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  1. #1
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    Captain's BB/Crankset click/thump

    Rather than crosspost an entire thread.....I have this post with replies going on in the Mechanics area.

    Trek-T900-BB-Crank-click-thump

    Wanted to see if anyone tandem specific has any suggestions, ideas.

    Should I start replacing things? Don't mind spending $$ to do it right...but don't need to spend $$$ just to have the lightest/ultegra level components, always been kind of a middle of the road approach to replacing parts/upgrading.

    The T900 now has ~1800 miles from the previous owner, and about 100 already from us riding it the past 2 weeks. And since I'm getting requests for daily tandem rides from my other 3 riders....it's going to get a LOT more.

  2. #2
    What??? Only 2 wheels? jimmuller's Avatar
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    I would expect the Mechanics forum to suggest most of the likely causes. You should start by checking all the things that could have loosened up, the crank arm bolts, the chainring bolts, the bottom bracket bearings, the pedal bearings, etc. For tandem-specific things, check that your timing chain isn't too loose, that it's alignment is okay, that neither timing gear is warped. Finally, it is possible that the problem is in the stoker's BB even though the thump seems to be coming from the captain's. So check all the obvious stuff back there too. Even check that the front derailleur isn't being hit by a crank arm.
    Real cyclists use toe clips.
    jimmuller

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    I always start with switching out pedals from another bike. Just last week it was the pedal, not the BB or crank bolts.

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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....closest LBS that has it is an hour drive one way.

    Will report back after I have it all together and tested.

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    After spending weeks troubleshooting similar noises on our tandem and replacing both bottom brackets, etc., I would just caution that it is very easy to be fooled by the source of noises on a tandem. In our case, it turned out that the noise originated in the rear wheel, even though it happened once per crank turn. It's helpful to use a stick or tube as a stethoscope to home in on the source if you can replicate the noise when not actually riding. On tandems, it's common for the stoker's BB to go first as it carries twice the power, so be careful about focusing too quickly on the captains BB.

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    Quote Originally Posted by reburns View Post
    After spending weeks troubleshooting similar noises on our tandem and replacing both bottom brackets, etc., I would just caution that it is very easy to be fooled by the source of noises on a tandem. In our case, it turned out that the noise originated in the rear wheel, even though it happened once per crank turn. It's helpful to use a stick or tube as a stethoscope to home in on the source if you can replicate the noise when not actually riding. On tandems, it's common for the stoker's BB to go first as it carries twice the power, so be careful about focusing too quickly on the captains BB.
    Thanks for the reply, and definitely understand the frustration of tracking down creaks/thumps that occur, especially on a tandem that carries more weight and torque.

    One thing about why I went ahead with the Captain's BB replacement (a new Shimano UN55 is now installed), is that the Modus BB definitely was gritty (felt like it had hardly any grease left, even a bit 'sandy' while turning) compared to the new Shimano (smooth as butta)....AND....the click/thump was happening every half revolution (top of every right/left stroke, or twice per one revolution).

    At this point, I'm really only out $28 for the part, and a few hours time....the $50 in tools will forever pay for themselves (as we have two tandems).

    The one thing about going to the LBS (Richardson Bike Mart in our case), is that they had about 20 tandems for the wife and kids to ogle (from $800 versions to a jaw dropping $12k Santana). Best thing was the wifey gave approval for a 'speedy' one when the kids legs are long enough. Priceless!

    Will report back after a test ride tomorrow evening....about 15 miles hopefully.

  7. #7
    PMK
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    FWIW, you might consider swapping the UN BB to the back and the stokers forward if they interchange.

    Richardsons, in Dallas? If so, yes it was pretty cool to visit the place while on a business trip a few years ago.

    PK
    2006 Co-Motion Roadster, flat bars, discs and carbon fibre fork, size 22 / 19
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