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Bunjabi
01-24-2012, 11:21 AM
Has this ever happened to you? (cue informercial music).

Lately, as I'm pedaling up the trail overpasses at National on the MVT, my bike will decide to shift to a higher gear, causing me much consternation and not just a little injury in the seat area (the chain seems to jump out of line as well, causing a few rounds of free spinning pedals).

I notice my shifters (old Panasonic DX-2000) move a bit while I'm pedaling, but the actual shifting only takes place when I'm putting a lot of force into the pedaling (up hills, etc).

Any ideas on what's going on here and how I might be able to fix it?

Tim Kelley
01-24-2012, 11:24 AM
Mark Blacknell would probably recommend a slight adjustment of the barrel adjuster on the rear derailleur. Or maybe time for new cables?

DismalScientist
01-24-2012, 11:53 AM
Tighten the bolt on the shifter. I assume this is a friction shifter and is not indexed. Even if it is indexed, tighten the bolt. Sometime the bolts have a little swing out piece of wire that allows you to do this without a screwdriver.

baiskeli
01-24-2012, 12:08 PM
Do you hear the chain rubbing?

PrintError
01-24-2012, 12:24 PM
Mine do that whenever the shifter cable or chain need replacing. Check both, replace what's needed.

JimF22003
01-24-2012, 12:30 PM
If the derailleur doesn't actually move, it's probably a worn chain or cassette.

Rootchopper
01-24-2012, 06:49 PM
If your shifter's cable is routed underneath the bottom bracket, it might be getting hung up on some gunk down there. Check to see if the cable is moving freely. If not, clean the area and lube the chain so that it slides freely.

Bunjabi
02-01-2012, 09:07 AM
Thanks for all the replies!

I fiddled with the bolt and looked at the cables. Apparently, all I needed to do was look, because the problem has stopped... for now. Not sure what I did, but it seems fixed.

I'm guessing the cables need a replacement anyway. Chain seems fine, no rubbing; derailleurs working fine as well.

If it starts again (or the chain explodes or something) I'll apply the suggestions here en force.

Thanks!

MCL1981
02-01-2012, 12:05 PM
Mine started doing the exact same thing in October. It would skip or magically shift itself under heavy load such as that of going up a hill. I quite literally feel your pain. It was the cable exhibiting symptoms of being 10 years old, rusty, and stretching. It can't hold back that kind of force when it stretches instead of holding.

Bunjabi
02-03-2012, 10:08 AM
Update!

This morning (2/3) it started again, but this time with the other gear set (front). I have a feeling the temperatures have an effect on the cables (contracting in cold weather?). We'll see how the ride home goes.

CCrew
02-03-2012, 01:00 PM
Cables really should be changed about once a year.

consularrider
02-03-2012, 02:00 PM
Cables really should be changed about once a year.

Or when they break. :D

DSalovesh
02-06-2012, 11:25 AM
I had this once.

Everything seemed fine on the stand, on little test rides, and even most of the time just riding around. But whenever I had to start fast after a light or climb a hill things would go all wonky.

I didn't figure it out until I took the wheel off and parts started shifting around: I had a broken axle. It was an old frame with 120mm dropouts and the narrowest hub I could get my hands on was 126mm. I had no trouble springing the frame apart to mount the wheel, but the extra stress and my city riding (plus a lot of weathering) had split the axle. The skewer kept everything more or less in place except in hard riding conditions, and I live with the problem for several months before I stumbled onto the answer.

Not sure any of if this applies to you, but it's quick and easy to check.