Rear Derailleur Shifts badly under tension

[antnee]

As I have successfully adjusted quite a few sets of new cables to rear derailleurs I am surprised to find that am having a few problem with this, because after fitting new cassette,chain and longer cage rear derailleur find that whole gear changing operation works perfectly when bikes on the work stand though as soon as any real pressure is put on the pedals more often than not chain either does not shift straight away or jumps two sprockets! I can only put this down to my inability to adjust the rear cable tension properly and can't think it could be anything else as the old setup with shorter cage derailleur worked quite well
I would be interested to hear anybody's thoughts on this
P.s Have tried adjusting during test rides but so far have have limited success. Many thanks

 

[screenman]

Is the hanger out of true?

That is my line

 

[Racing roadkill]

A common cause of odd shifting / indexing behaviour can be due to the hanger being a bit bent / misaligned. If it’s okay, look at the seating of the various bits and bobs on the cable outers, and that there’s nothing fouling the inners at the interface with the outers. If everything is seated and clean, and moving freely. If that’s okay put the bike into little ring / little sprocket, wind the indexing screw on the rear mech all the way in, then release the pinch bolt on the mech and give the cable a pull, retighten the pinch bolt, with the cable held taught. Then start the indexing again. The cable only needs to be the slightest bit slack and you can find that you run out of adjustment on the indexing screw before you’ve got it shifting cleanly. If you’re getting sync with the number of clicks from the brifter, and the number of sprockets ( you’re not finding that the chain is on the smallest sprocket, but you can still get a click from the brifter for example) then you don’t have to worry about the H screw adjustment on the mech. Likewise if you get to the biggest sprocket, and you don’t find the mech is trying to go through your spokes, when you move the brifter there’s no need to worry about the L screw. Check that the angle of dangle screw is in contact with the hanger, if there’s a gap, it won’t work properly.

That’s the B screw

There shouldn’t be a gap at the end of the screw ( the bit touching the hanger ).
Adjust the angle of dangle by winding the B screw clockwise, until the top jockey wheel is clear of the sprockets, through the range. If you’ve still got problems, the cable may be letting go / frayed, somewhere you can’t see it, and might need replacement.

 

[Smokin Joe]

Is the rear outer loop seated correctly in the adjuster and the stop on the chainstay?

 

[antnee]

Thanks for all your advice and will start to look into all the things you point out I have never given a thought to the hanger being bent Will follow your tips Racing Roadkill and Joe

 

[confusedcyclist]

It could be that your previous experiences of setting it up correctly were flukes and/or, this time around you were overconfident of working without instructions and thus not following the SOP of index adjustment correctly, possibly missing a vital step in the process.

Follow this guide from top to bottom and report back:
https://www.parktool.com/blog/repair-help/rear-derailleur-adjustment

I would be hesitant to start messing with hanger alignment until I was confident I had my index adjustment correct.

 

[antnee]

Thanks all I will start to do all the checks tomorrow

 

[screenman]

It could be that your previous experiences of setting it up correctly were flukes and/or, this time around you were overconfident of working without instructions and thus not following the SOP of index adjustment correctly, possibly missing a vital step in the process.

Follow this guide from top to bottom and report back:
https://www.parktool.com/blog/repair-help/rear-derailleur-adjustment

I would be hesitant to start messing with hanger alignment until I was confident I had my index adjustment correct.

Can you get indexing correct with the alignment out? I would always without fail start at the beginning with alignment.

 

[Racing roadkill]

Can you get indexing correct with the alignment out? I would always without fail start at the beginning with alignment.

You’d be right to do so

 

[Racing roadkill]

Also, if after aligning ( including the hanger )and indexing on a stand, the problem still happens, when riding / under load, check that the wheel is sitting correctly in the dropouts, align against the seat stays / chain stays, not the brake callipers, you may then find the callipers are not centered ( it won’t affect the shifting, ( the brake callipers thing, won’t the squiffy wheel alignment may do) . If not, adjust the centering with the little screw on top of the bridge.

 

[iluvmybike]

Check that the outer casing at the derailleur is not too long OR too short too

 

[confusedcyclist]

Can you get indexing correct with the alignment out? I would always without fail start at the beginning with alignment.

If I had the tool, and the experience to use it, then yes I would start there, but OP doesn't give that impression, nor did they mention a crash, bump or knock of the RD, or any reason to expect alignment is out, therefore I imagine that simply indexing is likely the issue. If shifting is still poor after following the instructions, time to start considering other options. Without the tool OP, can't fix this at home. So I stick to my original advice. Setup the RD from the guide, and report back.

 

[winjim]

Is it possible that the longer cage of the new mech is amplifying any minor hanger misalignment in a way that the original short cage mech wouldn't? I can imagine that as the chainline changes as it moves up and down the cassette, the sideways force on the mech cage could pull it out of line.

Is it a brand new mech, or a used one which may have been subject to some abuse? I had problems with a second hand Athena 11sp mech which meant I first had to straighten the hanger, and then use an adjustable wrench to twist the mech cage itself into the correct position. It's still not perfect and sometimes displays the symptoms mentioned in the OP, so I will have to get round to fine tuning it.

 

[confusedcyclist]

He doesn't need a tool to check it. There is the second wheel technique.

Never heard of this, can you point me toward some reference/guide?

 

[screenman]

Never heard of this, can you point me toward some reference/guide?

View: https://www.youtube.com/watch?v=T45tsSjyjDA