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Thread: Will LSD from a 1983 is e21 fit on my 1977 Euro e21?

  1. #1
    Join Date
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    Will LSD from a 1983 is e21 fit on my 1977 Euro e21?

    Just wondering if it is bolt on, if there are any issues with install, what is required..?

  2. #2
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    input and output flanges may be different. early input may be 3 bolt as opposed to later 4 bolt. output flanges on later cars use a 10mm hex bolt as opposed to early 12mm. unsure of when the changes occurred. i have a later car.

  3. #3
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    I think you can just get the half shafts from the 83 and you'll be in good shape.

    Current: '10 E70 X5 35d | All my e21 parts are for sale!
    Prior: '82 E21 320i | '80 E21 320i | '72 E3 Bavaria | '98 E36/5 318ti | '06 E46/2 325Ci | '83 E21 320iS


  4. #4
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    yes and no.

    yes the diff will bolt into the car,

    yes the 77 driveshaft will fit,

    yes the 77l half shafts will fit,

    no the CVs wont bolt up to the output flanges

    no you can't use half shafts from a 83

    however, the good news is it can be done, I myself am running a later LSD diff in a 77. I started a tread about the differences, let me find it and I'll get back to you.
    Tom D

    77 e21 - m42
    88 e30m3
    04 330 dinan3
    84 r1000rt
    02 r1150rs
    all of them gray
    14 f800gsa - red headed stepchild!

  5. #5
    Join Date
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    77 E21, 92 MR2 Turbo
    My 77 also has an LSD from an 80s car.

    It was swapped over by a forum member here by the name of "Firefight" so he may have more info on it.

    1977 320i - BBSs, Recaros, LSD, Zender bits

  6. #6
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    You will need the diff, cv joints/ axles, and outer cv flanges from an 80 plus car. I has posi in my 77

  7. #7
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    sorry josh, but you don't. the 77-79 have bigger and stronger cv joints so stay with them and the matching half shafts.

    also, if you go to later style half shafts and cv's then you need to change the axle stubs, which I assume you mean by 'outer cv flanges'. so in essences you need to buy the whole rear drive instead of just the pumpkin.
    Tom D

    77 e21 - m42
    88 e30m3
    04 330 dinan3
    84 r1000rt
    02 r1150rs
    all of them gray
    14 f800gsa - red headed stepchild!

  8. #8
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    75 2002 77 323irace 91M5
    Yes just put the 77 open diff drive flanges from your car in the late model lsd takes just a few seconds they just pop right out. The other way I have done it mostly with 2002's is put a early model cv. with the smaller bolts on one end of the half shafts and the late model with the big bolts on the other.

  9. #9
    Join Date
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    I wanna resurrect this thread from the dead to clarify before I undertake this swap.

    Is the general consensus that, in order to successfully install a late model LSD in to an early model, I would need to take the early CVs, half shafts and output flanges, and put them directly on the LSD? Do I have that right?

  10. #10
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    yes ....

    there is a differences between the output flanges though. early models are held in place with C-clips inside the diff, later models are held in place with spring clips inside the bearing caps. the older flanges can be inserted into a newer lsd without retainment clips and i see no problem with that, but on my own car i used the proper flanges that came with the lsd and redrilled them to fit the bolt pattern of the older CV joints.
    Tom D

    77 e21 - m42
    88 e30m3
    04 330 dinan3
    84 r1000rt
    02 r1150rs
    all of them gray
    14 f800gsa - red headed stepchild!

  11. #11
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    Quote Originally Posted by okieflats View Post
    Can the holes in an early output shaft be enlarged to accept 10mm bolts?
    no, the radius is different. i drilled new holes.

    - - - Updated - - -

    I've got a tread on the difference between years, there were 3 different layouts, but i wrote it as an argument and its not very well written. i wish someone would reorganize it for me.
    Tom D

    77 e21 - m42
    88 e30m3
    04 330 dinan3
    84 r1000rt
    02 r1150rs
    all of them gray
    14 f800gsa - red headed stepchild!

  12. #12
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    I'll have to get the diff out and compare the two, its difficult to follow from here.. The CVs definitely look differently, I cant yet discern differences between the output flanges. I feel like I may need to ask a machine shop to do this, right? Maybe not.

    Right now its a pain in the butt to get the driveshaft off. I wish I loosened those bolts out while I had the driveshaft connected to the transmission.

  13. #13
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    no shop needed. you have a 77 with 8mm bolt, large hub CV's, the 83 has 10mm bolts and the narrower CV's. all you need to do is to 'pop' the flange out of the 83 diff and insert the 77 flanges. you won't have any retainment so they may fall out when you lift it into place, i would fill it after install.

    removing the flanges from the 77 diff is a little more work. you first remove the rear cover. then following the flange drive to the center of the diff and you'll see a side gear on the end of shaft, there is a C clip holding the shaft to the gear, pull the clip and remove the flange.
    Last edited by Tom D; 11-18-2017 at 11:46 PM.
    Tom D

    77 e21 - m42
    88 e30m3
    04 330 dinan3
    84 r1000rt
    02 r1150rs
    all of them gray
    14 f800gsa - red headed stepchild!

  14. #14
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    Thanks Tom. I'll take a look tomorrow

  15. #15
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    Turns out 'tomorrow' is about a year and some change for me. I held this off til I did the suspension overhaul.

    For folks like me, it helps to have a picture, so here is the two side by side.
    Early to the left, late to the right.
    e21 early late output flanges.jpg
    Anyways, I can pretty much confirm all that you said above. I havent opened the diff cover on the late to find the lock ring, but you can see the groove on the output flange where it is held in place. For the early, once you open the cover, you can very easily see the clip at the very end of the output shaft.

    I dont really see the difference between the two, so I dont quite follow why you wanted to keep the same output flanges for the late? Im going to go with the early and see how it goes. Just will make sure I double check fitmet and sizing and everything.

    Hope this helps for whomever googles and lands on this thread.
    Last edited by jaredmac11; 03-14-2019 at 10:28 PM.

  16. #16
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    Just want to add some more confusion to this post! Apparently I've been running late model LSDs on my '78 with '79 half shafts for the last few years! Not sure how it works because the late model half shafts are almost an inch shorter than the '79s, but it worked for me for quite a while. Tomorrow I'll be putting my rear end back in the car so I'll try to do some test fitting with both half shafts and see what the deal is.

  17. #17
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    its not confusing.

    if your car is a 78 then it has 8mm bolts on the wheel flanges and you can not run 79 shafts because 79 shafts use 10mm bolts.

    80> half shafts are the same overall length as the 77-79 approx 410mm +/-. however the 80's shafts used a smaller cv (29mm vs 40mm) so the axle minus cv's is 22mm longer.
    Tom D

    77 e21 - m42
    88 e30m3
    04 330 dinan3
    84 r1000rt
    02 r1150rs
    all of them gray
    14 f800gsa - red headed stepchild!

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