Final Drive Gear Swap

[Beatyourface]

Hey Everyone, long time reader, first time poster. I have had many cars over the years. I have modified many of them as well. What I love is that every car has different focal points on how to improve it. My last car was a 2003 Mach1 and I was in the process of changing the gear ratio to a more aggressive 4.10 instead of the stock 3.55.

My question is has anyone swapped out the Final drive gears from the front and rear diffs to something more aggressive to increase their rate of acceleration? I'm hearing that the manuals have more aggressive gears so would it be possible to swap the diffs from a manual to the automatic? If not has anyone found or heard of anyone offering a different gear set?

I've been doing some research over the last week or so and haven't found anything yet. So now to the experts here!!!

There was one post on here somewhat related. However it was more for the gear ratio it's self and not about swapping diffs or gears.

Thanks in Advanced!!!!!

[sonic32]

Hey Everyone, long time reader, first time poster. I have had many cars over the years. I have modified many of them as well. What I love is that every car has different focal points on how to improve it. My last car was a 2003 Mach1 and I was in the process of changing the gear ratio to a more aggressive 4.10 instead of the stock 3.55.

My question is has anyone swapped out the Final drive gears from the front and rear diffs to something more aggressive to increase their rate of acceleration? I'm hearing that the manuals have more aggressive gears so would it be possible to swap the diffs from a manual to the automatic? If not has anyone found or heard of anyone offering a different gear set?

I've been doing some research over the last week or so and haven't found anything yet. So now to the experts here!!!

There was one post on here somewhat related. However it was more for the gear ratio it's self and not about swapping diffs or gears.

Thanks in Advanced!!!!!

Manuals have 6 gears DSG's have 7


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[Beatyourface]

I don't mean those kind of gears. I mean final drive gear ratios that are inside the differentials and not inside the transmission. If my understanding is correct the Manuals have roughly a 3.83 and the Autos have roughly a 3.55 final drive gear ratio. I want to know if there is a way to get something other than a 3.55 final drive gear ratio into our cars without swapping the transmission. I want the daily to be auto while the future drift car will be manual.

[jimrobbington]

I don't mean those kind of gears. I mean final drive gear ratios that are inside the differentials and not inside the transmission. If my understanding is correct the Manuals have roughly a 3.83 and the Autos have roughly a 3.55 final drive gear ratio. I want to know if there is a way to get something other than a 3.55 final drive gear ratio into our cars without swapping the transmission. I want the daily to be auto while the future drift car will be manual.

I've never seen anything like this available or done on an Audi. JHM has probably done some of the most extensive work with transmission/diffs that I know of. Most interesting thing I've seen are upgraded rear diff for B7 A4 that changes F/R bias allowing more power sent to the rear wheels. But still, never heard of anything like that. Try reaching out to Jake@JHM to see if they know of anything?

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[jachien]

I'd be interested in this as well. One thing you can do is maybe check eBay for some high res images of the rear end and make comparisons. I use that a lot for my Nissan. Hopefully it's just a direct swap over of the pumpkin and just hard wrenching.


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[jachien]

I cant/haven't looked hard enough for the old b8 information but apparently on audi's website, the new b9 a4/a5 uses a 4.27 for the ones equipped with dct, and the s4/s5 use a 2.848. Thats right.. a 2. Maybe that's a typo and its really a 3.848?

As far as the b8 goes.. according to driverside.com,

a4/a5: 2.85
s4/s5: 3.88
rs5: 4.38

based off a 2015 car. and it doesn't differentiate between the transmission types so data isn't entirely accurate

[theweebabyseamus]

That would be awful, the lower gears are already short enough as-is.

[SouthernBoy]

I don't mean those kind of gears. I mean final drive gear ratios that are inside the differentials and not inside the transmission. If my understanding is correct the Manuals have roughly a 3.83 and the Autos have roughly a 3.55 final drive gear ratio. I want to know if there is a way to get something other than a 3.55 final drive gear ratio into our cars without swapping the transmission. I want the daily to be auto while the future drift car will be manual.

My 2016 manual S4 utilizes a 3.68 rear. The 2017 automatic makes use of a very high 2.848 rear.

[Beatyourface]

I appreciate everyone's input. This would be a game changer if it could be done. I have a VW Master Tech I work with who is up for the task just less than super enthusiastic haha. I can't say I blame him. No one has done it yet so it'll be full of growing pains.

[jygesq]

My 2016 manual S4 utilizes a 3.68 rear. The 2017 automatic makes use of a very high 2.848 rear.

the specs fpr my 2015 S4 show 3.875 for FD. 7 speed DSG.

[Loe]

I would be up for that 4.38 FD with the extended rev limiters on some of these tune files, would put the B8.5 in some serious revs at the end of the 1/4 mile at dual-pulley levels.

[SouthernBoy]

the specs fpr my 2015 S4 show 3.875 for FD. 7 speed DSG.

Apparently Audi made some big changes when they dropped the DSG tranny in 2017.

[jachien]

I would be up for that 4.38 FD with the extended rev limiters on some of these tune files, would put the B8.5 in some serious revs at the end of the 1/4 mile at dual-pulley levels.

I've looked on eBay to try and find the rear end and what seems to be it, looks different than ours. I think if you want to do it, you'll need: rear diff, rear mounting plate, axles, and possibly the hub/knuckle.

That's by no means definitive, just based on visual observation. The rear track on the rs5 is a bit wider. But I'm not sure if that extra track width is due to different width wheels. Easy way might be just to grab the whole rear end off an rs5. Subframe and all and all.

Edit: I think the different pumpkins I've seen are non-sports diff vs sports diff. Since rs5 comes standard with sports diff, it seems to be a pretty close swap with those that also have sports diff equipped. Those with sports diff will have bigger output shaft housings on the sides, which house the torque vectoring components.

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