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Strange rear mech issue

AnonymousAnonymous Posts: 79,678
edited November 2015 in Workshop
This morning I installed a new mech hanger after my old one sheared off after a few knocks and bending it back had obviously considerably weakened it. It wasn't a catastrophic failure and the mech didn't go through the spokes - gently caught a couple of spokes when in the granny gear and broke off. Was at low speed so no damage. Anyway, the new one is installed and is adjusted (more or less) except for this one issue.

For some reason, the chain doesn't correctly sit in the bottom jockey wheel in the rear mech. It tends to jump out the teeth and sit 'outside' the jockey wheel, but remains sort-of in place due to the cage holding it in. The problem is worse when in a lower gear (larger cog at the back).

I've had 2 offs on this bike, on the delicate side, and in both cases bent the mech back. Is it possible that the cage has bent as well? Stupidly didn't take any photos. All I can say is when in the highest gear (50x11) the rear mech points ever so slightly inwards, so there is a slight curve in the chain as it straightens out when reaching the chainset.

Posts

  • veronese68veronese68 Posts: 24,682 Lives Here
    It's possible that it's bent. Could you have somehow got the chain threaded wrong? Might be worth checking the new hanger is straight. Have you got a straightening tool? You can have a play with mine some time if you want.
  • AnonymousAnonymous Posts: 79,678
    Definitely threaded correctly as I didn't remove the chain when refitting, just removed the 2 hanger parts and installed the new one.
    Can't see why the hanger wouldn't be straight as it's brand new from Halfords (for the Boardman), but it could be the mech which is bent.
    Don't have a straightening tool as I've usually always done it by eye.

    Thanks for the offer, but having learned the hard way I don't want to be bending it if at all possible. Would rather pony up for a new mech!
  • Ben6899Ben6899 Posts: 8,990
    Definitely threaded correctly as I didn't remove the chain when refitting, just removed the 2 hanger parts and installed the new one.
    Can't see why the hanger wouldn't be straight as it's brand new from Halfords (for the Boardman), but it could be the mech which is bent.
    Don't have a straightening tool as I've usually always done it by eye.

    Thanks for the offer, but having learned the hard way I don't want to be bending it if at all possible. Would rather pony up for a new mech!

    New hangers often need tweaking. For either of two reasons: the new hanger is slightly bent (not unheard of); the new hanger is straight as an arrow, but because of manufacturing tolerances, it actually needs to be a little bit bent to suit the frame (if a hanger is 1mm out, then shifting will suffer or you'll have noise from the drive train)... think how accurately a carbon dropout can be formed... to 1mm?

    So check the hanger alignment.
    Ben

    Bikes: Donhou DSS4 Custom | Condor Italia RC | Gios Megalite | Dolan Preffisio | Giant Bowery '76
    Instagram: https://www.instagram.com/ben_h_ppcc/
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  • AnonymousAnonymous Posts: 79,678
    Fair enough - Veronese I may need to take you up on that offer!

    How do I know if its the hanger or the mech which is bent?
  • Ben6899Ben6899 Posts: 8,990
    Fair enough - Veronese I may need to take you up on that offer!

    How do I know if its the hanger or the mech which is bent?

    If the mech is bent, then it'll be the cage. Sit it on a flat surface and check for daylight. The mech cage should be perfectly straight; the hanger may need to be a little bent to suit the dropout.

    (I'll wager the mech itself is fine)
    Ben

    Bikes: Donhou DSS4 Custom | Condor Italia RC | Gios Megalite | Dolan Preffisio | Giant Bowery '76
    Instagram: https://www.instagram.com/ben_h_ppcc/
    Flickr: https://www.flickr.com/photos/[email protected]/
  • veronese68veronese68 Posts: 24,682 Lives Here
    Fair enough - Veronese I may need to take you up on that offer!
    No problem, have you got my number after the crankset exchange?
  • SecteurSecteur Posts: 1,971
    The derailleur cage is bent, surely?
  • AnonymousAnonymous Posts: 79,678
    Realigned new mech - it was a bit bent. Ripped it off again though so had to single speed it for the rest of the ride.

    Time for another new mech hanger and may play it safe with a new mech as well!
  • veronese68veronese68 Posts: 24,682 Lives Here
    I feel partially responsible. Was it my magnificent tool or that you didn't know your own strength?
  • itboffinitboffin Posts: 19,964
    Are you by chance buying these hangers from the dairy section of your local supermarket?

    :D
    Rule #5 // Harden The censored Up.
    Rule #9 // If you are out riding in bad weather, it means you are a badass. Period.
    Rule #12 // The correct number of bikes to own is n+1.
    Rule #42 // A bike race shall never be preceded with a swim and/or followed by a run.
  • AnonymousAnonymous Posts: 79,678
    Haha that's genuinely what I first thought.

    The first one had taken a few knocks so I appreciate it may have been weakened. I am pretty annoyed about this one as it had barely covered 45 miles before shearing off, and it had been in 34x25 earlier in the day with no issues. I have since laid the mech down and the cage is a bit bowed so will get new one. Still pretty annoying and definitely feel like a ham fisted spanner monkey now

    Went to this
    22704935255_74aa3ff6e5_z.jpg

    then to this
    22715645551_2b8f0f47e5_z.jpg

    then about 30 miles later my other bike snapped a spoke so had to walk. I did do a damn good job of replacing it though
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