with the OS X and Linx drives both connected, boot Linux and open a terminal. Type
fdisk -l
to verify your Linux drive info, then type
sudo apt-get update
sudo apt-get purge grub grub-pc grub-common
When the menu screen comes up, select yes to purge Grub2 from the system. Then reboot. If it won't boot, then you have removed Grub successfully. Shut down, disconnect the OS X drive, boot with a Linux live cd and open a terminal. Type
fdisk -l
and verify the root partition of your Linux drive. Type
sudo apt-get install grub-common grub-pc
when the menu comes up, it will give you a selection of devices to install Grub2 on.
Select the drive/partition for your Linux install (say /dev/sda1 from your fdisk commmand was your Linux root partition you would select that) Then type
sudo update-grub
then, when the update is complete type
sudo shutdown -r now
to reboot