The gear turns slowly every time the cartridge is used. When it gets to the end of its range, a spring stops it from turning further and the printer will not print until the cartridge is replaced. When a cartridge is refilled, this flag gear must be reset or printer will think the cartridge is still empty and it will not work. You can also squeeze some extra life out of a used cartridge using this method. Caution: in cartridges that have a built-in waste toner reservoir, resetting the flag gear can result in continuing to print when the reservoir is full and spilling waste toner into your printer. This can ruin your printer, so be careful. In printers that have a separate waste toner receptacle, this is not an issue.

I just had this flag gear issue on a MFC-9840CDW, so I am going to give instructions for that cartridge.

1. Orient cartridge so that you are looking at the end of the cartridge with the developer roller to your left. (This is the opposite end from the filler cap). You should see 2 phillips head screws, one at the top right, one at the bottom left. You should also see part of the gray flag gear through an opening in the end cap.

2. Remove screws and the end cap they were holding in place (one or 2 gears may fall out when you do this, but they should be simple to pop back into place).

3. Note attachment point of the spring over flag gear, then temporarily remove it so you can reset the gear.

4. Remove the flag gear and reinstall it so that its teeth are just beginning to mesh with the adjoining gear.

5. Reinstall the spring.

6. Reinstall the end cap.


This is MUCH easier to do than to describe, like tying your shoelaces. Once you have done it and know what to look for, the entire process should take less than 1 minute.