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LC Final Drive Part Numbers / Compatibility

Discussion in 'GS Boxers' started by PineyMountainRacing, Jun 8, 2021.

  1. PineyMountainRacing

    PineyMountainRacing Oops....

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    looking online it seems my '17 GSA FD is PN 3374 8394 282. I don't need it ATM, but I have the opportunity to pick up a spare for cheap. always thought it'd be good to have one boxed up and ready to ship in case one of my trips goes sideways or a fellow traveller needs one.

    the pics of the used unit show a "8523952" stamped in the housing, I don't see any other numbers (that make sense) in the pics I have. Looking at parts diagrams even going back to pre-LC models I don't see that number anywhere. I do see a 852xxxx listed for a 2010. I'm not with my bike right now so I can't run out and compare the pics to my own. IDK if it came off a GS, GSA or RT, etc.. It is black, here's a picture with the number stamping.

    finaldrive 4sale.jpg

    so how do you tell what FD you have just by looking at it so I can decide if it's compatible with my 17?
    #1
  2. Lead Wrist

    Lead Wrist Mehr Gelände Weniger Straße

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    The number you're looking at on the housing is casting P# and that number is never listed in parts fiche diagrams. What is listed is final p# of finished and fully assembled FD ready to be installed... :deal

    You should double check the parts fiche but I believe all FDs for LC GS/GSAs, both 1200 and 1250, have same ratio 32/11=2.91 FD and the only difference would be the housing color.

    It's your money but you could probably use it more efficiently for other toys/farkles rather than getting spare FD. LCs haven't had known FD failures to warrant having the replacement FD on stand-by like previous platforms have - ymmv... :thumb
    #2
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  3. atwoodtja

    atwoodtja Been here awhile

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    It does seem like having a spare driveshaft is a better investment than the final drive itself. As long as the final drive seals stay intact, the LC one seems to last a long time.
    #3
  4. PineyMountainRacing

    PineyMountainRacing Oops....

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    I agree, but I can’t confirm what bike this came off of. And yeah, everything I looked up was 2.91.

    Knowing me, id probably pick up a driveshaft if the price was right :D
    #4
  5. Lead Wrist

    Lead Wrist Mehr Gelände Weniger Straße

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    Late Hexheads and all Camheads also had 2.91 FDs btw both GS and GSAs. 2.91 is GS/A only - RT/R and others have different ratio...

    If it is LH mount FD, then it's LC - Hex/Camheads were RH mounted.

    The housing p# is highly likely the same regardless of what ratio FD is assembled as so, unless you have p# for entire FD assembly to cross-check through parts fiche, it's safe to pass on it - ymmv... :thumb
    #5
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  6. PineyMountainRacing

    PineyMountainRacing Oops....

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    so, I’m just being curious here. If I had a FD in my hands, and I didn’t know what it was, would I be able to estimate the gear ratio without opening it up and finding a number or counting teeth? Say by comparing driven side to drive side turning by hand and counting revolutions? Maybe I’m being clear as mud, it’s hard to explain because I don’t have it in my hot little hands, I replaced R & P gears in my Ural FD years ago but that was the last time I actually held one up close.
    #6
  7. JimVonBaden

    JimVonBaden "Cool" Aid! Supporter

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    Basically yes. If you rotate the shaft, you will see a difference of about 3 to 1 on the wheel mount.
    #7
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  8. PineyMountainRacing

    PineyMountainRacing Oops....

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    Ty, as usual I was making it too complicated in my noggin :beer
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  9. Lead Wrist

    Lead Wrist Mehr Gelände Weniger Straße

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    If you buy a FD from LC R boxer bike, it'll have either 2.91 (GS/A) or 2.82 (R/RS/RT) ratio so you have 50-50 chances to get right one...

    Can you "estimate" which one is which by counting revolutions? I'd guess definitely maybe... :D
    #9
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  10. lkraus

    lkraus Long timer

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    On my 2006 RT, the 34/13 ratio is stamped on the bottom of the FD.
    fdratio.jpg
    #10