Join Date: Apr 2009
Location: New Rochelle, NY
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
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This is a common problem and usually easy to fix.
Look on the underside of the thumb pad and you'll see tiny coil spring that engages a tab. (BTW- you'll need good eyes and good light) It's job is to push the thumb pad up and disengage it from the lever cam. Three things usually go wrong.
1- on new levers, sometimes a bit of excess plastic on the hole surrounding the spring keeps it from working properly. Use a sewing needle to pick the spring out of the hole, and work it in and out until it wears the hole enough to work smoothly and reliably. Or since it's new bike let the LBS deal with it.
2- on some new levers the pivot where the thumb pad hinges to the metal lever itself can be a hair tight and the tiny spring just isn't strong enough to overcome friction here. Add a drop of light oil, (if you don't have something like sewing machine oil, olive oil works fine) and work the pivot back and forth until it's 100% free.
3- on older levers, especially during a hot summer, sweat wicks into the pad/lever pivot, causing rust. Depending on how bad it's corroded, the thumb lever assembly can be saved with a penetrating oil of the kind used to free rusty bolts such as "Kroil" or "Liquid Wrench". Apply, allow to wick in and work the pivot until it moves freely. Once done, flush the penetrating oil, and replace with a light lube. BTW- this problem is better prevented than fixed, so keep that pivot oiled with light oil, especially in hear (sweat) or wet weather.
Once you've got the thumb pad spring back up freely after you depress it, you're problem is solved.
An ounce of diagnosis is worth a pound of cure.
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