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View Full Version : Poor shifting, only in center cogs in rear?


zpl
04-26-2009, 05:48 PM
I've been having an issue with my bike since putting a new chain on it almost two weeks ago. I replaced the Shimano HG chain that came with the bike when I bought it back in August 08. Since then I've put about 1800 miles on the bike. The cogs do not look hooked at all (and I've seen ones that are pretty bad before, so I'm pretty sure I know what I'm looking for).

The new chain is a 10-speed SRAM PC-1070 that costs around $40.

Here's the thing - the rear derailleur shifts like a dream between the smallest three and largest three gears. But as soon as I get to the middle gears, it will miss shifts completely about 50% of the time. Adjusting the barrel adjuster in the midst of these missed shifts to correct them only ruins the shifting elsewhere.

The cogset is a Shimano 105 12-25 if that matters. I have semi-horizontal dropouts and made sure they are dialed in with identical depth.

Any ideas? I've always been told SRAM chains are at least as good quality as Shimano. I'm about ready to give up and take it to a shop, which I am loathe to do.

Scott

K'Tesh
04-26-2009, 10:27 PM
I've replaced my share of drivetrains and I think I know what the problem is.

When you replace a chain, or have replaced several chains, there's a good chance that your cogs have worn to match the old chain... Look at their teeth, do they have a hook shape worn into them (resembling a sharks fin)?

That you're only having the problem in the center cogs makes sense if you don't spend too much time climbing hills or on killer decents.

Best of luck!
K'Tesh

steve knight
04-27-2009, 09:31 AM
figure about 2500 miles on a chain. when you change a chain and shifting is bad then time for a new cogset. I got about 4 chains out of a 8 speed cogset about 2.5 out of a 9. the got to love improvments (G)

lynnef
04-27-2009, 09:41 AM
This could be reaching, on a bike as new as yours... I replaced a chain on a bike, and it started skipping, so badly that I couldn't ride it at all. Replaced the cassette. Still skipping.

I finally did take it in. "Did no one look at your front chainrings?!?!?!"

Problem fixed.

boneshaker
04-29-2009, 07:49 AM
Sounds like it is time for a new cassette Scott. I ususally replace mine every 2 or 3 chains. I'll be happy to put it up in the stand and take a look if you think a 2nd set of eyes will help. You can always use a spare cassette so it never hurts to have a few around anyway.

Speaking of which, doing a ~20ish mile ride Saturday if you'd care to join.

zpl
05-08-2009, 05:30 PM
The mystery is solved! I spent some zen time with the bike on the stand, shifting up and down, and trying to observe more than I had seen previously. Sure enough, I noticed that during the shifts that were missed, the rear derailleur was barely moving. This led me to notice the cable was not being pulled consistently.

After worrying for a bit that there could be something wrong with my shifter, I dropped by Bike Gallery for a few shift cables and went to replace mine, hoping I'd pull it out and find some corrosion on it.

Instead, I discovered that my cable was frayed right at the point it entered my shifter. Jackpot! The cable has now been replaced and the shifting is dialed in like the bike was brand new.

Scott

jr98664
05-08-2009, 08:36 PM
I've had my 2008 Trek Soho since the very beginning of 2008, and this very same thing has happened to me multiple times. Unfortunately, the first two times were out on moderately long rides, a good ways from a bike shop too. I was able to dial in the high screw so that it was one gear lower, and then just stand up and power my way back to town.

A few months ago, I was thankfully able to feel when the cabled started to fray and I simply stopped shifting in the rear. One interesting thing worth noting: when I only had three gears to use, I ended up averaging a noticeably higher speed.