Gears jumping

Can you bullet point your post, struggling to understand. 

You can take a photo of your cassette and chatgpt it to check wear 

Did what you said and put a picture of the cassette in Chat GPT. It said it looks used but not cooked.

Overall the read from Chat GPT seemed to think the cassette was fine. However I only get the issue when the bike is under load and is only on the last 5 cogs.

Chat GPT seems to reckon to try a new chain first. Thoughts?

• Deffo not a new chain if the cassette is worn. I never mess with old cassette and old chain without knowing the detail and use etc. even then it's a ball ache

Is it 12 speed 

I've had a warped/bent GX cassette before, could never get all gears shifting properly and a mate tried it on his bike with the same results. It looked like the 2 biggest cogs were the problem but as I'd lost the receipt and paid cash I had to fork out for another one. I've since read about people having them replaced on warranty so it wasn't a one off production fault and it looked brand new when I reluctantly binned it

Yeh it’s a 12 speed 10-50 T 12 speed XG cassette on an XD hub.

Ahh ok, so i reckon im going to have to just buy new.

Cheapeast i can find a cassette is £150, is there any other models i can go for? Has to fit an XD Hub and be 12 speed

Are these any good off ebay? or steer clear

For Sram XD 11/12 Speed 9-50T/10-50T/10-52T MTB freewheel Fits GX EAGLE Cassette | eBay UK

Mech hanger straight?

Haven’t tried that - would that affect more than just the bottom 5 gears though?

Also I only noticed an issue with the bike under load

Check the mech hanger, definitely, as that's the obvious thing.

Is the chain the right way round/ the right spot if it's narrow/ wide? Check the chain wear (measure it), and check by eye if the cassette's looking worn. 

Problems at one end of a cassette and not the other is very often twisted or bent hanger. It's one my (very) short list of quick hits for odd gear shifting performance.

I don’t think it’s the mech hanger - it looks pretty sturdy. It’s an Orange mech hanger and looks pretty thick.

I can try swapping the chain round the other way

Posted by: astura

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I don’t think it’s the mech hanger - it looks pretty sturdy

It doesn't need to be out by much to cause an issue, not necessarily obvious by looking at it. Try straightening it with the right tool - you'll need one sooner or later if you've gone 12sp.

Oh and are inner and outer cable definitely OK and routed correctly into the mech?

Is it worth just buying a new mech hanger just incase - looking at it I don’t think I would be able to move it with any pliers.

Just curious how come I would need one sooner or later with going 12speed?

Cable wise I’m pretty certain everything is fine there - it moves through the gears easy enough - it just jumps cogs under load

Plenty of cheaper XD cassettes out there. E13 in sales, Airbike etc

Posted by: astura

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looking at it I don’t think I would be able to move it with any pliers.

Just curious how come I would need one sooner or later with going 12speed?

Pliers are not the proper tool 😆 You'll probably need a mech hanger alignment tool at some time because 12sp can be sensitive to misalignment and having the right tool makes it simple to fix.

And some mechs are picky about how the cable is routed past the pinch bolt - if it's the wrong side it can affect shifting, so worth double checking.

12-speed is really sensitive to bent mech hangers. I swapped my 11-speed X01 for 12 speed XT and it was jumping on 2 or 3 sprockets. Re-indexed it loads of times, couldn't see why it wasn't working. Took the hanger off and put it on a flat surface, and it was just a tiny bit out of true. New hanger, no more jumping.

Mech hanger ordered. Won’t hurt to change.

Regarding the XD cassette, I checked Airbike and all the XD cassettes are out of stock, doesn’t seem much price difference with the E13 either from an SRAM cassette - any others worth giving a go?

Thanks for the help so far

Mech hanger ordered. Won’t hurt to change.

I'd be ordering the tool as well to check the new one is straight. As above, 12 speed is really sensitive to alignment. Needs to be checked every time you are indexing 12 speed. 

Only on the smaller cogs but not the bigger, and only under load? Give the B screw a few turns.

Tried the B - Screw, it changed it a bit but not enough to fix

Thanks all - after going through all the feedback, i think it could well be the Derailluer tool needed to sort it. I didnt even realise it was a thing but watching a youtube video of how its used made sense. New hanger and tool on order

Yeah, I finally got round to replacing my trusty 9-speed XT with 11-speed XT, and really noticed how sensitive it was to derailleur alignment - basically cause the tolerances between gear x and gear x+1 are that much tighter the more gears you have. Gears 1-6 are fine, gears 7-9 need some fiddling when shifting, and gears 10-11 are fine. An Aliexpress mech hanger straightener tool helped sort it a bit - unfortunately Cotic don't make the replacement hanger any more. 

And I can imagine 12-speed is even more picky about the mech being straight

Posted by: astura

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Thanks all - after going through all the feedback, i think it could well be the Derailluer tool needed to sort it. I didnt even realise it was a thing but watching a youtube video of how its used made sense. New hanger and tool on order

Always check a new hanger - just because it's new doesn't mean it's straight (at least not straight enough for 12 speed!)

Spent years working in a bike shop using the hanger alignment tool to sort out skipping gears, but I never bothered buying my own as I could always eye ball it.

Until 12 speed. I found that moving to 12 speed, the tolerances became so fine that it was critical to check, and as above, new doesnt always mean right. With lots of the bolt on hangers its easy for it to be slightly squint just with some thick paint on the frame recess or a bit of dirt under it. 

The mech hangers on newer bikes I've had do not bend, they snap clean off. Means that you don't get misalignment issues, but it also means you can't bend it back enough to get you home again. Arse! 

Mech hanger arrived today and DAG tool - I fitted the hanger tested it and the gears were jumping same as before.
I got the DAG tool and started looking at the alignment - no issues with the vertical, a slight bit on the horizontal bit and the end everything was close to touching the rim and looked like it should in the YouTube videos I watched.

Gears are still jumping in the same place (bottom 5 cogs), surely this has to be the cassette and chain now?

I would by a new cassette and chain and fit them. I think this stands a good chance of fixing the problem. 

Posted by: Bruce

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I would by a new cassette and chain and fit them. I think this stands a good chance of fixing the problem. 

Agreed

Have you measured the chain yet? If you don’t have a wear checker you just need a ruler.

If it’s really worn, there is a chance that a new one will work with your little used secondhand cassette, but will skip on your front chainring.

And I didn’t see a reply to an earlier question, is your chain a 12 speed one? If it’s 11, it will be too wide.

Replace all your consumable gearing parts, it's the only way to be sure to cure it, and will save you many an hour changing piece then riding then changing another piece and riding again....

• Gear cable and outer
• Chain
• Jockey wheels 
• Bottom bracket 
• Chainring 
• Cassette 

Expensive yes, but will work like it's new after 

And add a mech hanger to that list. Remember to buy the correct chain length, if in doubt then buy a long one and remove any required link/s. 

I was today years old when i found out you can take a photo of your cassette and chatgpt it to check wear. Mindblown bikerevive.... 

EDIT:

OP, have you got a tight chain link? Might slip off at the same point?