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forum
Weird lose of tension in rear derailleur
** 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.
If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.
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28 comments
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.
😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀😀
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 😀
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.
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.
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?
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.
shortening the chain is logical, as it could be that the rear mech is fully extended and there is still slack in the chain, especially if the chain is capable of passing round 52 at the front and 40 at the back. That;s a lot of teeth, reducing to 34x11 so you are looking for the rear mech to absorb 47
Of course if you never had this problem before it doesn't sound like the answer.
I'd try a bit of WD40 and grease on the rear mech pivot and spring.
Thank you.
From, memory. I would say there's less tension in the chain (114 and 112 links cut down version) throughout the entire possible range of gears, than there was before.
Shortening the chain would increase tension, which of course it at its lowest in the small-small combination. However, this won't help if the chain is an appropriate length in the first place. It may also cause problems when you try to run it in big-big. Although you have a very wide gearing range if it goes from 34x11 to 52x40! Shimano states max casette cog for the GS medium cage 105 is 34T.
Does the RD pivot turn freely? It can start to get stiff and the bolt seize, particularly if used a lot in the wet.
Alternatively it could be the freehub sticking. Do you have another wheel you could try it with? Put a cassette on it and try it across the range of gears as before.
While you're at it, check that the jockey wheels are in good condition and spin freely.
Thank you.
The pivot doesn't feel perfect, and cleaning it, didn't make any improvements.
I did check the freehub. That was replaced in May 2021, with 3490 miles on the clock. It looks in good condition, with no rusty water present. It looked/turned like new really.
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.
If it only happens when you stop pedalling, it could be a sticky freehub. I had this. Unfortunately, my freehub was shimano, which needs a massive hex key to remove, there are lots of different versions and servicing is not really possible as it's full of tiny ball bearings. As I was at the point of possibly getting a new rear wheel, I just sprayed a load of GT85 into it and that, so far, has worked. Done another 3k miles.
Good call.
Thank you.
I've only checked the stop pedalling part, when the bike was on a stand. And yes, it did sag when I stopped pedalling or pedalled backwards.
Edit: From memory, pedalling backwards wasn't possible.
That sounds about right. When you pedal backwards, you are tensioning the chain the other way,
so it won't sag.- actually this depends how much friction there is. Thinking back, I was able to turn the pedals backwards initially, but as it got worse, the freehub drag was more than the derailleur spring could handle and pedalling backwards just caused the hanger to move fully forward, with the chain still slopped all over the chain stay.The reason it only happens in the smaller cassette cogs is due to leverage. If the freehub is only dragging a little bit, then there's not enough force to cause the chain to sag when it's on the larger cogs.
Thank you.
So, to clarify should I be able to rule out the freehub body as the problem?
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.
Good plan. Hopefully it is the jockey wheels or derailleur pivot.
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.
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.
This is going to be a problem with either the jockey wheels being worn or the sprung movement being impeded by dirt and lack of lubrication.
I say jockey wheels because I had a bearing failure and the chain was hopping on and off the lower wheel which had massive play, semi-jamming and causing oddness including a sagging chain.
Otherwise it is the sprung movement failing to tension and winter riding will do that for you, make sure it is well lubricated and swinging freely.
You are right, shortening the chain would be silly. It probably is not the gear cable, as you rightly understand that it affects the gear change not the tension. However, of you've not cheated the gear cable and done a lot of miles, do check it, they have a habit of breaking in the changer itself. If you find you start fiddling with the tension to try and get the change back to its old sweet ways, that's the main clue.
Thank you.
The jockey wheels should be in fairly good condition (2150 miles). I don't have anything to compare them again. Apart from the old RD, if I still have it.
The spring motion of the RD (rear to forward, not side to side), doesn't feel like it should do. But again I've nothing to compare it to.
Replacing the gear cable would probably be a good place to start - they're cheap and they do wear out.
Thank you.
I'll change the cable tomorrow. It just eliminates a possibility, and generally helps with shifting. So there's nothing to lose.