I was at my parts guys' garage today and he claims he's got a 3.91 posi rear end? POSI???? 100% lockup? WTF?!??!?!? Identifiable by an "S" on the top of the casing he says..... I don't speak german great, but I swear thats what he said.. So is this something I should jump on as its a rare piece or is it a fluke?
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It's a Limited slip -
could be a vicous rear end from an iX, there the only ones i remember with something like that
but 100% lockup? dont think so.
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Originally posted by MR 325
si senorBEERTECH
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Some people reffer to limited slip diffs as posi. All of the LSDs have the S on the casing.
I don't know if the 3.91 was offered on anything other than "IX"s in Germany, but over here the only think that came with that ratio was the 325ix. Also, it is not a standard clutch limited slip. It is a Viscous LSD.
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I gotta look more into this.... it seems like it would be a LSD but he knows his shit.... Its a euro rear end so I guess anything is possible....
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ok.... explain viscious to me?
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Well, I don't know all of the exact details, but instead of using clutch packs like most of the other LSDs, the viscous diff used fluid. I don't know exactly how it works though, or why the IX got the viscous diff...Comment
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The term "Posi" is short for "Posi-Traction", a Chevy marketing word for a limited slip. Now commonly used to mean a limited slip. Don't get it confused with 100% lockup, a posi doesn't necessarily mean that.Originally posted by marakkaComment
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yes there is a dif with 3.91. My buddies maroon american specs 325 has one in it now. they arent all that hard to come by in germany. it is not 100% lockup. you cant even drive that on the street. it would only work on a drag strip where you drive in a straight line only. I am almost positive all"BMW" origional difs only have 25%-which is enough for "normal" hard driving.
max, it is probably a visco dif, unless you did see a "S" on it. the visco should have a "V" stamped with ink on the top of the dif.
the odd thing is that both 3,91 difs that I have had were small housing difs. meaning there is only 1 bolt on the bottom side of the rear cover. its not as strong, but will still work just fine for "normal" driving. the "V" difs are more wanted, but do you feel a difference---NO. and I have managed to blow up every kind of dif BMW makes, ---no i dont drive hard!Comment
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and by the way-- i want those side skirts now!!! (j/k) come by on monday if you have time.Comment
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Besides ix's, some UK-spec 325i Sports had 3.91LSDs IIRC.
And at least in the US, (early) M10-powered E30s had 3.91's. But those were small case obviously and I'm not sure how common LSD examples were.Comment
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That's a great read for anyone needing to know how LSD's and differentials work. Good stuff. If you keep going it starts talking about LSD'sYour signature picture has been removed since it contained the Photobucket "upgrade your account" image.
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Exactly!Originally posted by redhatpat
Genreally a diff with 100% lockup is called a spoolComment
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Originally posted by mikeedler
Its got the s stamped on the top. Seen it.... but he was going on and on about it in german that I couldn't understand. Only thing I got was 100 percent and he spun both sides. I dunno.... I'll get an interpretter over there and ask him. He's got more knowledge than I do about all this euro stuff.
So.... if the 3.91 came out of those cars.... where did this 4.46 come out of that I have? its a big case diff so I'm completely lost on that one. I know they offered way more options here in Germany than stateside as you can get a 2.71 here and not stateside.
If V diffs utilized fluid to make them LSD then they'd do some hydraulic stuff..... don't see where that would be more desirable... but anythings possible I guess.
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