bike rear derailer and chain troubles?

Question

I just recently tried to fix an older bike that had a bent derailer and i got another 10 speed and swapped the derailers. The bike doesnt shift properly and the chain seems to skip. I'm not sure if maybe i have the chain through the derailer wrong or if the chain itself is bad? Can anyone end my headache.

Answer 1

It sounds to me that the dropout- where the wheel goes into the frame- was bent at the same time that the derailleur met its fate. This must be correctly aligned for the derailleur to work. Unfortunately there is no good way to check this without an alignment tool.

If the chain only skips in one place it could also be that it got bent when the derailleur was damaged. The easiest way to check this is to watch the chain as it wraps around the derailleur. If it looks to "skip" around at any particular place as you pedal through slowly, then the chain is also a problem... you must pedal forward when you check this... pedalling backwards often masks any issues.

If you have the chain through the derailleur incorrectly then you'll need to look at a book or another bike to make sure it is correct.

Answer 2

Unfortunately there are so many things that could be wrong. The chain could be routing improperly. The derailleur may not be compatible with the shifters on the bike. However if the bikes were similar, I suspect that the indexing is not properly adjusted. Try adjusting the cable tension to make it so the derailleur engages each cog correctly. More tension makes it go up the cogset faster. Less makes it go down.

Answer 3

You also should check the chain. If it is badly stretched it will also cause the skipping you are talking about. Take a ruler and measure the chain. Two of the connecting pins shouls fall exactly 12 inches apart. If it is a little shy or a little long then you need to replace it.