Shimano GRX RD Skipping

Looking for some insight into an issue with a Shimano GRX RD-RX810. Whenever the derailleur is in the smallest sprocket it skips. This happens regardless of whether it’s in the large chainring or small chainring (I know in real life you wouldn’t use this but tested it), with the clutch on and off, and on different cassettes as it happens both indoors and outdoors. It means I’m losing the 46-11, which when you’re going downhill or with a strong tailwind is a loss.

I’ve fitted a new cable, changed the last bit of housing from a ridiculously stiff bit Orbea supplied to the Shimano recommended one, I’m pretty certain the H-screw is in the right place…

Any thoughts?

Video available here: https://youtu.be/UHaHR7xd58Y

I’d check for a bent derailleur hanger, and yes they can bend over time without an impact or force

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Thanks, I had thought of that and have had a look but can’t see any issue with my eye. I’ll ask a friend to double check in case it’s just me.

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Pedal slower and observe what is happening with the jump and how it’s riding on that particular tooth

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It can be very slightly bent and not appear bent, you really can’t eyeball them a lot of the time. Good idea to keep a spare anyway, so order one up and throw it on and see if it goes away.

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I just checked the B-screw after putting a message up and noting I hadn’t checked it, Hasn’t thought of it but the gap between the upper derailleur wheel and the bottom of the sprocket was huge, at least twice what it should have been. I’ve set that properly and it seems to be gone away.

To yourself and anyone else reading - would a B screw have that effect? If it comes back I’ll go down the new derailleur route.

No it shouldn’t if your RD hanger is straight…but will make the problem worse if it is bent.

Yea I’d still think there’s an underlying issue which was made worse by the B being off.

Have you checked to confirm the B gap when in the biggest cassette cog is now OK?

I set it whilst chain in largest sprocket and smallest chainring to about a 6mm gap between bottom of the sprocket and the upper pulley, everything looks good across the cassette.

As you say, having a spare derailleur hanger in the toolbox isn’t a bad thing so I’ll look for one at a good price and that will provide me with a back up solution.

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I got a wheels MFG one for my Emonda. It’s CNC machined and seems stronger than the injection mounded factory one that came with the bike. About $17 on Amazon for my application

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