Rear derailleur adjustment not working

njb01
njb01 Posts: 4
in Workshop
I bought a second hand electric mountain bike from a mate, knowing that it was a non runner after some kind of rear derailleur disaster. Sure enough, the derailleur hanger was sheared and the chain was wrapped around everything. After replacing the hanger, took ages to get the right one, everything is back together and working to a point. I lost 2 links of chain, but minor issues, so far.
My mate had told me that the rear gears had been playing up and jamming. Sure enough on the largest cog of the cassette, the rear derailleur is lying almost flat and actually meshes with the cog. You can get into 10th gear but you sure aren’t getting back out again.
I played with the b screw and things got a little better but there is still interference on 10th.
My thinking is either that the chain length is so critical that 2 links has caused this, or that the derailleur suffered some kind of misalignment at some point. As the gears were problematic prior to the final hanger failure, then who knows.
The bike is a Haibike Xduro rc, with Bosch motor and a 1 x 10 gear system and SLX rear derailleur. While I am on here, if I need a new chain, how do I work out the right one? There are just so many options.

Comments

  • njb01
    njb01 Posts: 4
    OK, so I have counted the links in my chain, having found it is marked HG-X which narrows it down to a specific Shimano range. The curious thing is that I have counted 110 links, whereas the standard length is 116. I know that I removed 2, but I seem to be 4 links shorter than that. To my mind, that cannot be good! Is that going to affect shifting performance?
  • arlowood
    arlowood Posts: 2,561
    A pic of the derailleur position where you are having problems might help. However from your description it sounds like your chain is way too short,

    I've used this chain length calculator for several years and it has worked fine for me

    http://www.machinehead-software.co.uk/bike/chain_length/chainlengthcalc.html

    Just input the number of teeth on your front chainring and the largest sprocket size at the rear together with the chainstay length and you'll get the correct chain length in inches or links
  • njb01
    njb01 Posts: 4
    That is a very useful calculator, thanks for sharing. With chainstay of 18.5, front 36 teeth, back 38 teeth, I end up at 57 inches. The Shimano links are around 1/2 inch, but I counted over 10 to get a more accurate answer. That says a chain of 112 links, which is not far from the 110 in there now and the standard 116 is a little long perhaps. Hopefully, the spring in the rear derailleur will pull out the extra and it is a long SLX derailleur which must eat up a few more links.
  • The Rookie
    The Rookie Posts: 27,812
    Setting your chain length isn't hard, but yes, your chain is too short.

    You set the chain length to the bike, they are sold in fixed lengths (as they wouldn't sell a dozen different sizes of each for obvious reasons) and 116 is common, someone then shortened it, possibly too short, possibly to the exact right length.

    Any ten speed chain will be fine (116 or longer) to budget, drop the rear shock pressure and find the suspension height with the longest chain stay effective length, then size it properly. Having posted in a roady section the advice above forgets that not all chainstays are fixed!
    https://www.parktool.com/blog/repair-help/chain-length-sizing
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.

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