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  1. #1
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    Straightening a bent hanger on Carbon frame

    I think I may have a bent rear derailleur hanger. I have access to the park tool straightener but before I try to straighten it, I wanted to check if its ok to put those forces on a carbon frame?
    Frame is a 2009 trek top fuel 9.8. The chain stays are aluminum, seat stays are carbon, joined together at the rear axle. (trek ABP pivot)

    I have a new extra hanger I could put on, and the $40 for another one won't kill me, but obviously I'd rather fix it if it's something that's safe to do on this frame.

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  2. #2
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    Just because you have the tool....doesn't mean you know how to use it.
    And seeing how you are asking....and state that you "think " you bent the hanger (you either did or didn't and it's pretty easy to tell)....
    Either take it to a good mechanic who knows how to straighten it....or put on the replacement (and make sure that is straight as you can tweak the mounting area)

  3. #3
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    Quote Originally Posted by the mayor View Post
    Just because you have the tool....doesn't mean you know how to use it.
    And seeing how you are asking....and state that you "think " you bent the hanger (you either did or didn't and it's pretty easy to tell)....
    Either take it to a good mechanic who knows how to straighten it....or put on the replacement (and make sure that is straight as you can tweak the mounting area)
    1. I've used the tool successfully before on aluminum frames. My question is clearly specific to frame material, which your answer didn't address.

    2. The reason I "think" its bent is only because I have not yet had the opportunity to use the tool to confirm. Seeing as how the same tool is used to diagnose and fix the problem, I decided to ask my question (again, specific to frame material) before beginning the process.


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  4. #4
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    Replace the hanger outright, for carbon frames. On Alu its perfectly acceptable to straighten them out, using the tool. Carbon... nope.
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  5. #5
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    Quote Originally Posted by Cayenne_Pepa View Post
    Replace the hanger outright, for carbon frames. On Alu its perfectly acceptable to straighten them out, using the tool. Carbon... nope.
    Thanks. I've seen conflicting info on this. Better safe than sorry.

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  6. #6
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    You will not damage a carbon frame straightening a hanger so long as you hold the wheel and not the frame when levering the straightening tool. The thru axle traps the hanger between the endcap on the hub and the insert in the frame causing the torque from the straightening tool to be transferred to the wheel and not the frame when levering the hanger. Just donít hold the frame while straightening and you wonít have a problem. I have never had an issue in over five years straightening hangers on carbon frames.

  7. #7
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    If your chainstay is aluminum....you aren't really dealing with the carbon part of the frame, are you?

  8. #8
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    Quote Originally Posted by the mayor View Post
    If your chainstay is aluminum....you aren't really dealing with the carbon part of the frame, are you?
    Not directly, but the way the seatstay is joined with the chainstay is what gives me a reason to pause. Here is a pic of the non drive side where the chain stay and seat stay meet.

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  9. #9
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    Quote Originally Posted by the mayor View Post
    If your chainstay is aluminum....you aren't really dealing with the carbon part of the frame, are you?
    There is some carbon there. The Trek ABP is basically a tweak on the Split Pivot design, which I have on my Bucksaw. I have carbon seatstays and alu chainstays on my bike, too. I have had mechanics tweak my hanger back more than once. One of those times, it was a Salsa rep who did the straightening. I would figure if straightening the hanger would be cause for concern on that frame, he would have refused.

    For those not familiar with this sort of rear suspension design, it's probably a bit different than some others WRT how the forces are distributed on the hanger. The rear axle threads into the hanger, which sits between the parts of the frame that also attach there and the rear hub. A nut preloads the rear suspension bearings and holds the stays together from the exterior. The ABP is a little different, but a very similar application.

    Judge Rules Trek's ABP Design Does Not Infringe on DW's Split Pivot Patent - Mountain Bikes News Stories - Vital MTB

    I doubt that straightening the hanger with the DAG tool puts much stress on any element of the frame at all.

    Straightening a bent hanger on Carbon frame-trek-remedy-9-27.5-studio-29-710x473.jpg

  10. #10
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    If you hold onto the portion of the wheel next to the end of the straightening tool when levering the tool all the forces are transferred from the hanger ---> axle ---> wheel. As long as you don't grab the frame while levering the straightening tool no force is applied to the frame.

  11. #11
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    Quote Originally Posted by Cayenne_Pepa View Post
    Replace the hanger outright, for carbon frames. On Alu its perfectly acceptable to straighten them out, using the tool. Carbon... nope.
    How so? So when you put that new hanger that isn't straight on what do you do? new hangers aren't always straight.

    If the frame is strong enough to handle the crash/hit that bends the RD hanger, why isn't it strong enough to handle the same forces using a tool?
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  12. #12
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    Quote Originally Posted by TwoTone View Post
    If the frame is strong enough to handle the crash/hit that bends the RD hanger, why isn't it strong enough to handle the same forces using a tool?
    Agreed. You have nothing to worry about. Just use the Park tool as you would on an aluminum frame. The carbon frame is likely stronger than it's aluminum counterpart would be.

  13. #13
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    Quote Originally Posted by BlownCivic View Post
    Agreed. You have nothing to worry about. Just use the Park tool as you would on an aluminum frame. The carbon frame is likely stronger than it's aluminum counterpart would be.
    Damn, I'm glad you said that. If the hanger is stronger than the frame, there are some fundamental design flaws in carbon mountain bikes......and a lot of people got ripped off (including me).

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