My New Chain Keeps Slipping

[bignutts13]

Please Help,
My new chain keeps slipping on my very last gear when i apply more pressure. Specs are 3 front/ 7 rear. My front chainset is new as well and works fine. It only slips on th final gear. no.21 if you like.

please help.

 

[daveornee]

Please Help,
My new chain keeps slipping on my very last gear when i apply more pressure. Specs are 3 front/ 7 rear. My front chainset is new as well and works fine. It only slips on th final gear. no.21 if you like.

please help.

I don't know how you are counting gears. However, you can learn how to adjust derailers from either Park Tool Repair section or Sheldon Brown site URL:

<http://www.sheldonbrown.com/derailer-adjustment.html>

If the slipping is happening in the rear... and your chain and chain wheels are new, it likely means your cassette or freewheel cog is worn. You will see a section in Sheldon's article that addresses that issue:
"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"
Lastly, if you mean 21rst gear is small front chain wheel and small rear cog... that is a cross-chaining position that you should never use... along with large front chain wheel and largest rear cog. Those positions are not efficient, not good on any part of the drive train, and the same final drive ratio is obtained in another combination that is much better all around.