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Chain falls when backpedalling in big- big crossover

iron-cloveriron-clover Posts: 737
edited March 2015 in Workshop
Hi all,
I've just upgraded from Shimano 2300 8 speed to 5700 10 speed, and now when in the big-big (and the 2nd and 3rd largest cassette sprockets) and backpedal, i.e. after stopping at traffic lights the bad chainline pulls the chain off of the big ring.

This was never a problem when just running 8 speed- is this something that cannot be prevented or should you be able to backpedal by 1/2 to 1 revolution in any gear ratio?
Would adding a couple of links to the chain help at all with the reduced chain tension?

When on flat roads I prefer pulling away in the large chainring as it minimises the amount of shifting needed to get back up to speed and will be a pain to get used to always changing to the small chainring before stopping.

Cheers!

Posts

  • jgsijgsi Posts: 5,027
    Put it on the workstand and check where and how the chain is being thrown and adjust acordingly.
  • I already have several times- it is being pulled off the big ring onto (hopefully) the inner ring by the angle of the chain when backpedaled in the crossover gears.

    Both front and rear deraileurs seem to be set up correctly and shift fine through all of the different gear combinations and does not throw the chain when pedalling forwards.
    It's the backpedaling I have a problem with, which in theory shouldn't be a problem but it is in reality when moving the cranks to a suitable position to start off again when stopped.

    I cannot see how adjusting the derailleurs will relieve this problem as it will just throw the indexing completely out- although I haven't played with the B screw yet.
  • trailflowtrailflow Posts: 1,311
    edited February 2015
    Do you have Hollowtech 2 BB outboard cups installed ? are there spacers on the drive side ? If there is try removing and puttng them on the non driveside.

    For the b screw, try turning it all the way in and look at the upper jockey wheel,is it touching the cassette ? You want about 5mm clearance.

    Make sure the tab on the derailleur is pushed against the tab on the hanger. Before turning the b screw.

    Check the chainring bolts are tight.

    Check for any stiff links in the chain.
  • Is the rear mech bent at all? If it had been pushed in at the bottom, that would try to pull the chain off the big ring when pedalling backwards.
  • deswellerdesweller Posts: 5,271
    My money's on a wonky derailleur hanger.
    - - - - - - - - - -
    On Strava.{/url}
  • keef66keef66 Posts: 13,123
    trailflow wrote:
    Do you have Hollowtech 2 BB outboard cups installed ? are there spacers on the drive side ? If there is try removing and puttng them on the non driveside.
    .

    Shouldn't be any spacers with a HT2 BB in a road frame / with a road crankset.

    I think Des is likely correct.
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