Chain sagging while freewheeling

[ruthinportugal]

Hi
Firstly apologies if I can't explain this problem very well!
I have started having a problem with the chain or gears on my bike. The chain and gears work fine when cycling on the flat or uphill but when freewheeling downhill or when I lift the right pedal in preparation to start off the chain sags down towards the floor like it is not being picked up properly by the rear gears. Does anyone know what's going on and if I can fix it and how?
It is an 18-speed mountain bike and I have had it for about 18 years so I suppose it does have an excuse to start playing up!
Thanks for your help!
Ruth

 

[Angelfishsolo]

Hi
Firstly apologies if I can't explain this problem very well!
I have started having a problem with the chain or gears on my bike. The chain and gears work fine when cycling on the flat or uphill but when freewheeling downhill or when I lift the right pedal in preparation to start off the chain sags down towards the floor like it is not being picked up properly by the rear gears. Does anyone know what's going on and if I can fix it and how?
It is an 18-speed mountain bike and I have had it for about 18 years so I suppose it does have an excuse to start playing up!
Thanks for your help!
Ruth

When was the chain and or chainset last changed?

Try moving the rear mech at the bent point. If could be a little stiff. Oil will sort that out.

Also take a tape measure and measure 6 links.

If the measurement is 6" the chain is perfect

6 and 1/8th" very soon needs changing

greater than 6 1/4" needs possibly changing along with chainset*.

*Due to the age of the bike the chainset may be steel rather than aluminium the former lasts far longer. Look for pointy teeth on the cogs rather than the flat tops that you would expect. If there are pointy teeth the chainset will need changing along with the chain

 

[ColinJ]

Hi Ruth - Welcome to CC.

Do you mean the top of the chain or the bottom of it?

If it is the top ... I was out riding with CC member bromptonfb a couple of weeks ago and he pointed out that my rear wheel wasn't freewheeling properly. The sprockets were continuing to rotate when I stopped pedalling and were making my chain sag forwards. He told me that he'd had an accident on his bike when the chain got snagged up doing that - it didn't sound like a problem which should be ignored!

So, I investigated the problem. It turned out that I had my Mavic quick release too tight and the excess pressure was causing something to bind in the freehub. I switched the QR for a Shimano one which didn't need to be so tight to hold the rear wheel in place. (I had only done the Mavic QR up that tight because I'd pulled the rear wheel out when standing for a climb.)

 

[gwhite]

Hi Ruth - Welcome to CC.

Do you mean the top of the chain or the bottom of it?

If it is the top ... I was out riding with CC member bromptonfb a couple of weeks ago and he pointed out that my rear wheel wasn't freewheeling properly. The sprockets were continuing to rotate when I stopped pedalling and were making my chain sag forwards. He told me that he'd had an accident on his bike when the chain got snagged up doing that - it didn't sound like a problem which should be ignored!

So, I investigated the problem. It turned out that I had my Mavic quick release too tight and the excess pressure was causing something to bind in the freehub. I switched the QR for a Shimano one which didn't need to be so tight to hold the rear wheel in place. (I had only done the Mavic QR up that tight because I'd pulled the rear wheel out when standing for a climb.)

Many people forget that when adjusting the cones of a wheel which uses a QR, there should be a little play to allow for the cam action of the Qr. It runs more smoothly too.

 

[Cletus Van Damme]

I had the same problem turned out to be a sticking freehub. See the thread with pics:

Sticking Freehub

I ended up having to buy a new rear wheel as the freehub was expensive and hard to source.

 

[ruthinportugal]

Hi guys
Thanks for your help- that's quite a few things for me to look in to.
I must admit the chain has never been changed because its never given me any trouble before so it's as old as the bike- I'll get the ruler out this afternoon. It is the top of the chain that sags, the bottom remains straight. If I reverse the bike slowly it works fine but freewheeling or lifting the pedal in preparation to push off it sags.
Cheers
Ruth

 

[Angelfishsolo]

Hi guys
Thanks for your help- that's quite a few things for me to look in to.
I must admit the chain has never been changed because its never given me any trouble before so it's as old as the bike- I'll get the ruler out this afternoon. It is the top of the chain that sags, the bottom remains straight. If I reverse the bike slowly it works fine but freewheeling or lifting the pedal in preparation to push off it sags.
Cheers
Ruth

One more thing. Just try oiling the chain.

 

[ruthinportugal]

Hi Angelfishsolo- that's the one productive thing I did do- that's about as far as my bike maintenance skills go! I must get better I got lazy by having my bike mad dad to do it for me when I lived close by him.
It does look v.much like the problem Cheesney Hawks has in his photo so it's a trip to the bike repair shop for me I think.
Thanks for the suggestions

 

[Angelfishsolo]

Hi Angelfishsolo- that's the one productive thing I did do- that's about as far as my bike maintenance skills go! I must get better I got lazy by having my bike mad dad to do it for me when I lived close by him.
It does look v.much like the problem Cheesney Hawks has in his photo so it's a trip to the bike repair shop for me I think.
Thanks for the suggestions

If that is the cause then it is a very cheep fix

 

[Jonny80]

Hi im new here and i have a problem with my chain sagging everytime i drop it onto the bottom cog on my cassette when i stop pedaling the chain keeps saggin and im afraid my derailer mite snap...the derailer keeps pulling and thats why it is sagging but i have no idea whats causing it.Ive removed a couple of links out my chain but still having the same problem so im just wondering does anybody have any idea to why this happning ill appriciate what ever help and advice you can give me thanks

 

[Globalti]

To the OP and the poster above.... I'm always on here saying that a bike shouldn't need a service because you should be constantly tweaking and maintaining it but in both your cases it does sound as if your bikes need professional attention.

 

[Dogtrousers]

Sounds like either the freewheel isn't freewheeling smoothly or the rear mech is misaligned/gunked up and the chain isn't running smoothly through the jockey wheels. Something isn't running smoothly back there.

 

[raleighnut]

^^^^^^ +1 sticky freewheel or freehub.

 

[boydj]

^^^^^^ +1 sticky freewheel or freehub.

Agree that this is most likely.

Another possibility is that the indexing is slightly out. When pedalling it works fine, but maybe a little noisily. However, if you back-pedal the chain does not run freely because it is not sitting on the cog properly.

 

[mickle]

It's a sticky freewheel mechanism. Final answer Chris.

New parts time; either a new freehub body or a new freewheel.