Differential case swap (188k)

mr_bizza_E86

Member
 Trento
Hi to all, I'm new here, and I've made a presentation post in the new members section. I've looked for information here in the forum on what's my purpose to swap the diff case, but found nothing specific (I say sorry in advance if my search was wrong).

Coming to details: my E86 3.0si m.y. 2006 is manual transmission and brings a 3.46 final gear ratio on its 188k differential. My car is equipped with a Quaife ATB unit, which I find wonderful on the road and makes the job in trackdays also, with compromises to be accepted jumping on the kerbs, as everybody knows.

I'd like to switch to a 3.73 final gear ratio and considering to refit the stock 188k case with its open diff and keeping it a spare part for future use or to sell. So I was wandering if I could find a spare full 188k case from other BMW model fitted with 3.73 final drive in which fit the Quaife and completely swap the stock.

Keeping on E85/86 platform I know the only option is 2.5 s.i. with smg, and there's also something in 3.64 (which I consider too short difference to value the job).

Of course the possibilities to find a 188k from an E85 2.5 s.i. smg are quite unusual so I was wandering if there are other models which can match.

Standing to RealOEM quite all the E89 range has a 3.73 final drive and 188k...the rear cover have the same OEM code. Any of you knows if the diff case from those models has the same attach points and can be directly fitted on E86?

Thanks in advance and sorry if I wrote something wrong

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I think you might be better off looking at the E46 diffs. I am not sure what ratios they come in, but I think the only difference between them and the Z4 diff is the rear cover (I think the Z4 has more cooling fins).

Don't take that as gospel, but more something to research further. Good luck!
 
I think you might be better off looking at the E46 diffs. I am not sure what ratios they come in, but I think the only difference between them and the Z4 diff is the rear cover (I think the Z4 has more cooling fins).

Don't take that as gospel, but more something to research further. Good luck!
I was so focused on the differential, that I completely forgot the first X3 range (E83) shared the mechanical base with E46 range (and E85/86 consequently)...so probably the differential case is the same on those models. I've also found out that X3 2.0d auto and 3.0si both had a 3.73. The 188k cases appear identical at sight...so I'm going to buy one and try...just the rear cover will be different...but eventually will be swapped.

Anyone had swapped differential from E83 to E85/6?
 
According to RealOEM the E85/6 diffs are unique to the Z4 but I'm interested if the only difference is "cosmetic" rather than physical mounting as I think I've got a bit of a graunchy diff and there's bound to be more E46 ones around. I was always surprised they had different part numbers since the Z4 was a bit of a parts bin special and assumed they had to redesign it for available space.
 
Quite all OEM codes for diffs are dedicated to every single range of models, mainly because of different gear ratios (they don't sell spare empty diff cases) I suppose. At the same time I think that it's easier to manufacture dedicated subframes, flanges, etc. for every single application to arrange fitment issues instead of producing dedicated cast iron stuff...or at least that's what I'm hoping...🤞

Output shafts flanges are Ø86 mm in every case (diameter of the shaft are different though). Probably some minor issues like driveshaft connection have to be managed...I don't know 100% but I assume for sure between MT and AT.

I've found an old thread in this forum in which they said there were similarities but at the same time there were also compatibility problems...:rolleyes:


As I said, finding the right stuff at good price, I will try. Worst case scenario I will take away the gears and fit them in my actual case
 
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