Drivetrain Problem!

[Velocibob]

I am having a problem with my chain sagging in the small chainring to small cog combination. I am aware that it is inadvisable to use this or the big chainring to big cog. I have a triple chainset with 46-36-24 and my cassette is an 11-32. I have put a new chain on and checked the length required using a calculator and also manually over big chainring, big cog according to advice on Park tools website. I have a long cage Shimano Deore XT rear derailleur which can handle up to 33 teeth. I've also calculated that my chainring/cassette combination is within the Total Capacity. I've adjusted the rear derailleur to Park Tools recommendations and it is changing the gears smoothly, but I still have this problem in the small to the small combination. My only thought is that there is something wrong with the derailleur. Can anyone out there advise me as to what to do, apart from buying a new bike?

[Jesper]

(09-02-2020, 07:50 AM)Velocibob Wrote:  My only thought is that there is something wrong with the derailleur. Can anyone out there advise me as to what to do, apart from buying a new bike?

Hi Bob,
How old is the bike, is the Rear derailleur original to the bike, and how old is/how many miles on the chain? Have you ever overhauled the derailleur? Have you tried it with one less chain link? Can the wheel be positioned farther to the rear in the dropout?

[Velocibob]

(09-02-2020, 10:38 AM)Jesper Wrote:  

(09-02-2020, 07:50 AM)Velocibob Wrote:  My only thought is that there is something wrong with the derailleur. Can anyone out there advise me as to what to do, apart from buying a new bike?

Hi Bob,
How old is the bike, is the Rear derailleur original to the bike, and how old is/how many miles on the chain? Have you ever overhauled the derailleur? Have you tried it with one less chain link? Can the wheel be positioned farther to the rear in the dropout?

Hi there Jesper, the bike is 32 years old. The derailleur is of a similar age. The chain is new and is cut to 54 links. I cut the old chain to 53 links and tried it. It did go up onto the big chainring/big cog, but the chain was too tight. The jockey arm was very straight with only a little bend of the chain around the jockey wheels. The chain still sags on the small chainring/small cog. Apart from replacing the jockey wheels like for like, cleaning the derailleur and lubricating it. It has never been overhauled. With regard to the wheel, there is no room for movement as the dropouts are vertical. I've also noted another problem. When I have the chain on the big chainring to the big cog or the one below that. If I turn the chainset backwards the chain will derail from the big chainring to the middle chainring, I think this may be due to the chain line being out. The only possible way of correcting this I can see. Is to move the bottom bracket to the left in the bottom bracket shell, but the amount of movement could be limited, but it might be enough. I'm going to try doing that in the morning. Apart from that, I don't know what else I can do. I find it difficult to understand why I am having this trouble now given how long I've had the bike and how many chains I've removed and replaced. The bottom bracket is the one recommended for the crankset I'm using.

[Nicholas]

Hello @Velocibob!
A couple of our BikeRide community members shared their opinion via Facebook:

Yannick: "Don't buy a new bike for a drivetrain issue, figure out the problem. The chain should not sag in this gear combination but you shouldn't use that combo if you want your components to last. If it wasn't sagging before the new chain, use your old chain length and use that length on your new one. If it was sagging before, then it is most likely a rear derailleur issue. See if the derailleur tensions the chain back by bringing the arm forward and releasing it. It should quickly snap back and tighten the chain. If not, that's your issue."

Mark: "It doesn’t sound like there is anything there’s wrong with your bike, it sounds like you are using the gears incorrectly. If you have a triple then a simple guide is that the largest front chainring should be used with the smallest half of your back cog range. I.e from about half way down to the bottom of the block, the middle chain ring for the middle part of your cog range I.e. not at either top or bottom but ok nearly everywhere else and the smallest ring for only the top half (bigger cogs) of your cogs. Its It’s ok to skirt the edges in a pinch , broken front mech, bad time to change etc. but you are better to get comfortable with changing your front mech and being in the right gear. If I drove my car in 1st at 60mph I’m sure it would skip a bit too, I wouldn’t take it to my mechanic though .... I’d just be using it wrong."

[Jesper]

(09-02-2020, 07:27 PM)Velocibob Wrote:  the bike is 32 years old. The derailleur is of a similar age.

I think you've found the answer to your problem. I would certainly try overhauling (completely dismantling)the derailleur and see if that corrects the issue; if not then I would probably replace the derailleur.

You should certainly be able to ride the bike as is, but with shifting not quite as smooth; although you are going beyond the limits of keeping a reasonable chainline. As the previous post states, it is not prudent to use your largest or smallest front rings in conjunction with sprockets of like proportion in the rear. If you are running your middle chainring than you may be okay to ride all of the rear gears while still maintaining a decent chainline, but that depends on how the drivetrain was set up in the first place (could have a "biased" chainline).

[Velocibob]

(09-03-2020, 03:07 AM)Jesper Wrote:  

(09-02-2020, 07:27 PM)Velocibob Wrote:  the bike is 32 years old. The derailleur is of a similar age.

I think you've found the answer to your problem. I would certainly try overhauling (completely dismantling)the derailleur and see if that corrects the issue; if not then I would probably replace the derailleur.

You should certainly be able to ride the bike as is, but with shifting not quite as smooth; although you are going beyond the limits of keeping a reasonable chain line. As the previous post states, it is not prudent to use your largest or smallest front rings in conjunction with sprockets of like proportion in the rear. If you are running your middle chainring than you may be okay to ride all of the rear gears while still maintaining a decent chain line, but that depends on how the drivetrain was set up in the first place (could have a "biased" chain line).

Hi there, I'm a newbie to this forum, but not to cycling. I've been cycling for 64 years and on this bike for 32 years. I know not to run big to big and small to small, I do have a problem with the chain line. Which is causing the chain to derail from the big chainring to the middle chainring when the chain is on the big cog or the one below that. This occurs when I backpedal. I have the bottom bracket fitted that is recommended for the crankset I am using. There is a possibility that I can reposition the bottom bracket by moving it left in the bottom bracket shell, moving the crankset closer to the frame, but the amount of adjustment may be limited. Going to try that this morning, so I might resolve one of my issues. A new derailleur with a higher total capacity might sort out the other. Thanks for your interest and advice.

---

(09-02-2020, 07:50 PM)Nicholas Wrote:  Hello @Velocibob!
A couple of our BikeRide community members shared their opinion via Facebook:

Yannick: "Don't buy a new bike for a drivetrain issue, figure out the problem. The chain should not sag in this gear combination but you shouldn't use that combo if you want your components to last. If it wasn't sagging before the new chain, use your old chain length and use that length on your new one. If it was sagging before, then it is most likely a rear derailleur issue. See if the derailleur tensions the chain back by bringing the arm forward and releasing it. It should quickly snap back and tighten the chain. If not, that's your issue."

Mark: "It doesn’t sound like there is anything there’s wrong with your bike, it sounds like you are using the gears incorrectly. If you have a triple then a simple guide is that the largest front chainring should be used with the smallest half of your back cog range. I.e from about half way down to the bottom of the block, the middle chain ring for the middle part of your cog range I.e. not at either top or bottom but ok nearly everywhere else and the smallest ring for only the top half (bigger cogs) of your cogs. Its It’s ok to skirt the edges in a pinch , broken front mech, bad time to change etc. but you are better to get comfortable with changing your front mech and being in the right gear. If I drove my car in 1st at 60mph I’m sure it would skip a bit too, I wouldn’t take it to my mechanic though .... I’d just be using it wrong."

Hi there, I'm a newbie to this forum, but not to cycling. I've been cycling for 64 years and on this bike for 32 years. I know not to run big to big and small to small, I do have a problem with the chain line. Which is causing the chain to derail from the big chainring to the middle chainring when the chain is on the big cog or the one below that. This occurs when I backpedal. I have the bottom bracket fitted that is recommended for the crankset I am using. There is a possibility that I can reposition the bottom bracket by moving it left in the bottom bracket shell, moving the crankset closer to the frame, but the amount of adjustment may be limited. Going to try that this morning, so I might resolve one of my issues. A new derailleur with a higher total capacity might sort out the other. Thanks for your interest and advice.

---

(09-02-2020, 07:27 PM)Velocibob Wrote:  

(09-02-2020, 10:38 AM)Jesper Wrote:  

(09-02-2020, 07:50 AM)Velocibob Wrote:  My only thought is that there is something wrong with the derailleur. Can anyone out there advise me as to what to do, apart from buying a new bike?

Hi Bob,
How old is the bike, is the Rear derailleur original to the bike, and how old is/how many miles on the chain? Have you ever overhauled the derailleur? Have you tried it with one less chain link? Can the wheel be positioned farther to the rear in the dropout?

Hi there Jesper, the bike is 32 years old. The derailleur is of a similar age. The chain is new and is cut to 54 links. I cut the old chain to 53 links and tried it. It did go up onto the big chainring/big cog, but the chain was too tight. The jockey arm was very straight with only a little bend of the chain around the jockey wheels. The chain still sags on the small chainring/small cog. Apart from replacing the jockey wheels like for like, cleaning the derailleur and lubricating it. It has never been overhauled. With regard to the wheel, there is no room for movement as the dropouts are vertical. I've also noted another problem. When I have the chain on the big chainring to the big cog or the one below that. If I turn the chainset backwards the chain will derail from the big chainring to the middle chainring, I think this may be due to the chain line being out. The only possible way of correcting this I can see. Is to move the bottom bracket to the left in the bottom bracket shell, but the amount of movement could be limited, but it might be enough. I'm going to try doing that in the morning. Apart from that, I don't know what else I can do. I find it difficult to understand why I am having this trouble now given how long I've had the bike and how many chains I've removed and replaced. The bottom bracket is the one recommended for the crankset I'm using.

Hi Jesper, I stated that my derailleur was a similar age to the bike frame. That was not correct. I had the frame modified to be able to take 9 speed. This happened not long after the introduction of 9 speed. I can't remember exactly when this was.

[Jesper]

(09-03-2020, 05:11 AM)Velocibob Wrote:  I had the frame modified to be able to take 9 speed. This happened not long after the introduction of 9 speed. I can't remember exactly when this was.

You probably still have a good 15 to 20 years of running that derailleur; enough that it should be serviced.

[Jesper]

Velocibob w' Wrote:  Hi Jesper, I stated that my derailleur was a similar age to the bike frame. That was not correct. I had the frame modified to be able to take 9 speed. This happened not long after the introduction of 9 speed. I can't remember exactly when this was.

Hi again Bob,
Wondering if you found a solution? I neglected to mention the option of up-sizing the jockey pulleys; add 1-2 teeth on the lower pulley. I don't know if changing the top pulley would affect shifting due to design and clearance. Going larger on the bottom should help, but you are still limited with the clearance between the pulleys for smooth chain function.

[Velocibob]

Hi there Jesper, I've gone out and bought a new rear derailleur. I'm pretty sure that this is the cause of my problem. I probably hit the derailleur, whilst lifting my bike over an awkward stile. I've spent a lot of time off-road during this strange time. Once I've got it fitted and fine tuned I'll be able to tell you if I'm right or not. Another contributor pointed out that the Chainring difference was 22 teeth, not 24. Either due to poor math or concentration on my part. The chainset is a TA one and they do advise not having more than 12 teeth difference between chainrings. So it looks like the chainset falls within what is tolerable.