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Oldtimerfahrer

Interchangeability of diff internals

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(edited)

Hi all,

A bit off topic, but I was wondering to what extent the innards of a 2002 diff will fit in later diffs. I know the E21 are compatible, I assume that the small case E30 also can share innards. I have an E30 with  3.45 rear diff, would like the 3.64 or 3.91 ring & pinion. I have a few good diffs lying around as spares for the 2002 but none for the E30.

Andrew 

Edited by Oldtimerfahrer
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As long as we're talking small cases.... then yes it'll fit in the case with a reshim of the side covers (standard pumpkin height is roughly 5.5" output bearing face to output bearing face).  The catch is to preemptively make sure the output flange knurling mates with the pumpkin.

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Quote

 The catch is to preemptively make sure the output flange splines mate with the pumpkin.

 

Made that more accurate for ya!  

 

heh

 

t

 

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THanks all for the input! Article is great, too bad the pictures are gone. I might look for an E36 diff instead of parting out a good diff as a donor!

Andrew

 

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Oh, thanks then maybe I will have to man up and do it myself...the description is too good.

Thanks!

Andrew

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(edited)

Another gem of a thread! I picked up an 85 318i for the injection system, trans/drivetrain. The diff appears to be a 391 LSD.  Haven't done a breakaway torque check yet but the passenger tire would turn with some resistance.

I reviewed and downloaded "Strongest 2002 LSD diff"  Awesome stuff there Thank you Andrew.

Haven't determined my 76s diff ratio yet (Greasy/leaky diff can't see nothing),with a 5 speed going in it would be  nice if it was 391 but most are 364 right?

What I have right now on the bench is this E30 391 LSD and an open diff from a 74 02 ratio unknown. Would like to fit the E30 LSD pumpkin and possibly ring and pinion gear into the 74 02 diff case.

Thats what I have to work with, not the strongest option but maybe an "acceptable" option for a mild street M10?

 

Edited by tech71

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The 3,91 with the od 5-speed would be my top choice. Even with a well modified motor, the 3,64 is too long.

A.

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(edited)
1 hour ago, tech71 said:

 

...Haven't determined my 76s diff ratio yet (Greasy/leaky diff can't see nothing),with a 5 speed going in it would be  nice if it was 391 but most are 364 right?....

 

 

U.S.-spec 1976 cars were bifurcated into:

 

1. 49-state versions, which came from the factory with an E21 head, no thermal reactor exhaust manifold, and a 3.90 differential (39-tooth ring gear, 10-tooth pinion gear), to recover some of the acceleration lost to emissions controls, and

 

2. California versions, which came from the factory with an E12 head, thermal reactor exhaust manifold, and the ever-popular 3.64 differential (40-tooth ring gear, 11-tooth pinion gear), because the California Air Resources Board (CARB) wanted BMW to re-certify the car with the new E21 head and differential and BMW said, “no thanks”!

 

So, among 1976 2002’s, there were originally far more 3.90’s than 3.64’s. But the miraculous survival rates of California cars may have muted, or even reversed, that advantage for the 3.90’s. I have not yet seen a factory 3.90 LSD. The 3.91 is an e21-era differential (43-tooth ring gear, 11-tooth pinion gear), and obviously many LSD’s were produced in this ratio.

 

Regards,

 

Steve

 

Edited by Conserv

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Thanks Steve, sounds like my car (49 state version) may have the 3.90 diff then. 

I should be able to fit this E30 LSD pumpkin into an 02 diff case and use my original 3.90 gear set. E30 diff case looks like a no go due to different mounts.

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