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  1. #1
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    keep bending derailleur hangers

    In the last few months I have bent 4 hangers and destroyed 2 rear derailleurs. I have a Trek 3700 and the derailleur is a shimano acera. I know it's low budget. The problem occurs when decending over roots or rocks (while the chain is slapping - normally less than 10mph or so). I'm in the small cog in the front and usually a larger cog in the rear. Also, the chain seems to drop off the crank (toward the inside often when decending). When it bends/breaks, the chain seems to get caught in the wheel spokes and tweeks the derailleur up and over - bending the hanger - or breaking the derailleur AND bending the hanger. Any ideas on why it happens so often? Chain too long - too short? Bent frame where the hanger mounts?
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  2. #2
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    Too much chain sounds like a possibility. You can check that easily - wrap the chain around the largest ring and largest cog (bypass the rear derailleur) - and add two links.
    Use it, use it, use it while you still have it.

  3. #3
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    Sounds like it might be a combination of the things you touched on. The chain sounds like it could be too long, the front derailleur might need adjusting to keep the chain on the chainring (check both the throw and the alignment/position) and the dr hanger might be out of whack, especially given the amount it's been tweaked.

    Also check the rear dr adjustment to make sure it stays out of the spokes when you're shifting to the biggest cog. It's not uncommon for there to be a little too much slack in the system that can cause the dr to go that little bit extra during the shift and push it into the spokes.

    Checking to make sure each of these things is right will definitely work you towards getting the problem sorted out.
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  4. #4
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    I have seen this before. It happened to my son several times until we figured it out. My guess is that the rear skewer (quick release) is not tight enough. What happens is that the hanger is very thin where it 'sisters' to the dropout. It is made to breakbefore something else gets broken, but if the skewer is not sufficiently tight, the hanger and the dropout are essentially two separate pieces. If the skewer is tight (along with the nut/bolt that hold the hanger to the dropout), the hanger and the dropout become one and make each other stronger.

    The rocks and other bumps bend/break the hanger, and the derailleur ends up in the spokes. Bad news and expensive to fix. Try tightening that rear skewer so much that you have to press the QR lever in pretty hard with the palm of your hand to close it and it kind of hard to undo it. Then your issues should cease.

  5. #5
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    When going down a hill you should have your chain on the the middle ring in front less ,chance of it falling/bouncing off, Are you shifting when or pedaling or coasting when it happens.

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    I'm with rangeriderdave, you shouldn't be descending in the small chainring. Try shifting into the middle when you are descending and it will give your chain more tension and keep it form bouncing so much.

    I don't think chain length or chain bounce can cause a bent hanger, bent hangers are much more common from hitting something on the trail, picking up a stick as you ride and it knocks the derailleur, laying your bike against the wall, laying your bike on the ground, crashing, or and this is a big one, shifting under pressure.

    Lighten up the pedal pressure you shift and always shift before you need to so you're always in the right gear. You don't shift your manual transmission car into a lower gear once you stall the engine, so try and think the same way on your bike. Also, make sure you bike is well tuned up before you ride, if there's a problem already then getting out on the trail will only make things worse.
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  7. #7
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    Quote Originally Posted by rangeriderdave View Post
    When going down a hill you should have your chain on the the middle ring in front less ,chance of it falling/bouncing off, Are you shifting when or pedaling or coasting when it happens.
    Bingo....

    Also ride smoothly

  8. #8
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    If your derailleur is going into the spokes you need to have some words with whoever is tuning your derailleur, especially since it's happened multiple times.
    All of the true things I'm about to tell you are shameless lies.

  9. #9
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    great thoughts...

    THANKS for all the thoughts and advice - I am going tomorrow and starting all over (at a different bike shop I might add). I will take heed all the advice - I'm gonna bring every one of these opinions to my LBS when I go tomorrow (and look over the techs shoulder). I'm gonna get a new hanger, derailluer and chain.

    As far as the downhill deal and the middle chain ring....I'm in NC, our uphills and downhills are quick ups and downs - so I keep the front on the smaller cog for peddling up the hills (its a 26 tooth cog) - I normally coast going DOWN the quick 20 second decents. Our uphills are about 200 - 400 yards up and about 200 - 400 yards down. I REST all I can on the downhills...LOL!
    Cycle tracks will abound in Utopia. ~H.G. Wells

  10. #10
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    I know I might open a can of worms with this one. But this is only a comment in addition to all the other (more valid) information that was already given. But next time, buy SRAM. The Shimano rear derr allows for a lot more chain slap just based on it's design. The SRAM design keeps the chain under a bit more control which will lessen the chances of it getting sucked in and destroying your drivetrain.

  11. #11
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    Quote Originally Posted by dbfutrell View Post
    As far as the downhill deal and the middle chain ring....I'm in NC, our uphills and downhills are quick ups and downs - so I keep the front on the smaller cog for peddling up the hills (its a 26 tooth cog) - I normally coast going DOWN the quick 20 second decents. Our uphills are about 200 - 400 yards up and about 200 - 400 yards down. I REST all I can on the downhills...LOL!
    Well, I think we all understand what you're saying... but you've been told what you should be doing?
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  12. #12
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    I have started riding alot more strait agressive trail riding with my AM Giant Reign as opposed to my DH bike and have been reallyy enjoying it. But the bent dr hanger has been driving me nuts 3 weekends in a row. I am probably rough shifting under extereme pressure, uphills. But I think i read that if you switch from a long cage to a med or short cage DR there is less leverage to force the bend in those really high stress /force situations.

  13. #13
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    Somewhat off topic but are there any tips to bending it "straight" again when out on the trail and need to get home?
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  14. #14
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    I use an adjustable crecent wrench and kind of twist it straight. You have to take the DR off the hanger first. Carry a smaller wrench in your camel back.

  15. #15
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    How much do you weigh? I know big guys who would flex the spokes outward; they'd tag the cage and rip it right off in the blink of an eye.

  16. #16
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    Some more simple thoughts to consider:
    1) Adjust your low (inward) limit on the rear derailleur so that it does not over shift and derail. I usually adjust it until it does derail and then adjust it until it won't get the lowest gear. Then I find middle ground. This tends to keep it well away from the spokes
    2) Check your spokes. You could have a bent or lose spoke from the first/previous derailleur failure and that is running real close to your derailleur.
    3) Acera is probably the cheapest derailleur there is. You may want to upgrade that at some point.
    4) Watch those lines. I've eaten a lot of derailleurs in my early biking. After awhile you become more cognizant of the fact that you have something hanging lower on that side and you need to avoid it when picking your lines between rocks, branches, etc.
    5) People are saying you should stay out of granny gear up front. If that isn't comfortable for you yet, you could at least get out of 1-1 when heading down a hill. That ought to keep some distance between your derailleur and your spokes as well.

    That's my 2 cents.

  17. #17
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    Quote Originally Posted by bryantaber View Post
    I have started riding alot more strait agressive trail riding with my AM Giant Reign as opposed to my DH bike and have been reallyy enjoying it. But the bent dr hanger has been driving me nuts 3 weekends in a row. I am probably rough shifting under extereme pressure, uphills. But I think i read that if you switch from a long cage to a med or short cage DR there is less leverage to force the bend in those really high stress /force situations.
    The lower pulleys don't exert force side to side, only force enough to take some slack out of the chain. Long vs short will only change how much metal you put in peril of being hit on trail obstacles.

    If you suspect you're shifting under pressure then that's your problem. Just stop doing that and you'll fix your issue.

    And remember, that even if you bend a hanger back into position you've introduced fatigue into the hanger and it will probably fail a little easier each time. Try a new hanger if you haven't in a while.
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  18. #18
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    Quote Originally Posted by False View Post
    If your derailleur is going into the spokes you need to have some words with whoever is tuning your derailleur, especially since it's happened multiple times.
    It's the spokes going into the derailleur so you won't see it on the bench.

    If you hanger is bent then the cage can also be pivoting out of line.

    Put your bike in a workstand and shift into the gear combo that this happens in. Grab the rear D and move it forward and back like you're hitting bumps. See if the back of the cage gets nearer to the wheel as you do this.

  19. #19
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    Carry a replacement derailleur hanger with you

    Quote Originally Posted by coopdad View Post
    Somewhat off topic but are there any tips to bending it "straight" again when out on the trail and need to get home?
    I always carry a replacement derailleur hanger in my camelbak. Jenson carries the full line of Wheels Mfg. replacement hangers.

    If the messed up one is just tweaked, not snapped, I'll take it home, clamp it on my work bench, and see if I can straighten it (comparing it to a new one). That will then become my emergency camelbak hanger.

  20. #20
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    when i say "shifting under pressure, i'm reffering to a situation like coming to an almost dead stop while balancing, shiffting down 3 gears and hard pedaling at the same time from a dead stop. It makes a huge racket and I did notice some mis-shifts soon after. it's not helping that I have been introduced to a lot new spots within the last 2 months which is the cause of some of the rough shifting. Not familiar with the upcoming terrain.

  21. #21
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    Quote Originally Posted by bryantaber View Post
    when i say "shifting under pressure, i'm reffering to a situation like coming to an almost dead stop while balancing, shiffting down 3 gears and hard pedaling at the same time from a dead stop. It makes a huge racket and I did notice some mis-shifts soon after. it's not helping that I have been introduced to a lot new spots within the last 2 months which is the cause of some of the rough shifting. Not familiar with the upcoming terrain.
    That's not what you want to do. The drive train needs to be spinning with minimal load to get a shift done cleanly.

    Doing it the way you describe is going to result in bent & broken parts.

    If you wind up stalled and need to drop gears you have to stop, put one foot down, put on the front brake and lift the rear. Do a one leg pedal and shift one gear at a time while the drive train is turning till you click smoothly into the right gear. Then you can carry on.

  22. #22
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    Quote Originally Posted by zebrahum View Post
    I'm with rangeriderdave, you shouldn't be descending in the small chainring. Try shifting into the middle when you are descending and it will give your chain more tension and keep it form bouncing so much.
    This^^^
    15mm is a second-best solution to a problem that was already solved.

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    Quote Originally Posted by bryantaber View Post
    when i say "shifting under pressure, i'm reffering to a situation like coming to an almost dead stop while balancing, shiffting down 3 gears and hard pedaling at the same time from a dead stop. It makes a huge racket and I did notice some mis-shifts soon after. it's not helping that I have been introduced to a lot new spots within the last 2 months which is the cause of some of the rough shifting. Not familiar with the upcoming terrain.
    I'm aware of what shifting under pressure means and doing so will destroy your bike. I tend to recommend to people who are unfamiliar with terrain to choose a gear lower (easier to pedal) than you would normally ride. Beginners typically push too large a gear anyway so a little spinning is good for most people.

    You really need to practice the art of spinning the pedals without applying force so that you can shift while on hills and not put your drivetrain in danger. I usually do it by giving a strong pedal stroke to build some momentum then shifting while just turning the pedals (instead of applying force to them). That way I can spin the pedals to shift gears but I'm not applying pressure so that when the chain "peels" off of the gear you are leaving it doesn't apply any bending force to the cassette or chainring teeth.
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  24. #24
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    Quote Originally Posted by zebrahum View Post
    You really need to practice the art of spinning the pedals without applying force so that you can shift while on hills and not put your drivetrain in danger. I usually do it by giving a strong pedal stroke to build some momentum then shifting while just turning the pedals (instead of applying force to them). That way I can spin the pedals to shift gears but I'm not applying pressure so that when the chain "peels" off of the gear you are leaving it doesn't apply any bending force to the cassette or chainring teeth.
    This is one of the most crucial mtb skills to develop.

    coming to an almost dead stop while balancing, shifting down 3 gears and hard pedaling at the same time from a dead stop.
    I'm physically wincing just reading that. Seriously, save yourself some time and just whack your drivetrain with an axe.
    15mm is a second-best solution to a problem that was already solved.

  25. #25
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    +1 Jeffj

    Quote Originally Posted by jeffj View Post
    I have seen this before. It happened to my son several times until we figured it out. My guess is that the rear skewer (quick release) is not tight enough. What happens is that the hanger is very thin where it 'sisters' to the dropout. It is made to breakbefore something else gets broken, but if the skewer is not sufficiently tight, the hanger and the dropout are essentially two separate pieces. If the skewer is tight (along with the nut/bolt that hold the hanger to the dropout), the hanger and the dropout become one and make each other stronger.

    The rocks and other bumps bend/break the hanger, and the derailleur ends up in the spokes. Bad news and expensive to fix. Try tightening that rear skewer so much that you have to press the QR lever in pretty hard with the palm of your hand to close it and it kind of hard to undo it. Then your issues should cease.
    An old thread I know, but though it worth posting to in case it saves someone from unnecessary spending. The same thing also happened to me on my Haibike Full FatSix but after already trashing my first dérailleur on a rock only two weeks earlier. So the when the 2nd XT 786 Shadow+ was destroyed in the wheel, I was starting to think it was a bigger or possibly design fault (e.g. cage too long/too low or chain too long). However I did remember afterwards that the axle was 2 turns undone. I put this down to the pressure on the wheel when the rear mech got caught in it, but in hindsight I now think it was actually the cause. I'd had a couple of slipped gear changes in the previous 1km which means it wasn't 100%. The Full FatSix needs all it's bolts checking before every ride. It's such a lump that it works free bolts on linkages, crank arms & Sprockets...and now axles/QR's.

    So before you do as I did and start working out expensive ways of shortening the mech cage by dropping to single speed, consider how many successful rides you have had on the bike, without trashing the derailleur, and if it's many, then it probably is just a blip.

    I now have a new hanger & rear mech ordered and will report in a few weeks after some hard riding.
    Last edited by SteviedSolve; 11-21-2016 at 06:55 AM. Reason: amendment

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