Swapping Differential Gearset

[Garageaholic]

How difficult is it to swap the gears on the medium case LSD diffs? It seems to be a relatively cheap alternative to going to a ratio like 3.07 or 3.15, but if I buy just the gear set for 188mm medium case, are the gears easy to swap?

I searched and couldn't find much on this subject, although I looked up some threads of people selling just the gears, so it shouldn't be too hard I assume.

[Wanganstyle]

How difficult is it to swap the gears on the medium case LSD diffs? It seems to be a relatively cheap alternative to going to a ratio like 3.07 or 3.15, but if I buy just the gear set for 188mm medium case, are the gears easy to swap?

I searched and couldn't find much on this subject, although I looked up some threads of people selling just the gears, so it shouldn't be too hard I assume.

not difficult if you have done a bunch before. or done similar rear end configuration.

3.07, 2.93, 2.79, 2.65 share one geometry of differential center.
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3.15, 3.23, 3.46, 3.64, 3.73, 4.10, 4.27, 4.88 share a DIFFERENT geometry of differential carrier.

Shims are sold by BMW and you can order them directly from germany in a setting package. quite a bunch of them in the kit (not cheap either)

Everything else is pretty standard :)

what are you trying to do?

[Garageaholic]

I'm going from S3.73 to S3.15 and I believe all I need is the gear set for 3.15 and can figure it out. I am getting that the consensus here is that it is relatively easy.

With S3.73 to S3.15, I don't think i will need any shims as it is the same gear set geometry, right? Thanks again,

[Wanganstyle]

I'm going from S3.73 to S3.15 and I believe all I need is the gear set for 3.15 and can figure it out. I am getting that the consensus here is that it is relatively easy.

With S3.73 to S3.15, I don't think i will need any shims as it is the same gear set geometry, right? Thanks again,

........

ONE THING OF NOTE; 3.15 AND 3.23 GEARSETs from WBS vin number M cars have M12 bolts. non-M cars have m10 bolts. Just some food for thought..... if trying to install a 3.15 in place of a 3.73 you will need to find one from a NON-M car otherwise the hardware will NOT FIT.

Have you ever set up a ring and pinion set from scratch? you might be better off just buying a 3.15 LSD as you do risk ruining BOTH 3.73 and 3.15 by doing this operation incorrectly. 3.15 LSD for a e30 is not that uncommon;

I have purchased complete units of (instead of custom building) OEM BMW 3.15 and a 3.23 (z3m) and 2.93 (e30 eta) for e30 fit in 188mm LSD - I have also a fully custom built 3.15 in my own e30, a pretty special need to build it full custom.

Sell the 3.73 and the 3.15 and buy the ratio diff complete you want.

plug and play 2.93, 3.07, 3.15, 3.23, 3.46 ALL avail. e30 diff case is the LONGEST run item by BMW. (e24/28/30/36-7). spans from 1979-2002

also for a proper install the bearings/races/seals need to be changed if you are going into this as the bearings installed on the Pinion will NOT match the races on the diff case.which are pressed in the diff case and don't go in with average garage tools happily).

...... you always need shims to set gearing properly.
one crush washer on pinion relationship needs to be replaced with brand new and crushed to proper loading on the 2 pinion bearings.
one spacer under the pinion race that needs to be properly set also. not as easy as it seems.


even the differential IN YOUR CAR RIGHT NOW could benefit from a reshim. they do wear you know.

It's a little more than just slamming a set of gears in a case. I have seen more than a few ugly improper gearing installs........and it does show up on the pattern and badwear/play.

if you want to know the factory instructions look up : e30 tis (m3). full OEM TIS service for rear diff.

[Garageaholic]

Thanks a lot for the very detailed response.

Looks like I might be better off just buying this:
http://www.ebay.com/itm/BMW-E30-M3-3...r#ht_500wt_999

and 40% lockup would be really nice, although I have no intention of drifting.


EDIT: The ebay ad doesn't even include the rack & pinion. Forget it.

[Holland]

^ If that is a 3 clutch then you could do it yourself for cheaper.

[Garageaholic]

........plug and play 2.93, 3.07, 3.15, 3.23, 3.46 ALL avail. e30 diff case is the LONGEST run item by BMW. (e24/28/30/36-7). spans from 1979-2002

So with that being said (Plug and play for the models you listed above),
I know this is a basic question, but If I buy an E36 S3.15 from say an E36 M3, how would I install this in my E30? I don't think the housing would bolt up.

I know that many E28/E24/E23 diffs bolt up if you exchange the output flanges and the back cover, but is that the case with E36 too?

Thanks again,

[Wanganstyle]

So with that being said (Plug and play for the models you listed above),
I know this is a basic question, but If I buy an E36 S3.15 from say an E36 M3, how would I install this in my E30? I don't think the housing would bolt up.

I know that many E28/E24/E23 diffs bolt up if you exchange the output flanges and the back cover, but is that the case with E36 too?

Thanks again,

Point of note: the ebay linked item is using USED BEARINGS, RACES.... nowhere does it state that they are matched items......

quite possibly a hodgepodge mix match of items. I would bet they are NOT starting with an original 3.15 e30 case dif........ not a full rebuild item.................. I would rather buy a complete used 3.15 instead of risking mix-match on bearing+ races......might be ugly. I can send you a used mystery 3rd clutch disc to create an ebay diff for $0. lol

e36M3 sedan and coupe use a different updated newer style of differential case.

e36-7; Z3 - it is a e36. you can fit an E30 diff into a E36-7 Z3, vice versa. Also e36 318ti compact uses the e30 diff standard -Many of them fit e30 units.

3.15 LSD was avail on 2.8L and 3.2L Z3 models.

e36-7 has funny output stubs somtimes, also slightly different rear backing plate cover to fit small speedo spider. but it is a plug and play item if you have the proper e30 output stubs installed and proper speed sensor in to match the e30 (e30's have 2 styles)