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  1. #1
    mtbr member
    Join Date
    Oct 2014

    Nexus 8 missing gears

    Hi all,

    I recently bought an used Shimano Nexus SG-8C20 from someone.

    I installed it on my bike and though it wasn't free-wheeling good, all gears were there.

    I opened the hub and did a degreaser bath followed by an ATF oil bath.
    I also put some marine grease to waterproof the hub.
    It was spinning a lot better but it started others probelms:

    Since I put it back on the bike, I've lost almost all gears.
    From 1 to 4 it feels like it's always 1st gear.
    5th is running fine.
    6 to 7 has no effect (keep in 5th)
    8th has some problems but it works.

    Is someone able to tell me what would be the problem ?

    I already put some time to align the yellow marks but it doesn't change anything.

    I experienced balls falling from the O'ring and it blocked the whole hub so it's not this.

    Also I noticed that the point on the 3 planetary gears are not aligned like in the service manual but I can't see how I can align them since they are synchronized.

    I will take the hub apart again this weekend and post some pics.

    Thanks !

  2. #2
    mtbr member
    Join Date
    Apr 2012
    Go here. Lots of good information, including completely stripping down and rebuilding the hub. Reading German or using translates (and figuring out what is meant) is almost necessary in some cases.

    Without seeing the hub, we're going to have an awful time actually figuring out what's wrong.

  3. #3
    mtbr member
    Join Date
    Nov 2011
    Is the cassettejoint(black parts to mount the cable in) moving back without resistance?

    What side did you open up the hub? I have never seen a nexus hub being opened on the drive side ending well. Theres a reason why spares for the drive unit does not really exist in shimanos catalog. You get the axle with the drive unit.

    My general experience with the 8 speed nexus hub is its a piece of junk though. They dont last that well, they are very heavy. And they are very maintenance needy. The freewheeling problem you had is pretty much there from day 1. I much rather prefer the 7 speed baby brother. Its a bulletproof little hub.

  4. #4
    mtbr member
    Join Date
    Oct 2014
    Nexus 8 missing gears-dscn3550.jpgNexus 8 missing gears-dscn3551.jpgHere is the pics of my hub.
    You can see the point on the top planetary gear but not on the two others, that's what bother me as in the manual, it is said that the three points on the three planetary gear should be aligned when repacking the hub.

    I know a lot of people have different stories with this hub but please keep it positive

    Thanks for the link. I already saw this page but i'm going to go through again.

    The cassette is okay, cleaned it thoroughly.

  5. #5
    mtbr member
    Join Date
    Oct 2014
    Strangely my hub started to work again after a few miles. It still pretty messed up but some gears were working again.

    I'm going to clean and inspect it again and check the shifter cable.

  6. #6
    mtbr member
    Join Date
    Oct 2014
    So I did overhaul the hub again. This time I went too far.
    I tried cleaning the axle unit and some coil popped and everything was in pieces :-(

    Thanks to the great Aaron's bicycle repair website, I was able to piece it together again.
    I also bought a ball retainer for the drive side as mine was pretty messed up.

    The funny part is I had no specific tools as seen on the service manual to disassemble the axle unit. I used a standard Ice Tools wrench key and another heavy wrench to hit back the assembly into place.

    The hub is now working again though 4th and 8th are slipping a little and the hub doesn't run really quiet and drag-less. I will do an oil bath after running it a couple days as I think maybe it need to bed in again.

    Also some things looks complicated in the manual but if you check the forums, you will see that if you can't rebuild the hub, something is not right. You don't need to align the planetary gears when putting back the carrier unit !

  7. #7
    mtbr member
    Join Date
    Oct 2014
    So a little retrospective of what I've done with this hub.
    Hope it help.

    The hub when I first bought it:
    Nexus 8 missing gears-dscn3507.jpg
    When I look at this picture, I feel stupid not being hinted at the condition of the hub internals.

    The drive side bearing was very worn, some balls were falling from the ring. I later, purchased an old bearing to replace it.
    Nexus 8 missing gears-dscn3514.jpg

    The internals after a degreaser bath, oil bath and some grease.
    Nexus 8 missing gears-dscn3537.jpg

    Note how the bearing race was pited:
    Nexus 8 missing gears-dscn3539.jpg

    Then I did a second, more thorough strip down:
    Nexus 8 missing gears-dscn3563.jpgNexus 8 missing gears-dscn3562.jpgNexus 8 missing gears-dscn3561.jpgNexus 8 missing gears-dscn3558.jpg

    Thanks to Aaron's bicycle repair website, I was able to piece together the axle unit.

    At the end, I learned a lot about IGH, but it took me a lot of time !
    The hub is running fine, it feels smoother week after week. I think it's "bedding" again.
    I also learned that it's risky to buy a used hub. You should at least test it and check the internals.

    I still have some slip in 4th and 8th but I need to check the cable tension.

    I compared it to my all new Sturmey-Archer 3 speed hub and it feels draggier but not as much as I tought it would be.

    I'll buy a new Alfine hub for my next bike and try to compare both.

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