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-   -   rear limited slip diff in an XI (http://forum.e46fanatics.com/showthread.php?t=820180)

gurov 01-31-2011 12:23 PM

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.

Kubica 01-31-2011 12:55 PM

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.

gurov 01-31-2011 01:25 PM

Quote:

Originally Posted by Kubica (Post 12753042)
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

SamDoe1 01-31-2011 03:21 PM

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.

Kubica 01-31-2011 04:00 PM

Quote:

Originally Posted by SamDoe1 (Post 12753760)
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?

gurov 01-31-2011 05:20 PM

Quote:

Originally Posted by Kubica (Post 12753962)
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 ?

lotar_6 02-01-2011 05:14 AM

don't the front and rear diff. ratios need to match??

Quote:

Originally Posted by gurov (Post 12754385)
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"!!!!!

gurov 02-01-2011 05:45 AM

Quote:

Originally Posted by lotar_6 (Post 12756839)
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.

sbiggi 02-01-2011 07:03 AM

Quote:

Originally Posted by gurov (Post 12754385)
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.

Kubica 02-01-2011 09:52 AM

Quote:

Originally Posted by sbiggi (Post 12756911)
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?

Mark M 02-01-2011 09:55 AM

I have a NV124 transfer case sitting on my workbench at home, let me know if you need me to do any tests.

gurov 02-01-2011 10:08 AM

Quote:

Originally Posted by Mark M (Post 12757301)
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.

sbiggi 02-01-2011 10:15 AM

Quote:

Originally Posted by Kubica (Post 12757294)
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.

colo330xi 02-01-2011 11:04 AM

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.

Kubica 02-01-2011 11:45 AM

Quote:

Originally Posted by sbiggi (Post 12757362)
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.

SamDoe1 02-01-2011 11:57 AM

Quote:

Originally Posted by Kubica (Post 12757703)
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.

Mark M 02-02-2011 08:45 AM

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.

sbiggi 02-02-2011 09:11 AM

Quote:

Originally Posted by Mark M (Post 12761807)
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.

SamDoe1 02-02-2011 10:12 AM

Quote:

Originally Posted by Kubica (Post 12753962)
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... :facepalm:

Kubica 02-02-2011 11:39 AM

Quote:

Originally Posted by sbiggi (Post 12761877)
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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