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E46 Xi Forum
The E46 XI was produced from 01-05 in sedan and touring body styles. Powered by either a 2.5L inline 6 in the 325xi or a 3.0L inline 6 330xi. Discuss all thing about BMW AWD E46 'Xi' here.

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Old 01-31-2011, 12:23 PM   #1
gurov
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rear limited slip diff in an XI

the auto differentials are 3.46, it's highly unlikely i'd be able to get anything for the front, but what about the rear ?

i'm seeing various 3.46 differentials on ebay for M3 e36, but i'm going to guess this ain't going to be a very easy task and will likely require some very custom mounts/modifications ?

and yes, i looked at turnermotorsports, and that would probably work, but forking over 3-4 grand for this is somewhat suboptimal.
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Old 01-31-2011, 12:55 PM   #2
Kubica
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You'll need to have a 3.46 lsd rear bulit.

www.diffsonline.com. Good people.

I don't believe an e36 diff will fit.
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Old 01-31-2011, 01:25 PM   #3
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Quote:
Originally Posted by Kubica View Post
You'll need to have a 3.46 lsd rear bulit.

www.diffsonline.com. Good people.

I don't believe an e36 diff will fit.
cool, thanks for the link.

i wasn't exactly expecting it to be a direct swap
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Old 01-31-2011, 03:21 PM   #4
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You could also swap in an E46 M3 LSD if you were to swap in the entire rear subframe. This includes the subframe, diff, halfshafts, carriers, etc... You might have to get a custom driveshaft though, but I'm not sure about that.
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Old 01-31-2011, 04:00 PM   #5
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Originally Posted by SamDoe1 View Post
You could also swap in an E46 M3 LSD if you were to swap in the entire rear subframe. This includes the subframe, diff, halfshafts, carriers, etc... You might have to get a custom driveshaft though, but I'm not sure about that.
Could you? Could you really?

Come on chief . . .what ratio does an M3 have?
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Old 01-31-2011, 05:20 PM   #6
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Quote:
Originally Posted by Kubica View Post
Could you? Could you really?

Come on chief . . .what ratio does an M3 have?
i'm sure one could obtain 3.46 M3 diff to go with the subframe, the fine people in the links mentioned above would be able to provide such a device.

that's not the point though... surely the differential mounts could be fabricated to hold any differential. the amount of work that would take is a whole different story, and that would be kind of crazy.

speaking of crazy, since the center diff is a fixed ratio, what would happen if the front driveshaft is simply removed ?
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Old 02-01-2011, 05:14 AM   #7
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don't the front and rear diff. ratios need to match??

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Originally Posted by gurov View Post
speaking of crazy, since the center diff is a fixed ratio, what would happen if the front driveshaft is simply removed ?
why???? just sell it and pick up an "i"!!!!!
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Old 02-01-2011, 05:45 AM   #8
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Quote:
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don't the front and rear diff. ratios need to match??



why???? just sell it and pick up an "i"!!!!!
yes, they do need to match.

and the other thing for dyno purposes, for example. dunno if I would do it tho.
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Old 02-01-2011, 07:03 AM   #9
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speaking of crazy, since the center diff is a fixed ratio, what would happen if the front driveshaft is simply removed ?
Its a open center diff, you would just sit there as the front output shaft spun.
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Last edited by sbiggi; 02-01-2011 at 07:04 AM.
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Old 02-01-2011, 09:52 AM   #10
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Its a open center diff, you would just sit there as the front output shaft spun.
How can you have an open diff with a fixed ratio?
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Old 02-01-2011, 09:55 AM   #11
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I have a NV124 transfer case sitting on my workbench at home, let me know if you need me to do any tests.
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Old 02-01-2011, 10:08 AM   #12
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Quote:
Originally Posted by Mark M View Post
I have a NV124 transfer case sitting on my workbench at home, let me know if you need me to do any tests.
hold rear output flange stationary, see if you can rotate input shaft with the rear output flange still. it should force the rear one to rotate as well as the front one.

what shouldn't happen is front one free spinning as the rear is held.
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2004 325xi turbo - megasquirt3 for engine, swapping to 5 speed build thread
1994 supra MKIV - single 72mm - aem v2, 1000CC ID, dual denso pump, j&s ultrasafeguard
2004 SE-R SpecV turbo - megasquirt3 j&s ultrasafeguard - SOLD
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Old 02-01-2011, 10:15 AM   #13
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Originally Posted by Kubica View Post
How can you have an open diff with a fixed ratio?
Different tooth count off the input shaft in the trasfercase. I havent seen inside one of these, but I imagine there is a set of spider or planetary gears in the center diff that outputs to the driveshaft.
http://www.automaticchoice.com/Catalogue/tb_nv_124.pdf

If it wasnt a open diff the car would bind up like a truck in 4x4 in parking lots.
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Old 02-01-2011, 11:04 AM   #14
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Here's a site with some more info on the T-case.

http://www.xiftw.com/?page_id=16

Looks like that planetary set gives you the differential action.
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Old 02-01-2011, 11:45 AM   #15
Kubica
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Originally Posted by sbiggi View Post
Different tooth count off the input shaft in the trasfercase. I havent seen inside one of these, but I imagine there is a set of spider or planetary gears in the center diff that outputs to the driveshaft.
http://www.automaticchoice.com/Catalogue/tb_nv_124.pdf

If it wasnt a open diff the car would bind up like a truck in 4x4 in parking lots.
It can be either open or fixed.

Torque is split 38/62, not speed. The front and rear diff is open. The TC is not.

You would only ever have one wheel getting power if there were open diffs and an open TC. It's obviously not 100% locked up, and can obviously slip a a bit. Think of it like an LSD with 99% lockup. Definitely not open.
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Old 02-01-2011, 11:57 AM   #16
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Quote:
Originally Posted by Kubica View Post
It can be either open or fixed.

Torque is split 38/62, not speed. The front and rear diff is open. The TC is not.

You would only ever have one wheel getting power if there were open diffs and an open TC. It's obviously not 100% locked up, and can obviously slip a a bit. Think of it like an LSD with 99% lockup. Definitely not open.
Right, the center diff is a locked (kinda) diff. The speed variation is done left to right not front to back. So the front and rear diffs account for the variation in wheel speed.
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Old 02-02-2011, 08:45 AM   #17
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Ok....here are the simple observations from the test of the NV124 case on my workbench.

- Spinning input shaft by hand.....both output shafts rotate
- Spinning input shaft by hand and holding rear output shaft stationary.....front output shaft rotates.
- Spinning input shaft by hand and holding front output shaft stationary.....rear output shaft rotates.

Caveat....these tests were done with spinning by hand, which does not simulate rear world forces transmitted into the driveline.

Thus, my conclusion, you can NEVER make an XI into a rear wheel drive by simply disconnecting front driveshaft. It will just send all the power to the front output shaft and spin endlessly without putting power to the rear.
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Old 02-02-2011, 09:11 AM   #18
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Quote:
Originally Posted by Mark M View Post
Ok....here are the simple observations from the test of the NV124 case on my workbench.

- Spinning input shaft by hand.....both output shafts rotate
- Spinning input shaft by hand and holding rear output shaft stationary.....front output shaft rotates.
- Spinning input shaft by hand and holding front output shaft stationary.....rear output shaft rotates.

Caveat....these tests were done with spinning by hand, which does not simulate rear world forces transmitted into the driveline.

Thus, my conclusion, you can NEVER make an XI into a rear wheel drive by simply disconnecting front driveshaft. It will just send all the power to the front output shaft and spin endlessly without putting power to the rear.
Like I said, its a open differential. Which is why the awd system on the XI sucks ass. Without DSC turned on, you have nothing to prevent all the torque being transfered to the tire with no traction. There is another thread where someone removed the front drive shaft and couldnt move his car if you need further proof.
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Old 02-02-2011, 10:12 AM   #19
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Could you? Could you really?

Come on chief . . .what ratio does an M3 have?
Sorry! Guess I wasn't thinking when I posted that. My bad...
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Old 02-02-2011, 11:39 AM   #20
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Which is why the awd system on the XI sucks ass.
Sell your xi then.

It's an amazing machine for a talented driver, which you most certainly are not with an opinion like that.
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