E30 Diff in e21 subframe...

**jjgbmw323** · 10-18-2009, 09:41 PM

Guys I am wondering if anyone has swapped and E30 diff into the e21.

I was thinking about going to a e30 LSD, and noticed that there are quite a few available. It also looks like you can even retrofit an old 7 series LSD and change the diff cover and the flange and presto you have a e30 diff.

Has anyone ever installed the e30 axles and e30 diff in the e21? How hard is it too do? They seem to have no problems with high HP applications...

Also the stock 323i diff is 3.64, I already have a 320i 3.9 lsd, but I have noticed that e30 diff come in many configurations:

2.93, and 3.46, 3.73. Which one work work best with the new 2.9 m20 I have in the works, and maybe someday a boosted M20?

**BoomerDJ** · 10-18-2009, 10:58 PM

had a friend look into this, all i know is that it will require extensive subframe and body modification to get the diff to fit

**FranzE21** · 10-18-2009, 11:37 PM

Uhh,

Hey aren't they still smallcase diffs no? Whats the point. All that work to get another reletively speaking, a weak diff.

**jrcook320** · 10-18-2009, 11:52 PM

Originally Posted by Big John

Uhh,

Hey aren't they still smallcase diffs no? Whats the point. All that work to get another reletively speaking, a weak diff.

4 cyl e30 = small case 168mm diff - 3.91 is rated at 240 ft-lbs of torque
6 cyl e30 = medium case 188mm diff - the 3.46 is rated at 420 ft-lbs of torque.

Go here, scroll to page 6:
metric-mechanic-differential-booklet.pdf

**kdanielson** · 10-19-2009, 12:00 AM

3.91 is WAY too low for any engine that makes serious HP. The 3.46 would be a good match with an overdrive 5th gear, the 2.93 would be best with a 1-1 5th gear.

ken

**nikch86** · 10-19-2009, 02:41 AM

Here is the question.
I know the mounting points on E30 small case diff are different from E21,
but can you swap the internals from E30 diff into E21 diff housing saving the output flanges. Or, is there any other differential that is suitable for this swap?

**jjgbmw323** · 10-19-2009, 06:48 AM

Originally Posted by jrcook320

4 cyl e30 = small case 168mm diff - 3.91 is rated at 240 ft-lbs of torque
6 cyl e30 = medium case 188mm diff - the 3.46 is rated at 420 ft-lbs of torque.

Go here, scroll to page 6:
metric-mechanic-differential-booklet.pdf

Thanks Josh..I know the e30 Turbo guys run the stock e30 diff and have no problems so I thought the e30 diffs where stronger.

Originally Posted by nikch86

Here is the question.
I know the mounting points on E30 small case diff are different from E21,
but can you swap the internals from E30 diff into E21 diff housing saving the output flanges. Or, is there any other differential that is suitable for this swap?

I do not know whats involved, but I know the Z3 diff is basically the same diff as the E30, and that even old 7 series diffs can swap the cover of the diff and the flanges and they become e30 diff. I am trying to figure out how to use either and E30 diff and axles on the e21 subframe, or as you said some other diffs internals. Not sure if you can fit and e30 diff internals in the e21 case, they look different and we would know about this by now someone would have tried it.
e30 diff internals

Originally Posted by BoomerDJ

had a friend look into this, all i know is that it will require extensive subframe and body modification to get the diff to fit

Thats too bad, because the M20 engine and M42 engines from the e30s fit into the e21, why wont the diff fit as well?

**jrcook320** · 10-19-2009, 11:03 AM

Originally Posted by kdanielson

3.91 is WAY too low for any engine that makes serious HP. The 3.46 would be a good match with an overdrive 5th gear, the 2.93 would be best with a 1-1 5th gear.

ken

agreed. I'm still running a 3.91 lsd right now because I'm over budget and out of time to rebuild my 3.45 into an LSD right now. I ran the 3.45 open for a few months this spring and loved it. The car felt so much more mature, comfortable, easier to drive, quieter on the highway and felt like it had longer legs. It also wasn't as violent in 1st or 2nd, but with the 3.91 1st gear is completely useless ( can't floor it in 1st without over revving it) and the car skates around in 2nd. I think you'll be happier with taller gears.

Originally Posted by nikch86

Here is the question.
I know the mounting points on E30 small case diff are different from E21,
but can you swap the internals from E30 diff into E21 diff housing saving the output flanges. Or, is there any other differential that is suitable for this swap?

I dont' think so, the ring gear and pinion are larger, it would take some serious machine work to do that. It would be easier to modify the subframe or just swap in a whole e30 rear subframe.

Originally Posted by jjgbmw323

Thanks Josh..I know the e30 Turbo guys run the stock e30 diff and have no problems so I thought the e30 diffs where stronger.

I do not know whats involved, but I know the Z3 diff is basically the same diff as the E30, and that even old 7 series diffs can swap the cover of the diff and the flanges and they become e30 diff. I am trying to figure out how to use either and E30 diff and axles on the e21 subframe, or as you said some other diffs internals. Not sure if you can fit and e30 diff internals in the e21 case, they look different and we would know about this by now someone would have tried it.

Thats too bad, because the M20 engine and M42 engines from the e30s fit into the e21, why wont the diff fit as well?

Doesn't the 7 series use the large case 210mm diff? Are you saying a large case diff fits the e30 with cover and flange swap?

The e30 diff doesn't fit because it's designed differently. Progress...

**jjgbmw323** · 10-19-2009, 02:18 PM

Josh I was reading an ad on ebay for an e30 diff that came out of a 7 series and was retrofited the e30 cover and flanges for the medium case diff.

I will see if I can find the ebay item number.

I just powdercoated my 323i Dinan subframe jet black and I when I install it I will be saving my old e21 rearsubframe. Next time I am the junkyard I will see If I can get a complete e30 rear subframe and diff. I dont know what modifications I need to do to the e21 one to make the medium case diff work, but If I have both of them out I bet it will be easy to see.

And after discussing it - I think Iwill have to get something like a 2.93 or 3.46 e30 LSD diff to work with in combo my 2.9 engine...

**superj** · 10-19-2009, 06:45 PM

why don't you use an e24 diff or old e12 diff? aren't those the same as the e21 diffs?

**rob0r** · 10-19-2009, 07:05 PM

Chopping the E30 centre section out and welding it into the E21 rear subframe, I think this guys has done a few of them

http://www.bmwe21.net/forum/viewtopi...r=asc&start=90

**nikch86** · 10-19-2009, 07:25 PM

Check this out. Read the description well

http://cgi.ebay.com/ebaymotors/BMW-2002-tii-E21-Limited-Slip-Differential-LSD-3-23_W0QQitemZ360193481960QQcmdZViewItemQQptZMotors_ Car_Truck_Parts_Accessories?hash=item53dd345ce8

I highlighted interesting details.

Here are the details:

Housing is from an E21, clleaned and painted.
Limited slip spool and gear set removed from an E30 323 euro car.
Spool machined to fit in E21 housing.
Spool disassembled and inspected for adverse wear. Reassembled. Tested for correct preload.
Entire diff assembled using new bearings and seals. Set up properly by a guy who has done 1000's of E21 and 2002 diffs.
Comes with double drilled drive flanges, hard anodized alumimum spacers, and longer bolts so you can bolt it right in your 2002.
Comes with new gasket, and plug crush seals.
Comes with 1 year warranty.

Does anyone has an idea how it was machined to fit e21 diff housing?
What part would have to be machined? The ring, lsd spool, pinion?
Or, can you bolt an lsd spool the the open diff ring? Actually, they say that only spool has been
machined to fit...

Sorry, but I'm just plagued by this idea after working with Nissans.
There, if you have a s13 240SX, you can swap lsd internals from Q45
to your diff housing.

**milotrain** · 10-19-2009, 08:11 PM

was there such thing as an E30 323?

**E21Adam** · 10-19-2009, 08:13 PM

Originally Posted by milotrain

was there such thing as an E30 323?

yup

**jjgbmw323** · 10-19-2009, 10:43 PM

Originally Posted by nikch86

Check this out. Read the description well

http://cgi.ebay.com/ebaymotors/BMW-2002-tii-E21-Limited-Slip-Differential-LSD-3-23_W0QQitemZ360193481960QQcmdZViewItemQQptZMotors_ Car_Truck_Parts_Accessories?hash=item53dd345ce8

I highlighted interesting details.

Here are the details:

Housing is from an E21, clleaned and painted.
Limited slip spool and gear set removed from an E30 323 euro car.
Spool machined to fit in E21 housing.
Spool disassembled and inspected for adverse wear. Reassembled. Tested for correct preload.
Entire diff assembled using new bearings and seals. Set up properly by a guy who has done 1000's of E21 and 2002 diffs.
Comes with double drilled drive flanges, hard anodized alumimum spacers, and longer bolts so you can bolt it right in your 2002.
Comes with new gasket, and plug crush seals.
Comes with 1 year warranty.

Does anyone has an idea how it was machined to fit e21 diff housing?
What part would have to be machined? The ring, lsd spool, pinion?
Or, can you bolt an lsd spool the the open diff ring? Actually, they say that only spool has been
machined to fit...

Sorry, but I'm just plagued by this idea after working with Nissans.
There, if you have a s13 240SX, you can swap lsd internals from Q45
to your diff housing.

Aye. I am interested also because it would appear the LSD internals from the e30 where swapped into an e21 housing. If so its the perfect solution to the problem that we are talking about in this thread.

In the ad is saws spool machined to fit in the e21 housing...what is spool machineD?

Spool machined to fit in E21 housing.
#
Spool disassembled and inspected for adverse wear. Reassembled. Tested for correct preload.

Originally Posted by superj

why don't you use an e24 diff or old e12 diff? aren't those the same as the e21 diffs?

I dont know if they are, or which year car to pull them from...and since my new 2.9 m20 engine started out in an e30 my thoughts turned to the e30 diffs which are ready available at any junkyard....

**Rickysbmw320i** · 10-19-2009, 11:15 PM

Who makes the most money here? they need to try to figure it out for the legion! GO JOE!

**reelizmpro** · 10-19-2009, 11:26 PM

E23?/E24/E28/E30 came with a bunch of diffs (2.79/2.93/3.25/3.46/3.64/3.73/3.91/4.10/4.27/4.45)

For a stroker M20, 3.73 is good. I run a 3.25 in my Turbo M20 powered Cabby.

**Layne** · 10-20-2009, 12:09 AM

E30 318i's and E36 318ti's (and presumably E30 323i's based on this ebay ad) have 168mm ring gears. You can install the ring gears in an E21 to change the ratio, but it isn't going to add any strength. There is no way you can put a 188mm ring gear in a 168mm case, they don't just leave extra space for kicks, it's damn tight as it is.

Joe, I'm sure you're talking about a e28/e24 medium case diff, which is the same as a e30 one except for the back cover.

SuperJ, the E12 one doesn't "fit". It can be made to fit with extensive modifications. It works the best though because the flanges are the same so you can use the same driveshaft and axle shafts.

**uberpanzer** · 10-20-2009, 12:16 AM

OK:

e30 323i was a euro car, not available in the US. Same motor as the e21 323i. Still no love for the US on that one.

Z3 diffs are BMW medium case diffs from the 80s-90s. So the same as the bigger e30 diffs, e28 diffs, etc etc. This INCLUDES the M Roadie and Coupe diffs, but those were built for a bit more torque (and there were also some Torsen diffs used in later Z3 M years). You can take the finned M Roadie cover and bolt it directly onto any other medium case diff (including the e30 M3) and have a nice cooling upgrade.

I'm not fully versed on some of the older diffs, but I thought e12's had side loaders. So that wouldn't work. Or is that the Bavaria's and the e9's?

Saying diff ratio X.XX:1 is no good (too high or low) for a specific power output is totally useless if you are not talking about any of the other gear ratios in the tranny. And that isn't even touching the topic of what the car is going to be used for. Someone just doing track and autoX or hell even lots of street driving may not want anything near what someone else with less HP wants if the other person does a lot of highway driving.

What it is going to boil down to though is the mounting points of the diffs and the flanges of the shafts, both input and output. You also have to take into account the geometry of everything once it is mounted, since too much of a difference in the positions of the shafts connecting up to the e30 diff will not translate well into connecting said diff to everything. The beauty of the small and medium case diffs used in the e30 were that you can swap freely between them. The mounting points and how all the shafts lined up were close enough to work just fine. Of course you wouldn't want to use a small case diff on a higher torque M20 or S14 application, but you could get away with it on a stock motor if need be (like to limp home after blowing a diff).

As for YOUR application Joe, how much torque are you REALLY making in this new motor? I haven't seen a dyno sheet for you yet, nor do I know what your gearing is in the tranny. From what I know of M20 builds though, without MS or a trick ITB set-up and a twin cam head, you're going to be hard pressed to be making much more than 230 ft-lbs of torque. The 2.5L M20 was running 167hp stock. A few years back the most tricked out NA M20 I had seen to date only had a smoking 290hp at the fly and was not making anything CLOSE to that in torque (wild cam for peaky high rpm power but sucking on twisting power). I'm pretty sure that was a 2.9L motor, but can't remember. It was one of the ones people were perplexed by since it was barely making 100hp/liter, but they were forgetting it was a single cam head which can hurt your air-flow a lot.

That MM tech article doesn't specify the e21 323i diff torque rating, but let's guess that since they talk of the 168 (small case) diffs having the 3.64 ratio you quoted your 323i having stock and you 3.91 you've got from a 320i, that both are 168 diffs. The 3.64 has a torque rating of 260ft-lbs, the 3.91 has 240. If you are making much more than 240ft-lbs of torque I would NOT try to drop in the 3.91 diff. You may damage it. I'm guessing that the 323i and 320i diffs are 100% swappable (size/shape/angles), which leads me to believe that they are both 168 as well. If that is the case, I'm not sure our rear subframes are set-up for many other diffs, especially looking at the casing there for the 168 2002 diff vs the e30 188 diff. I would think that you can mod the mounting points of the diff and subframe to get a 188 to fit, but would have to see it all apart to be sure, specifically whether the output flanges would line up correctly with the half-shafts. Going that route would work much better for you, putting that margin of caution/safety back into the torque load the diff can accept, even if you don't need ALL that extra room. But if you hope to go with forced induction on this motor in the future, you will NEED that growing space.

It does look like the limiting factory of swapping the 188 hardware into the 168 casing is the inner dimensions of the casing itself. You could investigate that machining option, but honestly I would think it would be easier (and give you more piece of mind) to swap in the 188 casing with internals vs milling down the internals to fit a 168 case. I haven't tried either though.....

**Layne** · 10-20-2009, 12:24 AM

Originally Posted by uberpanzer

I'm not fully versed on some of the older diffs, but I thought e12's had side loaders. So that wouldn't work. Or is that the Bavaria's and the e9's?

Yes, the E12 is a sideloader. But the flanges are the same and in the same locations as an E21. The housing is just different. (much bigger and mounted from the top) As far as I have understood, it is the ONLY bmw diff to share these dimensions with an E21, so ANY other diff will require a custom driveshaft (problem) or custom axles (big, big problem) in order to be swapped in. I don't know all the details, but Ken should be able to enlighten us soon with his large case diff install.

P.S. the E21 stub axles are still very twiggy by comparison to any other bimmer, so don't bother too much with diffs without considering a full subframe transplant.

**nikch86** · 10-20-2009, 03:12 AM

Here I found a good diagram of the internals of E21 differential. I can't find one for E30

I was just thinking.
Can I just swap a lsd unit from E30 small case diff? Will it bolt to my ring gear? Will the output flanges work?
Is the ring gear from E30 small case diff the same in diameter with E21 ring gear?

**Rickysbmw320i** · 10-20-2009, 03:24 AM

I can answer one question and that is the bavaria, the e12, and e9 all have a sideloader diff.

**jjgbmw323** · 10-20-2009, 07:07 AM

Doug, and everyone thanks.

For the purposes of this discussion, I would tell you I have no idea what my new engine is going to put out, but I bet its around 230 hp and 230 tq.
So I can make due with the 323i diff which I have that is not lsd and I think that is a 3.64 diff. I dont think I am going to run the 320i LSD as its geared to high.

The reason why I was asking about this was two fold:
1) A lot of people are doing swaps like Ken that require diffs.
2) I always wanted a m20 2.9 turbo, but I did not build one cause the tranny and diff can not handle this power.

Originally Posted by Layne

E30 318i's and E36 318ti's (and presumably E30 323i's based on this ebay ad) have 168mm ring gears. You can install the ring gears in an E21 to change the ratio, but it isn't going to add any strength. There is no way you can put a 188mm ring gear in a 168mm case, they don't just leave extra space for kicks, it's damn tight as it is.

Joe, I'm sure you're talking about a e28/e24 medium case diff, which is the same as a e30 one except for the back cover.

SuperJ, the E12 one doesn't "fit". It can be made to fit with extensive modifications. It works the best though because the flanges are the same so you can use the same driveshaft and axle shafts.

Yes I was talking about the medium case diff Layne, but it does not look like it can fit without and extensive redesign of the subframe.
I am not sure if the e30 medium case diff internals can be shoehorned into the e21 small case diff. No one I know has tried this, so we are in new territory.

I don't know anything about the e12 sideloader diff, I will have to look into getting one. Question: if you had 350-400 hp from a m20 turbo and where running a sideloader diff would the axles on the e21 handle this?

Oh well Interesting discussion. Guys thanks for the help, feel free to add any ideas about this that you have. Mostly likely Ken or Josh will come up with a solution to this, as they are very technical and good a fabrication.