Re: Derailleur rattling?

On 5/14/2025 2:47 PM, Mark J cleary wrote:

Guy brings me a bike to check out. A Specialized Sirrus from about 2014 8 speed DT. Says the derailleur was rattling and shifting on its own at times. I put in on the stand and it seemed to shift ok really/ He need the back wheel trued also and was really a wobble.
 I ask him if he did anything and he said he did go home and clean and lubed the chain. The chain look pretty clean too. So I managed to get the wheel trued and it is pretty decent not like truing a precise road machine with expensive wheels but it is fine.
 I then cleaned the chain good again and adjust the back V brakes. Was a bit off but now they are even on both side. I lubed some point of contact in the brakes at the frame and then clean the rear derailleur. I then drop some lube at the pivots on the RD.
 I made absolutely no adjustment to the RD. I did make a very small FD adjustment to take out some rub on the big cog in front in the middle ring when in the small rear.
 Right now on the stand the bike shifts perfectly in all combinations and quite good I might add. So do you think what this guts problem was all along a dirty non-lubed chain? I know if things not lubed it will shift funny is ghost shifting a product of dry chain? In the end ghost shifting suggest to me much more problems but frankly I had this back working in 20 minutes.

Did you take it for a test ride? I can't tell you how many times I went through "it worked great on the stand".
The phrases 'derailleur rattle' and 'chain rattle' are usually descriptors for chain misalignment by people with limited mechanical knowledge. Couple that with 'shifting on its own' and you have the classic maladjusted indexing - he may have been mistaking the 'rattle' for the chain misalignment and the 'shifting on its own' when the misalignment cause the chain to jump onto the next cog.
You seem to have that part of it figured out, but on the outside chance that there is some issue with frame flex when the frame is under load you might not see it until you take it for a spin.
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