E46 diff in to E31?

[Phil 840]

Hi guys, quick question regarding a diff swap. Would a BMW E46 M3 3.2 Differential 3.62 Ratio LSD Diff fit an E31 840?

Granted I would need to swap the cover bit what I'm really asking is if this is the big case diff.

Thanks guys.

[wokke]

The E31 cover would fit (same gasket at least) but the case appears to be different.

[Bryson]

swap the internals in and you'll have a nice M-vario LSD as well!

[Xpressions]

Would you elaborate, are you sugesting the all the internal parts of an M3 E46 LSD are interchangable with an 840 E31 open dif?

[8eights]

As long as it has a 210mm case.

[avee]

yes it will. Infact i have one for sale that has been completely rebuilt Diff has about 40k miles on it.

pm if you are interested

[Xpressions]

I would but your in the states, and I'm in Germany!

[Auraraptor]

swap the internals in and you'll have a nice M-vario LSD as well!

Indeed.

[whiteghost1]

How's about one from a e23 745i turbo?
Those were large case as well but I believe the housing would not be a bolt-in to the e31 chassis............
Someone correct me if I'm wrong???

[Auraraptor]

housing differs...

[BBmatic]

swap the internals in and you'll have a nice M-vario LSD as well!

I can only daydream about what an enhancement this could be on a stock 840

[Slimm]

Why not m5 differential?

[Ed Lyerly]

Why not m5 differential?

Or an e24 M6 (or M635) .... as they are large case 210mm units (both are LSD and 3.91 and 3.73 respectively)

[Ahmed303]

Or an e24 M6 (or M635) .... as they are large case 210mm units (both are LSD and 3.91 and 3.73 respectively)

If the 3.73 fits, I'd love to install one. IMHO it would be the most balanced for my car to have a great acceleration and still have not too high RPM at higher speeds.

[Ed Lyerly]

If the 3.73 fits, I'd love to install one. IMHO it would be the most balanced for my car to have a great acceleration and still have not too high RPM at higher speeds.

You will find the 3.73 in the euro M635 from '84-'86. These were "grey market" cars imported before the US got the e24 M6 in '87. The US M6 cars ('87-'89) came with a 3.91 to compensate for the extra weight they carried (5 MPH bumpers, side door beams, and rear AC unit) ... and smog equipment that robbed them of 30 HP.

These are 210mm (large case) differentials .... used only in the e24 "M" cars .... not the same as used in the standard e24 cars. It is my understanding that
the rear cover needs to be exchanged with yours ..... but otherwise is a drop in replacement, as the gear case is the same.

Someone please correct me if I am wrong.

[Noggie]

I went the other way, from a 3.45 to a stock euro 3.15lsd from an e32 750i, swapped the back cover and bolt on.

[Xpressions]

Was the 3.45 an LSD, if so do you want to sell it?

Steve

[Noggie]

Was the 3.45 an LSD, if so do you want to sell it?

Steve

No it was not LSD, and it failed spectacularly beyond salvage.
I got the 3.15 LSD before I knew it was bad (the failure came as a huge surprise) to get lower revs at cruise and to lower fuel consumption.
Fuel consumption is not the main concern when buying a V12, but with fuel prices having passed $2.50 a liter, a mixed consumption around 10mpg is getting a tad high, and when driving on long trips with fellow 8'ers the extra 10l I have to put in at every fuel stop started to get to me.
The fact that my car is supercharged also mean I don't need the gearing ratio, I have plenty of power anyway.

[Arsenic]

I can only daydream about what an enhancement this could be on a stock 840

I absolutely love the E46 3.62 LSD in a 210mm case on my 840. I have found no downside so far.

[chadderz2010]

I absolutely love the E46 3.62 LSD in a 210mm case on my 840. I have found no downside so far.

Interesting this type of diff is a lot more easy to get a hold of here in the UK compared to anything else I have been looking at.

So would this work then ?

http://www.ebay.co.uk/itm/BMW-e46-M3...item4d07d33e42

So I need to swap the insides into my case, how involved is this and is it something that I could DIY , special tools required etc?

NB I also noted a service bulletin for them SI 330102 (850) seems like just needs a fluid change and run in process.


Thanks

Chadderz

[JK840]

I have 3.64 LSD from an E32 750Li on my 840. It only needed the back plate swapped. The 3.64 LSD was an option for the 750Li.

[Xpressions]

I absolutely love the E46 3.62 LSD in a 210mm case on my 840. I have found no downside so far.

Out of curiosity, how is your MPG around town, say a weeks worth of relatively short trips?

Do you have any more details of the swap?

[Noggie]

when stick with the 3.45 my computer was pretty steady at 18l/100km, with consumption in mind I could get it to about 16l/100km
my best highway was 11l/100km, but the norm was 13l/100km.
And a trip to Germany with autobahn driving put me around 16l/100km, but that was speeds of ~180kph and some bursts above 250kph.

Expect a 3.64 to be slightly higher.

Edit: my car is an 850, so not directly comparable

[Auraraptor]

Out of curiosity, how is your MPG around town, say a weeks worth of relatively short trips?

Do you have any more details of the swap?

Mine was 15-16mpg, iirc.

[Noggie]

Mine was 15-16mpg, iirc.

Us mpg or Imperial mpg????

i.e my consumption of 18l/100km = 15.7mpg (imp) or 13mpg (US).
I ask because the person asking is from the UK, and there is a huge difference between the two.