No matter how I clean it according to the manual I cannot get the dark line to disappear on our fax machine copies

Per Brother's User manual,
http://www.brother-usa.com/ModelDocuments/Consumer/Users%20Manual/UM_IntelliFax_4100_4750e_5750e_EN_98.PDF

Clean the machine’s interior and the primary
corona wire of the toner cartridge This is a common cause for your printing/copying problem. This should solve your issue. Best of luck.
Greg

try cleaning all visible glass with glass cleaner

Dust in the scanner, clean the scanner line inside the refill  compartment

You have to clean the scanner.Open the dock feeder area,and make sure the scanner glass is clean sometimes the glass look clean but just a smaal dot on the glass can cause a line.Clean also the white area above the scanner.The white area above the scanner help for shading operation of the mchine.Make sure you clean with a sullotion that can remove ink but not damage plastic.

You can try using the menu to lighten the fax, but if all received faxes are dark, you may be experiencing a weak scan light. try making a copy instead of fax (which essentially is a fax printed to yourself) if also dark, its certainly your scanning imager that's failing. If that's the case I would recommend replacing the entire machine. Parts are expensive, and its a difficult to service part yourself. Also you may find that toner costs alone may pay for the replacement machine over this unit.

-Good Luck!

-FW

Check the drum- if there is any lines or ghost images replace it if not its problem with fixing unit.

Be sure that you cleaned your copy glass.

Pls. send the model of your machine.The G3 is fax protocol

That is comming from the scanner. If cleaning it well does not help, then it is one of the segments in the CCD assembly within the scanner that is the problem. That would requiring replacing tha scanner .
it could be a small scratch on that screen also.
Only thing you can try would be use some rubbing alcohol and a regular piece of 20 pound copy paper to clean the scanner glass/screen vigorously.

If the line is not on your recived faxes then you need to clean the area the paper passes over when sending. any marks could cause this.

try this take out drum( toner) clean machine see if there is a thin strip of glass on bottom inside the machine. make sure it is clean, this will give you black lines if dirty.

here is the manualit can guide you better, look for the troubleshooting and maintenance section

http://www.retrevo.com/s/canon+b640++manual?rt=tr&p=http%3A%2F%2Fwww.usa.canon.com%2Fcpr%2Fpdf%2FManuals%2Fb640_ug.pdf

good luck

How long has the drum been in there?
try this:
1-take out toner, look and see if it is ok. do you see stripes on it?
2- look at the drum are there any black rings on it? ( you did not specify white or black lines)
3- where the glass is on the opposite side ( the part you lifted to clean the glass, look at it standing from the back. you will see a white metal plate with some springs in it if you touch it. this is the reference that the fax has if there is/are a black dot on it it will give you a black line clean carefully. if it is scratched use white out to cover and make white again.

For the darkness try making a copy in photo mode if it is still too dark change drum.