The thumb shifter broke after the bike accidentally fell over. How do I replace it and where does the part come from?

You can buy one from most neighbourhood bike repair shops. This should be a pretty standard item for them.

STOP!!! Take it to a bike shop. You will probably need a new shifter now that parts are missing. In all likelihood it was never the shifter it was probably a poorly adjusted derailer which is a very easy fix. Unless you want to spend a hunk money on bike specific tools a book to show you how to use the tools, and the parts that need to be replaced, I suggest you take it to your local bike shop.

Hi and welcome to fixya,

Nice bike. The problem with flappy or loose shifters can be caused by worn out shifter linkages. These are ball joints connected to a rod which enable play forward or backward. You mentioned an excessive play, I suggest you replace these shift linkages, make the necessary adjustments and you'll be surprised how responsive your shifter will be.

I highly suggest you check on this part first before proceeding with transmission problems.

Other related concerns relating to poor shifting:
-Clutch release
-clutch spring adjustment (center of the clutch cage)


I hope this helps
levibit

The gear switcher (cycling terminology: Shifter) should be attached via a band with a simple bolt through it. The shifter will attach to the handlebar (right side for rear shifter/ left side for front shifter).
If you have shifters that are shaped like a barrel as in the picture, then you have to remove the grip on the side you will install the shifter. slide the shifter onto the bar and tighten the set screw in the housing (should be just back of where the cable comes out). Reinstall the grip and there you go.

This is a simple proceedure, however if things are not tightened properly you can get into an accident, for this reason I would recommend taking the bike to a bike shop and having them reinstall the shifter and make sure that everything is safe and functioning properly.

Final Note: If your shifter was on the bike and functioning properly and fell off, then you need to go into a bike shop. The shifter has something broken and either needs to be replaced or fixed. Shifters do not just fall off.

Maybe start here and if you can't figure it out, take it to a Bike Shop. Ther's only so much useful mechanical advice one can remotely lend with no details.

If it is an automatic transmission sounds like shifter cable broke or fell off. If it is a standard transmission,depending on manufacturer cable broke or fell off or linkage broke or fell off.

Shimano make an "EZ fire" which is an integrated shifter/brake lever combination and cheaper than buying seperate shifters and levers.


e.g.
http://www.tredz.co.uk/.Shimano-Acera-8-Speed-EZ-Fire-ShiftersBrake-Lever_24339.htm

if your talking about the one for your thumb,you need to find the hair pin in the lower part of the handle and remove it to pull the shifter handle of to replace it with a salvage yard one.

http://www.nashbar.com/bikes/SubCategory_10053_10052_200468_-1_200276_200313
this is where you can get the shifters, there should be instructions with them or go to the sram website

It sounds like you bent the shift fork, or at least the shaft that penetrates the case and holds the shift lever on the outside. If you are certain you are moving the shaft and the bike won't come out of first then you will have to open up the case and see what is bent or broken inside.