Hi. When I shift there is sometimes (more and more often) a delay between when I shift and the new gear engages. The tension seems to be gone, and the pedels go round once, twice or sometimes three times. Could anybody tell me what are the likely reasons for this? Thanks so much.
It sounds like your cable tension may be off.
To further help you we'll need to know a few more things about the problem.
Is the slow shifting happening at the front gears or the rear gears? Does it happen when you shift from a harder gear to an easier gear? or easier to harder?
Thanks for the quick reply. The problem usually happens when I am in the 3rd front gear going from the 4th to the 5th gear in the back. At its worst it may take 3 pedal strokes to make the change, and there is almost no tension during these strokes.
How many cogs (gears) are in back? By "3rd front gear", you mean the outer (furthest out from the frame) chainring? And by "4th to 5th" you're talking about going to the harder gear, further to the outside, right?
Hi. Thanks. Yes, the outter chainring on the front. I think there are 8 cogs on the back but I am not now near my bike to check (at work as it is daytime here now). The problem happens when shifting to a harder gear.
Sorry, I will have to leave this forum now as I have to catch a train to teach a class outside Tokyo. It will be about 7 hours before I can get back to my computer. I will check again for any any replies at that time. Again, thanks so much for your help.
Since you're changing to a higher gear in back, it sounds to me like it's most likely mis-adjusted cable tension. When upshifting, you're relying on the springs in the rear derailleur to pull it into place, but if the cables is too tight, the RD is hindered. Try loosening the cable a bit (turn a barrel adjuster clockwise, a little at a time, like 1/8 turn and test).
The other possibilities I can think of are a slightly bent derailleur hanger (any scratches on the RD?), worn/bent cog(s), worn spring on the RD. But these are more serious/less likely problems so hopefully the cable tension adjustment will work. Good luck.
One other thing, try to use the middle chainring most of the time, switching to the inner and outer as necessary. The middle was designed to be used with all the rear cogs, whereas the inner is meant for the first few (1, 2, 3..) and the outer for the last few (...6, 7, 8). There are times to use the outer ring with one of the lower cogs, but usually just for a quick climb during a descent which necessitates the outer ring.
This doesn't have much to do w/your problem, just a tip, but it would eliminate the situation you described...though you should fix the problem itself.
Since he said its from shifting 4 to 5 in back that means the rear derailluer is relying on the spring to shift. It sounds like you need to turn in the barrel adjuster on the rear derailluer about a half turn, or it could need lubed up.
I think more likely it may be that the inner cable is sticking in the cable outer which forms a loop before entering the rear der. This is infamous for sticking due to corrosion due to the tight loop of the cable. This prevents the tension spring in the der. from moving the chain to the smaller sprockets. Remove the outer and replace/oil.