How do I fix a gearshifter on a mountain bike ?

Hi the Gear Shifter on my Mountain bike doesnt work, whenever i go to change gear it doesnt stay on the gear i put it to it slides back down to gear 6 . So if i put it on gear 4 for instance it doesnt click into place and stay there unless I hold it. Hope that makes sense. How would I fix this ?How do I fix a gearshifter on a mountain bike ?
your cable is probably too tight and you need to adjust the barrel adjuster on the shifter to get some slack in the cable. DO NOT force the shifter because if you break it, that's it. Another possibility is that you need to adjust the rear derailleur too, but i think it is the shifter adjustment in this case. If you don't know what you're doing take it to a bike shop and let them do it, you don't want to make it worse- but that is how i learned...How do I fix a gearshifter on a mountain bike ?
My guess is that you have thumb shifters.



There should be a screw on top of the shifter. Make sure that the shifter and the bike are in position 6, then tighten the screw.