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  1. #1
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    Trek T900 BB/Crank 'click/thump'

    Have a 2010 Trek T900 tandem bought off of CL a few weeks ago. In very good shape....although, it's just developed a 'click' or 'thump' at the top of each stroke (meaning at the top of both right and left crank rotatation). Not a bad thump/click, just noticeable though. This is concerning the front crankset/BB, but the stoker can feel it. If I ride the bike alone, it still does it.

    So, with some searches here.....I see it's BB or crank issue most likely. Twisted the front crank arms every way possible, and it doesn't appear to be the BB (no apparent movement). However, when I move the crank arms side to side, like trying to push them out of either side of the BB, there is a <1mm lateral movement and corresponding click/thump.....hard to tell if this the same issue (but likely is).

    Can't tell a manufacturer on the BB. Crankset is Trutativ (don't know specific model from their website, probably a lower end option).

    Attached a pic. It's exactly like this, except that the BB tool locations are top, not on the bottom.

    Have an extensive set of tools, (like car mechanic would, as I've rebuilt cars/motors, and lots of bike related stuff) but nothing BB/crankset specific. No aversion to purchasing the right stuff to DIY.

    Any ideas or notes of what I'm going to need and what to look for once I have the tool(s)? Attached a pic of the stock bike...can send more detail if needed.

    I also looked at Sheldon Brown's page on BB and Crankset pages.....but still a bit confused.

    Thank you!

    11420.jpg

  2. #2
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    First of all, if you grab the arm and try to push and pull it to and from the frame of the bike, there should be absolutely zero play whatsoever. Any play at all means that something is loose in the BB and it needs to be taken apart and probably cleaned and regreased. If its a cartridge BB, then it will need to be replaced. It is also possible that the crank arm is loose/worn causing the play but usually its the BB itself.

  3. #3
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    Quote Originally Posted by bobotech View Post
    First of all, if you grab the arm and try to push and pull it to and from the frame of the bike, there should be absolutely zero play whatsoever. Any play at all means that something is loose in the BB and it needs to be taken apart and probably cleaned and regreased. If its a cartridge BB, then it will need to be replaced. It is also possible that the crank arm is loose/worn causing the play but usually its the BB itself.
    Ok....is there a recommended 'group' or set of BB/Crankset tools I'm going to need? Don't mind buying them, just looking for some guidance to get the 'right stuff' on the first purchase.

    While pushing/pulling on the crankset....it isn't the BB that's moving (unless it's moving internally where I can't see, allowing the crankset to move). It's the shaft/crankset moving through the BB.

  4. #4
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    Quote Originally Posted by hartphoto View Post
    Ok....is there a recommended 'group' or set of BB/Crankset tools I'm going to need? Don't mind buying them, just looking for some guidance to get the 'right stuff' on the first purchase.

    While pushing/pulling on the crankset....it isn't the BB that's moving (unless it's moving internally where I can't see, allowing the crankset to move). It's the shaft/crankset moving through the BB.
    Yeah, the shaft is what you will see the play in. The shaft rides on ball bearings that then ride in the cups/BB. When parts get worn, the shaft then moves in directions other than the rotational. You should feel zero movement in the shaft other than the expected obvious rotational movement.

    As for tools, generally you need a crank arm puller and a BB removal tool. I don't know what kind of crankset/bb that you have so I can't recommend the tools.

  5. #5
    Watching and waiting. jethro56's Avatar
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    Bobo's correct. Is there like a shell with notches on each side of the frame. If so there could be a part number on it.

  6. #6
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    Sincere thanks for the replies. The crankset is a Trutativ FiveD. Couple of other tidbits of info. It is the front (captain) position of a tandem, so it's only the timing chain setup (no derailleur). Eccentric bottom bracket setup. I can't find any info on specific BB info (other than the Trutativ is most likely a tapered square).

    Based on looking at it, plus the tools, it looks like I need the Park BBT-22 and the Park compact crank puller. Do I need two of the BBT-22? It's got the splined inset on both sides of the BB.

    I also know the bike has about 1800 miles on it, and the BB probably has been apart (or at least loosened/tightened). The previous owner had the timing chain replaced, which requires re-adjusting the eccentric BB setup.

    If things are worn, I don't mind replacing stuff. Want to get many many more miles out of this tandem.

    Here's two pics, one showing the eccentric setup, the other just the splined inset piece.

    photo1.jpgphoto2.jpg

  7. #7
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    Thanks for all the replies. Still working this issue.

    Short version is that I went to LBS and got a Park BBT-22, a CCP-22, and some Park grease this morning and now have the BB out.

    The BB is a square tapered sealed cartridge Modus 68-113 (which looks like a pretty low end piece). While it takes some extreme hand pressure (and nothing near the pressure when the cranks are on, then driven by legs), I can get a minute amount of play in it. However, it is quite 'gritty' while turning, so I might as well replace it.

    Looking to put in a Shimano UN55 68-113 BB (based on some reviews)....closest LBS that has it is an hour drive one way.

    Any opinions on the UN55? Seems like a middle of the product line option, and should last for awhile though.

  8. #8
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    How exactly does one loosen this Trek 900 eccentric wedge to adjust timing chain tension? The hex head set screw I understand tensions the wedge, but that's all I can fathom so far. I need to break it loose and move the BB.

    Thanks...: )

    Rog

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