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  1. #1
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    Downtube shifter problem?

    Rebuilding/upgrading a Centurion, no snide remarks I have already been trashed on Road Bikes, & having problem converting the Suntour downtube 12 speed shifter to a more modern 24 speed setup. The frame boss is on the top for the Suntour. LBS did not have a solution short of making a part to accept the new shifters. I do not want to drill the frame! Any ideas will be appreciated.

    Also, can you convert a 1" threaded fork setup to a threadless fork. If so how do you go about it?

    Thanks.

  2. #2
    Senior Member sydney's Avatar
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    Quote Originally Posted by oilman_15106
    Rebuilding/upgrading a Centurion, no snide remarks I have already been trashed on Road Bikes, & having problem converting the Suntour downtube 12 speed shifter to a more modern 24 speed setup. The frame boss is on the top for the Suntour. LBS did not have a solution short of making a part to accept the new shifters. I do not want to drill the frame! Any ideas will be appreciated.

    Also, can you convert a 1" threaded fork setup to a threadless fork. If so how do you go about it?

    Thanks.
    Ya you can make it threadless with a new fork,HS and stem. Your problem will be the centurion probably used a JIS HS rather than the ISO in current common usage. JIS cups are 30.0 rather than 30.2 of ISO. Crown race difference doesn't matter since you are ditching fork. There are no lack of clamp on down tube friction shifters. Finding a clamp on on for a Shimano or other index down tube is a much tougher job. Alternate solution is barends or sti shifters and a clamp on downtube cable stop.

  3. #3
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    Thanks for your input. I have looked high & low for a clamp to accept cable guides to go to barend or modern brifters. Any ideas? Could make a bracket for the top boss to accept cable guides?

  4. #4
    Senior Member demoncyclist's Avatar
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    DEMON

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  5. #5
    Car(e) Free! koine2002's Avatar
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    Quote Originally Posted by sydney
    Ya you can make it threadless with a new fork,HS and stem. Your problem will be the centurion probably used a JIS HS rather than the ISO in current common usage. JIS cups are 30.0 rather than 30.2 of ISO.
    Click here to see a threadless headset that is designed for the JIS that may work with your current setup. You will still need a new stem though. If you do upgrade the headset, be sure to do the proper frame and fork preparation if you want the HS to last.

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    No longer in Wimbledon... womble's Avatar
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    Quote Originally Posted by oilman_15106
    Thanks for your input. I have looked high & low for a clamp to accept cable guides to go to barend or modern brifters. Any ideas? Could make a bracket for the top boss to accept cable guides?
    Cable guides are readily available on ebay.

  7. #7
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    Thanks. Obtaining cable guides is not the problem. The frame has a a single top mount for the shifter not the more modern side tube mounting. Any ideas?

  8. #8
    Senior Member sydney's Avatar
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    Quote Originally Posted by oilman_15106
    Thanks. Obtaining cable guides is not the problem. The frame has a a single top mount for the shifter not the more modern side tube mounting. Any ideas?
    Yeah, unbolt what you can and throw it away.Then use a clamp on cable stop.

  9. #9
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    Are you looking a clamp-on DT shifters or cable guides or what?
    Rivendell may have some. I got mine from the old parts bin of my LBS.

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    Thanks again. I know you can clamp the shifter or cable guides to the frame but was hoping to find a way to use the top boss to attach either/or. Mostly for looks. I know this may seem petty to some but this project is really starting to come along. This is my "coffee shop cruiser/rails to trails" bike. Hope to have it done before the snow flys.

  11. #11
    Senior Member sydney's Avatar
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    Quote Originally Posted by oilman_15106
    Thanks again. I know you can clamp the shifter or cable guides to the frame but was hoping to find a way to use the top boss to attach either/or. Mostly for looks. I know this may seem petty to some but this project is really starting to come along. This is my "coffee shop cruiser/rails to trails" bike. Hope to have it done before the snow flys.
    Then sydney suggest you take it apart and see what you have to work with and then go from there. The heads up is that even if you can Arkansas engineer something, the cable routing will be goofy if not unworkable.sydney has a farme with that shifter setup on it but would rather go for a ride than tear it apart for no good purpose. The whole mechanism comes off the frame with one bolt, leaving a stud on the top of the downtube that would serve to secuely locate a cable stop.There is a bolt securing each shifter to the main body of the mechanism.If removing the shifter retaining bolts leavs a threaded hole on each side of the mechanism body,you have a starting place for possibly attaching stops,but you will have to worry about them rotating if there is not some sort of retainer as you would have have with a standard braze on boss. As stated, tossing it is the easy way.And if the retaining stud bothers you, grind it off and put a decal or wrap of duct tape over it.
    Last edited by sydney; 07-29-05 at 09:57 AM.

  12. #12
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    Very good Sydney. I have already taken apart the original Suntour shifter. No good. It was an Symmetric system & no option to modify. It was a very complicated design for a friction shifter. I am making a peice to replace the orig. & hold index shifter system. Will let you know how it works out. Told the guys I work with they could share in the design royalitites. With all the time in this thing they should sell for about $500 each. Thanks.

  13. #13
    Senior Member sydney's Avatar
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    Quote Originally Posted by oilman_15106
    Very good Sydney. I have already taken apart the original Suntour shifter. No good. It was an Symmetric system & no option to modify. It was a very complicated design for a friction shifter. I am making a peice to replace the orig. & hold index shifter system. Will let you know how it works out. Told the guys I work with they could share in the design royalitites. With all the time in this thing they should sell for about $500 each. Thanks.
    If it's the same as the one I go,that shifter was a short lived Suntour proprietary design. Idea behind it was that when the right lever was shifted, the left moved and trimmed the FD.

  14. #14
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    Use a clamp-on cable stop, then use the single boss for a cool bell mount. you said that this was a coffee gitter and trail bike, you need a bell to let others know that you are coming up on them, IMO. My trail bike is a SS conversion with unused shifter bosses. I used one of them for the bell, a little creative threading and the bell screwed right on! Looks cool and works great!

  15. #15
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    Thanks for all your suggestions. Made a "new" boss device to hold the downtube shifters. 3/8 set up friction. It is working pretty well except for one unusual problem. When I get up out of the saddle to climb or whatever, the front shifter drops to the most inside position, loss of tension on shifter device I guess. I do not experience this when riding in the saddle? The friction screw holding the thing on seems as tight as I can get it. I am thinking some kind of washer or something might help. Any ideas. Also 105 triple der on the front & Sora long cage 8 speed on the back if it matters.

  16. #16
    Senior Member rufvelo's Avatar
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    Sydney said ...

    'that shifter was a short lived Suntour proprietary design. Idea behind it was that when the right lever was shifted, the left moved and trimmed the FD.'

    - that is genius design, something I could really use. Anything to stop FD noise when at extreme or even close to extreme positions on the rear cluster - something I've always struggled with especially while really putting power into the crank. Sure I realize that one needs to keep the chain straight as far as possible and frame flex also contributes to the problem, still that Suntour principle is nice.

    I do agree with you though, a lot of the time spent tinkering with a perfectly good working bike is better spent riding

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