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Thread: e36 lsd internals fit into e21 case

  1. #1
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    e36 lsd internals fit into e21 case

    I finally got around to tearing into my 168mm e36 lsd. Upon attempting to simply swap the e36 internals into the e21 case, it was obvious that it just wasn't going to fit without modification to either the case or the lsd unit. The opening of the e21 case isn't as wide as the e36 case. I didn't want to modify any of the moving parts, so I figured the only way to accomplish the goal was to grind away the portion of the case that was preventing entry of the lsd unit and ring gear. Here are some pictures.


    Left: e36 Right: e21

    I cut off the speedo sensor wheel on the e36 unit.



    The opening on the e21 diff (right) is smaller than the e36. On the e36, the lsd/ring gear unit can be inserted straight in. With the e21 case, the unit must be inserted non ring gear side first, then rotated. A small amount of the case needed to be removed to allow the ring gear to clear.





    I started by grinding away at the already recessed portion in these pictures. This is on the ring gear side of the diff. The ring gear just wouldn't clear this part. I ended up removing almost 1/8" of material, a little bit at a time, until I had enough clearance.









    I was concerned that the large o-ring on the side cover wouldn't make a good enough seal with this amount of material removed, but I test fitted the side cover, and it seems to be fine.







    LSD unit with ring gear installed with both side covers on.

    NOTE: side covers must be from a non-lsd e21 diff. The LSD side covers are wider, and will not work.





    Now that I know it can physically fit, the rest should be easy enough. I'll have to swap pinion gears. I'll be getting all new bearings, seals and o-rings. If I have problems with gear mesh, I'll have to acquire some new shims, but I have all winter to pick at it.

    ***********************
    Update:

    I pulled the pinions from the e36 and e21 diffs. I measured them with a digital caliper, and all measurements were within .001" They are interchangeable.

    e36 pinion: left
    e21 pinion: right




    *****************

    Update (June 20, 2011)

    Diff has over 500 miles on it so far. No leaks, noise, etc. LSD feels great. Success.
    Last edited by joey79; 06-21-2011 at 12:12 AM.

  2. #2
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    This thread is relative to my interests.


    Quote Originally Posted by Tom D View Post
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  3. #3
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    That seem easy !!!
    Will see how this trun out !!!
    I like that your trying something new out.

    GOOD LUCK


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    Also, interests, relevant, etc etc

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    make it STICKY!!!

  7. #7
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    looks great nice work!

  8. #8
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    which is the e21 diff and which is the e36? you switch labels on us. is trhe e36 lsd also a 3.91 with 25% lock?


    '82 320is
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    Woah! Very interested. I did note that it appears your seal does have a bit of a gap where you ground out the side of the case. I wonder if there's a way to alter the very last portion of the griding to allow a bit more for the seal area.

    If this works and holds it will be earthshaking. Don't tell the E36 community, they'll start charging more for the diffs....
    I still drive daily with no commute...
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  10. #10
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    Did you grind both sides or just one?

  11. #11
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    It works been done several times in the uk

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  12. #12
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    Wow, so just to be clear, you take a regular E21 diff, and a LSD E36 diff, take the E36 internals and put it in the E21 case (with mods) and it will work? What gear ratio is the E36?

    Humm..next on my to do list.

    E21 LEGION

  13. #13
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    Quote Originally Posted by dictator View Post
    which is the e21 diff and which is the e36? you switch labels on us. is trhe e36 lsd also a 3.91 with 25% lock?
    Sorry, I had them labelled wrong. E36 is on the left, E21 on the right. The diff is a 3.45 (I believe 25% lock)from an e36 318is.

    Quote Originally Posted by midlifebmw View Post
    Woah! Very interested. I did note that it appears your seal does have a bit of a gap where you ground out the side of the case. I wonder if there's a way to alter the very last portion of the griding to allow a bit more for the seal area.

    If this works and holds it will be earthshaking. Don't tell the E36 community, they'll start charging more for the diffs....
    It's hard to tell from the pic, but the rubber is making complete contact, that dark area is just the groove in the metal that the o-ring sits in. I probably could have removed a bit less material as well. As is though, I'm confident that it won't leak.

    Quote Originally Posted by erok320i View Post
    Did you grind both sides or just one?
    Just the one side. I probably could have taken a bit off each side, but this worked fine.

    Quote Originally Posted by BoostedE21 View Post
    Wow, so just to be clear, you take a regular E21 diff, and a LSD E36 diff, take the E36 internals and put it in the E21 case (with mods) and it will work? What gear ratio is the E36?

    Humm..next on my to do list.
    Yeah, mod the e21 case and drop in e36 internals. The e36 diff I'm using is 3.45. The swap isn't complete yet, I still have to do the pinion gear.
    Last edited by joey79; 11-29-2010 at 02:44 PM. Reason: Automerged Doublepost

  14. #14
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    I like it! 3;91 would be great!

  15. #15
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    how much power can the e36 diff handle? Wow this is so cool, I have always wondered about doing this with the E30 diff, I never thought about it for the E36.
    "..Horsepower is a measure of work done over time, or the rate at which work is done."




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  16. #16
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    Quote Originally Posted by jjgbmw323 View Post
    how much power can the e36 diff handle? Wow this is so cool, I have always wondered about doing this with the E30 diff, I never thought about it for the E36.
    I'm not sure that it would handle any more power than the e21 internals. They're both 168mm diffs. I'm pretty sure the 168mm e30 internals are the same as the e36.

  17. #17
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    does it fit with the chopper wheel for the speedo output?


  18. #18
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    I think he deleted the speedo sensor since the E21 doesn't have one. Man, the 3.45 LSD would be great for crusing the highway...
    I still drive daily with no commute...
    The Hazard is All, Praise the Hazard!



  19. #19
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    Quote Originally Posted by TheNeek View Post
    does it fit with the chopper wheel for the speedo output?
    No, it won't fit with the speedo wheel.

    Quote Originally Posted by midlifebmw View Post
    I think he deleted the speedo sensor since the E21 doesn't have one. Man, the 3.45 LSD would be great for crusing the highway...
    Yup, sliced it off with a dremel.

  20. #20
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    The E36 gears fit on the E21 carriers - only thing that looks questionable to me is that under a load the pinion is trying to push the ring gear and carrier out through the rear - where you have removed the material.


    How much power are you planning on running?

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  21. #21
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    Wow, I'd like to see some more info on this.

  22. #22
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    Quote Originally Posted by OLD MAN View Post
    The E36 gears fit on the E21 carriers - only thing that looks questionable to me is that under a load the pinion is trying to push the ring gear and carrier out through the rear - where you have removed the material.


    How much power are you planning on running?
    Stock m20b23 for now. Maybe someday an m50 swap. It would be possible to remove material on the other side as well, so not as much would have to be removed from just the ring gear side.
    Last edited by joey79; 11-30-2010 at 01:02 PM.

  23. #23
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    Quote Originally Posted by joey79 View Post
    I'm not sure that it would handle any more power than the e21 internals. They're both 168mm diffs. I'm pretty sure the 168mm e30 internals are the same as the e36.
    IIRC the e30 and e36 diffs can withstand well over 300 hp, with our e21s not the case...
    "..Horsepower is a measure of work done over time, or the rate at which work is done."




    http://www.cardomain.com/ride/579694/1


  24. #24
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    Quote Originally Posted by jjgbmw323 View Post
    IIRC the e30 and e36 diffs can withstand well over 300 hp, with our e21s not the case...
    I think that would be for the 188mm diffs from the 6cyl cars. The diff i used is a 168mm from a 318.
    Last edited by joey79; 11-30-2010 at 01:18 PM.

  25. #25
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    i got about 8 e36 LSD for sale $250 plus shipping..

    i will try and do one myself and see how it turn out. very good idea by the way. awsome job.

    edit : my question to you now, is the half shaft. are they going to need any modifications ? and is the e21 half shaft gonna fit the e36 internal diff?

    i will assume the half shaft will need to be cut and shorten like an inch or 2. or no ?
    Last edited by charbel; 11-30-2010 at 07:42 PM. Reason: Automerged Doublepost

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