Bicycle Mechanics - slipping gear

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mendozer
10-02-07, 03:59 PM
hey everyone. my roomate's road bike is slipping on gears. when he pedals hard (going uphill) it slips to the next cog despite a new chain.

i told him it's probably worn down cogs or it needs a deraileur adjustment.


what do you think?

Al1943
10-02-07, 08:52 PM
This sounds like a need for a shift cable adjustment. Find the barrel adjuster where the shift cable meets the rear derailleur and turn it 1/2 turn counter-clockwise, see if that helps, then try another 1/2 turn if needed. If this stops the slipping problem shift through all of the gears to make sure they all work. If you go too far counter-clockwise the chain will not shift well to the smallest cog (sprocket).

Al
mendozer
10-02-07, 09:04 PM
is that making it tighter or looser?

RecumbentTriker
10-03-07, 06:19 AM
Here's a large online chapter (pdf file) on rear derailleurs: (2mb)




http://www.bbinstitute.com/BM5%20chap%2032.pdf
aaronspoker
10-04-07, 11:06 PM
If it was a worn cogs/chain, it would be slipping to the same gear, so if its skipping to the next gear, it's probably autoshifting due to frame flex. To confirm diagnosis, check for excessive shift cable friction. Lubricating the shift cable is what you should try first. Use a light oil of some sort. I use Prolink chain lube for this, but some people use grease.

If that doesn't fix it, search the net for "autoshifting" for other possible causes and cures. Or ask your bike shop.