i was wanting to know how can you tell what type of a rearend i have in my 89 firebird 305tbi 5 speed. any info on how to tell or were to go to find out will help out.

 

You have a 10bolt 3.08 non posi rear end if it is stock which 99% of the time it is.

 

so can i make it posi by buying an 10 bolt posi unit off some one, and will if fit into the stock rearend. thanks.

 

You should be able too. But you should really go with an eaton posi or an aburn posi. Those are strong posi's and really work great no matter how much horsepower you throw at it. I really wouldn't go with a factory posi because they never worked that great and wore out quick. So why you have your rear end open just do it right and spend a few extra bucks on a quality posi. And if you do decide to go with your friends posi out of his 10bolt, it should work as long as you have the same size carrier and same spline axles.