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Thread: BMW E46 M3 Diffs

  1. #1
    Registered User AndyMac's Avatar
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    BMW E46 M3 Diffs

    Hi All,

    Just wondering if anyone might know what's going on here.

    I've gotten a replacement diff for my M3, I had to remove the rear cover as it had new bushes in it.

    Found that the replacement diff looked very different to the one that came out of it.

    From the parts numbers, posts on other forums, I've gathered the replacement one is a clutch LSD - early spec E46 M3 or perhaps even CSL Spec, or custom.

    I know sweet fuck all about diffs - what am I even looking at here, and which one is better?

    Old Diff = more tapered, no yellow on gear, round holes
    New Diff = more squared, yellow on gear, "U" shaped holes

    Any help/information/advice as to what I'm looking at, which is better, etc, etc... Would be great.
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    Panzer Wagen

    M-Cars follow the idea that power should be felt & not seen

  2. #2
    Non Compos Mentos Gammaboy's Avatar
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    Is the old one even a LSD?
    The yellow on the ring gear is used to check the mesh pattern when the diff is built up.
    "Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."

  3. #3
    Non Compos Mentos Gammaboy's Avatar
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    Quick google says the old diff is a form of viscous LSD. Fuck that shit off, enjoy the plate LSD.
    Looking again, the new diff is the GKN Viscolock. Hmmm. What's the old one then?
    Last edited by Gammaboy; 16-02-18 at 10:19 AM.
    "Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."

  4. #4
    Registered User AndyMac's Avatar
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    What I understand is the old diff is a torsen, buy uses a pump effect to lock or whatever.

    The new one... Viscolock??? Is that bad?

    Might even be a z4m diff?

    Is the LSD one still better???

  5. #5
    Non Compos Mentos Gammaboy's Avatar
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    Quote Originally Posted by Gammaboy View Post
    Quick google says the old diff is a form of viscous LSD. Fuck that shit off, enjoy the plate LSD.
    Looking again, the new diff is the GKN Viscolock. Hmmm. What's the old one then?
    Found a thread that had a Z4 LSD and a M3 LSD side by side - showed the same differences.
    I presume all the LSD stuff in the old one is living on the crownwheel side of the spider gears, so when it locks up it ties one side gear to the housing, locking the diff up, but putting the torque load through the spider gears (vs the traditional lock both sides to the housing and unload the spiders)
    "Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."

  6. #6
    Non Compos Mentos Gammaboy's Avatar
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    From what I read about the viscolock, it's not like the pile of shit viscous LSDs that were in fashion in the 90s - instead of using shear of a non newtonian fluuid to do the work, it uses the shear to drive a piston that drives the plates in a clutch pack (which are clearly visible in your new one).
    "Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."

  7. #7
    Non Compos Mentos Gammaboy's Avatar
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    Looking at the pics again, and looking at the below link, I have a suspiscion that they may have the same clutch pack and associated other crap, it's just that one has the clutch pack living on the ring gear side of the spiders, and the other has the clutch pack on the non ring gear side. Possibly a change made for cost of manufacture/assembly reasons.
    http://www.m3post.com/forums/showthread.php?t=788992

    Might mean you have to swap the drive shafts from left to right.
    Last edited by Gammaboy; 16-02-18 at 10:45 AM.
    "Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."

  8. #8
    Registered User AndyMac's Avatar
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    Dumb question, and thanks, you're being a legend with all this information.

    Why would I need to swap driveshafts?

    The thing was supposed to be serviced and refreshed before I got it. I believe it was... But a little grindy on tight turns.

    Some people/info suggested that this might be normal bedding in?

  9. #9
    Non Compos Mentos Gammaboy's Avatar
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    Quote Originally Posted by AndyMac View Post
    Dumb question, and thanks, you're being a legend with all this information.

    Why would I need to swap driveshafts?
    Just realised the diff ends of the shafts are with the diffs - you're golden. If you pulled them out, I'll bet that the long one (look in the background of the pic of the dissassembled Viscolock - note the short and long slined axles) will be on opposite sides with the 2 diffs.
    Quote Originally Posted by AndyMac View Post
    The thing was supposed to be serviced and refreshed before I got it. I believe it was... But a little grindy on tight turns.

    Some people/info suggested that this might be normal bedding in?
    The new one? The state of the setup paint suggests it hasn't been used at all, so if it's had fresh plates put in it, it'll take a little while to bed in.

    Pics of M3 vs Z4M
    https://z4-forum.com/forum/viewtopic.php?f=9&t=50881

    That thread suggests BMW may have swapped OEMs of the LSD between E46 M3 and Z4M production
    "Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."

  10. #10
    No I'm Not Shonky Shonky's Avatar
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    Quote Originally Posted by AndyMac View Post
    The thing was supposed to be serviced and refreshed before I got it. I believe it was... But a little grindy on tight turns.

    Some people/info suggested that this might be normal bedding in?
    My 08/2004 (with factory diff as far as I know so getting near the end of E46 M3 production) does it a little when cold on the first one or two tight corners but after that is generally fine - maybe a real tight U turn or similar you might hear a little. I did get the oil replaced a 4 or 5 years back with some special Castrol stuff that had an FM (friction modified?) suffix.

    After installing the recommended process was to do tight figure 8s in the carpark.

    Doesn't seem to be going away although I don't push it hard.

  11. #11
    Registered User AndyMac's Avatar
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    Yeah, I'm using the BMW Factory Oil as per the realoem parts listing website, and confirmed by BMW Parts here.

    I believe its Castrol with FM added as well, I went OEM oil because I believed it was easy to fuck up the amount of FM used.
    Panzer Wagen

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  12. #12
    No I'm Not Shonky Shonky's Avatar
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    Actually now that you say that I looked it up. It was the BMW stuff

    https://www.ecstuning.com/b-genuine-...r/83222282583/

  13. #13
    Half Shafted. Madhatr's Avatar
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    Both LSD's of the same type.

    One on the left is the later model one, the whole lsd carrier is bigger and the unit itself has more clutches. I've seen people talking about differences in shear pump design, but I haven't met anyone that pulled one apart to rebuild. They are both still fluid vario lock ones though. GKN produced them for bmw.

    E46 M3 diffs are a bit noisy at low speed. Penrite make limslip additive if you want to quieten it down too. Factory fluid/the recommended castrol stuff are usually supplied with the friction modifier already added. Penrite make a fully synthetic lsd oil with modifier already added too. You can run just about any fully synth gl-5 rated 75w-140 gear oil for lsd's.
    Last edited by Madhatr; 16-02-18 at 08:54 PM.
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  14. #14
    Registered User AndyMac's Avatar
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    Thanks Hatr!
    Panzer Wagen

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  15. #15
    Half Shafted. Madhatr's Avatar
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    7-02-18 10:43 AM

    Mine in the LSE46 chattered a bit, so i used a little of the limslip additive without issue. Ive got to change the bushes on the rear cover too, so ive got some penrite oil to try.

    How much did it cost you for the rebuilt centre? I havent looked into aftermarket lsd carriers yet though, but in the non m3 centers the gear set was smaller than the stock open ones to fit the lsd plate stack into the diff center. Meant the aftermarket centers from cusco, kaaz, etc were actually weaker than the open diff.

    Ive been on the look out for an e36 m3 lsd center to swap over and go 4 clutch setup otherwise.

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