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Great list, Mike. What about the E32 cars? Specifically the 735i/750i that came with the 3.64 from '86 to late '87. IIRC, the case should be a bolt-on fit. Not sure about the cover.

What about the E32 cars? Specifically the 735i/750i that came with the 3.64 from '86 to late '87

Well, E23 ran thru model year 87. I have heard about some later diff's being adaptable IF you drilled and tapped some holes for mounting, but #1 I'm unsure if it's true, and #2 it is not a bolt up. There may be some that are, I just don't know about them.

Z3 differential also works from what I've read. It's an e30 rear subframe, swap rear cover and output stubs.

Jeremy

What about opening up diffs to swap ratios between LS and nonLS units?

This requires some tools, skills, and materials that are beyond the reach of many home and indy mechanics. It would probably be wise to assume that there is a learning curve to this and that the first try on doing this may not be entirely satisfactory.

The Factory Service Manual has fairly detailed information on how to go about this if you have the BMW special tools it uses. A shop press can be used to compress the crush sleeve on the pinion gear, but a rolling torque gauge is needed to determine when you have gone far enough.

The other tricky part is setting the rolling torque of the output of the diff. This is done by trial and error to find the correct thickness shims to get the rolling torque specified. One midwestern tuner who does a lot of diffs machines his own shims because of their general unavailability.

The 293 and lower ratios use a LS capsule that is dimensionally different than higher ratios, and requires fabrication of a ca. 175/1000" spacer plate to use with the higher ratio gear set. Apart from that the LS capsule from E32, E34, and E36 6-cylinder cars is the same as in 6-cyl E28s.

The clutches for LS units are reportedly NLA.

I was actually referring to the E32 735i and 750i, which I have been led to believe offered a 3.64, in the same case. Has anyone else heard this? I now know I had the build dates wrong; I was using realoem and not my aging memory, so it would be 1988 on.

This http://www.e30eta.com/ecdiff.htm link has some E30 diff info and the part numbers for various ring & pinion combos to achieve a particular ratio - all the way up to 5.00:1

rexmo wrote:What about opening up diffs to swap ratios between LS and nonLS units?

This requires some tools, skills, and materials that are beyond the reach of many home and indy mechanics. It would probably be wise to assume that there is a learning curve to this and that the first try on doing this may not be entirely satisfactory.

The Factory Service Manual has fairly detailed information on how to go about this if you have the BMW special tools it uses. A shop press can be used to compress the crush sleeve on the pinion gear, but a rolling torque gauge is needed to determine when you have gone far enough.

The other tricky part is setting the rolling torque of the output of the diff. This is done by trial and error to find the correct thickness shims to get the rolling torque specified. One midwestern tuner who does a lot of diffs machines his own shims because of their general unavailability.

The 293 and lower ratios use a LS capsule that is dimensionally different than higher ratios, and requires fabrication of a ca. 175/1000" spacer plate to use with the higher ratio gear set. Apart from that the LS capsule from E32, E34, and E36 6-cylinder cars is the same as in 6-cyl E28s.

The clutches for LS units are reportedly NLA.

This is ongoing...will be edited/updated as appropriate...

BMW Differential sizes are based on ring gear diameter:
Big diff = 210mm diameter gear
Medium diff = 188mm diameter gear
Small diff = 144mm diameter gear

Mike went through a large majority of the medium case diffs above.

Large case differentials are a little bit longer than the medium case differentials. Swapping between them is a non-issue in terms of halfshaft angle and fitment to the subframe in an E28 or E24. Although some have said that one needs to elongate a pair of holes on the subframe, I've never seen it or had to do it - my experience has all been for MY83 and later cars.

Big Diff interchangeability:
3.91:1 (US E28 M5, US E24 M6)
3.73:1 (Euro E24 M635, Euro E28 M5)
3.64:1 (Euro E24 635s)
3.45:1 (Euro E24 635s)
3.25:1 (Euro E28 3.5 engine, Euro E23s)
3.07:1 (Euro E23 745i)
2.93:1 (Euro E23 745i)
...*more fitments/interchange to come*

Cover for large case differential:
Required cover for E28/E24 fitment:
PN 33 11 1 210 668
Interchanges with:
E23 733i SEDAN, U.S. (up to 9/81 build date)
E23 735i SEDAN, Euro
E23 745i SEDAN, Euro
E23 728 SEDAN, Euro
E23 728i SEDAN, Euro
E23 730 SEDAN, Euro
E23 732i SEDAN, Euro
E23 733i SEDAN, Euro
E24 M6 COUPE, U.S.
E24 635CSi COUPE, Euro
E24 M635CSi COUPE, Euro
E28 M5 SEDAN, U.S.
E28 535i SEDAN, Euro
E28 M5 SEDAN, Euro
E28 M535i SEDAN, Euro


re: swapping LSD units in big diffs:
1. You will need to have the right tools and factory service manual, as stated above, since you need to remove the ring gear to swap out the LSD unit.
2. The big case LSD units are all interchangeable. There is no difference in the LSD case.

Koala Motorsports is one of the best, if not the best, rebuilder of differentials at the current moment. Cost is roughly $1400 to rebuild a LSD unit, and comes with a 3-year unlimited mileage warranty (as of March 2008).

FYI, parts cost (clutch disks, spacers, seals, bearings, etc) to rebuild an LSD are approximately $400-600 (see diffsonline.com). The majority of the cost of rebuilding a diff is the tooling and experience you get from professionals. You can no longer get a lot of the parts from BMW anymore, and most of the professional rebuilders source them from other places.

It may help to use some pictures for clarification, help yourself.

'82-'83 rear cover-medium case

Medium vs. Large Diff Guts

E28 Large Diff

different rear cover configurations

-Rod

rodpaine wrote:It may help to use some pictures for clarification, help yourself.

'82-'83 rear cover-medium case

Medium vs. Large Diff Guts

E28 Large Diff

different rear cover configurations

-Rod

Great pics...perhaps annotating them directly would be useful for some as well?

-Chris

That photo comparing the medium and large differential internals is interesting - I didn't realize there was that much difference in the size of the ring gear.

cgraff wrote:Great pics...perhaps annotating them directly would be useful for some as well?
-Chris

Chris,
I would have done that with the 3 Diffs pict, but I don't remember which Diff came from what cars. Been too long ago. If Someone can give me that info I'll label the picts and repost.
-Rod

So, I have something you may have never seen. Broken "big" diff. It's a S3.07 from a euro 3.5 with a busted input shaft. I haven't taken it apart yet to get details.

Anyway, the question I have and resulting answer that will be good for this thread is: are big diffs and medium diffs interchangeable? From what I can tell, all E28 subframes are the same and should accept either diff with the appropriate rear cover. The Big diff is a little longer, so the half shaft angle will not be the same, but it must be acceptable, no? Lastly, is a big case rear cover interchangeable with a medium case rear cover?

Skeen wrote:anyway, the question I have and resulting answer that will be good for this thread is: are big diffs and medium diffs interchangeable? From what I can tell, all E28 subframes are the same and should accept either diff with the appropriate rear cover. The Big diff is a little longer, so the half shaft angle will not be the same, but it must be acceptable, no?

Yes, it works fine.

Some have said they had to elongate the mounting holes in the subframe slightly, but it doesn't seem to be required all the time.

Skeen wrote:Lastly, is a big case rear cover interchangeable with a medium case rear cover?

Negative, definitely not.

Jeremy

Great thread guys! I wish I can find my pic of the 3 diff pics I took last summer. Keep it going WRT all the knowledge that we have as a whole group. Ted

BRRV wrote:Great list, Mike. What about the E32 cars? Specifically the 735i/750i that came with the 3.64 from '86 to late '87. IIRC, the case should be a bolt-on fit. Not sure about the cover.

Mike,
great list... Kudos to Chris, and Rod, as well.

Rick,
I'm the board member who posted about the e32 s3.64 bolt-on possibilities, the person who i sourced it from in Cal. noted that it was from a early model e32 and that it was a transition year unit with both mounting bosses for(e28) and later style(e32) sub-frames. I'll try to get more info., as far as build dates are concerned.
IIRC it is the larger diameter unit with 210mm ring gear.
It bolts right up; just swap rear cover and drive flange... then enjoy!
To try to make sense out of the confusion i also sourced a s3.64 out of a e32<?/?? unknown> that had mounted bosses that were un-tapped and un-drilled, but i passed on it.
Very akin to the transition in the mounting bosses on b35's.

The first pic. is of the diff. in my car now; note: drive flange and provisions for both e28 style sub-frames and e32 style sub-frame <side mounting bosses>



Second pic. was thrown in as a comparison, i believe the diff. to the left is a medium case diff. from a e28.




Third pic. is a e32 style diff with un-drilled/tapped mounting bosses, with provisions for e32 style sub frame only. note: this was the unit i contemplated drilling/tapping.




I hope this helps clearify things a little? And again i will try to find prod. dates.