Differentials

[Mike W.]

All about E28s and differentials

What came in mine?
It depends. All 533/535 came with 3.25 ratio diff's, some with Limited slip, most without. 82-87 528es (model year, not production date) came with 2.93s, again, some with, most without LSD. M5s came with 3.91 and limited slip. 88 Model year 528es, also known as Super es, used 3.25 with 5 speeds and 3.46 with autos.

What can I use in mine?
Most E28, 82 and later E23, 83 and later E24 and 6 cylinder E30. Note on the last one, only the 6 cylinder cars, with the exception of M3s.

What had what ratios?
Ah, the 64 dollar question. The following are all for US spec cars.
All 533/535 3.25:1
82-87 528e 2.93:1
88 528e 5 speed 3.25
88 528e auto 3.46
325e 2.93, though there may have been some 2.79's in early cars
83-84 633 3.25
82-84 733 3.25
85-87 735 3.46
85-87 635 3.46
88-89 635 auto 3.91
88-89 635 5 speed 3.64
89 on 325i auto 4.10
325 5 speed, all 3.73
M3 4.10


82 etas and E23s seem to have had a unique housing and cover plate that limits their interchangeability, however you can still use a later assembly in those cars, but you may not be able to swap cover plates.

One small problem with using an E30 diff in an E28, you need to change the rear cover and the drive flanges. The rear cover comes off easily, but be prepared, you may need a new gasket, the drive flanges also come off easily, but clean up around them first so you don't drop dirt in your nice new diff. The flanges "pop" off, you will need a screwdriver or two or a small prybar or two. Get the lever under the flange and give it a little pop, more probably than you can do by hand, but not all that much. There is a snap ring in there that locates it. Reassembly is similar, sometimes they don't want to go in, they should slide most of the way in by hand fairly easily, but you might have to play with them some to get them aligned, then once they go most of the way in, you have to pop them back in place. The drive flanges on all the 5/6/7 series cars above are all the same.

Rear Covers
Early, as in 82, may be unique, as I mentioned earlier. 83-84 are interchangable for 84 and earlier cars with the early type square diff mount. 85-88 rear covers fit the later cars, and you can mix and match the housings and the covers between 83 and 88. E28 and E24 cars use the same covers in the same years. E23s look like the later cover, but are different, they are somewhat longer. I've heard of people cutting a deeper mounting hole in the cover flange, but I wouldn't. The right parts are too cheap and easy to find. E30s use a completely different type of cover which doesn't even come close to fitting, but the diff does.

Limited slip.
They are marked with an "S" both on the ID tag on the diff which is mounted with one of the rear cover bolts, and with a paint mark on the top of the diff, a big "S" in white paint, which by now can be sometimes hard to read. The ID tag on the cover will have the "S" in front of the ratio, such as "S3.73" It can be very hard to read as the years go by and the tag rusts, I've had the best luck in kind of polishing them on my pants leg to clean them up to read them.

The "Big" diff.
These came on M cars and euro 3.5s. They are physically larger and presumably stronger, but since very few ever break a diff, the question is why. Bragging rights as near as I can tell.

What doesn't work?
No diffs from Bavs, E12s, E9 Coupes, 82 and earlier E24s will work, they are all a sideloader diff and mount completely differently. 81 and earlier E23s I don't think will work, even though they look similar. No diff from a 4 cylinder E21 or E30 will work, except M3s.

[BRRV]

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 W.]

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.

[Jeremy]

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

Jeremy

[rexmo]

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.

[BRRV]

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.

[louielouie]

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

[cgraff]

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.

[rodpaine]

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

[cgraff]

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

[stuartinmn]

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.

[rodpaine]

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

[Skeen]

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?

[Jeremy]

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.

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

Negative, definitely not.

Jeremy

[Ted in T.O.]

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

[alpinewhite]

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.