3.15 LSD from e36 m3 to 525i

[katit2]

Question, will it fit? I think original is 3.26, so it’s pretty close, gears will be longer what I like.

what about speedo?

[shogun]

E36 4-door M3 is a large case diff 210, but the 525 has 188. Also check bolt pattern, sizes etc, here is a thread about final drives
https://www.bimmerforums.com/forum/s...1#post29923871

[Layne]

E36 diffs have a different case, none of them fit E34's at all.

The speedo sensor is in the diff (output side), so changing ratios does not effect the accuracy.

[katit2]

I read that E34 (except M/540) have 188 diff. And so is E36 (except 3.2 M3). So, from what I gather - I can just swap E36 LSD internals into my non-LSD E34 diff. All internal dimensions is the same.

Is that correct?

[Layne]

I read that E34 (except M/540) have 188 diff. And so is E36 (except 3.2 M3). So, from what I gather - I can just swap E36 LSD internals into my non-LSD E34 diff. All internal dimensions is the same.

Is that correct?

That is true, but diff gears have to be expertly adjusted upon installation or they will fail in 50 miles. I wouldn't do it, and I went to college for it. Definitely not an easy DIY (although some people get lucky).

[katit2]

That is true, but diff gears have to be expertly adjusted upon installation or they will fail in 50 miles. I wouldn't do it, and I went to college for it. Definitely not an easy DIY (although some people get lucky).

Didn't know there is school that teaches how to adjust gears in BMW diff. (j/k)
From what I read - only bearing have to be preloaded correctly and it's not too hard to do. Any details on what else need to be adjusted? For me it's all about experimenting and learning, not huge deal.. Plus, diff would have to be refreshed with new parts (bearings, plates, seals) anyway. I thought why not do it all..

[moroza]

A BMW diff is no different to set up than any other, but the tolerances are tighter than normal. You have to correctly set: 1. pinion preload/drag, 2. carrier preload/drag, 3. carrier and pinion positions such that the wear pattern (which you check with paint) is centered correctly on the teeth, 4. total preload/drag, and 5. backlash. All five affect each other, and it's like fighting a 5-headed monster. I would not recommend it for your first diff. When I did mine, it was my third or fourth, and it mostly went well but I have a whining noise on deceleration because I slightly overdid pinion preload. I set it to within factory spec, but with used bearings I should've instead set it to how it came, somewhat looser. Also, I didn't change gears or cases, only input flange and crush sleeve.

US-spec M3 had medium-case diffs IIRC. European (and Japanese) spec had the 210mm large case. I do not know if the US M3's guts will interchange with the E34's. I'd cross-reference part numbers of diff internals to research further.

[katit2]

Decided not to start new topic since we talk differentials here. So, ok. I got whole donor car where I pulled LSD differential from. However, I have couple questions about differential itself. It's got at least 200k on it.

What can I do with it without disturbing all adjustments/pretention? Its pretty rusty and rear cover seems to be leaking.

1. Can I replace all seals without disturbing adjustments?
2. Can I somehow reseal rear cover ?

[moroza]

1. Yes, but make sure not to overtorque the input flange nut. The good news is that in my experience, there's a big margin for error - torque spec is 140ft-lb, while the crush sleeve takes well over 200 to start deforming. Just don't use an impact driver to tighten it.
2. Yes, just use RTV (OE gasket is thin crappy paper)

[katit2]

Cool! Sounds like I'm taking it to my sandblasting guy..

Is there something I can check while diff is out? I mean, can I check if it's working properly?

[BleedsBlue]

^Moroza is correct, US-spec cars had the medium case. Manuals '96-99 were 3.23, autos are 3.38. See fellow member Mykk for a similar idea, albeit he is going large-case E46 M to large-case E34.