Another diff question

[Ahmedsinc 414]

So I've been doing a bit of digging around on diffs and there's something I'd like to try.

According to bimmerdiffs.com the pinion tooth count is the same between 3.15 & 3.46 - both use a 13 tooth pinion gear.

Ring gear counts are different - 3.15 uses a 41 tooth, 3.46 has 45 teeth.

I have a 45 tooth 188mm ring gear from an E39 3.46 in the shed, but I'd like to get my hands on a complete 3.15 to have a go at swapping the crown wheels. My original idea was to swap the ring & pinion to another E36 case but unfortunately the E39 uses a much shorter input shaft, so that's a no - go.

So does anyone have a 3.15 medium case they'd be willing to donate or sell for a small fee? Overall condition is irrelevant as it's purely for research purposes, so if it's leaking oil everywhere or the bearings are stuffed thats perfect

Yes I know it would be easier to swap in a 3.46 from a Jap 328i auto but there's no fun to be had in that, is there

Thanks in advance

[yng_750 247]

Tooth count isnt everything. Id say the pinions are different shapes and sizes

[Ahmedsinc 414]

Yes, but it's a good start though. Might rip the centre out of the 3.73 and make some comparisons between the ring gear thickness and tooth height etc. Guess it's possible that they completely redesigned the diff internals when the E39 was released, but it would be handy if they didn't!

[allan 295]

If interested have a 3.46 to 1 medium case diff out of a 325i traveled around 108,000k

[Ahmedsinc 414]

Well, so far so good. Figured out how to disassemble the E39 diff and retrieved the ring gear. Did the same to the E36 diff and eyeballing the two suggests they're identical. Ring thickness, tooth depth, bolt pattern, thread & depth all look the same.

Will be borrowing a vernier caliper and hopefully a micrometer as well later on this week to take some proper measurements, also plan to give Mr Barrie a call and find out what he has to say too.

Seems silly to buy a diff when I have the bits I need already, and the opportunity to learn more about the dark art of differentials is too good to pass up. Wish me luck!

[BM WORLD 1283]

have 3.07 and 3.15 med diffs for sale .

[ashmill 68]

Interested - please advise price.

[Michael. 2313]

I have a a 3.15 ring gear and pinion for $50

[Ahmedsinc 414]

I have a a 3.15 ring gear and pinion for $50

Bummer it's not the complete diff. Pinion tooth count is identical on the .46 & .15 diffs, I need a complete unit to practice on before I go tearing my 3.15LS apart. Cheers for the offer though, if I can find the money in time I could definitely use your S50 midsection!

[jeffbebe 1560]

I have a 3.15 open diff... But large case, so probably not much good to you.

[jeffbebe 1560]

Swap meet?

I'll exchange my 3.15 large LSD for a 3.64 equivalent if anyone is game.

Go on.

I probably will be keen when I put in a six speed!

[Ahmedsinc 414]

I have a 3.15 open diff... But large case, so probably not much good to you.

Unfortunately yes. Thanks for the thought though

Surely someone has a ratty old med case 3.15 they could donate in the name of science and a little pocket money??