[jamie323i]

Hey guys, I'm looking to swap or replace the rear diff in my '06 323i 6mt. The question is, can i use the diff out of 323i AT...
Two part question really.
Is the jump in ratio too much?
And will the input and output flanges have to be swapped, if they are swappable at all?
The dealer wants $2540.00 plus tax for a new one, and I cannot find a single used 6mt one anywhere.

[jamie323i]

Also, by the looks of the realoem drawings and part numbers, the AT and MT share the same output flanges, due to the lack of a separate part number for AT output flanges.
So really all I should have to worry about is the input flange being different in some way right?
Might be worth the swap, the AT diff is significantly easier to find and cheaper...

[BOOSTLEE]

Originally Posted by jamie323i

Also, by the looks of the realoem drawings and part numbers, the AT and MT share the same output flanges, due to the lack of a separate part number for AT output flanges.
So really all I should have to worry about is the input flange being different in some way right?
Might be worth the swap, the AT diff is significantly easier to find and cheaper...

should be a direct swap, I have one from a 328 that I was going to use just the gearings and put them in my 330i but lost interest, now I'm thinking LSD.
I have the 3.73 differential forsale, pm me if you're interested, came from a 08 328i with 42K miles

[iBoost]

what happened to your diff, if you dont mind me asking?

[jamie323i]

As best I can tell without tearing the unit apart, the input bearing has failed. Just sounds and feels very rough at the forward end of the diff.
Unfortunately the 323i appears to have different output flanges from the 325, 328, and 330,. So I'd be hesitant to buy a 328i diff. Where the 323i AT looks like it may be a direct swap.Although at this point it would still be cheaper if I have to spend 1000 bucks modifying one to fit.

[jamie323i]

If anyone's interested I'll post pics of the swap, just bought an AT diff from a scrapyard.
Fingers crossed

[jamie323i]

The new (to me) diff showed up today, looks promising for fitment.
Not 100% sure what to use for gear oil, I've read that several people are using redline gear oil, 75/90 I think?
Anyways, I've got all new bolts for the input and output flanges, as well as a dew drain plug w/o-ring. Should be putting it on the car next week some time, stay tuned for some pics and results.

[cuco]

Check this site, I don't see the e90 323 but it seems like the MT cars have lowers final gears than the AT cars. Please post pics of the swap, Im thinking of swapping mine with a 328xi (3.91 gear ratio!).

http://www.bokchoys.com/differential/GearRatios.htm

[jamie323i]

Yeah I've pretty well determined that the ratio should be not unreasonable, my main concern now is that it bolts up without issue.

[mapleridge]

Another option for possibly close to the price you were quoted is the m3 lsd swap. Need the dif, half shafts and drive shaft to mate with yours.


Edit**

May need some hubs from the 335i as well.

[jamie323i]

Seems to me like m3 drive shaft, half shafts, and diff, plus other parts would far exceed the prices I've been looking at, no?

[cuco]

This guy swapped his diff with a m3 LSD. Not a simple task.

http://www.e90post.com/forums/showthread.php?t=321625

[jamie323i]

Yeah, the m3 swap looks like a little more than I'm willing to go for... These supposed list prices you see for parts on tischer and realoem are not even close to what it costs to get these parts in Canada

[mapleridge]

Originally Posted by jamie323i

Seems to me like m3 drive shaft, half shafts, and diff, plus other parts would far exceed the prices I've been looking at, no?

At $2500 plus tax, if you could source the parts and do the labor yourself, I think you would be pretty darn close and you'd have a massive upgrade.

Originally Posted by cuco

This guy swapped his diff with a m3 LSD. Not a simple task.

http://www.e90post.com/forums/showthread.php?t=321625

I read that whole thread. It actually seems pretty simple, except for the driveshaft, its all bolt off and bolt on. A decent shop could do it in a day.


EDIT***

The one thing that is not clear for our cars is if the m3 half shafts would fit into our wheel hubs. If that answer is a no then it is a huge operation as the wheel bearing carrier needs to be swapped for either M3 or 335.

[jamie323i]

Something tells me the 323i and m3 don't share the same wheel hub....

[mapleridge]

Originally Posted by jamie323i

Something tells me the 323i and m3 don't share the same wheel hub....

That is the million dollar question. The 335i and the M3 have the same splines in the hub so you can use the m3 half shafts. Just a matter of ours fitting or not. Although, if you are taking the drive shaft to be shortened and balanced, the same shop could probably mate the 323 half shaft end with the m3 for less than the cost of swapping out the knuckle.

Edit**

These are the hub p/n's between the following models

E90 323i 33416760056
E90 328i 33416760056
E93 328i 33416760058
E90 328xi 33416760058
E90 330i 33416760058
E90 335i 33416760058
E90 M3 33412283020

The flanges/hub numbers between the 335 and the m3 are different but its a direct fit. This retrofit looks like it would also fit an xdrive n52, e93 n52 & 330i as well with just the modification to the drive shaft. Who knows, it may also be a direct fit with the 328/323

[jamie323i]

Just seems like a lot of work to put an LSD on a car with such little power though, do you think it'd be worth it? I'm gonna stick with the 3.73 out of the 2007 323iAT that I've got, looks like it should make it a bit more fun to drive, as well as not making the horrible grinding noises my current diff is making. I'm only into it for about $1300 so far.

[mapleridge]

Originally Posted by jamie323i

Just seems like a lot of work to put an LSD on a car with such little power though, do you think it'd be worth it? I'm gonna stick with the 3.73 out of the 2007 323iAT that I've got, looks like it should make it a bit more fun to drive, as well as not making the horrible grinding noises my current diff is making. I'm only into it for about $1300 so far.

Depends what you plan to do with your car. LSD would make it more fun. Here is a realistic budget.

LSD $1200
Drive shaft. $120
Balancing. $200
Half shafts. $500

It seems like it would be a lot cheaper to stay with the 323 at diff you found. If you were starting from scratch might be more tempting.

[driverman]

Swapping diffs is a great way to increase the performance of our normally aspirated cars.

I don't know what diff ratio is stock for a 6MT 323 but my 2008 328i has a 3.23. If yours is the same, jumping from 3.23 to 3.73 should make a big difference in performance. You'll be putting down about 15% more torque to the rear wheels as you go through the gears, BUT each gear will net you less speed and your car will be revving higher while cruising on the highway, which will cut your gas mileage. Is that OK with you?

[StealYourFace]

I had a 3.64 lsd that broke, and was replaced but I chose to go to a 3.38. For me it is a better all around ratio for daily (let's face it, that 99% of what we drive our cars) autocross and track days. I don't know if your car has the same trans ratios. I do know that the 330i has a different gearbox, I just don't know if the ratios are wider/closer than other cars.

[jamie323i]

Originally Posted by driverman

Swapping diffs is a great way to increase the performance of our normally aspirated cars.

I don't know what diff ratio is stock for a 6MT 323 but my 2008 328i has a 3.23. If yours is the same, jumping from 3.23 to 3.73 should make a big difference in performance. You'll be putting down about 15% more torque to the rear wheels as you go through the gears, BUT each gear will net you less speed and your car will be revving higher while cruising on the highway, which will cut your gas mileage. Is that OK with you?

Yep the stock diff in my 323i 6mt is a 3.23, I think I'll be fine with the ratio change even on the highway. 99% of my driving is on rural roads anyhow, I'm actually quite excited to see how it feels. If all goes well I'll actually be kinda glad my diff failed 'cause I probably never would've attempted to swap it out otherwise.

[mapleridge]

Sorry. Im not the most knowledged in differential gearing. Can someone give me a quick breakdown of how it affects the driveability/power?