Rear derailleur problem....

Discussion in 'Bicycle Mechanics and Repairs' started by RegG, 15 Aug 2018.

  1. RegG

    RegG Über Member

    I am having problems with the 7 speed Shimano rear derailleur on a Raleigh Siren in that it will not shift into the largest cog on the cassette. It moves smoothly between the other six cogs on all three of the front chain rings. Before I start messing around adjusting screws etc can anyone on here give me some guidance please? I am attaching a photo of the derailleur in case that helps.


    This is the original derailleur, the bike being around 20 years old.
  2. Salty seadog

    Salty seadog Space Cadet...(3rd Class...)

    Has it previously worked OK and changed to the biggest cog?
  3. Try to get it to shift up onto the biggest sprocket by just turning the indexing barrel adjuster anti clockwise a bit at a time. If that doesn’t get it, turn the screw marked ‘L’ anti clockwise a little bit at a time, until it does.
    Dogtrousers likes this.
  4. Arjimlad

    Arjimlad Tights of Cydonia

    South Glos
    My top tip...

    Pop the bike up supported (on a stand ideally), shift into the smallest cog on the rear then push the derailleur itself towards the largest cog as you turn the pedals forwards.

    That will show you if the RD is adjusted to that it CAN shift onto that big cog if the cable does its part.

    It will also enable you to make sure that the RD cannot push the chain off the biggest cog and into the spokes!
    raleighnut and Dogtrousers like this.
  5. Sharky

    Sharky Veteran

    When it's on the smallest cog at the rear, is there any slack in the gear cable?
    raleighnut likes this.
  6. OP

    RegG Über Member

    I don't know is the simple answer; the bike came from my daughters and she has been using it on a turbo trainer for a couple of years.

    I will have to check this out tomorrow as I didn't think to check.

    Thanks also to Racing Roadkill and Arjimlad - I will give these ideas a try tomorrow.
    Salty seadog and Racing roadkill like this.
  7. Salty seadog

    Salty seadog Space Cadet...(3rd Class...)

    Sounds like the low limit screw as pointed out above. Should be a simple fix.
  8. Cycleops

    Cycleops Guru

    Accra, Ghana
    It's likely just an adjustment issue, probably the cable has become stretched.

    Disconnected the cable and push the derailleur body across by hand if you want to check. You'll find it should shift on to the big cog.

    Be worth replacing a new greased cable.
    Plenty if YouTube videos on adjustment.

    Illaveago and raleighnut like this.
  9. Smokin Joe

    Smokin Joe Legendary Member

    The limit screws would be the last thing I'd touch as they never go out of adjustment unless someone has been fiddling with them. Cable adjustment is the place to start as that will be the cause 90% of the time.
  10. raleighnut

    raleighnut Guru

    On 3 Wheels
  11. OP

    RegG Über Member

    Thanks for that. I don't like touching any adjustment screws on derailleurs as I have the knack of messing the settings up!
    Maz and raleighnut like this.
  12. BianchiVirgin

    BianchiVirgin Senior Member

    Norn Iron
    20 years old? Time for a new one. Could be loose and sloppy action in the derailleur itself.
  13. OP

    RegG Über Member

    Surprisingly the rear mech is in very good shape! Having adjusted the low limit screw the gears are changing very smoothly!
  14. Ajax Bay

    Ajax Bay Veteran

    East Devon
    Gear cables do not stretch (to the extent it makes a difference to accurate gear changing ie [edit: as opposed to reversible extension proportional to length and force factored by) Young's Modulus), in their lifetime.
    B*******x. Not surprised the RD is in good shape, @RegG. Many years life left in it.

    Try to push the RD by hand towards the spokes. If it won't go far enough to line up with the largest sprocket, the OP has a 'limit screw' issue and the 'L' one needs unscrewing, quarter of a turn at a time, till, on pushing manually, it lines up. If it will go far enough to line up with the largest sprocket, then this is a cable tension issue - see suggestions above. May have to undo the bolt that anchors the cable and complete indexing in the 'normal' way. If the OP doesn't know how to do this or can't learn from u-tube, their LBS will set this up perfectly, rather quickly. Doing it oneself is much more satisfying, though.
    Last edited: 20 Aug 2018
    raleighnut likes this.
  15. midlife

    midlife Guru

    Don't braided cables undergo constructional stretch? Must Google :smile:
    Illaveago and Cycleops like this.
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