Rear derailleur issues - chain short, wrong chain, gears?
Hi,
I've been having some issues on my home-build that i was hoping someone could offer some advice on?
The history:
I have restored an old 10-speed road bike and bought a new chain from my LBS. It has KMC XXSP on the chain so I presume that's the make and model of it. There has always been some issues with the running of the gears, for example the chain jumps off the front chain rings when changing gears every so often.
The bike uses the gear shifters on the down tube not on the handle bars and twice has the rear brake cable snapped which has led me to think something is very wrong as i know it shouldn't happen as often as it has.
As i'm fitting the new cable for the rear derailleur this weekend i thought i'd look more into the problem and get some advice
I'm starting to think possibly the chain is too short but when i bought it i didn't remove any of the links as it seemed the right length.
The above may not seem clear so here are pictures to show how things look at the moment.
This is with the chain most relaxed on small front small back:
And this is me attempting to put on Big front and big back (i know you're not supposed to ride like this):
You'll see the derailleur is at such an angle that the chain completely misses the jockey wheel and just routes round the bottom one.
The b-tension is completely relaxed.
At the moment it wont even switch onto big front and big at the back.
Any help is GREATLY appreciated.
I've been having some issues on my home-build that i was hoping someone could offer some advice on?
The history:
I have restored an old 10-speed road bike and bought a new chain from my LBS. It has KMC XXSP on the chain so I presume that's the make and model of it. There has always been some issues with the running of the gears, for example the chain jumps off the front chain rings when changing gears every so often.
The bike uses the gear shifters on the down tube not on the handle bars and twice has the rear brake cable snapped which has led me to think something is very wrong as i know it shouldn't happen as often as it has.
As i'm fitting the new cable for the rear derailleur this weekend i thought i'd look more into the problem and get some advice
I'm starting to think possibly the chain is too short but when i bought it i didn't remove any of the links as it seemed the right length.
The above may not seem clear so here are pictures to show how things look at the moment.
This is with the chain most relaxed on small front small back:
And this is me attempting to put on Big front and big back (i know you're not supposed to ride like this):
You'll see the derailleur is at such an angle that the chain completely misses the jockey wheel and just routes round the bottom one.
The b-tension is completely relaxed.
At the moment it wont even switch onto big front and big at the back.
Any help is GREATLY appreciated.
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Comments
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That chain looks too short to me. The quick way to get the correct length is to run the chain around the biggest cog on both the front and back, but not through the rear derailleur, to make a complete, taut loop and then add two links. Usually chains are supplied too long, since the correct length depends on the gearing and chainstay length. Modern groupsets are designed to allow big-to-big running, and while it's not recommended for long periods, it should be possible if everything is set up correctly. Certainly running big-to-big on the workstand while fettling will do no harm at all.
If the chain is coming off the front chainrings, the first thing to check is that the limit screws on the front derailleur are correct. Down-tube shifters for the front chainring are not usually indexed, but instead rely on the limit screws to ensure the correct movement range. My guess is that the arm is simply moving too far.
Brake cables are fairly tough things, so breaking one is rare, never mind two. Are you using a proper brake cable, or is it a gear cable (gear cables are a bit thinner)? If it's breaking where it clamps onto the brake, it might be that the clamp has a sharp edge on it, and it's cutting into the cable as the clamp is tightened. Knowing exactly where it's breaking would be useful.0 -
As ElecronSheperd says, big -big plus two is the usual recommendation.
For my benefit, is two links 'outer-inner', or 'outer-inner-outer-inner' ?0 -
I meant two links as outer - inner.0
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Apologies! I wrote rear brake cable has snapped twice, but i meant the rear derailleur cable!
And for the chain, yes I always suspected they sold them too long but could it be that as this is for an old bike it needs and even longer chain length than the modern chains are sold in? I didn't take any links off the chain once i bought it and suspected that it was too short even then.
Could anyone recommend a good and long-enough chain for an old 10-speed?
I'm thinking if it's not too expensive i may just buy a new chain and start again.0 -
Thanks ElectronShepard!
As for the limit screws, they all all correct. The chain seems to be jumping off more because when it is switching up to the big cog the chain sometimes does not sit on the teeth properly but 'over' them and then jumps off completely.0 -
The limit screw is not set correctly then.mikkybgs wrote:Thanks ElectronShepard!
As for the limit screws, they all all correct. The chain seems to be jumping off more because when it is switching up to the big cog the chain sometimes does not sit on the teeth properly but 'over' them and then jumps off completely.
Where does the rear cable break?0 -
Regarding the front deraileur, perhaps it is mounted too high on the seat tube. It should be only high enough for the bottom edge of the cage to clear the teeth on the big ring.
Also, shifting technique might be part of the trouble. I progressively 'ease' the lever when changing gears - I don't do fast 'maximum movement' changes with the lever. Typically the front cage has to be able to move a little further outboard to prevent rubbing when using the big ring / small cog.
Jay Kosta
Endwell NY USA0 -
Paul Onabike wrote:
The limit screw is not set correctly then.mikkybgs wrote:Thanks ElectronShepard!
As for the limit screws, they all all correct. The chain seems to be jumping off more because when it is switching up to the big cog the chain sometimes does not sit on the teeth properly but 'over' them and then jumps off completely.
Where does the rear cable break?
The cable snaps right at the shifter, as in at the nipple on the end of the cable.JayKosta wrote:Regarding the front deraileur, perhaps it is mounted too high on the seat tube. It should be only high enough for the bottom edge of the cage to clear the teeth on the big ring.
Also, shifting technique might be part of the trouble. I progressively 'ease' the lever when changing gears - I don't do fast 'maximum movement' changes with the lever. Typically the front cage has to be able to move a little further outboard to prevent rubbing when using the big ring / small cog.
Jay Kosta
Endwell NY USA
Thanks I'll check this out.
But also looking at the last picture i posted, is it normal for the derailleur to be at such an angle when you try and shift it to big-big?
The chain completely bypasses the jockey wheel this way, is it normal?
It seems the chain is under a lot of pressure.0 -
mikkybgs wrote:The cable snaps right at the shifter, as in at the nipple on the end of the cable.
For down-tube shifters, the cable passes through a hole and wraps around the lever body. I'd be looking at the hole the cable passes through, since if that has a rough edge, it might be cutting into the cable, one strand at a time.mikkybgs wrote:is it normal for the derailleur to be at such an angle when you try and shift it to big-big
No, it's not normal, but it's because the chain is too short. Also, I would get the chain length corrected before trying to fix the problems shifting onto the front ring, since setting the front derailleur up correctly with the chain as short as it is will be very tricky.0 -
ElectronShepherd wrote:mikkybgs wrote:The cable snaps right at the shifter, as in at the nipple on the end of the cable.
For down-tube shifters, the cable passes through a hole and wraps around the lever body. I'd be looking at the hole the cable passes through, since if that has a rough edge, it might be cutting into the cable, one strand at a time.mikkybgs wrote:is it normal for the derailleur to be at such an angle when you try and shift it to big-big
No, it's not normal, but it's because the chain is too short. Also, I would get the chain length corrected before trying to fix the problems shifting onto the front ring, since setting the front derailleur up correctly with the chain as short as it is will be very tricky.
To be honest this is what i suspected and I was hoping for confirmation of that. All the other issues are down to the chain being too short, i believe.
I just can't work out how it is too short considering I was told i was being sold a chain 'that was too long' and i'd need to shorten it to my preferred length. (As i have said, i never removed any links when installing as it seemed short)
I did get it from a modern high performance road bike shop. Could it be that the chain is used for modern 10 speeds that have smaller cogs and therefore need a shorter chain?
This is an old Dawes 10-speed and the front, larger cog, looks especially over-sized.
Could anyone recommend a chain / retailer that would be suitable for my needs?
Thanks for the help on this!0 -
mikkybgs wrote:Could anyone recommend a chain / retailer that would be suitable for my needs?
Thanks for the help on this!
KMC X10
http://www.wiggle.co.uk/kmc-x10-l-silve ... 5360258292
I've run KMC chains on all my bikes and they work well and have the benefit of a quick link connector for ease of fitting/ removal.
Use this link to work out the ideal chain length for the new chain from the large chainring/ largest cassette sprocket and chainstay length. Always works for me and saves the time and hassle of threading the chain round and judging the correct length.
http://www.epicidiot.com/sports/chain_l ... ulator.htm0 -
arlowood wrote:mikkybgs wrote:Could anyone recommend a chain / retailer that would be suitable for my needs?
Thanks for the help on this!
KMC X10
http://www.wiggle.co.uk/kmc-x10-l-silve ... 5360258292
I've run KMC chains on all my bikes and they work well and have the benefit of a quick link connector for ease of fitting/ removal.
Use this link to work out the ideal chain length for the new chain from the large chainring/ largest cassette sprocket and chainstay length. Always works for me and saves the time and hassle of threading the chain round and judging the correct length.
http://www.epicidiot.com/sports/chain_l ... ulator.htm
Thanks for the info.
Although i'm now completely baffled. Just did the calculation -
18 inches chain stay length
52 teeth on front big ring
28 on the back
--it gave me a chain length of 58 inches. Guess how big the one i have on is? 58! argh! :shock: :?0 -
Have you actually measured or counted the size of the chain?
With a 52x28 and, 18 inch c-t-c BB/axle - the min chain would be 56 inches.
52 ring is 26 links for half circumference.
28 gear is 14 links for half.
26 + 14 + 2(18 + 18) = 40 + 72 = 112 links = 56 inches
Jay Kosta
Endwell NY USA0 -
From what I can gather so far, from your replies, it looks like you may have been supplied with a modern 10 speed chain.
This is too narrow for your 2 x 5 setup. What you need is a 1/2" x 3/32" chain. That is a 7 or 8 speed chain, and would be the cause of the poor gear shifting.
The method used in calculating chain length works in theory but not always in practice - as it does not allow for the different position of the gear when mounted directly on the rear dropout, nor does it allow for the restricted tensioning ability of an older rear mech. If you look at the lower pivot and lower jockey wheel they are differently positioned to modern mechs, and you may not be able to use the full crossover gear range.
Your chain-stay length is longer than a modern frame due to the forward facing dropout design, therefore you are possibly going to need a longer than standard length chain. You should be able to get a bit of chain off-cut from your LBS and join it to your new 8 spd chain to make the correct length.
To work out the chain length you need to start with small/small rings and select the link which gives the longest length chain, while missing the top jockey wheel. If this does not allow you too use large/large as shown then the useable range of the rear mech is not enough and you will have to either:-
1. Leave it, and do not use the big ring for the largest 2 rear cogs.
2. Change the rear mech for a longer arm model (suntour vx gt)?
3. Change the rear block for a closer ratio version
IIRC short arm mechs were reserved for close ratio blocks such as 14-18 or 21 with a 42-52 front- as this was about as big a range as could be used.
Originally it would have had galvanized gear cables, which are a slightly larger diameter than some of the modern ones, what are you using? It could also be a quality issue, so might be worth just trying something from another supplier0 -
Paul Onabike wrote:From what I can gather so far, from your replies, it looks like you may have been supplied with a modern 10 speed chain.
This is too narrow for your 2 x 5 setup. What you need is a 1/2" x 3/32" chain. That is a 7 or 8 speed chain, and would be the cause of the poor gear shifting.
The method used in calculating chain length works in theory but not always in practice - as it does not allow for the different position of the gear when mounted directly on the rear dropout, nor does it allow for the restricted tensioning ability of an older rear mech. If you look at the lower pivot and lower jockey wheel they are differently positioned to modern mechs, and you may not be able to use the full crossover gear range.
Your chain-stay length is longer than a modern frame due to the forward facing dropout design, therefore you are possibly going to need a longer than standard length chain. You should be able to get a bit of chain off-cut from your LBS and join it to your new 8 spd chain to make the correct length.
To work out the chain length you need to start with small/small rings and select the link which gives the longest length chain, while missing the top jockey wheel. If this does not allow you too use large/large as shown then the useable range of the rear mech is not enough and you will have to either:-
1. Leave it, and do not use the big ring for the largest 2 rear cogs.
2. Change the rear mech for a longer arm model (suntour vx gt)?
3. Change the rear block for a closer ratio version
IIRC short arm mechs were reserved for close ratio blocks such as 14-18 or 21 with a 42-52 front- as this was about as big a range as could be used.
Originally it would have had galvanized gear cables, which are a slightly larger diameter than some of the modern ones, what are you using? It could also be a quality issue, so might be worth just trying something from another supplier
This is an excellent answer, thanks Paul.
So I'm going to get the recommended chain and see how that fairs. I was looking at this one:
http://www.ebay.co.uk/itm/50s-60s-70s-80s-5-or-10-SPEED-RACING-BIKE-CHAIN-116-LINK-1-2-x-3-32-TAYA-RAR-/181382079866?pt=UK_sportsleisure_cycling_bikeparts_SR&hash=item2a3b36e57a
I think at 116 links it may just be long enough. If not, a trip to the LBS as you suggested.
If it's still giving me grief after the new chain I think i'll take it in and admit defeat anyway.
I am using galvanised gears cable but as i said, i think they are snapping due to the pressure being put on them becuase the rear derailleur is struggling and that is caused from the wrong chain and it bering too short.
Thanks again for your answer. It has been incredibly helpful and you've saved me banging my head against the wall.
It's been fun doing up the bike but I just want to get out and ride the thing now!0
