Three alike differentials and one goal- 3.46 LSD...is it possible?

[Klug]

Hey guys-

So as I currently have my s52 e30 finished and up to par- the 4.10 open diff that was stock on the 325icA is not going to cut it. 1st gear is non existent, 2nd is first, 3rd is like 2.5 and 4th is like 3rd....pair that with an open diff and it's not fun, it's depressing.

Anyway, I've been searching for a 3.73 through 3.23 LSD and striking up empty handed. But today I was able to land a precious find- had to bare the snow in one of the coldest days of the year- a 3.46 4-bolt 188-Medium case from a 1985 e23 735i. Unfortunately there was no ratio tag but determined it was an open case, which sucked but from what the 24v people say- it's the best ratio to find.



So here is the thing. I currently have in my possession the following:
1. E23 735iA 3.46 Open Medium Case
2. E36 M3 3.15 LSD Medium Case (From S52 donor w/ CV Flange)
3. E30 325icA 4.10 Open Medium Case

So here is what I am thinking- Is it possible to remove the LSD from the e36 case and transplant it into the e23 case? Thus making the 3.46 LSD. Leave the diff cover out of the equation as I will take the one from the 4.10 that is currently installed.

I've been spending the night doing research and trying to figure this out.....It seems that swapping parts within the same "diff case size" family works, but I cannot find a definitive answer fas for swapping out the LSD mechanism.

And if this isn't feasible, I will continue my hunt for an LSD for my e30s52 and hope to trade all THREE of these diffs for an LSD that will work for my situation.

I appreciate any and all input! Now excuse me while I go wash off one of the worst smells in the entire world off of me- differential oil

[Klug]

Answered my own question outside of R3v- It's possible. Will post results later this week.

[TobyB]

Too late, but, yes, the LSD carrier will fit.
You'll have to set the ring gear position and preload
as well as pinion position and preload,
but it's all just trial and error.
I would first try keeping the shims from the gearset
with the carrier, and see how close that is.
From what I've experienced with small- case gears,
it seems to be the gear grind that varies the most.
However, if that's way off, then try the set from the case, and see
how that pattern turns out.
The BMW way makes things a bit difficult, as instead of a spacer
stack, you get one spacer- and then you have to change
that one spacer for another, etc., so you can't just have a
pile of .003' spacers and toss 'em in until it all works right...

t

[Wanganstyle]

the LSD unit you have pictured has 1 extra cut all the way around in the flange; this is because its from a WBS vin M car and has M14 hardware for the ring gear; you can reference this in real oem; also just remove the bolts from ring gear and compare with the screws fastening the 3,46 ring.

you will have to fit M14->12 adapters to down size to the 3,46 ring gear; the 188mm 3,46 ring gear only comes in M12 hardware

[Klug]

Originally Posted by Wanganstyle

you will have to fit M14->12 adapters to down size to the 3,46 ring gear; the 188mm 3,46 ring gear only comes in M12 hardware

You sir are right on the money! Didn't know this until I dove into it. Regardless, I was able to find these 10.9 Fastenal M12 "Shoulder Bolts" that have this thicker sleeve towards the head end. Worked out in my case. I was also reading about a guy on the e36 fourms who used the E30 M3 Head/Block Dowel that is the same size- ring diameter is M14 and center is M12- all you really need is a 1mm thick and 11mm long sleeve for the m12 bolts- but didn't want to spend an arm and a leg on dowel pins.

Anyway, once that was out of the way- I ended up using the original 3.46 e23 housing with pinion and ring with the LSD carrier and side covers with the original shims that were with the 3.46 case. The only thing I had to swap over other than the LSD carrier was the e30 half shaft input shafts to the diff- as the e23 ones were too big for the e30 axles.

So far so good! What a difference moving from 4.10 to 3.46LSD has been. I'm not 100% comfortable with this diff currently, but keeping a spare 3.74LSD around just incase.

Some pics