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ix differential compatible with all E30's?

Posted by Earendil 
Title pretty much says it all.
I have a 3.73 open diff in my car. I'm tired of parking one wheel on a half inch of snow, and having the car become immovable.
Up on craigs list is a 3.91 LSD from a '91 ix.
I don't care about a few higher revs on the freeway, I want an LSD! smiling smiley
Are the differentials a direct swap?

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles




Edited 1 time(s). Last edit at 01/13/2010 11:24PM by Earendil.
aww man... on my list... a slightly taller LSD

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Quote
Earendil
Title pretty much says it all.
I have a 3.73 open diff in my car. I'm tired of parking one wheel on a half inch of snow, and having the car become immovable.
Up on craigs list is a 3.91 LSD from a '91 ix.
I don't care about a few higher revs on the freeway, I want an LSD! smiling smiley
Are the differentials a direct swap?

It should drop right in. Note that the iX differential has a viscous clutch instead of the normal clutch pack.

To some drivers this makes a difference. The difference being that the viscous LSD is better in the snow and slippery conditions while the mechanical clutch pack is better in dry conditions.
wow, I wasn't aware that there were two different LSD types on the E30's. Color me surprised. I was about to ask what the difference is, when I decided I'd pop over to wikipedia and see if they had anything to say about a viscous clutch. Sure enough, they do!

I found this bit particularly interesting...

"Viscous LSDs are less efficient than mechanical types, that is, they "lose" some power. They do not stand up well to abuse. In particular, any sustained load which overheats the silicone results in sudden permanent loss of the differential effect.[5] They do have the virtue of failing gracefully, reverting to semi-open differential behavior. Typically a visco-differential that has covered 60,000 miles (97,000 km) or more will be functioning largely as an open differential;"

So unless BMW build there's differently, finding a Viscous LSD with only 80K* miles on it probably isn't such a great deal?
An increase in snow ability would be nice, but I would be doing it for the performance increase as well. If it's okay to suck power and revert to an open diff with time, it's probably not worth the effort to swap them. Anyone agree/disagree?



*When did I start thinking 80,000 miles was a small number? confused smiley

-----------------------------------------------------------------------------------
1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

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Archeo-peteriX
It should drop right in.

Oh, if only it would just drop in (he says, with the experiencing of "dropping" in a drive shaft way too fresh in his memory).

But, I know what you mean smiling smiley
Thanks for the answer!

-----------------------------------------------------------------------------------
1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles




Edited 1 time(s). Last edit at 01/14/2010 12:02AM by Earendil.
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Earendil
I found this bit particularly interesting...

"Viscous LSDs are less efficient than mechanical types, that is, they "lose" some power. They do not stand up well to abuse. In particular, any sustained load which overheats the silicone results in sudden permanent loss of the differential effect.[5] They do have the virtue of failing gracefully, reverting to semi-open differential behavior. Typically a visco-differential that has covered 60,000 miles (97,000 km) or more will be functioning largely as an open differential;"
You know how when you were in college, you probably had professors who wouldn't accept Wikipedia as a source? (If you didn't, you should have.) This is exactly why. Any yahoo with a keyboard can write stuff in Wikipedia, and they do.That Wikipedia entry is mostly BS based on a grain of truth. The grain of truth is that viscous couplings are subject to failure due to abuse. But the "abuse" that leads to failure is forcing one wheel to turn a lot faster than the other wheel for a sustained period of time. The viscous goo inside the diff is trying to keep the wheels turning at the same speed. If you force the wheels to turn at different speeds, the goo becomes overheated and destroyed.

Usually in iX's the diff that succumbs to this failure is the center diff, when people tow the cars with the rear wheels on the ground. This makes the rear wheels spin at road speeds, while the front wheels are stationary, and the center viscous coupling is destroyed. This has happened to a lot of iX's over the years, and is probably the main thing to look out for when buying one.

I've never heard of a rear diff suffering the same fate. I'm not saying it doesn't happen, but you would have to get awfully creative to make the left and right wheels turn at such drastically different speeds.

There are lots of iX's still on the road with 150K-200K miles (mine included) with the viscous couplings still in perfectly good shape. I have tested mine (at least the center one), and my experiences snow driving and ice racing bears out the results of the test. That 60K-mile life span claim is pure BS.

Having said that, you don't see many viscous LSDs used in performance applications -- it's mostly a snow/gravel/loose stuff thing (where it excels). For performance on tarmac, I'd be looking at a clutchpack diff (or a Torsen, which is the third kind of LSD, but which BMW doesn't make).

__________
Dave
'91 325iX
FYI, a guy on the iX mailing list is giving away two iX diffs for free (plus shipping from Dayton, OH). One is a 3.91 and one is a 4.10. Link is here (you need a yahoo account to view it):
http://autos.groups.yahoo.com/group/thebmw325ixclub/message/25363

__________
Dave
'91 325iX
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Dave_G

You know how when you were in college, you probably had professors who wouldn't accept Wikipedia as a source? (If you didn't, you should have.) This is exactly why. Any yahoo with a keyboard can write stuff in Wikipedia, and they do.

Which why I usually back up what the wikipedia yahoos say, with what you BENN yahoos say. It's all about how much value you place in your different sources of authoritarian knowledge.

Anyhoo, thanks for the break down. It sounds like the article had most the generalities correct, and messed up the facts (at least as they relate to our cars). It deductively makes sense to me that a viscous LSD would fail more "gracefully" and revert to an open diff. Is this correct? That is certainly a plus for the viscous diff.

Anyway, I have a buddy who wrecked a 325is. The only down side to that is, even if I save myself $50 taking his, I have to pull the thing myself. blah!

-----------------------------------------------------------------------------------
1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

Quote
Earendil
Anyhoo, thanks for the break down. It sounds like the article had most the generalities correct, and messed up the facts (at least as they relate to our cars). It deductively makes sense to me that a viscous LSD would fail more "gracefully" and revert to an open diff. Is this correct? That is certainly a plus for the viscous diff.
Yeah, the generalities were OK, and it is correct that a worn-out viscous coupling just leaves you with an open diff. A large proportion of the iX's still on the road have an open center diff as a result of being towed improperly.
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Anyway, I have a buddy who wrecked a 325is. The only down side to that is, even if I save myself $50 taking his, I have to pull the thing myself. blah!
It's good for you. It builds character. smiling smiley

__________
Dave
'91 325iX
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Dave_G
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Earendil
Anyway, I have a buddy who wrecked a 325is. The only down side to that is, even if I save myself $50 taking his, I have to pull the thing myself. blah!
It's good for you. It builds character. smiling smiley

I'm still recovering from the character additions that the drive shaft gave me ;-)

Actually, it would be good to bust a few bolts and break a few things on the wrecked car figuring out how it all comes apart, before I attempt to do the same thing to mine. The Diff just strikes me as the kind of job you want to do as few times as possible smiling smiley

-----------------------------------------------------------------------------------
1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles




Edited 1 time(s). Last edit at 01/15/2010 03:32PM by Earendil.
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