Diff sizes ???

[Sooty]

Do the E30's have two different diff case sizes? The reason for asking is, I'm having some trouble getting my head round the diff swap needed on my M50 fit.

The story so far...........
I removed the std diff from my 320i Cab & it has 6 bolts holding the rear cover on.
I get a 3.07 diff from an E28 & it has 8 bolts holding the rear cover.

OK says I, I've obviously got hold of a large case diff instead of the required small case diff. Bugger...another Ԛ£70 down the drain (courier costs, shotblasting & painting inc).

Then I start looking at various swaps that others have done........

Someone has fitted a Z3 diff cover to an E30 as a straight swap - very nice, but hold on....the Z3 cover has 8 bloody bolt holes... is going on here????

And just as an aside, forum wisdom has it that for an M50 swap with the E36 g/box, you can use a 3.25 diff from an E28 525e.
As far as I can find out, the 525e didn't come with a 3.25 ratio!!!

Can someone PLEASE give me straightforward answer because I'm getting a real mindf**k over this.

[old_skool]

Do the E30's have two different diff case sizes? The reason for asking is, I'm having some trouble getting my head round the diff swap needed on my M50 fit.

Yes, small and large case.

Someone has fitted a Z3 diff cover to an E30 as a straight swap - very nice, but hold on....the Z3 cover has 8 bloody bolt holes... is going on here????

Yes. 325I has large case diff with 8 bolts. I believe to change from the small case to the larger (same as the E28) you will need to change the driveshafts.

Just been outside to look at the underside of my 320 and that has a small case diff. The subframe is the same for all so the large case will bolt up to it and also the eye bush irons are in the same place. I think you'll just need new driveshafts

[Sooty]

You are a star of the highest order Sir
I owe you a

Iain S

[Brianmoooore]

Whoa, before you hand out the pints!
First of all, since we are bringing E28s into this, it's small case and medium case on E30s
E30s except the 325 have small case diffs. The 325 E30 diff is medium case. The two sizes are interchangeable without swapping anything else.
Some smaller E28s have the medium case diff, others have a large case diff and won't fit an E30 without extensive (but possible) mods to the E30.
The E28 medium case diff will fit straight into an E30 with a change of output flanges and rear cover from an E30 325 diff.
If you use an E30 gearbox with an M50 conversion, then ordinary E30 diffs will do, although the 240 box and small case diff from the smaller E30s will have a reduced life.
If you use an E36/E34 gearbox with an M50 conversion (1:1 5th gear instead of 4th ), then you will need a lower ratio diff, like the 525e one.
IIRC, the E30 M3 diff is 3.25, which will also do, although a bit high for my taste.

[old_skool]

So that is good news

[Brianmoooore]

They do have different part numbers, but their dimensions are the same. Output flanges are longer on the small case diffs.

[Sooty]

Bugger....I should have known it could'nt be that easy.

OK then....I've got the 328i ZF g/box so I know I need the E28 diff with a cover & flange swap.

My 320 cab had the small case diff, so the rear cover & flanges aren't going to be any use. That can go in the bin.

The diff I got from fleabay is a 525e, 3.07 pictured below




Question now is, is this a large case or a small case?

[old_skool]

Looks the same as the one one my 325, if you want a rear cover for that then I have one here you can have

[Brianmoooore]

Front half looks like an E30 fitting, so I think you're right so far. All you need to do now is find a rear cover and output flanges from a clapped 325 E30 diff, and someone who wants a nicely cleaned up rear cover for an E28 diff.
Did you buy this off ebay about three weeks ago. If so, there was a 2.7 engine advertised as well. I was watching them, and wouldn't have minded picking them up (Dorset or Hampshire, IIRC) as long as I got both. Was delayed somewhere, and missed the end of the auction.

[Sooty]

Yes, I got the diff from this guy based in Bournemouth.
http://stores.ebay.co.uk/Retro-Parts_W0 ... esstQQtZkm

TBH, I don't think I'd use him again because he got a bit arsey with me.

I sent him some emails requesting courier costs & received no reply.
Sent him another a week later, which he responded to claiming that he had'nt received anything from me & basically I was a tw*t because he checked his mails at least three times a day.

The only trouble was, all the emails were sent to the same address

Re the diff, I've had it in the car once & it fits so I think I'm going to be OK.
I take it the E28 large case diff does'nt fit the E30 axle beam?

Looks the same as the one one my 325, if you want a rear cover for that then I have one here you can have

Thanks for the offer m8, much appreciated, but a mate of mine is breaking a 325 Tourer locally, so I should be able to get the cover & flanges from him (fingers crossed).
I'll keep you posted

[Brianmoooore]

Yes, I got the diff from this guy based in Bournemouth.
http://stores.ebay.co.uk/Retro-Parts_W0 ... esstQQtZkm

TBH, I don't think I'd use him again because he got a bit arsey with me.

That's the same guy, and presumably the same diff.
I got the impression that customer relations wasn't his strong point as well.
Sent him a question asking what the ratio was, and had a rather curt reply stating all 525e's are 2.93:1, as if anyone over the age of five who didn't know this must be a total moron.

[Sooty]

Sent him a question asking what the ratio was, and had a rather curt reply stating all 525e's are 2.93:1,

LOL at that one.

The dozy tw*t obviously did'nt read the diff tag on the one he sent to me that quite clearly reads 3.07