Chain Jump

weyless

i need some help. this has been happening to me for about 5 months and i have done everything i can think of to try and correct the problem. so here is my problem.

my chain jumps when i am my highest cassette gear. i have two sets of wheels that i use. one set is my road wheels with a road cassette and the other is my mountain wheels with a mountain cassette. i have adjusted the rear derailuer numerous times, i have did my best to check the derailuer alignment and it appears to be aligned. the only thing i have not done is check the tightness of the cassettes, but i ruled that out because it does that same thing on both wheel sets.

if you place the bike on a repair stand it willnot jump, but under load it will jump.

any help or suggestions would be greatly appreciated.

Don Shipp

There are two small screws on the mech that limit its travel. Getting them right on the stand does not mean that they are right when under load, so you probably need to turn the outer one in a bit.
I would also say that you could reduce the load, and the number of times that you experience this problem, by using your lower gears more and spinning instead of mashing.

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weyless

thanks for the info. i tried setting these while i test rode the bike but it still did not solve the problem, but i will try it again.

aa9t8

how worn is the chain?

bikemech007

Check your chain line while your chain is on your largest toothed cog in the rear. If the chainline is too extreme, meaning that you see a very steep angle off the top of the cog moving toward the crank, then you have two options. [1] look at using a shorter bottom bracket spindle and [2] don't use that gear, shift down into a smaller gear using your crank's chainrings to avoid this extreme cross in chainline.

or as someone else mentioned, you could perhaps have a very worn chain that will only 'jump' under load. This is caused by the chains' contact points not hooking the cassette teeth and actually sliding over them under high amounts of torque.

good luck