Drivetrain Problem!

[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.