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  1. #1
    Veteran Member Four Rings coolgraymemo's Avatar
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    Verifying: Stasis LSD or stock differential

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    Records show that my car was previously outfitted with a Stasis 4:1 center differential and Stasis limited slip differential. I have felt the 4:1 when driving hard on damp pavement or on gravel. I have been unable to really feel the LSD.

    While looking at old posts, someone suggested that Stasis used clutch type LSDs. That led me to find that clutch type LSDs can be tested using a "static breakaway torque test."
    So what I did was jack up the driver's side rear tire, put the car in neutral (hand brake off), and turned the hub. The poster (james 408) suggested that new LSDs require 45lb/ft to turn, whereas used ones needing rebuild will require 25lb/fts.

    I was able to spin mine freely.

    It is safe to say that my LSD is worn and needing rebuild? Or would this suggest that my car no longer has a LSD? Or am I not testing this correctly?


    tia
    Santorin/Ebony '00 S4 6MT | K04/K16, Stasis LSD/4:1, Bilstein PSS9, Stoptech, SSR Comps, & more
    '01 S4 Avant 6MT | '00 1.8t Avant | '93 RS2'd S4 | '99.5 1.8t | '01 1.8t | '95.5 S6 Avant

  2. #2
    Veteran Member Four Rings MacDaddy's Avatar
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    Lift both wheels and see if they spin in the same direction with the car in neutral.

    What will kill an LSD is running a smaller tire on one side than the other (like a space saver spare) for an excessive amount of time, and that will only kill the clutch pack on one side, i got a bmw LSD that had that issue, i could nail sweet drifts going right but it would act like an open diff going left. Regular driving/matched tire sizes it shouldnt wear out, ive driven lots of 80ís BMWís and thir LSDís still locked up really well even after 20+ years and questionable maintenance.

    Also an LSD equiped car will turn in tighter (less steering angle required to make a turn) than a non LSD equipped car for a given model (when i swapped said BMW diff from open to LSD that was the biggest thing i noticed) so if it turns in better than a stock s4 you kind of have an answer, the 4:1 center diff may also do the same but i dont know for sure.

  3. #3
    Veteran Member Four Rings
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    Nov 04 2013
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    stg 3 widebody, 1990 miata, '05 gsxr 1000
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    Yeah breakaway torque does vary between designs, but I'd guess you should look into rebuilding it if it's got like none. The lifting the car in the air and spinning one wheel is basically the same test, it's just putting the torque at like nothing. In both cases this is merely a test of zero load breakaway torque, which fades as the clutchpacks wear. Now what should the static breakaway torque be for that diff, I'm not sure.

    On rwd it's really easy to test, you just drive in a circle, break the inside tire under power gradually, and if the outside never spins up, your diff's done done. On AWD street cars this doesn't work. You could soap up the tire and try it with a camera... If you can't figure it out definitively, the only other way I know of is to pull it apart.

    The turnin thing isn't really a very good test as it depends greatly on the type (1 way 1.5 or 2) and how you're measuring... two way diffs actually cause a fair bit of understeer on initial turnin (inside wheel gets linked towards the faster outside wheel rate which causes it to resist rotation initially; once you've broken traction though it will indeed rotate easier as one wheel won't regain grip at will).

  4. #4
    Veteran Member Four Rings
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    Nov 04 2013
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    stg 3 widebody, 1990 miata, '05 gsxr 1000
    Location
    Palo Alto, CA

    https://s14net.vbulletin.net/forum/s...eakaway-torque

    as an example. s2k forums and a few others all mirror the same basic tests and ranges of torque values.

    Also everyone generally agrees that if you're doing a bunch of autocross or other tight turn events you're going to go through diffs in a matter of a few dozen hours of hard use. It's not really a mileage thing so much as how it's used and for how long. Different wheel speeds sustained is what causes wear, and the general rule of heat accumulation applies.

  5. #5
    Veteran Member Four Rings
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    Nov 04 2013
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    My Garage
    stg 3 widebody, 1990 miata, '05 gsxr 1000
    Location
    Palo Alto, CA

    inside the diff housing, there's a series of clutchpacks if it's the stasis/clutchtype. You have to disasemble the lsd unit to see them. The clutches look like any other and the friction material eventually disapppears -- when it goes metal on metal, it will be an open diff.

    The rennlist guys had some good photos of it, they'd paid a dealership to pull it all apart, many of them -- matched up to static torque specs. Couldn't find the thread.

    One thing you might check if it's never been changed, is the fluid. If it's dry or black with friction material, not only is it time to change it, but that's probably your answer.

  6. #6
    Veteran Member Four Rings
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    Nov 04 2013
    AZ Member #
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    My Garage
    stg 3 widebody, 1990 miata, '05 gsxr 1000
    Location
    Palo Alto, CA

    https://www.cusco.co.jp/en/pdf/LSD%20Guide%20Final.pdf

    see page 7. I presume the stasis diff is more standard, especially as a rear -- which would mean yours is dunzo or stock. But some fronts in particular are set up with low initial torque, mild ramps, and low locking percentages. So I'm not sure the static load torque rating is always the best testing method, although for a rear diff 99% of the time, I assume it is.

  7. #7
    Veteran Member Three Rings
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    Mar 22 2013
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    Stasis lsd was a modified Paul Guard unit designed for the Porsche 944

  8. #8
    Veteran Member Three Rings okkim's Avatar
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    Dec 07 2004
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    Finland

    I have a Stasis rear LSD, and it is very easy to see if it's working or not. When I'm turning quite tight, the rear makes a jerking and banging sounds.

  9. #9
    Veteran Member Four Rings coolgraymemo's Avatar
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    I think itís safe to say that I currently have an open diff, due to wear.

    Iíll be replacing the fluid soon and Iíll start looking into a rebuild.

    Any insight on shops that can rebuild it?
    Santorin/Ebony '00 S4 6MT | K04/K16, Stasis LSD/4:1, Bilstein PSS9, Stoptech, SSR Comps, & more
    '01 S4 Avant 6MT | '00 1.8t Avant | '93 RS2'd S4 | '99.5 1.8t | '01 1.8t | '95.5 S6 Avant

  10. #10
    Veteran Member Three Rings
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    Mar 22 2013
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    Maybe your records are wrong and you do not have a LSD...that would be my guess............the Guard or the OEM Porsche LSD's are very robust and even with severe track duty they still work , limited lock up due to wear and tear but they never go out completely especially with light street duty.

    Goggle Kevin Gross, he can rebuild it and shim it properly, he sometimes posts here.

  11. #11
    Veteran Member Four Rings coolgraymemo's Avatar
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    The original owner verified that he installed a 60% lockup Stasis LSD. Itís had three owners since then, so another possibility would be that they removed it.
    Santorin/Ebony '00 S4 6MT | K04/K16, Stasis LSD/4:1, Bilstein PSS9, Stoptech, SSR Comps, & more
    '01 S4 Avant 6MT | '00 1.8t Avant | '93 RS2'd S4 | '99.5 1.8t | '01 1.8t | '95.5 S6 Avant



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