changing default grub entry??

[robert]

Hi sisters & brothers in unbuntu

I swaped my motherboard in a 16.04 box with 5 disks.

Now the boot sequence has changed.

I would like to have the 9th entry of the list that is displayed when I boot, to 
be default.

this is what I tried (and failed):

1. in /etc/default/grub

     GRUB_DEFAULT=9
     #GRUB_HIDDEN_TIMEOUT=0
     GRUB_HIDDEN_TIMEOUT_QUIET=true
     GRUB_TIMEOUT=10
     GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
     GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
     GRUB_CMDLINE_LINUX=""
2. update-grub

however, the default entry does not change.

thanks for your help

robert