[DeobandiPrince]

Hey guys,

Spent about an hour researching with no luck so thought I'd ask for help.

I have a 09 328i manual. Based on my research I have a 3.08 welded ring gear with the large diff case.

I wanted to get a 3.46 diff from a junkyard and get an LSD in there. From my research I understand that only pre 07 335i autos come with bolted ring gears in the large diff case (seems the small diff cases directly fit.)

I have 2 questions:

1. Is my research above true? Or did I misunderstand something.
2. If my research is right, will the diff fit in my car (driveshaft, flange etc etc into consideration)

Thanks for your help guys!

[Biginboca]

When I ordered my LSD I was told all 328i diffs were bolted, and as far as I know all the 328i use the small diff. The 330i (2006 only in the US) used a larger diff.

What is the source for your 328i having a welded diff?

If you ask me, get a 3.73 diff from any year 328i auto rwd for the easiest swap. That will be a direct bolt up to your car.

3.46 is not really a big enough difference to be worth the trouble. I ran a 3.73 in my manual for a couple years and it was the best mod I’ve done. Since then I’ve upgraded to a 3.91 diff from a xdrive auto and added a LSD to it. I went 3.91 because I wanted more than the 3.73. For the 3.91 from the xdrive auto I had to trim the pinion shaft and swap the yoke from a rwd diff, so it was more work than a simple bolt up.

One again… I would not even bother with 3.46

[DeobandiPrince]

Originally Posted by Biginboca

When I ordered my LSD I was told all 328i diffs were bolted, and as far as I know all the 328i use the small diff. The 330i (2006 only in the US) used a larger diff.

What is the source for your 328i having a welded diff?

If you ask me, get a 3.73 diff from any year 328i auto rwd for the easiest swap. That will be a direct bolt up to your car.

3.46 is not really a big enough difference to be worth the trouble. I ran a 3.73 in my manual for a couple years and it was the best mod I’ve done. Since then I’ve upgraded to a 3.91 diff from a xdrive auto and added a LSD to it. I went 3.91 because I wanted more than the 3.73. For the 3.91 from the xdrive auto I had to trim the pinion shaft and swap the yoke from a rwd diff, so it was more work than a simple bolt up.

One again… I would not even bother with 3.46

Ahh thanks for the info. I assumed that all cars post 07 had welded ring gears but that must be a 335i thing.

Wait, so does this mean I can purchase any ratio of final drive LSD and drop it into my pumpkin? (assuming it's made for 328 and not 335 of course.)

I will keep your advice in mind on the 3.46 gearing as well, appreciate your insight.

[Biginboca]

Originally Posted by DeobandiPrince

Ahh thanks for the info. I assumed that all cars post 07 had welded ring gears but that must be a 335i thing.

Wait, so does this mean I can purchase any ratio of final drive LSD and drop it into my pumpkin? (assuming it's made for 328 and not 335 of course.)

I will keep your advice in mind on the 3.46 gearing as well, appreciate your insight.

When I changed my final drives I swapped the whole rear diff assembly, pumpkin complete. You can buy a used take off differential on eBay for around $200-250 delivered and just swap the whole thing. When I did the 3.73 that’s what I did.

For the 3.91 I purchased another complete differential but this time had it shipped to the LSD installer who replaced the seals, installed the correct yoke, trimmed the pinion shaft, and installed the LSD. Then they shipped the complete diff to me and I installed it into my car.

I would not attempt to change a final drive inside your existing pumpkin unless you have experience with building diffs. The shimming of the pinion is a science that require accuracy to the thousandth of an inch and is best left to professionals in my opinion.

[DeobandiPrince]

Originally Posted by Biginboca

When I changed my final drives I swapped the whole rear diff assembly, pumpkin complete. You can buy a used take off differential on eBay for around $200-250 delivered and just swap the whole thing. When I did the 3.73 that’s what I did.

For the 3.91 I purchased another complete differential but this time had it shipped to the LSD installer who replaced the seals, installed the correct yoke, trimmed the pinion shaft, and installed the LSD. Then they shipped the complete diff to me and I installed it into my car.

I would not attempt to change a final drive inside your existing pumpkin unless you have experience with building diffs. The shimming of the pinion is a science that require accuracy to the thousandth of an inch and is best left to professionals in my opinion.

Wow this was very informative. I'm going to find a spare diff from any E9X 328i and go for a 3.73 LSD. Will try shopping around for the best deal on a 3.73 LSD.

Thanks for your help!

[Noir]

Would def follow big's route if you're planning to go all out - I used the same folks for my 3.91. Relatively quick at the time (pre-covid) followed the break-in procedure and I have nothing but good things to say about it