Where to buy a 4.10 lsd?

[Rally Culture]

I've been searching all over the internet (ebay, car-part, Craig'slist) but can't find a medium case 4.10 lsd for a good price. Also will my stock cv-axles bolt up to the bigger diff? Where are some other sites to look? Any advice helps thanks dudes!

[DesktopDave]

I'm not sure the medium-case was offered with a 4.1 ratio. If it was, you're only likely to find it in unusual circumstances like an E30 M3 Evo II. The 4.1 is a common ratio for the small-case. The 3.73 medium case is a far more common option, from being installed in so many E30 325i.

I have a 4.27 LSD for sale locally, 156K miles. It's still in the car, I believe it's a small-case.

Stock half-shaft/axles will bolt up to any small or medium case if they have the proper E30 output flanges. The E24/E28 output flanges have an ever-so-slightly larger bolt circle, they won't work. The front drive flange is the same between all the diffs I've seen. I've done the small-medium case swap myself, it works perfectly. If you find a good diff from an E24 or E28, be sure to grab a set of E30 MC output flanges. They're still avaliable new. The small case output flanges will not work with the medium case diffs as far as I'm aware.

[Warsteiner]

Dave is correct on this about changing the output flanges. The US E30 M3 had the medium case 4.10 diff. The Evo II was a Euro car which had a limited production and it ran with a dogleg box so therefore it only had a 3.15 ratio for the diff.  Those cars which had dogleg boxes also had options of the 3.25 and 3.46 ratio as well. All of these are too low for stock US boxes.

You may find a medium case 4.10 in an auto 325i. Not sure of pricing these days. My M42 Stroker has an E30 M3 diff in it due to power and torque and I wanted it to last.

Cheers,
~Ralph
 

[DesktopDave]

Also search for E23, E28, late model E24 (>'83), Z3 and 318Ti diffs. They're all compatible, if you have the correct rear cover and output shaft 'cups.' Rear diff covers are not the same between 210mm large case, 188mm medium case and 168mm small case. I have a medium case E30 rear cover with a good bushing if you can't find one cheap enough.

I'm running a 3.73 clutch LSD in my '91 318i (originally from an '87 325iS) and a 3.46 torsen LSD (from a '99 Z3 2.3) in my 635CSi.

You can also get a diff rebuilt with any gearing you'd like if you have a friendly & skilled mechanic locally. I usually look for a shop with cheap eurotrash exotics like 90s Landies, Alfas or a FIAT Brava in the front lot. Replacing the front bearing & crush sleeve is a pretty simple affair but setting up the ring gear lash, side shims, ramps and clutch packs requires expertise and special tools.