The rear balance shaft is on the oil pump. If you cut the b-belt, the rear shaft will still spin but now the vibration will be worse because you have this off balance shaft spinning. I know, I had a b-belt break but lucky it didn't take the t-belt out. Make sure your kit uses the Mitsu stub shaft with the oil groove or you may kill your oil pump. If you make serious power, push your car hard, race.. what ever. Its best to get the rear shaft machined to a normal looking shaft and re-install. This way the oil pump is on a shaft supported at both ends instead of a cantileverd shaft. This is strongest, safest way. You can remove the front b-shaft or leave it in as it won't spin. NO, mine is not done.