Bicycle Mechanics - gears slipping
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I have a Cannondale touring bike with a Shimano XT rear derailleur that slips. When I'm going up a steep hill and I think I have shifted into the lowest possible gear, I find that perhaps after 6 or 8 pedal revolutions, the chain THEN moves on to the largest cog on the sprocket cluster (in other words, the lowest gear where I already thought I was; it had actually been only at the second to lowest gear). Everything is fine from that point, provided the shock to my rhythm doesn't completely toast my climb! (I'm grunting when I'm down this low in my range of gears!)
I've had the chain measured to see if it has stretched; it appears to be within an acceptable range. Is there something else that might be causing this? I thought it might be a problem needing adjustment of the indexing, but having read about indexing, I begin to doubt that is the problem. Any suggestions? rcd
If a simple barrel adjustment doesn't take care of it, it could be a sticky housing. Probably the one that loops to the RD. Lube or replace it.
Thanks for the suggestion. Can you give me any further directions about how to do this? I know how to set the screws to limit how far in and out the dérailleur moves. But how and what does the barrel do? Help, as always, is most welcome! rcd
The barrel adjuster changes the effective length of the cable, setting the location of the dérailleur arm when the shifter is at a detent. (This is misleadingly called the "setting the cable tension".)
08-27-07, 01:52 PM
I agree with DMF - mostly likely a tension adjustment. If your chain skipped on the same gear, that's different. The only other thing that might be off is if the derailleur is not straight - if you have inadvertently pushed it out of alignment, this can wreak havoc as well.
Just because it's simple to turn the barrel adjuster doesn't mean that it's always easy to get right - you need some patience. Most rear derailleurs have a barrel adjuster that you can see from the rear. If you turn it counterclockwise, it tightens the tension (obviously the other direction loosens it). Usually, you start with it on the big chainring and the smallest cog. Shift once. If it doesn't make the shift at all, it's too loose, and you should really remove the slack from the cable (there's a pinch bolt that holds the cable). If it's too tight, then it will either shift two cogs, or more likely it will shift one cog and make noise because it's rubbing against the next cog. One technique is to tighten it until you can hear the noise of it being too tight, and then loosen it as you pedal until the noise just goes away.
Has it always slipped?
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