Back pedaling/reversing causes gear down shift

[martinza]

I'll google these and see if this could work, thanks

 

All I can suggest to the OP is to try a XSYNC 2 chainring if your cranks accepts 104bcd or direct mount chainrings. 

[DieselnDust]

And yet my 1x11 GX backpedals fine with a 28th front cog...

Lucky you. The overwhelming majority aren't as lucky.

Can you share the parts brands and models that make up your drive train and how old are the components?

[Headshot]

Lucky you. The overwhelming majority aren't as lucky.

Can you share the parts brands and models that make up your drive train and how old are the components?

 

Original since 2018 10-42 GX cassette - Low end SRAM 11 Speed Chain (newish i.e under 50%) and a RF 28 Tooth on an Aeffect crank

[BuffsVintageBikes]

Have you checked your derailleur hanger alignment?

[DieselnDust]

Original since 2018 10-42 GX cassette - Low end SRAM 11 Speed Chain (newish i.e under 50%) and a RF 28 Tooth on an Aeffect crank

Thanks that helps. Very likely that wear is a factor as the chain drop does improve as the cassette wears. The pick up ramps are likely worn a bit which doesn't catch the chain as it passes over those ramps. There's likely other factors at play too.

The mystery continues

[River Rat]

Have you checked your derailleur hanger alignment?

This^

 2 weeks ago I had piece of wire jam into my derailleur while doing 60kph on a gravel road, longest skid mark I have ever made and there was a long one on the road too. The end result was that the chain got caught between the spokes and the derailleur, ripped off 8 spokes on the RHS and pulled the derailleur into the cluster wrecking the inside arm. Replaced the broken derailleur parts including a pulley wheel but try as I might I could not get a smooth gear change going up and down the gears, it will be fine in the one direction but jumpy in the other. The give away was the fact that I dropped gears when I back pedaled so the remedy was to remove derailleur and using a large shifting spanner over the hanger (with some cloth protection) I bent the entire system to align with the frame. It's actually easily aligned by eye with bike upside down. No problems back pedaling and the smooth gear changes all round.

 

[Hairy]

As per a couple of suggestions check your hanger and the proper drivetrain setup.

 

Another one that has not been brought up. Remove your wheel and look for play in the cassette and freehub body. If the bearings are worn, or there is excessive "wobble" and play it could cause the chain to come off on the largest cog of the cassette.