Swapping a small case diff to a large case diff?

[supadave]

Can we swap our small case diff for a large case and use the same drive shaft?

[fabe]

yes, been there done that, many times..

[DesktopDave]

I did a medium case 3.73 LSD from a 325i.  Fits perfectly, just had to bend the little sheet metal tab for the rear diff mount a bit.

From what I've found, the large case (e34 535i, M5, 540i, e32 735i, e38 740ietc.) will not fit at all.  The e30 M3 ran a modified medium case diff.  What I'm calling a medium case might be what you're calling a large case though.  The small case, stock on M42s and M10 e30's has six cover bolts.  The medium case has eight bolts on the cover, and it's shared with many of the smaller e28 M20 cars.  There are detail differences in the cases though.  M30 diffs will not work, too big.

[funcrew]

I did a medium case 3.73 LSD from a 325i.  Fits perfectly, just had to bend the little sheet metal tab for the rear diff mount a bit.

From what I've found, the large case (e34 535i, M5, 540i, e32 735i, e38 740ietc.) will not fit at all.  The e30 M3 ran a modified medium case diff.  What I'm calling a medium case might be what you're calling a large case though.  The small case, stock on M42s and M10 e30's has six cover bolts.  The medium case has eight bolts on the cover, and it's shared with many of the smaller e28 M20 cars.  There are detail differences in the cases though.  M30 diffs will not work, too big.

Do you have to replace the axles, driveshaft, or other parts to 325i stuff, or just the diff itself?

[supadave]

Thanks Dave

[bmwm42]

yup only medium or small case diffs i have 3.73 medium open diff on mine

[funcrew]

Do the axles bolt up, in other words same axles between 318i and 325i?

[DesktopDave]

Identical output flanges.  The medium case is fatter, but the output shafts are shorter to compensate.

Check mine out:
http://s729.photobucket.com/albums/ww299/desktopdave/Diff%20Job/

325is medium-case 3.73 LSD on the left; worn out 318i 4.10 open on the right.
The only item that was different was the vehicle speed sensor.  Swap the sensors, or if you strip the little 10mm bolts (like I did) splice the donor car's connector into yours.  Also note that the iS has a far heavier rear mount.  It's solid & adds a tiny bit more road noise.  However, it won't wear out.

[funcrew]

Identical output flanges.  The medium case is fatter, but the output shafts are shorter to compensate.

Check mine out:
http://s729.photobucket.com/albums/ww299/desktopdave/Diff%20Job/

325is medium-case 3.73 LSD on the left; worn out 318i 4.10 open on the right.
The only item that was different was the vehicle speed sensor.  Swap the sensors, or if you strip the little 10mm bolts (like I did) splice the donor car's connector into yours.  Also note that the iS has a far heavier rear mount.  It's solid & adds a tiny bit more road noise.  However, it won't wear out.

Thanks for that - but I'm being dense here; the flange-to-flange width is the same for both diffs?

[revmachine]

So my question is this:
I have a friend with a 94' 318i 4 door automatic. The POS is on it's last legs. It has a 4.44 LSD in it for some reason i do not understand. Normal 91' 318is's come with a 4.10 open small case differential. My friend will gladly give me his if he still has a diff to use so the car can run and be used. I have a spare 4.10 open small case.
The housings are too different to try and just slightly modify the mounting points and make everything work out okay. I am going to have to swap the ring gear and pinion on them if this plan is to work.
Where can i get a rebuild kit for these 2 differentials?
It seems no one (including BMW themselves) really likes messing with the internals of BMW rear ends.
Also, On Korman's site, it mentions that they are able to make a BMW diff in 50% and 75% lock unlike the factory 25% which is not very much IMHO. That leads me to believe that you can just put in more "clutch packs" (if the space is provided for it) into them to achieve a higher percentage lock. Where can i obtain such kits?
Lastly, If the price is not through the roof, I am also considering purchasing a Quaife instead of the internal swap from the 94' 318i automatic.
Anyone running a Quaife? how do you like it and have you driven a BMW e30 (very spirited driving or any type of track driving) with LSD and how do the 2 compare? What percent lock was the LSD? Where or how was the Quaife obtained (if it was a self bought and install of the quaife unit itself and not a purchased, complete differential with the quaife installed) and if you recall the rough cost of such a unit.
Any help on any of these topics would be very much appreciated and I thank whom ever in advance for sharing such knowledge with me.

[DesktopDave]

I've never done this myself, but IIRC, the diff just needs thicker plates or steeper ramps on the clutch.  Here's a good rebuild thread (I wish it still had pics) and another one over at BimmerForums.

Mechanical units like the Quaife or KAAZ are very expensive.  I'd assume one is roughly $2000 installed properly.  Any race or transmission shop should be able to do that for you.  Haven't done any of this myself.  I have heard a few people compare a OBX unit to them, but they need some work before they're installed.

Why don't you just buy the stock BMW torsen geared diff?  They were  installed on six-cyl Z3s from '98-'02.  Perfect fit for the e30.  Check this link out.

I'd definitely go for a Z3 donor...the housings are basically the same.   You might need to swap the output shafts...and I'd have a good look inside before installing one.  All you'll need is the gasket and the special BMW diff oil.  Be sure the speedo sensor is intact...the torsen uses a unique one.  So if you're really into a torsen and want to save a lot of money, look for the '99+ Z3 six cyl.