sounds exactly as a cassette that is more worn then the chain. the reason that you don´t se it in the working stand is that there is no load on the chain/cassette there.

The weird thing is I had the same problem with my nokon cables and when I put back on my shitty chain again they shifted just fine. This happened under load when cycling after I adjusted in the shop. Gerry annoying as I thought I was going crazy.

Anyway I got a new cassette to go with my new chain.

ok try to test with a new cassate.thanks

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Parlee Z3sl - 5 kg

Passoni Xxti- 6.2 kg

Test it. Just ride it in the big or small in the rear and it probably won't do it. Cassettes are normally worn out in the middle gears because that is what everyone uses.

Ok guys,i have the results, its my brand new KMC 10sl chain who do the jumping !

we have tested an used shimano ultegra and a brand new ultegra chain without any problem.

i am not sure why kmc are not compatible or manufacture defect.

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Parlee Z3sl - 5 kg

Passoni Xxti- 6.2 kg

the big jump as well

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Parlee Z3sl - 5 kg

Passoni Xxti- 6.2 kg

i guarantee you it's the cassette. the shimano chain likely comes a little looser out of the box, so is slightly more tolerant of the worn cassette. your new chain will not last long on that cassette.

Sorry WShiong....but the other guys are absolutely correct and the comment re the shimano chain being a little more tolerant of worn cassettes is probably correct also.
You may get away with the shimano chain (the KMC is likely built to a tighter tolerance hence it is skipping but the the shimano one is acting like it is partially worn) and it may even "bed in" and ride ok for a while but it's life span will be shortened by the sloppy fitting cassette. At this point, you will be risking: chain, cassette, and chainrings (they get "sharks toothed" quickly on over-long chains). Now, it starts getting pretty expensive as your new chain will be toast too....full drive chain rebuild earlier than expected and it now includes your chainrings.
This all assumes you didn't make a tight link and installed the joining link on the KMC correctly, and that the chain is jumping at the back (not the front chainring.....which IS possible but only if it is severely worn).
Not what you want to hear, but highly likely.

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Used to race....got too wrinkly and old Updated: Racing again! Thought this was unlikely! Eventually, I may even have a decent race!

I am not sure how the bike shop install the KMC chain. And now i am using the YBN chain something similar to KMC and it works fine.

Probally need to save up for a new cassate soon.

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Parlee Z3sl - 5 kg

Passoni Xxti- 6.2 kg