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E30 medium case into a 2002, yes you can with OEM parts!


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If you can weld, this isn't a difficult project.

For those of you interested in the E30 medium case differential swap, I’ve got some very good news on how you can do it for next to nothing. The main concern I, and others, had was about needing custom axles to fit. Well, fear not, the early E21’s(77-79) with a 6bolt 10mm flange on the trailing arm side and 6 bolt 8mm flange on the diff side are the PERFECT length when using 2002 trailing arms and the E30 medium case differential. The E30 output flange bolt pattern is the same as the later E21s

The differential still doesn’t bolt to the rear subframe, but it isn’t hard to jig it up and cut/weld it in. Now, the only problem is the differential height. If you make a jig on the OEM subframe(I used an old driveshaft joint cut off and welded to the subframe) the differential will stick farther back, but should still clear the gas tank/spare tire well by about an inch. For height you have two options, either attach the diff lower on the subframe and notch the subframe to clear the driveshaft, or mount it in the stock ’02 location(height wise) and cut/raise the trunk floor a bit. I plan on cutting the trunk floor to keep the driveshaft in its OEM alignment. Height wise we’re talking about raising the center of the trunk floor between the shock towers about 1”. After looking at this again, it looks like you'll only need to bump up a small portion of the trunk floor, possibly even a hammer would do it.

I hope to stick this under my car in the next 3 weeks or so, I'll post up again with whatever mods to the body need to be done.

OEM parts you need

-02 rear subframe

-02 trailing arms

-E30 medium case di fferential + mounting bolts

-77-79 E21 halfshafts + 12 10mm bolts from trailing arm/halfshaft side

-e36 diff cover which has two hanger mounts(not absolutely necessary, but much better than the E30 diff cover with only one mount)

-4bolt flange from an old driveshaft, side that bolts to the differential

It's hard to see with the pic but that actually is just over .5" instead of under. The halfshaft in place fits just like it does on the stock '02 setup. Cycled through it's travel it doesn't come close to straining the cv joint or compressing it more than it does on the stock setup.

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Now lets see some 400hp turbo M20 and turbo M10 2002s!

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Looks like its getting there! What's up with the 2 tabs in front of the U joint? What is the modified mount from? Where can one source the half shafts? I looked today for a reseller and couldnt find one.

Edit: tabs are the jig... How are you building the mount? Triangulated from the subframe to diff to body?

This would be sweet to do but not sure I'd be willing to chop and hack at a good rear subframe, just for me to screw it up.

75 2002 "Project Turb02"

95 Hellrot M3 *Sold

95 332is *Sold

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parts list is in the first post

I was originally going to weld on that portion of the E30 rear subframe, but now I think I'll use something like 1/8" plate and make a cage similar to what 2002haus did, there isn't much room for variation because the exhaust needs to go between the inner trailing arm mount and diff. That's why I'm not using the e30 portion, it block the exhaust route. The E30 subframe is thinner than 1/8", looks like 0.083, so 1/8" should be plenty.

It'll take a few weeks, still need to finish up my agave, but I'll post my finished subframe in my build blog when it's done.

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So the E30 medium case is the same size as the E36 medium case?

Hmm, ive got a 3.23 from my old M3...I might take a look at this after all...

Where would be the best place to source the half shafts?

75 2002 "Project Turb02"

95 Hellrot M3 *Sold

95 332is *Sold

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I just spent the better part of 2 days replacing a broken subframe in a 318is this looks real familiar. What is the difference of the output flange geometry front to back on the e30 diff vs. the 2002 diff? Is the stock configuration the same as the new one? The photo appears to show some deflection but it may just be the angle of the camera shot.

Ahlem

'76 2002

'90 M3

'90 535i 5 speed

'89 325is '91 318is

'87 325is

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So the E30 medium case is the same size as the E36 medium case?

Hmm, ive got a 3.23 from my old M3...I might take a look at this after all...

Where would be the best place to source the half shafts?

I'd check a junk yard or bimmerforums for the E21 halfshafts. That car doesn't have as big of a following so finding them might be kinda tricky. E30 medium case differentials are the same size internally but I don't know what their width is or what the output flanges look like. I'd look for an E30 medium case open diff and swap your internals/diff cover into it.

The diff is roughly 1" further back, deflection is less than 5 degrees. This is only due to where I attached it, obviously you could mount it further forward. I'll have to check mine again but I believe you could get it back to 0 degrees of deflection with out running into subframe beam/driveshaft clearance issues. I'm going to leave it there, I really don't believe 5 degrees will destroy the CV. Different application, but we ran our FSAE diff as far back as possible for weight dist, those halfshafts were over 10 degrees and we never had a problem in 3 years with them.

If you did mount it 1/2" further forward, you could use an E30 eta big flange driveshaft behind an Getrag 265 on the M10 for a perfect fit. Basically a bolt in 400hp driveline. The Getrag 265 is 2" longer than the M10's Getrag 245.

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That trans is what Ill be installing for my turbo setup. Itd be nice to be able to use the E36 medium case diff that I have and just have to source the half shafts.

I wonder how the motor would act with the 265 gearing and a 3.23 lsd? May not be optimal. possibly a 3.36 would be better?

75 2002 "Project Turb02"

95 Hellrot M3 *Sold

95 332is *Sold

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It should be fine. It will take a bit longer to build boost, but you'll be able to stay in boost for longer. I've got a 3.73, but I plan on replacing it with something around 3.46, maybe even lower.

265 gearing is almost identical to 245, so that's not going to be a problem.

This will help.

Diff guide

http://www.metricmechanic.com/pdfs/metric-mechanic-differential-booklet.pdf

Eta cars with the larger output flange transmission(driveshaft is what you want) are 86/87, possibly 88 on the 325 cars(super eta motor), not the 325i. Standard "i" output flange is the same bolt pattern as the Getrag 240/245

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