Problem with rear deralleur

kimcalif
kimcalif Posts: 3
edited June 2018 in Workshop
I have a new full 105 11 speed group on my last build.

Te problem is the rear derailleur. When the gears are perfectly indexed all gears works perfectly except the lowest gear. It skips between the lowest and second lowest gear. The limit screws are set right and I can move the derailleur by hand in to the lowest and while holding it there it works. But it seems like the cable don't get tight enough to keep it there. If I tighten it so it stays in the lowest gear, it starts shifting bad from the middle of the cassette and down. Another thing that is strange is that when in the big ring in the front it works on the lowest gear at the back, so big-big works but small-big does not. Strange since the chainline should be much more crossed on big-big.

I really don't understand what could be wrong. I have built a lot of bikes, but never ran into thos problem before. It seems like have to chooes between having all the gears except the lowest working perfectly, or haveing the lowest gear working and then have poor shifting and noises from the middle of the cassette and down.

Any suggestions of what the problem could be?

Comments

  • Mad_Malx
    Mad_Malx Posts: 5,000
    Bent derailleur ?

    I splashed out on an alignment tool last year, and it's made a big difference to several of the family's bikes.
  • gazza1286
    gazza1286 Posts: 45
    The limit screw for the lowest gear should be backed off in my opinion. The setting should be based upon what the shifter is 'capable' of achieving. It shouldn't be set based upon what you can do with your hand. So long as it's not possible for the shifter to move the chain beyond the largest ring and into the spokes you'll be fine. As you've discovered the barrel adjuster won't be of use in respect of adjusting the derailleur for gears on the extreme ends of the cassette.

    RJ the bike guy provides the clearest explanation that I've come across

    https://youtu.be/OV1AVcdNjMM
  • keef66
    keef66 Posts: 13,123
    Bent mech or bent / loose mech hanger?

    I've just completely recabled my 10 year old 105 5600 and it's shifting like new.
  • Mad_Malx
    Mad_Malx Posts: 5,000
    keef66 wrote:
    Bent mech or bent / loose mech hanger?

    Yes - I meant hangar rather than derailileur itself.

    I can't see what else other than this or limit screws as above.
  • kimcalif
    kimcalif Posts: 3
    Mad_Malx wrote:
    keef66 wrote:
    Bent mech or bent / loose mech hanger?

    Yes - I meant hangar rather than derailileur itself.

    I can't see what else other than this or limit screws as above.


    But if the hanger is bent, shouldn't that affect the other gears aswell? Because that is what I find odd, that everything shifts perfectly except it won't get into the largest sprocket at the back when in the small ring up front. It also goes up there when it is on the big ring in front.
  • Mad_Malx
    Mad_Malx Posts: 5,000
    edited June 2018
    kimcalif wrote:
    Mad_Malx wrote:
    keef66 wrote:
    Bent mech or bent / loose mech hanger?

    Yes - I meant hangar rather than derailileur itself.

    I can't see what else other than this or limit screws as above.


    But if the hanger is bent, shouldn't that affect the other gears aswell? Because that is what I find odd, that everything shifts perfectly except it won't get into the largest sprocket at the back when in the small ring up front. It also goes up there when it is on the big ring in front.

    When I had bent hanger it only affected shifting on 1 and 2 on cassette. I guess the alignment is a bit less forgiving at the end of the swing. I don’t remember what happened cross chaining.
  • milemuncher1
    milemuncher1 Posts: 1,472
    Bent / misaligned hanger would be my guess, get an alignment tool, it’s a great thing to have in the tool kit.