what BMW diffs are interchangeable

[mike e30]

Iav 2 questions in relation to this 1st off is there a medium and small casin diff
For e30 iam lookin for a diff For my 325 and was wondering what ones will fit as I tryd a 4.10 ratio out of a e30 318 which didn't line up.
2nd question is it possible to take the 4.10 pinion out of that
And fit it in to the diff of my e36 323 I no its possible to switch the internals of a e28 into a e36 wasn't sure if the same could be done with a e30 into a e36.
Sorry for the essay just fairly stuck thanks

[DaveM-sport]

E30 318 is small case, E30 325, E28 and E36 323 are medium case so the E30 318 cwp isn't of any use to you unless your putting it into an E36 316, 318i, 318is or 320i diff.


For your E30 to have a 4.1, you'll either have to buy a complete E30 4.1 medium case diff (rare as only certain 325i autos and US spec M3s had them) or else get a diff from an E28 518 or 520 and swap the back cover from the E30 diff onto it and it'll fit.


To get a 4.1 diff for an E36, it has to be made up. Using the cwp and differential unit from the medium case diffs mentioned above and put everything into your 323, 325 etc diff casing.

[mike e30]

E30 318 is small case, E30 325, E28 and E36 323 are medium case so the E30 318 cwp isn't of any use to you unless your putting it into an E36 316, 318i, 318is or 320i diff.


For your E30 to have a 4.1, you'll either have to buy a complete E30 4.1 medium case diff (rare as only certain 325i autos and US spec M3s had them) or else get a diff from an E28 518 or 520 and swap the back cover from the E30 diff onto it and it'll fit.


To get a 4.1 diff for an E36, it has to be made up. Using the cwp and differential unit from the medium case diffs mentioned above and put everything into your 323, 325 etc diff casing.

Cheers for that Dave think I got fairly sorted today
got a 4.4 diff and drives for the 323. From what u were saying so
I should be able to use the original medium case diff out of my 323 in my e30 325

[age]

Cheers for that Dave think I got fairly sorted today
got a 4.4 diff and drives for the 323. From what u were saying so
I should be able to use the original medium case diff out of my 323 in my e30 325

no!
the e36 and e30 casing is different, but they are both 188mm so the internals will swap.
the 323's diff will be way to long for the e30 as the e36 box has a 1:1 final gear.

[mike e30]

Cheers for that iam useless when it comes to this crack