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Do you ever have to replace derailleurs?

sophie99sophie99 Posts: 4
edited October 2016 in MTB workshop & tech
I have an old, cheap and much abused hybrid. The rear shifting is getting worse and worse - to change into a smaller cog you now have to click down twice and back up once. But the gears have been reset by a mechanic and it changes up perfectly, so I'm wondering if there is something wrong with the mech rather than the indexing - that there's not enough force to move the chain.
Do derailleurs ever wear out? Or bits of them? Would taking it apart and cleaning it help?
(Or should I just buy a new bike :D )

Posts

  • First thing I'd check is cables - old cables can get sticky and cause shifting issues. To answer your question, normally only as a result of crash damage, jockey wheels do wear out which can lead to sloppy shifting and eventually the pivots can wear out but only after mega miles or lots of abuse.

    And yes the real answer is you need a new bike.
  • fat daddyfat daddy Posts: 2,632
    never replaced a derailleur ... but had those exact symptoms every time

    (1) the chain is worn
    (2) the cassette is worn
    (3) the cables are worn
    (4) the cables are dirty
    (5) the gearset NEEDS a clean
    (6) one of the shifters broke

    all of the above can be rectified easily by buying a new bike :D
  • The RookieThe Rookie Posts: 27,747
    Sticking cables is most likely but the old mech on my commuter did this and the issue was actually gummed up pivots on the mech, lots of GT85 and manipulating it by hand to get the crud out then a drop of 3:1 oil on each pivot.

    You have your shifting analogy back to front, shifting up is to a higher number gear which is a smaller cog at the back.

    Dérailleurs do wear out, but usually its just a maintenance issue.
  • cooldadcooldad Posts: 32,904
    By changing down you actually mean up, to a smaller cog, which is normally a cable problem. Replace that, inner and outer before you buy anew mech.
    I don't do smileys.

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  • fat daddyfat daddy Posts: 2,632
    new bikes also come with new cables if its easier
  • fenixfenix Posts: 5,437
    Mechs do wear out -and the springs lose their power over time - you could try taking it off and taking it apart to clean everything - but it might be a better use of time to buy a new one.
  • keef66keef66 Posts: 13,286
    As above, poor shifting in one direction is usually down to resistance somewhere in the cables. To be absolutely sure, replace the lot, inners and outers, and make sure the cut ends of the outers are square and properly opened up. I find a Dremel very good for tidying up cut outers.

    Occasionally the pivots in a derailleur will start to seize up to the point that the return spring is less effective. You can eke out a few more months of service by thoroughly cleaning and lubing the thing and moving it back and forth through it's full range of movement, but the fix will only be temporary.

    Given how cheap they are, these days I'd just replace a front or rear mech that was giving me hassle. Probably the same with brake calipers...
  • I had similar problems to this - my RD cable was all frayed to buggery at the shifter end, where it rotated over the ratchet. It was a right PITA to get all the fragments out.

    Now I check it every few months and replace the cable if it shows the slightest sign of fraying. Haven't had to replace the outer yet though.
    Is the gorilla tired yet?
  • keef66keef66 Posts: 13,286
    I had similar problems to this - my RD cable was all frayed to buggery at the shifter end, where it rotated over the ratchet. It was a right PITA to get all the fragments out.

    Now I check it every few months and replace the cable if it shows the slightest sign of fraying. Haven't had to replace the outer yet though.

    Shimano 105? My RH shifter eats the inner cable every couple of years. A lot easier to sort if you catch it before it actually snaps
  • larkimlarkim Posts: 2,284
    Shifting to the smaller cog effectively relies on tension in the cable being released, thus allowing the spring to pull the mech outwards until the balance of tension (spring resisting the cable) is restored.

    So that either implies that there's friction within the route of the cable somewhere which is making it harder for the spring to pull the mech outwards than it is designed to do, or there is friction in the mech assembly somewhere which is resisting against the spring, or the spring has reduced power.

    Eradicate the first two and you'd be left with that conclusion about the final one.
    2015 Canyon Nerve AL 6.0 (son #1's)
    2011 Specialized Hardrock Sport Disc (son #3s)
    2013 Decathlon Triban 3 (red) (mine)
    2019 Hoy Bonaly 26" Disc (son #2s)
    2018 Voodoo Bizango (mine)
    2018 Voodoo Maji (wife's)
  • When I replace a derailleur, I always notice how solid the new one feels compared the old one which always feels sloppy like the metal has worn around some of the pivots.
    A new mech always seems to give 'better' shifting than the old one.
  • Thanks everyone, I wasn't expecting a response so quickly!
    Sorry about the up/down shifting confusion. I will literally never remember which way is which.
    The feedback is all really useful. I think I'll try the maintenance options first - I'll replace the cables first and then the mech if that doesn't work. It'll be good to get some more hands-on maintenance practice, and ... since there's so much positive feedback for just buying a new one, I can still do that if it all goes wrong. :D
    I'll let you know how it goes... Wish me luck!
  • The RookieThe Rookie Posts: 27,747
    I'm guessing you don't drive a car or ride a motorbike if up/down gears confuses you....up and down is based on the gear number, top gear being 9 is up from lowest gear (biggest rear cog) being first, like it says on the shifter (unless you removed the display).
  • larkimlarkim Posts: 2,284
    I do think many lay people instinctively think "up the cassette" (looking at the chain on top of the cassette) when they talk about gears going "up" or "down". I'd agree that gear 1 is by definition the easiest ratio gear.

    Having said that, some things go up as the number goes down - e.g. the music charts ("moving up the charts from 9 to 2 in this weeks album charts is...") so its not completely illogical to get ups and downs the opposite way round.
    2015 Canyon Nerve AL 6.0 (son #1's)
    2011 Specialized Hardrock Sport Disc (son #3s)
    2013 Decathlon Triban 3 (red) (mine)
    2019 Hoy Bonaly 26" Disc (son #2s)
    2018 Voodoo Bizango (mine)
    2018 Voodoo Maji (wife's)
  • cooldadcooldad Posts: 32,904
    That's why it's easier to use big/small ring and big(ger)/small(er) cog.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • larkimlarkim Posts: 2,284
    ^^^^^^^
    Definitely avoids confusion!
    2015 Canyon Nerve AL 6.0 (son #1's)
    2011 Specialized Hardrock Sport Disc (son #3s)
    2013 Decathlon Triban 3 (red) (mine)
    2019 Hoy Bonaly 26" Disc (son #2s)
    2018 Voodoo Bizango (mine)
    2018 Voodoo Maji (wife's)
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