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Discussion Starter · #1 ·
This year I have decided to try some harder hills and I am noticing a few things. When I am in 5th gear climbing the hill and pushing down hard on the pedals the chain seems to skip or jump. This only happens when I apply too much force to the pedal. I don't seem to notice this on other gears. However, when I gear down to 4th I can't seem to get a smooth pedaling motion but that could be technique but either way it makes tackling steep hills very tough when I am fighting the bike as much as the hill.
I have a Trek 820 bike. You may require more information which I can provide but I just don't know it right now off-hand. Has anybody heard of the problems that I am seeing in my 5th gear?
 

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What "front" gear are you in?
"5th" shouldn't be giving you too much trouble, but when you're in the lowest front gear, you want to keep the chain inside, on the larger rear cogs (1-4) to maintain the best chainline. When you're torquing on the drivetrain, and your chain line is angled, there is a chance the chain will try to change cogs, which results in skipping. Geared bikes can operate in all gears, but when you're really mashing on the pedals, you want to train yourself to use a gear combination with a decent chainline.

Aside from technique, there could be several mechanical issues:
- Worn chain
- Poorly adjusted rear-derailleur
- Broken or worn "5th gear" cog
- Improper chain length/tension
 

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Discussion Starter · #4 ·
After checking last night - my left-side gear shift was set to "2" (Out of 3) - when I was referring to the 5th gear. During my ride last night I did change my left gear to "3" and still had the same problem of the gear skipping when I press down too hard. I will continue to test your "chainline" theory though. When riding on a gear lower than "5" I was constantly getting a slack chain feel whereby when I press down on a pedal it almost feels like I go back about an inch and then when press forward on the other pedal the chain catches and jerks forward - I am sorry if I am not explaining this right. This is the part that I feel I have bad technique which is causing this though I don't remember having this problem in the past. Granted, I haven't ridden this much in years but something still feels wrong.
 

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Here's a bit from Sheldon Brown's troubleshooting page:

Skipping/Autoshifting

Do your pedals sometimes 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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