# Sagging Chain



## ChrisMartin (Sep 13, 2011)

Hi,

Newbie and relatively new to cycling properly (ignoring plenty of short rides on a cheap mountain bike as a child!), so apologies if I get terminology wrong etc.! I bought my first road bike six months ago second-hand (having borrowed a friend's for a month and got into it) and am having a little bit of trouble with the chain.

When I'm free-wheeling and go over bumps or if I'm pedalling backwards (not something I tend to do too often!), then the chain goes slack on the top, i.e. where it returns from the front chain ring back to the rear mech set. This means that it drops on to the frame and has been known to sag to the extent that it rubs on the spokes.

A friend had a look at it and suggested the chain was too long. Although I think he was correct (when on both the largest sprockets, the rear derallieur was still probably slightly left of vertical) and I'm sure shortening it has helped the bike, it hasn't really solved my problem.

He then suggested cleaning the hub. I removed the pawls and springs etc., cleaned everything meticulously, re-greased and put everything back in (the attached picture shows how much I disassembled the hub). I can tell that has definitely helped my problem, but the problem is still there.

What would people recommend is the next thing to try? Dismantle the hub again and replace the bearings?

My setup is Hope hubs (not sure what model) and Ultegra groupset. Another thing, is that the problem seemed to occur relatively quickly, rather than slowly appearing and getting worse over time.

Thanks in advance for any advice!


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## odyofael (May 14, 2011)

Make sure all your bearings are freely moving when everything is assembled. Also if you have an adjuster for end play, make sure you don't put to much pre load. This will make the freehub stick and will make you chain sag everytime you stop pedaling.


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## Mike T. (Feb 3, 2004)

> I think he was correct (when on both the largest sprockets, the rear derallieur was still probably slightly left of vertical)


If you mean by this that you're in the "big/big" combo and the derailer arm is just about vertical then you have way too much chain. In this combo the derailer arm must be almost stretched out fully.

The correct length is "round big and big when not going through the derailer plus two links (1")". You will find how to do it here - 

Park Tool Co. » ParkTool Blog » Chain Length Sizing


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## bikerjulio (Jan 19, 2010)

nothing but a heavy oil like Phils, or very light application of light grease to the pawls and ratchet, otherwise the freehub will drag and cause the problem you have.


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## FBinNY (Jan 24, 2009)

Easy freewheel test.

Hold the wheel in your hands (cassette to the right) and spin it forward (top away from you). The cassette will likely spin with it, which is fine. Now put your thumb against the cassette. It should stop easily while the wheel keeps spinning, and need only light force to keep it stationary.

BTW- get used to how hubs and cassettes feel when spinning. Once you're used to it the spin inn hands method is a quick and easy diagnosis that you should do every time you service the hub or suspect a problem. I do it every time the wheel is off as a quick bearing test, since rust or dirt damage has to be pretty severe before you'll feel or hear it riding.


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## ChrisMartin (Sep 13, 2011)

Thanks all for the responses.

odyofael: How would I know if I have an adjuster for end play? Would that be the same as the B-screw that adjusts the derailer body angle?

Mike T: In the big/big combo, the derailer was just about vertical, but I've now taken out a couple of links and has sorted that.

bikerjulio: I was careful not to put too much grease back in when I cleaned it up, however the problem was there before that anyway.

FBinNY: I'll check the wheel tomorrow. I remember it felt like it span and stopped ok when I'd just put the cassette back on after cleaning it, however I don't really know how easily it should stop. If it stops OK, would you suggest that the problem is that the rear derailer is not putting enough tension on the chain? How would I sort that? And if it doesn't then would it be that the bearings in the hub probably need replacing?

Thanks again for all the advice. Any other thoughts? Please feel free to ask more questions if it's going to help you solve my problem! I'd rather not have to take it to be repaired if I can do it myself!


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## JCavilia (Sep 12, 2005)

Freewheel drag. Nothing to do with the hub bearings themselves (the ones the axle turns on). 

The bearings and seals for the freehub, or the freewheel pawls and ratchet themselves, are the source of the problem.

Do FB's test. If there's excessive drag, try to figure out where it's coming from.

I suspect it was gummy or dirty before, and you improved it somewhat, but maybe put a bit too much heavy grease somewhere.


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## FBinNY (Jan 24, 2009)

ChrisMartin said:


> Thanks all for the responses.
> 
> : .... If it stops OK, would you suggest that the problem is that the rear derailer is not putting enough tension on the chain? How would I sort that? And if it doesn't then would it be that the bearings in the hub probably need replacing?
> 
> !


You have to separate adjustments and potential problems. Anything RD related, such as low spring tension, B screw adjustment, or even an overly long chain would cause the lower loop to sag.

If the lower loop isn't sagging when off the bike, but the upper is when coasting it'll be a freewheel friction problem. The sticking freewheel is creating enough drag to pull the chain forward against the resistance of the RD cage and transfer slack from the lower loop to the upper. 

As the cage winds up the spring tension increases (or you reach the stop) resisting more transfer. The stickier the freewheel is the more sag you get.

There may be other factors contributing, but the key issue will be in the freewheel unit.

***In the above I use _freewheel_ to describe the overrunning clutch or ratchet mechanism which allows coasting. The same applies whether it's a screw-on freewheel or a freehub/cassette wheel.


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## ChrisMartin (Sep 13, 2011)

I have just done the freewheel test mentioned above. When I spun the wheel away from me, the cassette didn't rotate at all. Any thoughts?


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## Kerry Irons (Feb 25, 2002)

*Please clarify*



ChrisMartin said:


> I have just done the freewheel test mentioned above. When I spun the wheel away from me, the cassette didn't rotate at all. Any thoughts?


Are you saying that when you spin the wheel, the cassette moves so easily that it stays in place while the wheel rotates? I have never seen a freewheel or freehub friction with that low.

Please re-read FBinNY's post on how to figure this out. Your description does not make sense.


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## ultraman6970 (Aug 1, 2010)

The only time that happens is if the RD is not aligned right or when the chain line is wrong like for example if the OP is using the mortal big chainring and big sproket, the chain gets so missaligned that is jams pedaling backwards.

What gear combination you were using when this happened?? or happened in all the gear combos??


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## ChrisMartin (Sep 13, 2011)

Well I'm not really sure how I could have done the freewheel test wrong. I stood behind the bike, and picked it up by the seat post. With the other hand, I spun the top of the wheel away from me, i.e. how it would rotate if I was travelling forwards. When doing that, the cassette stayed in place. I did find that puzzling, as from what I understand, that's a good thing and would suggest that could not be the cause of the problem I'm having, so I did re-read FBinNY's post to confirm that I was doing it correctly. To be honest, I haven't really paid attention to what gear combination I have been (when the problem occurs or when I did the freewheel test) - I'll try to find out today.

As I mentioned, when I cleaned the hub up and re-greased it (I was particularly careful to ensure I didn't over-grease it), the problem improved significantly. What would be expected as reasonable sag? If you go over a large bump, would you expect the chain to touch the frame? (I'm just wondering if I'm now getting overly into the problem and it's actually now about as good as it's going to get!)

Thanks again for all the advice!


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## wim (Feb 28, 2005)

ChrisMartin said:


> Well I'm not really sure how I could have done the freewheel test wrong.


You were supposed to take the wheel _out of the frame _ and spin it while holding it at the axle ends.


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## FBinNY (Jan 24, 2009)

ChrisMartin said:


> .... I stood behind the bike, and picked it up by the seat post. With the other hand, I spun the top of the wheel away from me, i.e. how it would rotate if I was travelling forwards. When doing that, the cassette stayed in place. ...
> 
> ... What would be expected as reasonable sag? If you go over a large bump, would you expect the chain to touch the frame? (I'm just wondering if I'm now getting overly into the problem and it's actually now about as good as it's going to get!)


While I suggested taking the wheel out to get a hand feel of the cassette drag torque, what you did is fine since it showed that the cassette wasn't spooling chain to the upper loop. The gear does make a difference since the resistance force depends on the chain's leverage on the cassette. Chain sag when it does occur will always be worst in high gear, and least in low.

Meanwhile, I'm beginning the think you don't have a problem anyway. A bit of relaxing of chain tension in the upper loop is normal, and it's common for chains to slap the chainstay on bumps. Or more precisely, the chainstay comes up and slaps the chain whose inertia keeps it from rising out of the way.

How much chain slap you get depends on the distance from the chain to the stay, so it's more common in higher gears. Some bikes have the higher chain stays which increases the chances of chain slap. If that's the problem, the solution is as simple as buying or making a chainstay protector. 

Chainslap is worse on mtn bikes than road, so many mtn bikers make heavy duty chainstap protectors by wrapping the stay in an old inner tube, or with padded handlebar tape.


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## wim (Feb 28, 2005)

FBinNY said:


> While I suggested taking the wheel out to get a hand feel of the cassette drag torque, what you did is fine since it showed that the cassette wasn't spooling chain to the upper loop.


Sure, but _not_ taking the wheel out confused the discussion to some degree. Hence my post.


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## ChrisMartin (Sep 13, 2011)

Thanks again for comments. Today when I was riding I tried to think more about exactly when it is the problem occurs. I noticed that at one point the chain sagged down past the chainstay, which, even if it if a large bump, I'm sure isn't really normal. Also, if I'm not on the bike and rotate the pedals backwards, the chain doesn't appear to sag very much at all. So that leads me to think that it suggests maybe there is something that is making it more susceptible to bumps - is such a thing even possible?!? I'll try to pay more attention to what gear I'm in when I next go out (although obviously the problem being greater in higher gear would not be specific to my bike, as it's purely down to geometry).

As there appears to be very little friction in the hub, is there a chance that it could be the RD? Although from feel it appears to be putting a fair amount of tension on.... Is it worth trying to screw the B-screw all the way in to see if it helps? Or could I cause a problem by putting too much tension on (assuming I avoid the big/big combo)?


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## Jetmugg (Sep 22, 2010)

I think you still need to check the freehub operation by taking the wheel out of the frame, spinning it by and, and feeling the level of resistance in the freehub with your own hands.


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## ChrisMartin (Sep 13, 2011)

OK, have just done the freewheel test again, properly this time! The cassette spins with the wheel when I rotate it and seems to stop fairly easily. I guess the issue is that I don't really know how easily it should stop. I was able to stop it with my finger, so I guess it only required only light force. However as that is the most likely source of my problem, I'm wondering whether I should expect to feel even less force (I know you can't really answer that!)? Maybe I'm best of taking the rear wheel into a bike shop and getting them to spin it, as they'd know what they should be feeling. If that is the problem, what exactly could the issue be? I thought I'd cleaned it fairly thoroughly last time and was careful not to put too much grease back on - any ideas?

Thanks in advance (and sorry for my ignorance - much rather try to learn this way than just take it somewhere to get it fixed for me)!


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