Gears changing by itself

[LOCO TACO]

Hello,
This is my first post and I am so glad I found this site. I have an Specialized hybrid bike that I bought about 5 years ago. I mainly ride it on the weekends. About a year ago, I noticed that when I hit a bump, the gears shift by itself. I know I need to tighten something but I just don't know what. Hope someone can help. thanks..

[Painkiller]

need more info like what type shifters? are they grip shift, or low end thumb top mounts, trigger style. also a few pics might help

[LOCO TACO]

(08-30-2011, 09:02 PM)painkiller Wrote:  need more info like what type shifters? are they grip shift, or low end thumb top mounts, trigger style. also a few pics might help

....they are grip shifters, shimano (augusta?). Thanks