Grub and HD clone

[Francesco Carsana]

I've made a script that uses partimage to backup an entire hard disk
(without swap partition).
In this script I save MBR and extended partitions table with:

dd if=/dev/hda of=backup.mbr count=1 bs=512
sfdisk -d /dev/hda > backup.sf

To clone hda in hdb:

dd if=backup.mbr of=/dev/hdb
sfdisk --force --quiet --no-reread /dev/hdb < backup.sf

and then I restore the partitions with partimage.

When I reboot (with cloned disk as master), GRUB doesn't start!
How can I solve this problem? Is there a way to backup grub?