl to 4.11:1. [...]

Nitpicking: that would be front diff, not center one. Center one is Torsen unit, it's purpose is to distribute torque between front and rear, it doesn't have a "drive ratio" per se.

[TozoM8]

I would pull the front diff cover and count the ring and pinion gears to be sure.