@Cris_To I check the hanger and it’s fine. You may be right about the limits as it grinds the loudest on the smallest cog. When the bike wheel is back on the bike everything’s ok. I’ll try the limits next.
Thank you
Yeah, the chain isn’t loose but it’s the smallest cog that’s giving me problems. I’ll have to do a bit more adjusting and see what happens.
Thank you
If it is only the very smallest gear then it may be the limit screw is too tight and stopping it moving far enough out.
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Yes, I think you’re right. I’ll have a go again this week.
Thank you.
Check your B screw adjustment. Problems on only half the cassette, if it’s not indexing and it’s not hanger alignment, might point to B gap. Your derailleur’s preferred B gap will very likely be different if you’re going from a 42 to a 28. And you might think that it would only affect the larger cogs on the sprocket, but it’s one of those things that often fits into the “huh, you’d think…” category.
If it’s only acting up on the smallest cog, high limit might be an issue as Chris mentioned. If it’s acting up on the next cog as well, that won’t be the limit at work, if it can still shift into the smallest too.
(You can check the limit by turning the cranks forward, and slowly screwing in the limit screw until the chain jumps to the next cog. Then keep turning, and back the screw out until in drops back to the small cog. Turn very small increments until you don’t hear any noise.)
Hi @Tom_J Yes i thought the B screw only affected the larger cogs. I’ll have a play with the limits and B screw and hope for the best.
Cheers
Getting the top pulley closer to the cogs will improve shifting.
Another thing to consider is that shifting well at one end of the cassette and poorly at the other can be caused by poor alignment of the derailleur hanger. Bike shops have an alignment gauge to check this.
You should be able to find what the B gap needs to be set at with a little googling. It’ll depend on the make and model. There are SRAM and Shimano tools out there for measuring. The higher end the derailleur, and the more cogs you have, the more precise the gap needs to be. I’ve had 12sp setups shift poorly when the B gap was 1-2mm off from recommended. Some are the opposite of what you’d think, too–they’ll tell you to set the gap much larger than you’d think.
If you can’t find the spec by googling, let me know what derailleur you’re working with and I’ll see what I can find.
A few people have mentioned the hanger, I’ll have check it again before I start messing with the limits etc.