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I have a KM set up with an xt/lx drivetrain. On a recent ride I started getting a major skip under strain. It appears to happen only while in the 2nd ring upfront and 4th cog in the back. I can only make it happen under major strain so it's difficult for me to isolate.

Any ideas how to isolate the problem? It would seem it would have to be in the rear but I am not sure (I had to file the teethe a bit on the center ring up front for chain suck a few months ago if that plays into the picture).

Also, I have heard of people running 6 speed systems with xt deraileurs, where can you find out how to set one of those up?
 

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Read the huge 6sp thread.

From http://sheldonbrown.com/derailer-adjustment.html#chain

Skipping/Autoshifting

Do your pedals sometims jump forward when you pedal extra hard? This is a common complaint, especially when a rider stands up to pedal. Indeed, this dangerous condition is one very good reason for remaining in the saddle and spinning in your lower gears, rather than standing up and pumping in a higher gear.

Although jumping/skipping/autoshifting is often blamed on the derailer, it is only very rarely the result of a derailer malfunction.

This jumping may be one of two totally unrelated problems: skipping or autoshifting. The first step in troubleshooting this problem is to determine whether the problem is simple skipping or autoshifting.

* Skipping involves the chain jumping over the tops of the sprocket teeth under load. After the chain jumps, it remains on the same sprocket. This is usually caused by wear to the chain and/or the sprockets. This is most likely to happen on the smaller rear sprockets, especially if they are used in conjunction with the small chainwheel in front. This issue is addressed in considerable detail in my article on Chain Wear.

A form of skipping, not necessarily under load, sometimes also results from stiff links.

* Autoshifting feels just like skipping, except that after the jump you find that the rear derailer has shifted up to the next smaller sprocket. Autoshifting is commonly caused by a combination of frame flex and cable friction. The mechanism of this is explained in detail in a separate article on Autoshifting.
 

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Schmucker is right

Schmucker said:
Read the huge 6sp thread.

From http://sheldonbrown.com/derailer-adjustment.html#chain

Skipping/Autoshifting

Do your pedals sometims jump forward when you pedal extra hard? This is a common complaint, especially when a rider stands up to pedal. Indeed, this dangerous condition is one very good reason for remaining in the saddle and spinning in your lower gears, rather than standing up and pumping in a higher gear.

Although jumping/skipping/autoshifting is often blamed on the derailer, it is only very rarely the result of a derailer malfunction.

This jumping may be one of two totally unrelated problems: skipping or autoshifting. The first step in troubleshooting this problem is to determine whether the problem is simple skipping or autoshifting.

* Skipping involves the chain jumping over the tops of the sprocket teeth under load. After the chain jumps, it remains on the same sprocket. This is usually caused by wear to the chain and/or the sprockets. This is most likely to happen on the smaller rear sprockets, especially if they are used in conjunction with the small chainwheel in front. This issue is addressed in considerable detail in my article on Chain Wear.

A form of skipping, not necessarily under load, sometimes also results from stiff links.

* Autoshifting feels just like skipping, except that after the jump you find that the rear derailer has shifted up to the next smaller sprocket. Autoshifting is commonly caused by a combination of frame flex and cable friction. The mechanism of this is explained in detail in a separate article on Autoshifting.
I have experienced chain skipping systematically on my brand new road bike and I used to experience the same on my previous MTB which led me to change cassette for no reason because there was no real wear and it did not fix the problem.
I personally believe it is caused by the frame flexing and if you are in a small ring/ small cog gear, the chainline is already crossed which accentuates the sensitivity to the matter.
My 0.02.
If you're heavy like me, don't cross your chainline or don't go out of the saddle.
PS: I run a 1x3 now and need to be out of the saddle often but most of the time on the largest cog (more teeth engaged) and in a perfect chainline. No problem
 
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