Looking for corona wife for brother 8860dn MFD.

Corona wires are in the drum cartridge, small screen or grid over them. usually there is a colored slide that you can move back and forth to clean coronas.

The wire is on the drum (where the toner cartridge fits in). The green or blue piece slide cleans the coroner wire.

Brother MFC MFC 7840W User Manual Cleaning The Corona Wire

I don't think there is any hard and fast time scale or number of prints to when it's time to clean the drum, but I would suggest that if you are getting any unwanted marks appearing on your print out's, then it could be time to clean the drum and the corona wire.

Not much in the way of an answer, but it's how I judge when to clean my laser printer's drum's.

Happy printing. Good luck.

This can be due to a bad corona wire, or drum. You will want to consider having the unit repaired by a professional. if you need further assistance please let me know.
Thank you,
Lee

Try this link. Hope it works!
http://welcome.solutions.brother.com/bsc/public/us/us/en/dlf/download_top.html?reg=us&c=us&lang=en&prod=mfc8860dn_all

Replace the drum. The drum is failing.
When you replace the drum open the front door of the machine where thr drum and toner is.
Hit the clear/back button. Press 1
That resets the drum count after you replaced the unit.

Replace the drum. The drum is failing.
When you replace the drum open the front door of the machine where thr drum and toner is.
Hit the clear/back button. Press 1
That resets the drum count after you replaced the unit.

Good luck!

Open front cover

Remove drum unit and toner cartridge assembly

Put drum unit and toner cartridge assembly back in machine, but do no close front cover.

Press Clear/Back
You will get a message "Replace Drum?"
Select Yes to confirm