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I have a set of DA 7800 shifters and a DA 7700 braze on front deraileur. Is it common for there to be chain rub in the big front ring and third biggest back ring (21T on a 12-25)?

I have tried to adjust the upper limit screw. The barrel adjuster is very tight and doesn't seem to have much of an effect.
 

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Just Plain Bitter
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There should be a level of trim with your left shift lever that will clear the rubbing. Just a half click should do the trick here. That high up on the cassette the angle is pretty steep from the big ring.
 

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Not the limit screw

Streamwood Steve said:
I have a set of DA 7800 shifters and a DA 7700 braze on front deraileur. Is it common for there to be chain rub in the big front ring and third biggest back ring (21T on a 12-25)?

I have tried to adjust the upper limit screw. The barrel adjuster is very tight and doesn't seem to have much of an effect.
Adjusting the limit screw is NOT the fix for this issue. If you have cage rub with the larger cogs, then the chain is rubbing on the inside of the cage and if you force the cage toward the frame with the limit screw, then you will likely have chain rub on the outside of the cage on the smallest cogs. As rward325 said, you have a trim position on your shifter. If you are in the "lower" trim position and you still have chain rub, then use your barrel adjusters to change the cable "tension" (it's actually cable length, but everybody calls it tension).
 

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Some chain-rub is normal in certain combination's of front-rear gearing. Shimano makes a chart of this and send's them out with their FD's - sometimes. This is for triple chainrings:

 
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