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Weird lose of tension in rear derailleur

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  • January 9, 2022 at 5:27 pm #31922
    0-0

    ** Edit: Solved **
    When riding yesterday, I experienced a lose of tension in my RD.
    If I deliberately put the bike in the 9th gear (or above), whilst still in the lower chainring, the chain would become extremely loose and saggy. spilling over the chainstay.

    I appreciate you’re not supposed to cross chain. But I’ve not had this issue before. Example, like when the bike is on a stand and you’re cleaning the chain, running it through all gear combinations.

    I took the bike to Halfords. They suggested cleaning the drivetrain, shortening the chain and replacing the gear cable.
    I’ve cleaned the parts and shortened the chain. But shortening the chain doesn’t seem logical, as I’d want the RD to move towards the rear of the bike to maintain tension.
    I haven’t replaced the cable (only tried to add tension), because I thought the cable only moved the RD in/out and not towards the rear or front of the bike.

    The RD was bought from Halfords last July, so it’s still under warranty. I unsure if I’ve still got the old one, so maybe I could refit it, to check the tension.
    The chain isn’t worn and neither are the other parts of the drivetrain.

    The bike is a 105 R7000 11 speed. 52-34 on the front and 11-40 on the rear. Chain is normally 114 links (standard no. of links in packet), now 112 links.
    I’ve used this setup for many thousands of miles and never had any issues until yesterday.

    Thanks for any advice.

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  • January 10, 2022 at 5:31 pm #988373
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    0-0

    IanMSpencer wrote:

    IanMSpencer wrote:
    I’ve always been quite surprised by the amount of brain power that is required to maintain bicycles.

    About 5 years ago, I did write a diagnostic app for bikes, a little database of symptoms, diagnostic tests and possible solutions, along with a component mileage wear assessment driven by Strava rides, with some attempt to weight it by mileage.

    For example, wobbly back wheel, check quick release, check bearings for play (how), check frame for crack. Solution: tighten quick release, adjust bearings (cone), replace bearings (sealed), repair or replace frame.

    I gave up when just keeping up with Android releases seemed to take 90% of the development effort.


    Agreed. But I wouldn’t let anyone from Halfords see the first sentence ?

    January 10, 2022 at 4:48 pm #988371
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    IanMSpencer

    I’ve always been quite
    I’ve always been quite surprised by the amount of brain power that is required to maintain bicycles.

    About 5 years ago, I did write a diagnostic app for bikes, a little database of symptoms, diagnostic tests and possible solutions, along with a component mileage wear assessment driven by Strava rides, with some attempt to weight it by mileage.

    For example, wobbly back wheel, check quick release, check bearings for play (how), check frame for crack. Solution: tighten quick release, adjust bearings (cone), replace bearings (sealed), repair or replace frame.

    I gave up when just keeping up with Android releases seemed to take 90% of the development effort.

    January 10, 2022 at 3:28 pm #988369
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    0-0

    Thank you all very much for
    Thank you all very much for your help and sorry for the delay in replying.
    The problem was the pivot and spring on the rear derailleur.
    I disassembled, cleaned (I wasn’t dirty) and relubed it. Now it works fine.
    So knowledge gained on how to fix another part on the bike.

    ???????????????????????

    January 10, 2022 at 3:14 pm #988367
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    jaymack

    Give it a clean and if the
    Give it a clean and if the solution’s not immediately obvious take it to your local bike shop. The likelihood of them being surprised by your bike’s baffling mystery is as near to nothing as makes no odds.

    January 10, 2022 at 12:51 pm #988365
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    TheBillder

    0-0 wrote:

    0-0 wrote:

    No I don’t have any spare wheels.

    Wheels can be expensive but a humble spare one can be very handy. Perhaps it’s just me, but I’ve had pawls and spokes break without warning, and then had to wait for parts / the weekend / competence to fix them. My spare rear wheel was £60 and it’s frankly a bit crap but it works and has kept me rolling a few times when my slightly less crap main one has been out of service. Worth considering.

    January 10, 2022 at 11:58 am #988363
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    Grahamd
    Chris Hayes wrote:
    If you can’t fix it yourself take it to a mechanic – but clean it throughroughly first and then you won’t embarrass yourself.  No point in posting tech questions here, there are too many variables to prescribe a diagnosis on a thread.  

    Agree with this.
    FWIW I have wasted large amounts of frustrating time trying to diagnose and fix problems that my LBS resolved and fixed in minutes for a modest fee, that anything like this I would always ask them to fix now. 

    January 10, 2022 at 11:19 am #988361
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    IanMSpencer

    If the end breaks off in the

    If the end breaks off in the shifter you don’t need a new shifter, but it can need resilience, patience, innovation, a variety of pokey tools, and careful thought to retrieve the little blighter which is like some hyper-intelligent device out of The Matrix for resisting coming free. Never had one I couldn’t fix, but it has taken up to 45 minutes to get the thing freed.

    January 10, 2022 at 10:35 am #988359
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    Chris Hayes

    If you can’t fix it yourself

    If you can’t fix it yourself take it to a mechanic – but clean it throughroughly first and then you won’t embarrass yourself.  No point in posting tech questions here, there are too many variables to prescribe a diagnosis on a thread.  

    January 10, 2022 at 9:15 am #988357
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    matthewn5

    I’ve had that happen with

    I’ve had that happen with lower end Shimano freehubs – the sort that need a massive hex key to remove. The freehub bearings go stiff and then the chain starts to misbehave. The other thing is that the pawls can stick and you’ll suddenly find you have no forward motion at all – usually just when you’re trying to get out of the way of a lorry. Sounds like it needs a service. Also check the jockey wheels. Replace the gear cable – if the end breaks off in the shifter you’ll need a new shifter.
    I’d suggest going anywhere but Halford’s based on the erroneous advice they’ve given you so far.

    January 10, 2022 at 9:14 am #988355
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    Podc

    When in small/small with the

    When in small/small with the chain all slack, if you physically push the derailleur back, does it go back into it’s normal position with the chain held in tension? If so, and assuming the derailleur is mounted correctly (bottom lug against the mech hanger lug) and all tight, and the mech hanger tight, then it’s likely dirt or corrosion in the derailleur pivot. I’ve seen it a few times but usually on old kit that has suffered a few winters with no TLC and not on the newer style Shimano derailleurs (front ones are a different story – seen plenty on the newer style ones all gummed up and sticky). The pivot can be stripped and cleaned. 

    If the chain only goes slack when the wheel is spinning without the pedals being spun, is there a spoke protector dragging on the cassette?

    January 9, 2022 at 9:28 pm #988353
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    0-0

    Dingaling wrote:

    Dingaling wrote:

    I had this problem once on a ride. IE the chain fell onto the chainstay when I stopped pedalling and I could only ease the problem by slackening the pressure caused by closing the quick release. I had previously had the freehub off to clean and grease it. On reassembly I had forgotten a washer that belonged on the inside outer end of the freehub that kept the clamping forces of the quick release off the freehub.

    Finding the problem is not initially easy because when you take the wheel out of the bike the hub rotates freely with no pressure on it. Leave the wheel in the bike, take the chain off and see if the hub freely rotates backwards.

    That might all be useless info but all I can think of.


    Thank you.
    No, not useless info. It gives me more options to try out.

    January 9, 2022 at 9:16 pm #988351
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    Dingaling

    I had this problem once on a

    I had this problem once on a ride. IE the chain fell onto the chainstay when I stopped pedalling and I could only ease the problem by slackening the pressure caused by closing the quick release. I had previously had the freehub off to clean and grease it. On reassembly I had forgotten a washer that belonged on the inside outer end of the freehub that kept the clamping forces of the quick release off the freehub.

    Finding the problem is not initially easy because when you take the wheel out of the bike the hub rotates freely with no pressure on it. Leave the wheel in the bike, take the chain off and see if the hub freely rotates backwards.

    That might all be useless info but all I can think of.

    January 9, 2022 at 9:11 pm #988349
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    HoarseMann

    Good plan. Hopefully it is

    Good plan. Hopefully it is the jockey wheels or derailleur pivot.

    January 9, 2022 at 9:05 pm #988347
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    0-0

    HoarseMann wrote:

    HoarseMann wrote:

    Sorry, that was a bit of a rambling brain dump!

    I don’t think you can rule out the freehub body. It does sound like that could be the problem.


    Thank you.
    I’ve just found my old RD in the attic. The “arm” movement feels perfect, compared to the one on the bike.
    I’ll fit it tomorrow, if I get the tension back, I’ll either 1. get a new replacement from Halfords 2. swap the current jockeys wheels onto the old one 3. try and find out if it’s possible to service the interior parts of the pivot mechanism (outside parts are clean).

    If I don’t get the tension back. I’ll order a new freehub body, to rule that out.

    January 9, 2022 at 8:51 pm #988345
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    HoarseMann

    Sorry, that was a bit of a

    Sorry, that was a bit of a rambling brain dump!

    I don’t think you can rule out the freehub body. It does sound like that could be the problem.

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