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E46 Xi Forum
The E46 XI was produced from 01-05 in sedan and touring body styles. Powered by either a 2.5L inline 6 in the 325xi or a 3.0L inline 6 330xi. Discuss all thing about BMW AWD E46 'Xi' here.

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Old 05-11-2019, 11:36 PM   #1
Hot_tub
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Front and rear diff 3.46 swap

QUESTION:

I have a 2004 325xi and i'm considering the idea of swapping both the front and rear differentials with 3.46 gear ratio. My question is; is my theory correct? would this provide the benefit that the rwd e46's enjoy by swapping out their rear diffs?

Does it matter if the differential was from a manual vs auto vehicle? If it does, what's the conflict?

Thanks in advance for insight
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Old 05-12-2019, 10:11 AM   #2
infoboy
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Quote:
Originally Posted by Hot_tub View Post
QUESTION:

I have a 2004 325xi and i'm considering the idea of swapping both the front and rear differentials with 3.46 gear ratio. My question is; is my theory correct? would this provide the benefit that the rwd e46's enjoy by swapping out their rear diffs?

Does it matter if the differential was from a manual vs auto vehicle? If it does, what's the conflict?

Thanks in advance for insight
The 3.46 diff comes on auto 323 and 325 only

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Old 05-12-2019, 03:01 PM   #3
Hot_tub
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Originally Posted by infoboy View Post
The 3.46 diff comes on auto 323 and 325 only

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Correct. The idea would be to yoink it off that one, and slap it in mine.
What's the difference between differential's for a standard vs an automatic?
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Old 05-12-2019, 03:40 PM   #4
infoboy
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Originally Posted by Hot_tub View Post
Correct. The idea would be to yoink it off that one, and slap it in mine.
What's the difference between differential's for a standard vs an automatic?
Well automatic e46's have a shorter diff ratios than manual ones.shorter ratio diff improve the auto transmission e46 acceleration because auto are slower in changing gears and with high ratio its even worse+they are heavier than manual ones.i dont know about the front diffrential setup,but the rear diff is straight swap from auto.NB: 323/325 are the same.328/330 are different from the 323/325.im talking about the rear diff,so make sure from what car the new diff is removed.

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Old 05-16-2019, 01:37 PM   #5
Hot_tub
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To clarify, the 325iT is equipped with the 3.46 diff, Would that be comparable with a manual 325xi?
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Old 05-18-2019, 03:10 PM   #6
WilloCO
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Hey @OP, I did this on my car and I like it. Let me dredge up some info for you from my brain...
My car has a six speed transmission, but TBH I barely ever touch 6th even with the 3.46s.
A great reference is here: http://www.bokchoys.com/differential/GearRatios_E46.htm

1) Get both front and rear diffs from an auto, they have stickers that indicate the ratio.
2) You also want to get the front drive shaft from the same car if you can. Otherewise get one from another auto.
My 05, and think your O4 will have a different style connector between the front diff and the driveshaft. (so you need to get he matching style of driveshaft)

3) This will be a good time to service the front axles since you need to pull them to get the diff out. Get new BMW axle clips, sometimes the old ones get mangled.
There is a shop in denver that rebuilds GKNs for our cars if your CVs need to be replaced. cvjaxle. I used them on mine and have no regrets.
4) Get new Strut clamp bolts the old ones will have some rust. (If you unbolt the strut from the tower, you will need an alignment, if you separate at the knuckle, you won't.

Final thoughts - penetrating lube, use it everywhere and preferably a day or two before you start working.
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Old 05-18-2019, 03:27 PM   #7
Hot_tub
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That's awesome that you've been able to pull this off. it certainly made sense to me on paper.

You're saying that i should source the front + rear 3.46 from a touring? I believe that's the only vehicle that can supply the front + rear diff and driveline components from the same car.

Is that the car you took from?


As for front axles, i'm on some good ole' amazon axles i got for $120. Not to mention the car sits on ksport coilovers as low as possible in the front. the front springs are O-12.5-160 and it sits just a bit too high in the front, even with the coils as optimized as possible by threading. The back sits perfectly IMO
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Old 05-18-2019, 03:44 PM   #8
WilloCO
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touring doesn't matter, just automatic. I found a local parts shop that had both, IIRC it cost me like $300 for the pair. For me that was worth not crawling around in the u-pull. I sourced the drive shaft for $40 on ebay. I live in the mountains, so it's an hour of driving to get to any parts sources.
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I bedded my pads when I switched from ceramic to my PDF-Z pads. They actually caught fire during bed in.
05 330xi 6 speed
RIP: 86 e30 w/E36 M3 suspension build
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Old 05-18-2019, 04:14 PM   #9
Hot_tub
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You're referring to an automatic 325xi correct? It will have 3.46 front & rear? Just trying to clarify while i have you on the line.

Also can you describe the benefit/performance differences before vs after the swap?
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Old 05-18-2019, 04:39 PM   #10
WilloCO
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yeah, mine came from a 325xi.
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I bedded my pads when I switched from ceramic to my PDF-Z pads. They actually caught fire during bed in.
05 330xi 6 speed
RIP: 86 e30 w/E36 M3 suspension build
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Old 05-18-2019, 04:59 PM   #11
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Quote:
Originally Posted by WilloCO View Post
yeah, mine came from a 325xi.
As for before and after performance differences?
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Old 05-18-2019, 05:30 PM   #12
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My review is subjective, and I took my car off the road for a year while I did a bunch of work that included the diffs. So I don't have a good week before/after experience.

What I will say is that the car puts power to the ground a bit harder than before. Acceleration is better. This is very good for me as I cover 5000ft of elevation change in my commute.
Driving up the hills is better, I'm glad I made the change.

In the end I combined this with headers and I found some ZHP cams and I upped the redline by 200-300rpm when I unlocked the MS43. (I've done many things to my car --I get bored.) The combo is pretty satisfying and still runs on low grade gas.

While I was in there, I replaced the diff mount bushings, it's not bad with the right tools.
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I bedded my pads when I switched from ceramic to my PDF-Z pads. They actually caught fire during bed in.
05 330xi 6 speed
RIP: 86 e30 w/E36 M3 suspension build
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Old 05-18-2019, 06:17 PM   #13
Hot_tub
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If you put in the effort and did the job and aresaying you're happy you did, then i can agree it will probably be worth the effort. I also plan on dropping in a pumpkin at some point so it's good i'm not the only one doing this 'upgrade', but i need to sort out the driveline.

I'm following the list you made above and i'm just trying to confirm this is the specific part you're referring to when you say to replace the front drive shaft with an auto one

https://www.ebay.com/itm/Driveshaft-...-/322178200560
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Last edited by Hot_tub; 05-18-2019 at 06:18 PM.
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Old 05-18-2019, 07:45 PM   #14
WilloCO
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Some people with 5 speeds hate the change. Do the drivetrain math - the pirate 4x4 calculator is pretty educational.
I love the acceleration on my car, my only complaint is at the high end. To be honest, my family never complains about the car being too slow.
(Also, I have to say when I'm at 5kft and below the car is stellar)

I also run Bilstein B8s with eibach springs. I'm going to add some extra padding on the rear because my current tires rub a little now and then.

The change is a fair PITA, but if you don't mind the wrench work it's fun as hell.
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Quote:
I bedded my pads when I switched from ceramic to my PDF-Z pads. They actually caught fire during bed in.
05 330xi 6 speed
RIP: 86 e30 w/E36 M3 suspension build
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Old 05-18-2019, 08:32 PM   #15
Hot_tub
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Good insight; see https://www.ebay.com/itm/322178200560
Is that the correct front drive shaft you're referring to in your earlier post?
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Old 05-19-2019, 05:16 PM   #16
WilloCO
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Yeah, that's the style you need for the auto diff up front.
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I bedded my pads when I switched from ceramic to my PDF-Z pads. They actually caught fire during bed in.
05 330xi 6 speed
RIP: 86 e30 w/E36 M3 suspension build
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