Comment 4 for bug 1306928

On 14.04 we need to manually remove bcmwl-kernel-source, and use brcmsmac.
Just for informations :

Remove bcmwl and install linux-firmware-nonfree :
sudo apt-get purge bcmwl-kernel-source
sudo apt-get install linux-firmware-nonfree

Then you need to blacklist b43 and wl :
echo "blacklist b43" | sudo tee -a /etc/modprobe.d/blacklist.conf
echo "blacklist wl" | sudo tee -a /etc/modprobe.d/blacklist.conf

sudo modprobe -r b43 wl brcmsmac
sudo modprobe brcmsmac

And reboot.